Expanded clay concrete (ECC) is a promising structural material for buildings due to its light weight and heat- and sound-insulating properties. Adding basalt fibers (BFs) in ECC reduces its brittleness and enhances its mechanical properties. The heat treatment (HT) of BF-reinforced ECC can significantly accelerate the strength growth during cast-in-situ construction, which allows the reduction of the turnover of the formwork and the construction period, as well as leading to lower construction costs. This paper presents an HT technology for load-bearing structures, containing a BF-reinforced ECC mix and using infrared rays for cast-in-situ construction. The issue of the strength growth of BF-reinforced ECC during HT has been studied. Microsilica and fly ash were added to the ECC mix to obtain a compressive strength of more than 20 MPa. Four different mixes of ECC with chopped BFs in the ratios of 1:0, 1:0.0045, 1:0.009 and 1:0.012 by weight of cement were studied. Test specimens were heated by infrared rays for 7, 9, 11, 13, 16 and 24 h. Then, the heat-treated specimens were tested for compressive strength after 0.5, 4, 12 and 24 h cooling periods. The analysis and evaluation of the experimental data were carried out based on probability theory and mathematical statistics. Mathematical models are proposed for forecasting the strength growth of BF-reinforced ECC during cast-in-situ construction.

Basalt fibres (BF) are increasingly studied in structural applications due to its environmental friendliness and good mechanical properties. Mass production of high-strength concrete (HSC) in Russia is mainly associated with the use of organomineral modifiers of the MB series, containing in their composition microsilica, fly ash, hardening regulator and superplasticizer C-3 in different ratios. In our study we produced HSC specimens (without BF, and with 1 wt.% chopped BF) using the modifier MB10-30, with the dimensions of 100x100x100 mm, 100x100x400 mm, 100x100x400 mm with the artificial crack of 25 mm deep in the middle of the span, and also 100х75х400 mm (75 mm height was taken equal to the height of the section above the crack of the 2nd type of prisms). The compressive strength, the tensile strength at bending, the strength at axial tension, the cracking moment, and also the parameters of fracture mechanics, such as: the critical stress intensity factor and the critical energy release rate, at the curing periods of 7, 14, 28, 60 days, have been determined. We also evaluated the influence of crack in the bend element on the value of the cracking moment. The results showed that the inclusion of BF in MB modifier based HSC resulted in a decrease in the compressive strength, however, significantly enhanced its flexure behavior.

Self-compacting concrete (SCC) is an innovative concrete that does not require vibration for placing and compaction. Thermal treatment (TT) of SCC can significantly accelerate the strength growth during cast-in-situ construction. This paper presents a technology of TT of structures for cast-in-situ construction with SCC. Application of this technology allows to reduce the turnover of formwork, the labor costs for construction, and the construction period. We also studied the issue of strength development of SCC during TT. For our study, we used SCC of grade C25. Test samples were cured with TT by infrared radiators for 7, 9, 11, 13, 16 and 24 hours. Then warmed samples were tested for compressive strength after 0.5, 4, 12 and 24 hours of cooling period. Study was carried out on the basis of analyzing, generalizing and evaluations of experimental data. A mathematical model is proposed for determining the compressive strength of SCC after one day of curing of SCC with TT.

The shuttering forms, equipped by inventory frames with transparent cover, are the simple solar energy equipment for heat treatment of reinforced concrete elements during their manufacturing at the plants. They are similar with solar collectors by their design and thermal-physical processes, taking place in them, with difference that the heat sink is hardening concrete. The research results of influence of transparent cover construction on efficiency of concrete heat treatment in shuttering forms with employment of solar energy in different climatic conditions are given in the article. The volume of energy, consumed and lost by concrete during its direct heating by solar energy in the simple solar energy equipment like solar collector, depends on the transparent cover construction. Under other same conditions, the increase of cover layers affects its transparency, which is characterized by the solar energy transmittance, but in this case, it reduces heat losses in environment, which are characterized by the coefficient of heat losses through transparent cover. One-layer and two-layer transparent covers are chosen for assessment of efficiency of heat treatment of concrete elements, because the increase of cover layers more than two reduces intensity of the heat sink warming in the daytime and it is accepted by scientists in solar energy field as pointless. Optimal number of transparent material layers in cover construction is determined based on energy assessment in result of thermal- physical calculation and experimental research. The economic losses for production of transparent cover due to the increase of its layers are taken into account in addition with energy assessment

The speed of concrete curing and design concrete strength depend on the environmental conditions of construction site. Dry and hot climate conditions intensify the process of water evaporation from concrete and cause the concrete shrinkage and the loss of the potential concrete strength. The research work is devoted to study the layer changes of the concrete strength; determination of the minimum period of care for concrete; assessment of negative impact of dry and hot climate conditions on modified concretes, prepared on the composite binders with various chemical additives. The results and methodology, as well as the information about concrete composition and the boundary conditions of the experiments are given in the research work. The obtained research results show that chemical additives and composite binders with low water consumption contribute to get the design strength in spite of the environmental conditions. They also allow concluding that the minimum period of care for concrete should be determined by not the time of its curing, but the critical strength, which it gets to the moment of ending of caring. This concrete strength is able to resist various destructive processes.