Properties of Alkali-Activated Concrete Made Using the Optimum Combinations of Precursor Materials and Activation Parameters

Abstract

This paper presents the results of a study conducted to investigate the properties of alkali-activated concrete (AAC) mixtures prepared using the optimum combinations of four precursor materials (red mud, limestone powder, silicomanganese fume, and natural pozzolana) and four activation parameters (activator to precursor ratio, silica modulus, sodium hydroxide molarity, and water to precursor ratio). In order to examine the beneficial effects of inclusion of ordinary portland cement (OPC) and curing regimes on the properties of AAC, three dosages of OPC (in the range of 10% to 30% by weight) and two types of curing (steam and air curing) were considered. Tests were conducted on the mixtures of AAC to determine different properties that included the density, void ratio, water absorption, compressive and tensile strengths, modulus of elasticity, drying shrinkage, and loss of weight and strength after exposure to acid and sulfate salt solutions. Additionally, microstructural investigations (x-ray diffraction and scanning electron microscopy with energy dispersive spectroscopy) were conducted on the alkali-activated binders to justify the trends of the experimental data pertaining to different properties of the AAC mixtures. The results of the tests indicated that the properties of AAC were significantly affected by inclusion of OPC and curing regimes. It was found that almost all properties of the AAC were significantly enhanced when the OPC dosage was increased from 10% to 20%. Further, the AAC mixtures having more than 10% OPC exhibited better properties as compared to the traditional OPC concrete mixture. The use of OPC as a construction material is one of the major contributing factors to environmental damage. Multiple alternative materials have been suggested as a replacement for OPC such as alkali-activated industrial byproducts and natural minerals. However, these possible materials are not as well studied as OPC in terms of their strength development, volumetric stability, and resistance to extreme environments. In this work, the performance of different AAC made with natural minerals and industrial waste materials was evaluated, and we compared their performance to typical OPC concrete. The present investigation shows that the developed alternative concrete mixtures perform in a comparable or better manner to OPC concrete mixtures in terms of strength, volume change with age, acid resistance, and sulfate resistance while reducing the OPC content by 70% to 90%. The study scope, however, does not extend to study the economic viability and carbon footprint of the proposed AAC mixtures.