Study of the Temperature Influence on Concrete Hydration Exothermic RateAbstract: Recent achievements about concrete hydration exothermic models based on Arrhenius equation have improved computation accuracy for mass concrete temperature field. But property of activation energy and gas constant (Ea/R) has not been well studied yet. From latest experiments it is shown that Ea/R obviously changes with the hydration degree without fixed form. In this paper, the relationship between hydration degree and Ea/R is studied and a new hydration exothermic model is proposed to use it and testify it. With those achievements, mass concrete temperature field with arbitrary boundary condition can be calculated more precisely.Key words: hydration exothermic model, Arrhenius equation, activation energy, hydration degree, temperature rise model.1 IntroductionThermal crack is one of the most common cracks of concrete 1, 2. Hydration exothermic behavior of the concrete should be taken into consideration when calculating mass concrete temperature field 3, 4. Adiabatic temperature rise can be measured by concrete adiabatic temperature measuring device or back analyzed by the data of field experiment 5, 6. Adiabatic temperature rise got by concrete adiabatic temperature measuring device is more accurate and less expensive than back analysis from field experiment. However, hydration exothermic rate of the concrete is influenced by concrete temperature duration which should be taken into consideration 7-10. There have been several concrete adiabatic temperature rise models to solve this problem and several of them are based on Arrhenius equation 11-14. However there are some common problems: (1) For those models, the ratio between the activation energy and the gas constant is reduced to a constant or simply considered as a fixed function type. Laboratory tests in this paper showed that those reductions are not proper for all kinds of concrete.(2) For those models, adiabatic temperature rise got by device can not be directly applied in calculation because different placement temperatures can lead to different adiabatic temperature rise. So they should be changed into adiabatic temperature rise based on equivalent time, or hydration exothermic rate under normal situation. However, laboratory tests in this paper showed that the most direct factors influencing hydration exothermic rate are hydration degree and concrete own temperature. If there is a hydration exothermic model directly basing on hydration degree and concrete own temperature, calculation precision can be improved.The above problems are studied and the corresponding solutions are presented in this paper.2 Relationship between hydration degree and activation energy2.1 Theoretical baseHydration degree is the ratio between quantity of hydrated cementing materials and total quantity of cementing materials. Equal amount of cementing materials can generate equal amount of hydration heat. So hydration degree can also be expressed by the ratio between released hydration heat and total quantity of hydration heat 12: (1)where: is released hydration heat, is total quantity of hydration heat.Hydration rate of concrete blocks with same materials and hydration degree satisfies Arrhenius equation 11, 12. According to Eq. (1), exothermic rate has the same form with Arrhenius equation and can be expressed by: (2)where: is hydration rate, A is a constant, is the activation energy（）, is the gas constant, is temperature of the concrete.Suppose there are two concrete blocks with same materials and hydration degree, then: (3)where: is hydration exothermic rate of concrete with temperature , is hydration exothermic rate of concrete with temperature .From Eq.(3), Ea/R can be expressed by: (4)2.2 Adiabatic temperature rise experimentThis experiment contains three concrete blocks with same materials (block A, block B and block C). The adiabatic temperature rises of the three concrete blocks were measured by concrete thermal parameter measuring equipment (shown in Fig.1, equipment type: HR-2). (a) Experiment devices (b) Placement temperature of block A (c) Temperature duration of block B (d) Placement temperature of block CFig.1 Experiment devices and measured temperatureThe dosage and temperature of raw materials are shown in Tab.1. The placement temperatures of three blocks are 9.5, 20.7 and 28.5, terminal adiabatic temperature rise values of three blocks are 39.82,38.32 and 37.62 respectively. The difference between three blocks in terminal adiabatic temperature rise values is caused by heat loss during concrete mixing. When mixing block A, the heat loss can be neglected for low temperature of raw materials原因？. When mixing block B or block C, the heat loss can