Study On Temperature Field And Strength Development Of Early-Age Concrete Slab Under Different Curing Methods

A complex physical-chemical exothermal process, which is related to the temperature and moisture history, is developing after the concrete placed, and it would lead to the change of material properties including strength and modulus. All these changes mainly happened in the early age of concrete. If the volume shrinkage of the concrete slab caused by the change of temperature or moisture field was restrained, residual tensile stresses will generate. The stress are decided by the conditions, such as material, the structure boundary constraints, environment and curing methods. As a result, early age cracking will provoke when the tensile stress overtake the strength under unfavorable combination of the conditions. And this kind of cracking and damage would be a significant reason for the reduction of durability in the concrete pavement. So, it needs in-depth studies of the early age behaviors of concrete slab to decrease, even avoid this kind of cracking or damage.Curing methods would become a most important influence ingredient of early age behaviors in concrete slab. It has attracted the attention of many researches and several curing technical measures have been offered in the specifications. However, it's in lack of studies in the curing effect. Since the regular water supplement according to the weather could keep the moisture of concrete slab in a relative constant level, different curing methods would mainly contribute to the variety of temperature field, which also leads to the different development of concrete's early age properties. As a result, early-age behaviors of concrete slabs would vary with the change of curing methods.Based on the above analysis, this paper finished some important work from two aspects: temperature field and strength development, which are as follows:(1) The full scale test road with five different curing methods respectively, were constructed, and temperature field of the test road along with meteorological conditions in situ were monitored. Besides, some simultaneously curing cubic specimens were tested at the expected time. All these experiment results will provide basic data to the analysis of performance of early age concrete.(2) The temperature fields are quite complex with different curing methods. there are some similar properties, as well as much differences. From the point of view of time and space, the similar properties include the volatility, posteriority, distinctive hydration and heterogeneity in space. Further way, two time points were chose, and from three aspects: the average temperature of the slab, the temperature difference between the top surface and the bottom surface of the slab, temperature nonlinearity along the depth of the slab and the complexity in the top layers, respectively, analysis shows that the thermal parameters such as the absorption ratio of solar radiation, heat change coefficient, are quite different.(3) The degree of hydration was calculated by the equivalent age, and Finite element model and user subroutine based on the ABAQUS code were created to calculate the temperature field of concrete pavement in the early ages involving hydration heat of cement. Besides, the back-calculation formulas were deduced based on the difference principle and the thermal parameters of each curing methods and concrete were calculated. In addition, the thermal parameters and FEM models were verified by real data measured in situ. At last, the temperature fields of concrete slab under each curing methods were simulated at the first sixty hours after placing and the influences of each curing ways were accessed.(4) The strength increasing tendency of concrete has its own characteristics under different curing methods, and it goes to two different trend. Prediction effects of each maturity algorithms and relationship models between strength and maturity were evaluated in this paper with the real data. Besides, this paper also put forward strength predicting models and simplified algorithm to estimate the strength under nonstandard curing conditions in situ.The researches above all will give a reference when choosing the curing methods and the quality controlling. Besides, the user subroutine to calculate the temperature field and the model to predict the strength are important start work for the simulation of the stress field and curling of the concrete slab.