A consideration on the one-part mixing method of alkali-activated material: problems of sodium silicate solubility and quick setting

Mohammad Idris Rasuli,Yuyun Tajunnisa,Akifumi Yamamura,Mitsuhiro Shigeishi

doi:10.1016/j.heliyon.2022.e08783

Mohammad Idris Rasuli, Yuyun Tajunnisa + Show 2 more

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https://doi.org/10.1016/j.heliyon.2022.e08783

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Abstract

This research investigates the properties of alkali-activated materials (AAMs) using sodium metasilicate, with the ratio of SiO2:Na2O equals 1. This study was conducted to achieve the following three aims. Firstly, to understand the solubility mechanism of granular sodium metasilicate pentahydrate (Na2SiO3.5H2O) when used in a one-part mixing method. Secondly, to investigate the properties of AAMs when a sodium metasilicate aqueous solution is used as an alkaline material and as a source of silica. Lastly, to study the retardation effect of sucrose on AAMs. 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, which is about 2% of the weight of the solid precursors, was added to modify the reaction process between the precursors and the alkaline materials. Four types of samples were prepared: M1, M2, M3, and M4, with the fly ash, slag, and silica fume ratios of 80:20:0, 70:30:0, 75:20:5, and 100:0:0, respectively. The research conducted solubility test of the alkaline materials, flowability, 7-, 28-, 56-day compressive and flexural tests, drying shrinkage test of mortar samples, and the setting tests of pastes with and without sucrose. The results show that the dissolution time of the NaOH was much shorter, whereas Na2SiO3.5H2O needed a solvent with a temperature of around 40 °C to be fully dissolved. This problem of solubility decreases the quality of AAMs formed using the one-part mixing method. Among the mortar samples, the M4 had the highest flow rate, while M3 had the lowest flow rate. M2 had the highest compressive and flexural strength of 43.4 MPa and 6.1 MPa, respectively. The setting time test shows that sucrose retards the reaction process in AAM.

Highlights

Portland cement concrete is the most commonly used construction material in the world
The reaction between aluminosilicate precursors and alkaline materials is vital for producing geopolymers and activated materials (AAMs)
One-part mixing method was studied by many researchers to make ease in the production of AAMs and geopolymers and to generalize the materials

Summary

Introduction

Portland cement concrete is the most commonly used construction material in the world. Annual global production of ordinary Portland cement (OPC) reaches 4 billion tons [1]. It is not environmentally friendly as it is responsible for 8% of global CO2 emissions [2]. Byproducts of some materials have a negative influence on the environment of the world. Coal-based power plants burn more than 8 billion tons of coal every year [3]. The production of unused fly and bottom ashes from coal-based power plants is mainly disposed of and negatively influences the environment and groundwater quality due to the metals leaching from the ashes [4]

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