Dimitar Boshnakov
PhD Thesis SUMMARY
The PhD thesis focuses on studying and analyzing the behavior of fresh and hardened concrete, prepared with mechanically activated water. The aim is to outline the new opportunities, beyond the traditional ones, to intensify the process of cement hydration, to modify the microstructure of concrete in order to improve the mechanical properties.
However, in the field of concrete works, there is a marked trend to improve not only the performance characteristics of concrete, but to achieve significant financial goals by costeffective production. Concrete producers constantly seek then ways to ensure higher mechanical properties at lower cost and mechanically activated water provides such an opportunity.
The main tasks can be determined in the following way: first, to establish the influence of mechanically activated water, in combination with other mix design factors, on strength, strain and structural properties of concrete; second, to study the strength development during the time and third, to examine the microstructure and its influence on the properties of concrete.
PhD thesis gives a brief overview of some of the popular theories about the structure of water, of the ways to change this structure, respectively the properties of water and of the manufacturing of "mechanically activated water".
The impact of the many factors is evaluated: quantity of cement, ratio between fine and coarse aggregate and time from activation of the water until its use in concrete. A comparison between performances of concrete with mechanically activated water and that with ordinary water is made as well.
The results for compressive strength of concrete at the age of 3, 7 and 28 days, prepared with activated water are presented, and they are compared with those of concrete with plain water. These results are combined with studies on macroparameters of concrete (such as capillary absorption, saturation and permeability) and on the microstructure (using differential thermal analysis - DTA, weight - thermogravimetry - TG) and mercury intrusion porosimetry –
MIP, in order to evaluate the influence of the mecanically activated water on the porous structure of concrete and to predict the influence on the durability. These studies have shown that the mechanically activated water leads to a decrease of total and capillary porosities of hydrated portlandcement stone by achieving better hydration of the cement – a bigger quantity of hydration products have been observed and the part of fine gel crystals has increased, which contribute substantially to the strength increase of cement stone, and hence - of the concrete itself. Moreover, the modified porous structure determines a higher durability of concrete with mechanically activated water.
The PhD thesis is a pilot study in the field of construction materials science, proving the possibility to produce concrete with higher strength characteristics without increasing quantity of cement and / or adding chemical admixtures (plasticizers). Since the concrete is among the most used building materials, the results of the conducted research and the main conclusions might have a significant economic effect for concrete manufacturers.