Study On The Performance Of High Strength Concrete Modified With Rubber Powder After High Temperature

Spalling of high strength concrete at high temperature will reduce the load-carrying capacity of a structure, and this disadvantage will also prevent high strength concrete from application to more constructions. In the last decades, many investigators have tried their best to improve the property of high strength concrete at high temperature, and have provided us some good methods. On the other hand, when the tyres contributing themselves to our civilization, the waste it produced has also brought great threat to our society. Based on the improvement of the high temperature capacity of high strength concrete, this thesis explores a new green construction material, and provides a new method to improve the spalling property of high strength concrete by modifying with recycled rubber powder. The main work in this thesis including:1. The spalling phenomenon and mechanism of high strength concrete at high temperature were reviewed and discussed in terms of macrostructure and microstructure. The vapor pressure mechanism was discussed in details in conformity to experimental results.2. The high strength and high performance concrete with excellent flow-ability and durability, and a high compressive strength of more than 80MPa had been developed by using ordinary materials, low cementation dosage and traditional technology. The compressive strength, splitting strength, flexural strength, axial compressive and elastic modulus were investigated in this thesis. Durability research by electricity flux and chlorine hydronium seepage test was also carried out in this thesis. The microstructure of hard cement matrix was studied by SEM electron scan. Pictures showed that the high strength concrete has excellent mechanics property and compact microstructure.3. The high strength concrete is tested under fire. The compressive strength and the flexural strength were tested after fire. At the same time, the change of the color of specimen was observed and the mass loss rule was obtained. In order to explain the change of macrostructure of UHSC, the SEM micrographs of cementation after fire were taken. The results showed that the performance of high strength concrete (apparent integrality, compressive strength, flexural strength and microstructure) drop down after fire.4.Based on the high strength concrete, the workability, surface density and compressive strength of rubber powder modified concrete materials with the addition of 15 meshes (1120μm), 40 meshes (420μm), 60 meshes (250μm) and 80 meshes (178μm) of fine rubber powder respectively were studied in this thesis. Four different contents of rubber powder, such as 1%, 2%, 3% and 4% of the dosage of cementation, were added to the mixture or replaced the sand in the mixture. The results show that the workability of rubber modified high strength concrete, which didn't influenced by the dosage of rubber powder, is excellent. The density of rubber powder modified high strength concrete decreases with the increase of the contents of rubber powder, and is different when the granule of rubber powder is change. The compressive strength decreases with the increase of rubber powder, and the loss of compression strength will be lower than 10% when the addition of rubber is smaller than 10.8 kg/m~3.5. Experiments have been taken to study the property of rubber powder modified high strength concrete after fire. The compressive strength and flexural strength after different fire temperature are obtained. At the same time, the change of the color of specimen appearance is observed and the degree of mass loss is revealed. As the research shows that the strength and the mass of rubber powder high strength concrete had a little drop after 500℃temperature, and the spalling failure happened in some of specimens. The strength and the mass of rubber powder high strength concrete deteriorated, and most of the specimens spall after 800°C. The low dosage of 15 meshes and 40 meshes rubber powder can reduce the risk of HSC spalling under fire.6. The SEM micrographs of cementation after fire are taken in order to explain the change of macrostructure of rubber powder high strength concrete and discuss the spalling resistance mechanism of high strength concrete improved with rubber powder.