Combined use of recycled concrete aggregate and glass cullet in mortar: Strength, alkali expansion and chemical compositions

Abstract

The promotion of fine recycled concrete aggregate (FRCA) is the main way to alleviate the conflicts between scarce natural resource and huge construction demand. However, its utilization alone would result in a remarkable strength reduction. Therefore, this study attempts to co-utilize FRCA with the particle size of 1.18–4.75 mm and fine recycled glass cullet (FRGC) with the particle size of 0.15–1.18 mm to prepare recycled mortars. Compressive strength, alkali-silica reaction (ASR), X-ray diffraction (XRD), differential thermogravimetry (DTG), and Fourier transform infrared spectroscopy (FTIR) tests are carried out. Results show that without ASR inhibitors, the optimum replacement ratio of river sand by this combination in mortar is 40 vol%, where the strength reduction at 28 days is 2.64% and the ASR expansion at 14 days is 0.08%. The good performance can be attributed to the internal curing of FRCA at an early age and the pozzolanic activity of FRGC. Correspondingly, this combination does not change the phase composition deriving from cement hydration but can reduce portlandite and increase calcium silicate hydrate gel. In particular, compared with previous studies applying FRCA and/or FRGC, the replacement ratio of 40 vol% is satisfactory because of the lowest strength reduction. Future attempts could be further made to improve the replacement ratio of this combination to 60 vol% by using ASR inhibitors.