Set-Accelerator refers to an additive, which can increase the mortar strength and has no significant effect on the later strength. According to the chemical composition, it is divided into two types: organic and inorganic.The organic includes Calcium Formate , Triethanolamine, Triisopropanolamine, Urea, etc. And the inorganic includes Sulfate, Chloride and so on. The effect of different Set-Accelerators is not the same.
Calcium formate is an additive that does not have any corrosive effect on reinforcing steel. It mainly accelerates the hydration of tricalcium silicate in cement and increases the early strength of cement mortar. The effect of calcium formate on the strength of cement mortar depends mainly on the content of tricalcium silicate in the cement. The early strength is better with less tricalcium silicate.It will not attenuate the late strength of the cement mortar, and it has a certain degree of frost resistance at low temperatures.
There are two main reasons for adding the Set-Accelerator to the polymer mortar: First, some construction sites require a certain construction schedule. The polymer mortar will have higher strength in the early stage and meet the external force requirements by adding the Set-Accelerator.Second, the strength of the mortar increases slowly when the temperature is low, moreover, the lower the strength when the ice is frozen, the greater the damage to the mortar.The frost damage of the mortar at an early stage of low strength can cause permanent damage to the mortar, so Set-Accelerators must be added at lower temperatures.However, even if the Set-Accelerator is added at a low temperature, the strength of the cement mortar can be reduced. The first reason is when construction is carried out in a low temperature environment, the hydration speed becomes slow and affects the efficiency of construction. When the temperature is lower than the freezing point, the water turns into ice, and the volume expands, some phenomenonprone to occur, like emptying, falling off, etc.After the water evaporates, the internal voids increase and the strength of the mortar decreases.
Secondly, the strength of mortar depends mainly on the reaction rate and reaction time of cement and water. Carrying construction at temperatures below 0°C, water freezes. Of course, the hydration reaction is an exothermic reaction with a certain hydration temperature and the cement reaction efficiency is reduced. Melting above 0°C, the hydration reaction continues, and the strength of the cement will inevitably decline from this cycle. Thirdly, the minimum film-forming temperature of general re-dispersible latex powders is above 0°C, while that of EVA product is generally around 0-5°C. Films cannot be polymerized or have poor film formation at lower temperatures, which affects the flexibility and adhesion of polymer mortar. In addition, cellulose ether dissolves slowly at lower temperatures, which affects the adhesiveness and workability of the mortar. Therefore, construction should be performed at a temperature above 5°C to ensure its quality.