EFFECT OF AMBIENT TEMPERATURE AND HOLDING PERIOD ON THE PROCESSING CHARACTERISTICS OF SELF-ADJUSTABLE POLYMERCEMENT FIBRO CONCRETE MIXTURES
Abstract
An analysis of the current technical condition of hydraulic structures in Ukraine shows that a significant part of them are in need of current and major repairs. The main material for the repair work on the structures is concrete. Concrete, which is designed for such work, has increased requirements for its characteristics: high processability, increased strength, frost resistance, crack resistance, corrosion resistance, water resistance. Particularly relevant is the problem of repairing structures in hard-to-reach places, in conditions of high concentration of structural reinforcement and remoteness from the places of concrete mixes. The solution to the problem can be the use of self-reinforced polymer cement fiber-concrete mixtures in the technology of repair and restoration works, which is obtained by modifying traditional concrete mixtures with a complex organo-mineral additive. The main components of the additive are polycarboxylate superplasticizer, active microfiller (silica fume, metakaolin), polymer latex and polypropylene fiber. The use of organic-mineral additives allows to obtain a concrete mixture of high mobility (spreading of the cone ≥ 550 mm), and concrete based on it with high physicomechanical properties (compressive strength ≥50 MPa).
The fundamental problem of developing and introducing self-compacting concrete mixtures into production is to ensure their high workability, providing for the maximum avoidance of labor-intensive operations of laying and compacting and ensuring the necessary properties of concrete, including strength. The basic technological characteristics of concrete mixes include workability, which is characterized by mobility, and viability, which is determined by the time of loss of mobility to a value at which it becomes impossible to use the concrete mix as self-compacting. According to the “European guidelines for self-propelled concrete,” the diameter of the cone of such mixtures should be ≥ 550 mm.
After mixing with water, as a result of the hydration processes, the mobility of the concrete mix changes over time, and depending on the mobility, its viability changes. In addition, the viability of the concrete mixture is influenced by the ambient temperature. Depending on the temperature, the rate of hydration and evaporation of water from a concrete mix can vary over a wide range, which leads to a change in its viability and workability.
The aim of the work is to study the technological characteristics of self-compacting polymer-cement fiber-concrete mixtures and the effect on them of the ambient temperature and the holding time before installation.
As a result of research, experimental - statistical models have been obtained that express the influence of ambient temperature and holding time before laying on the mobility of self-compacting mixtures and the influence of ambient temperature and mobility on their viability. With the help of models, it is possible to determine the permissible holding time of the concrete mix prior to laying at a certain temperature - this is the time at which the cone of the concrete mix is ≥ 550 mm. It has been established that, depending on the ambient temperature and the exposure time, until the conclusion of the spreading of the cone of the mixtures is 450...780 mm. With increasing temperature and increasing exposure time, the spread of the cone decreases. Depending on the mobility and ambient temperature, the viability of the mixtures varies from 3,1 to 10,1 hours. Pot life increases with mobility of mixtures and decreases with increasing temperature of the medium. In the temperature range of 5...35°C self-compacting polymer-cement fiber-concrete mixtures for 6...8 hours retain the necessary mobility
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