Study On Durability Of Steel Fiber Reinforced High Content Fly Ash SCC

Self-Compacting Concrete(SCC)is more prone to plastic cracking than ordinary concrete due to its low water binder ratio,high sand ratio and large amount of cementitious materials.Which increases the probability of cracks.Once the cracks appear,water,CO2,salt and other corrosive substances will invade through the cracks,which will lead to leakage,steel corrosion and other problems,and accelerate the deterioration of concrete,The concrete durability is insufficient and the fracture accident occurs,Using fly ash and steel fiber to modify SCC can not only improve its durability,but also improve its fracture mechanical properties.In this paper,the influences of fly ash substitution rate(0%,40%,50%,60%,70%)and steel fiber content(0%,0.25%,0.50%,0.75%,1.00%)on the impermeability,carbonization and sulfuric acid resistance of SCC was studied by chloride ion penetration test,carbonation test,sulfate attack test,three-point bending fracture test,microscopic scanning electron microscope and mercury intrusion test,and the mechanism of action was analyzed,and the following conclusions were drawn:(1)Study on chloride ion permeability and mechanism of SCC: Along with the increased of fly ash substitute,the electric flux of SCC first decreases and then increases.When the content of fly ash is 40%,the electric flux is the lowest,which belongs to the negligible permeability level,indicating that 40% fly ash can improve the compactness of SCC and improve the impermeability of SCC;The mercury injection test shows that the comprehensive analysis of the fractal dimension of pore structure and pore connectivity can more accurately predict the chloride ion permeability resistance of SCC.(2)Study on the carbonation resistance of SCC: The carbonization depth of SCC is positively correlated with the growth of carbonization age,while the growth rate slows down with the increase of carbonization age,and increased with the increase of fly ash substitution rate;After carbonization,the compressive strength first decreased and then increased,and the time when the minimum value of compressive strength appears is advanced with the increase of fly ash content,indicting that the existence of fly ash reduces the carbonization resistance of SCC,and the fly ash content is higher,the carbonization phenomenon is more significant.(3)Study on the sulfate attack of SCC: with the increase of fly ash content and dry wet cycle times,the evaluation index of SCC sulfate resistance first increased and then decreased.The corrosion resistance of SCC is optimized with the addition of steel fiber,and the optimization effect increases with the increase of steel fiber content.When the attack was 15 times,fly ash content was 40% and steel fiber 0.75%,the evaluation indexes reached the peak value.Therefore,the appropriate amount of fly ash and steel fiber is beneficial to the corrosion resistance of SCC.(4)Study on fracture mechanical properties of SCC before and after sulfate attack:before sulfate attack test,the fracture toughness and peak load of SCC first decreased and then increasd with the increase of fly ash and steel fiber content.The optimal value reaches when fly ash is 50% and steel fiber is 0.75%.The critical opening displacement and fracture energy first decreased and then increased with the increase of fly ash content and steel fiber content.The optimal value reaches at 70% fly ash and 0.75% steel fiber content.After 30 times of sulfate attack,the fracture properties of SCC increased first and then decreased with the increase of fly ash content,and increased with the increase of steel fiber content.The results show that the fracture toughness and peak load increased first and then decreased after sulfate attack,and the change rate increased first and then decreased with the increase of fly ash and steel fiber content.The maximum change rate of fracture toughness reaches 57%when the fly ash content is 50% and steel fiber content is 0.75%.The fracture energy and critical opening displacement decreased after sulfate attack,and the decreased rate decreased first and then accelerates with the increase of fly ash content,and continues to accelerate with the increase of steel fiber content.When the fly ash is 40%,the change rate of fracture energy reaches the lowest value of 3%,and the maximum value of 69% when the fly ash is 70% and the steel fiber is 0.75%.