Cement Type Selection For Mass Concrete Structure

With the rapid development of the construction of infrastructure in China, many large or extra-large structures have been built throughout the country. In these engineering projects, many parts are typical mass concrete structures. The temperature and thermal-stress-induced cracking control is always the emphasis and key point during the construction of mass concrete structures. When using moderate-and low-heat cement in the construction of mass concrete structure, it can effectively reduce the maximum internal temperature rise of the structure and hence mitigate the temperature control pressures. However, when the projects adopt such cements, there usually exist the following problems:the strength ofconcrete is not fully developed at the early stage after placing; large amount of such cements need to be purchased and stored in advance; transportation over long distance might be in need; temperature control measures shall be taken as usual; the cost of project is increased significantly. However, there are also many cases in which ordinary Portland cement is used to construct the mass concrete structures. Consequently, a dilemma for the project is caused in choosing the type of cement. Therefore, it is of great significance to reasonably choose the mixing materials, especially the type of cement, and design an applicable concrete mixture proportion to meet the requirements of engineering under the limit of mixing material supply and temperature control measures. In this paper, based upon the mass concrete projects of a building bridge, the design of mixture proportion and selection of cement type were done. The major works are as follow:(1) Firstly, on the basis of the experiments of the concrete mixture proportion design, the influences of the content of binding materials, the content of fly ash, the sand ratio, and the content of admixture on the thermal and mechanical properties of concrete are studied.(2)Secondly, to choose the applicable type of cement, the concrete mixture proportion using ordinary Portland cement, medium-heat Portland cement, and low-heat Portland cement are designed, and the corresponding thermal and mechanical properties were compared.(3) Thirdly, two kinds of structures, i.e. the pile cap of the main tower poured layer by layer, and the pile cap of the secondary towers poured one-time, are chosen to investigate the effect of cement type on the in-situ temperature control. With the parameters gained from the property tests, some temperature control measures were presupposed, and the finite element simulation was performed. The development of thermal stress at the feature points on the structures and the overall safety factors were compared. Then, the mixture proportion were determined for the construction of the pile caps of the main and secondary towers.(4) Finally, the research results were applied in the construction of the pile caps of the main and secondary towers. With the analyses of the monitoring temperatures, the effect of ordinary Portland cement, medium-heat Portland cement, and low-heat Portland cement on the actual construction of those mass concrete structures were further compared. The concluded points can provide some useful experience for construction of mass concrete structures in the future.