Abstract
Two types of alkali-activated material (AAM) concretes were exposed to various sulphate bearing-solutions for over two years. Physical changes to the concrete specimen and chemical changes in the exposure liquid were studied in an attempt to understand how sulphate attack occurs in such binders and the role the mix variables play in offering resistance against such attack. The mix variables of alkali-activated slag concrete (AASC) included water-to-binder ratio, percentage of alkali, and the SiO2/Na2O ratio (silica modulus, Ms); for alkali-activated slag/fly ash (AA-S/F) concrete, the mix variables included slag/fly ash ratio and the SiO2/Na2O ratio. The exposure solutions included water, magnesium sulphate (5%), sodium sulphate (5%), calcium sulphate (0.2%), and two concentrations of sulphuric acid solutions, pH 3 and pH 1. The physical changes studied were length and mass change, visual appearance, and change in compressive strength. The exposure liquids were analysed for change in pH and ionic composition. Findings show that the AA-S/F blend performs better than AASC in sulphate environments, based on strength and change in length. Exposure to water resulted in the most expansion/shrinkage in all mixes studied. An empirical model was proposed for predicting the change in compressive strength for AAS&AA-S/F concretes based on mass gain. Further, a simple performance criterion was put forward for mixes in sulphate environments based on mass gain.
Highlights
Carbon dioxide (CO2 ) emissions and energy consumption due to Portland cement (PC)production accounts, respectively, for at least 5–8% of the world’s total CO2 emissions [1]and 10% of the world’s energy [2]
An empirical model was proposed for predicting the change in compressive strength for AAS&activated slag/fly ash (AA-S/F) concretes based on mass gain
Alkali-activated materials (AAM) concrete is produced by combining a precursor with a high alumina silicate content, such as ground granulated blast-furnace slag (GGBS) and pulverised fuel ash (PFA), with water and an activator
Summary
Carbon dioxide (CO2 ) emissions and energy consumption due to Portland cement (PC)production accounts, respectively, for at least 5–8% of the world’s total CO2 emissions [1]and 10% of the world’s energy [2]. Carbon dioxide (CO2 ) emissions and energy consumption due to Portland cement (PC). The second most consumed material on earth after water is concrete; currently, in excess of 10 billion tons per year are produced [2]. These factors have led, in recent years, to renewed research into alternative binder systems. Alkali-activated materials (AAM) concrete is produced by combining a precursor with a high alumina silicate content, such as ground granulated blast-furnace slag (GGBS) and pulverised fuel ash (PFA), with water and an activator. The drive has been to develop binder systems for exposure environments where Portland cement-based systems are not the best for achieving long term performance viz., acidic and sulphate-rich environments, biogenic environments, and fire protection systems. Shi et al state that in GGBS-based AAMs, an alternative to PC-based concrete, the reduction in alkali content increases the resistance to MgSO4 solutions [4]
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