Effect of Geopolymer Aggregate on Strength and Microstructure of Concrete

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Title: Effect of Geopolymer Aggregate on Strength and Microstructure of Concrete

Author(s): Chamila Gunasekera, David W. Law, and Sujeeva Setunge

Publication: Materials Journal

Volume: 115

Issue: 6

Appears on pages(s): 899-908

Keywords: fly ash; geopolymer aggregate; microstructure; pore structure; strength; X-ray tomography

Date: 11/1/2018

Abstract:
The properties and microstructure of a novel manufactured geopolymer coarse aggregate have been investigated. The analysis has included compressive and tensile strengths of concretes made with the manufactured geopolymer coarse aggregate and a comparative natural crushed coarse aggregate. In addition, the microstructure and pore structure development of both concretes at the interfacial transition zone (ITZ) and bulk cement matrix were studied though scanning electron microscopy and X-ray computed tomography. The data showed that the novel geopolymer coarse aggregate satisfied the requirements of Australian Standard AS 2758.1 and is comparable to the natural aggregate. The dry density of the geopolymer aggregate concrete was less than that of the natural aggregate being just over 2000 kg/m3 (124.9 lb/ft3), with a mean 7-day strength in excess of 30 MPa (4.44 ksi) and a mean 28-day compressive strength in excess of 40 MPa (5.8 ksi). Moreover, it showed a 60% reduction in porosity between 7 and 28 days with a well compacted and dense ITZ observed at 28 days. In addition, the flexural strength demonstrated a good correlation with compressive strength, comparable to that of the natural aggregate concrete. Overall, the geopolymer investigated in this research shows potential as a lightweight coarse aggregate for concrete, with the additional benefit of reducing the environmental impact of fly ash from coal-fired power generation.