Inhibition of the Alkali-Carbonate Reaction Using Fly Ash and the Underlying Mechanism

Xin Ren,Wei Li,Zhongyang Mao,Min Deng

doi:10.3390/cryst10060484

Abstract

In this paper, fly ash is used to inhibit the alkali-carbonate reaction (ACR). The experimental results suggest that when the alkali equivalent (equivalent Na2Oeq) of the cement is 1.0%, the adding of 30% fly ash can significantly inhibit the expansion in low-reactivity aggregates. For moderately reactive aggregates, the expansion rate can also be reduced by adding 30% of fly ash. According to a polarizing microscope analysis, the cracks are expansion cracks mainly due to the ACR. The main mechanisms of fly ash inhibiting the ACR are that it refines the pore structure of the cement paste, and that the alkali migration rate in the curing solution to the interior of the concrete microbars is reduced. As the content of fly ash increases, the concentrations of K+ and Na+ and the pH value in the pore solution gradually decrease. This makes the ACR in the rocks slower, such that the cracks are reduced, and the expansion due to the ACR is inhibited.

Highlights

In 1940, Stanton [1] first discovered the alkali-aggregate reaction (AAR), which has attracted the attention of many researchers
The AAR is divided into alkali-silicate reactions (ASRs) and alkali-carbonate reactions (ACRs)
We reduced the alkali equivalent of the 28 days in 1mol/L NaOH solution, the expansion of the concrete microbars prepared with SJW mixed with 10%–30% fly ash was greater than 0.10%

Summary

Introduction

In 1940, Stanton [1] first discovered the alkali-aggregate reaction (AAR), which has attracted the attention of many researchers. The AAR is divided into alkali-silicate reactions (ASRs) and alkali-carbonate reactions (ACRs). Gillott [2] believed that the expansion is the result of an increase in the solid volume due to water absorption by the clay, where dolomitization only provides a way for clay to absorb water. Tang and Tong [3,4,5] believed that, the absolute volume of the solid phase of the alkali-dolomite reaction is reduced in theory, the rearrangement and crystallization of the reaction products in a restricted space causes the expansion and cracking of the aggregate, respectively, leading to concrete cracking. Katayama [6,7,8] believed that the ACR is the combination of harmful expansion caused by the ASR of microcrystalline quartz and harmless dolomitization

Objectives

Methods

Results

Conclusion