The usage of industrial and agricultural wastes for building materials production plays an important role to improve the environment and economy by preserving nature materials and land resources, reducing land, water and air pollution as well as organizing and storing waste costs. This study mainly focuses on mathematical modeling dependence of the compressive strength of high performance concrete (HPC) at the ages of 3, 7 and 28 days on the amount of rice husk ash (RHA) and fly ash (FA), which are added to the concrete mixtures by using the Central composite rotatable design. The result of this study provides the second-order regression equation of objective function, the images of the surface expression and the corresponding contours of the objective function of the regression equation, as the optimal points of HPC compressive strength. These objective functions, which are the compressive strength values of HPC at the ages of 3, 7 and 28 days, depend on two input variables as: x1 (amount of RHA) and x2 (amount of FA). The Maple 13 program, solving the second-order regression equation, determines the optimum composition of the concrete mixture for obtaining high performance concrete and calculates the maximum value of the HPC compressive strength at the ages of 28 days. The results containMaxR28HPC = 76.716 MPa when RHA = 0.1251 and FA = 0.3119 by mass of Portland cement.

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Introduction: there is practically no information on the utilization of ash and slag waste (ASW) application in technology of special (noncontracting, expanding, self-stressing) cements, which predetermines the relevance of research in this direction. The study investigates the properties of experimental samples from cement, ash-and-slag and sand mixtures based on sulphoaluminate Portland cement (SAC) with an additive of the ASW. Materials and methods: a fine-particle binder material consisting of the SAC produced by the Podolsk Cement factory with a fine-grained ASW additive was used to obtain a binder mixture. Silica sand functioned as fine aggregate. All the raw materials used were local to the Russian Federation. The setting time, soundness, and strength of the binder mixture were determined according to GOST 30744-2001 standard. The specific surface area of the Portland cement was established through the use of the air permeability method utilizing of PMTs-500 instrument. The microstructure of the hardened binder mixture was studied employing electron microscopic analysis and X-ray phase analysis. Results: the work investigates the effect of 10 %, 15 %, 20 %, and 50 % ASW additive on the water demand, strength, and setting time of the SAC. The article also explores the kinetics of hardening and structure formation of samples from the binder mixture based on the SAC and ASW for hardening under normal conditions. Conclusions: results of the investigation allow recommending the ASW characterized by high dispersion as an additive for production of special cements without significant reduction of their properties. In the presence of the ASW, setting times of the cement mixtures virtually do not change as compared with the pure SAC. With limiting the amount of the ASW in the composition of the Portland cement, the strength characteristics do not practically change through the entire period of hardening.

Cement-concrete pavement not only has a long service life even at high loads but also has competitive production costs and fewer significant maintenance costs. The concrete road surfaces, thus, are rather economical. In this article, the Vietnamese Standard TCVN 9382 - 2012 was used to determine the heavyweight concrete composition for rural road construction. Assessment of the crack appearance in the concrete block body was made by the temperature field analysis, the thermal stress and cracking index. The conducted studies' result provided with the possibility of obtaining heavyweight concrete from Vietnam local raw materials regarding to the concrete mixture workability of 11-13 cm standard cone, 31-36 MPa compressive strength of heavyweight concrete at the age of 28 - day - normal hardening and 0.30 - 0.42 MPa average water resistance of samples. Using natural pozzolan to replace 20% of mass cement in the concrete mixture leads to a decrease in the concrete strength characteristics at different ages. The concrete compressive strength of composition No2 decreased mostly by 23% at the age of 3 days and least by 14% at the age of 28 days in comparison these values of composition No1. However, all of these concrete compressive strengths at the age 28 days are higher than 30 MPa. Replacing 20% of the mass Portland cement by natural pozzolan in a concrete mix will decrease price for 1 m3 concrete of 219.96 rubles. By applying the computer program MIDAS CIVIL, the maximum temperature in the concrete block center which was determined after 12 hours from the commencement of mixing of raw materials with water, equals to Tmax = 34.61 0С. At the same time, the structure temperature difference between the center (node793) and surface (nodes 120 and 898) of the concrete pavement can be neglected because of its insignificance. Besides, the cracking indexes at three hazardous locations of investigated structure are higher than 1, the cement-concrete pavement will be considered as non-appearance of cracks. However, the cracking index at center (node 793) is always less than this on the surface (nodes 120 and 898), equally to higher thermal crack occurrence at center. Therefore, it is necessary to monitor the development and expansion of thermal cracks to ensure the concrete mixture proper care during the hardening process.