Influence of chemical additive and reduced initial temperature of structure formation and hardening on parameters of structural strength of cement composites

Introduction. Comparative experimental studies have been conducted to study the regularities of the combined effect of low temperatures and concentration of accelerating antifreeze additives on the processes of early and late structure formation and hardening of cement composites. At the same time, the power and energy characteristics of crack resistance are evaluated from the standpoint of structural fracture mechanics for structural materials. Materials and methods. The following components are used to fabricate experimental samples: Portland cement with the activity of 41.8 MPa, limestone crushed stone of the fraction of 5 to 10 mm, Sura river sand with the fineness modulus of 1.57, an accelerating antifreeze additive based on a mixture of three Akrikhin plant salt wastes. Water-cement ratio in all compositions is 0.53. Concentration of the additive in the compared sample series Nos. 1 to 5 is respectively 0, 0.75 %, 1.5 %, 3.0% and 6.0 % by weight of cement. Type I prism samples with an artificial crack obtained in the process of sample molding are tested for three-point bending with non-equilibrium mechanical tests according to GOST 29167-91 which involves the use of an acoustic emission method to study the real-time fracture process of compared series samples. Results. Quality parameters of the structural strength are obtained for the compared series cement composites at the ages of 40 days and 575 days. The parameters reflect the processes of the early and late stage of structure formation and hardening after the initial 28-day environmental exposure with the temperature of +2 °C. Conclusions. Results of the research indicate that not only increase of magnitude of the long-term axial compression and tension-in-bending strength, but also increase of the mechanical-acoustic crack resistance criteria occurs for the modified and unmodified structures of cement composites in the considered time interval. This is a clear consequence of the positive effect of concentration of the accelerating antifreeze additives on the mechanical behavior of the samples from the standpoint of structural mechanics of materials destruction, which plays an important role in the design of the structural strength of dispersed cement heterogeneous systems.