Polypropylene/Basalt Fiber Concrete In Typical Northwest Environment Repair Performance Study

The complex working environment is an important reason for the deterioration of mechanical properties and durability of concrete structures during service.The territory of our country is very vast,the natural climate and environment of different regions are different,and the corrosion diseases of concrete in the region are not the same.Northwest China is hot in summer and cold in winter,with large temperature difference between day and night and humidity difference.There are also a large number of saline-alkali lands in the region,which contain highly corrosive sulfate and chlorine salts,etc.The complex climate environment causes the water-facing reinforced concrete structures in the region to be influenced by various factors.The compound action of sulfate,dry and wet cycle and freeze-thaw cycle is the main cause of water-facing concrete disease in this area.A series of chemical and physical reactions occur when sulfate enters the concrete,resulting in the deterioration of local mechanical properties and durability of concrete,and the demolition of the whole structure consumes time and energy,so it is of great significance to repair and strengthen the local corroded part.Based on the previous research and test results of the research group,this paper takes "Research on the properties of polypropylene/basalt fiber reinforced concrete-Uniaxial mechanical properties of fiber reinforced concrete under the combined action of sulfate attack,dry and wet cycle and freeze-thaw cycle-Shear resistance of the interface between new and old concrete under the combined action of sulfate attack,dry and wet cycle and freeze-thaw cycle" as the main research line.The specific research contents are as follows:(1)By adding different amounts of polypropylene fiber and mixing with basalt fiber to ordinary silicate concrete and sulfate resistant cement concrete,the effects of single polypropylene fiber and mixed fiber on compressive strength,splitting tensile strength and volume stability of concrete were explored,and the comprehensive performance of concrete was evaluated by the efficiency coefficient method.The results show that a large amount of fiber will cause the loss of compressive strength of concrete,but will enhance the splitting tensile strength of concrete,and fiber has a limiting effect on the volume change of concrete.By using the efficiency coefficient method,the concrete mix ratio with good comprehensive performance was selected and used as the evaluation index of compressive strength,splitting tensile strength and volume change rate.(2)Select the mix ratio of two groups of concrete with good comprehensive evaluation performance in test(1)to study the uniaxial compression performance of concrete under the combined action of sodium sulfate,dry and wet cycle and freeze-thaw cycle.The results show that the fiber can improve the internal structure of concrete,and form a binding force on the inside of concrete,which can resist the expansion force caused by the accumulation of sulfate corrosion products and the expansion force of frozen water in the freeze-thaw cycle,and improve the sulfate corrosion resistance and freeze resistance of concrete matrix.Compared with single polypropylene fiber,mixed polypropylene basalt fiber can form a better three-dimensional network structure in the concrete interior,and has a stronger binding force on the concrete interior,which can better constrain the development of micro-cracks and the increase of voidage in the concrete interior.(3)Select the mix ratio of two groups of concrete with good performance after comprehensive evaluation in test(1)to conduct shear resistance test of new and old concrete bonding specimens under the combined action of sodium sulfate,dry and wet cycle and freeze-thaw cycle.The results show that the shear resistance of new and old concrete is closely related to the compressive strength of old concrete base.The strength of the old concrete base decreases little in the early stage of corrosion,and the damage mainly occurs at the interface of the new and old concrete.The strength of the old concrete base decreases greatly in the later stage of corrosion,and the damage mainly occurs in the old concrete base.