| Summary: | Alkali–silica reaction (ASR) attack is one of the most significant durability concerns in cement-based materials. In this paper, the drinking water treatment sludge (DWTS), which is a typical by-product from the drinking water treatment industry, was reused as supplementary cementitious material to mitigate the degradation of mortar resulting from ASR attack. DWTS was milled and calcined at 800 °C for 2 h before being used as a replacement for cement. Glass sand was used as the reactive fine aggregate. Properties of four mortar mixtures prepared with 0%, 5%, 10%, and 20% of calcined DWTS replacement of cement were firstly assessed, including compressive strength, flexural strength, and water sorptivity. The mortar specimens were then exposed to an ASR-attacked environment for 28 days, the changes in specimen length were monitored, and the uniformity of mortar was measured via Ultrasonic pulse velocity (UPV). The results showed that 10% replacement significantly improved the mechanical properties of mortar. The specimens with 20% of the calcined DWTS exhibited comparable strength relative to the reference group and exhibited superior resistance to ASR attack. Additionally, a water sorptivity test showed that higher contents of the calcined DWTS can lead to lower water capillary absorption of mortar.
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