Research On Preparation And Performance Of Frost-resistance Concrete

At present, air entraining had become a major means to improve the frost resistance of concrete, the air content of concrete was controlled to control the frost resistance of concrete was a method commonly used in engineering application. There were mainly two problems in the application of frost-resistance concrete, the first problem was the contradiction between improving the frost resistance by increasing air content and keeping compressive strength of concrete; the second problem was the loss of air content and resulting in the air content of concrete entity less than the design value and reduce frost resistance.In this paper, from the perspective of concrete preparation, the effect of air-entraining agent on performance of concrete was studied first, and then three optimized pore structure of concrete ways including changing W/B, dosage of chemical admixture and mixing time were used to optimize pore structure of concrete, and the influence of production technology and construction conditions of concrete on loss of air content and slump was discussed at the same time. Reveal the basic rules were as follows.(1) The dosage of air-entraining agent in the range of 0 to 0.06%, influence of C30 and C40 was in good agreement. Air content and slump of fresh concrete increased with increasing the dosage of air entraining agent, compressive strength and elastic modulus of concrete decreased with increasing the dosage of air entraining agent. Ratio of flexural strength to compressive strength increased with increased dosage. The frost resistance of concrete was significantly improved with air-entraining agent and early shrinkage cracking of concrete was inhibited effectively. The resistance of early shrinkage cracking increased with increased the dosage of air-entraining agent.(2) W/B in the range of 0.33 to 0.51, air content of concrete first increased and then decreased with increasing W/B, when W/B was 0.39, air content was the highest. The compressive strength, elastic modulus and frost-resistance decreased, average chord length increased, spacing factor first decreased and then increased with increasing W/B. Spacing factor was highest when W/B was 0.39.(3) Air content would be reduced with single or double of fly ash and slag. The dosage in range of 0 to 30%, slump decreased with increasing dosage of slag and slump first decreased and then increased with increasing dosage of fly ash, slump was the highest when dosage of fly ash was 10%. The mechanical properties decreased with increasing dosage of fly ash and first increased and then decreased with increasing dosage of slag. The frost resistance of concrete would be increased, average chord length would be refined and spacing factor would be decreased with chemical admixture. It was significantly affected when dosage of fly ash was 30%.(4) Mixing time in the range of 80 s to 140 s, air content first increased and then decreased with extending mixing time, air content of C30 and C40 were highest when mixing time were 120 s and 100 s. Slump was highest when mixing time was 100 s. There was no-influence on mechanical properties with mixing time. The frost-resistance level was F300 when mixing time was 120 s. Average chord length decreased and spacing factor first decreased and then increased with extending mixing time and spacing factor was the lowest when mixing time was 120 s.(5) The initial air content and slump increased with increasing dosage of superplasticizers. The initial air content and loss of air content with PCC were grater than concrete with NFS. The construction time was efficiently extended by adding superplasticizers second time. Whether it was bleeding was mainly affected by dosage of adding superplasticizers second time and compressive strength was mainly affected by dosage of adding superplasticizers first time.