Improvement of ornamental stone wastes as sand replacement in concrete using silane coupling agent

This study investigates the replacement of fine aggregates in concrete with untreated and silane-treated marble and granite waste (MGW) in different ratios of 3 wt.-%, 5 wt.-%, 10 wt.-% and 30 wt.-%. Fresh, mechanical, durability, microstructural, and synergistic properties of all concrete mixtures were assessed by conducting slump test, compressive strength test, water absorption test, and Scanning Electron Microscopy (SEM) and Fourier Transform Infrared Spectroscopy (FTIR) analyses, respectively. The results illustrated that mixtures with untreated MGW aggregates achieved a maximum reduction of 58 % in their water absorption when replacing sand with 3 wt.-% MGW, while a maximum reduction of 30 % in the water absorption of concrete was achieved when replacing sand with 30 wt.-% treated MGW. Moreover, all mixtures with MGW (treated and untreated) showed an improvement in their compressive strength at 28 days compared to the control, where a maximum increase of 20 % was achieved when replacing sand with 5 % silane-treated MGW. Microstructural and synergistic analyses revealed that mixtures with untreated MGW appeared to develop fewer microcracks, less distribution of hydration crystals (i.e., ettringite), and higher content of C–S–H than the control. In addition, as appeared in the SEM analysis, the incorporation of treated MGW into concrete resulted in the formation of microcracks that are more noticeable and prominent than the microcracks that were formed in concrete with untreated MGW