Analysis And Control Of Gradation Variation In Construction Process Fof Asphalt Pavement

The construction process of asphalt mixture is complex and the construction quality will affect the performance of pavement.Gradation is an important parameter of asphalt mixture and its variation has a certain impact on the pavement performance and service life.In order to improve the quality of construction,this paper studied the gradation variation in the construction process and its control methods,mainly including the following four aspects:Firstly,the influencing weights of high temperature stability,low temperature crack resistance and water stability for seven different types of mixtures(AC-13,AC-16,AC-20,SMA-13,SUP-13,SUP-20 and SUP-25)were determined by the combination of the entropy weight method.Then the relationship between the passing percentage of each sieve and the pavement performance was analyzied through and gray correlation theory to determine the control sieves.The results showed that the passing percentage of 4.75 mm and 0.075 mm sieves have significant impact on pavement performance of all types of mixture and passing percentage of 2.36 mm has significant impact on the performance for AC-13 and SUP-13.Furthermore,particles larger than 9.5mm have a close relationship with the performance of asphalt mixture,which should be strictly controlled under the situation of weak control of large particles.Secondly,the fluctuation of aggregate,gradation variation of asphalt mixture in construction process and their influencing factors were studied.As an important components of the mixture,the passing percentage by weight for aggregate is ustable.When the particle size range was larger,the possibility and degree of aggregate variation was greater.The index of fluction was introduced to evaluate aggregates.At the same time,the paper studied the gradation variation of asphalt mixture based on practical projects.It was found that under the current construction capacity,the mixing process had little impact on the gradation of the mixture and the gradation variation in transportation process was the largest.The paving process had a certain improvement effect on segregation mixture.In the construction of asphalt mixture,the change of gradation was complex and the variation of gradation did not develop in a certain adverse direction.The subsequent construction process might not only enhance the variation of gradation,but also reduced the variation.Through the influencing factors of gradation variation,it is found that the gradation variation was affected by pavement grade,mixture type,nominal maximum size of aggregate,transportation condition and transportation time.When the construction level is close to each other,the mixture gradation with large nominal maximum particle size,low road grade,poor road condition and long transportation time is more likely to be severe.Thirdly,back-calculation method of allowable fluctuation range for aggregate gradation was proposed based on the allowable control range of mixture.The results showed that the allowable fluctuation range of aggregate passing rate was wide.P-P method and K-S test were adopted to study the probability distribution of passing percentage under normal construction conditions.The results showed that the passing percentage of each sieve presented a normal distribution law in the process of mixing,transportation,paving and compacting.Based on the construction data,the matching degree of the current construction capacity and the allowable deviation range in specifications was verified.The allowable gradation deviation ranges in the construction process was modified and new control range of gradation according to the current construction capability was determined for high-grade highway.Finally,the method of grading monitoring based on image block processing was studied.Compared with single threshold processing,it was found that this method could improve the recognition accuracy of aggregate particles by about 10%,which could improve the problem of insufficient recognition accuracy of aggregate particles under natural light conditions to some extent.By modifying the Xbar-R chart in SPC control method,a grading dynamic control system was established for the control sieve in sensitive process of gradation variation to ensure the stability of the construction process.