New Pavement Anti-cracking Layer Material And Its Pavement Performance Study

Numerous early-built cement concrete pavements are damaged badly under traffic and rainfall,and can’t satisfy people’s increasing travel requirements in China.One problem,which should be solved peremptorily,is to transform old cement concrete pavements to improve quality by repaving asphalt overlay.The asphalt overlay on old cement concrete pavement(CC+AC)is the form of pavement structure widely used at home and abroad.Rigid base can greatly improve the bearing capacity of pavement structure and asphalt overlay enhance the driving comfort effectively.Nevertheless,the key technical problem of this pavement structure is how to deal with the reflective cracking.Focusing on the application of anti-cracking layer material in old cement concrete pavement retrofitting,studied the asphalt cement of anti-cracking layer material.A new asphalt material for pavement structure anti-cracking layer were developed by using China National Offshore Oil Corporation70,asphalt thermoplastic styrene-butadiene rubber(SBS),crumb rubber modifier(CRM)and plasticizer(DBP)as raw material.The results show that the SBS dosage was 5%,the DBP dosage was 4%and the CRM dosage was 4%,and the pavement performance was evaluated by the United States SHRP asphalt evaluation system.A new grading design method for anti-cracking layer material was developed by optimizing the new SAC grading design method.A set of the reasonable distribution of the anti-cracking layer was designed and the rationality was verified by bailey method.Respectively used Superpave mathematical estimation method(Superpave method)and asphalt film thickness estimation method(DA method)to forecast the asphalt content for design gradation of anti-cracking layer material,got the predicted oil-stone ratio,Superpave method is 7.5%,DA method is 7.7%.The optimum oil-stone ratio mathematical formula calculation method for anti-cracking layer material was studied by gyration compaction(SGC)and Marshall test,and the best compaction times in Marshall test is 75 in the form of double compaction.The technical requirements of anti-cracking layer material in Marshall test were determined by regression analysis on the results from two tests,and the optimum oil-stone ratios of design grading were calculated as following,gyration compaction(SGC)test is 7.6%and Marshall test is 7.5%.The low-temperature performance,high-temperature performance and water stability of asphalt mixture in anti-cracking layer were studied by wheel tracking test,low temperature bending test and immersion Marshall test.Three different composite specimens were made and were tested by concentrated load fatigue test and partial load fatigue test.The contrastive analysis of anti-cracking performance was done and the results show that anti-cracking layer material has good pavement performance and delays the generation and extensions of reflective cracking effectively.The study results can provide important reference for the application of anti-cracking layer material in old cement concrete pavement retrofitting.