Key Technology Of Dry Shrinkage Performance Of Recycled Old Concrete Road Base Material

The cement-stabilized old concrete mixture has high stiffness and strength,and good water stability and frost resistance.Due to the rough surface of the old concrete aggregate covered with a large amount of hydration products such as cement mortar,loose and porous,large water absorption,etc.indoor tests and practical engineering applications have confirmed that the semi-rigid base course using the old concrete aggregate is prone to shrinkage,deformation and cracking in the environment where the temperature and humidity are alternately changed,which limits the application of the old concrete aggregate in the road base course.This study conducted a detailed study on the properties of recycled aggregates and how to reduce the shrinkage of cement stabilized recycled aggregate base.The research contents mainly include:(1)testing the physical and mechanical properties of the aggregate,analyzing the internal components of the aggregate,and studying its apparent morphology.(2)Four methods for improving the shrinkage of road base were explored.The methods of mechanical stirring,carbonization,grading improvement,and addition of metakaolin were used to test the changes in physical and mechanical properties and shrinkage of the cement stabilized recycled aggregate base mix after treatment,and explain the reasons for the changes.(3)Indoor test research on engineering test sections.The main research results are as follows:(1)There are two different growth rate regions for the shrinkage of cement stabilized recycled aggregates base.When the water loss rate is less than certain point,the dry shrinkage strain increases slowly;when the water loss rate is greater than that point,the dry shrinkage strain increases obviously.(2)Mechanical agitation,carbonization,grading improvement,and adding metakaolin can all reduce the shrinkage of water-stable base mixes to varying degrees.(3)After 14 days of carbonization of the aggregate,the optimum moisture content of the base mix was reduced by 6.23%,and the total shrinkage and total water loss rate of 27 days were reduced by 13.8% and 13.7% respectively.(4)After replacing the recycled fines in the mix with natural fines,the 27 d total dry shrinkage of the base mix was reduced.R100W(100% recycled aggregates use natural fines instead of recycled fines)is better than R100 Reduced by 22.3%.(5)Substituting metakaolin for a small part of the reclaimed fines in the mixture can not only increase the strength of the base,but also reduce the shrinkage of the base.(6)The mechanical agitation method is the most cost-effective way to reduce the shrinkage of the water-stable concrete aggregate base course.After 500 rpm treatment,the total shrinkage and total water loss rate for 27 days are reduced by 20.7% and 13.4% respectively compared with the untreated.