Mechanical and Microstructural Properties of Alkali Pozzolan Cement (APC)
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RESEARCH PAPER
Mechanical and Microstructural Properties of Alkali Pozzolan Cement (APC) Chandana Kulasuriya1 • W. P. S. Dias2 • Vanissorn Vimonsatit1 • P. De Silva3 Received: 15 September 2019 / Revised: 2 May 2020 / Accepted: 5 June 2020 Ó Iran University of Science and Technology 2020
Abstract Alkali Pozzolan cement (APC) comprises a high volume of fly ash, lime, ordinary Portland cement (OPC), and a dry Na2SO4 activator. APC can be stored in dry form and only requires water to create a cementitious binder. Mechanical and microstructural properties of APC were investigated to determine the compressive strength and hydration products of different APC pastes. Air-cured APC pastes (w/b = 0.3) were found to gain 65–77% of the strength of similar OPC pastes at 28 days, while being 75% greater than that of corresponding high-volume fly ash ones. Microstructural properties studied using X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and thermal analysis were able to explain the observed mechanical properties. The attacking of the smooth fly ash spheres (observed via SEM) by Ca(OH)2, evidenced by a reduction in the latter (observed through thermogravimetry) over a period of 112 days, could be linked to the strength gain of APC over that period. This strength gain could also be associated with the formation of ‘broad humps’, at the relevant 2h values (around 29° and 32°) in XRD curves, which became more pronounced with time. Strength could also be correlated to the percentage of hydrate bound water, with the differing amounts of lime consumption by fly ash partly responsible for scatter. Keywords Fly ash Lime Blended Portland cement Dry Na2SO4 activator Microstructural analysis Strength– microstructure correlation
1 Introduction Alkali Pozzolan Cement is an alternative low-carbon cement developed by the authors [1]. It comprises nonhazardous chemicals that can be cured under normal & Chandana Kulasuriya [email protected] W. P. S. Dias [email protected] Vanissorn Vimonsatit [email protected] P. De Silva [email protected] 1
Department of Civil Engineering, Curtin University, Perth, Australia
2
Department of Civil Engineering, University of Moratuwa, Moratuwa, Sri Lanka
3
School of Science, Australian Catholic University, North Sydney, Australia
conditions and stored as a dry powder. The name ‘Alkali Pozzolan Cement’ (APC) is used, since its main components are alkali and pozzolanic materials. Our investigations reported here have been carried out on the hardened cement paste, which is both appropriate and common when the focus is on the cementitious component. For example, OPC paste [2], HVFA cement paste [3], pozzolanic cement paste [4, 5], geopolymer paste [6, 7], and hybrid cement paste [8] have been used by researchers to investigate the properties of pure cementitious mixtures. Furthermore, microstructural testing such as X-ray diffraction (XRD) and thermal analysis (TA) require t
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