Experimental And Engineering Study On Mechanical Properties And Microstructure Of Large Area Concrete

With the development of social economy, the urban population anfexpands rapidly, increasing the number of private cars,parking pressure is getting more and more obvious. The large area concrete of the underground garage of modern building not only meet the need of structure, but also relieve the stress of parking issue. The special environment of the under-garage propose a higher requirement for it’s concrete, which is higher impermeability and crack resistance requirements,The penetration of concrete as well as the development of shrinking crack can be effectively reduced by using additive like dense agent. Above all, the research on the mechanical properties and inner micro-structure of concrete mixed with dense agent is urgently needed.Based on basement construction of Longwan first phase residential project, Macro mechanical property test, micro pressure mercury and scanning electron microscopy(SEM) were used to study the basic mechanical properties and microstructure of concrete. A comparative study of the C30, C40 of different strength grade of concrete in different FS102 compacting agent addition amount of mechanical properties and micro structure of the situation, through the field measurement of strain and stress analysis, thus provide the experimental basis for the practical engineering.This study was carried out mainly from the following aspects:1.The Basic Mechanical Properties of ConcreteThe mechanical properties of C30 and C40 concrete which had the same mixture proportion with the practical engineering, including compressive strength, splitting tensile strength, axial compressive strength and elastic modulus, all were tested in the age of 3d, 7d, 14 d, 28 d after standard curing condition of different proportion of compacting agent(proportion was 0%, 0.21%, 0.25%). Through the horizontal contrast of the concrete with the same grade and water cement ratio but with the different(0%、0.21%、0.25%), and through the comparison of the concrete all mechanical properties were analyzed by the age. Studies have shown that for the same concrete grade, FS102 with proportion of 0.21% overall performance is superior to the proportion of 0% and 0.25%, larger dosage solid agent against the development of the mechanical properties of concrete.2. Field Stress and Strain TestBased on the mechanical properties of concrete laboratory research situation, in the engineering measurement, chose FS102 proportion of 0% and 0.21% of the concrete were analyzed.By embedding vibrating wire strain gauge in the entity of project pouring, thermocouple and other related equipment before pouring concrete,the statistic record has been carried out to find out the change rule of concrete strain and temperature strain that changed with age. It has been verified that concrete splitting tensile strength outweighed the temperature stress, thus the concrete of the project entity met the requirements, which can effectively resist and prevent the crack development.3. Impermeability TestAccording to the nationand the industry standard, the impermeability of specimens that were kept in standard condition for 28 days were tested. It showed that the concrete were greater than permeability grade requirements of project, meet the engineering requirements.4. Micro-structure TestIn order to reveal the internal microstructure evolution with the change of age, the scanning electron microscope(SEM), pressure mercury test of the 28 d concrete microstructure were analyzed. The results showed that,with the same strength, the concrete internal porosity under 0.21% internal porosity and hole number decreased. The concrete microstructure tended to be dense, the penetration was reduced as well as the strength and the impermeability got higher.