METHOD FOR REDUCING CEMENT CONSUMPTION WHEN MANUFACTURING FLEXIBLE REINFORCED CONCRETE STRUCTURES WITHOUT PRE-STRESSING

Abstract

An analysis was made of publications in which other methods of reducing the consumption of cement for the manufacture of bent reinforced concrete structures were studied, in which void formers, liners, slags were used, optimal selection of sizes and ratios of sand and crushed stone, heat treatment, replacement of Portland cement with slag-alkali binder, addition of ash to concrete.

Subject of study. The article presents studies on reducing the consumption of cement in the manufacture of reinforced concrete bending structures without prestressing on examples: 1) prefabricated beam; 2) monolithic floor slab, 3) prefabricated floor slab with round voids.

Materials and methods. The relevance, possibility and expediency of implementing the task of reducing the consumption of cement in the manufacture of bent reinforced concrete structures are substantiated. Attention is drawn to the fact that concrete in the tension zone does not actually affect the bearing capacity of the bending structure, since the tensile strength of concrete is very low and therefore is not taken into account in the calculations. Attention is also drawn to the fact that currently concrete of the same strength is used in the tension zone as in the compressed zone. In the tensile zone, it is proposed to use low-strength concrete, and when designing and calculating elements of bending structures, take into account that in individual elements concrete changes its bearing capacity, namely: compression to tension and vice versa, tension to compression. In such places, and these are, as a rule, supporting sections in continuous structures, it is necessary to install additional transverse and longitudinal reinforcement. Examples of calculations for reducing cement consumption are given: 1) for a prefabricated beam 600×60×20 cm in size, 2) a monolithic reinforced concrete floor slab 24 cm thick, 3) a prefabricated beam floor slab with dimensions 630×150×22 cm with round voids with a diameter of 159 mm.

Results. The proposed method allows to reduce the consumption of cement by 22% in the manufacture of beams, 32% in the manufacture of a monolithic reinforced concrete floor slab and 33% in the manufacture of a prefabricated beam floor slab measuring 630×150×22 cm.

Conclusions. The proposed method for reducing cement consumption in the manufacture of bent reinforced concrete structures without prestressing is possible and expedient, and is also a good addition to the known methods for reducing cement consumption given in the Literature Review section. The difference of other methods from the proposed one is that concrete of the same strength (class) is used in the stretched and compressed zones of the bent structures, that is, in the proposed method, a new, previously not used, solution is adopted: reducing the consumption of cement in the stretched zone of the bent structures. The implementation of the proposed method does not provide for special additional costs. In the future, it is planned to study the possibility and feasibility of extending the proposed method to prestressed reinforced concrete bent structures, test full-scale samples, optimize the reduction in the concrete class in the stretched zone of bent structures, as well as compare theoretical and practical results.