The present study is mainly devoted to focus on the effect of elevated temperature on concrete properties and micro structure to avoid as possible as we can the various undesired effects of the severe environmental impacts, which affect the service life of concrete. The concrete casted with basalt aggregate was subjected to elevated temperatures (300, 600, & 800 o C) with a rate of 5 o C/min, and an exposure time of two hours. Furthermore, the obtained results showed that the mechanical properties of the heated concrete, associated with the internally induced chemical changes are attributed to temperature elevation effect. Both laboratorial investigations and mineralogic study revealed by using reflected light microscopic study on polished slabs, SEM investigation, confirmed the effect of elevated temperatures on cement paste and aggregates.
Concrete is exposed to elevated temperatures when subjected to accidental fires in buildings, or when is close to furnaces and reactors, as encountered in some industrial applications. Research studies indicate that a serious reduction in concrete strength may result in such cases, and that the type of aggregate used is an important parameter. In thus study, the influence of high temperatures (100–600°C) on the residual compressive and bond strengths of concrete made from limestone aggregates is experimentally investigated. The main test parameters involved were the maximum temperature, the time of exposure at the maximum temperature, the method of cooling, the age of concrete at the testing date, and the cement content. The results showed that exposure of limestone aggregate concrete to such temperatures may result in a noticeable reduction in its strength, especially in the range 400–600°C.
The resources of refractory gold ores are abundant, and their effective treatment can bring good economic benefits. This paper investigated the kinetics of leaching gold from refractory gold ores by ultrasonic-assisted electro-chlorination. The effects of ultrasound time ratio, initial hydrochloric acid concentration and leaching temperature on the kinetic parameters were discussed. It is found that the leaching ratio goes up with all the factors increasing. The reaction kinetics is controlled by diffusion. When ultrasound improves the diffusion by reducing the diffusion resistance, the activation energy increases to 37.1 kJ/mol.