Research On The Improvement Of Water Stability Of Single-component Polyurethane Mixture

Polyurethane mixtures with excellent road performance and low energy consumption and emissions during construction are expected to replace asphalt mixtures in areas such as bridge deck paving and snow and ice removal,but the lack of hydrolysis resistance of polyurethane leads to poor water stability and becomes an obstacle to the promotion and application of polyurethane mixtures.Studies have been tried to adjust the isocyanate index,glass transition temperature or the ratio of soft and hard sections of polyurethane,or to change the aggregate type and grading structure of the mixture,but the actual improvement is limited and even has a negative impact on other road properties.Therefore,this article improves the water stability of polyurethane mixtures by adding modifiers to enhance the hydrolysis resistance of polyurethane adhesives and the adhesion between polyurethane and aggregates.Firstly,this paper uses single-component polyurethane as an adhesive to improve the water stability of polyurethane blends in terms of both hydrolysis resistance and adhesion,and adds two different kinds of polymerized carbodiimide compounds(PCDI)with different characteristics to enhance hydrolysis resistance and two different kinds of silane coupling agents(SCA)to enhance the adhesion performance at 0%,1%,2%,3% and 4%.The recommended dosing range and optimum dosing of each modifier were determined by water absorption,tensile test and surface energy test.The results show that the use of two PCDI modifiers can reduce the water absorption of polyurethane adhesives,improve the tensile strength and tensile strength retention after water immersion,and improve the hydrolysis resistance of polyurethane adhesives.The use of 2 SCA modifiers can make the adhesion work of polyurethane under water-free condition increase,while the absolute value of peeling work under water condition decreases,so the modified polyurethane has better adhesion performance and resistance to water damage.The recommended dosage of PCDI1 is between 1～2%,PCDI2 is between 2～3%,SCA1 is between 2～3% and SCA2 is between 1-2%.Next,microscopic tests were performed on the modified polyurethane.Field emission scanning electron microscopy(FESEM)and atomic force microscopy(AFM)tests were performed to observe the microscopic surface morphological changes of polyurethane specimens,and Fourier transform infrared spectroscopy(FTIR)and X-ray diffraction(XRD)tests were performed to detect the changes of functional groups and chemical composition of the materials.The results showed that FESEM was difficult to determine whether the damage on the surface of the specimens was caused by water damage or by the preparation and maintenance of the specimens,so it was not suitable for directly judging the improvement effect.the AFM results showed that PCDI improved the hydrolysis of polyurethane and the degree of separation of the microphase regions in the soft and hard segment regions,and SCA caused an increase in the agglomeration of the hard segments in polyurethane,resulting in an increase in the roughness of polyurethane.FTIR determined the constitutive form of polyurethane by the peak of each functional group,and the change of C=O and-NH peak intensity of urethane in polyurethane proved that PCDI effectively inhibited the hydrolysis of polyurethane,and the stretching vibration peak of alkoxy dehydration condensation product Si-O-Si proved that SCA reacted with polyurethane,which caused the change of functional group characteristics of polyurethane.The peak changes in XRD characterized the effect of PCDI on the inhibition of hydrolysis and the effect of SCA on the increase of cross-linking and cohesion of polyurethane.Finally,OGFC-13 polyurethane blends were prepared for road performance tests and the significance of the improvement effect was evaluated by ANOVA method.The results show that for the high and low temperature performance tests,both unmodified and modified polyurethane mixes have sufficient resistance to high temperature rutting and low temperature cracking,and far exceed the technical requirements for asphalt mixes in the technical specifications for road asphalt pavement construction,so the polyurethane mixes can meet the requirements for road pavement use.However,for the PCDI type modifier,it may slightly reduce the low temperature crack resistance of the polyurethane mixture.The water stability test showed that two PCDI modifiers and two SCA modifiers can significantly improve the water Marshall stability and freeze-thaw splitting strength of polyurethane mixture specimens,and the effect of SCA class modifiers is more significant than PCDI class,in addition,the water stability performance of modified polyurethane mixture growth trend and modified polyurethane mechanical tensile strength,peeling work trend with The trend of water stability of modified polyurethane blends was consistent with the trend of mechanical tensile strength and peeling work of modified polyurethane.The water Marshall stability of the modified polyurethane mixture is above 20 k N,which is much higher than the technical requirement of not less than 3.5k N for the Marshall stability of OGFC asphalt mixture,and also much higher than the water Marshall stability of 5k N～7k N for the same grade of asphalt mixture.The freezethaw splitting strength of the modified polyurethane mixture is above 1.0MPa,which exceeds the freeze-thaw splitting strength of 0.3MPa～0.6MPa of the same grade asphalt mixture.This indicates that the water stability of the modified polyurethane mix was improved,and the stability,mechanical strength and high and low temperature properties were significantly better after water immersion compared with the OGFC asphalt mix.In terms of improvement effect,SCA1 modifier is recommended,which has a more obvious improvement for the water stability of single-component polyurethane mixtures,and also has a certain gain effect on the high and low temperature performance of the mixture.