Abstract
Alkali-activated slag concretes are being extensively researched because of its potential sustainability-related benefits. For such concretes to be implemented in large scale concrete applications such as infrastructural and building elements, it is essential to understand its early and long-term performance characteristics vis-à-vis conventional ordinary portland cement (OPC) based concretes. This paper presents a comprehensive study of the property and performance features including early-age isothermal calorimetric response, compressive strength development with time, microstructural features such as the pore volume and representative pore size, and accelerated chloride transport resistance of OPC and alkali-activated binder systems. Slag mixtures activated using sodium silicate solution (SiO2-to-Na2O ratio or Ms of 1–2) to provide a total alkalinity of 0.05 (Na2O-to-binder ratio) are compared with OPC mixtures with and without partial cement replacement with Class F fly ash (20 % by mass) or silica fume (6 % by mass). Major similarities are noted between these binder systems for: (1) calorimetric response with respect to the presence of features even though the locations and peaks vary based on Ms, (2) compressive strength and its development, (3) total porosity and pore size, and (4) rapid chloride permeability and non-steady state migration coefficients. Moreover, electrical impedance based circuit models are used to bring out the microstructural features (resistance of the connected pores, and capacitances of the solid phase and pore-solid interface) that are similar in conventional OPC and alkali-activated slag concretes. This study thus demonstrates that performance-equivalent alkali-activated slag systems that are more sustainable from energy and environmental standpoints can be proportioned.
Highlights
The demand for constructed facilities has been increasing in both the developed and the developing world, and ordinary portland cement (OPC) concrete is among the most used materials in infrastructure
The greenhouse gas emissions associated with Portland cement production (Mehta 2007)1 necessitate the development of alternate cementitious materials to replace a part of OPC concretes, and alkaliactivated aluminosilicates are among the novel materials that are expected to fit this bill
This section reports the results of early age hydration response, compressive strength, pore structure, and chloride transport resistance of conventional and alkali-activated slag concretes and facilitates a comparison of their properties
Summary
The demand for constructed facilities has been increasing in both the developed and the developing world, and ordinary portland cement (OPC) concrete is among the most used materials in infrastructure. A fairly rigorous understanding of slag as a cementitious material exists, and alkali activation of slag produces C–S–H gel as the reaction product, similar to OPC systems but typically with a lower Ca/Si ratio (Yip et al 2005; Song et al 2000) This has led to extensive studies on the alkali activation of slag (Fernandez-Jimenez et al 1999; Bernal et al 2012; Ravikumar et al 2010; Chithiraputhiran and Neithalath 2013; Ravikumar and Neithalath 2012a). The energy requirement towards the production of activators and the associated environmental impact plays an important role in determining the sustainability of alkali-activated systems, along with their potential to replace large amounts of OPC
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