Influences of Silica Fume on Compressive Strength and Chemical Resistances of High Calcium Fly Ash-Based Alkali-Activated Mortar

Kantiya Sothornchaiwit,Warayut Dokduea,Chanachai Thongchom,Suraparb Keawsawasvong,Chai Jaturapitakkul,Weerachart Tangchirapat

doi:10.3390/su14052652

Kantiya Sothornchaiwit, Warayut Dokduea + Show 4 more

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https://doi.org/10.3390/su14052652

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Abstract

Although elevated temperature curing can increase the compressive strength of alkali-activated mortar, its field applications are still limited. In this study, alkali-activated mortars were prepared using high calcium fly ash (FA) as a precursor. Small amounts of silica fume were used to partially replace high calcium fly ash at 3–9% by weight to increase the strength of alkali-activated mortar. All mixtures had a liquid to binder ratio of 0.60 and sand to binder ratio of 2.75 by weight. A ratio of NaOH to Na2SiO3 solution was kept at 2:1 by weight. Mortar flow was also held between 105–115 using a superplasticizer. Compressive strength and durability were investigated in terms of acid and sulfate resistance. The effects of silica fume addition and curing temperature on compressive strength were found to be significant. The optimum content of silica fume was 6%, providing compressive strength as high as that of alkali-activated mortars cured at 45 °C. The weight loss of alkali-activated mortar due to sulfuric acid attack decreased with increasing silica fume content and curing temperature. All alkali-activated mortars were found to have a better performance than (ordinary) Portland cement (OPC) mortars and mortars containing 40% FA. Alkali-activated mortars immersed in magnesium sulfate solutions had compressive strength that decreased with an increase in curing temperature. The expansion of alkali-activated mortar due to sodium sulfate attack increased with increasing silica fume content, and the expansion decreased with increased curing temperature. All alkali-activated mortars performed better than OPC mortars after 98 days of sulfate attack.

Highlights

Each ton of cement produced today results in approximately 0.35–0.55 tons of carbon dioxide emission [1]
The comThe compressive strength increased with increasing curing time, after 7 days
This paper presents the properties of alkali-activated mortars with silica fume and curing at an ambient temperature

Summary

Introduction

Each ton of cement produced today results in approximately 0.35–0.55 tons of carbon dioxide emission [1]. Supplementary cementitious materials (e.g., fly ash, silica fume, blast-furnace slag, metakaolin, and biomass ash) are used to reduce Portland cement consumption by replacing it in concrete [2,3,4]. Portland cement is still the primary binder used to produce mortar and concrete. Alkali-activated materials are an environmentally friendly, well-known, and conventional alternative to cementitious materials as cement binders. Alkali-activated mortar can be made by the reaction of an alkali solution with pozzolanic materials containing high silica and alumina components (e.g., fly ash, silica fume, and rice husk ash) [8,9,10]

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