Introduction: the article discusses the effect of the complex of active mineral additives consisting of silica and fly ash, and a fine aggregate, including finely ground natural-white quartz sand for partial replacement of river sand, on the mechanical properties of high-strength concrete containing steel fiber. Materials and methods: high-strength concrete containing Dramix^®3D 65/35 steel fiber in the amount of 100 kg per 1 m³ of concrete mixture was suggested where 22% to 100% of river sand was replaced by finely ground white natural sand of the particle size of 5 to 1800 μm and containing the complex of active mineral additives for partial replacement of cement as part of a multicomponent binder, consisting of low-calcium fly ash of thermal power plants and silica and containing, respectively, 20, 30, 40% fly ash and from 5 to 15% silica by weight of the binder. Results: research results have shown that 100% replacement of river sand with finely ground natural white sand, in concrete containing 20% of the mass as part of a multicomponent binder, fly ash and from 5 to 15% by weight of silica, contributes to the increase of its strength properties: the values of concrete compressive strength after 28 days were in the range from 118.5 to 128 MPa, tensile strength during bending and splitting, respectively, from 18.8 to 25.4 MPa and from 10.2 to 11.9 MPa, which is higher than the strength of concrete samples containing river sand. Conclusions: the achieved results have demonstrated the efficiency of using finely ground natural white sand as an alternative to river sand for producing high-strength concrete, thus helping to save the river sand resources in Vietnam. The use of fly ash and micro silicon, which are power and metallurgy wastes, as part of a multicomponent binder in order to partially replace cement reduces the carbon footprint in the production of binders and will also have a beneficial effect on environmental protection against industrial waste pollution.

Concrete composition modifying by different electrically conductive components is one of less laborious but relatively effective methods between wide variety of electrode concrete heating effectiveness improvement methods. The purpose of this study is investigation of special aspects of cement systems modified by powdered shungite (Ssp 400 m2/kg) in combination with active mineral and plasticizing admixtures that harden under electrode heating at below zero temperatures. By the method of differential thermal analysis anomaly of exothermic reaction of cement stone specimens was discovered, that is due to formation of hydrated calcium silicate С2SH (A) discovered by the method of quantitative XRDA, and is verified by results received from scanning electron microscopy method, which among other factors provides higher strength and low permeability to these composites. Stability of cement systems modified by shungite and curing under electrode heating has been proved.

Similar to most of the other developing countries, Vietnam has national programs for industrial waste recycling including fuel, ash, and slag. In which, fly ash (FA) has been used commonly as a pozzolanic additive in the roller-compacted concrete (RCC) mixture for the dam construction of hydropower projects. This usage allows reducing the concrete cost, the hydration heat, and the thermal cracking during the construction process of the RCC. In this study, the optimal concrete mixture and the maximum temperature of the RCC dam were determined using the experiment planning method, Matlab, Maple 13, and Midas Civil. In addition, the mathematical model has been used to adequately describe the influence of the intensity concreting (IC) and the initial temperature of the concrete mixture (ITC) on the temperature regime of the RCC dam. The calculation of the temperature regime during the construction of the RCC dam of 45 m high and 1 m thick in Vietnamese climate conditions was performed with considering the IC and the ITC. As the results, the maximum temperature of the RCC dam was determined depending on the IC and the ITC. Calculation found that at IC = 0.6 m/day and ITC = 20°C, the maximum temperature in the central dam zone reached 36.38°C after 1800 hours from the beginning of construction. The results of the present study further support the safe and durable construction of the RCC dam in the future.

This study built theoretical and practical models to evaluate the corrosion resistance of concrete for coastal offshore structures in Vietnam. A mathematical model was developed in the form of a system of nonlinear partial differential equations characterizing the diffusion “free calcium hydroxide” in a solid of a concrete structure. The model describes the process of non-stationary mass conductivity observed in the “concrete structure—marine environment” system under non-uniform arbitrary initial conditions, as well as combined boundary conditions of the second and third kind, taking into account the nonlinear nature of the coefficients of mass conductivity k and mass transfer β. It was shown that the solution of the boundary value problem of non-stationary mass conductivity allows us to conclude about the duration of the service life of a concrete structure, which will be determined by the processes occurring at the interface: in concrete—mass conductivity, depending on the structural and mechanical characteristics of hydraulic structures, and in the liquid phase—mass transfer, determined by the conditions of interaction at the interface of the indicated phases.

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