Abstract:
This thesis investigates the influence of local sand grain characteristics on the mechanical performance of engineered cementitious composites (ECC), containing Nylon66 fiber. The study of mechanical performance included compressive strength, modulus of elasticity, Poisson’s ratio, stress-strain behavior in compression, splitting tensile strength, flexural strength, flexural behavior, and toughness. The novelty of this research is the utilization of available local silica sand, which is significantly different from the high-cost commercial pure fine silica sand used to produce ECC. Though micro-silica sand with a maximum grain size of 250 μm was recommended for standard ECC production, the effectiveness of reduction of particle grain size and effects of larger grain size particle or a mixture of smaller and larger grain size particle on mechanical properties of ECC has not yet been established.
To clearly understand the effect of different grain size range particles on mechanical properties of ECC, local silica sand with four sand grain size ranges (150 -300 µm, 300-600 µm, 600-1190 µm, 150-1190 µm or FM 2.5) were adopted as fine aggregates. After finalizing the mix design proportions four types of mix were prepared based on the above-mentioned grain size of sands. A series of slump flow tests for fresh properties were carried out. Tests for compressive strength, modulus of elasticity, splitting tensile strength, and flexural strength tests were performed on a total number of 180 samples to study hardened mechanical properties.
Smaller grain size range sand mixture exhibited lower slump value compare to larger grain size mixtures. Sand mix having grain size range 150-1190 µm exhibits self consolidation property with higher slump value. All size ranges of sand mixes developed a considerable amount of compressive strength which satisfy the recommended compressive strength values for ECC, though grain size range 150-300µm sand and 300-600µm sand exhibit higher compressive strength. Specially, 300-600µm grain size sand gains higher compressive strength at an older age. Sand with grain size 300-600µm shows a strain hardening property with large ultimate strain capacity. Poisson’s ratio for all the mixtures samples were in the range prescribed by other researchers for ECC. Also, no major changes in Poisson’s ratio values were seen with the change of grain size range. All size ranges of sand mixtures samples developed a considerable amount of flexural strength which satisfy the recommended flexural strength values of ECC. Variation of flexural toughness was seen for different grain size ranges sand. Larger grain size sand shows higher flexural toughness at an early age, though no major variation of toughness was found for older curing age samples. No major difference was seen for the equivalent flexural strength ratio with the variation of the grain size range. The cement-based composites made of sand grain size in the range 300-600 μm, performed better in compressive strength, flexural strength, and tensile strength. Though the silica percentage of available silica sand in Bangladesh is not as good as pure silica sand, it is good enough to satisfy the requirements of mechanical properties such as workability, compressive strength, modulus of elasticity, Poisson’s ratio, tensile strength, flexural strength, etc. The use of local fine aggregates in ECC products can lower its cost.
