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 M_s 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 M_s, (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.

The pore- and micro-structural features of a novel binding material based on the carbonation of waste metallic iron powder are reported in this paper. The binder contains metallic iron powder as the major ingredient, followed by additives containing silica and alumina to facilitate favorable reaction product formation. Compressive strengths sufficient for a majority of concrete applications are attained. The material pore structure is investigated primarily through mercury intrusion porosimetry whereas electron microscopy is used for microstructural characterization. Reduction in the overall porosity and the average pore size with an increase in carbonation duration from 1 day to 4 days is noticed. The pore structure features are used in predictive models for gas and moisture transport (water vapor diffusivity and moisture permeability) through the porous medium which dictates its long-term durability when used in structural applications. Comparisons of the pore structure with those of a Portland cement paste are also provided. The morphology of the reaction products in the iron-based binder, and the distribution of constituent elements in the microstructure are also reported.

This paper reports the influence of activator type and concentration on the rheological properties of alkali-activated fly ash suspensions. A thorough investigation of the rheological influences (yield stress and plastic viscosity) of several activator parameters, including: (i) the cation type and concentration of alkali hydroxide and (ii) the alkali-to-binder ratio (n) and silica modulus (M_s), and (iii) the volume of the activation solution, on the suspension rheology is presented. The results indicate a strong dependence on the cation and its concentration in the activation solution. The viscosity of the activation solution and the volumetric solution-to-powder ratio are shown to most strongly influence the plastic viscosity of the suspension. The suspension yield stress is predominantly influenced by the changes in fly ash particle surface charge and the ionic species in the activator. A shift from non-Newtonian to Newtonian flow behavior is noted in the case of silicate-based suspensions for M_s ≤ 1.5. This behavior, which is not observed at higher M_S values, or when the fly ash is dispersed in hydroxide solutions or pure water, is hypothesized to be caused by colloidal siliceous species present in this system, or surface charge effects on the fly ash particles. Comparisons of the rheological response of alkali-activated suspensions to that of portland cement-water suspensions are also reported.

Design of novel infrastructure materials requires a proper understanding of the influence of microstructure on the desired performance. The priority is to seek new and innovative ways to develop sustainable infrastructure materials using natural resources and industrial solid wastes in a manner that is ecologically sustainable and yet economically viable. Structural materials are invariably designed based on mechanical performance. Accurate prediction of effective constitutive behavior of highly heterogeneous novel structural materials with multiple microstructural phases is a challenging task. This necessitates reliable classification and characterization of constituent phases in terms of their volume fractions, size distributions and intrinsic elastic properties, coupled with numerical homogenization technique. This paper explores a microstructure-guided numerical framework that derives inputs from nanoindentation and synchrotron x-ray tomography towards the prediction of effective constitutive response of novel sustainable structural materials so as to enable microstructure-guided design.