Synthesis of zeolite A using sewage sludge ash for application in warm mix asphalt

Conventional landfill disposal of Sewage Sludge Ash (SSA) generates increasing environmental and economic concerns. This study aims to develop an innovative measure to solve this waste disposal problem by means of synthesizing zeolite A from the SSA and using it as a Warm Mix Asphalt (WMA) additive, which can decrease the construction temperature of asphalt pavement, thus reducing the associated energy consumption and pollutant emission. Alkaline fusion followed by hydrothermal reaction was implemented to synthesize zeolite A from the SSA. The orthogonal experimental design was carried out to optimize the synthesis conditions. The synthetic products were characterized using a Thermogravimetry-Differential Thermal Analyzer (TG-DTA), an X-ray Diffractometer (XRD) and a Scanning Electron Microscope (SEM). The zeolite product synthesized under the optimized conditions showed a desirable thermal property of gradual release of crystalline water up to 18.5% when heated to 200 °C. Its XRD spectrum validated the presence of zeolite A with high purity. The SSA-derived zeolite A was then used as a WMA additive to produce asphalt mixture at lower construction temperatures, which proved to reduce the construction temperatures of asphalt mixture by 25 °C. The approach to use SSA-derived zeolite can decline the environmental and economic burden and it can be a cleaner production method of WMA additive for environmental benefits.