Performance of Alkali-Activated Materials Using Precursors with High Impurity Contents

The presence of impurities, such as anhydrite (calcium sulfate) and unburnt carbon, in fly ash and other industrial wastes greatly limits the utilization of these materials in the construction industry. In addition, alkali-activated materials using precursors with high impurity contents should be closely monitored to ensure long-term durability. This study investigates the performance of alkali-activated materials using precursors with high impurity contents. Successful alkali-activated mixes have been developed and comprehensive tests have been conducted on the mechanical properties, volume stability, and durability. The research determined that a new mixing procedure could significantly enhance various properties of high-impurity alkali-activated materials (HI-AAMs). The study investigated both short- and long-term mechanical properties, as well as the durability of the specimens. The hardened samples exhibited reasonable 28-day compressive strength (38 MPa (5500 psi)), and rapid strength gain (28 MPa (4000 psi)), after 3 days. HI-AAMs also demonstrated acceptable long-term properties: drying shrinkage similar to that of normal concrete after four months; resistance to 5% sodium sulfate after 180 days of exposure; passing the ASTM 1260 ASR test, and smaller creep values compared to conventional concrete samples with similar compressive strengths. With similar or even superior performances to ordinary Portland cement (OPC), HI-AAMs could be a sustainable building material suitable for a host of structural and non-structural applications. Therefore, employment of the novel mixing procedure is recommended in fabricating AAMs with high impurity contents to optimize performance, cost, and environmental benefits.