Effect of microfibers on mechanical and durability properties of cement mortar mixtures

In this thesis the effects of various types and amounts of microfibers on mechanical and durability properties of cement mortar mixtures were investigated. In the experimental study, in addition to control mixture containing no fiber, 9 different mortar mixtures containing 3 different microfibers i.e., steel, polypropylene (PP) and polyvinyl alcohol (PVA) in three different usage rates i.e., 0.50%, 0.75% and 1% by the volume of the mixture were prepared. The cement content (532 kg/m3), maximum aggregate size (4 mm), water / cement ratio (0.48) and fine aggregate / cement ratio (2.75) were kept constant in all of the mixtures. The flow, water absorption and sorptivity of the fresh mixtures as well as the compressive strength, splitting tensile strength, flexural strength, toughness, freezing-thawing, drying shrinkage, sulfate resistance and drying shrinkage of the hardened mixtures were studied comparatively. A reduction in flow values, an increase in water absorption and a negligible change in sorptivity of the fresh mixtures were recorded. Steel fibers increased both the compressive and splitting tensile strength of the mortar. Particularly, compared to those of control mixture the increase in compressive and tensile strength was found to be 8% and 35%, respectively. Adding of steel fibers increased the weight loss upon freezing-thawing. The positive effect of steel fıbers on loss of strength was only observed at 150 cycles of freezing-thawing. From drying shrinkage point of view only 1% steel fiber-bearing mixture and from sulfate resistance point of view 0.75% steel fiber-containing mixture showed superior results than the control mixture. Steel fibers had a negligible effect on the flexural strength; however they increased the toughness 2-6 times. The effect was more significant at higher fiber contents. In all incorporation levels, PP fibers decreased the compressive strength, increased slightly the splitting tensile strength, decreased the loss of weight and on strength upon 150 cycles of freezing-thawing. From drying shrinkage view point merely 1% PP-bearing mixture and from sulfate resistance view point 0.75% as well as 0.50% PP-bearing mixtures showed better results than those of the control mixture. PP fibers had a negligible effect on the flexural strength; however, they increased the toughness 4-5 times. The effect increased by increasing the fiber content. Addition of PVA fiber was found to decrease the compressive strength of the mixture. Particularly, among the tested mixture, the lowest compressive strength was recorded in 1% PVA-bearing mixture. However, PVA fiber increased the splitting tensile strength as well as sulfate and freezing-thawing resistance significantly. Besides, 1% PVA-containing mixture showed the lowest drying shrinkage value among all of the tested mixtures. PVA fiber increased the flexural strength slightly. However, it increased the toughness considerably (9-19 times). The effect became more significant upon increasing the fiber content of the mixture.