Influence of nano- and micro-silica additions on the durability of a high-performance self-compacting concrete

The main purpose of the research is to examine the effects of binary and ternary mixtures of nSi and mSi on the durability of a high-performance self-compacting concrete (HPSCC). Compressive strength at 28 days, accelerated carbonation processes after 60 and 200 days of exposure to CO2, resistance to freeze-thaw cycles and capillary suction coefficient, were analyzed. In addition, microstructural characterization was carried out by Mercury Intrusion Porosimetry (MIP). Ten blends were manufactured: one without additions as control, three with 2.5%, 5% and 7.5% of nSi, three more with 2.5%, 5% and 7.5% of mSi and three using both admixtures, with 2.5%/2.5%, 5%/2.5% and 2.5%/5%, of nSi and mSi, respectively. The highest compressive strength is achieved in the ternary admixture with 2.5%/2.5%. A wider particle size distribution creates a low porosity, improves packing density, decreases water demand in comparison with mixtures with the same amount of total addition using only nSi, provides higher compressive strength and an improved durable performance. The porous network in mixtures with nSi involved a smaller pore diameter with respect to control, proportional to the amount of nSi. In concretes with mSi, there was a lower total porosity with an average pore size similar to the reference concrete. In ternary mixtures, the porous network presented concretes with a smaller average pore size and a smaller total porosity. This produced concretes with a high compactness and improved durability properties, with a lower capillary absorption and a lower susceptibility to carbonation and freeze-thaw cycles. The low capillary absorption deduced in this type of concrete might prevent the penetration of aggressive agents afflictively and hence, increases the life span of concrete structures in aggressive environments.