EFFECTIVENESS OF HYBRID FIBER REINFORCEMENT ON ENHANCEMENT OF THE MECHANICAL PROPERTIES OF CEMENT BASED HIGH STRENGTH COMPOSITES EXPOSED TO ACID ATTACK

Abstract

The high strength concrete having an improved compressive strength can be produced by addition of the fibres which eliminates inherent weakness of brittle failure due to lack of tensile strength. This thesis presents an experimental study on enhancement of the mechanical properties of high performance cementitious composites by the use of either single type (steel or glass) fiber or hybrid steel-glass fibers with different volumetric ratios. Moreover, the effect of partial replacement of ordinary cement with silica fume (SF) on the fresh and hardened properties HPCC was also investigated. Another stage of the experimental program is evaluation of the effect of aggressive sulfuric acid (H2SO4) exposure on HPCC. Hence, understanding the role of SF and steel-glass fiber reinforcement on the performance of HPCC under acidic environments is the main aim of the thesis. In the experimental program, fourteen mixes in two series were prepared. The first series was based on only cement as the binder, while the second series consisted of 85% OPC and 15% SF. Unreinforced plain mix was considered as a control group. The percentages of fibres by the volume of mixtures were 0.5% and 1.0%. Water to binder ratio was fixed as 0.25 for HPCC production. A series of destructive and non-destructive tests were done at different ages 28, 56 and 90 days of moist curing. For acid attack a number of samples were exposed to 7% sulfuric acid solutions for one month and two months after 28 days of curing. The tests on the nonexposed specimens were carried out for comparison. The experimental results indicated that specimens with a hybrid combination of 0.5% steel-0.5%glass fiber with 15% SF exhibited a higher flexural strength and lower capillary water permeability. Also, specimens with 1.0% of steel fiber and 15% SF showed higher compressive strength at all ages. Nevertheless, addition of glass fibers decreased compressive strength. Furthermore, the results showed that SF mainly enhanced the HPCC resistance against sulfuric acid exposure.