Optimization of Composition and Technological Factors for the Lightweight Fiber-Reinforced Concrete Production on a Combined Aggregate with an Increased Coefficient of Structural Quality

In recent years, developing lightweight concrete with both the necessary and sufficient strength characteristics is essential in the construction industry. This article studies the influence of the volumetric composition of lightweight fiber-reinforced concrete (LFRC) and the method of its distribution during the preparation of the fiber–concrete mixture on the strength and deformation characteristics of LFRC on a combined aggregate. The optimal grain size of the porous filler was calculated by the mathematical planning method of the experiment. Regression models of the strength and deformation characteristics on the volumetric content of fiber and its distribution method were obtained. The most effective combination of these factors has been determined. The model shows that the increase in compressive strength was 12%, the value of the prismatic strength increased by 25%, the bending tensile strength increased by 34%, and the axial tensile strength increased by 11%. The ultimate strains during axial compression decreased by 10%, axial tension decreased by 12%, and the elasticity modulus increased by 11% compared to the test results of the control composition samples without fiber and pumice. The coefficient of constructive quality (CCQ) of the LFRC on a combined aggregate compared to concrete with the control composition without fiber and pumice showed an increase of more than 32%. It was also found that fiber reinforcement with basalt fibers with a combination of heavy and porous aggregates achieves a synergistic effect together.

Research of Mechanochemical Processes of Activation of Building Materials by Air-Impact Method

To increase the specific surface area of the binder and accelerate the strength gain of fast-hardening concrete mixtures, a model has been created for calculating aeroactivators as part of mobile complexes based on new equipment for cement activation, sand enrichment, local materials, and production waste. The proposed model establishes the dependence of the rate of destruction of the dusty shell of particles on the mechanical impact of the beaters and materials` physical and mechanical characteristics. To improve the operational characteristics of the cement aeroactivator, experimental studies were carried out, the results of which made it possible to determine the rational parameters of the developed installation. Based on the test results, it was found that the use of the cement activation process with additives accelerates the hardening process of concrete and mortar mixtures in the initial period, increases the design strength of concretes and mortars by 20–40% in comparison with the strength of the control composition at the same cement consumption, and also reduces the consumption cement up to 17% to obtain concretes and mortars equal to the control composition at the design age.

Creep study of carcass composites reinforced with steel fiber of the Dramix type

The results of a creep study of disperse-reinforced building composites made by carcass technology are presented. In the experiment, steel fiber «Dramix» type fiber was used as dispersed reinforcement, the content of which was 1…3 % by volume of the composite. The impregnation matrix was made on the basis of portlandcement and a superplasticizing additive of the brand Melflux 1641 F. In the creep test, the samples-beams were loaded according to a 4-point scheme. The level of load applied to the samples was 30, 50 and 70 % of the maximum values. An unreinforced carcass composite was taken as a control composition. The tests continued until the moment when the value of the deflection became constant. Based on the data obtained, graphical dependencies «relative deflection – exposure time» were constructed. On the obtained creep curves of carcass composites in the general case, four sections of the kinetics of deflection change can be distinguished: the initial section, in which an intense, almost linear, increase in deflections occurs; the curved section where the attenuation of the process of growth of deflections is observed; a linear section in which the increase in deflections is insignificant and has a quasi-permanent character; the final section, when the stabilization of the deflections occurs, and their values become constant. The minimum deflection values were obtained for an unreinforced carcass composite, and the maximum for composite reinforced with 1 % «Dramix» fiber. When the composition of the carcass composites contains 2–3 % fiber, a significant decrease in the deflections was observed, but their values were higher than that of the control composition. This is explained by the different load applied to the reinforced and unreinforced samples of carcass composites, as well as the positive effect of increasing the content fiber to 2–3 % on their bending strength and stiffness. The studied dispersion-reinforced carcass composites can be used for the manufacture of monolithic industrial floors, foundations and pavements, working under the influence of increased mechanical influences.

COMPOSITION LINEAR CONTROL IN STIRRED TANK CHEMICAL REACTORS

This work studies loop control composition in continuous chemical reactors with simple structures, due to its large acceptance in chemical industry. A linear cascade composition control (master/slave) is proposed, designed with basic control structures based on Laplace tools. Two configurations are designed, which were evaluated in a dynamic model of continuous stirred tank. From a stability analysis it is noted that, for such configurations, system assent time is 7 to 8 times reduced if compared to the assent time without loop control. Besides, the system shows a good performance when coming to the asked reference. Implementation of such control configurations can solve the problem of loop control composition.