Research On Thermal Stress Of Mass Concrete During Construction Period

Thermal stress is one of major factors inducing temperature cracks of mass concrete. According to statistical analysis, the cost of temperature control to prevent temperature cracks accounts for 3% of the whole cost, while the cost of mending cracks account for 5%-10%. Even so, temperature cracks would delay the construction progress and result in greater losses. Thus, the study on thermal stress of mass concrete is of great significance to design effective measures of temperature control.In this thesis, the thermal stress of mass concrete, as well as temperature control measures, is researched with different materials (including roller compacted concrete, normal concrete and high strength concrete) and different structural types (including gravity dam, high arch dam and the U-aqueduct). This thesis consists of the following four parts:(1) As a kind of the thin layer mass concrete, it's very difficult to control the temperature of the bedding concrete to prevent temperature cracks. Based on the test temperature data of concrete, it is corrected that the main material thermal parameters by inversing. And then, it is analyzed that the causes why there are cracks in the bedding concrete of LongHuakou: Bedding concrete was poured in summer, which caused the peak value of interior concrete temperature reaching 45℃. After that, the temperature fell fast and thermal stress came about by the action of the constraint forces of the bedrock. In addition, the tension stress was increased when consolidation grouting. They caused the cracks in the bedding concrete.(2) Considering the problems of Longhuakou RCC dam construction period expanding and concrete pouring in hot summer, the influence of the construction progress and surface heat preservation on the thermal stress of concrete is researched by 3D simulation. Moreover, some measures of temperature control for crack prevention are offered, which could be used as references for the middle and small hydraulic.(3) It's vital and difficult to control the temperature in order to prevent temperature cracks in high arch dams. Pre-cooling the concrete aggregate is one of the main engineering measures to control the temperature. Connecting with the Xiluodu high arch dam, the simulation shows the influence of pre-cooling the concrete aggregate on the existing concrete, which could be used as references for temperature control in high arch dams.(4) As a special thin-walled structure of mass concrete, the temperature of the concrete of aqueduct changes greatly in a short period under the influence of the variation of the ambient temperature, concrete adiabatic temperature rise, placing temperature and steam curing system, which would cause high thermal stress. With the research on temperature and stress field simulation during the construction period for Shahe aqueduct in Mid-Line of South-North Water Transfer Project, it is studied the influence of steam curing system on the thermal stress of high-strength concrete, which can be used as references for the temperature control and anti-cracking design of Shahe aqueduct.