Experimental Analysis of the Thermal Behaviour of Concrete under Low-intensity Short Duration Cyclic Compressive Loads

Experimental researches conducted in recent years at the Non Destructive Testing Laboratory of Politecnico di Torino have revealed an unexpected thermal response of concrete subject to short duration cyclic compressive tests: a cooling phenomenon has been observed on medium-quality concrete cores and this contradicts Kelvin’s thermodynamic laws. Such a decrease in temperature is not to be ascribed to the evaporation of absorbed water, while it depends on the applied load intensity, the application frequency and the total number of cycles performed. Moreover, the cooling phenomenon is accompanied by such mechanical effects as performance enhancement and increasing brittleness, observed through static tests performed at the end of cyclic compression: an increase in the failure strength and the elastic modulus of the material as well as a reduction in max. displacement at failure are seen to occur. The present research takes its starting point in the above observations and aims to investigate the relations between thermal and mechanical effects in concrete, in order to check the possibility to use the variation of temperature at the end of a short duration cyclic compressive test as an indicator for the evaluation of damage, the final aim being to develop in the future a methodology for diagnosis of existing structures.