Synergistic effect of RHA and FCW in alkali-aggregate reaction mitigation

Marlova Piva Kulakowski,Maurício Mancio,Patrícia Guillante,Aguida Gomes De Abreu,Claudio De Souza Kazmierczak

doi:10.1590/s1678-86212019000200306

Marlova Piva Kulakowski, Maurício Mancio + Show 3 more

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https://doi.org/10.1590/s1678-86212019000200306

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Journal: Ambiente Construído	Publication Date: Apr 1, 2019
Citations: 3	License type: CC BY 4.0

Affiliation: Universidade do Vale do Rio dos Sinos

Abstract

Abstract Pozzolans rich in silica, such as Rice Husk Ash (RHA), contribute to compressive strength gain but at the same time might increase alkali-aggregate reaction (AAR) in mortar mixtures. Pozzolans that have aluminates, such as Fired Clay Brick Waste (FCW), can be efficient to mitigate AAR but tend to lead to a slower compressive strength development. The association of different types of pozzolans, however, may result in a synergistic effect, compensating individual deficiencies. This paper presents a study of mixtures containing RHA, FCW and these two materials combined, aiming to obtain benefits in the mechanical behavior and in the durability regarding AAR. A substitution rate of 20% Portland cement by pozzolanic material was used. Through accelerated AAR tests and compressive strength measurements, it was found that while RHA is considered harmful to AAR - even when using an innocuous aggregate - FCW presents benefits, also avoiding this deleterious effect when combined with RHA. The same occurs in the compressive strength development, where RHA compensates a small loss of compressive strength associated with the use of FWC alone.

Highlights

Abundant in the south of Brazil, Rice Husk Ash (RHA) is a byproduct from the combustion process of rice husk as a source of heat generation required for the drying of rice grains (DAL MOLIN, 2007)
The present study investigates the individual and combined effects of a siliceous pozzolanic material (RHA) and an aluminosilicate (FCW), using a reactive and an innocuous aggregate, in order to evaluate the synergistic effect of the RHA and the Fired Clay Brick Waste (FCW) in the alkaliaggregate reaction (AAR), as well as its effect in axial compressive strength
It can be verified that the pozzolanic materials are different from each other: while RHA is basically composed of silica, the FCW presents, besides silica, considerable amounts of alumina and iron

Summary

Introduction

Abundant in the south of Brazil, Rice Husk Ash (RHA) is a byproduct from the combustion process of rice husk as a source of heat generation required for the drying of rice grains (DAL MOLIN, 2007). RHA can present high pozzolanic activity depending on the combustion process, which varies depending mainly on the type of equipment used (grate, fluidized bed, open air), the temperature and time of exposure (POUEY, 2006). RHA obtained with combustion control and burning temperature between 500 oC and 600 oC shows amorphous characteristics. Higher temperatures lead to the formation of crystallized silica (cristoballite), with well-defined peaks of tridimite and cristoballite above 800 oC (HAMAD; KHATTAB, 1981). Considering that the amorphism grade of a material indicates its potential reactivity, the control of temperature in the calcination process is important. When evaluating the chemical contribution of RHA incorporated in cementitious matrices, several studies (SILVEIRA, 2007; MADANDOUST et al, 2011; ZAIN et al, 2011; JAMIL et al, 2013) have observed that typically there is an increase in the compressive strength over time in relation to the control samples. The benefits are associated with the formation of secondary C-S-H, in addition to the filler effect, which promotes pore filling and pore refinement

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