Experimental Study On Durability Of Recycled Concrete With Lithium Slag Under ASR-freeze-thaw

In recent years,with the rapid development of the country’s construction industry and industry,more and more construction waste and industrial waste from building demolition have been formed.After the relevant national policies put forward the strategy of sustainable development of environmental protection,how to deal with these construction waste and industrial waste has become a research question for many experts and scholars.Therefore,some scholars have proposed that the disused waste concrete be crushed and recycled for reuse as a recycled aggregate and incorporated into the concrete,which is not only green and environmentally friendly,but also can alleviate the demand for natural aggregates.Lithium slag powder,as an industrial waste for the production of lithium salts,is also a mineral admixture with a certain pozzolanic activity.Some scholars have incorporated lithium slag as a mineral admixture into concrete,which has a negative impact on the mechanical properties and properties of concrete.The durability performance has a certain improvement effect.Freeze-thaw cycles and alkali-silicic acid reaction(ASR)are important factors that affect the durability of concrete structures in Xinjiang.Further research on freeze-thaw damage and ASR of lithium-slag recycled concrete will help the promotion and application of lithium-slag recycled concrete in practical engineering.In this paper,the single action and composite action of ASR and freeze-thaw cycle of lithium-slag recycled concrete are mainly studied through the rapid mortar rod method and the concrete prism method.The results of the rapid mortar rod method show that: lithium slag powder can effectively inhibit the ASR of concrete,and the greater the amount,the more obvious the inhibition effect.However,the incorporation of recycled aggregate will aggravate the ASR of concrete,and as the replacement rate of recycled aggregate increases,the expansion of the mortar rod will gradually increase.The research results of the concrete prism method show that: when ASR and freeze-thaw cycle have a single effect,the appropriate addition of lithium slag significantly slows down the progress of concrete ASR,and at the same time significantly improves the frost resistance of concrete.The 20% lithium slag content is the best.The addition of recycled aggregates will aggravate the ASR of concrete to a certain extent and reduce the frost resistance of concrete.During the combined action of ASR and freeze-thaw cycles,the alkali silicic acid gel generated in the early stage of ASR will absorb water and swell,forming micro-cracks.Water penetrates into the concrete through the micro-cracks,increasing the content of freezeable water inside the concrete.The expansion and mass loss of large concrete reduce the dynamic elastic modulus and compressive and flexural strength of the concrete,thereby reducing the durability of the concrete in the later period.The early freeze-thaw damage will promote the penetration of external alkali and water,accelerate the occurrence of ASR between alkali and active aggregate,thereby aggravating the expansion and mass loss of concrete,and reducing the dynamic elastic modulus and compressive and flexural strength of concrete.The more serious the damage,the more serious the damage caused by the later ASR.When ASR and freeze-thaw cycles act on concrete together,the two promote each other,thereby reducing the mechanical properties and durability of concrete,which manifests as a cooperative destruction effect.The proper addition of lithium slag can improve the mechanical properties and durability of concrete,and the effect of 20%lithium slag is the best;the addition of recycled aggregates will reduce its mechanical properties and durability to a certain extent.