IMPACT OF FORMULA-TECHNOLOGICAL FACTORS ON CONCRETE STRENGTH INDICATORS FOR INJECTING WITH TWO-STAGE EXPANSION

Abstract. Objectives The aim of the study is to clarify the dependence of the cement stone strength on additional porosity that is formed owing both to the cement stone’s development of free deformations and the expansion of the hardening concrete in the second stage as caused by the action of the expanding additive. Method The study is based on the introduction of a sulphoaluminate-type expanding additive in the composition of a binder based on alumina cement, natural gypsum stone and nitrilotrimethylphosphonic acid. Results It is shown that an important role is played in the technology of expanding concrete not only by the degree of expansion of the cement stone, but also by its strength, both during the development of deformations and following stabilisation. Among factors influencing the kinetics of hardening are not only recipe-related (composition and dosage of the additive, mineralogical composition of Portland cement clinker, composition of the concrete, presence of chemical additives), but also technological (fineness of cement grinding, hardening temperature, etc.) that makes the management of the processes of structure formation quite complex. The dependence of the strength of cement stone on the additional porosity formed due to the growth of the cement stone own free deformations and expansion of the hardening concrete in the second stage due to the action of the expanding additive is revealed; dependence of the influence of kinetics of the structure formation regulator - nitrilotrimethylphosphonic acid - on the consistency of the development of the intrinsic free expansion deformations and the formation of the strength of the cement stone in the second stage; the dependence of the strength of the cement stone on the additional porosity formed due to gas evolution and expansion of the mixture in the first stage due to the action of the gas-forming additive; the influence of the constraint of expansion on the formation of the structure of cement stone and its strength; the effect of hardening conditions on the strength characteristics of concrete with a two-stage expansion. Conclusion The process of expansion under the conditions of deformation free development is accompanied by an increase in the porosity of the cement stone of up to 9% and a regular decrease in the strength of the cement stone by compression up to 19.3%. The effect of hardening conditions on the compressive strength of concrete with a two-stage expansion is established: when exposed to air for 28 days at a temperature of 5 ºC, the strength decreases to 50% relative to normal conditions, and at a temperature of 35 ºС - to 14 %. With water aging the strength is reduced to 33% due to intensive expansion in the second stage. The dependence of the ratio of tensile strength to compressive strength for concretes with a two-stage expansion is specified, taking into account the hardening conditions.

concretes for injection with two-stage expansion, formula and technological factors, strength indexes, additional porosity, intrinsic free deformations, expanding additive, regulator of structure formation kinetics, nitrilotrimethylphosphonic acid, gas-forming additive, constraint of expansion

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