Properties of a Lightweight Fly Ash–Slag Alkali-Activated Concrete with Three Strength Grades

Huailiang Wang,Baoquan Cheng,Yuhui Wu,Lang Wang,Huihua Chen

doi:10.3390/app11020766

Abstract

Lightweight alkali-activated concrete (LAAC) is a type of highly environmentally friendly concrete, which can provide the benefits of both alkali-activated material and lightweight concrete. The study aimed to investigate the influence of different water/solid (W/S) ratios on the properties of normal-weight/lightweight fly ash–slag alkali-activated concrete manufactured at ambient temperature. The relative performance of the alkali-activated concrete (AAC) mixes with limestone and sintered fly ash lightweight aggregates as the coarse aggregates was also compared to the conventional ordinary Portland cement (OPC) concrete mix in terms of their compressive stress–strain relationship, splitting tensile strength and fracture parameters. The morphologies and microstructure of the four types of interfacial transition zones (ITZs) were characterized by scanning electron microscopy (SEM). Results indicated that the AAC had a higher tensile strength, stress intensity factor, brittleness and lower elastic modulus than its cement counterpart. With the decrease in the W/S ratio, the density, compressive and tensile strength, ultrasonic pulse velocity, fracture energy, brittleness and elastic modulus of the AAC increase. However, the influence of the W/S ratio on the mechanical properties of the LAAC with lightweight porous aggregates was less than that of the normal-weight AAC. Predictive models of the splitting tensile strength, fracture energy and elastic modulus of the AAC were also suggested, which were similar to those of the OPC concrete. Furthermore, the microstructure investigation showed that no wall effect occurred in the ITZ of the AAC. The ITZ structure of the hardened AAC was also more compact and uniform than that of the OPC concrete.

Highlights

Concrete is the most widely used building material on this planet, which is mainly produced by ordinary Portland cement (OPC), natural aggregates and other components.Cement production needs to consume natural resources and releases large amounts of carbon dioxide (CO2 ) into the environment
After adding the ash and blast furnace slag powder (BFSP), the products of the chemical interactions between the paste fly ash and BFSP, the products of the chemical interactions between the paste and sodiumand sodi silicate solution can penetrate into the lightweight aggregates (LWAs) particles down to a certain of 21depth, wh silicate solution can penetrate into the LWA particles down to a certain depth, which 18 served served to enhance the bonding and interlocking action between them
In this study, prepared with different cementitious mamaterials and ratios at room temperature to evaluate the effects of the mixed ratios terials and W/S ratios at room temperature to evaluate the effects of the mixed ratios and and aggregate types mechanical andfracture fractureproperties

Summary

Introduction

Concrete is the most widely used building material on this planet, which is mainly produced by ordinary Portland cement (OPC), natural aggregates and other components.Cement production needs to consume natural resources and releases large amounts of carbon dioxide (CO2 ) into the environment. Alkali-activated concrete (AAC), known as “geopolymer concrete”, can be manufactured through an activation process between alkaline liquids and materials rich in silica and alumina, such as blast furnace slag powder (BFSP), which is a by-product from the steel making, and fly ash (FA), which is a by-product of coal combustion from coal-fired power plants. It has become a promising green construction material for sustainable development and attracted much attention from the academic field in recent years [2,3].

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