Table 1. Properties of Cement Used
Concrete is basically a brittle material and possesses very low tensile strength. To overcome this weakness, we generally introduce reinforcement to the concrete. For this study, we are aiming to analyze the strength parameters of concrete under the influence of fibers as a reinforcing material. During the last 30 years, different types of fibers and fiber materials were introduced and are being continuously produced in the market as new applications. Usage of fibers in concrete helps to improve resistance to cracking and fragmentation. For this study, Polypropylene fiber is used as a reinforcing material. We have used M40 and M25 concrete and a comparative study on strength parameters is made with and without the presence of these fibers. The compressive, flexural strength tests were performed by using fiber weight content from 5%.
Concrete is one of the most versatile and has been leading building materials. It can be casted in to fit any structural shape. It is readily available in urban areas simply at an affordable cost (Shetty, 2005). Though, Concrete is strong under compression but weak under tension. Practice of concrete provides the following advantages as, high durability, good fire resistance, negligible maintenance and most importantly grater compressive strength. Concrete also offers some limitations as, poor tensile strength (which could be altered by providing reinforcement) and formwork requirement (which is un ignorable).
Concrete material is very weak in tension (Bureau of Indian Standards, 2000). So, to add tensile property to concrete, reinforcement is added.
Tensile strength of concrete is typically 8% to 15% of its compressive strength. This weakness has been dealt with over many decades by using a system of reinforcing bars to create reinforced concrete, so that concrete primarily resists compressive stresses and steel bars resist tensile and shear stresses (Wafa, 1990).
Generally, we use HYSD (High Yielding Strength Deformed Steel) bars (Raju & Pranesh, 2003), mild steel, steel fibers (Ghaffar et al., 2014; Shende et al., 2012) and other materials to reinforce the concrete in-situ. This process of reinforcing is greatly efficient of increasing the tensile and flexural strength of concrete. It also brings many disadvantages along with it including increasing the self- weight of the structure, being non-economical, demanding resources like transportation, cost for bar bending etc.
Whereas, few studies stated that few fibers are capable of replacing the regular reinforcement with few special fibers. Such concretes can be simply called as Fiber Reinforced Concrete.
Fiber Reinforced Concrete (FRC) is a concrete containing fibrous material as a reinforcing material to enhance the tension developing in the concrete (Arunakanthi & Kumar, 2016). These fibers act as an alternative material to the reinforcing materials like HYSD bars.
This concrete contains short discrete fibers that are uniformly distributed and randomly oriented. Fibers include steel fibers, synthetic and natural fibers each of which lend varying properties to the concrete. The characteristics of fiber-reinforced concrete are influenced by the type of concrete, fiber materials geometrics and other factors (Rai & Joshi, 2014).
This study primarily aims to use Polypropylene fibers as a reinforcing material for the concrete.
Kandasamy and Murugesan (2011), in their study on “Fiber Reinforced Concrete Using Domestic Waste Plastics as Fibers” and have presented their results as, using 0.5% of polythene fibers to concrete, there is an increase in the cube compressive strength of concrete in 28 days to an extent of 5.12%, increase in the split tensile strength to an extent of 1.63%, and increase in the various mechanical properties of the concrete mixes with polythene fibers is not in same league as that of the steel fibers.
Shende et al. (2012) have worked on the concept of “Experimental Study on Steel Fiber Reinforced Concrete for M-40 Grade” and have vividly explained their results as, compressive strength, split tensile strength and flexural strength are on higher side for 3% fibers as compared to that produced from 0%, 1% and 2% fibers. All the strength properties were observed to be on higher side for aspect ratio of 50 as compared to those for aspect ratio 60 and 67. Finally, it was observed that compressive strength increased from 11 to 24%, flexural strength increased from 12 to 49%, split tensile strength increased from 3 to 41% with addition of steel fibers.
Rai et al., (2014) have worked on the concept of “Applications and Properties of Fiber Reinforced Concrete”, and have stated their results as, fiber addition improves ductility of concrete and its post-cracking load-carrying capacity. In FRC crack density is increased, but the crack size is decreased. The addition of any type of fibers to plain concrete reduces the workability. Fibers are also capable of enhancing the toughness of Concrete.
Krishna and Rao (2014), have done research on “Experimentalstudy on behavior of fiber reinforced concrete for rigid pavements”, and have attained the following results. Compressive strength enhancement ranges from 8.38% to 16.37% when % of fiber increases from 0.1% to 0.3% for PFRC compared to the conventional concrete at 28 days. At the age of 28 days, there is a significant improvement in the flexural strength with the addition of fibers. The increment in the flexural strength is from 12.42% to 41.13% when % of fibers varied from 0.1% to 0.3% respectively. 0.3% is observed as the optimum value. By addition of polyester fiber in concrete, the pavement thickness is decreased by 20%, which is economical when compared to plain cement concrete.
Ghaffar et al. (2014) have done an intensive research on “Steel Fiber Reinforced Concrete”, and have found that, workability decreases with increase in fiber content. The wet and dry density (7 and 28 Days) goes on decreasing as the percentage fiber volume fraction increases and ductility of concrete is found increasing with inclusion of fibers at higher fiber content.
Gupta & Malhotra (2018), have done “A Case Study on Fiber Reinforced Concrete”, and have attained the following results. There was an increase in compressive strength of 10% upon increase of 0.25% of fibers in the concrete. High quantities of fiber produced concrete with poor workability and segregation, higher entrapped air and lower unit weight. The fiber concrete fails in more ductile mode opposite the plain concrete that shattering into pieces.
Cement is one of the basic construction material that will be generally in powdered form and hardens upon the addition of water to it. It can serve as a binding material to aggregates to obtain strength. It possesses cohesive and adhesive properties. The cement used for this study is Portland Pozzolana Cement of 53 Grade (BIS, 2013).
The properties of the cement used for this study are presented in Table 1.
Table 1. Properties of Cement Used
The aggregate passing through IS: 4.75 mm sieve could be called as fine aggregate. Generally, fine aggregate is a filling material for the concrete. The fine aggregate used for this project is river sand collected from local RMC plant. The specific gravity of the fine aggregate used for this study is 2.65.
The aggregates passing through IS: 20 mm sieve and retained on IS: 4.75 mm sieve could be called as coarse aggregate (BIS, 2016). Generally, coarse aggregate is a material that enhances the strength and stability for the concrete. The coarse aggregate used for this study is collected from Miyapur Quarry. The specific gravity of coarse aggregate used is 2.83.
Water is the main ingredient used to mix all the contents. Potable water is used, as usage of any other water may contain salts and cause decrease in strength of concrete.
Recron 3s fibers are manufactured in an ISO 9001:2000 facility for use in concrete as a “Secondary Reinforcement” at a rate of dosage varying from 0.1% to 0.4% by 0.9 kg/m³ - 3.6 kg/m³. Fibers comply with ASTM C 1116, Type 111 Fiber Reinforced Concrete. All the properties of Polypropylene fibers are shown in Table 2.
Table 2. Properties of Fibers
For this project, initially we have adopted 2 concrete mixes. They are M40 concrete (Design Mix) which is made with respect to BIS (2009), and M25 Concrete (Traditional Mix). The proportions for these mixes are, M40 (1:1.67:2.92) and M25 (1:1:2) and the water cement ratio is 0.5 for both the mixes. The process of mixing is done by hand mixing. Mixing of reinforced concrete is shown in Figure 2 and the applying is shown in Figure 3.
Figure 2. Mixing of Fiber Reinforced Concrete
Figure 3. Freshly Mixed Fiber Reinforced Concrete
For fiber reinforced concrete, 5% of fibers are added to the mix on the weight of cement and are casted in the form of cubes and prisms. After hardening, they are proceeded for curing and testings.
After the specimens are done with the certain period of curing, they are subjected to compressive strength and flexural strength tests. For this study, we have adopted immersion curing for the concrete specimens. Each test result is tabulated and analyzed.
Compression Test is done by subjecting compression load on the concrete cube surface in Digital Compression testing machine, asshown in Figure 4 and the cube specimen after testing is presented in Figure 5.
Figure 4. Compression Testing for Cube specimens
Figure 5. Cube Specimen After Compression Testing
Size of cube for compression testing = 150 x 150 x 150 mm
Compressive strength of concrete = Compressive Load/ (Surface Area of cube).
The results of this test are shown in table 3, and the variation in compressive strength for M40 & M25 are shown in Figure 6 & 7 respectively.
Table 3. Compression Test Results for Various Concretes and Concrete Grades
Figure 6. Variation of Compressive Strength in M40 Concrete for Nominal and Fiber Reinforced Concretes
Figure 7. Variation of Compressive Strength in M25 Concrete for Nominal and Fiber Reinforced Concretes
Flexure test is done on concrete prism, by subjecting the flexural load in flexure testing machine, as shown in Figure 8. The prism specimen looks as shown in Figure 9.
Figure 8. Flexure Testing Machine
Figure 9. Concrete Prism Specimen after Flexure Testing
According to BIS (2000), the flexural strength of concrete at 28 days age would be 0.7* (fck)0.5 MPa. (where, fck is the grade of concrete).
Size of prism for flexure testing = 500 x 100 x 100 mm.
Flexure Strength of concrete = (Maximum Flexure Loadx length of prism/ width x depth2).
The results for this test are presented in Table 4 and the variation in flexural strength for M40 and M25 are shown in Figure 10 and 11 respectively.
Table 4. Flexure test Results for Various Concretes and Concrete Grades
Figure 10. Variation of Flexural Strength in M40 Concrete for Nominal and Fiber Reinforced Concretes
Figure 11. Variation of Flexural Strength in M25 Concrete for Nominal and Fiber Reinforced Concretes
We, ChallaDatta Karthik and Gourishetty Ruthvik,would like to take this opportunity to thank our Project Guide Mr. G. Siva Vignan for helping us throughout this study. We would also like to thank our Department of Civil Engineering, St. Martin's Engineering College for supporting us. We like to thank our parents for imposing so much of faith and love on us.