Preparation Of Organic Montmorillonite By Freeze-Drying Method And Its Application In Modified Asphalt

Montmorillonite(MMT)is a kind of lamellar mineral clay type asphalt modifier which is widely studied at present.It has hydrophilic properties due to its high surface free energy,so it is prone to agglomeration when mixed with asphalt.Therefore,it is not conducive to its uniform dispersion in the asphalt.In order to improve the compatibility of MMT with asphalt,the organic montmorillonite(OMMT)is prepared and the surface of the OMMT can be changed into a lipophilic property,so that the OMMT is uniformly dispersed in the asphalt.Currently,OMMT is prepared by vacuum hot drying method,but surface hardening occurs in OMMT during drying processs and ball milling is required to obtain OMMT of the required particle size.Furthermore,ball milling inhibits the enlargement of the OMMT sheet spacing while the yield of the prepared OMMT is not high.Therefore,the OMMT was prepared by freeze-drying method in this paper to overcome the shortcomings of preparing OMMT by vacuum thermal drying method,and its structural properties as well as the application of OMMT in modified asphalt were studied.The main contents are as follows:Firstly,the freeze-drying process was optimized.We found that when the mass ratio of deionized water to MMT is 15:1,OMMT has the shortest drying time;The OMMT was characterized by X-ray diffraction(XRD)and scanning electron microscopy(SEM).The results show that freeze-drying can enlarge the OMMT slice spacing and refine OMMT particles.Secondly,OMMT modified asphalt was prepared by incorporation of OMMT prepared by freeze-drying method.Three major indexes(softening point,ductility and penetration),Brookfield viscosity and dynamic shear rheological(DSR)tests were carried out on different amounts of OMMT modified asphalt to study the physical properties and high temperature rheological properties of modified asphalt.The modified asphalt was treated by film oven(TFOT)and pressure aging vessel(PAV)to simulate short-term aging and long-term aging of asphalt,respectively.Three major indexes,DSR and low temperature bending beam rheology(BBR)tests were carried out on the modified asphalt after aging.The effect of OMMT on the thermal aging resistance of the modified asphalt was studied,and the optimum OMMT dosage was explored.The results show that the softening point and failure temperature of OMMT modified asphalt are significantly improved,and the ductility,penetration and Brookfield viscosity are decreased.OMMT makes the modified asphalt obtain better resistance to high temperature rutting.In addition,the introduction of OMMT can effectively delay the degradation of the modified asphalt after aging,and determine the optimal OMMT content is 3wt%.Finally,on the basis of determining the gradation of the mixture and the optimum ratio of oil to stone,the asphalt mixture is prepared by using the optimal amount of OMMT modified asphalt,and the water stability,high temperature rutting resistance and low temperature crack resistance of the mixture are obtained.The test was conducted to study the effect of OMMT on the road performance of the modified asphalt mixture.The results show that the OMMT modified asphalt mixture has good water damage resistance and high temperature rutting resistance,and its low temperature crack resistance is slightly reduced,but it still meets the"Technical Specifications for Highway Asphalt Pavement Construction"(JTG F40-2004)requirements for the performance of modified asphalt.