Papers by Keyword: Massive Concrete

Abstract: The article deals with issues of the thermal cracking resistance in massive concrete and reinforced concrete structures during the building period. The paper lists the calculation results of the NPP reactor foundation mat thermal stressed state and thermal cracking resistance. The research also considers the concrete hardening temperature influence on its thermo-physical and deformation characteristics. The deformation criterion is used to calculate the concrete thermal cracking resistance. In addition, the paper focuses on the assignment of safe concrete pouring technological parameters in the winter period. Furthermore, the article estimates the necessity of the structure peripheral electric heating during the building period.

Abstract: In the construction process, the concrete has been get fully utilized, there have been a variety of concrete strength grade configuration requirements and the corresponding raw materials. In the pouring process large volume concrete base, since the temperature stress generation will produce concrete temperature cracks, so the concrete pouring, raw material selection, after pouring temperature control measures have higher requirements. Based on a practical project, the construction of the control temperature stress did some exploratory research.

Abstract: During the construction process of massive concrete, the construction must forecast and control the temperature forming of massive concrete in order to avoid the temperature crack owing to the thermal stress caused by the concrete heat. The discussion on the concept of grey system interval and grey number predication applies to the temperature rise prediction of massive concrete in the construction process. The previous temperature rise data is divided into the white part and grey part based on real numbers. And the interval grey number forecast computing models are established, so we can finish the temperature rise prediction during construction process. The forecasting results of case show that, this model has fast convergence and remarkable precision. Then, it is possible to realize the accurate temperature rise prediction of massive concrete.

Abstract: A massive concrete structure has a lot of micro-cracks due to the hydration heat. In general, conventional electric sensors have a certain limit in measuring cracks because of the noise. The durability is also badly influenced by corrosion. Recently, optical fiber sensors have demonstrated their superiority over conventional sensors and are able to solve these problems. Thus, in this work, embedded Fiber Bragg Grating (FBG) sensors for measurement of cracks in massive concrete due to hydration heat are developed and investigated. The developed sensor has the potential to perform strain measurement under harsh conditions in the presence of electrical noise and electromagnetic interference. Particularly, these FBG strain sensors are easily installed and found to be durable for massive concrete structures such as dams, bridges, nuclear structures, etc.

Abstract: In order to make the temperature controlling measure of massive concrete mixing with slag powder and fly ash effectively. Taking Guangzhou East Bridge sand cap-based temperature control project for example，the pile caps transient temperature field calculation model is established by finite element method. The different water cooling time and hydration rate are analyzed. The results show that the cooling time extending has less effect on central maximum temperature of double-doped concrete in early stage, but the times arriving corresponding stable temperature is earlier. The hydration rate has more effect on maximum temperature.

Abstract: For concrete double mixing with slag powder and fly ash, in order to more accurately measure the temperature and crack, the calculation model of transient temperature field is established by finite element method, as taking the temperature controlling of massive concrete mixing with slag powder and fly ash of pile cap in Dongsha Bridge for example. The effect of cooling water temperatures and pouring temperature on temperature field of pile cap are analyzed. The results show that the cooling water temperature has less effect on central maximum temperature in early days, but more effect on cooling rate in late stage. The pouring temperature has more effect on maximum temperature. The temperature peak will rise with pouring temperature increasing, but the time of temperature peak arising is invariant.

Abstract: with the continuous development of bridge engineering，the massive concrete has been widely used in large-scale bridge foundation engineering. But it often has the problems of crack and deformation, which infuenced the entirety and durability of the whole structure seriously. In this paper, a hydration heat analysis of the platform of a corrugated steel webs bridge is carried out by using MIDAS/Civil structure finite element method analysis program, the analysis summarizes the temperature distribution regulation of platform concrete influenced by hydration heat and the temperature changing regulation affected by time. Meanwhile, some countermeasures of preventing the crack of concrete are put forward.

Abstract: In the first phase of the project of AnHui Province New Broadcasting Center, the CT-1 foundation of tube cushion cap in main building is 3.5m in thickness which belongs to massive concrete. In order to prevent the crack caused by the excessive hydration heat in massive concrete, the project take several actions including optimizing dosage of cement concrete mixture, setting post-cast strip, cant layered casting and temperature monitoring after concreting, etc. All these actions regulate the concrete temperature and restrain crack generation successfully, while insuring the construction quality of massive concrete cushion cap.

Abstract: In this paper, based on the principle of heat balance, the computing equation of temperature field which used the thermal coefficient, surface coefficient, and heat as the basic parameters of the heat conduction equation is derived, and thereafter the FEM computation procedure about temperature field named RCTS which used the thermal diffusivity as basic parameter is modified. The modified procedure can reasonably reflect the temperature field of composite construction which is made of a great variety of material with different thermal property, and also can simulate the effect of surface heat preservation at arbitrary periods and arbitrary parts of the bulk concrete structure. According to the calculation example, the similarities and differences of the heat preservation effect on the heated board calculation by using different methods: the equivalent surface coefficient method, the equivalent thickness method, the thermal conductivity method and the thermal diffusivity method are analyzed. The calculation results show that the computing results of the thermal conductivity method are closed to the result of the equivalent surface coefficient method, the results of the equivalent thickness method have certain differences but not quite because it is the approximation process of the equivalent surface coefficient method, and the reasonable result is often missed by using the thermal diffusivity method.