Zhang Jie
CCCC First Public Bureau Southwest Engineering Co., Ltd
Abstract: Through the study of rutting hazards, the construction scheme of semi-flexible rutting anti-rutting asphalt mixture is proposed. After the analysis of the selection of raw materials and construction equipment, the analysis and discussion of the construction process of semi-flexible asphalt pavement were carried out from the aspects of original pavement milling, large void base mixture paving, grouting construction, and plastering. It is found that the use of semi-flexible rut-resistant asphalt pavement can effectively improve the rutting hazards of the original road, reduce the deflection, improve the overall bearing capacity and flatness of the road, and effectively control the road structure through the surface scraping technology.
Keywords: asphalt pavement; Mix ratio design; construction technology; grouting technology;
About author:ZHANG Jie(1990—),male,undergraduate,bachelor,engineer,research direction:road and bridge construction technology.;
0 Introduction
Under the combined action of high temperature and heavy load, asphalt pavement is very prone to plastic deformation and rutting. Through the analysis of the semi-rigid pavement, it is found that the semi-rigid pavement has good rutting resistance. At the current stage, the more common semi-flexible pavement comprises the poured semi-flexible pavement, the cement asphalt concrete pavement and the cement emulsified asphalt concrete pavement, among these pavements, the shrub semi-flexible pavement has been most widely used, according to the numerical analysis of the mechanical properties of the pavement, it can be seen that this pavement has strong shear deformation resistance.
1 Project Overview
Under the influence of factors such as road structure, environment and vehicle load, the rutting phenomenon in areas such as intersections and traffic stations is very prominent, and some road sections even have very serious pothole problems. Despite several renovations, these problems have not been completely eradicated. In order to ensure the safety and comfort of vehicles and improve the traffic efficiency of the city, the project plans to use semi-flexible rut-resistant asphalt pavement at an intersection with the most serious rutting in an urban area. Due to the severe damage of the original pavement layer, it needs to be repaired. The test section of the semi-flexible rutting resistant asphalt pavement of the highway is 900 m long and 5~16 m wide, and the treated pavement structure is 5~6 cm thick semi-flexible SFP-13, emulsified asphalt adhesive layer oil, 6~7 cm thick high-modulus modified asphalt mixture, emulsified asphalt adhesive layer oil, and the original pavement after milling treatment from top to bottom. The specific structure is shown in Figure 1.
2. Raw materials and construction equipment
2.1 Basic quality parameters of raw materials
For the large-porosity asphalt mixture of SFC-13 semi-elastic pavement, the porosity should be between 27%~29% with reference to the design requirements of drainage pavement material, the asphalt is modified by SBS, and the dosage is 2.9%, and the JGM-301 semi-flexible pavement grouting material produced by Subote Material Company is used, the water-to-material ratio of the grouting material is 0.49, and it is brown-black powder at room temperature, the initial flow rate is 11.3 s, and the flow rate of 30 min is 12.1 s, the initial setting time was 0.9 h, the final setting time was 1.5 h, the pressure resistance was 15.2 MPa for 2 h, the pressure resistance was 46.9 MPa for 28 h, and the drying shrinkage was 0.12% for 28 days. This type of slurry has the advantages of good fluidity, low shrinkage, high strength, etc.
Fig.1. Asphalt pavement structure Download the original drawing
MA103 high modulus asphalt modifier was added to AC-20 with a design ratio of 0.3%. Through the study of the Marshall dynamic stability, 38 500 times/mm, and freeze-thaw-split-crushing rate of 97.3% of SFP-13, good rutting resistance was obtained[1].
2.2 Construction equipment
On this basis, cement-based mixtures with excellent fluidity, permeability, segregation, water leakage and other indicators should be used. Therefore, in the grouting process of semi-flexible asphalt pavement, the special pulping machine of semi-flexible asphalt pavement produced by Subote Materials Company is used, and there is no need to configure a slurry machine, and the equipment is transported to the site by trailer, and the material measurement used is automatically measured. It can solve the problems of low work efficiency and poor pavement appearance quality brought about by the simple use of slurry mixer at present. The specific steps of semi-flexible asphalt pavement construction: high modulus asphalt mixture paving and rolling, large void asphalt mixture paving and rolling, grouting, etc., and conventional construction equipment is used in the construction of other links.
2.3 Mix design
According to the work experience, the ratio of oil and stone was set to 3.0%, and a sample was made by 50 times of compaction on both sides, and the porosity and Marshall stability of the sample were measured, and the sample test results are as follows:
Gradation 1: stability 4.05 k N, to meet the needs of more than 3.0 k N, flow value 33.7 (0.1 min), to meet the needs of 20~40 (0.1 mm), porosity 27.8%, to meet the needs of 25%~31%, maximum theoretical relative density 2.763.
Gradation 2: the stability is 4.28 kN, which is not less than 3.0 kN, the flow value is 30.8 (0.1 mm), which meets the maintenance between 20~40 (0.1 mm), the porosity is 29.4%, and the maintenance is between 25%~31%, and the maximum theoretical relative density is 2.762.
Gradation 3: stability 4.51 kN, not less than 3.0 kN, flow value 2.77 (0.1 mm), maintained at 20~40 (0.1 mm), porosity 31.5%, slightly higher than the upper limit of the required range, maximum theoretical relative density of 2.761.
According to the above gradation, three different oil-stone ratios of 2.7%, 3.0% and 3.3% were preliminarily selected, and the samples were made by the method of 50 times on each side, and the porosity and Marshall stability of the samples were measured, and the optimal oil-stone ratio was obtained, and the test results were as follows: when the oil-stone ratio was 2.7%, the stability of the sample was 4.41 k N, which was greater than 3.0 k N, and the flow value was 27.2 (0.1 mm), which was maintained at 20~40 (0.1 mm), and the porosity was 30.6%, which was maintained at 25% ~31% (0.1 mm), the highest theoretical relative density is 2.771, when the oil-stone ratio is 3.0%, the stability is required to be 4.75 k N, the flow value is 30.5 (0.1 mm), 20~40 (0.1 mm), the porosity is 29.5%, the maintenance is 25%~31%, the maximum theoretical relative density is 2.760, when the oil-stone ratio is 3.3%, the stability is 4.81 k N, and the stability is 3.0 k The flow value is 32.7 (0.1 mm), which meets the requirements of maintaining in the range of 20~40 (0.1 mm), the void ratio is 28.8%, and the maximum theoretical relative density is 2.752[2].
The results show that the technical properties of the asphalt mixture meet the design requirements within the range of the ratio of oil and stone. However, when the two-phase ratio of oil and stone is 2.7%, the porosity in the mixture has reached the maximum allowable value, which will affect the construction process, and the ratio of 3.3% of oil and stone is slightly insufficient, so that the optimal oil-stone ratio of 3.0% is obtained.
3. Construction of the test section
3.1 Milling of the original pavement
Before paving the semi-flexible pavement, it is necessary to mill the original pavement that does not meet the design thickness requirements, and the milling depth must be controlled, and the transverse joints should be vertical flat joints [3]. After milling, a comprehensive cleaning is carried out to ensure that the original road surface after cleaning is free of peeling and loose particles. If there is serious damage on the original road, it is necessary to take treatment measures. In addition, in order to improve the bonding capacity between the layers, the original road is sprayed uniformly, and the spray area between the semi-rigid base layer and the surface layer is 0.7~1.2 and 0.4~0.7 respectively, and the spray area of the junction between the asphalt and the curb and the rest of the road surface is increased to 1.5.
3.2 Large void base mixture paving
The construction of large void base mixture specifically includes the steps of base asphalt preparation, transportation, paving and rolling. In these steps, the mixture preparation, transport and paving are carried out in accordance with the construction requirements of the OGFC drainage asphalt pavement. By demulsifying the emulsified asphalt, the paving of large pores is realized. When paving, the looseness coefficient of the mixture is controlled between 1.10~1.15, and the 12 t drum roller is used to oscillate and roll three times in a row on the joint part of the new and old road surface and the contact surface between the road surface and the curb; on the newly laid road surface, the 12 t drum roller is used to hydrostatically press 7~9 times outside the lap joint and the dividing line, and the overlapping ratio between the wheel and the wheel is 1/3~2 times; in the mixing process, when the temperature of the mixture drops to 80 °C, it is leveled. Two initial pressure tests were performed at a rate of 1.5~2.5 km/h, 3~4 times at a rate of 2.5~3.5 km/h, and then 2~3 times at a rate of 4.0~6.0 km/h. The compactness of the base mixture with large pores must be greater than 97%, and the maximum and average values of flatness must not exceed 10 mm. In areas where the flatness and density are unqualified, the static pressure should be re-pressed with the drum until it is qualified. For substrates with large porosity, the temperature is determined according to the nature of the asphalt used, on the basis of the large porosity. The construction temperature control requirements of the semi-flexible asphalt pavement are shown in Table 1.
Table 1 Requirements for temperature control of large void base mixture Download the original drawing
3.3 Improvement of grouting methods
The grouting technology directly affects the efficiency and quality of grouting construction, and the two methods are compared. In the pump pressure grouting mode, the pulping equipment does not need to pass through the asphalt concrete pavement, and there will be no damage such as tire pressure pits, in a short time, in order to quickly reduce the temperature of the concrete pavement to within 50 °C, the pump pressure grouting mode can be adopted, which not only has high construction efficiency, but also can greatly reduce the grouting waiting time after the asphalt concrete paving and rolling of large gaps, and shorten the whole construction period. Semi-flexible pavement of different widths is pumped with pressure grouting, which can be carried out simultaneously on multiple lanes.
3.4 Grouting construction
Combining the efficacy characteristics of the slurry material with the convenience of engineering construction, under normal circumstances, the preparation of the slurry is carried out on site, and the slurry material and water can be prepared by special pulping equipment, and the auxiliary material crane, transport vehicle and water wheel can also be carried out on the site, so as to ensure the continuity and efficiency of the construction. Cement mortar is a special asphalt mortar, which has good permeability, fast improvement of early strength, no shrinkage, uniform color and good effect. The performance of cement mortar material is shown in Table 2, before the grouting, when the mixture of large holes has not been completely cooled, the periphery of the mixture is covered with edge banding material to prevent the mixture from polluting the surrounding road surface and curb after overflowing, and create favorable conditions for the subsequent grouting and plastering construction. The prepared cement slurry is filled with a water pump in time to avoid long-term shelving and adverse impact on the engineering properties of the cement slurry. In asphalt concrete with large porosity, grouting should be carried out under conditions below 40°C, and after the construction starts, the concrete slurry should be pumped onto the large-pore asphalt pavement to be constructed, so that the concrete slurry will permeate in a self-flowing state under the influence of gravity [4].
Table 2 Properties of cement mortar materials Download the original figure
In the grouting process, it is necessary to monitor the grouting saturation of large-hole concrete in real time, and use the filling rate of the slurry hole to reflect the grouting saturation. Specifically, firstly, the basic parameters such as the amount of grouting material, the pouring construction area, and the paving thickness are determined, and then the actual amount of slurry and the volume of asphalt mixture are calculated, and then the volume of cement mortar slurry, the volume of asphalt mixture, and the connected porosity of large void mixture are used as the basis to determine the void filling rate of the slurry. The test shows that the porosity of asphalt concrete is 87.2%~92.7%, which meets the design index of not less than 85%.
3.5 Match-facing construction
In the construction process of semi-flexible asphalt pavement, the selection of plastering tools and their quality control should also be carried out to obtain better pavement construction depth and better pavement shape effect. In view of the fact that the construction scope of semi-flexible asphalt pavement is very small, and mechanized surface plastering construction equipment cannot be adopted, so in the test stage, the scraping effect of manual plastering tools such as rubber steel harrow, brush harrow, cork wood harrow, and ordinary wood rake is compared. The results show that the coating effect is the best when the brush rake scraping method is used, the semi-flexible asphalt pavement has uniform color, clear texture, no floating slurry, the largest structural thickness, and the best anti-skid performance. Therefore, in this test section, a brush is mainly used for manual shaving and plastering. In order to improve work efficiency and facilitate quality management, the brush is modified into a handheld semi-automatic scraper with adjustable vibration frequency, so that it can easily move forward, and within its working radius, the semi-flexible pavement will basically not appear floating slurry, and more than 90% of the construction depth can be controlled between 0.7~1.0 mm.
4 Effect evaluation
4.1 Evaluation of carrying capacity
Adopt the Beckman beam method, the deflection performance of this semi-flexible asphalt pavement before and after construction is tested, and based on the results of the test, the bearing capacity of the pavement is evaluated, the deflection of asphalt pavement before and after paving is shown in Figure 2, it can be seen from the figure below, before paving, the deflection range of semi-flexible asphalt pavement is 0.24~0.46 mm, after paving, the deflection range of pavement is 0.08~0.23 mm, and after paving, the deflection range of pavement is 68%; The pavement technology improves the bearing capacity of the asphalt concrete pavement and improves the rutting resistance of the asphalt concrete.
4.2 Evaluation of anti-slip performance
After the completion of the project, the structural thickness of the semi-flexible asphalt pavement was tested, and it was found that the structural thickness was in the range of 0.8~1.0 mm (as shown in Figure 3), which fully met the requirements of the "Highway Asphalt Pavement Design Code". At the same time, it also shows that in the construction process of this semi-flexible asphalt pavement, the control of surface scraping and the like is better, the value of structural depth is more reasonable, and the anti-skid performance is better.
Fig.2 Comparison of bending before and after asphalt paving of semi-flexible rut-resistant highway Download the original image
Fig.3. Structural depth test before and after paving Download the original drawing
5 Conclusion
In the upgrading of the road, the successful application of semi-flexible rut-resistant asphalt pavement has greatly improved the bearing capacity, rutting resistance and anti-skid performance of the original pavement, and increased the ornamental nature of the pavement. Compared with AC-13+0.3% anti-rutting agent pavement and SMA-13 pavement, the rutting deformation of semi-flexible pavement is smaller and has better stability.
bibliography
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