Optimizing Precursors and Reagents for the Development of Alkali-Activated Binders in Ambient Curing Conditions

Dhruv Sood,Khandaker M Anwar Hossain

doi:10.3390/jcs5020059

Abstract

Alkali-activated binders (AABs) are developed through the activation of aluminosilicate-rich materials using alkaline reagents. The characteristics of AABs developed using a novel dry-mixing technique incorporating powder-based reagents/activators are extensively explored. A total of forty-four binder mixes are assessed in terms of their fresh and hardened state properties. The influence of mono/binary/ternary combinations of supplementary cementitious materials (SCMs)/precursors and different types/combinations/dosages of powder-based reagents on the strength and workability properties of different binder mixes are assessed to determine the optimum composition of precursors and the reagents. The binary (55% fly ash class C and 45% ground granulated blast furnace slag) and ternary (25% fly ash class C, 35% fly ash class F and 40% ground granulated blast furnace slag) binders with reagent-2 (calcium hydroxide and sodium sulfate = 2.5:1) exhibited desired workability and 28-day compressive strengths of 56 and 52 MPa, respectively. Microstructural analyses (in terms of SEM/EDS and XRD) revealed the formation of additional calcium aluminosilicate hydrate with sodium or mixed Ca/Na compounds in binary and ternary binders incorporating reagent-2, resulting in higher compressive strength. This research confirms the potential of producing powder-based cement-free green AABs incorporating binary/ternary combinations of SCMs having the desired fresh and hardened state properties under ambient curing conditions.

Highlights

Ordinary Portland cement (OPC) is the most common cementitious material used in concrete construction industries [1]
The production process of geopolymers requires, comparatively, 60% less energy and releases approximately 80 to 90% less greenhouse gas emissions compared to the production of OPC [15,16,20,21]
The following conclusions are drawn from the study: (1) Binary (FA-C and ground granulated blast furnace slag (GGBFS)) and ternary (FA-C, fly ash class F (FA-F), and GGBFS) binder compositions having a GGBFS content of 40% to 50% incorporating reagent-1 (Ca(OH)2:Na2SiO3·5H2O = 1:2.5) and reagent-2 (Ca(OH)2:Na2SO4 = 2.5:1) were determined to be optimized compositions in terms of desired workability and 28-day compressive strength (>38 MPa)

Summary

Introduction

Ordinary Portland cement (OPC) is the most common cementitious material used in concrete construction industries [1]. One ton of cement is produced per capita each year [3]. The ongoing urbanization, especially in developing countries like China, India, etc., has led to the rapid development of cement concrete industries [4]. There are about 2.8 billion tons of cement products manufactured every year, which in turn are responsible for approximately 5–7% of global carbon dioxide emissions [6,7]. The partial substitution of cement with industrial/domestic waste products is already being practiced globally [9,10]. The complete replacement of cement with recycled waste and industrial by-products using alkali activation technology/geopolymerization seems to be an optimum solution to reduce global carbon emissions and tackle the waste disposal problems [11]

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Conclusion