Back Analysis Of Mass Concrete And The Adjustment Of Temperature Control Measures Based On Monitoring Temperatures

With the large-scale development of infrastructure in China, many civil engineering projects are becoming larger in size, longer in span, higher in height, and more comprehensive in their functions. Due to the needs of bearing capacity and durability, mass concrete structures are continuously emerging. During the placing and curing process, high temperatures are generated within mass concrete because of the heat liberated from the hydration reaction of cement. A relatively high center-surface temperature differential is then formed, which leads to the temperature deformation of concrete. If this deformation is restrained internally and externally, thermal stress will then come into being. Once the thermal stress exceeds the tensile strength of concrete, there will be a high possibility of thermal-stress-induced cracks. These cracks pose a huge damage to the integrity, serviceability, and durability of the structure, which makes the temperature control during the construction phase a necessity. In this dissertation, based upon the existing theories, the temperature control program was designed for the pile cap of a bridge. With the help of a wireless temperature monitoring system, this program was implemented on site. After analyzing the monitoring temperature data, a back analysis of temperature filed of the pouring layer was done on the software Midas FEA, which helped to adjust the temperature control measures. The main works in this dissertation are as follow:(1) Firstly, a comprehensive temperature control program was designed for the construction of the pile cap of a building bridge. The mixing materials and mixture proportion were provided, and then some controlling measures were presupposed. A simulated analysis was performed on the software Midas Civil to verify the applicability and efficiency of those measures. Eventually, the temperature control criteria and measures were determined for this projects.(2) Secondly, a full-scale in-situ temperature monitoring scheme was cooperatively designed with others, which helped to implement of the temperature control program on site. By laying temperature sensors appropriately, a large amount of temperature data were gained. The general distribution of temperatures were analyzed first. Then, the temperature variation rules between two cooling pipes in the horizontal and vertical directions and those along the transverse axis, were particularly demonstrated. Moreover, a comparison of temperature indices of distinct pouring layers with the same or the different construction methods was done to check the effectiveness of those methods. All of these analysis and discussion provided assistance for the implementation and adjustment of the temperature control program.(3) Finally, the 2nd layer on the right part of the pile cap was picked up to carry out a back analysis of temperature field on the finite element software Midas FEA. The finite element model was modified, and then the thermal stress was calculated, whose results revealed the excessive thermal stress and a high risk of cracking on this pouring layer. Based on the modified finite element model, the adjustment of temperature control measures and their effects on the thermal stress were conducted from the perspectives of mixing materials and in-situ temperature control measures. Results showed that the relatively high amount of heat released by the hydration reaction of the primary cement and the strong restraint of the 1st pouring layer on the 2nd layer were the principal reasons for the excessive thermal stress on the 2nd layer. Through the back analysis and other validation analysis, the adjusted mixing materials and temperature control measures were determined, and then applied in the subsequent construction, which achieved a better result.