The results of experimental researches of short-term heating effect up to +90°C on strength, modulus of elasticity and ultimate strains under axial compression of modified high-strength concrete of C70÷C90 classes were presented. The concrete was obtained with the modifier application MB 10-50C. Temperatures of tests − +20°C; +50°C; +70°C; +90°C. Lifting speed of temperature during heating − 15°C/h. The decrease of concrete strength under axial compression was installed in short-term heating conditions up to +50°C; +70°C; +90°C respectively 20%, 23%, 28% by comparison with tests at the normal temperature. Meanwhile, the modulus of elasticity decreased 18%, 20% and 22% respectively. The ultimate compressive strain of concrete increased 15%, 9%, 11% respectively at the same temperatures. This work was carried out within the frameworks of the grant of FNI Ministry of construction of Russia and RAASN on the topic 7.4.15-18 «Fundamental scientific researches of the elevated temperatures’ influence up to 200°C on the characteristics of physical-mechanical and rheological properties of modified high-strength concrete of C70÷C90 classes».
Contemporary trends inrock mechanics display a general attempt to improve and elucidate new phenomenological systems on which to base the theory of this subject. The reason for this is that the classical theory of elasticity cannot describe the diverse processes which occur in actual rock masses.Methods relying on elasticity theory do not provide any radically new results and cannot solve a number of important practical questions, chiefly because the representation of solid rock as a linearly elastic medium often is not in accord with the facts. Such phenomena as floor heave in workings, the effect of standing time on exposed roof stability, the relationship between the elasticity modulus and the rate of deformation, and the deformationtime curve and its relationship to the stressed condition bear witness to the changes which take place in the stressstrain state of a sedimentary rock mass. Therefore, solutions based on elasticity theory cannot be used as a basis for forecasting stability of mine workings at considerable depths, for selecting the necessary resistance and yield reserves in face supports and special types of support, or for determining the permissible duration and area of roof exposures, etc.It was this search for a more complete description of the true properties of a rock mass which forced many research workers to make increasing use of the methods of plasticity and creep in studies of the stress and strained state of rock. The inherited-creep theory has found greatest popularity in rock mechanics [1], and is based on a representation of the rock as a linear "hereditary" medium, the condition of which can be expressed by the integral Volterra equation with an Abel creep nucleus.Methods based on the theories of plasticity in creep are mathematically more difficult than elasticity theory calculations. It is therefore necessary to develop experimental methods for examining the stress-strain condition of rock with consideration of its theological properties.In experimental investigations of stress in a rock mass, use is made of modeling techniques involving equivalent materials or electrohydrodynamic analogs employing various types of electrical integrators. Other methods involve optical interference methods using photoelastic materials,* one of these being the optical polarization method.Simulation using equivalent materials has the advantage that the various technological operations involved in mineral mining can be easily modeled; therefore, it is possible to examine stress manifestations for various rates of advance, face support systems, and roof control methods. However, this method has shortcomings because the information on stress and strain is purely local; furthermore, there are no technically proved methods of measuring the stresses, and not enough is known about the theological properties of the equivalent materials themselves.In fact, what is studied in equivalent-materials modeling is not the stress condition, but rattier the reactions of pickups or transducers, which are largely functio...
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