Research On Foaming Characteristics And Pavement Performance Of Foamed Warm-mix Asphalt

Foamed Warm mix asphalt mixture is a pavement material that mixing the aggregate with low viscosity foamed asphalt,it can mixing and compaction at lower temperature,and 1%-5% water of asphalt is needed in the foaming process,which has the advantages of economy and environment protection.At present,the foamed warm mix asphalt mixture mainly exists the problems of asphalt foaming and aggregateasphalt adhesion.Based on the above analysis,the foaming and rheological properties of asphalt were studied,the interface adhesion of aggregate and foamed asphalt was analyzed by surface free energy theory,the influence of admixture on the performance of asphalt foaming and foamed warm mix asphalt mixture was investigated,and the pavement performance of foamed warm mix asphalt mixture and hot mix asphalt mixture was compared.First,the foaming characteristics of 70# virgin asphalt and SBS modified asphalt were studied,the influence of foaming water content,foaming temperature and gas flow rate on asphalt foaming effect was mainly analyzed,and the action mechanism of admixtures on asphalt foaming was explored.The best foaming parameters of 70# virgin asphalt: foaming water content is 1.5%,foaming temperature is 150?,gas flow rate is1.5m3/h;the best foaming parameter of SBS modified asphalt: foaming water content is1.5%,foaming temperature is 170?,gas flow volume is1.5m3/h.The result shows that,foaming Water content is the most important factor affecting asphalt foaming,foaming temperature and gas flow have little effect on the foaming characteristics of asphalt,the addition of sixteen alkyl three methyl ammonium bromide significantly improves the stability of foamed asphalt.Secondly,using the dynamic shear rheometer(DSR)study the effect of foaming process to virgin asphalt and SBS modified asphalt,the high temperature rheological and fatigue properties of foamed asphalt were tested based on temperature scanning mode and time scanning mode respectively,and the low temperature performance of foamed asphalt was evaluated by glass transition point.The foaming process has a certain influence on the rheological properties of the virgin bitumen and SBS modified asphalt.Compared with the foam asphalt,SBS modified foam asphalt has better high temperature stability,low temperature cracking resistance and fatigue performance.Then,the adhesion between aggregate and foamed asphalt was studied based on the surface free energy theory,and the influence of foaming process on the surface free energy and it's component of virgin asphalt and SBS modified asphalt was analyzed,and cohesive strength,adhesion work indexes(in the case of water and without water)were used to evaluate aggregate-asphalt adhesion strength,and the influence of foaming process and admixtures on aggregate-asphalt adhesion characteristics was explored.Foaming process can reduce the aggregate-asphalt adhesion work with water,while the addition agent sixteen alkyl three methyl ammonium bromide changes the dispersive and polar components of asphalt,and improve the cohesion of foamed bitumen,which is favorable for the adhesion of foam asphalt to aggregate.Finally,through the mix design of foamed warm mix asphalt mixture,the compaction characteristics of foamed warm mix asphalt mixture and SBS modified foamed warm mix asphalt mixture were analyzed based on voidage index,the influence of compaction temperature and admixture sixteen alkyl three methyl ammonium bromide on pavement performance of foamed warm mix asphalt mixture were studied,and the pavement performance of foamed warm mix asphalt,SBS modified foamed warm mix asphalt and its corresponding hot mix asphalt mixture was compared.The result shows that,the addition of sixteen alkyl three methyl ammonium bromide can enhance the adhesion strength of aggregate and foam asphalt,which is beneficial to the water damage ability and high temperature stability of foamed warm mix asphalt mixture.The pavement performance of SBS modified foamed warm mixed asphalt mixture is equivalent to that of SBS modified hot mix asphalt mixture,the water stability of foamed warm mix asphalt mixture needs to be improved,the addition of sixteen alkyl three methyl ammonium bromide into the foamed asphalt is an effective way to improve the water stability of the foamed warm mix asphalt mixture,so it can replace hot mix asphalt.