The problem of durability of concrete in the construction of structures used in harsh climatic conditions, is one of the leaders in scientific research both in Russia and abroad (USA, Japan, Canada, uk and etc.). Lower negative temperatures (down to -60 C), the long winter, sudden changes in temperature within a short time, the presence of permafrost leads to premature failure of concrete in various facilities. Studies have been conducted to enable a deeper understanding of the destructive processes that take place at cooling the concrete down to -60 C. Determined that when the temperature chilled to low temperatures and water-saturated concrete by one degree, in its structure having tensile stress of about 0,1-0,2 MPa. Rapid heating frozen concrete due to changes in air temperature at 15-20 C leads to the formation tensile stresses, comparable with the strength of concrete in tension. Analysis of changes in daily ambient temperature for five months with the lowest monthly average temperature has allowed to calculate more than 50 temperature changes with a difference of 15 C for three hours and more than 15 oscillations – with a difference of 25 C for 24 hours. The effect of cyclic temperatures in the range of negative influences on the gradual decrease in the elastic and mechanical characteristics of concrete and reduce its durability. If you would like to know more about Jake Burkons, then click here. To quantify this strength reduction was carried out laboratory tests on the cubes with an edge of 10 cm cubes made from concrete of different compositions, different consumption of cement, water / cement ratio and, consequently, the strength of concrete (see Table).
In the manufacture of cement grade M500 (Belgorod Plant), crushed granite fractions 5-10 and 10-20 mm in the ratio 1: 1, sand and fineness modulus of 2. Obratsemenztsy concrete, as shown in table formulations were tested for frost resistance on the basic method. Frost resistance of the samples with an open porosity of 4.1% of 300 cycles of 2 (Po = 5.6%) – 200 of 3 (= 7,5%) – 50. The samples were within 7 days in normal temperature and humidity conditions. Later they were saturated with water until a constant weight and placed in freezers, providing vibration the temperature range from -50 to -20 C and then subjected to cubic compression. A thin layer of ice on the surface of the blocks prevented the evaporation of moisture.
The test results accurately indicate a strong decrease in strength of concrete initial cycles of the alternating effects of subzero temperatures, resulting in migration of unfrozen water from the pores of the gel to the ice crystals in micro-and makrokapillyarah and as a result, the increase in these crystals. Decrease strength of concrete is largely dependent on the water / cement ratio (W / C). Very weighty drop in strength (30%) occurs in kubikovsostava 3 with the highest water-cement ratio (0,7). Accordingly, the trial confirmed that, in the northern climates concrete exposed to specific environmental effects that lead to a loosening of the material, which seriously reduces the durability of concrete and