Improvement of the durability of steam-cured reinforced concrete members of hydraulic structures

Abstract

It is a well-known fact that two opposite processes take place in concrete being cured by steam. One, which is beneficial, consists in the shaping and hardening of the texture of the setting concrete; the other, which is destructive, involves the deterioration of the texture as a result of the appearance of thermal and humidity gradients, as well as other causes. The application of surface-active admixtures may substantially improve the properties of steam-cured concrete and, primarily, increase its durability.Surface-active admixtures may be incorporated in the cement during pulverizing, or to the concrete mix along with the water. Surface-active substances have long been used for cast-in-place structures in hydraulic construction, but they have been rarely utilized in the production of precast elements at factories and construction yards. This is due to the fact that the admixtures used up to now (abietic resin, saponified wood pitch, naphthenate soap, sulfite-alcohol residue, and so on) in addition to having favorable effects on the characteristics of the steamcured products, including improvement of the impermeability, frost-resistance, and deformation properties, exhibit also undesirable effects on the concrete strength, especially in the case of severe heat-humidity treatment. In order to obtain a strength equal to that of concretes of similar composition, but lacking admixtures, it is necessary either to increase the amount of cement or to maintain the products under aging for a long time before subjecting them to the heat treatment. Long preliminary aging of the products is not economically advantageous for the factories.The work conducted at the department of construction materials of the V. V. Kuibyshev MISI (Moscow Civil Engineering Institute) in collaboration with the personnel of a chemical group of factories, as well as with various other organizations, indicated that if in the preparation of concrete mixes use is made of hydrophobic cements containing especially chosen admixtures (made from diverse products of the petroleum industry), then reduction of the strength of the products does not take place, even when particularly severe heat treatment and short preliminary aging are applied.The favorable results of preliminary investigations made it possible in 1964 to organize at a cement factory the production of two experimental batches of hydrophobic portland slag cement with an admixture of oxidized petrolatum, and then to place under service conditions, experimentally, the steam-cured products made with these cements.It is known that products made with portland slag cements are characterized by a lower frost-resistance as compared with ordinary portland cement products. For this reason the effect which may be obtained (from the standpoint of improvement of the frost-resistance) by the application of surface-active admixtures to portland slag cements is relatively lower than for portland cements. However, in connection with the fact that during the last years flag cement is being increasingly used i...