EVALUATING 3-D PRINTING WITH CONCRETE AT THE ALACHUA COUNTY PUBLIC DEFENDER’S OFFICE IN GAINESVILLE, FL

By

SAMANTHA L. LEONARD

A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT

OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE IN CONSTRUCTION MANAGEMENT

UNIVERSITY OF FLORIDA

2017

© 2017 Samantha L. Leonard

To my mother and father, for their endless support and all they continue to do for me

ACKNOWLEDGMENTS

I first would like to thank my Chair, Dr. Larry C. Muszynski, who has not only

helped me through the entirety of my graduate thesis process, but also through my

undergraduate years at the M. E. Rinker, Sr. School of Construction Management. Dr.

Muszynski helped to develop my love for building materials, with a special emphasis on

concrete, and stressed the importance of the impacts that they can make on any form of

construction. His supreme expertise combined with his unwavering support and positive

attitude provided me with the tools necessary to succeed with my graduate thesis.

I would also like to thank Dr. R. Raymond Issa and his contributions to my

educational experience at the University of Florida. As my graduate professor, “National

Association of Women In Construction” student organization advisor, and Co-Chair for

my graduate thesis, he has supported my scholastic journey and individual growth for

many of my years at the Rinker School.

Dr. Damon Allen, serving as the third member on my thesis committee, also

deserves special recognition for his resolute commitment and constant involvement with

my educational interests and topics. As my undergraduate instructor for the course in

temporary structures, he exhibited a passion for his work that I truly admire and wish to

emulate in my future career endeavors. I would like to thank him for being such a valued

asset to my graduate thesis research, as well as a constant source of inspiration and

support throughout my time at the Rinker School.

I would also like to thank the remainder of the M.E. Rinker, Sr. School of

Construction Management faculty and staff that have become my family during the past

five years. I was fortunate to be welcomed into this program that recognized my desire

to be involved, and helped me to grow as a person. Through the cultivating

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environment at the Rinker School, I have learned that we will not be going into the world

looking to only design and build structures and landscapes, although that is a large part

of what we desire; we are looking to build strong futures, enduring relationships, and

fulfilling lives, and the lessons we have learned here at the University of Florida will help

us to accomplish those goals, and more.

Last but not least, I would like to thank my parents for their endless support

throughout the entirety of my school career at the University of Florida. I am so grateful

for their sacrifices, motivation, and guidance that has helped me become the woman I

am today. They have helped to provide the primary foundation for my achievements,

and with my determination to succeed, I am honored that one day I will be representing

the University of Florida as a thriving member of the construction industry.

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TABLE OF CONTENTS page

ACKNOWLEDGMENTS .................................................................................................. 4

LIST OF TABLES ............................................................................................................ 8

LIST OF FIGURES .......................................................................................................... 9

LIST OF ABBREVIATIONS ........................................................................................... 10

ABSTRACT ................................................................................................................... 11

CHAPTER

1 INTRODUCTION .................................................................................................... 13

Statement of Hypothesis ......................................................................................... 14 Objective of Research............................................................................................. 15

2 LITERATURE REVIEW .......................................................................................... 17

Automation and Mechanization in Manufacturing ................................................... 17 Prefabricated Construction Components ................................................................ 18 Precast Concrete .................................................................................................... 18 Modularization Technique ...................................................................................... 19 Quality, Schedule, and Cost Differences ................................................................ 20 Safety Improvements and Sustainable Applications ............................................... 22 3-D Printing Technology ......................................................................................... 23 Large Scale 3-D Printing in Architecture ................................................................. 26 3-D Printing with Concrete for Construction ........................................................... 27 Instances of 3-D Printing with Concrete ................................................................. 29 Construction Skilled-Trade Shortage and Decrease in Efficiency .......................... 31

3 RESEARCH METHODOLOGY .............................................................................. 34

Goal of Research .................................................................................................... 38 Research Procedure ............................................................................................... 34 Concrete Masonry versus Tilt-Up Construction ...................................................... 35

4 CALCULATIONS AND RESULTS .......................................................................... 38

Assumptions for Calculations ................................................................................. 38 Total Cost and Material Calculations ...................................................................... 38 Scheduling Calculations ......................................................................................... 57 Wind Loading, Strength, and Quality Calculations .................................................. 58

6

5 CONCLUSIONS ..................................................................................................... 74

6 RECOMMENDATIONS .......................................................................................... 77

LIST OF REFERENCES ............................................................................................... 80

BIOGRAPHICAL SKETCH ............................................................................................ 84

7

LIST OF TABLES

Table page 4-1 Materials ordered, 2016 inflation costs, and resulting cost increase. .................. 38

8

LIST OF FIGURES

Figure page 4-1 Plan view of walls W1-W21. ............................................................................... 51

4-2 Elevation view of wall W1, .................................................................................. 51

4-3 Section view of wall W1. ..................................................................................... 52

4-4 Elevation view of wall W2. .................................................................................. 52

4-5 Elevation view of wall W3. .................................................................................. 53

4-6 Elevation view of wall W4. .................................................................................. 53

4-7 Elevation views of walls W5 and W6, ................................................................. 54

4-8 Elevation views of walls W7 and W8. ................................................................. 54

4-9 Elevation views of walls W9, W10, W11, W12, W13, and W14. ......................... 55

4-10 Elevation views of walls W15, W16, W17, and W18. .......................................... 55

4-11 Elevation views of walls W19, W20, and W21. ................................................... 56

4-12 3-D printed truss design of a typical printed concrete wall at 50% scale, ........... 56

4-13 Basic wind speed, V, for Gainesville, FL. ........................................................... 68

4-14 Wind Directionality Factor, Kd, for MWFRS. ....................................................... 69

4-15 Internal Pressure Coefficient, GCpi, for an Enclosed Building. ............................ 70

4-16 Velocity Pressure Exposure Coefficient, Kz. ....................................................... 71

4-17 External Pressure Coefficients, GCpf. ................................................................. 72

4-18 External Pressure Coefficients, GCp. .................................................................. 73

9

LIST OF ABBREVIATIONS

ABC Associated Builders and Contractors Inc.

AEC Architecture, Engineering, Construction

AGC Association for General Contractors

AM Additive Manufacturing

ASCE American Society of Civil Engineers

BIM Building Information Modeling

C&C Components and Cladding

CECU

CMU

Career Education Colleges and Universities

Concrete Masonry Unit

CRAFT Center for Rapid Automated Fabrication Technologies

FDM Fused Deposition Modeling

LEED Leadership in Energy and Environmental Design

MEP Mechanical, Electrical, Plumbing

MWFRS Main Wind Force Resisting System

NRMCA National Ready Mixed Concrete Association

SCO Smart Construction Object

VDC Virtual Design and Construction

VGM Van Goettling Masonry, Inc.

WASP World’s Advanced Saving Project

3-D Printing Three-Dimensional Printing

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Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the

Requirements for the Master of Science in Construction Management

EVALUATING 3-D PRINTING WITH CONCRETE AT THE ALACHUA COUNTY PUBLIC DEFENDER’S OFFICE IN GAINESVILLE, FL

By

Samantha L. Leonard

August 2017

Chair: Larry C. Muszynski Cochair: R. Raymond Issa Major: Construction Management

The number of skilled tradesmen for construction has decreased since the

market crash in 2008, and from this shortage came innovations in automation that may

inevitably replace the skilled construction trades. Currently in Florida there are

shortages of skilled tradesmen, thus creating schedule disruptions to large construction

projects when looking at time and cost due to the labor involved. Concrete masonry has

been identified as a trade that is short of skilled tradesmen, and predictably any

masonry block work will be negatively affected, including but not limited to quality of

work. Automation through 3-D printing with concrete may be able to solve more of these

everyday issues in the construction industry, creating positive changes by way of

schedule, cost, and quality.

The scope of this research is to evaluate the implementation of 3-D printing with

concrete to potentially replace concrete masonry by looking at concrete masonry units

(CMUs) as a material, the time it takes to install, the cost of labor involved with placing

them, and the quality of the final product in the form of a case study on the Alachua

County Public Defender’s Office located in Gainesville, FL. The principal purpose of

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this research is to determine whether automation through the use of 3-D printing with

concrete provides a feasible and practical option to concrete masonry on construction

projects.

The research in this particular case study found the calculations for 3-D printing

with concrete produced a feasible alternative based on the parameters of cost,

schedule, and building quality.

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CHAPTER 1 INTRODUCTION

There has been an influx of information on the process of three-dimensional

printing (3-D printing) and its applications within smaller, investigational developments

and assignments in this time of technological renaissance. Yet, the application of 3-D

printing in projects of larger scale have been slim, whether it be due to financial

feasibility or lack of applicable nature. 3-D printing has been in development since the

first patent application was filed in 1980, but the technique is considered somewhat

novel now that it has become an available resource to the general public. Proclaimed as

a possibility for defining the next Industrial Revolution, 3-D printing has the conceivable

potential to become the standard in manufacturing practices, especially in the building

industries, despite the traditional lethargy of the construction industry to acclimate to the

ever evolving technological environment. Specifically, China and Dubai have

progressed ahead of the curve by quickly developing and successfully implementing

3-D printing within both residential and commercial construction projects, and with the

capacity for production inside a factory setting as well as directly in the field (Sevenson

2015, Millsaps 2015). Rapid fabrication, delivery, and assembly have consistently been

valued portions of the typical schedule in building construction, and as construction

continues to grow into one of the prolific industries of this generation, it will be required

to continue supplying the demand to remain successful. To keep up with this demand,

the need for skilled-trade worker jobs will significantly increase, but whether they will be

able to be filled is up for debate, especially in the United States where high schools

push students towards a four-year college education rather than a vocational school

education. Mechanization has become a solution to this problem that has not been fully

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realized, and the concept of 3-D printing with building materials such as concrete

replacing the work of skilled tradesmen will comprise the emphasis of this investigation.

Statement of Hypothesis

For this case study, the following hypothesis has been determined after

evaluating various studies, professional research papers, construction- related articles

and other relevant pieces in this area:

Hypothesis: Utilizing 3-D printing with concrete in comparison to concrete masonry to construct a two-story building given the same on-site conditions will result in a method with an equal or greater value, especially in regards to the parameters of project schedule, construction budget, and structure quality.

The likelihood of more mechanization in the construction industry becomes

imminent as more construction work becomes available and less people enter the

workforce of construction trades. 3-D printing with concrete for commercial construction

thus has become more of a reality now that it has been experimented with and used to

produce different types of buildings around the world in places like the Netherlands, the

Philippines, China, Dubai, Russia, and even in the United States. With the elimination of

human error found in the skilled trades, the method of 3-D printing with concrete

provides a way to build an equivalent concrete structure at an equal or expedited rate

and at an equal or lower cost. These factors can compound together to potentially save

the building parties the time and money they need to increase production rates, which

equates into a greater profit margin at the end of a project when compared to

conventional methods. These savings can then be passed on to the owner group, who

will be able to fully utilize their structure faster and can collect revenue from it in turn.

The research addresses that by using a 3-D printer to construct a concrete structure of

a building, a contractor should benefit by equal or reduced overhead costs and

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construction time on the project, and the owner group should benefit by seeing an equal

or faster return on investment on their structure.

Objective of Research

The purpose of this research is to compare the newest construction method of

3-D printing with concrete with the more traditional method of concrete masonry work.

The fundamental goal of the research will be to determine the potential for an alternate

method of concrete construction in the wake of a skilled labor shortage. It will elucidate

whether 3-D printing with concrete is a construction method that provides the possibility

for equal or improved project cost, construction schedule, and structure quality when

comparing the construction of a two-story masonry-built structure under the same

on-site conditions. Recent changes to building processes have included prefabrication

and factory-based assembly, both of which have provided improvements to construction

projects on the aforementioned parameters. This research will provide an emphasis on

the concept of mechanization in construction and how “innovated changes usually arise

from a need to improve a given situation” (Bernold et al.1990), with the “given situation”

referring to the skilled labor shortage and the antiquated conventional methods in which

our buildings are constructed.

This case study will demonstrate that there lies the potential to provide a similar

building by the unconventional construction method of 3-D printing with concrete,

contributing an alternative to the current way construction is accomplished. It will also

acknowledge how the construction industry should consider new methods of

construction involving technology despite push-back to invest and assimilate. It will also

provide information for both examined methods on a commercial construction project for

the following three factors; project cost, project schedule, and structure quality. Building

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professionals including architects, engineers, and contractors will benefit by recognizing

that there is an additional, non-conventional method to add to their construction

repertoires and how applicable this method is in practice. Owner groups, investors, and

beneficiaries may also benefit from this research by allowing them to become more

aware and willing to participate in an innovative practice that may soon be the future of

concrete construction.

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CHAPTER 2 LITERATURE REVIEW

Automation and Mechanization in Manufacturing

Equipment automation has become more commonplace in the construction

industry, meaning that construction has become more mechanized through the

development of machines that have the capability of building the structures themselves.

This can be through assembling pieces of buildings in factory settings, or placing

structures directly on site. Thus, in the midst of the technological renaissance,

automation has become less the exception and more the rule amongst many of the

dominant industries (Paulson 1985). As one of the oldest and leading industries, the

construction industry has been traditionally set in the ways of conventional methods and

has had a difficult time adapting to new methods and technologies. However, as the

skilled trades in the construction industry experience a decline in employment and by

extension, productivity, equipment automation may become a necessity rather than a

luxury in the field.

Automated technologies and robotic processes have the capability of solving

several issues that cause distress within the industry, including but not limited to those

in schedule, cost, quality, safety, and skilled labor accessibility (Kumar et al. 2008).

“Robots are used in phases of construction work for production of material, construction

of different works (quality control), maintenance and operations (including inspection

and monitoring), and performance in hazardous environments” (Kumar et al. 2008).

However, there are drawbacks to using automated technologies for construction, such

as machinery having the intrinsic characteristic of needing to be reprogrammed for

different projects, making them inflexible to change (Paulson 1985). There is also the

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fact that a majority of newly developed automated equipment can be very large, and

therefore expensive to support for construction projects due to factors such as

transportation, startup, and specialized operator know-how.

Prefabricated Construction Components

Prefabrication is the act of manufacturing a complete construction assembly from

raw materials within a factory setting, from which these complete assemblies are then

shipped to the construction site to be installed into the structure. This act of

preassembly is used as a timesaving technique in the construction industry, and has

become increasingly common in the design of structures around the globe due to

aesthetic customizability, control over quality, shortened schedule, reduced

environmental impacts, and ease of installing preassembled products on site (Tam et al.

2009). The technique can be as simple as placing concrete in a factory setting, or as

complicated as assembling whole four-walled modules that make up portions of entire

buildings. Prefabricated elements can also come in a variety of sizes; however, it is

most economical for a project if these assemblies are more compact so shipping costs

can be rationalized, but it should be recognized that there are many instances where

larger assemblies are constructed in-factory, shipped, and delivered.

Precast Concrete

Prefabrication is an incorporating term for many different forms of construction

material assembly, and prefabricated concrete is one such method that is widely used in

the construction and engineering industry. Also referred to as precast concrete, a

special concrete mixture is formed up and reinforced in a controlled environment, curing

into the desired shape and finish that the specifications for a project calls for. To

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achieve the desired smooth concrete finish that precast concrete typically gives, fine

aggregate is used in the composition of the concrete mixture rather than larger

aggregate that can be found in cast-in-place concrete. Both interior and exterior wall

panels and slabs are common precast concrete elements, and can be used to construct

entire buildings, or for improved aesthetic façade cladding, soundproofing, and fire

resistance. By using this method to simplify concrete placement, it creates a way to

form walls and elevated slab structures while foundations are being placed and cured. It

works to save time in the schedule by using crane erection to install the prefabricated

panels rather than completing twice as much crane work to erect formwork for cast-in-

place walls, not to mention “the possibility of delays due to weather conditions and

traffic impeding concrete trucks” (Leonard 2016). Precast concrete is also a common

material for forming substructure utility piping for mechanical, plumbing and electrical

(MEP) applications, as well as sewage and storm water drainage infrastructure.

Modularization Technique

Modularization is a method of prefabrication that involves constructing complete

volumetric units that span the size of typical rooms and are fully fitted with MEP

connections, finishes, and furnishings (Lawson et al. 2012). These units are designed

and engineered to interconnect with each other to form a single building, either

functioning in a single level capacity or a multistory structure that is stabilized by a

central core system composed of steel and concrete elements (Leonard 2016). The

modules, also referred to as pods, have the capacity to be varied in their individual

designs or identical in nature. This has to do with the ultimate purpose of the building,

but the design of each pod also depends on location within the building, i.e. modules for

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corner locations will be structurally supported differently than modules for side-walls

(Leonard 2016). For multistoried structures, because each pod acts as its own room or

portion of a room, the modularization method provides dualistically insulated floors,

walls, and ceiling systems when they are interlocked with neighboring units. This

double insulation between modules provides extra sound barriers and better fire

resistance between areas, as well as easier regulation of temperature (Lawson et al.

2012). The use of this prefabrication technique of is a type of off-site construction, and

when used, is most commonly for the construction of hotels, apartments, and cruise

ships. The preassembled units provide the full assemblages for the erection of the

structure, requiring a crane to lift the pods into place and a crew to connect each

module to its adjoining unit.

Quality, Schedule, and Cost Differences

Automation and mechanization of construction, whether in a factory situation or

directly on-site, has greater potential to provide a certain level of quality that

conventional methods of construction cannot provide. Through using these methods in

the construction process, automated equipment can provide a calculated, auditable

method for designer, builder, and owner groups to assess the creation of portions of a

structure (if not the entirety of a structure) that can be altered if desired through

adjustments in the equipment without negatively effecting project schedule (Li et al.

2014). These pieces of machinery have the ability to be calculatedly precise, speedy in

production, and able to output a volume of product that humans are ultimately incapable

of without computer aid. These factors directly affect the schedule of a project, greatly

reducing the time for production as automated equipment does not necessarily have the

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restrictions that the human body does, such as the need for sustenance and rest, and

can hypothetically run on a 24 hour-a-day schedule if needed. In a study done on

multistory apartment buildings in Australia, results of faster construction times up to

50%, build times reduced to 40-50% that of traditional on-site construction, and better

predictability for product delivery to the site were found when using off-site construction

methods using automated equipment (Boyd et al. 2013). In that same study, it was

determined the quality was deemed superior due to factory-based quality control

methods, as well as up to 10% less costly in terms of capital costs distributed through

involved building parties.

Apis Cor is a Russian-based company that developed a 3-D printer used to print

entire concrete buildings on-site, and their statistics on quality, schedule, and cost

savings support that 3-D printing buildings will improve on these aspects (Apis Cor

2017). With only one mobile crane needed to transport the 2-ton machine and two

people needed to operate the printer, the 3-D printer saves on costs of transportation

and man-power. A claimed 30 minutes are needed for installation and set-up, meaning

the printer can be delivered, set up, and begin printing on the same day, saving time on

construction schedule. The printer can also print concrete at a rate of up to 10 m/min

(about 33 ft/min) at its fastest rate, printing up to 100 m2 (about 1076 ft2) of effective

area per 24 hours. The company claims that there is a 40% increase in overall value

when compared to a “regular concrete building”, with specific quantity breakouts for

building phases as follows: foundation work at minus 15% cost, building frame

construction at minus 25% cost, outer and inner finishing at minus 60% cost, services at

minus 20% cost, and logistics at minus 20-30% cost (Apis Cor 2017). Cost is one of the

21

foremost driving factors for construction, and automated construction is shown to

provide a way to effectively reduce cost, along with the previously discussed benefits of

improved quality and reduced schedule in terms of production in building timeline.

Safety Improvements and Sustainable Applications

A major incentive for the use of automated equipment in the construction industry

is the ability to increase safety measures and minimize accident risk for skilled workers

in the field (Bernold et al. 1990). Unfortunately, construction has become an industry of

liability, but automation provides the ability to place humans out of dangerous working

conditions, i.e. welding in a factory setting on the ground floor rather than welding in the

field on a high-rise building. “The cost of safety is significant” (Kumar et al. 2008),

however it may be the single most important aspect of construction and the ability for a

project to be successful, allowing automated equipment to become another solution to a

supreme problem in the industry. By implementing automated equipment in the place of

skilled workers, “robots could provide welcome relief from the safety and health

problems construction workers face every day” (Paulson 1985).

Sustainability has become an important factor in the construction industry that

needs to be considered long before a construction project can begin. Corporate social

responsibility by owner groups are pushing sustainable practices in design and

construction onto renovation and new construction projects (D’Silva et al. n.d.). This is

supplemented by expectations in the construction industry as well, coming from third-

party organizations such as the U.S. Green Building Association and their certification

for green buildings called “Leadership in Energy and Environmental Design” (LEED)

(U.S. Green Building Council 2017). Automated construction has the ability to create

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less waste through using exact amounts of material; “once a template is designed and

engineered to the desired final product, it can be entered into an automated system

where components are cut to size and either assembled by the use of robotics or skilled

laborers, quickly and systematically” (Leonard 2016). Any waste that remains from this

process can be recycled by using that material in subsequent products or another

project. Energy savings can be attained through efficiency gained in automated

equipment, and noise pollution can be reduced by containing construction within one

physically enclosed area rather than disrupt the surrounding areas (i.e. homes, roads,

businesses) near the construction site (Lawson et al. 2012).

In a study done on multistory residential buildings built modularly in Europe,

safety was improved greatly both in the factory setting for the initial building phase and

on site for the assembling phase, estimating that reportable accidents were reduced by

over 80% relative to construction completed by conventional methods (Lawson et al.

2012). Construction waste was reduced to 5% with a greater chance to recycle waste in

a factory setting, from 10-15% on a conventional construction site. Noise pollution was

reduced from 30-50% when the construction/assemblage phase was taking place on

site (Lawson et al. 2012).

3-D Printing Technology

Three-dimensional printing (3-D printing) is not a new concept, and has been in

development for the past 30 years (Matias and Rao 2015) to go from an idea to what

some call the forerunner of the next industrial revolution (Nigro 2016). The process of

3-D printing an item starts as an idea that can be referred to as a fragment of data, a file

with the information necessary to go from binary zeros and ones into a physical

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representation of the computer formulated model. Because this process is entirely

computer-based, it allows for the ability to collect facts and figures on the product

through the sum of its life that could potentially streamline manufacturing the product.

By having the capability to correct productivity errors in the manufacturing process, 3-D

printers can be considered as smart construction objects (SCOs), or “construction

resources that are made smart by augmenting them with technologies conferring

autonomy, awareness, and the ability to interact with their vicinity (Niu et al. 2016).

Artificial intelligence facilitates better decision-making by using data gathered in real-

time and using mathematical formulas to solve problems and perform at a more efficient

level. This is directly related to the 3-D printing process, for when a printer layers

material to “build up” a product, it must choose the path of least resistance to construct

the most efficient product. It does this by being “aware” of its surroundings and acting

accordingly (Niu et al. 2016).

3-D printing is considered an “additive” manufacturing technique, which involves

placing layers of the same or different materials on top of each other to produce a

complete, 3-D product. Therefore, it does not involve any “molds, complex

manufacturing procedures, special fixtures, or tools” (Lu et al. 2016) to form a finished

product. As creatively stated by Lu et al., 3-D printing as an additive manufacturing (AM)

technique achieves “use of almost any material to fabricate any part, in any quantity and

any location, for any industrial field” (2016). Any material includes liquids, powders,

metals, or sheet material (“AM Basics - What is Additive Manufacturing?” 2017) and

even includes biological tissue material to print sheets of cells to form skin, as well as

larger, more solid structures such as organs for transplantation uses (Murphy and Atala

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2014). Any part includes architectural models, prosthetic limbs (Scott 2017), and knick-

knacks created on personal sized machines, which transitions into any quantity. Any

quantity speaks to the speed at which the AM machine can produce 3-D goods, as a

machine can build up any number of items for 24 hours per day if necessary, not limiting

production time to a typical person working an 8-hour day. Any location speaks to the

various sizes of AM machinery, and the possibility of transportability; at a greater size,

3-D printers can either produce large items within the confined space of the frame, or if

on a track can move to fabricate large structures. Any location also includes the

International Space Station, where tools and other items have been printed in space

from files transmitted from Earth (Harbaugh 2014). Lastly, any industrial field covers just

that, any trade that involves the need for creating products through the AM technique,

such as the aerospace industry by creating new ways to construct structural and load-

bearing parts by using unique shapes that can only work effectively when printed as a

single piece (Lu et al. 2016).

There are also a number of different formats that a 3-D printer can be used to

effectively print an item. Fused Deposition Modeling (FDM) is the most common 3-D

printing method for small 3-D printers, building the printed item from the bottom up with

any overhanging portions needing support material to hold them in place before being

removed at printing completion. It is also referred to as the Contour Crafting method

when large-scale items are being printed with the ability to provide a clean finish to the

product by use of an adjustable outer rim at the printing nozzle that “prevents material

from flowing out unimpeded” (Teizer et al. 2016).

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Large Scale 3-D Printing in Architecture

The beauty and wonder that has been derived out of architecture through history

is immeasurable, and unfortunately the capabilities of traditional construction practices

have not always allowed for architectural creativity to become reality. Building

Information Modeling (BIM) and Virtual Design and Construction (VDC) were created to

serve this need, as well as to foresee errors in design and engineering before becoming

an issue in the implementation phase on site. By providing these tools for the

architecture, engineering, and construction (AEC) trades to communicate wants, needs

and abilities of the design, the building industries have been given the ability to create

bolder designs that could conceivably be constructed using conventional building

methods (Lu and Korman 2010). However, in some ways these tools could not reach

their full capacity, as the optimum amount of architectural creativity could not be

realized in physical form. With the commercial availability of the 3-D printer, the use of

BIM and VDC could make hypothetical models on the computer screen into the reality

of physical models and true-to-scale building elements.

Architectural companies all over the world have been looking to implement 3-D

printing not only in miniature scaled models to exhibit conceptual designs to clients, but

also into their fundamental designs and prospective construction projects. “In

architecture, 3-D printing is being used to fabricate architectural design models.

Architects divide architectural structures into load-bearing structures and

embellishments. 3-D printing, with its ability to fabricate complex structures, will no

doubt play an important role in embellishment design in this field” (Lu et al. 2016). While

Lu et al. has acknowledged that 3-D printing will have a profound effect in

26

“embellishment design”, it can also be deigned with some certainty that under the right

conditions, 3-D printing will be able to tackle the structural “load-bearing” aspects of

construction in the future (2016). One such company taking on this challenge is DUS

Architects out of the Netherlands and their initiated project “3D Print Canal House”

located in North Amsterdam (DUS Architects 2017). 3-D printing in architecture has the

opportunity to bring the construction industry into the technological fold, and the more

the profession delves into the possibilities of 3-D printing, the greater the chance that

construction will take it on in the future.

3-D Printing with Concrete for Construction

While the idea of printing items with concrete paste is not necessarily a new idea,

printing items that can withstand structural loads out of concrete material is a concept

that has been experimented with in recent years for construction purposed. The World’s

Advanced Saving Project (WASP) has been experimenting with their idea of printed

beams with reinforced concrete material for housing applications, a more sustainable

option than using other more commonly used materials. This method of 3-D printing

reinforcing elements like beams with concrete not only eliminates the need for concrete

forms, but also works to lighten the physical load of the beam itself due to the hollows in

the design, thus saving material in the formwork sense, but also that of raw material

going into the beam itself (Millsaps 2015).

Contour Crafting was created specifically for its potential in automating the

entirety of the construction process by Dr. Behrokh Khoshnevis of the University of

Southern California (USC) (University of Southern California 2014). Dr. Khoshnevis, the

director of the Center for Rapid Automated Fabrication Technologies (CRAFT) believes

27

that one day through his method that there will exist the ability to construct homes, in a

single run, with embedded conduits for electrical, plumbing and air-conditioning, but is

first looking into applications for basic housing purposes (Krassenstein 2015). His

Contour Crafting machine has the capability of fabricating walls and other building

components by a constant layering of concrete material without the use of formwork and

that stands on its own as the material builds itself up due to calculated curing speed.

Contour Crafting has the possibility to span from commercial applications, low-income

and emergency housing, and even as far out as space colonization prospects

(University of Southern California 2014).

There has been concern over the increased use of concrete in construction over

the years due to expelled carbon dioxide emissions during the curing process (Murray-

White 2016), but 3-D printing with concrete can, prospectively, be very environmentally

friendly. It can eliminate construction waste from a project by removing the need for

concrete formwork. It can lead to less total material use, including the need for steel

reinforcement within the concrete. It can reduce transportation of material, equipment

and people thus leading to less carbon emissions from vehicles and heavy construction

equipment. It can lead to durable, long lasting structures that do not need to be replaced

or renovated as often, as well as less-susceptible to damage due to seismic activity

(University of Southern California 2014). 3-D printing with concrete provides several

positive reasons, especially within the environmental realm, for the construction industry

to consider future applications and feasibility.

28

Instances of 3-D Printing with Concrete

One of the first successful implementations of 3-D printing with concrete occurred

in Excelsior, Minnesota in the United States by Andrey Rudenko, a father who wanted

to give his daughter a tree house, but 3-D printed a 12 foot, castle-playhouse for the

backyard instead (Rudenko 2015). Rudenko constructed his own enlarged 3-D printer

after building a small, tabletop printer that extruded a plastic material for printing, and he

is currently working on perfecting the enlarged printer so that it can print at a rate of 24-

hours per day at maximum capacity (Rudenko 2014). “A new era of architecture is

inevitable, and I'm excited to see where the next few years will lead in terms of

construction and design. I have previously been sure I could print homes, but having

finished the castle, I now have proof that the technology is ready.” (Rudenko 2014).

Rudenko was also a crucial partner in developing the Lewis Grand Hotel addition

located in the Philippines. The villa “party house” was printed from the ground-up using

local materials including sand and volcanic ash mixed into the extruded concrete. The

villa, meant for couples, also included a printed Jacuzzi in the living room for added

glamour, and each room had a printed hot tub (Alec 2015).

The Yingchuang Building Technique (Shanghai) Co. Ltd, commonly known as

WinSun, a company based out of Shanghai, China has had success in printing entire

building structures, their first achievements being 10 basic concrete houses printed on-

site in 2013 (Boston Consulting Group 2016). The company went on to complete a 6-

story apartment complex and a stately manor using a machine measuring 20 feet tall,

33 feet wide and 132 feet long (Sevenson 2015), mimicking the design originated by Dr.

Khoshnevis from USC for his concept of Contour Crafting. However, these buildings

29

were constructed offsite by the printer and assembled on-site, which was not intended

by Dr. Khoshnevis’s method. WinSun claims that they were “able to save 60 percent of

the materials typically needed to construct a home, and can be printed in a time span

which equates to just 30 percent of that of traditional construction. In total, 80 percent

less labor is needed, meaning more affordable construction, and less risk of injury to

contractors” (Sevenson 2015). The company experiments with various types of

materials, including recycled construction waste mixed into a concrete base, however

the apartment complex and the manor was constructed using a mixture of cement,

sand, reinforcing fibers, and certain additives to print the central structure (Boston

Consulting Group 2016).

Progress has also been made in Dubai, United Arab Emirates, as the “Dubai 3D

Printing Strategy” global initiative presented the first 3-D printed office building in 2016,

claiming that it took a total of 17 days to print one top and one bottom unit, each office

coming to 2,000 SF of space for meeting purposes and team exercises. They used a

machine measuring 20 ft tall, 40 ft wide and 120 ft long, as well as a special mixture of

reinforced concrete (Millsaps 2016). They cite benefits of reduced production time by

50-70%, reduced labor cost by 50-80%, and reduced construction waste by 30-60%

(Millsaps 2016).

Apis Cor, the aforementioned company with several statistics on their 3-D printer,

now has a printed house to show for their published data. After the project was

announced in December 2016, the 38 m2 (about 410 SF) residence was completed in

February 2017 in under 24 hours for a cost of $10,134, not to mention it was built on-

site during Russia’s coldest time of the year, and the concrete could only be placed at

30

above 5°C (about 41°F) (“The First On-Site House Has Been Printed in Russia” 2017).

The printer was placed in the center of the circular home, printing around itself to

produce the reinforced walls of the structure, and after completion a crane lifted it out

from the inside of the structure. The foundation and roof were placed before and after

the walls were completed by supplemental installers, respectively. Insulation was added

by skilled tradesmen for this particular project, but Apis Cor noted that this process

would likely be automated in the future. Outdoor and indoor finishing were also

completed on the house instead of leaving the exposed horizontal lined-look that the

machine typically leaves after layering the concrete (“The First On-Site House Has

Been Printed in Russia” 2017).

Construction Skilled-Trade Shortage and Decrease in Efficiency

In the past decade, the United States has seen a noticeable decrease in

employment within the construction industry, due in part from the Great Recession

spanning from 2007 to 2009 (Rohner 2015). However, this decline began in 2006, and

hit its peak three years after the recession ended in 2012, when 16.6% of construction

businesses had disappeared, and 29.8% of industry personnel (or 2.3 million) had been

let go from their jobs (Rohner 2015). Although about one million of those jobs have

returned after this downturn, a large issue remains in the recovery of the industry.

Career Education Colleges and Universities (CECU) reported that a possible reason for

the difficulty in finding employees was the lack of hiring and/or training young workers

(Dakduk 2016). There also exists the idea that the younger population has not found the

field of construction attractive, and have thus been looking elsewhere for career

advancement rather than enter vocational schools or apprenticeships with the skilled

31

trades (Slowey 2015). In 2015, seeing the need for the younger generation to enter the

construction industry, the Association for General Contractors (AGC) developed a

“Workforce Development Plan” (AGC 2015) that outlined applicable ideas for the United

States to filter young people back into the skilled trades. Locally, the state of Florida is

no stranger to the scarcity of the skilled trades in construction. Issues such as the

economic downturn in the late 2000s, traditionally low pay, Florida heat, older workers

retiring, and younger people not interested in the industry directly contribute to this

shortage (Griffin 2015). Steve Cona III, the president and CEO of the Florida Gulf Coast

Chapter of the Associated Builders and Contractors Inc. (ABC) organization is quoted

saying that finding skilled workers is “our biggest challenge facing the entire industry

right now” (Griffin 2015).

Decrease in construction efficiency from various areas is another factor that has

been studied in the construction industry, and efficiency has not been helped by the

shortage of skilled workers. When there is a decline of skilled labor, there is a direct

negative correlation on project schedule; as skilled worker availability decreases, project

schedule increases (Lucie 2017). Claims have also been made that construction

productivity has declined in part due to “its slow adoption of information technology,

robotics and operations innovation (Said et al. 2014).” This is a possible and probable

solution to increases in industry efficiency, as the number of skilled workers entering

and being retained in the industry declines. There is also the factor of human error to be

considered in the efficiency equation; equipment automation in building technology

allows for less error, thus resulting in the decrease of possible schedule setbacks due to

human error (Lu and Korman 2010). Other factors that go into construction efficiency

32

include precision and accuracy, speed and volume produced, and waste generated, all

of which could hypothetically be affected positively by the introduction of equipment

automation. Precision and accuracy is maximized by coded instructions input into

computers, speed and volume produced is maximized by lack of error in the coded

instructions and ability for automated equipment to work as long as necessary (24 hours

per day, 7 days per week if necessary), and minimized waste due to accuracy of the

automated equipment and its ability to build efficiently in the path of least resistance

(Niu et al. 2016).

33

CHAPTER 3 RESEARCH METHODOLOGY

To accomplish the objectives of this research, project information and construction

documents were obtained from the Alachua County Public Defender’s Office building

project. The documents for this building are public record, and can be obtained without

concern for proprietary rights. Signed and sealed 100% Construction drawing and

specification sets, accepted bid proposals from the masonry subcontractor, approved

submittal packages and testing documents from the masonry subcontractor, sample

calculations from the engineer of record, and construction schedules from the general

contractor were utilized. The documents relating to the concrete masonry units (CMUs)

installed were utilized to reference the measurements and dimensions of the CMU

structure, material specifications, material quantities installed, installation practices,

installation cost, and installation time.

In using these documents obtained from the Alachua County Public Defender’s

Office building project, an overall schedule, a total cost, and the tested quality were

determined for the concrete masonry work completed for the construction of the

estimated 21,360 square foot, two-story building.

Goal of Research

The goal of this comparison of methods research is to determine whether 3-D

printing with concrete has the potential to be a comparable or better construction

method than concrete masonry work in the areas of schedule, cost, and quality. The

skilled labor trade is struggling to find experienced tradesmen, or at least those willing to

partake in apprenticeships to learn the trade, and robotics and automated technology

may be the solution that the construction industry needs to supplement the labor

34

shortage, if not to improve the current building methodology. The results of this research

have the potential of providing construction professionals with a solution to the lack of

skilled labor currently experienced in the industry, as well as providing researchers with

preliminary information for performing supplementary research on 3-D printing with

concrete.

Research Procedure

To begin the research process, a critical difficulty of the current construction

industry and its methods was established, followed by the evaluation of a suitable

substitution that would provide a comparable construction method. The next stage of

this research was to acquire documents from a recently completed, local building that

were public record so that if questions arose about information in the documents, they

could be resolved without added effort on external parties. Once the project was

selected, the next step in this research was to complete calculations for the conjectural

use of 3-D printed concrete in the areas being compared between building methods.

Once these calculations for using 3-D printed concrete in place of concrete

masonry for the Alachua County Public Defender’s Office were made, the results were

analyzed and comparisons for each method would be made to assess differences in

total cost, project schedule, and structure quality to draw a conclusion. If the results for

3-D printed concrete demonstrate a reduction in the total cost and project schedule, as

well as a constancy of structure quality or one that is exceedable, it can be said that 3-D

printing with concrete may prove to be another construction method to be seriously

considered in the changing construction climate.

35

Because the method of 3-D printing with concrete is not widely used as a

conventional construction process, there is no published, comparable data of printed

concrete walls from a similar project. As a result, published data from a smaller project

produced by Apis Cor in Russia was used to complete comparable calculations for the

hypothetical printing of the concrete masonry portions of Alachua County Public

Defender’s Office. To make up for any discrepancies in the quality of the materials used

in Russia as compared to those materials used the United States, calculations were

made to determine the ultimate compressive strength and wind loads so that the

theoretical printed concrete walls could provide at the very least the equivalent

attributes that the CMU walls give the structure. It should be noted that Russia uses

different categorical descriptions for concrete, such as concrete grade, strength class,

and densities displayed in metric units. Appropriate conversions were made to correct

any discrepancies in the contrasted relationships, and are disclosed in the calculations.

Concrete Masonry versus Tilt-Up Construction

In evaluating suitable substitutions for the construction industry’s current building

methods, it was considered that tilt-up construction may provide a more direct

comparison to 3-D printed concrete than concrete masonry unit construction would. It

can be disputed that the precast concrete of tilt-up panels may be made up of a more

similar material to that of the concrete layers that make up the walls of a 3-D printed

concrete structure, however the fact remains that the design of the 3-D printed concrete

walls is more akin to that of the spaces found in concrete masonry units. 3-D printed

concrete walls are not just layered planes that make up a solid wall; they are designed

to provide a web-like wall system with spaces in between the printed angle web

36

members. These spaces can be filled with grout or insulation if the specifications of the

project call for it, just as in concrete masonry units. A possible difference between the

3-D printed walls and the concrete masonry units is the need for steel reinforcement,

which would be determined by the specific machine and 3-D printing method selected to

construct the walls. The printed concrete also has the potential to use fibrous

reinforcement or a similar material in the concrete mix for reinforcement.

37

CHAPTER 4 CALCULATIONS AND RESULTS

Assumptions for Calculations

The following assumptions were made when completing calculations for concrete

3-D printed walls. Not all of these assumptions reflected in the literature, but are

being made to be conservative in the calculations of this thesis.

• Assumed design for a typical wall is truss-like, with a total wall thickness of

12 inches, exterior partitions 1.5-inch-thick, and 1.5-inch-thick interior

alternating supports angled at 45 degrees.

• Assumed concrete material waste factor at 4%.

• Assumed cost of concrete at $110 per cubic yard.

• Assumed 3-D printer printing efficiency at 75%.

• Assumed $5,000 per day rental cost for 3-D printer.

• Assumed $2,000 per week rental cost for additional equipment.

Assumed $90,000 yearly salary for a construction engineer.

Total Cost and Material Calculations

To determine the total cost of the concrete masonry work that took place on the

$4.5 million Alachua County Public Defender’s Office, the original estimate was

taken from the masonry subcontractor that outbid the other subcontractors by

giving the lowest guaranteed maximum price (GMP) estimate for the total cost of

work, which included labor, materials, and contractor fee. Van Goettling Masonry,

Inc. (VGM) won the project with a total bid of $446,750 for the project, as found in

the bid documents that are filed as public record. This price was not broken out

into line items, however an addendum to the original bid opening on November

2nd, 2015 was issued on November 18, 2015 giving a cost increase in materials

38

for the year 2016. These cost increases totaled to $9,135, which included the unit

prices for the block, brick, and precast, as well as including the mortar, concrete

for cell fill, and masonry accessories for the structure into those unit prices. The

amount of materials used and their unit price increases are shown in Table 5-1.

Table 4-1. Materials ordered, 2016 inflation costs, and resulting cost increase. Material Type Quantity Ordered 2016 Inflation Total Increase

8-inch block 13,600 $0.20 $2,720

12-inch block 6,500 $0.25 $1,625

Brick 42,000 $0.07 $2,940

Precast 1 $1,850 $1,850

$2,720 + $1,625 + $2,940 + $1,850 = $9,135 (4-1)

When taking the cost increase for 2016 totaling $9,135 and dividing it by

the original total GMP estimate of $446,750, it came to an inflation increase of

2.045% from 2015 to 2016.

$9,135$446,750

= 2.045% 𝑖𝑖𝑛𝑛𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑖𝑖𝑓𝑓𝑛𝑛 𝑖𝑖𝑛𝑛𝑖𝑖𝑖𝑖𝑖𝑖𝑓𝑓𝑖𝑖𝑖𝑖 𝑓𝑓𝑓𝑓𝑖𝑖 2016 (4-2)

This inflation increase could then be used to find the cost of each masonry

item used on the project. Using this inflation increase, the total cost of each block

was found by first dividing the cost increase for each set of blocks, brick, and

precast by the calculated inflation increase percentage. This gave the total cost

of the blocks, brick, and precast in the original estimate of $446,750.

8-inch block: $2,7202.045%

= $133,022 (4-3)

12-inch block: $1,6252.045%

= $79,471 (4-4)

Brick: $2,9402.045%

= $143,782 (4-5)

Precast: $1,8502.045%

= $90,475 (4-6)

39

$133,022 + $79,471 + $143,782 + $90,475 = $446,750 (4-7)

The original estimate of $446,750 was then divided by the number of units

that were used on the project to disclose the cost per unit in the original estimate.

At this point, the brick and precast calculations were no longer needed as only

the cost of the concrete masonry units at 8-inches and 12-inches were being

compared to the 3-D printed concrete in this study.

8-inch block: $133,02213,600 𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏

= $9.78 (4-8)

12-inch block: $79,4716,500 𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏

= $12.23 (4-9)

From here, the unit cost increases for 2016 were added to the original cost

per block to find the total cost per unit. It is important to note that this cost per

CMU block encompasses the installed cost which includes raw material, labor

and fees.

8-inch block: $9.78 + $0.20 = $9.98 𝑝𝑝𝑖𝑖𝑖𝑖 8-𝑖𝑖𝑛𝑛𝑖𝑖ℎ 𝑏𝑏𝑓𝑓𝑓𝑓𝑖𝑖𝑏𝑏 (4-10)

12-inch block: $12.23 + $0.25 = $12.48 𝑝𝑝𝑖𝑖𝑖𝑖 12-𝑖𝑖𝑛𝑛𝑖𝑖ℎ 𝑏𝑏𝑓𝑓𝑓𝑓𝑖𝑖𝑏𝑏 (4-11)

These estimated installed unit costs were compared to that of the

RSMeans Building Construction Cost Data 2015 for high strength concrete

masonry units at 3,500 psi (Plotner 2015). The value listed for 8-inch CMU block

was $8.69 per block, and the value listed for 12-inch CMU block was $12.82 per

block. These values include the material cost and the labor cost involved with

installing the CMU block and associated materials such as mortar, grout and

joints. The raw material numbers for each CMU block was $3.92 for 8-inch CMU

block and $4.72 for 12-inch CMU block. It should also be noted that for laying

these types of CMU block, the labor crew considerations are noted as D9, which

40

translates to three bricklayers and three bricklayer helpers in the RSMeans

Building Construction Cost Data 2015.

To verify that the estimate for the number of blocks used for the Alachua

County Public Defender’s Office building was correct, calculations were

completed to find the number of square feet of concrete masonry units that

comprised the walls of the project. From there, that square footage was

converted into the total number of blocks it should take to construct the walls of

the building. The office building is two stories high, standing at a height of 32

feet; two out of the 32 feet are made up of 8 inch concrete blocks located below

grade, making the total height of each floor 15 feet. There is also an exterior

three-walled screen structure standing at 8’-8” tall to obstruct views of

mechanical equipment. It is important to know that the Alachua County Public

Defender’s Office building has many openings for windows and doors, and these

are constructed into the CMU block walls. Therefore, finding the area of each

wall excluding those openings was necessary to find the total CMU block square

footage. There are 21 CMU block walls that make up the main structure of the

building; walls W1 through W8 make up the exterior walls that are comprised of

both 8-inch CMU block and 12-inch CMU block (refer to Figures 4-1, 4-2, 4-3, 4-

4, 4-5, 4-6, 4-7, and 4-8). Walls W9 through W14 make up the interior walls for

the two stairwells in the building, and are comprised of only the 8-inch CMU block

(refer to Figure 4-9). Walls W15 through W18 make up the interior walls for the

elevator shaft in the building, and are comprised of only the 8-inch CMU block

(refer to Figure 4-10). Lastly, walls W19 through W21 make up the exterior three-

walled screen structure and are comprised of only the 8-inch CMU block (refer to

41

Figure 4-11). Taking all of this into account and estimating the areas of each wall,

the 21 walls came to a total square footage of 15,800 SF.

𝑆𝑆𝑆𝑆𝑆𝑆 𝑓𝑓𝑓𝑓 𝑤𝑤𝑓𝑓𝑓𝑓𝑓𝑓𝑖𝑖 𝑊𝑊1 𝑓𝑓ℎ𝑖𝑖𝑓𝑓𝑆𝑆𝑟𝑟ℎ 𝑊𝑊8: 10,820 𝑆𝑆𝑆𝑆 (4-12)

𝑆𝑆𝑆𝑆𝑆𝑆 𝑓𝑓𝑓𝑓 𝑤𝑤𝑓𝑓𝑓𝑓𝑓𝑓𝑖𝑖 𝑊𝑊9 𝑓𝑓ℎ𝑖𝑖𝑓𝑓𝑆𝑆𝑟𝑟ℎ 𝑊𝑊18: 4,020 𝑆𝑆𝑆𝑆 (4-13)

𝑆𝑆𝑆𝑆𝑆𝑆 𝑓𝑓𝑓𝑓 𝑤𝑤𝑓𝑓𝑓𝑓𝑓𝑓𝑖𝑖 𝑊𝑊19 𝑓𝑓ℎ𝑖𝑖𝑓𝑓𝑆𝑆𝑟𝑟ℎ 𝑊𝑊21: 900 𝑆𝑆𝑆𝑆 (4-14)

10,820 𝑆𝑆𝑆𝑆 + 4,020 𝑆𝑆𝑆𝑆 + 900 𝑆𝑆𝑆𝑆 = 15,740 → 15,800 𝑆𝑆𝑆𝑆 (4-15)

To find the total number of blocks, the total SF was multiplied by 1.125

block per SF to find a rough value for how many CMU blocks were needed for

the project. When 15,800 SF was multiplied by 1.125, 17,800 was the number of

CMU blocks needed for this project on average.

15,800 𝑆𝑆𝑆𝑆 × 1.125 𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑆𝑆𝑆𝑆

= 17,800 𝐶𝐶𝐶𝐶𝐶𝐶 𝑏𝑏𝑓𝑓𝑓𝑓𝑖𝑖𝑏𝑏𝑖𝑖 (4-16)

Since there are two different nominal sizes of CMU block to consider in

the composition of each of the 21 walls, the 17,800 CMU blocks needed to be

divided into two amounts. To make up for the discrepancy in CMU block size, the

square footages of the walls were added together, divided by the total height of

the wall, and then multiplied by the height of the type of CMU block the wall was

made from. For walls W1 through W8, the walls were made from 8-inch CMU

block for the bottom 20 feet of the wall, and 12-inch CMU block for the remaining

top 12 feet of the wall. This was done for both types of CMU blocks.

For 8-inch CMU block used:

𝑆𝑆𝑆𝑆𝑆𝑆 𝑓𝑓𝑓𝑓 𝑤𝑤𝑓𝑓𝑓𝑓𝑓𝑓𝑖𝑖 𝑊𝑊1 𝑓𝑓ℎ𝑖𝑖𝑓𝑓𝑆𝑆𝑟𝑟ℎ 𝑊𝑊8: 10,820 𝑆𝑆𝑆𝑆 (4-17)

10,820 𝑆𝑆𝑆𝑆32 𝑓𝑓𝑓𝑓

= 338 𝑓𝑓𝑓𝑓 (4-18)

338 𝑓𝑓𝑓𝑓 × 20 𝑓𝑓𝑓𝑓 𝑏𝑏𝑓𝑓𝑓𝑓𝑖𝑖𝑏𝑏 ℎ𝑖𝑖𝑖𝑖𝑟𝑟ℎ𝑓𝑓 = 6,760 𝑆𝑆𝑆𝑆 (4-19)

42

𝑆𝑆𝑆𝑆𝑆𝑆 𝑓𝑓𝑓𝑓 𝑤𝑤𝑓𝑓𝑓𝑓𝑓𝑓𝑖𝑖 𝑊𝑊9 𝑓𝑓ℎ𝑖𝑖𝑓𝑓𝑆𝑆𝑟𝑟ℎ 𝑊𝑊18: 4,020 𝑆𝑆𝑆𝑆 (4-20)

𝑆𝑆𝑆𝑆𝑆𝑆 𝑓𝑓𝑓𝑓 𝑤𝑤𝑓𝑓𝑓𝑓𝑓𝑓𝑖𝑖 𝑊𝑊19 𝑓𝑓ℎ𝑖𝑖𝑓𝑓𝑆𝑆𝑟𝑟ℎ 𝑊𝑊21: 900 𝑆𝑆𝑆𝑆 (4-21)

6,760 𝑆𝑆𝑆𝑆 + 4,020 𝑆𝑆𝑆𝑆 + 900 𝑆𝑆𝑆𝑆 = 11,680 𝑆𝑆𝑆𝑆, 8-𝑖𝑖𝑛𝑛𝑖𝑖ℎ 𝐶𝐶𝐶𝐶𝐶𝐶𝑖𝑖 (4-22)

For 12-inch CMU block used:

𝑆𝑆𝑆𝑆𝑆𝑆 𝑓𝑓𝑓𝑓 𝑤𝑤𝑓𝑓𝑓𝑓𝑓𝑓𝑖𝑖 𝑊𝑊1 𝑓𝑓ℎ𝑖𝑖𝑓𝑓𝑆𝑆𝑟𝑟ℎ 𝑊𝑊8: 10,820 𝑆𝑆𝑆𝑆 (4-23)

10,820 𝑆𝑆𝑆𝑆32 𝑓𝑓𝑓𝑓

= 338 𝑓𝑓𝑓𝑓 (4-24)

338 𝑓𝑓𝑓𝑓 × 12 𝑓𝑓𝑓𝑓 𝑏𝑏𝑓𝑓𝑓𝑓𝑖𝑖𝑏𝑏 ℎ𝑖𝑖𝑖𝑖𝑟𝑟ℎ𝑓𝑓 = 4060 𝑆𝑆𝑆𝑆, 12-𝑖𝑖𝑛𝑛𝑖𝑖ℎ 𝐶𝐶𝐶𝐶𝐶𝐶𝑖𝑖 (4-25)

Using these SF values, the number of CMU blocks for the 8-inch CMU

block type and the 12-inch CMU block type was found using the conversion

factor of 1.125 block/SF of wall area. This conversion factor was the same for

both the 8-inch block and the 12-inch CMU block since the heights of both are

nominally 8 inches.

For 8-inch CMU block:

11,680 𝑆𝑆𝑆𝑆 × 1.125 𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑆𝑆𝑆𝑆

= 13,140, 8-𝑖𝑖𝑛𝑛𝑖𝑖ℎ 𝐶𝐶𝐶𝐶𝐶𝐶 𝑏𝑏𝑓𝑓𝑓𝑓𝑖𝑖𝑏𝑏𝑖𝑖 (4-26)

For 12-inch CMU block:

4,060 𝑆𝑆𝑆𝑆 × 1.125 𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑆𝑆𝑆𝑆

= 4,570, 12-𝑖𝑖𝑛𝑛𝑖𝑖ℎ 𝐶𝐶𝐶𝐶𝐶𝐶 𝑏𝑏𝑓𝑓𝑓𝑓𝑖𝑖𝑏𝑏𝑖𝑖 (4-27)

According to the quote given by VGM for the amount of materials

purchased for this project, 13,600 8-inch CMU blocks and 6,500 12-inch CMU

blocks were quoted for use on the project. When the amount of CMU block

needed is subtracted from the amount quoted, there are discrepancies. 460 8-

inch CMU blocks should be left over, and 1930 12-inch CMU blocks should be

left over if there were no waste on the project, such as broken CMU blocks.

13,600 𝑞𝑞𝑆𝑆𝑓𝑓𝑓𝑓𝑖𝑖𝑞𝑞 − 13,140 𝑓𝑓𝑖𝑖𝑓𝑓𝑆𝑆𝑓𝑓𝑓𝑓 = 460 𝑓𝑓𝑖𝑖𝑓𝑓𝑓𝑓𝑓𝑓𝑙𝑙𝑖𝑖𝑖𝑖 8-𝑖𝑖𝑛𝑛𝑖𝑖ℎ 𝐶𝐶𝐶𝐶𝐶𝐶𝑖𝑖 (4-28)

43

6,500 𝑞𝑞𝑆𝑆𝑓𝑓𝑓𝑓𝑖𝑖𝑞𝑞 − 4,570 𝑓𝑓𝑖𝑖𝑓𝑓𝑆𝑆𝑓𝑓𝑓𝑓 = 1,930 𝑓𝑓𝑖𝑖𝑓𝑓𝑓𝑓𝑓𝑓𝑙𝑙𝑖𝑖𝑖𝑖 12-𝑖𝑖𝑛𝑛𝑖𝑖ℎ 𝐶𝐶𝐶𝐶𝐶𝐶𝑖𝑖 (4-29)

The idea behind 3-D printing walls using concrete is that there will be

effectively no waste in construction materials since the concrete would be made

or delivered on-site in an exact, calculated amount that would be extruded from

the nozzle directly onto previous layers of the walls. This would not just be a

more sustainable method, but would have the potential to save costs for the

project that could be used elsewhere. However, zero waste is an unreasonable

assumption, and a 4% waste factor was used in the calculations to determine a

more accurate amount of materials used. To find the cost of just the CMU block

material and labor for this project, the estimates that were given by VGM were

multiplied by the cost of each type of block found in the RSMeans Building

Construction Cost Data 2015, totaling to over $200,000 worth of CMU block for

the Alachua County Public Defender’s Office.

For 8-inch CMU block:

13,600 𝑞𝑞𝑆𝑆𝑓𝑓𝑓𝑓𝑖𝑖𝑞𝑞 × $8.69 = $118,200 (4-30)

For 12-inch CMU block:

6,500 𝑞𝑞𝑆𝑆𝑓𝑓𝑓𝑓𝑖𝑖𝑞𝑞 × $12.82 = $83,330 (4-31)

$118,200 + $83,330 = $201,530 (4-32)

If the actual amounts of CMU block used for the project per the SF

calculations were used, the total amount of material and labor cost would be

closer to $172,800, saving about $28,730 off the top.

For 8-inch CMU block:

13,140 𝑞𝑞𝑆𝑆𝑓𝑓𝑓𝑓𝑖𝑖𝑞𝑞 × $8.69 = $114,200 (4-33)

For 12-inch CMU block:

44

4,570 𝑞𝑞𝑆𝑆𝑓𝑓𝑓𝑓𝑖𝑖𝑞𝑞 × $12.82 = $58,590 (4-34)

$114,200 + $58,590 = $172,800 (4-35)

Since the calculations for the CMU block revealed that there was

$201,514 worth of CMU block material purchased and labor used for the project,

the calculations for 3-D printing those same walls from concrete needed to be

done to compare costs. There were a couple of design decisions that were made

for ease of comparison to the CMU block, but it should be noted that there are

several different ways to design and print suitable exterior walls for a building like

the Alachua County Public Defender’s Office. For the case of the theoretically

printed walls, it is possible to use 3000-3500 psi concrete to create a direct

comparison to the CMU block used on this project, however, printed concrete

walls of that strength would be engineered to most likely need reinforcing steel

and possibly need to be filled with a grout or a type of insulation material, much

like the CMU block walls. Conversely, it would hypothetically be possible to

construct the walls without this additional reinforcing material and still achieve the

same amount of structural strength. It is possible for a fibrous material to be used

to reinforce the printed concrete, making steel rebar unnecessary for supporting

the walls. It is also possible for the concrete to be of such a great strength that

the concrete mix would compensate for the lack of reinforcement material all

together, i.e. 10,000 psi concrete. The concrete mix might also have a concrete

setter accelerant additive, as the concrete would need to have a fast setting time

to support the next layer of concrete that would be placed on top of the previous

layer in the printing process. There are also a few other restraints for the

concrete that would be used to print the walls, such as a slump of no more than

45

two to three inches since the concrete needs to be rigid enough to stand on its

own when layer upon layer is stacked. More engineering would be necessary to

define the exact specifications of the 3-D printed walls, but these assumptions

were used when referring to the printed concrete in this study.

The basis of design for a typical wall had a truss-like design, with two

exterior partitions acting as the envelope for the interior alternating supports

angled at 45 degrees (refer to Figure 4-12). This truss like design is reminiscent

of how the CMU blocks have two hollow spaces within the block that provide

support for the wall. For the purpose of this study, the total wall thickness is 12

inches deep, with 1.5-inch-thick exterior partitions enveloping the 1.5-inch-thick

interior alternating supports. To find the total amount of concrete that would be

used for the entirety of the structure to replace the concrete block, a cross-

section of the truss design would need to be taken and multiplied by a length of

12 inches, as well as multiplied by a height of 12 inches to find the total amount

of concrete needed per SF of wall surface area.

1.5 𝑖𝑖𝑛𝑛 + 1.5 𝑖𝑖𝑛𝑛 + 1.5√2 𝑖𝑖𝑛𝑛 = 5.121 𝑖𝑖𝑛𝑛 (4-36)

5.121 𝑖𝑖𝑛𝑛 × 12 𝑖𝑖𝑖𝑖𝑓𝑓𝑓𝑓 𝑏𝑏𝑓𝑓 𝑤𝑤𝑤𝑤𝑏𝑏𝑏𝑏

= 61.46 𝑖𝑖𝑖𝑖2

𝑓𝑓𝑓𝑓 𝑏𝑏𝑓𝑓 𝑤𝑤𝑤𝑤𝑏𝑏𝑏𝑏 (4-37)

61.46 𝑖𝑖𝑛𝑛2 × 12 𝑖𝑖𝑖𝑖𝑓𝑓𝑓𝑓 𝑏𝑏𝑓𝑓 𝑤𝑤𝑤𝑤𝑏𝑏𝑏𝑏

= 737.5 𝑖𝑖𝑖𝑖3

𝑆𝑆𝑆𝑆 𝑏𝑏𝑓𝑓 𝑤𝑤𝑤𝑤𝑏𝑏𝑏𝑏 (4-38)

After finding the value of 737.5 in3 of concrete per SF of wall surface area,

this value needed to be converted to cubic yards. Using the previous value of

15,800 SF for the total CMU block wall SF in the Alachua County Public

Defender’s Office, the cubic yard value was multiplied by the total wall SF and a

waste factor of 4%.

46

737.5 𝑖𝑖𝑖𝑖3

𝑆𝑆𝑆𝑆 𝑏𝑏𝑓𝑓 𝑤𝑤𝑤𝑤𝑏𝑏𝑏𝑏 × � 1 𝑓𝑓𝑓𝑓

12 𝑖𝑖𝑖𝑖�3

× �1 𝑦𝑦𝑦𝑦3 𝑓𝑓𝑓𝑓

�3

× 15,800 𝑆𝑆𝑆𝑆 × 1.04 𝑤𝑤𝑓𝑓𝑖𝑖𝑓𝑓𝑖𝑖 = 260 𝑦𝑦𝑞𝑞3 (4-39)

To determine how many conventional trucks of concrete that would be

needed to print these walls, the total cubic yards of concrete needed were

divided by 10 cubic yards of concrete per truck. This measurement is for

reference to conventional concrete use, as the method for concrete mixing is

different for 3-D printing walls; smaller batches of concrete are needed so that it

can be more efficiently printed without the time constraint that larger batches

have. Larger batches being brought to the site may dry up if not used in the 90-

minute time limit or 300 barrel rotations a concrete truck has before the batch is

unusable, and the print capacity of the printer may not suit this time limit.

In 2014, the National Ready Mixed Concrete Association (NRMCA)

published the national average cost for concrete was $98.23 per cubic yard

(Villere 2015), so for the purposes of this study $110 per cubic yard of concrete

was used to estimate the total cost of concrete needed to print this project to

account for any fluctuation or inflation in cost.

260 𝑦𝑦𝑞𝑞3 × $110𝑦𝑦𝑦𝑦3

= $28,600 𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓 𝑖𝑖𝑓𝑓𝑖𝑖𝑓𝑓 𝑓𝑓𝑓𝑓𝑖𝑖 𝑖𝑖𝑓𝑓𝑛𝑛𝑖𝑖𝑖𝑖𝑖𝑖𝑓𝑓𝑖𝑖 (4-40)

Since the previous cost calculated for the CMU block also included labor,

labor needed to be factored in to the total cost, as well as equipment cost for the

3-D concrete printer since its purpose is to take the place of skilled laborers.

According to the published information from Apis Cor, one material handler

manipulator crane to transport and lift the 3-D printer on and off the transport

vehicle, one 3-D concrete printer, and one operator and one printing process

assistant are needed to control and manage the printer. It should be noted that

47

there are other methods of 3-D printing that may require more equipment and

labor, but for the purpose of this study these were the assumptions. In

Gainesville, FL, a 14-ton crane truck that could lift the 3-D concrete printer on

and off the truck rents for a total of $600 per day or $1,800 per week, and would

be needed throughout the project to move the 3-D printer from place to place on

the project, with set-up totaling 30 minutes each time it is moved. This weekly

cost was rounded to $2,000 to account for any fluctuation or inflation in cost of

equipment. A larger 3-D printer would not need to be moved as much or at all,

but it may be costlier that way. The model 3-D printer used in this study can print

a total of about 1076 SF of wall surface area per day at maximum capacity, but

the assumption of 75% efficiency is used to give a total of 807 SF of wall surface

per day. Using this information, the total number of days to complete the project

were calculated, giving the maximum number of days a crane would be needed.

15,800 𝑆𝑆𝑆𝑆807 𝑆𝑆𝑆𝑆

= 19.6 𝑞𝑞𝑓𝑓𝑦𝑦𝑖𝑖, 𝑖𝑖𝑓𝑓𝑆𝑆𝑛𝑛𝑞𝑞𝑖𝑖𝑞𝑞 𝑓𝑓𝑓𝑓 20 𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓 𝑞𝑞𝑓𝑓𝑦𝑦𝑖𝑖 (4-41)

20 𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓 𝑞𝑞𝑓𝑓𝑦𝑦𝑖𝑖 = 2 𝑤𝑤𝑖𝑖𝑖𝑖𝑏𝑏𝑖𝑖, 6 𝑞𝑞𝑓𝑓𝑦𝑦𝑖𝑖 𝑂𝑂𝑂𝑂 5 𝑤𝑤𝑓𝑓𝑖𝑖𝑏𝑏𝑤𝑤𝑖𝑖𝑖𝑖𝑏𝑏𝑖𝑖 (4-42)

𝐴𝐴𝑖𝑖𝑖𝑖𝑆𝑆𝑆𝑆𝑖𝑖𝑛𝑛𝑟𝑟 𝑤𝑤𝑓𝑓𝑖𝑖𝑏𝑏𝑤𝑤𝑖𝑖𝑖𝑖𝑏𝑏𝑖𝑖: 5 𝑤𝑤𝑖𝑖𝑖𝑖𝑏𝑏𝑖𝑖 = $2,000 × 5 = $10,000 𝑓𝑓𝑓𝑓𝑖𝑖 𝑖𝑖𝑖𝑖𝑛𝑛𝑓𝑓𝑓𝑓𝑓𝑓 (4-43)

The actual cost for renting the 3-D printer for concrete is an unknown.

Since this is new technology, there is a not much information on the cost to rent a

3-D concrete printer, only to purchase the technology. It is not reasonable to

assume that a contractor would purchase a 3-D concrete printer unless that

contractor had the proper personnel to operate and manage the machinery.

Therefore, rental of the printing equipment was the more likely option, and the

cost needed to be estimated for its use over the course of the project. A 3-D

concrete printer might be comparable in cost per day to a 75-ton crane, which

48

runs at $2,000 per day on average to rent, and costs around $140,000 to

purchase outright. The 3-D printer Apis Cor sells currently runs for $300,000 to

purchase outright, and when compared to the 75-ton crane, could potentially run

about $4,290 to rent per day.

75-ton crane:

$2,000𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑑𝑑𝑟𝑟𝑑𝑑

$140,000 𝑝𝑝𝑝𝑝𝑝𝑝𝑏𝑏ℎ𝑤𝑤𝑏𝑏𝑎𝑎 (4-44)

3-D concrete printer:

𝑏𝑏𝑏𝑏𝑏𝑏𝑓𝑓𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑑𝑑𝑟𝑟𝑑𝑑

$300,000 𝑝𝑝𝑝𝑝𝑝𝑝𝑏𝑏ℎ𝑤𝑤𝑏𝑏𝑎𝑎 (4-45)

Assume equivalence of ratios:

$2,000𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑑𝑑𝑟𝑟𝑑𝑑

$140,000 𝑝𝑝𝑝𝑝𝑝𝑝𝑏𝑏ℎ𝑤𝑤𝑏𝑏𝑎𝑎=

𝑏𝑏𝑏𝑏𝑏𝑏𝑓𝑓𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑑𝑑𝑟𝑟𝑑𝑑

$300,000 𝑝𝑝𝑝𝑝𝑝𝑝𝑏𝑏ℎ𝑤𝑤𝑏𝑏𝑎𝑎 (4-46)

𝑖𝑖𝑓𝑓𝑖𝑖𝑓𝑓 𝑝𝑝𝑎𝑎𝑖𝑖𝑓𝑓𝑤𝑤𝑏𝑏𝑦𝑦𝑤𝑤𝑦𝑦

=$2,000𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑑𝑑𝑟𝑟𝑑𝑑 × $300,000 𝑝𝑝𝑝𝑝𝑝𝑝𝑏𝑏ℎ𝑤𝑤𝑏𝑏𝑎𝑎

$140,000 𝑝𝑝𝑝𝑝𝑝𝑝𝑏𝑏ℎ𝑤𝑤𝑏𝑏𝑎𝑎 (4-47)

𝑖𝑖𝑓𝑓𝑖𝑖𝑓𝑓 = $4,290 𝑝𝑝𝑎𝑎𝑖𝑖𝑓𝑓𝑤𝑤𝑏𝑏𝑦𝑦𝑤𝑤𝑦𝑦

(4-48)

This $4,290 per day rental cost for the 3-D printer equipment was used to

give a baseline cost to the 3-D printer rental, however, since this is newer

technology, an additional $710 was added to cover any uncertainty in price

estimation, making it an even total of $5,000 per day rental cost.

$5,000 × 20 𝑞𝑞𝑓𝑓𝑦𝑦𝑖𝑖 = $100,000 𝑓𝑓𝑓𝑓𝑖𝑖 3-𝐷𝐷 𝑝𝑝𝑖𝑖𝑖𝑖𝑛𝑛𝑓𝑓𝑖𝑖𝑖𝑖 𝑖𝑖𝑖𝑖𝑛𝑛𝑓𝑓𝑓𝑓𝑓𝑓 (4-49)

For personnel to operate the 3-D printer, average salaries for construction

engineers were used to calculate a daily amount for each person on the project.

It should be noted that in order for the 3-D printer to print anywhere from 75%

efficiency to full capacity, it should be running for 18 to 24 hours per day with two

49

personnel operating the printer. PayScale, Inc. estimates the average salary for a

construction engineer is $81,872 (PayScale 2017), however to account for any

fluctuation or inflation in cost this average salary was rounded to $90,000 which

is about a 10% increase in cost. Since a 3-D concrete printer needs two people

on site while it is printing, this put the daily jobsite cost of $1,480 per 24-hour day.

$90,000 𝑝𝑝𝑎𝑎𝑝𝑝 𝑎𝑎𝑖𝑖𝑒𝑒𝑖𝑖𝑖𝑖𝑎𝑎𝑎𝑎𝑝𝑝365 𝑦𝑦𝑤𝑤𝑦𝑦𝑏𝑏

× 2 𝑖𝑖𝑛𝑛𝑟𝑟𝑖𝑖𝑛𝑛𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖 × 3 𝑏𝑏ℎ𝑖𝑖𝑓𝑓𝑓𝑓𝑏𝑏𝑦𝑦𝑤𝑤𝑦𝑦

= $1,480 𝑝𝑝𝑖𝑖𝑖𝑖 24-ℎ𝑓𝑓𝑆𝑆𝑖𝑖 𝑞𝑞𝑓𝑓𝑦𝑦 (4-50)

$1,480 × 20 𝑞𝑞𝑓𝑓𝑦𝑦𝑖𝑖 = $29,600 𝑓𝑓𝑓𝑓𝑖𝑖 20 𝑞𝑞𝑓𝑓𝑦𝑦𝑖𝑖 (4-51)

The total cost, then, for using the labor and equipment to 3-D print the

walls for the Alachua County Public Defender’s Office came to a total of

$139,600 for 20 days of work.

$10,000 + $100,000 + $29,600 = $139,600 (4-52)

When this value was added to the total amount for the concrete material,

the final total for the 3-D printed concrete came to a total of $168,200.

$139,600 + $28,600 = $168,200 (4-53)

In comparing the cost used by VGM for the Alachua County Public

Defender’s Office for CMU block at $212,500, to the conjectural estimate for 3-D

printing those walls with concrete at $168,200, 3-D printing with concrete would

have saved $44,300 on the project, or saving just under 21% on the project cost.

$212,500 − $168,200 = $44,300 (4-54)

$44,300$212,500

× 100 = 20.85%, 𝑖𝑖𝑓𝑓𝑆𝑆𝑛𝑛𝑞𝑞𝑖𝑖𝑞𝑞 𝑓𝑓𝑓𝑓 21% (4-55)

50

Figure 4-1. Plan view of walls W1-W21, 2015. Courtesy of Alachua County Public Records.

Figure 4-2. Elevation view of wall W1, 2015. Courtesy of Alachua County Public Records.

51

Figure 4-3. Section view of wall W1. This is a typical section for all exterior walls, 2015. Courtesy of Alachua County Public Records.

Figure 4-4. Elevation view of wall W2, 2015. Courtesy of Alachua County Public Records.

52

Figure 4-5. Elevation view of wall W3, 2015. Courtesy of Alachua County Public Records.

Figure 4-6. Elevation view of wall W4, 2015. Courtesy of Alachua County Public Records.

53

Figure 4-7. Elevation views of walls W5 and W6, 2015. Courtesy of Alachua County Public Records.

Figure 4-8. Elevation views of walls W7 and W8, 2015. Courtesy of Alachua County Public Records.

54

Figure 4-9. Elevation views of walls W9, W10, W11, W12, W13, and W14, 2015. Courtesy of Alachua County Public Records.

Figure 4-10. Elevation views of walls W15, W16, W17, and W18, 2015. Courtesy of Alachua County Public Records.

55

Figure 4-11. Elevation views of walls W19, W20, and W21, 2015. Courtesy of Alachua County Public Records.

A B

C Figure 4-12. Photos courtesy of author. (Gainesville, FL: 2017.) 3-D printed truss design of a typical printed concrete wall. A) Plan view of 3-D printed concrete wall design, B) Section view of 3-D printed concrete wall design, C) Sketch of truss design with measurements.

56

Scheduling Calculations

To determine the total time that the concrete masonry took to complete on

the Alachua County Public Defender’s Office, the final updated building schedule

for the project was taken from the building contractor. This schedule was drafted

by the project team at the outset of the project, and was constantly updated

throughout the project to reflect any changes that occurred on site. The structure

was completed in November 2016, and the first drafted schedule for the project

had projected the concrete masonry work to take a total of 40 weekdays to

complete. Since the preliminary schedule was not blocked out into specific tasks,

this was a broad number that was used as a placeholder for future schedules.

After several schedule revisions, the concrete masonry work was recorded to

have a taken a total of 54 weekdays to complete. Five days were used to prepare

and install CMU foundations, 42 days were devoted to installing the CMU above

the slab on grade, two days were used to prepare and install the CMU

foundations for the screen wall structure, and five more days were devoted to

constructing the CMU screen wall structure. These 54 total weekdays were not

all consecutive, and took from February 11, 2016 to June 13, 2016 to complete,

totaling to 87 weekdays. The main building CMU foundations and wall installation

were consecutive, beginning on February 11 and ending on April 15. The exterior

screen wall structure foundations and wall installation began on May 31 and

ended on June 13, with a week spanning between the foundation installation and

the wall installation. The reason for this gap week in the schedule was so that a

slab on grade could be placed for the screen area and have a proper amount of

time to cure before the CMU screen walls could be placed.

57

As outlined in the previous “Total Cost and Material Calculations” section,

the number of days a 3-D concrete printer at 75% efficiency would take to print

these same walls would take a total of 20, 18- to 24-hour days for all walls

(including the screen wall structure). If a parallel in terms of schedule were to be

made in that the screen wall would be placed after the building walls, it would be

recommended that this design constraint be altered for the sake of cost; returning

the 3-D printer to be rented out again, or keeping it for addition time on site when

it would not be used incurs additional cost on the project, and it would be

beneficial if all printed concrete work occurred at one time. This difference in

time to print the walls with concrete creates a difference of 34 total days.

54 𝑞𝑞𝑓𝑓𝑦𝑦𝑖𝑖 𝑓𝑓𝑓𝑓𝑖𝑖 𝐶𝐶𝐶𝐶𝐶𝐶 𝑏𝑏𝑓𝑓𝑓𝑓𝑖𝑖𝑏𝑏 − 20 𝑞𝑞𝑓𝑓𝑦𝑦𝑖𝑖 𝑓𝑓𝑓𝑓𝑖𝑖 3-𝐷𝐷 𝑝𝑝𝑖𝑖𝑖𝑖𝑛𝑛𝑓𝑓𝑖𝑖𝑞𝑞 𝑖𝑖𝑓𝑓𝑛𝑛𝑖𝑖𝑖𝑖𝑖𝑖𝑓𝑓𝑖𝑖 = 34 𝑞𝑞𝑓𝑓𝑦𝑦𝑖𝑖 (4-56)

It should be noted that there is a difference in the way work days operate

for each method. The skilled laborers for concrete masonry did not work 24 hours

per day (three, 8 hour per day shifts) on the Alachua County Public Defender’s

Office, and they did not work on the weekends. A machine like a 3-D printer has

the maximum capability of working 24 hours per day, and requires only two

personnel to operate the machine. With a range of 18 to 24 hours of printing

time, it speeds up the schedule to accomplish the work in just under three weeks,

rather than span the course of four months to complete the concrete masonry

work in its entirety.

Wind Loading, Strength, and Quality Calculations

To determine the quality of the current building construction with concrete

masonry, testing results and wind load calculations were reviewed for the CMU

block material used on the Alachua County Public Defender’s Office. These

58

deductions were then used to perform calculations to provide comparable

associations with a 3-D printed concrete design that would be at least equal to

the current CMU block structure. Taken from unit load calculations from breaking

test results of a 12-inch block, the net average unit load on the block came to

3000 psi, meaning that the printed concrete would need to be as strong or

stronger, especially since the design of the printed walls do not have any

reinforcing steel inserts or grouted cells like CMU block walls did. As previously

discussed, it is possible to construct the walls without additional reinforcing

material and still achieve the same amount of structural value, counting on the

fact that there is fibrous reinforcement in the concrete mix design. For the

purpose of this study, this assumption has been made.

Using the ASCE/SEI 7-10 Standards – Minimum Design Loads for

Buildings and Other Structures, the set of codes used by the engineer for this

project, wind loads were calculated to determine the loading requirements on the

structure. These results would create a concrete requirement that would equate

or surpass the current quality of the structure. These wind loads were found

using the Envelope Procedure in Section 26.1.2.1 on the Main Wind Force

Resisting System (MWFRS), and using the Analytical Procedures in Section

26.1.2.2 on the Components and Cladding (C&C). The MWFRS is defined by

Section 26.2 as “an assemblage of structural elements assigned to provide

support and stability for the overall structure”, and the C&C is defined as

“elements of the building envelope that do not qualify as part of the MWFRS”.

The following basic wind load parameters were determined and were necessary

to find the wind load requirements:

59

𝐵𝐵𝑓𝑓𝑖𝑖𝑖𝑖𝑖𝑖 𝑤𝑤𝑖𝑖𝑛𝑛𝑞𝑞 𝑖𝑖𝑝𝑝𝑖𝑖𝑖𝑖𝑞𝑞,𝑉𝑉

𝑊𝑊𝑖𝑖𝑛𝑛𝑞𝑞 𝑞𝑞𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑓𝑓𝑖𝑖𝑓𝑓𝑛𝑛𝑓𝑓𝑓𝑓𝑖𝑖𝑓𝑓𝑦𝑦 𝑓𝑓𝑓𝑓𝑖𝑖𝑓𝑓𝑓𝑓𝑖𝑖,𝐾𝐾𝑦𝑦

𝐸𝐸𝐸𝐸𝑝𝑝𝑓𝑓𝑖𝑖𝑆𝑆𝑖𝑖𝑖𝑖 𝑖𝑖𝑓𝑓𝑓𝑓𝑖𝑖𝑟𝑟𝑓𝑓𝑖𝑖𝑦𝑦

𝑇𝑇𝑓𝑓𝑝𝑝𝑓𝑓𝑟𝑟𝑖𝑖𝑓𝑓𝑝𝑝ℎ𝑖𝑖𝑖𝑖 𝑓𝑓𝑓𝑓𝑖𝑖𝑓𝑓𝑓𝑓𝑖𝑖,𝐾𝐾𝑧𝑧𝑓𝑓

𝐺𝐺𝑆𝑆𝑖𝑖𝑓𝑓-𝑖𝑖𝑓𝑓𝑓𝑓𝑖𝑖𝑖𝑖𝑓𝑓 𝑓𝑓𝑓𝑓𝑖𝑖𝑓𝑓𝑓𝑓𝑖𝑖,𝐺𝐺

𝐸𝐸𝑛𝑛𝑖𝑖𝑓𝑓𝑓𝑓𝑖𝑖𝑆𝑆𝑖𝑖𝑖𝑖 𝑖𝑖𝑓𝑓𝑓𝑓𝑖𝑖𝑖𝑖𝑖𝑖𝑓𝑓𝑖𝑖𝑖𝑖𝑓𝑓𝑓𝑓𝑖𝑖𝑓𝑓𝑛𝑛

𝐼𝐼𝑛𝑛𝑓𝑓𝑖𝑖𝑖𝑖𝑛𝑛𝑓𝑓𝑓𝑓 𝑝𝑝𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑆𝑆𝑖𝑖𝑖𝑖 𝑖𝑖𝑓𝑓𝑖𝑖𝑓𝑓𝑓𝑓𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑛𝑛𝑓𝑓,𝐺𝐺𝐶𝐶𝑝𝑝𝑖𝑖

To start, the office building is considered as a low-rise building as defined

in section 26.2 of ASCE/SEI 7-10, being that the mean roof height was less than

60 feet, and the mean roof height did not exceed the least horizontal dimension.

The building is enclosed, and is considered a regular shaped building since it

does not have any unusual geometrical irregularities. This sets the building up for

simpler wind load calculations.

For basic wind speed, V, 135mph was determined to be the appropriate

wind speed from Figure 26.5-1A in ASCE/SEI 7-10 (see Figure 4-13) shown of

the eastern United States. The Gainesville, Florida region falls between the

140mph and 130mph line, and averaged together 135mph was obtained.

𝐵𝐵𝑓𝑓𝑖𝑖𝑖𝑖𝑖𝑖 𝑤𝑤𝑖𝑖𝑛𝑛𝑞𝑞 𝑖𝑖𝑝𝑝𝑖𝑖𝑖𝑖𝑞𝑞,𝑉𝑉 = 135 𝑆𝑆𝑝𝑝ℎ (4-57)

For wind directionality, Kd, the structure type does not have any element to

it that would require an increased directionality factor value, and taken from

Table 26.6-1 in ASCE/SEI 7-10 (see Figure 4-14), the directionality factor would

be 0.85 for both the MWFRS and the C&C structural elements.

𝑊𝑊𝑖𝑖𝑛𝑛𝑞𝑞 𝑞𝑞𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑓𝑓𝑖𝑖𝑓𝑓𝑛𝑛𝑓𝑓𝑓𝑓𝑖𝑖𝑓𝑓𝑦𝑦 𝑓𝑓𝑓𝑓𝑖𝑖𝑓𝑓𝑓𝑓𝑖𝑖,𝐾𝐾𝑦𝑦 = 0.85 (4-58)

For exposure category, there were three exposures to choose from in

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Section 26.7.3; Exposure B, Exposure C, and Exposure D. Exposure B is the

best fit for exposure category as is described as “for buildings with a mean roof

height of less than or equal to 30 ft (9.1 m),” and is located in the

urban/suburban, downtown setting of Gainesville, Florida.

𝐸𝐸𝐸𝐸𝑝𝑝𝑓𝑓𝑖𝑖𝑆𝑆𝑖𝑖𝑖𝑖 𝑖𝑖𝑓𝑓𝑓𝑓𝑖𝑖𝑟𝑟𝑓𝑓𝑖𝑖𝑦𝑦 = 𝐸𝐸𝐸𝐸𝑝𝑝𝑓𝑓𝑖𝑖𝑆𝑆𝑖𝑖𝑖𝑖 𝐵𝐵 (4-59)

For topographic factor, Kzt, there are none that would apply to the site as

there are no hills, ridges, or escarpments of any type. Therefore, per Section

26.8.2 the coefficient of 1.0 is used since topographic factor had no effect.

𝑇𝑇𝑓𝑓𝑝𝑝𝑓𝑓𝑟𝑟𝑖𝑖𝑓𝑓𝑝𝑝ℎ𝑖𝑖𝑖𝑖 𝑓𝑓𝑓𝑓𝑖𝑖𝑓𝑓𝑓𝑓𝑖𝑖,𝐾𝐾𝑧𝑧𝑓𝑓 = 1.0 (4-60)

For the gust-effect factor, G, since the building is considered as rigid per

Section 26.9.1, the parameter is to be taken as 0.85.

𝐺𝐺𝑆𝑆𝑖𝑖𝑓𝑓-𝑖𝑖𝑓𝑓𝑓𝑓𝑖𝑖𝑖𝑖𝑓𝑓 𝑓𝑓𝑓𝑓𝑖𝑖𝑓𝑓𝑓𝑓𝑖𝑖,𝐺𝐺 = 0.85 (4-61)

For the enclosure classification, the building is considered enclosed rather

than partially enclosed or open per Section 26.10.1 since the envelope of the

structure is sealed, rather than partially enclosed or open.

𝐸𝐸𝑛𝑛𝑖𝑖𝑓𝑓𝑓𝑓𝑖𝑖𝑆𝑆𝑖𝑖𝑖𝑖 𝑖𝑖𝑓𝑓𝑓𝑓𝑖𝑖𝑖𝑖𝑖𝑖𝑓𝑓𝑖𝑖𝑖𝑖𝑓𝑓𝑓𝑓𝑖𝑖𝑓𝑓𝑛𝑛 = 𝐸𝐸𝑛𝑛𝑖𝑖𝑓𝑓𝑓𝑓𝑖𝑖𝑖𝑖𝑞𝑞 (4-62)

Lastly, for the internal pressure coefficient, GCpi, because the enclosure

classification has the building as enclosed, the GCpi is +0.18 and -0.18 per Table

26.11-1 in ASCE/SEI 7-10 (see Figure 4-15). The plus and minus signs in the

coefficient are to signify that there exists pressures that act toward and away

from the internal surfaces, respectively. It should be noted that later this variable

will cancel itself out to be “0” for the MWFRS wind loading calculation, but not for

the C&C calculations.

𝐼𝐼𝑛𝑛𝑓𝑓𝑖𝑖𝑖𝑖𝑛𝑛𝑓𝑓𝑓𝑓 𝑝𝑝𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑆𝑆𝑖𝑖𝑖𝑖 𝑖𝑖𝑓𝑓𝑖𝑖𝑓𝑓𝑓𝑓𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑛𝑛𝑓𝑓,𝐺𝐺𝐶𝐶𝑝𝑝𝑖𝑖 = ±0.18 (4-63)

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Now that the wind load parameters are defined, the MWFRS wind loads

for an enclosed building can be determined with a few more variable definitions.

𝑉𝑉𝑖𝑖𝑓𝑓𝑓𝑓𝑖𝑖𝑖𝑖𝑓𝑓𝑦𝑦 𝑝𝑝𝑖𝑖𝑖𝑖𝑖𝑖𝑆𝑆𝑖𝑖𝑖𝑖 𝑖𝑖𝐸𝐸𝑝𝑝𝑓𝑓𝑖𝑖𝑆𝑆𝑖𝑖𝑖𝑖 𝑖𝑖𝑓𝑓𝑖𝑖𝑓𝑓𝑓𝑓𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑛𝑛𝑓𝑓,𝐾𝐾𝑧𝑧

𝑉𝑉𝑖𝑖𝑓𝑓𝑓𝑓𝑖𝑖𝑖𝑖𝑓𝑓𝑦𝑦 𝑝𝑝𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑆𝑆𝑖𝑖𝑖𝑖, 𝑞𝑞𝑧𝑧

𝐸𝐸𝐸𝐸𝑓𝑓𝑖𝑖𝑖𝑖𝑛𝑛𝑓𝑓𝑓𝑓 𝑝𝑝𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑆𝑆𝑖𝑖𝑖𝑖 𝑖𝑖𝑓𝑓𝑖𝑖𝑓𝑓𝑓𝑓𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑛𝑛𝑓𝑓,𝐺𝐺𝐶𝐶𝑝𝑝𝑓𝑓

For the velocity pressure exposure coefficient, Kz, Table 28.3-1 in

ASCE/SEI 7-10 (see Figure 4-16) was used. The height above ground level is 30

feet, and since the exposure category was determined earlier to be Exposure B,

the velocity pressure exposure coefficient is 0.70.

𝑉𝑉𝑖𝑖𝑓𝑓𝑓𝑓𝑖𝑖𝑖𝑖𝑓𝑓𝑦𝑦 𝑝𝑝𝑖𝑖𝑖𝑖𝑖𝑖𝑆𝑆𝑖𝑖𝑖𝑖 𝑖𝑖𝐸𝐸𝑝𝑝𝑓𝑓𝑖𝑖𝑆𝑆𝑖𝑖𝑖𝑖 𝑖𝑖𝑓𝑓𝑖𝑖𝑓𝑓𝑓𝑓𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑛𝑛𝑓𝑓,𝐾𝐾𝑧𝑧 = 0.70 (4-64)

For the velocity pressure, qz, Section 28.3.2 states that Equation 4-65 in

psf can be used using previously defined variables. Kz at 30 feet was defined as

0.70, Kzt was defined as 1.0, Kd was defined as 0.85, and V was defined as

135mph.

𝑞𝑞𝑧𝑧 = 0.00256𝐾𝐾𝑧𝑧𝐾𝐾𝑧𝑧𝑓𝑓𝐾𝐾𝑦𝑦𝑉𝑉2 (4-65)

𝑞𝑞𝑧𝑧 = 0.00256(0.70)(1.0)(0.85)(135) (4-66)

𝑉𝑉𝑖𝑖𝑓𝑓𝑓𝑓𝑖𝑖𝑖𝑖𝑓𝑓𝑦𝑦 𝑝𝑝𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑆𝑆𝑖𝑖𝑖𝑖, 𝑞𝑞𝑧𝑧 = 27.76 𝑝𝑝𝑖𝑖𝑓𝑓 (4-67)

For the external pressure coefficient, GCpf, the wall loads were determined

from the minimum design wind loads, where wind pressures that were acting on

opposite faces of each building were considered. With a roof angle of 0 degrees

since the building has a flat roof, the wall values taken from Load Set A and Load

Set B from Figure 28.4-1 in ASCE/SEI 7-10 (see Figure 4-17) reflect that roof

angle. From there, the variables 1E and 4E, and 1 and 4 were taken from Case A

to find the end and main building wall pressures respectively, and variables 5E

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and 6E, and 5 and 6 were taken from Case B to find the end and main building

wall pressures respectively.

𝐶𝐶𝑓𝑓𝑖𝑖𝑖𝑖 𝐴𝐴 𝐸𝐸𝑛𝑛𝑞𝑞: 𝐺𝐺𝐶𝐶𝑝𝑝𝑓𝑓 = (1𝐸𝐸 − 4𝐸𝐸) = 0.61 − (-0.43) = 1.04 (4-68)

𝐶𝐶𝑓𝑓𝑖𝑖𝑖𝑖 𝐴𝐴 𝐶𝐶𝑓𝑓𝑖𝑖𝑛𝑛: 𝐺𝐺𝐶𝐶𝑝𝑝𝑓𝑓 = (1 − 4) = 0.40 − (-0.29) = 0.69 (4-69)

𝐶𝐶𝑓𝑓𝑖𝑖𝑖𝑖 𝐵𝐵 𝐸𝐸𝑛𝑛𝑞𝑞:𝐺𝐺𝐶𝐶𝑝𝑝𝑓𝑓 = (5𝐸𝐸 − 6𝐸𝐸) = 0.61 − (-0.43) = 1.04 (4-70)

𝐶𝐶𝑓𝑓𝑖𝑖𝑖𝑖 𝐵𝐵 𝐶𝐶𝑓𝑓𝑖𝑖𝑛𝑛: 𝐺𝐺𝐶𝐶𝑝𝑝𝑓𝑓 = (5 − 6) = 0.40 − (-0.29) = 0.69 (4-71)

𝐸𝐸𝐸𝐸𝑓𝑓𝑖𝑖𝑖𝑖𝑛𝑛𝑓𝑓𝑓𝑓 𝑝𝑝𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑆𝑆𝑖𝑖𝑖𝑖 𝑖𝑖𝑓𝑓𝑖𝑖𝑓𝑓𝑓𝑓𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑛𝑛𝑓𝑓,𝐺𝐺𝐶𝐶𝑝𝑝𝑓𝑓 = 0.69, 1.04 (4-72)

From these defined variables, the MWFRS wind pressures that the

building walls should be designed to withstand can be determined from Section

28.4.1 by using the equation p = qz(GCpf - GCpi) in psf. The GCpi value canceled

itself out to equal “0”.

𝐶𝐶𝑓𝑓𝑖𝑖𝑖𝑖 𝐴𝐴 𝐸𝐸𝑛𝑛𝑞𝑞: 𝑝𝑝 = 𝑞𝑞𝑧𝑧 �(1𝐸𝐸 − 4𝐸𝐸) − 𝐺𝐺𝐶𝐶𝑝𝑝𝑖𝑖� = 27.760�(1.04) − 0� = 28.87 𝑝𝑝𝑖𝑖𝑓𝑓 (4-73)

𝐶𝐶𝑓𝑓𝑖𝑖𝑖𝑖 𝐴𝐴 𝐶𝐶𝑓𝑓𝑖𝑖𝑛𝑛: 𝑝𝑝 = 𝑞𝑞𝑧𝑧 �(1 − 4) − 𝐺𝐺𝐶𝐶𝑝𝑝𝑖𝑖� = 27.760�(0.69) − 0� = 19.15 𝑝𝑝𝑖𝑖𝑓𝑓 (4-74)

𝐶𝐶𝑓𝑓𝑖𝑖𝑖𝑖 𝐵𝐵 𝐸𝐸𝑛𝑛𝑞𝑞: 𝑝𝑝 = 𝑞𝑞𝑧𝑧 �(5𝐸𝐸 − 6𝐸𝐸) − 𝐺𝐺𝐶𝐶𝑝𝑝𝑖𝑖� = 27.760�(1.04) − 0� = 28.87 𝑝𝑝𝑖𝑖𝑓𝑓 (4-75)

𝐶𝐶𝑓𝑓𝑖𝑖𝑖𝑖 𝐵𝐵 𝐶𝐶𝑓𝑓𝑖𝑖𝑛𝑛: 𝑝𝑝 = 𝑞𝑞𝑧𝑧 �(5 − 6) − 𝐺𝐺𝐶𝐶𝑝𝑝𝑖𝑖� = 27.760�(0.69) − 0� = 19.15 𝑝𝑝𝑖𝑖𝑓𝑓 (4-76)

To determine the C&C wind loading requirements, the same equation to

find the MWFRS wind pressures was required, but in this case the GCpi value

remains at the ± 0.18 value, and the GCp values were taken from Figure 30.4-1.

Since the roof of the building was flat, Note 5 from Figure 30.4-1 in ASCE/SEI

7-10 (see Figure 4-18) stated the GCp values were to be reduced by 10% from

those values found on the chart. Using the effective wind area of 10 SF for

regions 4 and 5 of the building, the joint Region 4 and 5 value was 0.9, the

Region 4 value was 0.99, and the Region 5 value was 1.26. 63

𝑂𝑂𝑖𝑖𝑟𝑟𝑖𝑖𝑓𝑓𝑛𝑛 4 𝑓𝑓𝑛𝑛𝑞𝑞 5 𝑓𝑓𝑓𝑓 10 𝑆𝑆𝑆𝑆: 1.0 × 0.90 = 0.90 (4-77)

𝑂𝑂𝑖𝑖𝑟𝑟𝑖𝑖𝑓𝑓𝑛𝑛 4 𝑓𝑓𝑓𝑓 10 𝑆𝑆𝑆𝑆: -1.1 × 0.90 = -0.99 (4-78)

𝑂𝑂𝑖𝑖𝑟𝑟𝑖𝑖𝑓𝑓𝑛𝑛 5 𝑓𝑓𝑓𝑓 10 𝑆𝑆𝑆𝑆: -1.4 × 0.90 = -1.26 (4-79)

From these defined variables, the C&C wind pressures that the building

walls should be designed to withstand can be determined from Section 30.4.2 by

using the equation p = qz(GCp - GCpi) in psf.

Region 4:

𝑝𝑝 = 27.76�(0.90) − (-0.18)� = 29.98 𝑝𝑝𝑖𝑖𝑓𝑓 (4-80)

𝑝𝑝 = 27.76�(-0.99) − (0.18)� = 32.48 𝑝𝑝𝑖𝑖𝑓𝑓 (4-81)

Region 5:

𝑝𝑝 = 27.76�(0.90) − (-0.18)� = 29.98 𝑝𝑝𝑖𝑖𝑓𝑓 (4-82)

𝑝𝑝 = 27.76�(-1.26) − (0.18)� = 39.97 𝑝𝑝𝑖𝑖𝑓𝑓 (4-83)

The largest value obtained from the minimum wind pressure calculations

of the MWFRS and C&C system was taken to be used in moment calculations for

the conjectural printed concrete walls; this value was 39.97 psf, or 40.0 psf.

Using the ACI 318-11 – Building Code Requirements for Structural

Concrete, the set of structural concrete codes used by the engineer for this

project, nominal and ultimate moment capacities were calculated to determine

the loading requirements on the printed walls. The nominal moment, Mn,

multiplied by the strength reduction factor ϕ, should be greater than or equal to

the ultimate moment, Mu, to meet the strength requirements for the printed walls.

Φ𝐶𝐶𝑖𝑖 ≥ 𝐶𝐶𝑝𝑝

To find Mn, the equation used was Mn = 0.85fcSm. The design strength

value, fc, is 10,000 psi, the strength of the concrete being used for the

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calculations. This design strength value is very large, and is being used for

certainty in the wall strength without steel reinforcement. The design strength has

the possibility of being much lower for actual use, especially if fibrous

reinforcement and a concrete setter accelerant additive is used. The elastic

section modulus, Sm, needed to be calculated using Equation 4-87. The moment

of inertia, I, needed to be calculated using Equation 4-84, with variables b and d

equaling 12 inches for the height and depth of the wall section respectively, and

variable t equaling 1.5 inches for the thickness of the extruded concrete being

printed.

𝐼𝐼 = 2( 112𝑏𝑏𝑓𝑓3 + �𝑏𝑏𝑓𝑓 �𝑦𝑦−𝑓𝑓

2�2�) (4-84)

𝐼𝐼 = 2( 112

(12 × 1.5)3 + �12(1.5) �12−1.52

�2�) (4-85)

𝐼𝐼 = 999 𝑖𝑖𝑛𝑛4 (4-86)

After I, the moment of inertia was calculated, it was used to find Sm, the

elastic section modulus.

𝑆𝑆𝑚𝑚 = 𝐼𝐼𝑦𝑦 (4-87)

𝑆𝑆𝑚𝑚 = 99912

(4-88)

𝑆𝑆𝑚𝑚 = 83.3 𝑖𝑖𝑛𝑛3 (4-89)

From there, the nominal moment, Mn, was calculated.

𝐶𝐶𝑖𝑖 = 0.85 × 𝑓𝑓𝑏𝑏 × 𝑆𝑆𝑚𝑚 (4-90)

𝐶𝐶𝑖𝑖 = 0.85 × 10,000 𝑝𝑝𝑖𝑖𝑖𝑖 × 83.3 𝑖𝑖𝑛𝑛3 (4-91)

𝐶𝐶𝑖𝑖 = 708,050 𝑖𝑖𝑛𝑛-𝑓𝑓𝑏𝑏𝑖𝑖 (4-92)

With the Mn value calculated, the ultimate moment, Mu, was found by

finding the applied moment, Mapplied, by first using Equation 4-93, which is also

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the maximum bending moment of the wall section. The wind pressure, w, is

taken from the previous wind pressure calculations at 40.0 psf, the span length,

L, is taken as 15.0 feet since the height of wall before the second-floor slab is

placed is 15 feet, and the unit width, s, is taken as 1.0 feet.

𝐶𝐶𝑤𝑤𝑝𝑝𝑝𝑝𝑏𝑏𝑖𝑖𝑎𝑎𝑦𝑦 = �𝑤𝑤𝐿𝐿2

8� 𝑖𝑖 (4-93)

𝐶𝐶𝑤𝑤𝑝𝑝𝑝𝑝𝑏𝑏𝑖𝑖𝑎𝑎𝑦𝑦 = �(40 𝑝𝑝𝑏𝑏𝑓𝑓)(15 𝑓𝑓𝑓𝑓)2

8� (1 𝑓𝑓𝑓𝑓) (4-94)

𝐶𝐶𝑤𝑤𝑝𝑝𝑝𝑝𝑏𝑏𝑖𝑖𝑎𝑎𝑦𝑦 = 1,125 𝑓𝑓𝑓𝑓-𝑓𝑓𝑏𝑏𝑖𝑖 (4-95)

Using these values, Mu was calculated using Equation 4-96, with 1.6

representing the factor of safety for wind loading, and 12 inches representing the

unit width of the wall in inches.

𝐶𝐶𝑝𝑝 = 1.6 × 𝐶𝐶𝑤𝑤𝑝𝑝𝑝𝑝𝑏𝑏𝑖𝑖𝑎𝑎𝑦𝑦 × 12 𝑖𝑖𝑛𝑛 (4-96)

𝐶𝐶𝑝𝑝 = 1.6 × 1,125 𝑓𝑓𝑓𝑓-𝑓𝑓𝑏𝑏𝑖𝑖 × 12 𝑖𝑖𝑛𝑛 (4-97)

𝐶𝐶𝑝𝑝 = 21,600 𝑖𝑖𝑛𝑛-𝑓𝑓𝑏𝑏𝑖𝑖 (4-98)

To determine if these calculations meet the strength requirements for the

printed walls, the nominal moment, Mn, multiplied by the strength reduction

factor, ϕ, should be greater than or equal to the ultimate moment, Mu. The

strength reduction factor is represented by 0.6 per ACI 318-11 Section 9.3.5 for

flexure, compression, shear, and bearing of structural plain concrete.

Φ𝐶𝐶𝑖𝑖 ≥ 𝐶𝐶𝑝𝑝

(0.6) × 708,050 𝑖𝑖𝑛𝑛-𝑓𝑓𝑏𝑏𝑖𝑖 ≥ 21,600 𝑖𝑖𝑛𝑛-𝑓𝑓𝑏𝑏𝑖𝑖

424,830 in-lbs ≥ 21,600 in-lbs, TRUE

Since the value for ϕ Mn ≥ Mu was true, the minimum design strength was

calculated by using Equation 4-99.

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𝑓𝑓𝑏𝑏 𝑚𝑚𝑖𝑖𝑖𝑖 =𝑀𝑀𝑢𝑢Φ0.85𝑆𝑆𝑚𝑚

(4-99)

𝑓𝑓𝑏𝑏 𝑚𝑚𝑖𝑖𝑖𝑖 =(21,600 𝑖𝑖𝑟𝑟-𝑟𝑟𝑙𝑙𝑙𝑙)

(0.6)0.85

(83.25 𝑖𝑖𝑟𝑟3)

(4-100)

𝑓𝑓𝑏𝑏 𝑚𝑚𝑖𝑖𝑖𝑖 = 509 𝑝𝑝𝑖𝑖𝑖𝑖 (4-101)

With a minimum compressive design strength of 509 psi, using 10,000 psi

would be more than adequate for use in the printed concrete mix design. The

wind loading and strength calculations demonstrated that the minimum

compressive design strength needed was less than the CMU concrete blocks

used that averaged a net unit load of 3000 psi. This demonstrated that using the

3-D printed walls would give a more than comparable quality to the building in

regards to building strength.

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Figure 4-13. Basic wind speed, V, for Gainesville, FL. Adapted from American Society of Civil Engineers. (2013). “Figure 26.5-1A Basic Wind Speeds for Occupancy Category II Buildings and Other Structures.” ASCE/SEI 7-10 Standards – Minimum Design Loads for Buildings and Other Structures, chart, American Society of Civil Engineers.

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Figure 4-14. Wind Directionality Factor, Kd, for MWFRS. Adapted from American Society of Civil Engineers. (2013). “Table 26.6-1 Wind Directionality Factor, Kd.” ASCE/SEI 7-10 Standards – Minimum Design Loads for Buildings and Other Structures, chart, American Society of Civil Engineers.

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Figure 4-15. Internal Pressure Coefficient, GCpi, for an Enclosed Building. Adapted from American Society of Civil Engineers. (2013). “Table 26.11-1 Main Wind Force Resisting System and Components and Cladding - Internal Pressure Coefficient, GCpi.” ASCE/SEI 7-10 Standards – Minimum Design Loads for Buildings and Other Structures, chart, American Society of Civil Engineers.

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Figure 4-16. Velocity Pressure Exposure Coefficient, Kz. Adapted from American Society of Civil Engineers. (2013). “Table 28.3-1 Velocity Pressure Exposure Coefficients, Kh and Kz.” ASCE/SEI 7-10 Standards – Minimum Design Loads for Buildings and Other Structures, chart, American Society of Civil Engineers.

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Figure 4-17. External Pressure Coefficients, GCpf. Adapted from American Society of Civil Engineers. (2013). “Figure 28.4-1 (cont.) Main Wind Force Resisting System - External Pressure Coefficients (GCpf).” ASCE/SEI 7-10 Standards – Minimum Design Loads for Buildings and Other Structures, chart, American Society of Civil Engineers.

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Figure 4-18. External Pressure Coefficients, GCp. Adapted from American Society of Civil Engineers. (2013). “Figure 30.4-1 (cont.) Components and Cladding - External Pressure Coefficients (GCp).” ASCE/SEI 7-10 Standards – Minimum Design Loads for Buildings and Other Structures, chart, American Society of Civil Engineers.

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CHAPTER 5 CONCLUSIONS

This study had the aim of contributing an analysis of 3-D printing with

concrete to compare it to the existing method of construction known as concrete

masonry. The probability of more automation in the construction industry is

becoming greater as more money is being filtered into construction endeavors

while conversely, fewer people exhibit interest in entering the workforce of the

skilled construction trades. The skilled labor trades have been challenged in

finding practiced tradesmen, not to mention those willing to learn the trade by

partaking in apprenticeships; robotics and automated technology may be the

solution that the construction industry needs to supplement the labor shortage, if

not to improve the current building methodology.

As one of the oldest remaining industries, the construction industry should

be at the very least making itself aware of these new methods of building,

especially as technology continues to advance at its current rate. Even if these

newer technologically practical methods are not perfect now, it is important to

recognize that they have the potential to be developed into something that may

provide future building projects with benefits not only in aspects of cost and

schedule, but also in the quality, safety, and sustainability features of structures.

In learning and considering these now-unconventional methods, building

professionals will be able to understand that there are not only additional

methods that have the potential to be used during the construction process, but

that they may be superior to the current methods. This has the potential to

transfer over to owner groups investing in construction, who will appreciate the

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knowledge of innovative practices employed by architects, engineers, and

contractors that could ultimately provide untold benefits to a future project.

By studying the method of 3-D printing the walls of a structure with

concrete, this study has shown that there lies the possibility of it providing a way

to build an equivalent concrete structure at an expedited rate and at a lower cost.

It is a viable option that may prove worthwhile to utilize on site in the future, and

more research and development should be utilized to examine this possibility. In

the case of the Alachua County Public Defender’s Office, the prospective greater

rate of construction in both cost and time could have utilized the owner’s funds in

a much more efficient fashion. Given that the cost of the 3-D printed concrete

material and labor gave almost 21% savings in comparison to the calculated cost

of the CMU block used on the building, that money had the potential to be used

for other improvements to the structure, or could have been saved and invested

in another future project for the county. The calculated time saved on the project

was 34 workdays, and those additional saved days on the project could have had

the building potentially open and operational at an earlier time, serving the county

for almost seven workweeks more than it has.

The bottom-line is that more non-conventional methods construction

should be looked at for future use, especially those involving heavy use of

technology. 3-D printing with concrete has the possibility to produce an

equivalent, and even better yet, a superior construction method to that of

concrete masonry work in the examined areas of schedule, cost, and quality.

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In summary:

• 3-D printing with concrete has the possibility of providing a way to

build an equivalent concrete structure at an expedited rate and at a

lower cost.

• The construction industry should make itself aware of new building

methods, especially as technology continues to advance at its

current rate.

• This study has shown that 3-D concrete printing is a viable option

that may prove worthwhile as a future building method.

• The almost 21% in cost savings could have been used for other

structure improvements, or been saved and invested in other

projects.

• The 34 workdays saved could have had the building open and

operational for almost seven more workweeks.

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CHAPTER 6 RECOMMENDATIONS

To further develop this subject of using 3-D printing with concrete for use in

construction, there are many ways that future research could contribute to the findings

established in this study. In this study, the type of 3-D printer for concrete was not

discussed, as there are many different varieties of 3-D printers currently developed and

being developed. Some have been created for on-site printing, while others have been

designed specifically for factory settings. Some were designed to be constructed around

a building footprint, while others were designed to be placed and moved when the limit

to the printing nozzle has been reached. Some were designed to be placed inside the

building on the slab, while others were designed to remain on the exterior of the

building. Determining a best-printer for this project was not an objective of this study,

but more research in that area might provide more insight into cost and scheduling

specifics for a structure being printed.

Additionally, this study did not cover the possible methods in which structures

can be printed. Those developing methods in which to 3-D print with concrete are in

various stages of research that will ultimately determine specific approaches to printing

with concrete and other materials for use in construction projects. Some methods

involve framing a building and printing over the framing, while other methods involve

placing reinforcement in the building by skilled labor as it is being printed. Still other

methods involve using higher strength concrete that can be printed without rebar, as

discussed in this study. It was not an objective of this study to determine the best 3-D

printing method for construction, but further research could isolate which method would

77

be best used in which building environments, and would make for noteworthy data

additions to this topic.

This study also did not cover specific concrete design mixtures to be used with

the 3-D printer, though certain possible restraints were discussed. Data concerning the

appropriate concrete design that would allow printed walls to stand up to the current

structural concrete codes with and without reinforcing materials would be very useful for

future on-site implementation. Extensive concrete testing of these mix designs printed

into structures would also be necessary for future implementation in construction, as

that data has either not been completed, or has not been published.

This study was completed using a comparison-of-methods approach, and used a

single structure that was built in a single area with conventional methods to compare

cost, schedule, and quality data to the unconventional method of 3-D printing. Since,

access to a 3-D printed structure was not possible due to scarcity, this study could be

further expanded on by performing cost, schedule, and quality analyses on structures

that were printed using concrete.

In summary:

• Concrete 3-D printers need to be compared – which machine builds best,

and for what conditions?

• Concrete 3-D printing methods need to be compared – which method

provides a superior product?

• Concrete mix designs need to be evaluated, and concrete testing needs to

be performed.

78

• Use concrete 3-D printers to perform cost, schedule, and quality analyses

on structures for actual statistical comparisons to contribute to research.

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BIOGRAPHICAL SKETCH

Samantha L. Leonard was born in South Florida, and resided in Weston, Florida

for her pre-college life. She attended Cypress Bay High School and graduated in 2012

with honors. The first in her family to attend college in Florida, Samantha was accepted

to the University of Florida with the intent of pursing a medical career.

Upon completing her freshman year, Samantha decided that the medical

profession was not the career she desired, and transferred into the construction

management program at the M.E. Rinker Sr., School of Construction Management. In

the spring of 2016, she graduated with a Bachelor of Science in Construction

Management with highest honors and was also awarded the Best Overall Capstone

Project and the Academic Excellence Award. Samantha was very involved in student

organizations within the Rinker School, and held a number of leadership roles. She

acted as President of the Sigma Lambda Chi Construction Honor Society, the National

Association of Women in Construction chapter, and the Design-Build Institute of

America organization and competition team. While staying involved at school,

Samantha also worked for a local general contractor in a project engineer capacity, and

managed smaller projects under the supervision of her project manager.

While Samantha was an undergraduate student, she decided to apply for

admission into the combined degree program the Rinker School offered and was

accepted starting in the summer of 2016. During her time as a graduate student, she

remained active within the Rinker School and continued to work for the local general

contractor. Samantha graduated with a Master of Science in Construction Management

in the summer of 2017, and pursued a career in the industrial construction industry.

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