Study On The Water Content Testing And Microstructure Of Concrete In Dry Climate With Big Temperature Change

Concrete has been widely used in the construction of infrastructures. The preparation and use of concrete are always in special environments, some of which are harsh, for example, dry climate, big temperature change and corrosive substances etc. These bad conditions not only bring some difficulties to the preparation of concrete and quality control, but arise serious damages to the concrete structures. The problems caused by the bad conditions will be harmful to the durability and reduce the service life of the structure, which will result in great repair expense.This thesis focuses on the effect of regional climate, which is dry and big temperature change, on the properties of concrete. The technique of water content controlling when preparing concrete and the influence of the region environment on the microstructure concrete at early ages are studied. In this thesis, a special equipment—the water-content checker in fresh concrete (W-Checker)—was used; the micro-hardness testing machine and scanning electron microscopic (SEM) were used to analyze the interfacial transition zone (ITZ) of concrete; the mercury intrusion porosimeter (MIP) and optics microscope were used to investigate the porosity and pore size distribution of concrete. The feasibility of applying a new water content test technique in fresh concrete is studied. Characteristics and formation mechanism of the microstructure in the dry and big temperature change environment is investigated.According to the research results, following conclusions are obtained:1. The W-Checker can test the water content of fresh concrete via testing its air content and bulk density quickly and precisely. By using this technique, it is possible to monitor the water content, adjust the concrete mix proportion and control the concrete quality in the construction site.2. In the dry and big temperature change environment, the width of ITZ becomes wider and the mean values of the lowest micro-hardness decreased obviously than that in concrete sample cured in standard condition. At the same time, the adherence between the aggregate and cement paste becomes weak and the microstructure is loose and the porosity is high. There are some micro-cracks observed in the ITZ. The deterioration of the ITZ causes the degradation of the macro-properties, for example the strength of concrete.3. When the exposing time in the environment of dry and big temperature change is extended, the total porosity and mean pore diameters increase gradually as well. Contrarily, the total pore surface area decreases gradually. The proportion of harmful pores augments gradually. The peak values of the pore size distribution curve shift to the big pore diameter portion. Contrarily, the air void spacing factor becomes smaller.4. The key mechanisms of the influence of dry environment with big temperature change are the formation of temperature and humidity gradients inside the concrete, which arise deterioration in the ITZ and changes of the pore structure.