Investigations on Chemical, Mechanical, and Long-Term Characteristics of Alkali-Activated Concrete

Abstract

AbstractThe global annual production of 4.1 billion tons of portland cement (PC) causes significant carbon dioxide emissions and depletion of natural limestone reserves. Alkali-activated binder (AAB) is a possible sustainable solution to this problem. AAB is produced by the reaction between an aluminosilicate-rich precursor (such as low calcium fly ash, blast furnace slag, and metakaolin obtained as industrial waste and by-products) and an alkaline activator composed of sodium silicate and sodium hydroxide. AAB is a potential substitute for PC to lower the carbon footprint and prevent industrial waste disposal into utilizable land. The present formulation of AAB needs thermal curing, which is energy-intensive for plant and field productions. In-situ thermal curing at 60–80 °C is impracticable and limits AAB usage to precast members only. This study focuses on developing AAB mixtures cured at ambient temperature and characterizing their mineralogical, chemical, and mechanical properties for varying precursor proportions (fly ash to slag ratios) and activator modulus, Ms, calculated as (sodium silicate: sodium hydroxide). Using these proportions, the compressive strength and bond strength of alkali-activated concrete (AAC) cured under ambient conditions are evaluated at room temperature and under the influence of high exposure temperatures up to 900 °C. AAC prepared using 70% fly ash, 30% slag, and Ms of 1.4 with ambient curing is proposed as optimal from this study.KeywordsAmbient curingAlkali-activated concreteHigh-temperature exposureCharacterizationStrengthOptimal design mix