Effects of Initial Surface Evaporation on the Performance of Fly Ash-Based Geopolymer Paste at Elevated Temperatures

Thathsarani Kannangara,Sam Fragomeni,Maurice Guerrieri,Paul Joseph

doi:10.3390/app12010364

Abstract

Geopolymer concrete is a valuable and alternative type of concrete that is free of traditional cement. Generally, geopolymer concretes require a source material, which is rich in silicon and aluminum. Furthermore, fly ash-based geopolymer concretes have been proven to have superior fire resistance, primarily due to their ceramic properties, and are inherently environmentally-friendly given their zero-cement content. This paper presents the effects on initial evaporation on the performance of fly ash-based geopolymer pastes after exposure to elevated temperatures of 400 °C and 800 °C. The fly ash (FA) samples used in the present study included: Gladstone and Gladstone/Callide. The results for sealed samples placed in the oven during curing were much more consistent than the samples that were not kept covered. In addition, Gladstone fly ash-based geopolymer samples that were sealed recorded an initial maximum compressive strength reading of ca. 75 MPa, while sealed Gladstone/Callide fly ash-based geopolymer samples, of the same mix design, only recorded an initial maximum compressive strength reading of ca. 50 MPa (both subjected to oven curing at 60 °C for 24 h). However, Gladstone/Callide fly ash-based geopolymer samples exhibited a significant strength gain, ca. 90 MPa, even after being subjected to 400 °C.

Highlights

Geopolymer (GP)-based concrete, first brought into light in the 1970s by a French scientist Joseph Davidovits, is an environmentally-benign material with a relatively lower carbon footprint compared to conventional concrete made from ordinary Portland cement (OPC) [1,2,3,4]
The alkaline activator, which is another important factor that determines the performance of GP-based materials, can be sodium hydroxide (NaOH) or potassium hydroxide (KOH), which is taken in conjunction with other compounds such as sodium silicate (Na2SiO3) or potassium silicate (K2SiO3), sodium sulfate (Na2SO4), etc. [12,13]; due to the availability and cost effectiveness, NaOH and Na2SiO3 solutions are generally employed [7,14,15,16,17,18]
Other related studies [18,23,24,25,26] have indicated that components such as fly ash (FA), slag, and metakaolin are often used as the source material(s) as they are rich in oxides of silica and aluminum

Summary

Introduction

Geopolymer (GP)-based concrete, first brought into light in the 1970s by a French scientist Joseph Davidovits, is an environmentally-benign material with a relatively lower carbon footprint compared to conventional concrete made from ordinary Portland cement (OPC) [1,2,3,4]. The compressive strength of FA-based GP pastes, reinforced with carbon and basalt fibers at 0.5, 1, and 1.5% by weight, after being exposed to temperatures of 200, 400, 600, and 800 ◦C was tested [26]. While numerous studies on the behavior, based on durability, strength, and other such mechanical properties of GP concretes at various exposure levels are available, research on the effects of the initial surface evaporation on FA-based GP pastes is very limited. The effect of moisture retention on the performance of the cured samples were mainly evaluated through several tests for measuring the density, setting times, initial compressive strengths, residual strengths, and mass losses after exposure to elevated temperatures. There are no previously published systematic studies pertaining to the influence of moisture evaporation on FA-based GP paste samples that are made from different mix compositions

Materials and Methods

Materials

Specification of the Mix Design

Findings

Conclusions