“STRENGTH ANALYSIS OF CONCRETE EMBEDDED WITH STEEL FIBER, POLYPROPYLENE FIBER & CLASS-F FLY ASH”
1Harshit Kumar Pandey, 2Prof. Charan Singh Thakur, 3Anil Sanodiya Department of Civil Engineering, SRGI, Jabalpur, Madhya Pradesh, India
Abstract - In construction industry concrete is major material used nowadays. Concrete has better resistance in compression while steel has more resistance in tension.
Conventional concrete has limited ductility, low impact and abrasion resistance and little resistance to cracking. To improve the pre cracking and post cracking behavior of short discontinuous and discrete fibers are added to the plain concrete to make it fibrous concrete.
The concrete containing cement, water, aggregates and discontinuous discrete fibers is called Fiber Reinforced Concrete (FRC). The ductility of FRC depends on the ability of the fibers to form bridging cracks at higher levels of strain due to higher loads applied. The fibers interlock and stay around aggregate particles and considerably reduce workability, while the mix becomes more cohesive and less to segregation. The fibers are dispersed and distributed randomly in the concrete during mixing and thus improve concrete properties in all directions. The brittle character of concrete that limits its application, can be overcome by the inclusion of fibers (like steel, glass, carbon, polypropylene, and natural) and can be practiced among others that minimizes the weaknesses of concrete, such as low growth resistance, high shrinkage cracking, low durability, etc.
To enhance the characteristics of concrete; hybrid fibers are incorporated besides fly- ash. In this effort a variety of fiber additives can be combined with concrete to design for specific applications and optimize chemical and strength properties. The combination of fibers, often called hybridization, is introduced by using different fiber proportions of steel and polypropylene.
The fly-ash contributing 5-10 percentage were used in concrete mixes by volume of cement and poly-propylene fiber, steel (crimped) fibers and hybrid fiber( poly-propylene and steel (crimped) fibers) of various proportions i.e. ranging from 0 – 4% as additives for each of the concrete mixes of M30 grade as per IS code method of mix design. Super plasticizer was also used in all mixes to make concrete better in workability.
Besides cubes and beams of M30 grade concrete were cast 5 and 10 % fly ash and different percentages of steel fiber and polypropylene fiber and hybrid fibers respectively, by volume of cement and identifies fiber combinations that demonstrate maximum compressive and flexural strength of concrete. Finally we obtained that by addition of fiber and mineral admixture the concrete increase their properties as compare to normal concrete mass.
Keywords: Fibrous concrete, polypropylene fiber, steel fiber, hybrid fabric, strength – properties, fly-ash.
1 INTRODUCTION
The infrastructure needs of our country is increasing day by day and with concrete is a main constituent of construction material in a significant portion of this infra-structural system, it is necessary to enhance its characteristics by means of strength and durability. Concrete is a relatively brittle material. Addition of fibers to concrete makes it more homogeneous and isotropic and transforms it from a brittle to a more ductile material. Plain cement concrete has some shortcomings like low tensile, limited ductility, little resistance to cracking, high brittleness poor toughness.
The cracks generally develop with time
and stress to penetrate the concrete, thereby impairing the waterproofing properties and exposing the interior of the concrete to the destructive substances containing moisture, bromine, acid sulfate, etc. The exposure acts to deteriorate the concrete, with the reinforcing steel corrosion. To counteract the cracks, a fighting strategy has come into use, which mixes the concrete with the addition of discrete fibers.
Experimental studies have shown that fibers improve the mechanical properties of concrete such as flexural strength, compressive strength, tensile strength, creep behavior, impact resistance and
toughness. Moreover, the addition of fibers makes the concrete-reinforcing fibers include metal, polymer, and various others. Among them, polymer fibers and the steel fibers enjoy popularity in the domain of concrete .It is obvious that the behavior of HFRC depends on the aspect ratios, orientations, geometrical shapes, distributions and mechanical properties of fibers in concrete mixtures. from a brittle to a more ductile material.
2 MATERIAL INTRODUCTION-
Concrete is a composite material, and consists of several different constituent parts. These parts are cement, water, aggregate (sand and stone) and usually one or more special additives to ensure that the concrete has the desired properties.
2.1. Cement
Cement is a hydraulic binding agent, which means that it’s a binding agent that hardens when water is added. The cement type that is used today is called Portland cement, because of its colour which is similar to the colour of stone from the island of Portland. Specifications to the
Portland cement are described in the Norwegian standard. The cement is mainly consisting of four minerals which constitute 90-95% of the blend. These are made up of oxides of calcium (Ca), silicon (Si), aluminium (Al) and iron (Fe). In addition to the “main minerals” the cement contains small amounts of oxides of manganese (Mn), sulphur (S),potassium (K) and sodium (Na) The main minerals in the blend influence its properties like heat generation, development of strength, the final strength and its durability. These properties may be controlled by changing the proportionality of the main minerals.
Even though the rest of the minerals make up a small part of the cement, these can have important effects on the cement’s properties as well. The potassium- and sodium oxides (the alkalies) are important. They can make the cement harden faster and make it expand. When the different minerals in the cement react with water there will be heat generation. As a result of this it is important to keep the concrete damp while hardening to avoid dehydration and cracking.
Main Ingredients of Cement
Name Chemical formula Symbol
Tricalcium silicate 3CaO∙SiO2 C3S
Dicalcium silicate 2CaO∙SiO2 C2S
Tricalcium aluminate 3CaO∙Al2O3 C3A
Tetracalcium aluminate Ferrite 4CaO∙Al2O3∙Fe2O3 C4AF 2.2 Aggregate
The aggregate in the concrete consists of sand and stone and makes up 60-70% of the concrete volume. As this is the largest part of the concrete the properties of the aggregate may greatly influence the properties of the concrete. Even though there can be specific requirements to the aggregate in a special blend, there are certain general requirements that should always be followed:
Should not be porous
Should not be efflorescent, micaceous or buttery or have schistose structure.
Should not contain sulphates (alum slate), silicates (phyllite, flint, opal) or chlorides (sand from earlier littoral zones)
Should not contain much humus, mud and clay.
The aggregate is often evaluated by its material grading, grain shape and superficial structure. The material grading means the distribution of different grain sizes in the aggregate. It is desirable to have a good distribution of the grain sizes, that the amount of each size is approximately the same. This will lead to few hollows and a low air content in the concrete which is an advantage as large air content will reduce the strength of the concrete. If the hollows between the aggregate particles are small the amount of cement adhesive necessary to bind them together is small.
The grain shape and superficial structure means how the shapes of the grains are. Natural aggregate (sand, gravel and pebbles) is often rounded and
smooth, while human made aggregate like crushed stone has sharp edges and rough surface. Usually these parameters are important for filling compounds for road construction, but there are rarely requirements for these properties for concrete.
However, if the distribution is too good the concrete can be a bit hard to work with. Figure 1 shows an example of a aggregate grading curve.
2.3. Chemical Admixture
The chemical admixtures are additives that are added to the fresh concrete to give it desired properties either in fresh or hardened condition. These additives were to a large degree developed in the 70’s and 8 0’s and today virtually all concrete blends contain some amount of additives.
The most important categories of chemical admixtures are described below.
2.4. Plasticizers
The plasticizers are the most usual additives and are added to increase the workability of the fresh concrete so that it’s easier to cast, without having to add more water and thereby reduce the concrete’s capacity. This happens because the plasticizers reduce the water’s surface tension, thus reducing the friction between the components in the mix, and the thickness of the water film around the aggregate grains is reduced and releases water. The plasticizers belong to two categories; plasticizers and superplasticizers. The plasticizers are based on a material called lignosulfonate which originates from the wood processing industry. At high dosages the plasticizer may have a retarding side effect. This means that the concrete dries slower and this is not always desirable.
The superplasticizers usually have a better plasticizing effect than the regular plasticizer (12-40% water reducing effect against only 8% for plasticizers). A positive side of the superplasticizers is that they have fewer deterious effects, e.g.
the retarding effect is smaller. They have a short working period (1/2-3/4 hour), but can be added several times without having negative effect on the concrete strength On the downside it must be mentioned that they are quite expensive.
2.5 Retarders
Retarders restrain the hydration of the cement by forming a slowly dissolving membrane around the cement grains.
They are used when it’s desirable to delay the solidification time of the concrete. As examples this may be desirable for long transportation, to elongate the concrete’s processing time in the casting frame or when casting in warm weather to avoid fast solidification. As the plasticizers have retarding as a side effect, the retarders have plasticizing as a side effect.
2.6 Accelerators
The effect of the accelerators is quickening of the hardening process.
These additives are relatively rarely used in Norway. It may be necessary with accelerators when casting in the winter to obtain early removal of the casting frame and frost resistance, and when producing pre stressed concrete. A problem when using accelerators is that the accelerated hardening process may produce a lot of heat. This can then cause the concrete to crack, increase the concrete’s potential for shrinkage or lessen the strength of the hardened concrete.
2.7 Air Entrainments
The air entrainments bind many small and evenly distributed air bubbles into the cement when the concrete is mixed.
The point with this may be to enhance the frost resistance of the concrete, because the air bubbles allow water in the concrete to expand without cracking the concrete. Another advantage given by high air content is that the air bubbles enhance the concrete’s cast ability. The problem is that high air content will reduce the strength of the concrete by 5%
per each % of added air.
2.8 Fiber
Fiber is a natural or synthetic substance that is significantly longer than it is wide.
Synthetic fibers can often be produced very cheaply and in large amounts compared to natural fibers, but for clothing natural fibers can give some benefits, such as comfort, over their synthetic counterparts.
2.9 Fiber Types Natural fiber Man made fiber
Natural Fiber – Natural fibers develop or occur in the fiber shape, and include those produced by plants, animals, and geological processes. They can be classified according to their origin.
Vegetable fibers Wood fiber Animal fibers Mineral fibers Biological fibers
Man-made Fiber – Man-made or chemical fibers are fibers whose chemical composition, structure, and properties are significantly modified during the manufacturing process. Man-made fibers consist of regenerated fibers and synthetic fibers.
Synthetic fibers Semi-synthetic fiber metallic fibers
2.10 Fiber Types/Properties
There are many different types of fibers that can be used in fiber reinforced concrete. Manufacturers make fibers out of steel, polymers and basalt, among others. Historically there have also been used many types of fibers of natural origin in buildings. One of these is asbestos. Asbestos was used as reinforcement in fiber cement wallboards (eternity or asbestos cement) in the middle of the last century. This is forbidden today because the substance is carcinogenic.
2.11 General View of Fibers
Since ancient time, fibers have been used for reinforcing the brittle materials. The efficiency of fiber reinforcement is apparent in accordance with enhancement of two criteria: strength and toughness of matrix. Now, in modern days, different types of reinforced concrete were produced with discontinuous short fibers which have gained immense popularity. The modules and geometrical size of fiber affect the performance of FRC.
Therefore, usage of suitable type and percentage of fibers improves overall mechanical performance of concrete.
Generally, fibers have different classification based on elastic modulus and origin of the material. Some of them have low modulus and some others have high modulus in comparison with cement matrix. Polypropylene, nylon, and cellulose are in first category, while steel,
glass, carbon and asbestos belong to the second one. Table.1 presents properties of common fibers dominating various industries. These days, the applications of FRC are as varied as the types of fibers which are produced in various forms, bars, cables and different cross section, stirrups, sheets, channels and angles.
3 LITERATURE REVIEW 3.1 General
In this chapter, the works relevant to this study which are conducted in past has been mentioned. In early days, Concrete was characterized as a brittle material with low tensile strength and low strain capacity. To reduce the brittleness and increase the resistance to cracking, reinforcement with short randomly distributed fibers has been successfully used and the resulting composite is known as fiber reinforced concrete (FRC).
The performance of FRC depends on many factors such as fiber material properties, fiber geometry, fiber volume content, matrix properties and interface properties. Most types of FRC used in practice contain only one type of fiber.
However, it is known that failure in concrete is a gradual, multi-scale process.
The pre-existing cracks in concrete are of the order of microns. Under an applied load, these cracks grow and eventually join together to form macro-cracks. A macro-crack propagates at a stable rate until it attains conditions of unstable propagation and a rapid fracture is precipitated. The gradual and multi-scale nature of fracture in concrete implies that a given fiber can provide reinforcement only at one level and within a limited range of strains. For optimal result therefore different types of fibers may be combined and the resulting composite is known as hybrid-fiber-reinforced concrete (HFRC). Several studies has been conducted related to this topic which are mentioned in this chapter.
3.2 Previous Related Studies
Darole J S (2013) studied the Effect of hybrid fibers on mechanical properties of concrete and gave result the hybrid fiber (steel and polypropylene) with 0.5
%volume fraction by volume of concrete better than normal concrete.
Vikrant S. Vairagade and Kavita S. Kene (2012) researched on
Experimental Investigation on Hybrid Fiber Reinforced Concrete and they study on the effect of hybrid fibers with different proportions of hook end steel of 30mm length and 0.5 mm dia. And fibrillated 20 mm cut length polypropylene fiber were used can done a promising work as there is always a need to overcome the problem of brittleness of concrete. The following conclusions could be drawn from this investigation. Compressive Strength and Split Tensile Strength is increase as high strength as compare to other combinations and Slump Value Increasing the percentage of steel fiber in hybrid Combination reduces the slump value, to maintain the constant slump to increase the super plasticizers dose in concrete.
S C Patodi and C V Kulkarni (2012) researched on Performance Evaluation Of Hybrid Fiber Reinforced Concrete Matrix concluded that to use different volume fractions of Recron 3S fibers (polyester fibers) and continuously crimped steel fibers to produce HFRC and thus to evaluate its performance under compression, tension, flexure, shear and impact types of loading. Based on I.S.
Code method of mix design, proportion of different ingredients was obtained to get M20 grade concrete. Samples were prepared with and without fly ash and by varying the volume fraction of fibers from 0 to 1%. Total 12 different types of HFRC matrices were considered for performance evaluation. The improvement in mechanical properties of a matrix having volume fraction hybridization of 0.3%
Recron and 0.7% of steel fibers was found to be the best.
Deepa A Sinha (2012) studied on Strength Characteristics of hybrid fiber reinforced concrete and concluded that the optimum dosage of fibers to get maximum strength for the M30 grade concrete is found and the properties of concrete i.e workability, compressive strength and flexural strength are found.
Maniram Kumar (2014) researched on Strength Evaluation of Steel-Nylon Hybrid Fiber Reinforced Concrete and concluded that hybrid reinforced concrete is made by using steel and nylon 6 fibers. The inclusion of both steel and nylon 6 fibers are used in order to combine the benefits of both fibers;
structural improvements provided by steel
fibers and the resistance to plastic shrinkage improvements provided by nylon fibers. So the aim of this is to investigate the mechanical properties (compressive strength, flexure strength and split tensile strength) of hybrid fiber reinforced concrete under compression, flexure & tension. The total volume of fiber was taken 0.75 % of total volume of concrete. In this experimental work, four different concrete mix proportions were casted with fibers and one mix without fibers. Four different mix combinations of steel- nylon 6 fibers were 100-00%, 75- 25%, 50-50% and 25-75%. Super plasticizer was used in all mixes to make concrete more workable.
M Tamil Selvi and Dr. T S Thandavamoorthy (2013) researched on Studies on the Properties of Steel and Polypropylene Fiber Reinforced Concrete without any Admixture and concluded that the durability properties of M30 grade of concrete reinforced individually with 4% of steel and polypropylene fibers, respectively, as well as with hybrid fibers consisting of 2% steel and 2%
polypropylene fibers, respectively, and to evaluate their strength at 7, 28, and 90 days. Using three types of fibers with 4%
by volume of cement the results were compared with the conventional concrete specimen. The concrete mix with 4% steel fiber shows that the concrete was stiff and difficult to compact. In addition to this, concrete with shorter fiber has better workability as compared to longer fiber.
The concrete mix with 4% Endura-600 Macro synthetic Polypropylene fiber shows that concrete was more slippery and difficult to compact. Increase in compressive strength of SFRC was observed to be in range of 3 per cent to 60 per cent between 7 and 28 days. The compressive strength of PPFRC was observed to increase between 10 per cent and 18 per cent for 7 and 28 days.
Corresponding values for Hybrid concrete was increased by 3 per cent to 22 per cent for 7 to 28 days when compared to conventional concrete. In conventional concrete, specimen splits into two halves exactly under the loaded area, but using SFRC, PPFRC, Hybrid fibers cylinders did not split into halves under the loaded area. Because of toughness it did not yield to sudden breakage. An increase in ductility of the specimens by the
introduction of fibers was observed in this investigation. Chloride Permeability for conventional concrete and Hybrid specimens was low and a SFRC and PPFRC specimen was medium according to ASTMC 1202 criteria. Water absorption results of SFRC and Hybrid specimens are equal to conventional concrete. But in the case of PPFRC it was 4% increase than conventional concrete.
4 MATERIALS AND METHOLODOGY 4.1 General
In this chapter, we will discuss aout the materials used in this thesis work. The materials was collected from different locations and the information about the material has been obtained. A view on these materials has been given and the properties of these are shown.
4.2 Materials
In this study, materials used are ordinary Portland cement, fine aggregate, coarse aggregate, steel fibers and polypropylene fibers. Fly ash are also used as mineral admixture. Super plasticizer was also used in all mixes to make concrete better in workability.
4.3 Cement
The Ordinary Portland cement of 43 grade confirming to IS 8112-1989 manufactured by Ultra tech Company was used in this experimental work. Cement with specific gravity 3.12 was used for the preparation of test specimens. In a general sense, cement is a adhesive and cohesive material which are capable of bonding together particle. There are different type of cement; out of that we have used 43 grade ordinary Portland cement(OPC).
Initial and Final setting time of cement respectively is 90 min and 360 min.
4.4 Fine and Coarse Aggregate
Broken stone from the local quarry of size 20 mm and 10 mm in the ratio of 60:40 respectively confirming to IS: 383-1970 was used as coarse aggregate. The specific gravity of 10 mm and 20 mm coarse aggregate were taken as 2.72 and 2.74 respectively. Water absorption for 10 mm and 20 mm aggregate were 0.17 and 0.15
% respectively. Fineness modulus of 10 mm and 20 mm were 2.31 and 2.65 respectively. Locally available river sand of zone II conforming to IS 383-1970 with
specific gravity 2.69, water absorption 1.82 % and fineness modulus 2.86.
4.5 Water
Clean and portable water from tape was used for mixing of concrete and curing the concrete as per IS: 456-2000 in the entire experimental program fresh water are also accept for all purposes for this investigation. Water shall be free from objectionable quantities of oil, acid, alkali, salt, or other materials.
4.6 Super-Plasticizer
A commercially available super-plasticizer (SIKA 150) was used in all mixes. The super plasticizer was added 0.6% by weight of cement to all mixes conforming to IS 9103:1999. Super plasticizer was also used in all mixes to make concrete better in workability.
4.7 Fly Ash
We have used mineral admixture as fly- ash. It is ultra fine and replacement of cement 5%, and 10% by weight of cement.
Fly ash is one of the most extensively used by-product materials in the construction field resembling Portland cement. It is an inorganic, non combustible, finely divided residue collected or precipitated from the exhaust gases of any industrial furnace. The fly- ash available from Hind Cement Plant, near Katangi was used. Class C fly ash was used in this study. Its specific gravity was 2.10 with non plastic consistency.
The chemical composition of fly ash was:
SiO2 - 63.75%, Fe2O3 - 30.92%, CaO- 2.35%, MgO - 0.92%.
4.8 Steel Fiber
Steel fibers with Hooked end & Flat crimped were used in the mixes. The steel fibers had a length of 50 mm and a diameter of 0.75mm (an aspect ratio of 100). The density of the fibers was 7.65 g cm-3 and the young’s modulus was 210 GPa.
4.9 Polypropylene Fiber
Fibrillated 20 mm cut length fibers were used. Polypropylene fiber had a length of 20 mm and a diameter of 1mm(an aspect ratio of 100). The specific gravity of polypropylene fiber is 0.9.
4.10 Laboratory Tests
A series of laboratory test were conducted on concrete reinforced with fiber layer on different percentage of fly ash. Concrete was reinforced in sets of two fiber reinforcement and few tests were done on sample. Following test were conducted on prepared samples and materials also as per relevant IS code of Practice:
1. Sieve analysis Test 2. Fineness Modulus Test 3. Specific Gravity Test 4. Slump Cone Test
5. Compaction Factor Test 6. Compressive Strength Test 4.11 Compressive Strength Test
The compressive strength of concrete is one of the most important Properties of concrete in most structural application concrete is implied primarily to resist compressive stress. Numbers of cubes tested for different proportions with conventional concrete and at different percentage of fly ash concrete as shown in table and graph.
Table No.1 Casting and Curing of M30 Grade of Concrete with different % of Fly Ash and different % of Hybrid Fiber
S.NO. MIX FLY ASH STEEL POLYPROPYLENE HYBRID FIBER
1 M1 0 0 0 0
2 M2 5 0 0 0
3 M3 5 2 0 0
4 M4 5 0 2 0
5 M5 5 1 1 2
6 M6 5 4 0 0
7 M7 5 0 4 0
8 M8 5 2 2 4
9 M9 10 0 0 0
10 M10 10 2 0 0
11 M11 10 0 2 0
12 M12 10 1 1 2
13 M13 10 4 0 0
14 M14 10 0 4 0
15 M15 10 2 2 4
Table No. 2 Compressive Strength of Grade M30 as M1, M2, M3, M4, M5, M6
Mix M-1 M-2 M-3 M-4 M-5 M-6
Fly as (%) 0 5 10 5 5 5
STEEL FIBER (%) 0 0 0 2 0 0
POLYPROPLENE
FIBER (%) 0 0 0 0 2 0
HYBID POLYPROPLENE
FIBER(%) 0 0 0 0 0 2
Test age
(days) 3-3 SAMPLES
COMPRESSIVE STRENGTH (N/mm²) 7
22.0 22.5 22.0 Av=22.1
22.6 22.5 22.6 Av=22.56
23.3 23.2 23.4 Av=23.3
23.7 23.8 23.9 Av=23.8
25.3 25.5 25.1 Av=25.3
24.8 24.0 24.4 Av=24.4 14
25.0 25.0 25.6 Av=25.2
26.7 26.8 26.9 Av=26.8
27.7 27.8 27.9 Av=27.8
28.4 28.3 28.5 Av=28.4
29.0 31.8 30.4 Av=29.4
29.2 30.5 28.5 Av=29.8
28 29.5
29.5 29.5 Av=29.5
30.0 31.0 32.0 Av=31
32.2 32.3 32.4 Av=32.3
32 33 31 Av=33
34.5 32.5 33.5 Av=33.5
35.0 33.0 34.0 Av=34 Table No. 3 Compressive strength of grade M30 as M7, M8, M9, M10, M11, M12
Mix M-7 M-8 M-9 M-10 M-11 M-12
Fly as (%) 10 10 10 5 5 5
STEEL FIBER (%) 2 0 0 4 0 0
FIBER POLYPOPLENE
FIBER (%) 0 2 0 0 4 0
HYBRID
POLYPROPLENE 0 0 2 0 0 4
FIBER(%0 Test age
(days) 3-3 SAMPLES
COMPRESSIVE STRENGTH (N/mm²)
7 24.0
23.1 25.1 Av=24.07
27.9 27.9 27.9 Av=27.9
24.9 26.5 26.3 Av=25.9
26.3 26.2 27.0 Av=26.5
23.7 25.5 26.9 Av=26.7
26.0 28.3 27.6 Av=27.3 14
29.6 28.0 28.8 Av=28.8
31.2 30.8 31.5 Av=31.2
32.4 31.4 30.4 Av=31.4
31.5 33.7 31.6 Av=32.6
31.4 31.5 32.9 Av=32.8
31.8 32.6 31.9 Av=32.9
28 34.5
32.5 33.5 Av=33.5
32.0 34.0 33.1 Av=34
34.0 35.0 34.5 Av=34.5
34.5 33.5 35.5 Av=34.5
34.8 33.8 35.8 Av=34.8
37.0 35.8 33.9 Av=35.9 Table No. 4 Compressive strength of grade M30 as M13, M14, M15,
Mix M-13 M-14 M-15
Fly as (%) 10 10 10
STEEL FIBER (%) 4 0 0
POLYPROPLENE
FIBER(%) 0 4 0
HYBRID POLYPROPLENE FIBER (%) 0 0 4
Test age
(days) 3-3 SAMPLES
COMPRESSIVE STRENGTH (N/mm²) 7
22.8 26.8 21.8 Av=23.8
24.0 25.0 26.0 Av=25
26.1 27.5 26.5 Av=26.7 14
27.4 29.3 28.5 Av=28.4
29.0 31.0 30.0 Av=30
33.6 31.7 32.5 Av=32.6
28 36.6
35.6 34.6 Av=33.6
36.0 36.0 36.0 Av=36
38.5 36.5 37.5 Av=37.5
Graph No. 1: Showing the variation of fly ash and fiber percentage versus compressive strength in n/mm2 of M30
grade
Graph No.2: Showing the variation of fly ash and fiber percentage versus compressive strength in n/mm2 of M30
grade.
Graph no.3: Showing the variation of fly ash and fiber percentage versus compressive strength in n/mm2 of M30
grade
5 RESULTS AND DISCUSSIONS
Compressive strength of concrete mixes made with and without fly ash and steel fiber, polypropylene fiber and Hybrid polypropylene steel fiber with different percentage and variation in fiber were determined at 7, 14, and 28 days of curing. The test results are given in table and shown in figure. The maximum compressive strength was obtained for a mix having a fiber. 10% fly ash and fiber content of 4% by weight and increase in strength over plain concrete and fly ash concrete without fiber content
The 7 day compressive strength of fly ash based hybrid polypropylene steel fiber concrete was found to be high as 26.7 Mpa. Which is more than ordinary concrete and fly ash concrete. Similarly 28 day compressive strength was found to be about 37.5 Mpa which is more than that of ordinary concrete and fly ash concrete. The behavioual change in the compressive-strength of concrete exhibits an exceptional enhancement in the strength parameter. The inclusion of Steel-fibre, Polypropylene fibres & Hybrid polypropylene leads to a remarkable enhancement in the strength. For a constant proportion of Fly-ash, with a variety of combination of those additives, there is an increment in the strength. The conventional concrete with 10 percentage of fly-ash when incorporated with a fixed
percentage of steel-fibres, polypropylene fibres or Hybrid polypropylene fibres leads to a higher value in a progressive way.
Initially, the conventional- concrete does its part well. Later, the inclusion of steel- fibres alone as 4%, shows the strength level as 23.8 in 7 days, 28.4 in 14 days and 33.6 in 28 days.
Moreover, the addition of polypropylene fibres alone as keeping the percentage proportion the same as 4%;
gives us a right shift of the strength from 25 in 7 days, 30 in 14 days to 36 in 28 days. Thus, the second inclusion seems to be better combination.
Further, the conclusive statement comes as when the conventional-concrete added with the 10 percentage fly-ash super-imposed by 4% of Hybrid- polyproplene alone, that gives us a truly magnified view by exhibiting the strength show as 26.7 in 7 days, 32.6 in 14 days and lea to 37.5 in 28 day.
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