Mechanical performance and phase analysis of an eco-friendly alkali-activated binder made with sludge waste and blast-furnace slag

A new eco-friendly alkali-activated material (AAM) using two waste materials, including drinking water treatment sludge (DWTS) and ground granulated blast furnace slag (GGBFS), was developed in this study. DWTS is a by-product generated from drinking water purification processes. Using DWTS and GGBFS to manufacture alkali-activated binder to replace cement provides an economical engineering solution for these industrial wastes and alleviates adverse environmental effects of cement production. In this study, the workability, mechanical performance, durability, and microstructure properties of AAM-derived mortar were evaluated with different DWTS/GGBFS proportions and sodium silicate (SS) to sodium hydroxide (SH) ratios. Moreover, this study investigated the formation of hybrid tobermorite-like C-(A)-S-H and zeolite-like N-A-S-H phases on different mixtures. The results showed that mortar samples made with AAM containing the DWTS/GGBFS ratio of 40/60 and SS/SH ratio of 1.5 had the highest compressive strength (67 MPa). The porosity results analysed using mercury intrusion porosimetry showed that 40% DWTS contents could refine pore structure and promote geopolymerisation. The x-ray diffraction pattern and Fourier-transform infrared spectroscopy identified the hybrid C-(A)-S-H and N-A-S-H phases. The element analysis on the AAM matrix using the energy-dispersive x-ray spectroscopy technique demonstrated that the co-existence of these two phases could improve the mechanical performance and microstructure. In addition, the results obtained from backscattered electron images showed that excessive alumina in the samples with more than 60% DWTS might lead to an incomplete reaction and a porous gel structure.