Improving recycled aggregate concrete by compression casting and nano-silica

Abstract

Improving and reusing recycled aggregate concrete (RAC) is an ideal approach to develop sustainability in the construction industry. In this article, a newly proposed physical compression casting method was used in combination with a treatment of nano-silica (NS) particles to enhance the properties of RAC. Although using NS contributed to accelerating hydration, promoting pozzolanic reaction, and increasing calcium-silicate hydrate gel, the enhancement in strength and reduction in porosity was found to be limited. Thus, the compression casting method was used to compensate for the weaknesses. The effects of compression casting, NS, and their combinations on the properties of RAC were investigated. At the macro-level, the stress-strain responses were evaluated by examining the compressive strength, peak strain, and modulus of elasticity. At the micro-level, the porosity and pore distribution along the interface transition zones (ITZs) were investigated using mercury intrusion porosimetry analysis and scanning electronic microscope imaging technology. Compared with normal RAC, the compressive strength achieved by using NS particles, compression casting, and their combination were increased by 37, 88 and 143%, respectively. The compression casting or combination of compression casting and NS particles treatment can effectively reduce the total porosity of the mortar and pore ratio along the ITZs.