Effects of alkali-treated plant wastewater on the properties and microstructures of alkali-activated composites

Abstract

Naturally available plants such as fiber, straw, sawdust, and wood used as reinforcing additives in building materials require an alkali treatment to reduce the moisture sensitivity of additives and to interlock matrix and additive. However, the discharge of alkali-treated plant wastewater (ATPW) is extremely detrimental to the environment. The purpose of this study is to evaluate the effects of recycled ATPW from NaOH-treated sisal leaves, poplar leaves, poplar stems, and corn stems on the characteristics and microstructures of alkali-activated composite materials (AACMs) made from solid wastes. The ATPWs were produced by soaking green and dead plants for 24 h in a 15% NaOH solution. The AACMs were manufactured using ATPW as an alkaline activator and a mixture of slag powder, red mud, fly ash, and steel slag as a binder. The fresh and hardened properties, such as electrical conductivity (EC), fluidity, flexural strength, compressive strength, and density, were examined along with drying shrinkage resistance. Furthermore, SEM, EDS, CT, and FTIR techniques were used to observe and evaluate the pore distributions, morphologies, and products. The results demonstrate that the effects of ATPWs produced from dead sisal leaves were remarkable on the properties and microstructures of AACMs. The sample (DSL) with ATPW exhibits an increase of 43.08% in fluidity and a drop of 50.00% in EC, 44.30% in density, 34.25% in dry shrinkage, 84.44% in flexural strength, and 88.50% in compressive strength, relative to the control without ATPW. Moreover, AACMs physically sequester the organic components of ATPW during the early stage of hardening. The ATPW serves as a unique physical foaming agent in AACMs. The results provide original data on the dual recycling of industrial wastewater and solid waste to promote clean operations.