Title: Long-Term Mechanical Properties of Geopolymer Aggregate Concrete

Author(s): Charitha Seneviratne, Chamila Gunasekara, David W. Law, Sujeeva Setunge, and Dilan Robert

Publication: Structural Journal

Volume: 118

Issue: 5

Appears on pages(s): 135-147

Keywords: fly ash; geopolymer aggregate; mechanical properties; micro-structure; nanoindentation; sustainability

DOI: 10.14359/51732823

Date: 9/1/2021

Abstract:
Geopolymer aggregate (GPA) is a novel coarse aggregate synthesized from low-calcium fly ash with a highly alkaline activator. It is also classified as a lightweight aggregate, having a density of 1709 kg/m3 (106.7 lb/ft3). This paper reports the findings of the detailed investigation of mechanical properties of GPA concrete, which was observed up to a period of 1 year. The characteristics of GPA concrete were benchmarked against conventional basalt aggregate concrete. Compressive, flexural, and splitting tensile strengths, elastic modulus, and Poisson’s ratio of GPA concrete ranged from 42.1 to 50.81 MPa (6.1 to 7.37 ksi), 4.75 to 5.27 MPa (0.69 to 0.76 ksi), 3.02 to 3.66 MPa (0.44 to 0.53 ksi), 20 to 20.5 GPa (2900 to 2973 ksi), and 0.13 to 0.11, respectively within a 90- to 365-day period. The correlations between existing concrete standards and major mechanical properties of GPA concrete are discussed. Relationships are developed between compressive strength and mechanical properties including flexural strength, splitting tensile strength, and elastic modulus using statistical regression analysis. The suitability of using the existing relation-ships in Australian standards and American Concrete Institute codes for GPA concrete are critically examined. In addition, the microstructure of GPA concrete was examined using scanning electron microscopy (SEM) imaging and microhardness testing. The thickness of the interfacial transition zone (ITZ) is estimated to be 55, 50, and 45 μm (21.65 × 10–4, 19.68 × 10–4, and 17.72 × 10–4 in.) at 28, 90, and 365 days, respectively. Overall, the observations of this study verify the potential of using GPA concrete in various structural applications, making it a viable and sustainable alternative to conventional aggregate concrete.