| Abstract [eng] |
Calcium hydrosilicates α-C2SH and kilchoanite are synthesized under hydrothermal conditions. These compounds have a low CaO content, which means that significantly less carbonate rocks are required to prepare the binder mixture. Although α-C2SH and kilchoanite do not have hydraulic properties, they are carbonized, and the strength of the samples increases during the solidification of CO2 in the atmosphere. Since carbonization is determined by diffusion processes, the hardening process depends on many parameters: CO2 pressure, retention time, moisture content, peculiarities of concrete preparation, etc. It is important to examine and reconcile all of them. The aim of the work: to determine the influence of hydrothermal synthesis parameters on the processes of α-C2SH and kilchoanite formation and to produce concrete hardening in CO2 environment from them and sand mixtures. Raw materials and obtained products were studied by X-ray diffraction, chemical analysis, thermal analysis, Fourier transform - infrared spectroscopy, scanning electron microscopy methods. Initial mixtures of raw materials with a molar ratio of CaO/SiO2 of 1.5; 1.75; 2; 2.25, and the water/solid particle ratio w/s = 10, were hydrothermally treated at 200–220 °C saturated water vapor temperature, keeping isothermally 4; 8; 12; 16; 24; 48; 72 hrs. with stirring (100 rpm) and without stirring the suspensions. The optimal conditions for the formation of α-C2SH, a kilchoanite binder, were found to be in an immiscible suspension with an initial molar ratio C/S of 1.5 to the mixture after isothermal treatment for 8 h. At a temperature of 200 °C. It was also investigated that α-C2SH, which has a higher basicity, is obtained by synthesis by stirring the suspension (C/S = 2) at 200 ° C for 12 h. To determine the physical and mechanical properties of the binder, cylindrical (ø 36x36 mm) samples were prepared from the synthesis product and standard sand (1:3 in the molding mixture) with different amounts of water and cement ratrio w/c = 0.2; 0.25; 0.3; 0.35. Samples were autoclaved, 25; 35; 45; 55; At 65 °C, 15 bar of carbon dioxide in a CO2 atmosphere with an isothermal holding time of 4; 8; 16; 24; 48; 72 hrs. The optimal moisture content of the mixture was determined to be w/c = 0.3, as it is used to obtain concrete samples of the highest strength. It was investigated that by hardening products formed from α-C2SH, kilchoanite and sand mixtures at 25 ° C, the compressive strength of the samples consistently increases and reached 16.15 MPa during the first 24 hours of carbonation. The increase in temperature has a positive effect on the mechanical properties of the concrete: the highest value of compressive strength was obtained after hardening the samples at 45 °C for 24 hours – 20.23 MPa. Samples with the predominant binder α-C2SH showed slightly higher compressive strength values at 25 °C temperature after 24 h. curing: 16.85 MPa, 45 °C to 23.44 MPa, respectively. Thus, products made of α-C2SH and kilchoanite binder are equal in strength to conventional concrete and suitable for the production of innovative products. |
