A Consideration on the One-Part Mixing Method of Alkali-Activated Material: Problems of the Sodium Silicate Solubility and Quick Setting

This research investigates the properties of alkali-activated materials (AAM) using sodium metasilicate, which has a SiO2:Na2O ratio of 1. This study was conducted to achieve the following three aims. To understand the solubility mechanism of granular sodium metasilicate pentahydrate (Na2SiO3.5H2O) when used in a one-part mixing method. Second, properties investigation of AAM when the sodium metasilicate aqueous solution is used as one of the alkaline materials and as a source of silica. Lastly, study the retardation effect of sucrose on AAM. This research used aluminum silicate precursors such as low calcium fly ash, slag, and micros silica, alkali activators such as NaOH pellets and Na2SiO3.5H2O, and standardized sand. The alkaline activators were first dissolved in water using a water bath shaker to achieve the alkaline solution. Sucrose, 2% by the weight of the solid precursor, was added to modify the precursors and alkali reaction process. The authors prepared four types of samples, M1, M2, M3, and M4, with the fly ash, slag, and silica fume ratios of 80:20:0, 70:30:0, 75:20:5 100:0:0, respectively. The research conducted solubility test of the alkaline materials, flowability, 7, 28, 56-day compressive and flexural tests and drying shrinkage test of mortar samples, and the setting tests of pastes with and without the sucrose. The results show that the dissolution time of the NaOH was much shorter while Na2SiO3.5H2O needed a solvent with a temperature of around 40°C to be fully dissolved. This problem solubility decreases the quality of AAM made by the one-part mixing method. The M4 had the highest, and M3 had the lowest flow rate among the mortar samples. M2 had the highest compressive and flexural strength of 43.4MPa and 6.1 MPa, respectively. The setting time test shows that sucrose retards the reaction process in AAM.