Analysis Of Compensation Effect Of MgO Concrete And Causes Of Cracks Of Changsha Arch Dam

This paper is concerned with the compensation effect of the micro-inflation of MgO concrete on dam's tensile stress. The model of the micro-inflation of MgO concrete obtained by experiment is coupled to the calculations of temperature field and temperature stress by means of software of ANSYS. Simulations are carried out for two dams, one is made of concrete added a certain amount of MgO in certain location, and the other is made of the normal concrete. At last, the causes of cracks of Changsha arch dam are given based on the numerical simulation results together with the strength curves of experiment of MgO concrete.Elastic module's variation with time, relaxation of concrete, the environment's temperature and the amount of MgO, whose distribution is strictly according to actual MgO's quantity used in the construction of dam, are taken into consideration in the simulation. The period of the inflation of MgO concrete is taken about three years, which is from the start of construction to the initial application. The calculated temperatures of the dam are coincided with that of the actual test. The study indicates that the temperature of the period of construction is higher, the temperature decreases from the middle of the dam to the upstream face and downstream face. The gradient near the face of the dam is greater than that of the inner. The maximum temperature rise of a construction block is 21 ℃ higher than that of the beginning, the highest rise of temperature or the peak of temperature usually occurs in the block, whose temperature is high at beginning, and the highest temperature of dam is about 42 ℃. The smaller tensile stress appears on the upstream face, while larger tensile stress appears on the downstream face in the construction period. The research shows that it is an effective method to reduce large tensile stress by adds a certain amount of MgO in the concrete. The effect of compensation of MgO is obvious especially in the tensile state or location of dam. The study also indicates that the compensation is related with deformation of MgO, and compensation almost disappears in the early period, and it increases gradually in the later. The effect of compensation is also related with stress state, temperature, time and so on. Finally, the cracks of arch end and the cracks nearby the dam crown around elevation 210m on downstream is the preliminary studied, and the research shows that they are caused by the large temperature stress in construction period. The paper will help to understand MgO technique in actual application in constructing arch dam.