Structure and Compressive Strength

Chapter 1

Abstract

hardness of the ITZ.

1. Introduction

3

perlite rock, Portland cement

The Influence of Interfacial

Alkali-Activated Concrete

Oleksandr Kovalchuk and Oleksandr Gelevera

Pavel Krivenko, Oleh Petropavlovskyi,

Transition Zone on Strength of

A process of structure formation taking place in the interfacial transition zone (ITZ) "cement stone-aggregate" was studied on a variety of concretes made with artificial and real aggregates. The study of these processes in the case of artificial aggregate prepared from a mixture of clay loam and alkali-activated slag cement showed that not only active SiO2 and Na2O but also other substances of both cement and aggregate are involved in the formation of the ITZ. This results in the formation of alkaline and alkaline-alkali-earth aluminosilicate hydrates which strengthen the ITZ and improve strength and durability of the concrete. Thus, the alkali-silica reaction (ASR) transforms from a destructive one (negative effect) into a constructive one (positive effect). The study on the ITZ in the alkali-activated cement concretes made with real alkali-susceptible aggregates selected from crushed basalt rock, glassy waste product from basalt fiber production, crushed perlite rock, and expanded perlite suggested to make a conclusion on the possibility to prevent the destructive processes in the ITZ through the addition of the metakaolin additive into the cement composition in quantities of 5–10% by mass. These conclusions were supported by the long-term testing of strength of these concretes, by measuring the deformations "shrinkage-expansion" as well as the results of study on

Keywords: alkali-activated cement, alkali-aggregate reaction (AAR), alkali-silica reaction (ASR), alkali-susceptible aggregate, alkaline and alkaline-alkali-earth aluminosilicate hydrates, basalt rock, interfacial transition zone (ITZ), metakaolin,

Nowadays, concrete is recognized as one of the basic constructional materials. However, strict requirements to its performance properties, in particular durability, are not met in all cases allowing big concerns to occur. With worsening of the ecological situation and larger volumes of use of off-standard materials as concrete constituents, durability became a main criterion of concrete quality. One poorly studied and "hidden" reason explaining low durability of concrete in some cases is the so-called internal corrosion occurring in a cement paste/aggregate interfacial transition zone (ITZ) in concrete, where the cement paste with thicknesses of a few
