Abstract. The aim of the study is to show the improvements on durability of prestressed concrete elements by introducing in concrete mass a certain quantity of fibres. Random distributed fibres provide a significant increase in the tensile strength, having also favourable consequence on other mechanical and durability characteristics. The prestressed concrete elements are under a permanent stress state that is not optimal in all their sections and zones. One of the most unfavourable effects is the reduction of material durability, especially in aggressive environments, in which prestressed reinforcements are more sensitive to utilization than reinforced concrete components. The authors present the result brought up by the use of steel fibres in the improvement of the durability of concrete elements, in relation with the volumetric steel ratio, and the geometrical ratio of steel fibres, leading to a favourable effect on prestressing efficiency.
Starting from the disadvantages of the polystyrene system -the most important being that they are not biodegradable and their life cycle is relatively small, up to fifteen years -there were conceived several structures for outside walls made of perforated bricks vertically disposed and filled with granular materials. In this manner the thermal resistance is improved knowing that in gaps bigger than twenty millimeters there appear convective streams which substantially decrease the isolation properties of the houses. Another aspect that was studied deals with the improvement of indoor air temperature during summer period. This temperature can also be obtained by using two unconventional solutions. First of them is given by the utilization of geothermal energy, and the second one represents the heat absorption phenomenon through water vaporizations. Using these ideas there were considered different methods for heat transfer from an area to another by using some devices that allow fluids to pass through different aggregation forms.
The present paper analyses the deficiencies of current technologies of concrete curing acceleration by heat treatment and based on the unused supplies of these methods, and also aims at designing new procedures of heat treatment with a significantly shortened treatment cycle in order to increase the efficiency of precast manufacturing plants. It is well-known that in conditions of ordinary hardening, the mineral composition of concrete influences over time the speed of concrete strength gain through the ratio between the volumes of the cement stone's crystal component and gel component. It is demonstrated that the strength of the cement stone and the speed of increasing this strength depend on the mineral nature. Great initial strength (type I) and alumina cements, deemed to be high-quality, have higher hydration speed providing a significant gain of concrete strength in the first hours of placing, while slow-hardening cements provide concrete with long-term strength gains. It is also a known fact that cement batching up to 400 kg/m 3 has a positive influence on the increase of concrete strength and concrete grade; above this level the influence of actual batching is not significant.
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