Study On Deformation Characteristics Of Micro Expansion Concrete Of MgO-Admixed

The hydropower industry plays an important role in the energy industry of China. Development of energy is closely related with economic development. The hydroelectric power is not only the renewable energy actively developed by countries throughout the whole world, but the important part of China’s energy supply. Large-sized hydropower projects being constructed and under construction in the west area mostly applied the structure with the200m high dam and the concrete structure will be the choice for a long time. Temperature stress and temperature control are the bottlenecks during construction of concrete dam. Mixing of MgO into hydraulic mass concrete can not only simplify the temperature control measures and accelerate the construction period, but improve the concrete cracking resistance. The major results include:(1) According to the research, cement paste with mixed dead-burn MgO and cement paste with dead-burn MgO included are not applicable to engineering practice. According to the research on autogenous volume deformation of the typical MgO concrete under different constant temperatures, MgO concrete will basically become stable within about3a hours. Autogenous volume deformation of MgO concrete in3a-5a hours is stably changed and free from mutagenic infinite expansion and rebound phenomenon. The concrete is stable in autogenous volume deformation on a long term basis and free from obvious deformation increment.(2) To study the autogenous volume deformation discipline under different temperature and different dosage conditions, by summarizing the current research results and combining engineering practices of Guangdong Changsha dam (West region of Guangdong) and Bamei dam (North region of Guangdong). By applying autogenous volume prototype monitoring to Changsha dam which is the first in China to apply the quick dam construction technique of mixed MgO concrete irrespective of cross joint, the author makes the comment that10micro-strained autogenous volume of MgO concrete are still slowly increased after observation for3a. The proposal that the prototype observation time shall be preferably subject to annual increment of autogenous volume deformation which shall be not more than3micro strains and not less than5a.(3) This paper studies the autoclave-treated expansion values of cement base specimens(paste, mortar, one grading concrete and two grading concrete) under different MgO dosage conditions and raises the proposals that the one grading concrete shall be applied as the base for autoclave-treated test and mixing activity shall be subject to dry screening. In the autoclave-treated stability test of mixed MgO cement paste and mortar and cement, the paper studies relationship among expansion deformation, compressive strength and flexural strength under different dosage conditions to determine the evaluation method standard and control target of stability.It states that the autoclave-treated stability standard shall be subject to no reduction of compressive strength and flexural strength to determine relevant limit content. This paper gives the autoclave-treated content yield ratioζ; and concludes that autoclave-treated content yield ratio of mortar and one grading and two grading concretes with different MgO content shall fall between0.95～1.03. The MgO content under autoclave-treated expansibility0.5%multiplying autoclave-treated content yield ratio (0.95) can be used as a basis for evaluating limit content of MgO.(4) Upon systematic study on autogenous volume deformation characteristic, the paper adopts hyperbolic model acceptable to engineering industry and obtains the relevant parameters from28d age and final expansion value, as well as corrects and substitutes the weak points of conventional methods with equivalent age method. It also analyzes on a real-time basis the expansion deformation increment of autogenous volume deformation introduced in the equation and compiles software on the basis of Ansys platform to achieve the APDL secondary development.(5) The paper systematically studies the autogenous volume deformation characteristic of MgO concrete and first designs the autogenous volume deformation proposal under slow temperature reduction condition to study the deformation characteristic. This paper analyzes in detail the current status of Changsha dam cracks and conduct the data analysis of cold wave impact by combing engineering practice. Application of Mgo-mixed concrete dam construction technique is not a necessary cause for cracks appearing in the downstream dam face. Thin cracks of l～2mm have no serious harmful hazard on overall safety of Changsha dam. It should be defined that protection of concrete face shall be mandatorily treated as a permanent work. As for areas where cold wave occurs frequently (above1.5～2.0in October) due to condition limit, the surface of the concrete shall be protected on a permanent basis.