Development of nanomodifiedrapid hardening fiber-reinforced concretes for special-purpose facilities

Abstract

Experimental studies confirmed that the development of rapid-hardening concretes with high resistance to a high-velocity impact for special-purpose facilities is achieved through the multilevel modification of the structure. The introduction of dispersed fibers ensures optimization of a structure at the macro- and mesolevel. At the micro- and nano-leves ‒ by energetically active ultra- and nanofine mineral additives and a high-reducing polycarboxylate superplasticizer. We established high efficiency of the influence of an organo-mineral nanomodifier containing polycarboxylate superplasticizer, micro- and nano-silica on the workability of the concrete mixture and the kinetics of concrete hardening based on it. We detected a directional formation of the structure and the preset properties of concretes of highly flowing mixtures at both early and late stages of hardening. We established that the early strength of nanomodified concretes increases by 4.8‒5.1 times, and strength after 28 days ‒ by 2.0‒2.3 times. The study showed that an increase in the number of contacts, reduction in size and the number of initial defects and increasing the homogeneity of nanomodified concrete leads to the creation of a dense, fine-porous, less defective structure. Ensuring such a structure of nanomodified fiber-reinforced concretes leads to an increase in deformation characteristics, specifically stiffness and elasticity, which make it possible to withstand greater stresses at a constant value of relative deformations. We carried out tests on resistance of nanomodified fiber-reinforced concretes under conditions of action of a high-velocity impact that indicate their increased impact viscosity. Thus, we can argue about the relevance of a mechanism for the formation of regulated properties of nanomodified fiber-reinforced concretes and about practical attractiveness of the proposed technological solutions.