Effect of concentrated potassium alum water on the properties of concrete

Abstract

Potassium alum is an aluminum and sulphate compound. When added to the concrete mixing water, it accelerates the cement hydration. This paper is aimed at investigating the influence of concentrated potassium alum water on the properties of concrete. To achieve the research objectives, potassium alums were milled to powder form and were dissolved in water at different proportions of 2.5%, 5%, 7.5%, 10%, 12.5%, 15%, 17.5%, and 20% relative to the water/cement ratio of 0.6. Then the dissolved water solution was used as mixing water. A total of ninety-eight concrete cubes of 150 x 150 x 150 mm in accordance with BS EN 12390-2 were produced with potassium alum solution at different proportions of 2.5%, 5%, 7.5%, 10%, 12.5%, 15%, 17.5%, and 20%. Also, twelve (12) concrete cubes produced with clean mixing water were used as a benchmark for samples produced with concentrated alum water. Mix ratio of 1:2:4 was adopted. The concrete cube specimens were cured according to BS EN 12390-2 and were preserved from dehydration. All the samples (108) were tested for failure at 7, 14, 21, and 28 days. Results confirmed that 1 to 2.5% addition of potassium alum into the mixing water improved the compressive strength (CS) by 3%. Potassium-concentrated alum water reduces initial CS. An increase in potassium alum content results in a decrease in workability and CS and the reduction in workability is attributed to the high mixing water demand for potassium alum. Potassium alum absorbs water more than Portland limestone cement.