NANO - SILICA (SiO2) CONTRIBUTION TO MECHANICAL AND MICROSTRUCTURAL CHARACTERISTICS OF HIGH PERFORMANCE CONCRETE PAVEMENT

الملخص

High performance concrete pavement appears to be the best choice for layer with high strength and low cost. In this paper, the mechanical properties were investigated which considered essential for design and requirements of rigid highway pavement. These properties were examined by compressive strength, flexural strength and modulus of elasticity. Previous test investigations were imposed for concrete mixes with different Nano SiO2 (size of 30 nm) percentage (0, 0.5, 1,1.5, & 2) % by wright of cement as mineral admixture. Also, X- Ray Diffraction (XRD) and X-Ray Fluorescence (XRF) tests were conducted to indicate the chemical composition of the used admixture. Energy Dispersive Spectroscopy (EDS) was conducted to visualize the micro structural behaviour of concrete during hydration process. Wet and dry mixing methods were utilised to prepare the modified concrete mixes and the results of the more effective method, were adopted. Scanning electron microscopy (SEM) was utilized to investigate the microstructure and morphology of nano concrete mixes. The results of SEM indicated that the microstructural distribution of C-S-H gel were comparable for all the nano mixes. The decrease in thickness of nano concrete layer was associated with the increment in the percentage of nano silica add to the mixes when the other factors remain the same. The best percentage of nano silica was 1.5% by weight of cementitious materials (by using dry mixing method). This percentage satisfied all requirements of fresh and hardened concrete mixes for highway pavement and achieved well microstructure with significant decrement in the thickness of concrete layer which positively reflected on construction cost.