Optimization Of C50 Concrete For Pier In The Cold Area

With the need of economic development,highway bridge has become an important part of transportation system,and the strength and durability of pier concrete are the decisive factors to ensure the safety performance and service life of bridge.The cold climate and snow in northeast China have great influence on the service l ife of highway bridge.Because the construction and maintenance of highway bridge is expensive,the excellent durability of pier concrete will reduce the huge economic losses to the country.Industrial production has discharged a large number of fly ash,mineral powder and silica fume and other industrial by-products,not only pollute the environment,but also lead to waste of resources.Replacing cement in concrete with industrial by-products can not only improve the durability of concrete,but also reduce the cost of concrete,more conducive to the full use of resources,but also protect the environment.Therefore,studying the frost resistance,chloride ion permeability and shrinkage of pier concrete,optimizing the mix ratio with good durability and low cost can not only prolong the service life of highway bridge,but also avoid the waste of resources.Therefore,the topic selection has practical significance.According to the current Technical Specification for the Application of High performance concrete and the requirements of this project for the raw materials and properties of concrete,the main parameters of concrete are determined,and the water-to-gum ratio is determined according to the Paul rice formula.On this basis,high performance concrete mix ratios are designed.The mixture mixture of 30%,40%and 50%was mixed with an appropriate amount of air entraining agent,so that the gas content of concrete mixture was 3%,4%and 5%,respectively.The effects of admixture and gas content on the frost resistance and chloride ion permeability of concrete were studied by rapid freezing method and rapid chloride ion transport coefficient method(RCM method).The following conclusions are drawn from the above studies:The suitable ratio of fly ash and mineral powder can improve the frost resistance and chloride ion permeability of concrete;the frost resistance and chloride ion permeability of concrete increase with the increase of mineral admixture type;the increase of silica fume content can further improve the frost resistance and chloride ion permeability of concrete;the appropriate admixture compound content can improve the frost resistance of concrete,and the increase of admixture compound content can improve the chloride ion permeability of concrete;the increase of gas content of suitable mixture can increase the freezing resistance of concrete and increase the gas content will reduce the chloride ion permeability of concrete;The shrinkage of concrete will be promoted by wollastonite,and the shrinkage of concrete will be reduced by the increase of compound admixture;The optimum mix ratio of fly ash and mineral powder is 22.5%,silica fume is 5%and air content is 4%.