The Effect of Accelerators and Mix Constituents on the High Early Strength Concrete Properties

The present research study focused on the high early strength concrete properties that can be produced with large replacement of cement by fly ash. Also, the effects of adding fibres on the compressive strength gain and early age strength gain properties are determined. Tests were conducted on different high strength concrete specimens, where fly ash was substituted for cement up to 50%. Different types of concrete specimens were casted and tested for different fine-to-coarse aggregate ratio, metallic fibre content, cement-to-total-aggregate ratio, and accelerator dosage. The test results indicated that high early strength concrete (50.7？MPa at 7 days) was obtained for higher F/C ratio of 0.8, C/TA ratio of 0.24, and higher dosage level of steel fibre at 1.5%. 1. Introduction High-early-strength-based cementitious materials are of vital importance for the present expanding civil infrastructure. However, the deterioration of civil infrastructure all over the world has led to the realization that cementitious materials must be improved in terms of their engineering property and durability. The use of admixtures such as fly ash has little effect on pozzolanic properties to improve the engineering properties of fly-ash-substituted concrete. In a structural concrete durability should be high, as presented by water-to-binder ratio (W/B). A concrete structure is said to be durable if it withstands the conditions for which it has been designed, without deterioration for the entire period of life [1–5]. However, use of chlorides may cause corrosion in steel reinforcing and is prohibited in some countries, so that calcium nitrates can be potentially used to achieve high early strength concrete. These techniques are especially useful in the prefabrication industry, wherein high early age strength enables the removal of the formwork within 24 hours, thereby reducing the cycle time, resulting in cost-saving benefits [6]. Pozzolana increases the later age strength of concrete as it reacts with calcium hydroxide and turns it into calcium-silicate-hydrates (C-S-H). However, Portland pozzolana cements have higher activation energy and, therefore, their rate of hydration is lower as compared to ordinary Portland cements [7]. In a similar context, the addition of steel fibers improves the concrete matrix in all mechanical properties of concrete such as compressive strength, spilt tensile strength, flexural strength, and toughness. Steel-fiber-reinforced concrete is made for cement-based composite material reinforced with randomly distributed steel fibers diameter. It