Study On Compaction Characteristics Of Polyurethane Mixture

Polyurethane mixture is a new road paving material that completely replaces asphalt with polyurethane as adhesive.Different from the strength formation mechanism of asphalt mixture,the bonding strength of one-component moisture-curing polyurethane adhesive is affected by various factors such as temperature,humidity,catalyst and time.Premature compaction will make the mixture to inflate,and when it is compacted too late,the mixture is cured to a high degree and is difficult to compact.Therefore,it is difficult to grasp the timing of the compaction after mixing during the construction process.In this paper,we studied the effects of the different curing conditions on the compaction characteristics of polyurethane mixture and revealed the root cause of the complex changes of the compaction characteristics,then proposed the determination of the optimal timing of the compaction after mixing for the one-component polyurethane mixture to provide a basis for the application and promotion of this new material.In the mix design study,a one-component moisture-curing polyurethane adhesive was used as the adhesive of AC-13 mixture.A design method based on performance balance was proposed.The initial adhesive aggregate ratio was determined to be 6.0%~8.0%by mixing the mixture and observing the adhesion and the leak test,without the occurrence of"flowering material"and the leakage loss rate?0.3%.In this range,we studied the variation of the volume characteristics and road performance of polyurethane mixture with the adhesive aggregate ratio,and found that with the increase of the adhesive aggregate ratio,the strength,high temperature,low temperature performance and water damage resistance indexes of the polyurethane mixture are improved,however,the anti-sliding performance was the only index that decreased.In order to ensure the compactness and anti-slip of the mixture,we uesed the air voids(VV)?4%and the friction coefficient(BPN20)?60 as the mix design control standards to determine the optimum adhesive aggregate ratio rage from 6.2%to 6.8%,and the optimum adhesive aggregate ratio was 6.5%.In the study of the compaction characteristics,we used temperature(5°C,25°C,45°C),humidity(20%,50%,80%),catalyst content(0%~1%),curing time(40min~120min)to obtain polyurethane mixture with different curing degree.By the compaction molding method,the compaction energy index(CEI)?air voids(VV)and 15°C split strength(R_T)were used to quantify the compaction characteristics of the polyurethane mixture..The compaction states of polyurethane mixture were divided into three categories by SPSS cluster analysy,which were easy-to-compact and inflate state(CEI<500,VV>6%,1.5MPa<R_T<2.0MPa)?compactable state(500?CEI?1000,VV?6%,R_T?1.5MPa)?hard-to-compact state(CEI>1000,VV>6%,RT<1.5MPa).We found that the change of curing degree of polyurethane mixture was the root cause of the complex change of compaction characteristics.Only when the curing reaction of polyurethane mixture was carried out to a proper degree for real-time pressure,the CO2overflow in the mixture had little effect on the void of the mixture,and The mixture was also in a state of being easily compacted,and the mixture after complete curing had a small void ratio and a high splitting strength.In the study of the optimal timing of the compaction after mixing,by studying the relationship between void ratio,the split strength and CEI under different curing conditions,the optimal compaction state of AC-13 polyurethane mixture was determined to be 600?CEI?800with void ratio?4%and the peak value of splitting strength,which indicated that CEI can judge the optimal timing of the compaction after mixing of polyurethane mixture.In order to adapt to the construction,based on the principle of impact penetration,we designed a set of simple equipment suitable for engineering to make the CEI penetration test.The impact penetration depth was used to reflect the curing degree of the polyurethane mixture.The 40th penetration depth of the 20mm penetration diameter was selected as the penetration evaluation index,and its fitting degree with CEI was R~2=0.93 that showed the feasibility of impact penetration to determine the optimal timing of the compaction after mixing.We determined that the penetration depth range of the AC-13 polyurethane mixture was 41mm~47mm,and the method of determining the optimal timing of the compaction after mixing by impact penetration was proposed and verified by rationality.