INFLUENCE OF FILLER QUALITY ON CONCRETE THERMAL CONDUCTIVITY

Abstract

Studies on the effect of grain composition on the thermal conductivity of lightweight concrete, it was shown that the mineral composition of filler (aggregates) substantially reflects the thermal conductivity and density of concrete. The grains of the component have a slightly higher effect on the thermal conductivity than the material itself. The proof of this position is that the thermal conductivity of bulk materials is always slightly lower than cellular materials of the same average density. In an absolutely dry porous body, heat transfer can occur not only through thermal conductivity but also through the solid skeleton of the body, located in the air pores, but also by convection and radiation between the pore walls. With a pore diameter of less than 1 mm, convective heat transfer is practically zero, and the coefficient of radiant heat conductivity can be neglected only when the pore diameter is less than 0.5 mm. Therefore, with the same porosity, the thermal conductivity coefficient will be the greater, the larger the pores of the material. Therefore, the creation of a finely porous structure of lightweight concrete and the use of finely porous aggregates contributes to the production of concrete with reduced thermal conductivity. The proof can be the results of experiments and the curves presented. An increase in the pore size on the surface of the grains of the aggregates leads to an increase in intergranular voids of the mixtures. As a result of mineralogical-petrographic studies of artificial porous aggregates, it was established that aluminosilicate phases with a disordered structure — clay amorphized with firing and acidic glasses — predominate in expanded clay, agloporite, and expanded perlite. Slag is characterized by a predominance of crystalline phases - low-basic calcium silicates than calcium and magnesium aluminosilicates. The glassy phase is present only in the form of an impurity of 15 - 20%. When analyzing the experimental data, we came to the conclusion that the thermal conductivity of expanded clay increases with increasing density. However, at the same density, expanded clay of different batches of the same plant and especially of different plants, differ in the values of the coefficient of thermal conductivity.