| Macroporous polyurethane mixture is a new type of permeable road pavement material,which uses polyurethane instead of asphalt as adhesive.It has excellent road performance,can be constructed at normal temperature,has the characteristics of energy saving and environmental protection,and can help the construction of "sponge city".It is a key research direction of new pavement materials in the future,but the defect of insufficient water stability has become the bottleneck of its popularization and application.Therefore,aiming at the defect of insufficient water stability of macroporous polyurethane mixture,this paper analyzes the strength formation mechanism of polyurethane mixture,starts with the improvement of hydrolysis resistance of polyurethane adhesive and interfacial adhesion between polyurethane and stone,and seeks the scheme to improve the water stability of macroporous polyurethane mixture,and verifies the comprehensive road performance of the improved mixture.Firstly,in the research of improving the hydrolysis resistance of polyurethane adhesive,by analyzing the hydrolysis mechanism of one-component polyurethane adhesive,an improvement scheme of adding Polymerized Carbodiimide(PCDI)to inhibit the hydrolysis of polyurethane was put forward.The water absorption,tensile strength and elongation at break of one-component polyurethane with different PCDI content(0%,0.5%,1%,1.5%,2%,3%)were tested to study the influence of PCDI content on water absorption,tensile strength and elongation at break of polyurethane specimens.The results showed that with the increase of PCDI content,the water absorption of polyurethane first decreased and then increased,and when PCDI content was 0.5%,the water absorption was the lowest.With the increase of PCDI content,the tensile strength first increased and then decreased.When PCDI content is 1%,the tensile strength is the highest.The reason is that with the increase of PCDI content,PCDI reacts with carboxyl groups in polyurethane hard segment,which leads to the decrease of hard segment content.When the hard segment content reaches a certain level,the tensile strength reaches its peak value,while if the hard segment content is too high or too low,the tensile strength will decrease to a certain extent.The elongation at break has no obvious change with PCDI content,but it is significantly higher than that of the specimen without PCDI.To sum up,adding PCDI can effectively improve the hydrolysis resistance of polyurethane,and the best content is 1%.Secondly,in the study of improving the interfacial adhesion between polyurethane and stone,silane coupling agents(KH550 and KH560)were added to improve the adhesion between polyurethane and stone.The contact angle and peel strength tests were carried out on polyurethane samples with different silane coupling agent contents(0%,1%,2%,3%,4%,5%),and the effects of silane coupling agent types and contents on polyurethane surface energy,adhesion work and peel strength were studied The results show that with the increase of silane coupling agent content,the surface energy of polyurethane first decreases and then increases.The optimum content of KH550 and KH560 is 2% and 4%,respectively,and the surface energy is 21.22 m J/m2 and 26.31 m J/m2,respectively.The adhesion work first increased and then decreased,and the best content of KH550 and KH560 was 2% and 3%,respectively,and the adhesion work increased by 18.56% and 13.99% compared with ordinary polyurethane respectively.The peel strength first increased and then decreased.The best dosage of KH550 and KH560 was 2% and 3%,respectively,and the peel strength increased by 20.65% and 16.66%respectively compared with ordinary polyurethane.The reason is that with the increase of silane coupling agent,the generation of Si-O-Si cross-linked network structure in polyurethane adhesive will be promoted,thus improving the adhesion between polyurethane and stone,but it will also lead to the increase of micro-phase separation between hard and soft segments in polyurethane.When the micro-phase separation increases,the force between hard and soft segments will be reduced to a certain extent,resulting in the decrease of adhesion between polyurethane and stone.Therefore,there is the best dosage of silane coupling agent.To sum up,KH550 is selected,and the best dosage is 2%.Finally,the road performance of the improved macroporous polyurethane mixture(adding 1% PCDI and 2% KH 550)was verified.Road performance tests include Marshall stability,dynamic stability,low-temperature bending test and water stability test,among which water stability tests adopt three conventional test methods: immersion flying,immersion Marshall and freeze-thaw splitting test,which are compared with the proposed optimized water stability test method.The results show that the Marshall stability,dynamic stability and low-temperature flexural-tensile strain of the improved macroporous polyurethane mixture are 46.25 k N,37,474 times/mm and 34,250.50με,has no significant difference with ordinary polyurethane mixture,but far exceeds OGFC asphalt mixture of the same class.As far as water stability is concerned,because the mass loss of polyurethane mixture can still keep a small value when the strength of polyurethane mixture is greatly reduced,the immersion flying test is not suitable for evaluating the water stability of polyurethane mixture.For immersion Marshall test,freeze-thaw splitting test and optimized water stability test,the stability residual ratio,DSR and residual splitting strength ratio of the improved macroporous polyurethane mixture are 89.03%,76.33% and 82.36% respectively,which are significantly higher than those of ordinary polyurethane mixture,and increase by 50.80%,98.31% and 60.07% respectively,while DSR and residual splitting strength ratio are slightly lower than those of OGFC asphalt mixture It shows that the water stability of the improved macroporous polyurethane mixture has been significantly improved,which is close to OGFC asphalt mixture,and its comprehensive road performance is significantly better than OGFC. |
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