Experimental study on the development of compressive strength of early concrete age using calcium-based hardening accelerator and high early strength cement

• This paper focused on developing compressive strength without steam curing of precast concrete.
• Calcium-based hardening accelerator for C3S was used for early-stage strength.
• Compressive strength of concrete was more than 10 MPa after 9 h of curing at 20 °C experimentally.
• Hardening accelerator 1–3% of cement mass is proper for setting time and compressive strength.

Steam curing is necessary to be used in the manufacturing of precast concrete, thus, a large amount of energy is consumed and the turnover of forms is low. This practice leads to reduction in productivity. This paper focuses paper focuses on developing early stage strength for precast concrete of more than 10 MPa after 6 h of curing at room temperature without steam curing. Various micro-analysis tools such as TG/DTA, Conduction Calorie Meter, XRD, SEM and MIP were conducted on concrete and cement paste with the amount used of calcium-based hardening accelerator (CHA) for tricalcium silicate (C3S). Results show that the reaction effect of the CHA was terminated before reaching 12 h, the initial setting of concrete was in 80 min with 3% of CHA. The rate of heat evolution is increased in the mechanism of developing the compressive strength in early age and the yield of Ettringite, Ca(OH)2 and C–S–H is increased at early age due to the fact that the CHA stimulates tricalcium aluminate (C3A) and C3S in high early strength cement when using calcium-based hardening accelerator into high early strength cement. Additionally, the pore volume of range of 20–100 nm decreased with the CHA content.