Study On Preparation Technology Of Low Temperature Sensitive Concrete

The cement concrete is a heterogeneous material that is composed of multiple composition with hardened cement, aggregate, pore, admixture and so on. When the concrete serves in the environment with drastic temperature variation, different thermal volumetric changes caused by the components and hence thermal strain in the interface is generated. Then the thermal cracking takes place in the Interfacial transition zone of concrete, which effects the Macro-mechanical properties and Microstructure durability of concrete. In this paper, a experimental research was carried out to study the concrete injury caused by drastic temperature variation (35℃～85℃) in Inner Mongolia area. The thermal deformation of hardened cement and aggregate are studied by using macro-and microscopic tests. Fly ash, silica fume and styrene-acrylic latex are added to adjust the coefficient of thermal expansion of concrete material. Then the preparation technology of low temperature can be found. The main conclusions are:(1) Distinct thermal mismatch between the hardened cement paste and a coarse aggregate in concrete exists in the range of room temperature to85℃. After number of cyclic temperature variation, cracks in the interfacial transition zone of concrete are observed, propagating along the edge of the aggregates. The thermal cyclic shocks lower the compressive strength of concrete.(2) The addition of fly ash, silica fume and styrene-acrylic latex lowers the thermal expansion rate and coefficient of hardened paste. The increase of addition level is accompanied by the decrease of the thermal expansion coefficient. The styrene-acrylic latex is the most effective in lowering the thermal expansion coefficient.(3) The addition of fly ash and silica fume could reduce the amount of Ca(OH)2in concrete and improve its pore structure, while the thermal expansion rate of the materials was thus limited. Besides, the addition of styrene-acrylic latex in concrete formed a impermeable membrane in the internal concrete. As a deformation adsorption layer, the membrane thus enhanced the ductility of the material and lowered its thermal expansion coefficient.(4) The low temperature sensitive concrete with specific coefficient of thermal expansion could be designed and prepared by the preparation of hardened cement with specific coefficient of thermal expansion.(5) The effects of fly ash, silica fume and styrene-acrylic latex on the thermal properties of hardened concrete are similar to those on cement paste. By adding fly ash, silica fume or styrene-acrylic into concrete, the thermal sensitivity is greatly reduced and hence the thermal stability is optimized by changing the microstructure of concrete.