A sludge and modified rice husk ash-based geopolymer: synthesis and characterization analysis

There are many studies on the system of sludge and rice husk ash applied as the construction materials, but in most cases, the sludge needs to be incinerated, which induced the environmental contamination. This research investigated the viability of a novel geopolymer derived from non-calcined sludge and modified rice husk ash blend. The variable factors such as rice husk ash/sludge ratio, liquid alkaline activator/solid ratio and alkalinity on mechanical properties were studied, and the optimum mix ratio was then determined. The results indicate that compressive strength first increases and then decreases with the increase of the ratio of modified rice husk ash to dried sludge (RHA/DS). And at the RHA/DS ratio of 0.35 and liquid to solid ratio of 1.2, the geopolymer got the highest compressive strength. Mercury intrusion porosimetry (MIP) and X-ray diffraction (XRD) demonstrate that the decrease of the number of macropores (larger than 200 nm) improve the internal microstructure and amorphous phase with some crystalline as fillers. And the same results are confirmed by scanning electron microscope (SEM) analysis. Toxicity characteristic leaching procedure (TCLP) shows the new geopolymers have good environmental performance, with good sorption properties for heavy metals. However, relatively low mechanical properties, uncertainty in raw materials' chemical composition and in long-term performance as well as durability, are a principal inhibition to use this material immediately. (C) 2019 Elsevier Ltd. All rights reserved.