Choosing the effective modes of compaction of hard concrete mixtures

In the manufacture of reinforced concrete products and structures, one of the main labor-intensive operations is the compaction of concrete mixtures. All the basic physical and mechanical properties of the molded products, such as density, strength, frost resistance and others, as well as the specified shapes and high-quality surfaces, depend on the quality of mixture compaction. A decrease in the density of a product after compacting concrete mixes by 1% leads to a decrease in the strength of hardened concrete by 5-7%, and when molding products from hard mixtures – up to 13%. The effectiveness of vibration molding of concrete and reinforced concrete products is largely determined by the methods and modes of compacting concrete mixtures in molds. These questions are especially relevant when compacting hard and very hard concrete mixes. The analysis of the existing modes of molding reinforced concrete products from hard concrete mixtures is carried out in this paper. The equipment used for molding reinforced concrete products applies different types of compaction: vibration, shock-vibration and shock. The main parameters of vibroforming machinery are frequency, amplitude and acceleration of the working body, which can be symmetric and asymmetric. The advantages of using asymmetric shock-vibration modes are shown, and a method for creating shock-free asymmetric vibrations is proposed. The results of theoretical and experimental studies are presented, which have shown the high efficiency of compaction of hard concrete mixtures in shock-free asymmetric modes.