Novel agricultural waste based hardening accelerator for early strength development of fly ash-based concrete

Abstract

Rapid urbanization is leading to a rise in demand for precast elements to reduce the time and cost of construction. However, precast elements consume the time to remove formwork during production depends on the early strength development of fresh concrete. On the other hand, thermal power plants produce a significant amount of fly ash, which also cause environmental issues. One solution to this problem is to use fly ash in cement and concrete to enhance their pozzolanic properties and address environmental concerns. However, using fly ash can delay the early strength development of concrete resulting deacceleration in the production cycle of precast elements. To speed up the process, some may opt for chemical-based hardening accelerator and high temperature curing. However, this may negatively impact the hydration kinetics of the concrete, pose environmental risks, and compromise the reinforced concrete’s durability.To overcome such limitations, impurity free C-S-H seed based hardening accelerator was synthesized from agricultural waste product namely, bagasse ash using novel chemical synthesis process which could effectively accelerates the early strength development of concrete without altering the conventional hydration process. The proposed synthesis process provides a platform for the reaction between the target calcium and silicate ions simultaneously eliminating the harmful elements (like chloride etc.) responsible for degradation of health of reinforced concrete structure.In order to study the effectiveness of a synthesized C-S-H seed, a blended ordinary Portland cement (OPC) was prepared by replacing 10%, 15%, and 20% of the cement weight with fly ash. Various amounts of the C-S-H seed were then added to the blend. Presence of developed C-S-H seed effectively reduced the setting time and eliminated the induction period during hydration of fly ash blended cement. Presence of additional seeds effectively reduces the critical free energy of nucleation which in turn accelerates the precipitation of hydration product responsible for the early strength development of fly ash-based concrete. Based on the setting time and heat of hydration analysis, it has been observed that the presence of C-S-H seed has the potential to accelerate the early strength gain process of fly ash-based concrete.