Improving engineering properties of cement-based materials by internal curing

Cement-based mixtures are assumed to be saturated right after placement, other than the air bubbles. Hydration of cementitious materials results in the formation of cement matrix, and change the state of the mixture from plastic to a weak solid. Further moisture loss, due to water consumption during hydration reactions or water evaporation from the free surface, leads to the development of negative capillary pore water potential. Excessive pore water potential is recognized as the source of capillary tension and increased early-age shrinkage cracking potential. Internal curing by lightweight fine aggregate substitution is an alternative curing method to uniformly provide extra water through the whole volume of the mixture and compensate the capillary pore water potential. Internal curing water is sucked out of the pre-saturated porous lightweight fine aggregate as of increasing capillary pore water potential in the matrix. Providing extra moisture results in extended hydration and strength development as well as delayed pore water potential development in the cement matrix, which significantly decreases early-age shrinkage strain and cracking potential. This dissertation aims to study the effects of internal curing on the hydration and pore water potential development in early ages as well as mechanical and transport properties of cement-based materials (with various water-to-cement, supplementary cementitious materials and lightweight fine aggregate substitutions) under different curing (sealed and standard moist curing methods) and exposure (ambient temperature and relative humidifies) conditions. The results indicate that internal curing is a very effective method to delay pore water potential development, especially for the mixtures with low water to cementitious materials ratio, or incorporating fine supplementary cementitious materials like silica fume. It is also beneficial in high-temperature exposure conditions to suppress pore water potential development. In addition, the results of isothermal calorimetry and setting time tests confirmed that internal curing extended the hydration and lead to higher heat generation while initial and final setting time are not meaningfully changed, compared to the control mixture without lightweight fine aggregate. The effect of substitution of fine aggregate with lightweight fine aggregate on the mechanical and transport properties of concrete mixtures in both sealed and standard moist curing conditions are also investigated. The results show that the coefficient of thermal expansion of mixtures is linearly decreased by increasing lightweight fine aggregate substitution. In addition, substitution of lightweight fine aggregate up to 30% results in a slight increase in the compressive strength of concrete mixtures, particularly highlighted for the mixtures with low water to cementitious materials ratio. Internal curing is even more beneficial in increasing electrical resistivity of mixtures, particularly in sealed curing condition. The optimum lightweight fine aggregate substitution depends on absorption/desorption properties of lightweight fine aggregate, water to cementitious materials ratio, type and quantity of cementitious materials, and the target property