Utilizing polypropylene fibers.pdf

Utilizing polypropylene fibers to improving concrete

durability and cracking level

R. Bagherzadeh, A.R. Faramarzi, and M. Gorji

Abstract :

The use of polypropylene fiber to reinforce the mechanical properties of concrete & cement products is an effective method. In this research, the effect of polypropylene (PP) fiber with different weight percent and length on the physical and mechanical properties of concrete is studied. The test result shows that with adding of PP fiber to concrete, plastic shrinkage is properly decreased. The increase of aspect ratio (L/D) of PP fibers improves the capability of fibers to reduce cracks. In addition, the use of the certain amount of PP fibers in concrete mixture leads to intensifying of some mechanical properties and durability parameters while the other mechanical properties of concrete remain almost unchanged.

Result and discussion

Mechanical properties of fiber concrete

Table 4 shows the result of the strength of fiber reinforced concrete. Fibers added have no influence on7 and 28 day samples. Excremental bending results show that fiber reinforced samples have higher bending strength than without fiber samples. Figure 4, shows slipping of the polypropylene fiber during the bending test. A little change through the tensile test is observed on samples with 0.3% fiber that is due to contribution of fiber in tensile load before fracture of the samples. Toughness is based on the total energy absorbed prior to complete failure. The main properties influencing toughness and the maximum loading of fiber reinforced concrete are based on the type of fibers used, volume fraction of the fiber, the aspect ratio and the orientation of the fibers in the matrix.

What should be pointed out is that it is a kind of supplement effect rather than an increasing strength effect when adding a low volume fraction of PP fibers with a low elastic modulus to make the long-term tensile strength of concrete goes up. As the elastic modulus of PP fibers is only one fourth of that of hardened concrete, according to the simple law of mixture, the PP fiber reinforced concrete will lose some strength compared with control concrete[15,16]. From the results of Table 4, we can find that at the early age, the strengths of concretes containing PP fibers are all lower than that of the corresponding concrete with no fibers. However, after 28 days, with the increase of shrinkage and micro-defects of control concrete, the tensile strength sensitive to micro cracks descends. For those concretes containing fibers, due to the anticracking effect of PP fibers, which reduce the formation and growth probability of micro cracks, and keep the integrality of concrete, the tensile strength improves synchronously with the hydration process as the compressive strength.

Bending toughness results of sample (area under curve of load – displacement) are shown in table 5. It can be concluded that fiber using in concrete has a significant effect on toughness and its indexes as shown in table 6. Furthermore with increase in fiber length and dosage, energy absorption and toughness indexes improved. Crack width decrease as a result of energy absorption improvement.

By adding the fiber in concrete durability parameter of concrete was improved as it shown in table 6. Also it can be concluded that because o f low concrete density, the effect of fiber length and dosage have no significant effect on the samples.