A review on the properties of recycled aggregate concrete (RAC) modified with nano-silica

The present study reviews the properties of recycled aggregate concrete (RAC) modified with nano-silica (nS). It has been observed in previous studies that the RAC possesses weaker mechanical properties as compared to natural aggregate concrete (NAC). There are many interfacial transition zones (ITZs) present in RAC. Several attempts have been made in the past to use some mineral additives in the RAC to enhance its mechanical performance. The use of nS is one such choice in this regard. nS possesses high filling ability due to its very small size. It can fill the micro and nano-sized pores and cracks present in RAC. It also improves the weak ITZs. It also has high pozzolanic activity. It reacts with the calcium hydroxide formed during the cement hydration and, in turn, produces additional calcium silicate hydrate (CSH) gel. This additional CSH gel densifies the microstructure of RAC. It is found that the synergistic effect of the two factors, that is, high filling ability and high pozzolanic activity of nS improves the internal structure of the RAC and is responsible for the enhancement of RAC's properties. It has been observed that the incorporation of nS into the RAC results in a concrete whose strength is comparable to the strength of NAC.