STRUCTURE FORMATION IN FOUNDATION SLAB CONCRETE

Abstract

Purpose. The work involves identifying the dependence of structural and mechanical properties of the concrete on the composition of used modifier additives, the nature of changes of structural and mechanical properties depending on the period of concrete hardening of test and modified samples. Methodology. The applied microstructural, fractographic, microprobe analyses and physico-mechanical tests revealed the required dependencies. Findings. The microstructure of the cement stone under equal conditions of concrete mix selection depends on the composition of used raw materials and production technology. This paper investigates the structural changes in the setting time of hard mixture concrete and effect of component parts of the complex modifier additive PLKP (produced by «Logia», Dnepropetrovsk) on morphology, dispersion and chemical composition of the cement stone, as well as the mechanical characteristics of concrete for the foundation slab. The study of the structural and physical-mechanical characteristics of the test samples and modified concrete at various hardening stages showed that the use Ukrainian hyper-plasticizer PLKP contributes to the formation of nano-structured concrete. The addition of hardening accelerators to the super-plasticizer additive reduces the diameter of crystal whiskers, increases the structural homogeneity and stability and improves the complex of the concrete mechanical characteristics. Application of new PLKP polycarboxylate additives in the production of concrete mixtures for the foundation slab allows eliminating the steaming from the foundation slab production technology. The absence of salt component in the additive improves the concrete durability. Originality. The paper showed that modification of the concrete with complex additive PLKP facilitates the formation of the most homogeneous structure of cement stone, which consists of compact crystals surrounded by fibrous crystals that are tightly intertwined in the pore space. This structure contributes to the maximum characteristics of the concrete compressive strength. Herewith the steaming by traditional technology helps to increase the size of the primary ettringite crystals having a tendency to restructure during the operation of concrete products at temperatures of around 200°C. Practical value. Adjustment of foundation slab production parameters, namely – steaming temperature reduction or elimination of this operation from the concrete sleeper production cycle, using PLKP additives, can improve the structural homogeneity and stability, increase the density of the concrete and result in positive effect on its durability.