Abstract
This research aimed to present the improvement of the cementitious material in high-volume fly ash using only one alkali activator. Fly ash was used as a partial replacement for Portland cement type I, varying from 0 to 60% by weight of the binder. Concentrations of NaOH varying from 0.00 to 1.25 molar were used as alkali activator. Paste properties and mortar compressive strength at the ages of 3, 7, 14, 28, 60, and 90 days of water curing were investigated. The results reveal that fly ash paste with an alkali activator provides shorter initial setting time when compared to control paste without alkali activator. The use of 0.50 molar NaOH concentration in mortar containing fly ash not exceeding 50% by weight of binder provides the highest compressive strength at any age of curing. At that concentration, there is a significant increase in the 28-day compressive strength of up to 45% over that of the control mortar. In addition, higher NaOH concentration (not exceeding 1.00 molar) has a significant positive effect on the compressive strength of mortar with higher fly ash content, especially over longer curing periods.
Highlights
The use of industrial waste or by-products materials in concrete has become increasingly common in construction
This study will investigate the use of a single type of alkali at different concentrations to activate the pozzolanic reaction in high-volume fly ash mortar, to improve compressive strength
The results showed that higher sodium hydroxide concentration and higher fly ash replacement level influenced increased flow in the cement paste
Summary
The use of industrial waste or by-products materials in concrete has become increasingly common in construction. More recent studies have investigated the use of cementitious materials using high volumes of pozzolanic materials activated by alkali (Li et al, 2019; Luukkonen et al, 2019; Manzi et al, 2020; Sun et al, 2020). The focus of such studies has been on using pozzolan-based binder materials to totally replace Portland cement in concrete work, or as much as possible. This study will investigate the use of a single type of alkali at different concentrations to activate the pozzolanic reaction in high-volume fly ash mortar, to improve compressive strength. The results from this study may serve as a guide for the development of the mechanical properties of concrete made with other pozzolanic materials without having to improve their particle finesses
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