Knowing how the microstructure of cement based materials (CBMs) develops at an early hydration age is of vital importance, since it directly affects the physical and mechanical properties and thereby the functional properties of the hardened CBMs. The research for the following master’s thesis was conducted within the international COST TU1404 project and is based on the study of hydration kinetics and the development of CBMs mechanical properties at an early age. Using an advanced ultrasonic (US) method, characteristic setting and hardening points of CBMs were determined. The frequency spectrum of the US waves method has proved to be reliable and accurate in monitoring changes in the CBM microstructure. The results of nuclear magnetic resonance (NMR) in monitoring the development of the CBM structure are very promising.
The main part of the thesis focused on the comparison between advanced and standardized testing methods on hardened CBMs. Simultaneous longitudinal and shear US waves transmission velocity measurements enabled us to determine dynamic elastic parameters. These were compared to static elastic parameters obtained through standard methods. The correlation between the compressive strength and the dynamic elastic modulus and shear modulus was analyzed. Since the velocity of US waves travelling through CBMs depends mainly on their elastic moduli, which are closely related to their strength, a further analysis of the interdependence between the compressive strength and the travel velocity of longitudinal and shear US waves was carried out. Results have shown that both transmission velocity of longitudinal US waves and transmission velocity of shear US waves are an effective parameter for estimating the rigidity and strength of early - age CBMs.
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