myths, facts and fallacies · comparing materials: the “functional unit” 4. the three pillars...

ERMCO

F Biasioli

1

SUSTAINABILITY

AND CONSTRUCTION MATERIALS:

MYTHS, FACTS AND FALLACIES

Francesco Biasioli

Secretary-General

ERMCO, the European Ready-Mixed Concrete Association

ERMCO

F Biasioli

2

1. WHO IS DICTATING THE CONCRETE AGENDA?

2. COMPARING MATERIALS: MYTHS AND FACTS

3. COMPARING MATERIALS: THE “FUNCTIONAL UNIT”

4. THE THREE PILLARS OF SUSTAINABILITY

5. PERFORMANCE VS PRICE

6. THE « SUSTAINABLE COLUMN »

7. CONCLUSIONS

F. Biasioli - Sustainability and costruction materials: myths, facts and fallacies

CONTENTS

ERMCO

F Biasioli

Looking from « outside », other

sectors seem to « dictate « our

agenda:

Sustainable development

CO2 footprint

Energy intensive product

Depletion of natural resources

FSE - Fire Safety Engineering

Structural efficiency

PEF - Product Environ. Footprint

3

WHAT IS HAPPENING TO THE

CONCRETE SECTOR?

ERMCO

F Biasioli 4

Some of the answers of the concrete

sector:

Recarbonation after demolition

Life Cycle Asssessment (LCA) based

on a «cradle to grave» evaluation

Thermal mass

…….etc etc

Are these answers too « weak »

and/or too difficult to be explained?

Are we « scraping the bottom of the

barrel »?

WHAT IS HAPPENING TO THE

CONCRETE SECTOR?

ERMCO

F Biasioli

Why concrete?

5

Would it not be bettert to simply recall the many good reasons

WHY (reinforced) concrete (after water)

was and remains the most used construction material

in the world?

To answer this question, we have to go BACK TO BASICS!

ERMCO

F Biasioli

6







7. CONCLUSIONS


CONTENTS

ERMCO

F Biasioli

Misleading information

7

“…Timber (“legno”) is the construction material with the highest

strength (“resistenza”) to specific weight (“peso specifico”) ratio:

very efficient!” “…A well-designed timber structure has a section

similar to one made of (reinforced) concrete (“cemento armato”),

and weight similar to a steel (“acciaio”) one…” (WONDERFUL!)

The perfect

construction

material?

ERMCO

F Biasioli

Strength/specific weight ratio f/w

8

Loading a sample of a material to collapse gives

the collapse load F. Dividing F by the sample

area A the (compression) collapse strength is

f = F/A (F = f A)

If w is the “specific weight” (weight per unit

volume) of a prismatic element of height h, area A

and volume V = h A, its total weight is

W = w V = w (h A)

What is the maximum height of a column of area A made with

such material before it collapses under its own weight W?

W = F w (hmax A) = f A hmax = f / w

ERMCO

F Biasioli 9

hmax = f / w

The greater the height, hmax, the better the material?

Steel (“s”) hmax,s = (4000x104) /7850 = 5100 m

Concrete (“c”) hmax,c = (400x104) /2500 = 1600 m

Timber (“t”) hmax,t = (400x104)/500 = 8000 m

According to the strength/specific weight ratio, timber

seems to be the “most efficient” construction material.

Very impressive, but ….what happens in the real world?

Strength/specific weight ratio f/w

ERMCO

F Biasioli

THE REAL WORLD

10

Source:wikipedia

Sequoia sempervirens

U.S. California Nat Park

h = 116 m

ERMCO

F Biasioli

The engineer’s approach

11

1) Collapse strength f design strength fd = fk / m (d = “design)

2) Uniform section A section varying with height

3) “Buckling” does not allow to go that high “slenderness” limits

Source:wikipedia

ERMCO

F Biasioli

Comparing materials

13

« Common sense » conclusion

when it comes to floating in water, wood is the best

material - as steel and concrete apparently can’t float.

ERMCO

F Biasioli

The real world

1

4

Floating wood

HMS Bounty

replica (1960)

55 m long Photo courtesy of

Inverclyde Views

Floating steel

“Seawise Giant”

( 2005)


marine insight

Floating concrete

2nd WW “Mc Closkey” ships

HMS Talbot (1943 – 1945)


marine insight

ERMCO

F Biasioli

Comparing materials

15

The world’ largest

“floating dock”

Composite steel and

(lightweight) concrete

Genoa, 1980

Turkey, 2007

Photo courtesy: Il Secolo XIX

Floating steel AND

concrete

ERMCO

F Biasioli

The real world conclusion

16

As « …the upward buoyant force exerted on a body

immersed in a fluid is equal to the weight of the fluid the

body displaces…” the “specific weight” (weight for

unit volume) of timber is lower than the specific weight

of water, those of concrete and steel are higher.

Archimedes, 287- 212 B.C.

Comparison based on inherent properties of materials are

always misleading

ERMCO

F Biasioli

17







7. CONCLUSIONS


CONTENTS

ERMCO

F Biasioli

The FUNCTIONAL UNIT

The good (and only) questions should be:

• what materials are used for?

• what FUNCTION and what PERFORMANCES are

required from ELEMENTS built with these materials?

shipping a given quantity of goods by sea;

supporting a given load

protecting people and goods…….

The answer identifies a ship, a slab, a beam, a column,

a building…….in general a « FUNCTIONAL UNIT »

18

ERMCO

F Biasioli

CONCLUSIONS

19

As comparisons cannot be based on material

properties alone, in the case of structural elements

what reasonable methodology should be applied?

The “IDC rule”

IDENTIFY – DESIGN - COMPARE

ERMCO

F Biasioli

THE IDC RULE

20

1) IDENTIFY a “functional unit”, “boundaries” included;

2) DESIGN the f.u. using a reference material at its

maximum performance, then design the same f.u.

with other materials to match that performance;

3) COMPARE the different solutions considering the

three “pillars” of sustainability..

ERMCO

F Biasioli

21





5. PRICE VS PERFORMANCE


7. CONCLUSIONS

CONTENTS

ERMCO

F Biasioli

22

The assessment of “sustainable development” is based on

three “pillars”

1) Social: in very broad terms, everything related to

citizens’ welfare, protection and safety

2) Economic: includes the overall cost of any solution

3) Environmental: impact on the environment

How can these pillars be considered when it comes to

“functional units” made of construction materials ?

The three « pillars »

ERMCO

F Biasioli

THE SOCIAL PILLAR: SAFETY

2

3

Let’s consider of a building:

• a short column (to eliminate buckling, to be fair to timber),

• of constant area A,

• designed to support a given axial force NEd (bending not

considered at this stage) according to the relevant European

design standard (Eurocode).

The maximum acting force the column may support is:

Timber NRdt = At fco,d = At fco,k /t

Steel NRds = As fsd = As fsk /s

ERMCO

F Biasioli 25

NRdrc = Ac (ac fcd ) ac = 1 + (fyd/fcd – 1) = As/Ac

Four (five?) “degrees of freedom” :

1) section area Ac /shape

2) concrete stregth class fcd

3) steel strenght class fyd

4) ordinary steel area As

[5) Prestressting steel quality and area AP]

Reinforced concrete designers’

« degrees of freedom»

ac > 1 is the “ (concrete) strength enhancement coefficient”

depending on , the quantity of ordinary reinforcement

ERMCO

F Biasioli 26

NRdrc = Ac (ac fcd ) ac = 1 + (fyd/fcd – 1) = As/Ac

Reinforced concrete designers’

« degrees of freedom»

ERMCO

F Biasioli

THE ECONOMIC PILLAR

COST = QUANTITY X UNIT COST

Costs are always related to LOCAL conditions (availability,

competitive pressure, local culture and traditions….)

(Local) unit costs of construction materials (and of finished

works) are usually PUBLICLY available, as producers’ or

Chamber of Commerce “street price lists” :

- for architects and engineers, to prepare tenders,

- for public authorities, to control works’ offers prices.

27

ERMCO

F Biasioli 2

8 F. Biasioli - Sustainability and costruction materials: myths, facts and fallacies

Looking at costs (without infringing

competition rules!)

ERMCO

F Biasioli

Construction materials costs may be:

• either at the “(construction) gate” or “put in place”;

• by weight (€/kg – steel) or volume (€/m3– concrete, timber – if by weight, multiply by specific weight w (€/kg) x (kg/m3) = €/m3)

In the following, costs C are:

• at the construction gate;

• by unit volume “c” of the functional unit

Cost C/l of a 1 m of an element of area A (m2) and length l :

- C = c V = c (A l) C/l = c A (€/m3) x (m2) = (€/m)

- Ct = ct At Cs = cs As Crc = crc Ac

29

Looking at costs (without infringing

competition rules!)

ERMCO

F Biasioli

The (r.c.) cost enhancement coefficient

As for strength, for reinforced concrete, the unit cost crc

depends of the quantities of concrete Ac and reinforcing

steel As and their unit costs “cc” and “crs”:

3


ERMCO

F Biasioli

The (r.c.) cost enhancement coefficient

Gross concrete area Ac reinforcing steel area As , net

concrete area (Ac – As)

Unit costs by volume: concrete “cc” , steel “cs” ,

reinforced concrete “crc”:

Crc = crc Ac = (Ac – As) cc + As crs = Ac cc [1 + (crs/cc-1)]

crc = acc cc acc = 1 + (crs /cc – 1) = As/Ac

acc > 1 is the (r.c.) “cost enhancement coefficient”

similar to the “strength enhancement coefficient” ac = 1 + (fyd/fcd – 1)

3


ERMCO

F Biasioli

THE ENVIRONMENTAL PILLAR

Among the many environmental aspects of sustainability, the

best known to the public refers to CO2 emissions into air.

“ The cement production process emits CO2 ! ”

“Cement is a major source of CO2 !”

SO WHAT?

1) The most relevant source of CO2 is CATTLE: are we

planning to kill all the world’s sheep? and cows? and pigs?

2) We don’t build CEMENT (or aluminium, or steel): we

build functional units using (a limited quantity of) cement.

32

ERMCO

F Biasioli

THE EMBODIED CO2

For materials, information about CO2 may be (and is

usually given) as

“embodied CO2” ECO2

and expressed as (kg CO2/kg material).

ECO2 data are usually PUBLIC available

- in specific databases, and/or

- in international literature.

3

3

ERMCO

F Biasioli

THE EMBODIED CO2

ECO2 data depend on the information on:

a) the constituents of each construction material;

b) their production process, transport included

c) their Life Cycle Assessment (LCA)

ECO2 data are (today) assessed in a non-standard way.

WHAT A MESS!

One of the many reasons why we need standardized

materials’ EPDs - Environmental Product Declarations

(work is in progress in CEN TC 350).

3

4

ERMCO

F Biasioli

The r.c. “enhancement coefficients”

36

STRENGTH ac = 1 + (fyd/fcd – 1)

COST acc = 1 + (crs /cc – 1)

ECO2 aco2c = 1 + (eco2rs / eco2c –1)

For the functional unit column these coefficients are:

Different formulae may be developed for other

functional units - slabs, beams etc

ERMCO

F Biasioli

37







7. CONCLUSIONS

CONTENTS

ERMCO

F Biasioli 38

Humans are “economic animals”

When you buy something (in a shop, at the restaurant, at the

market) you ALWAYS makes a (conscious or inconscious)

PRICE vs. PERFORMANCE EVALUATION

“Eaten well, good price!” “Pay two, take three”

“ Rabatt! Special sales!” “Incredible offer!”

This should be the attitude of engineers, construction

companies and also….politicians! but it rarely happens.

PRICE VS PERFOMANCE

39

Numbers may be

slightly different in

the different

countries but

results don’t

change too much

= As/Ac

reinforcing steel:

1€ /kg 7850 €/m3

C20/25 C30/37 C40/50 C20/25 C30/37 C40/50

fck 20 30 40 20 30 40

fcd 13,3 20,0 26,7 13,3 20,0 26,7

a c a c fcd (N/mm2)

1,0% 1,32 1,21 1,15 17,5 24,1 30,7

1,5% 1,47 1,31 1,23 19,7 26,2 32,8

2,0% 1,63 1,41 1,31 21,8 28,3 34,8

2,5% 1,79 1,52 1,38 23,9 30,4 36,9

3,0% 1,95 1,62 1,46 26,0 32,4 38,9

cc (€/m3) 60 75 90

a cc

1,0% 1,70 1,61 1,53 102 121 138

Cost 1,5% 2,06 1,92 1,80 123 144 162

2,0% 2,41 2,23 2,06 144 167 186

2,5% 2,76 2,53 2,33 166 190 210

3,0% 3,11 2,84 2,59 187 213 233

eCO2 (kg/m3) 290 385 480

1,0% 1,22 1,16 1,13 354 448 542

1,5% 1,33 1,24 1,19 386 479 573

2,0% 1,44 1,33 1,26 418 511 604

2,5% 1,55 1,41 1,32 450 542 635

3,0% 1,66 1,49 1,39 481 574 666

Concrete class, fck, fcd (N/mm2)

Embodied

CO2

a cc cc (€/m3)

a cC02 eCo2c (kg/m3) a cCO2

Strength

ERMCO

F Biasioli

“Tuning” the solution

4

0

IN THIS COUNTRY the minimum cost/strength is for C40/50, = 1,0% while the minimum cost/kg EC02 is for C40/50, = 3%.


cc (€/m3) C20/25 C30/37 C40/50 C20/25 C30/37 C40/50

1,0% 5,8 5,0 4,5 130% 112% 100%

Cost 1,5% 6,3 5,5 4,9 140% 122% 110%

2,0% 6,6 5,9 5,3 148% 132% 119%

2,5% 6,9 6,3 5,7 155% 140% 127%

3,0% 7,2 6,6 6,0 160% 146% 134%

eCO2 (kg/m3) C20/25 C30/37 C40/50 C20/25 C30/37 C40/50

1,0% 20,2 18,5 17,6 118% 108% 103%

1,5% 19,6 18,3 17,5 115% 107% 102%

2,0% 19,2 18,1 17,3 112% 105% 101%

2,5% 18,8 17,9 17,2 110% 104% 101%

3,0% 18,5 17,7 17,1 108% 103% 100%

a cc cc/a c fcd €/(m kN)

a cc/a cCO2 kg/(m kN)

Embodied

CO2

ERMCO

F Biasioli

“Tuning” the solution

4

1

The specifier may look for the minimum cost/strength or minimum cost /kg EC02 (or whatever balance he wants!)

As a GENERAL RULE, the HIGHER the strength class, the BETTER the overall r.c. perfomance for COST, SAFETY and the ENVIRONMENT!

Why ENGINEERS DON’T make the best possible choice in the interest of their client, the general public and the environment? Higher strength class, less f.u. cost, increased durability, less pollution…..

WHY?


ERMCO

F Biasioli

42


2. WHY CONCRETE?






7. CONCLUSIONS


CONTENTS

ERMCO

F Biasioli

NUMERICAL EXAMPLE

4

3

Timber: class C30, fc0,k = 23 N/mm2 t = 2,40

fc0,d = fc0,k / 2,40 = 9,6 N/mm2

Section (300x300) mm

NRd = At fc0,d = 90000 x9,6x10-4= 864 kN (86,4 t)

Steel: class S355, fyk = 355 N/mm2 s = 1,05

fyd = 355 / 1,05 = 338 N/mm

Minimum required section:

As = NRd / fyd = 86400/338 = 2555 mm2

Tube (dxs) (168,3 x 5)mm

As = 2570 > 2555 mm2


ERMCO

F Biasioli 4

4

Concrete: class C30/37, fck = 30 N/mm2

t = 1,50 fcd = fck / 1,50 = 20 N/mm2

Reinforcing steel: class B450C fyk = 450N/mm2

t = 1,05 fyd = fyk / 1,50 = 435 N/mm2

Assuming = 1,5% ac = 1,31 (+31%)

Ac = NRd /(ac fcd ) = 86400/ (1,31x20) = 4320 mm2

Section (200x200) mm at least four 12 mm diam. bars required

(one in each corner) As = 4x113 = 452 mm2

= As/Ac = (452/2002) x 100 = 1,13%

ac = 1 + (fyd/fcd - 1) = 1+ 0,0113 (435/20 – 1) = 1,23

NRd,c = Ac (ac fcd) = 40000 x1,23 x 20x 10-4 = 98,7 > 86,4 t F. Biasioli - Sustainability and costruction materials: myths, facts and fallacies

EXAMPLE: COLUMN, NO BUCKLING Příklad: sloup bez vlivu štíhlosti

ERMCO

F Biasioli 4

5

In this specific country and for this functional unit, compared

to timber the reinforced concrete solution:

uses 56% less material

occupies 56% less space

costs 76% less

has 154% more ECO2 but

the cost of 1 kg of ECO2

is about 1/10 than the

timber one!


EXAMPLE: COLUMN, NO BUCKLING

units Timber Steel R. conc.

m2 0,09 0,003 0,04

% 100% 3% 44%

m2 0,09 0,02 0,04

% 100% 25% 44%

€/m 27,0 32,3 6,5

% 100% 120% 24%

kg/m 7,2 24,2 18,3

% 100% 336% 254%

€ /kg 3,8 1,3 0,4

% 100% 36% 9%

Element area

Foot area

Cost C

ECO2

C (ECO2)

ERMCO

F Biasioli 4

6

Using CO2 dutch data and all the rest unchanged, for this

functional unit, compared to timber the reinforced concrete solution:

uses 56% less material

occupies 56% less space

costs 76% less

has 18% more ECO2 but

the cost of embedding

1 kg of ECO2 is about 1/5

than the timber one!


USING CO2 DUTCH DATA

units Timber Steel R. conc.

m2 0,09 0,003 0,04

% 100% 3% 44%

m2 0,09 0,02 0,04

% 100% 25% 44%

€/m 27,0 32,3 6,5

% 100% 120% 24%

kg/m 7,2 24,2 8,5

% 100% 336% 118%

€ /kg 3,8 1,3 0,8

% 100% 36% 20%

Element area

Foot area

Cost C

ECO2

C (ECO2)

ERMCO

F Biasioli

QUESTIONS

4

7

1) In a period of limited resources, how much are the

public authorities and the society ready to pay for

playing the CO2 game?

2) Why should we “concrete” people be worried about

discussing CO2 arguments using “concrete”

arguments (based on RELIABLE CO2 data)?


ERMCO

F Biasioli 4

8

3) Instead of spending time “scraping the bottom of the barrel”

(“recarbonation”, “thermal mass”, “cradle to grave”, “fire”,

“recycling”),

“

why not to show to the world outside how

cost effective and environmentally friendly

our (consciously selected) solutions are?


QUESTIONS

ERMCO

F Biasioli

OTHER ARGUMENTS

4

9

A number of other good arguments show how effective

concrete solutions are compared with timber and steel:

• Concrete solutions today may be a “tailor made cocktail” of

materials to suit even the most demanding customer’s needs

(no waste!)

• Concrete solutions have other inherent relevant performances

(thermal mass, resistance to fire….) at no extra cost

• Ready mixed concrete (and a number of precast products also),

is a nearly ”km 0” product contributing to local well being

etc. etc.


ERMCO

F Biasioli

50


2. WHY CONCRETE?






7. CONCLUSIONS


CONTENTS

ERMCO

F Biasioli

CONCRETE TODAY

5

1

REINFORCED CONCRETE:

THE FLEXIBLE,

COST- EFFICIENT,

ENVIRONMENTAL FRIENDLY,

CONSTRUCTION MATERIAL


ERMCO

F Biasioli

52

SUSTAINABILITY

AND COSTRUCTION MATERIALS:

MYTHS, FACTS AND FALLACIES

THANKS FOR LISTENING!

Francesco Biasioli

ERMCO, the European Ready Mixed Concrete Association

myths, facts and fallacies · comparing materials: the “functional unit” 4. the three pillars...

Documents