Research For The Coefficient Of Thermal Expansion Of Manufactured Sand Concrete At Early Age

The early cracking phenomenon of concrete structures often happens, which influences the safety and service life of concrete structures. Researching the coefficient of thermal expansion (CTE) of manufactured sand concrete at early age is important for preventing the early cracking of manufactured sand concrete and improving the service life of concrete structures.The particle shape of manufactured sand and stone powder was analyzed by using Imagepro Plus software. The concrete mix proportion was designed based on the equal paste volume method and the least paste theory, considering the influence of stone powder. The mechanical property, working performance, porosity and pore size distribution at early age of manufactured sand concrete were studied by changing the manufactured sand type and the stone powder content. The CTE of manufactured sand concrete at early age was studied by using a self-made test device for measuring the CTE of concrete at early age. The main conclusion can be listed as follows:1. According to the proposed evaluation system for the particle shape of manufactured sand and stone powder, it is founded that the particle shape of manufactured sand and stone powder is very different. The content of elongated and angular particles in manufactured sand is more than that in natural sand. In the sand whose particle size is greater than 0.6mm, the content of circular particles in natural sand is higher than that in manufactured sand. In the sand whose particle size is less than 0.6mm, most of the natural sand particle shape is square, while most of the manufactured sand particle shape is square and triangle. The particle shape of three kinds of stone powder studied in this paper is close to roundness. When the particle size of stone powder becomes smaller, the number of square particles and angular particles increases.2. A test device for measuring the CTE of manufactured sand concrete at early ages was developed by ourselves. Corrugated pipe molds and a "fast variable temperature" method were used to reduce the impact of other shrinkage(such as self shrinkage, drying shrinkage, etc) of concrete at early age on deformation measurement effectively, "suspension method" invented by ourselves was adopted to reduce the friction and disturbance in the test.3. The CTE and compressive strength of manufactured sand concrete have a good linear relationship at curing age of one day. The greater the compressive strength is, the greater the CTE is. The porosity of concrete at curing age of one day has the relatively good linear relationship with the CTE of concrete at curing age of one day. The larger the porosity, the less the CTE. Then the explanation that the CTE is effected by the porosity is verified.4. The CTE of manufactured sand concrete at early age increases with the increase of the content of limestone powder and siliceous limestone powder. The content of tuff powder has little influence on CTE. The types and content of stone powder would affect the concrete porosity, and then affect the CTE of concrete. But in general, the influence of type and content of stone powder on the CTE of manufactured sand concrete at early age is little. In addition, the CTE of manufactured sand concrete is influenced by the CTE of manufactured sand. The greater the CTE of manufactured sand, the larger the CTE of concrete is.5.The experimental data about the CTE of manufactured sand concrete at early age were fitted by using lstOpt software, and the fitting effect was good, and the calculation formula of the CTE of concrete at early age was got, which considered the influence of age, stone powder content and the CTE of fine aggregate.