The effectiveness of setting and hardening accelerators for sprayed concrete

For evaluating the effectiveness of the admixtures by their physical-mechanical properties a model composition, containing cement, filler and superplasticizer was used. For more detailed research of hydration kinetics of the cement stone with addition of accelerators a calorimetric study of cement pastes was carried out. This study found that alkali-free setting and hardening accelerators for sprayed concrete, based on aluminum compounds, when added in cement paste after 20 minutes after preparation, provide a sharp rise in heat generation and temperature, and significantly accelerate the setting and hardening of cement paste. Effectiveness of the admixtures can be arranged as follows: the most effective is the admixture Centrament Rapid 650, second place – Sigunite L-53, after that – MEYCO SA 167 and Relamiks Torkret. The effect of these admixtures in the presence of superplasticizer Muraplast FK63, that belongs to a group of polycarboxylates, slightly increased. The combined effect of accelerators and plasticizers can be connected with mutual influence on each other, this should be considered in design of the concrete mix.