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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Abstract. At the beginning of XXI century in civil engineering and buildings of transport infrastructure, such as tunnels, elements of bridges, viaducts and roads, it is more expedient to use conventionally vibrated concretes which have almost universally replaced prefabricated constructions. However, in objects with high congested reinforcement or in cases where vibration is impossible it is more preferable to apply self-compacting concrete (SSC) mixtures. SCC possesses the ability to take form shape without any mechanical aid. The most important requirement for SCC is high flowability without the segregation of aggregate during placement. Despite the low water-cement ratio of the fresh self-compacting concrete mixture the bleeding is still possible. That is why fillers such as natural pozzolana, calcined clay (metakaolin), silica fume, fly-ash, slag, and quarry dusts should be used. Furthermore, mineral admixtures can improve energy efficiency and particle packing, decrease cost and permeability of self-compacting concrete. In this study, the properties of SCC with limestone powder as partial replacement of Portland cement was established by applying mathematical experiment planning method. The obtained SCC gave high early compressive strength within 3 days in the range of 41.3 MPa while its 28 day strength ranged of 69.0 MPa. The result of this study indicated the possibility of adding limestone powder in SCC with optimum percentage content around 38 %. The researched SCC had density of hardened and fresh concrete mix in the ranges of 2438 kg/m3 and 2452 kg/m3 respectively. The investigated SCC concrete with limestone powder showed high rate of water permeability in the range of 1.6 MPa (W16) and high frost resistance in the ranges of F2400. It can be explained by additive's high water retention capacity and increase of hydration degree and, as a consequence, decrease of capillary porosity. That is why the developed SCC with limestone powder has high compressive strength and excellent durability performance.Аннотация. На объектах гражданского строительства и транспортной инфраструктуры в конструкциях, имеющих высокий коэффициент армирования, и в случаях, когда вибрирование бетонных смесей осуществить не представляется возможным, необходимо применение эффективных самоуплотняющихся бетонных смесей, которые получили широкое распространение в последние десятилетия в мировой практике. В работе представлены результате экспериментальных исследований при разработке состава самоуплотняющегося бетона для объектов транспортной инфраструктуры с использованием наполнителей на основе отходов дробления карбонатных пород. Для оптимизации состава применялся трехфакторный метод математического планирования эксперимента, композиционный план на кубе типа В3, обеспечивающий максимальную прочность при достижении требуемых технологических показателей.Установлено, что введение эффективного разжижжителя в виде гиперпластификатора, значительно снижает водосодержание бетонной смеси, что предотвращает расслаиваемость самоуплотняющегося ...

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