experimental studies on viability of using geosynthetics ... · steel is the strongest commonly...

INTERNATIONAL JOURNAL OF APPLIED ENGINEERING RESEARCH, DINDIGUL Volume 1, No1, 2010

© Copyright 2010 All rights reserved Integrated Publishing Association

RESEARCH ARTICLE ISSN 09764259

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Experimental Studies on Viability of Using Geosynthetics as Fibers in Concrete

K.Rajeshkumar 1 , N.Mahendran 2 ,R. Gobinath 3 1,2 Department of Civil Engineering, PSNA CET 3 Department of Civil Engineering, VSB EC

[email protected]

ABSTRACT It is evident from literature review that in the recent decades the thrust for finding an alternative to the costly steel reinforcement is increasing, several alternatives have been tested across the globe. Some viable alternatives are found, also many techniques of replacing the steel and addition of tensile strength to concrete is studied. The methods which are found to be cost effective and feasible are also tried in construction in various areas. Once such alternative technique is providing subsidiary reinforcement in the way of addition of natural or artificial fibers to the concrete. Several fibers are also tried with concrete, some proved to be successful in adding strength and durability to the concrete but still now many fibers are in research stage only. Copious materials were introduced as additional fibers to concrete such as polypropylene, glass fibers, FRP, coir etc. This paper describes an attempt made to incorporate geosynthetics, a material is used reinforced soil as fibers in concrete. Geosynthetics are used widely aa soil reinforcement, separators, drainage, filters and also used across the globe in various infrastructure projects. In spite of several studies being done in Geosynthetics with soil, Geosynthetics fiber had never been added with concrete. This paper details the attempt made to check the viability of using geosynthetics as fibers in concrete.

Keywords: FRC, FRP, GFRC, Geosynthetics.

1. INTRODUCTION 1.1 Fiber Reinforced Concrete Fiber reinforced concrete (FRC) is concrete containing fibrous material which increases its structural integrity. It contains short discrete fibers that are uniformly distributed and randomly oriented. Fibers include steel fibers, glass fibers, synthetic fibers and natural fibers. Within these different fibers that character of fiber reinforced concrete changes with varying concretes, fiber materials, geometries, distribution, orientation and densities. It is true that plain cement concrete posses a very low tensile strength. Limited ductility and little resistance to cracking .internal micro cracks are inherently present in the concrete and its poor tensile strength is due to the propagation of such micro cracks, eventually leading to brittle fracture of the concrete. In the past, attempts have been made to import improvement in tensile improvement in tensile properties of concrete members by way of using conventional reinforced steel bars and also by applying restraining techniques. Although both these methods provide tensile strength to the concrete members, they however, do not increase the inherent tensile strength of concrete itself




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In plain concrete and similar brittle materials ,structural cracks develop even before loading ,particularly due to drying shrinkage or other causes of volume change .the width of these initial cracks seldom exceeds a few microns, but their other two dimension may be of higher magnitude. When loaded, the micro cracks propagate and open up, and owing to the effect of steer’s concentration, additional cracks form in places of minor defects .the structural cracks proceed slowly or by tiny jumps because they are retard by various obstacles, changes of the direction in by passing the more resistant grains in the matrix. The development of such micro cracks is the main cause of the inelastic deformation in the concrete. It has been recognized that the addition of small, closely spaced and uniformly dispersed fibres to the concrete would act as a crack arrester and would substainly improve its static and dynamic properties. This type of concrete is known as fibre reinforced concrete Fibre reinforced concrete can be defined as composite material consisting of mixtures of cement, mortar or concrete, uniformly dispersed suitable fibres. Continuous meshes, woven fabrics and long wires or rod are not considered to be discrete fibres. Fiberreinforcement is mainly used in shotcrete, but can also be used in normal concrete. Fiberreinforced normal concrete are mostly used for onground floors and pavements, but can be considered for a wide range of construction parts (beams, pillars, foundations etc) either alone or with hand tied rebar’s. Concrete reinforced with fibers (which are usually steel, glass or "plastic" fibers) is less expensive than handtied rebar, while still increasing the tensile strength many times. Shape, dimension and length of fiber is important. A thin and short fiber, for example short hairshaped glass fiber, will only be effective the first hours after pouring the concrete (reduces cracking while the concrete is stiffening) but will not increase the concrete tensile strength. A normal size fibre for European shotcrete (1 mm diameter, 45 mm length—steel or "plastic") will increase the concrete tensile strength. Steel is the strongest commonly available fiber, and come in different lengths (30 to 80 mm in Europe) and shapes (end hooks). Steel fibres can only be used on surfaces that can tolerate or avoid corrosion and rust stains. In some cases, a steelfiber surface is faced with other materials. Glass fiber is inexpensive and corrosionproof, but not as ductile as steel. Recently, spun basalt fiber, long available in Eastern Europe, has become available in the U.S. and Western Europe. Basalt fibre is stronger and less expensive than glass, but historically, has not resisted the alkaline environment of Portland cement well enough to be used as direct reinforcement. New materials use plastic binders to isolate the basalt fiber from the cement. The premium fibers are graphite reinforced plastic fibers, which are nearly as strong as steel, lighterweight and corrosionproof. Some experimenters have had promising early results with carbon annotates, but the material is still far too expensive for any building.

1.2 Types of Fibres Reinforcement 1.2.1 Steel Fibre Reinforcement Steel fibres have been used for a long time in construction of roads and also in floorings, particularly where heavy wear and tear is expected. Specifications and nomenclature are important for a material to be used as the tenders are invited based on specifications and nomenclature of the items. In a work where steel fiber reinforced concrete was used for overlays just like flooring, the following nomenclature can be adopted for concreting of small thickness.




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1.2.2 Polymer Fiber Reinforced Concrete Polymeric fibers are being used now because of their no risk of corrosion and also being cost effective (Sikdar et al, 2005). Polymeric fibers normally used are either of polyester or polypropylene. Polymer fiber reinforced concrete (PFRC) was used on two sites with ready mix concrete and Vacuum dewatering process. In a site, fiber reinforced concrete was used over a base cement concrete of lean mix of 1:4:8 (Figure 2) while in other site it was laid over water bound macadam (WBM) (Figure 3). When dewatered concrete it has no problem of water being coming out on surface during compaction process but when it is done over WBM, a lot of concrete water is soaked by WBM and thus the concrete loses the water to WBM and the water which comes out during dewatering/compaction process is not in same quantity asin case of lean concrete. It appears that it is better to provide base concrete than WBM as the base. The groove was made in one case before setting of concrete and also panels were cast with expansion joints in one direction. No cracks were observed in the direction in which expansion joints were provided assuming this is longitudinal direction. In lateral direction, no joints were provided and the width of such panel was about 12 m. It was later observed that cracks have developed in this direction.

As it is known that the width of 12 m is too long for expansion/ contraction. It has been observed that almost at about one–third of the panel width, such cracks developed i.e. size of panel from one side is about 4 m and from other side it is about 8m. From the site observation, it is therefore inferred that the panel should have the size of about 4m x 4m in the temperature conditions of Delhi however small variation can also be made as per site conditions. In other case, the contractor delayed the cutting of grooves and thereafter the area was occupied due




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to some urgent requirements, the cracks in both the directions developed. The cracks were almost in line. Later on the grooves were made through cutters. It has been observed that the distance of cracks in one side was almost near to 4 m and on other side at about 7 to 9 m (Figure 5). Thus from this case study also, inference can be made that grooves if made in panels of 4m x 4m, it would be appropriate.

In both the cases, no lateral grooves were made, as working was not a problem due to use of vacuum dewatering process. In both the cases, horizontal line cracks have been observed indicating that the grooves in other direction are also essential. From this, it is imperative that polymer fiber reinforced concrete should be laid in panels or grooves should be provided so that concrete acts like in panels. Cutting grooves is easy as it can be made after casting of the concrete. But it should not be delayed for long and should be made before concrete achieves its desired strength. The size of panels may be kept around 4m x 4m.

1.2.3 Glass Fiber Reinforced Concrete Glass Fiber Reinforced Concrete (GFRC) is a type of fiber reinforced concrete. Early conventional borosilicate glass caused reduction in strength due to alkali reactivity with the cement paste. Alkali resistant glass fibers (AR glass) were then produced resulting in long term durability, but other strength loss trends were observed. Better durability result was observed when AR glass is used with a developed low alkaline cement. Glass fiber concretes are mainly used in exterior building façade panels and as architectural precast concrete. This material is very good in making shapes on the front of any building and it is less dense than steel. ''Glass fiber reinforced composite materials consist of high strength glass fiber embedded in a cementitious matrix. In this form, both fibers and matrix retain their physical and chemical identities, yet they produce a combination of properties that can not be achieved with either of the components acting alone. In general fibers are the principal loadcarrying members, while the surrounding matrix keeps them in the desired locations and orientation, acting as a load transfer medium between them, and protects them from environmental damage. In fact, the fibers provide reinforcement for the matrix and other useful functions in fiberreinforced composite materials. Glass fibers can be incorporated into a matrix either in continuous lengths or in discontinuous (chopped) lengths. The most common form in which fiberreinforced composites are used in structural application is called a laminate. It is obtained by stacking a number of thin layers of fibers and matrix and consolidating them into the desired thickness. The fiber orientation in each layer as well as the stacking sequence of various layers can be controlled to generate a wide range of physical and mechanical properties for the composite laminate. The design of GFRC panels proceeds from a knowledge of its basic properties under tensile, compressive, bending and shear forces, coupled with estimates of behaviour under secondary loading effects such as creep, thermal and moisture movement. There are a number differences between structural metal and fiber reinforced composites. For example, metals in general exhibit yielding and plastic deformation whereas most fiberreinforced composites are elastic in their tensile stressstrain characteristics. However, the dissimilar nature of these materials provides mechanisms for highenergy absorption on a microscopic scale comparable to the yielding process. Depending on the type and severity of external loads, a composite laminate may exhibit




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gradual deterioration in properties but usually would not fail in catastrophic manner. Mechanisms of damage development and growth in metal and composite structure are also quite different. Other important characteristics of many fiberreinforced composites are their noncorroding behaviour, high damping capacity and low coefficients of thermal expansion.

1.3 HISTORICAL PERSPECTIVE The concept of using fibers as reinforcement is not new. Fibers have been used as reinforcement since ancient times. Historically, horsehair was used in mortar and straw in mud bricks. In the early 1900s, asbestos fibers were used in concrete, and in the 1950s the concept of composite materials came into being and fiber reinforced concrete was one of the topics of interest. There was a need to find a replacement for the asbestos used in concrete and other building materials once the health risks associated with the substance were discovered. By the 1960s, steel, glass (GFRC), and synthetic fibers such as polypropylene fibers were used in concrete, and research into new fiber reinforced concretes continues today.

1.3.1 Effect of Fibers in Concrete Fibers are usually used in concrete to control plastic shrinkage cracking and drying shrinkage cracking. They also lower the permeability of concrete and thus reduce bleeding of water. Some types of fibers produce greater impact, abrasion and shatter resistance in concrete. Generally fibers do not increase the flexural strength of concrete, so it cannot replace moment resisting or structural steel reinforcement. Some fibers reduce the strength of concrete. The amount of fibers added to a concrete mix is measured as a percentage of the total volume of the composite (concrete and fibers) termed volume fraction (Vf). Vf typically ranges from 0.1 to 3%. Aspect ratio (l/d) is calculated by dividing fiber length (l) by its diameter (d). Fibers with a noncircular cross section use an equivalent diameter for the calculation of aspect ratio. If the modulus of elasticity of the fiber is higher than the matrix (concrete or mortar binder), they help to carry the load by increasing the tensile strength of the material. Increase in the aspect ratio of the fiber usually segments the flexural strength and toughness of the matrix. However, fibers which are too long tend to "ball" in the mix and create workability problems. Some recent research indicated that using fibers in concrete has limited effect on the impact resistance of concrete materials. This finding is very important since traditionally people think the ductility increases when concrete reinforced with fibers. The results also pointed out that the micro fibers is better in impact resistance compared with the longer fibers.

1.3.2 BENEFITS OF FIBER REINFORCED CONCRETE

• Controlled Plastic Shrinkage • Minimized Crack Growth • Reduced Permeability • Improved Surface Durability • Uniform Reinforcement In All Directions




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Polypropylene fibers can

• Improve mix cohesion, improving pumpability over long distances • Improve freezethaw resistance • Improve resistance to explosive spalling in case of a severe fire • Improve impact resistance • Increase resistance to plastic

2. DEVELOPMENTS IN FIBER REINFORCED CONCRETE

The newly developed FRC named Engineered Cementitious Composite (ECC) is 500 times more resistant to cracking and 40 percent lighter than traditional concrete. ECC can sustain strainhardening up to several percent strain, resulting in a material ductility of at least two orders of magnitude higher when compared to normal concrete or standard fiber reinforced concrete. ECC also has unique cracking behavior. When loaded to beyond the elastic range, ECC maintains crack width to below 100 µm, even when deformed to several percent tensile strains. Recent studies performed on a highperformance fiberreinforced concrete in a bridge deck found that adding fibers provided residual strength and controlled cracking. There were fewer and narrower cracks in the FRC even though the FRC had more shrinkage than the control. Residual strength is directly proportional to the fiber content. A new kind of natural fiber reinforced concrete (NFRC) made of cellulose fibers processed from genetically modified slash pine trees is giving good results. The cellulose fibers are longer and greater in diameter than other timber sources. Some studies were performed using waste carpet fibers in concrete as an environmentally friendly use of recycled carpet waste. A carpet typically consists of two layers of backing (usually fabric from polypropylene tape yarns), joined by CaCO3 filled styrenebutadiene latex rubber (SBR), and face fibers (majority being nylon 6 and nylon 66 textured yarns). Such nylon and polypropylene fibers can be used for concrete reinforcement. Polymeric fibers such as polyester or polypropylene are being used due to their cost effective as well as corrosion resistance though steel fibers also work quite satisfactorily for a long Fiber reinforced concrete has advantage over normal concrete particularly in case of time. It appears that fiber reinforced concrete should be laid on base concrete of lean mix such as 1:4:8 cement concrete rather than over WBM and provided with grooves in panels of about 4m x 4m to avoid expansion/ contraction cracks. Grooves can be made after casting of concrete through cutters.

3. GEOSYNTHETICS: Geosynthetics is the term used to describe a range of generally polymeric products used to solve civil engineering problems. The term is generally regarded to encompass six main product categories: geotextiles. Geogrids, geonets, geomembranes. Geosynthetic clay liners, geofoam and geocomposites. The polymeric nature of the products make them suitable for use in the ground where high levels of durability are required. Properly formulated, however, they can also be used in exposed applications. Geosynthetics are available in a wide range of forms and materials, each to suit a slightly different end use. These products have a wide range of applications and are currently used in many civil, geotechnical, transportation, hydraulic, and private development applications including roads, airfields, railroads, and




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embankments, retaining structures, reservoirs, canals, dams, erosion control, sediment control, landfill liners, landfill covers, mining, aquaculture and agriculture.

3.1 GEOTEXTILES Geotextiles form one of the two largest groups of geosynthetic materials. Their rise in growth during the past 30years has been nothing short of awesome. They are indeed textiles in the traditional sense, but consist of synthetic fibers (all are polymerbased) rather than natural ones such as cotton, wool, or silk. Thus, biodegradation and subsequent short lifetime is not a problem. These synthetic fibers are made into flexible, porous fabrics by standard weaving machinery or they are mailed together in a random nonwoven manner. Some are also knitted. The major point is that geotextiles are porous to liquid flow across their manufactured plane and also within their thickness, but to widely varying degree. There are at least 100 specific application areas for geotextiles that have been developed; however, the fabric always performs at least one of four discrete functions; separation, reinforcement, filtration and/or drainage.

3.2 GEOGRIDS Geogrids represent a rapidly growing segment within geosynthetics. Rather than being a woven, nonwoven or knitted textile fabric, geogrids are polymers formed into a very open, grid like configuration, i.e., they have large apertures between individual ribs in the machine and cross machine directions. Geogrids are (a) either stretched in one or two directions for improved physical properties, (b) made. On weaving or knitting machinery by standard textile manufacturing methods, or (c) by bonding rods or straps together. There are many specific application areas; however, they function almost exclusively as reinforcement materials.

3.3 GEONETS Geonets, called "geospacers" by some, constitute another specialized segment within the geosynthetics area. They are formed by continuous extrusion of parallel sets of polymeric ribs at acute angles to one another. When the ribs are opened, relatively large apertures are formed into a netlike configuration. Their design function is completely within the inplane drainage area where they are used to convey all types of liquids.

3.4 GEOMEMBRANES Geomembranes represent the other largest group of geosynthetics and in dollar volume their sales are even greater than that of geotextiles. Their initial growth in the USA and Germany was stimulated by governmental regulations originally enacted in the early 1980s [5]. The materials themselves are relatively thin impervious sheets of polymeric materials used primarily for linings and covers of liquid or solid storage facilities. This includes all types of landfills, reservoirs, canals and other containment facilities. Thus the primary function is always containment functioning as a liquid and/or vapor barrier. The range of applications is very great, and in addition to the geo environmental area, applications are rapidly growing in geotechnical, transportation, hydraulic, and private development engineering.

3.5 GEOSYNTHETIC CLAY LINERS




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Geosynthetic clay liners, or GCLs, are an interesting juxtaposition of polymeric materials and natural soils. They are rolls of factory fabricated thin layers of bentonite clay sandwiched between two geotextiles or bonded to a geomembrane. Structural integrity of the subsequent composite is obtained by needlepunching, stitching or physical bonding. GCLs are used as a composite component beneath a geomembrane or by themselves in geoenvironmental and containment applications as well as in transportation, geotechnical, hydraulic, and many private development applications.

3.6 GEOFOAM Geofoam is a product created by a polymeric expansion process resulting in a “foam” consisting of many closed, but gasfilled, cells. The skeletal nature of the cell walls is the unexpanded polymeric material. The resulting product is generally in the form of large, but extremely light, blocks which are stacked sidebyside providing lightweight fill in numerous applications. The primary function is dictated by the application; however separation is always a consideration and geofoam is included in this category rather than creating a separate one for each specific material.

GEOCOMPOSITES A geocomposite consists of a combination of geotextiles, geogrids, geonets and/or geomembranes in a factory fabricated unit. Also, any one of these four materials can be combined with another synthetic material (e.g., deformed plastic sheets or steel cables) or even with soil. Collage of geosynthetic products

3.7 BASIC CHARACTERISTICS OF GEOSYNTHETICS Noncorrosiveness Highly resistant to biological and chemical degradation Longterm durability under soil cover High flexibility Minimum volume Lightness Ease of storing and transportation Simplicity of installation Speeding the construction process Making economical and environmentfriendly solution Providing good aesthetic look to structures

3.8 APPLICATIONS OF GEOSYNTHETICS Geosynthetics are generally designed for a particular application by considering the primary function that can be provided. As seen in the accompanying table there are five primary functions given, but some groups suggest even more.

3.8.1 Separation Separation is the placement of a flexible geosynthetic material, like a porous geotextile, between dissimilar materials so that the integrity and functioning of both materials can remain intact or even be improved. Paved roads, unpaved roads, and railroad bases are




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common applications. Also, the use of thick nonwoven geotextiles for cushioning and protection of geomembranes is in this category. In addition, for most applications of geofoam, separation is the major function.

3.8.2 Reinforcement Reinforcement is the synergistic improvement of a total system ’ s strength created by the introduction of a geotextile or a geogrid (both of which are good in tension) into a soil (that is good in compression, but poor in tension) or other disjointed and separated material. Applications of this function are in mechanically stabilized earth walls and steep soil slopes. Also involved is the application of basal reinforcement over soft soils and over deep foundations for embankments and heavy surface loadings.

3.8.3 Filtration Filtration is the equilibrium soiltogeotextile interaction that allows for adequate liquid flow without soil loss, across the plane of the geotextile over a service lifetime compatible with the application under consideration. Filtration applications are highway under drain systems, retaining wall drainage, and landfill leach ate collection systems, as silt fences and curtains, and as flexible forms for bags, tubes and containers. Drainage is the equilibrium soilto geosynthetic system that allows for adequate liquid flow without soil loss, within the plane of the geosynthetic over a service lifetime compatible with the application under consideration. Geopipe highlights this function, and also geonets, geocomposites and (to a lesser extent) geotextiles.

3.8.4 Drainage Drainage applications for these different geosynthetics are retaining walls, sport fields, dams, canals, reservoirs, and capillary breaks. Also to be noted is that sheet, edge and wick drains are geocomposites used for various soil and rock drainage situations.

3.8.5 CONTAINMENT Containment involves geomembranes, geosynthetic clay liners, or some geocomposites which function as liquid or gas barriers. Landfill liners and covers make critical use of these geosynthetics. All hydraulic applications (tunnels, dams, canals, reservoir liners, and floating covers) use these geosynthetics as well.

4. PRESENT STUDY Current study conducted at PSNA College of Engineering and Technology is a sponsored program from a testing agency. The study aimed to check the viability of using Geosynthetics in whole or as fibers in the concrete and also to study the strength and durability properties of the concrete with incorporated Geosynthetics fibers. The proposed study was started on June, 2009 and still in the preliminary stage but majority of the viability study was conducted. Since there are no codes or design procedures available for adding Geosynthetics fibers with concrete as a whole experimental verification of the whole process is done with batch studies.

4.1 Study method of incorporating Geosynthetics in concrete Initially the question was the durability of the Geosynthetics fibers in the concrete since the reaction of cement in concrete is a chemical reaction, but it was proved in several studies that




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Geosynthetics are used in any type of environment, even in marine conditions and proved to be durable. Several types of Geosynthetics are resistant to acid attack, alkali reaction, etc which proves them to be viable alternative fibers that can be added in concrete. Figure 6 shows the way the Geosynthetics are added as fibers in the concrete as similar to the glass and polypropylene fibers added to the concrete.

Figure 6 : Image showing Geosynthetics fibers mixed with concrete.

There are several ways to add the Geosynthetics fibers to concrete as listed below 1. Addition of Geosynthetics as small fibers in the fresh concrete 2. Addition of Geosynthetics as small pieces instead of fibers in the concrete 3. Addition of large length of Geosynthetics in the direction perpendicular to the load

application in the structural members. 4. Combination of the above mentioned methods.

Figure 7 shows the image of the type of Geosynthetics used in the studies, the sample is cut into 15 cm X 15 cm piece and added in the concrete cubes and also as 10 X 10 X 50 cm piece and added in three layers in the beams. Beams are also cast with one layer and two layer of Geosynthetics to check the viability of addition of Geosynthetics.

Figure 7 : Image showing the types of Geosynthetic used in concrete

There are several types of Geosynthetics available in the market and the current study also aims to find the best suitable Geosynthetics which can be impregnated in the concrete. Few of




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them cannot be used in the concrete due to their brittle nature but they can be used as supporting reinforcement in several areas such as beam column joints or surrounding the columns instead of tie ups since they take load uniaxially. Figure 8 shows the image of a type of Geonet used in the studies with cylinder specimens.

Figure 7: Image showing Geonet and Geogrid

Test specimens were cast with the M20 concrete mix and M15 concrete mix after doing mix design for arriving the quantity of the components of concrete. The water cement ratio is fixed as 0.5 for initial studies, further studies are proposed with varying water cement ratio in high strength concrete. Separate specimens are cast for testing on 7 days, 28 days strength as per code requirements and the test results are given below.

4.2 TEST RESULTS AND DISCUSSION:

Several tests were conducted for testing the quality of the Geosynthetics used and the properties were found to be quite satisfactory for using it with concrete, the tensile strength and durability of the Geosynthetics used were found to be good enough. Figure 8 shows the Geosynthetics being cut for adding into the specimens casted.

Figure 8 : Image showing Geosynthetics being prepared for adding into concrete




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The following test are conducted on aggregates they are listed below and table 1 shows the results obtained in various initial tests conducted

1. Specific gravity 2. Crushing test for aggregate 3. Abrasion test 4. Soundness test 5. Fineness test 6. Impact test aggregate.

Table 1 : Test results of various test conducted

S. No TEST CONDUCTED RESULTS 1 Specific gravity of fine aggregate 2.66 2 Specific gravity of coarse aggregate 2.78 2 Crushing value of Coarse aggregate 24% 3 Abrasion value of Coarse aggregate 25.5% 4 Aggregate Impact value of Coarse aggregate 28% 5 Fineness Test on fine aggregate 2.66 6 Test for Soundness of Coarse aggregate 14% 7 Mix design used 1:2:4 8 Slump Value of fresh concrete without fibers 160 mm 9 Slump Value of fresh concrete with fibers 110 mm 10 Flexure strength test on hardened concrete

without Geosynthetics 0.86 N/mm 2

11 Flexure strength test on hardened concrete with Geosynthetics

1.2 N/mm 2

12 Compressive Strength in alternate orientation on hardened concrete without Geosynthetics

16 N/mm 2

13 Compressive Strength in alternate orientation on hardened concrete with Geosynthetics

17 N/mm 2

The fine aggregate and coarse aggregate are graded properly before using it with the concrete and the results obtained in workability are found to be satisfactory. Moderate vibration were used using vibratory table for compacting the concrete in the moulds, it was found that bleeding occurs in the concrete added with Geosynthetics fibers to a large quantity. Initial studies proved that the Geosynthetics fibers may not allow the concrete to mix properly in the layer it was spread, few small holes were made on the surface of the Geosynthetics to allow the bonding of concrete.

4.3 Viability Studies To check the durability of Geosynthetics in concrete two types of tests were conducted

• Mortar cudes of size 70mm X 70 mm X 70 mm was prepared without and with Geosynthetic fibers in the direction perpendicular to the applied load.

• Geosynthetics fibers ( various types) are added with cement paste of good consistency and cured for 30 days to check the durability of fibers




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The study results proved that it is feasible to use Geosynthetics with concrete and the cement reaction while setting and heat of hydration is not affecting the fibers. The Geosynthetics are removed from the cement paste set and studied under Electron microscope compared with the original fibers. It shows that small disorientation of fibers with non polymer based Geosynthetics but polymer and plastic based Geosynthetics resist the action of cement and there are no notable changes from original.

4.4 Strength Studies To check the increase in strength by addition of Geosynthetic fibers control specimens were cast with 1:2:4 ratio of required amount and tested, the initial tests conducted on the control specimens gave the confidence that the introduction of Geosynthetics may increase the strength. It is decided to study Flexure and compression strength initially, beam and cube specimens were casted as per IS 516 of required number with varying Geosynthetic proportion and type of Geosynthetic and tested. Figure 9 shows the Geosynthetics added in the beam specimen casted for flexure testing.

Figure 9 : Image showing the Geosynthetics added in the beam specimen

All the test specimens were cured for required period of time in quality water without chloride content or any other harmful impurities present. Figure 10 shows the way the Geosynthetics are added in the concrete cube and cylinders.

Figure 10: Image showing addition of Geosynthetics fibers in specimen

The studies were conducted in the compression testing machine and flexure testing apparatus, the results found to be there is an increase of nearly 30% in the load carrying capacity of the beam and cube members after the addition of Geosynthetics. Further testing is going on to find the splitting tensile strength with varying proportion of fibers in the concrete.




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5. CONCLUSION Fiberreinforced concrete weighs much less than regular concreteas much as 75

percent less in some cases. This allows for reduced shipping costs. GFRC has a very high strengthtoweight ratio and can be used to make complex shapes, since it is reinforced internally. It can also be sprayed into forms and molds, making better finished products, as there is no chance for air bubbles to form. It also does not crack as easily as regular cement and does not chip when it is cut. It is found from the studies conducted that the Geosynthetics can be used as a whole in the concrete or also as fibers in the concrete for adding strength and durability of concrete. Geosynthetics are available plenty in the market and the cost per Square meter is less than Rs.60 which makes it as an economical choice also. The strength and durability of concrete using Geosynthetic is to be studied further for arriving into any conclusion but initial studies proved the viability of using them in tandem with other constituents of concrete.

6. RFERENCES

• IS: 14324 (1995) Indian Standard for geotextiles—methods of test for determination of water permeability/permittivity. Bureau of Indian Standards, New Delhi

• IS: 14706 (1999) Indian standard for geotextiles—sampling and preparation of test specimens. Bureau of Indian Standards, New Delhi.

• IS 516: 1959 Method of test for`strength of concrete

• IS 2386 ( Part IVIII): 1963 Methods of Test for Aggregates for Concrete

• IS 383:1970 Specification for coarse and fine aggregates from natural sources for concrete

experimental studies on viability of using geosynthetics ... · steel is the strongest commonly...

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