This article briefly describes the setting time of concrete, why it is important, and how different weather condition could affect it. We will later review some of existing methods that are used to estimate the setting time of concrete on-site.
Setting Time of Concrete
As ASTM C125-15b, setting is defined as “the process, due to chemical reactions, occurring after the addition of mixing water, that results in a gradual development of rigidity of a cementitious mixture.” As ACI CT-13, initial setting time is defined as “the time required for a freshly mixed cement paste, mortar, or concrete to achieve initial setting.” Final setting time is defined as “the time required for a freshly mixed cement paste, mortar, or concrete to achieve final set.”
Why is Setting Time of Concrete Important?
The knowledge about the setting time is helpful to estimate the time required for initial curing of concrete, surface preparation, leveling and polishing. This can effectively control the surface cracking at early ages. Hot weather and cold weather can significantly affect the setting time of concrete. Mis-estimating setting time at wintertime can cause delay in effective surface preparation, leveling and polishing. Hot weather can reduce the setting time of concrete; while cold weather can increase the setting time of concrete.
On-site Estimation of Setting Time
Beside the standard laboratory test for measuring the setting time of concrete by penetration method (ASTM C 403), the following methods have successfully been utilized in measuring the setting time of concrete:
1- Maturity Method
The maturity method is mostly used to evaluate the strength development of concrete at early ages, specially in wintertime when the development of strength is critical. However, the method has been used by some researchers to predict the setting time of concrete (Min-Cheol Han, Cheon-Goo Han 2010). In this research the very concept of equivalent age was used for estimating the setting time of concrete.
2- Ultrasonic Pulse Velocity (UPV) Method
UPV method has been used by researchers to study the setting time of concrete. Piyasena et al. (2013) studied the effectiveness of UPV method for estimating the setting time. In their studies, they discovered that the UPV becomes relatively constant near to the setting time.
Peter Taylor and Xuhao Wang (2014) examined the use of UPV method (using shear wave) for evaluating the setting time. Shear waves are reported to be more sensitive to the phase transition between fresh and hardened concretes. The speed of propagation of shear wave within liquid phase is significantly lower when compared to solid phase. Therefore, shear wave may better track the transition from fresh concrete to hardened concrete. This transition results in gradual evolution of shear wave velocity within concrete, helping to precisely find out the setting time of concrete.
3- Electrical Resistivity of Concrete
Zongjin Li et al. (2007) demonstrated the effectiveness of electrical resistivity measurements for predicting the setting time of concrete. Electrical resistivity can be used to track the development of concrete microstructure, setting time, and early age strength.
