Fang Xinyu and Ceng Hui
(China Changzhou Jiangsu Hengji Road and Bridge Co., Ltd., 2 13002)
Combined with the application example of slurry seal technology in the expansion project of Shanghai-Nanjing Expressway, it summarizes its construction and quality control, and makes a comparative analysis of its application effect, so as to lay a good foundation for its popularization and application. Key words: slurry seal; Technology; quality
Construction technology and quality control of slurry seal coat
Fang Xinyu, Ceng Hui
(Hangjie Road, Jiangsu & China Changzhou Bridge Engineering Co., Ltd., 2 13002)
Abstract: Connecting with the construction practice of Shanghai-Nanjing Expressway widening project, this paper sums up the construction methods of widening project.
The construction technology and quality control of slurry seal coat are compared and analyzed, which lays a foundation for the popularization and application in the future.
Key words: slurry seal; Technology; quality
1 preface
The slurry seal coat is similar to the micro-surfacing, and the paving method of on-site cold mix asphalt mixture is adopted. According to Technical Specification for Asphalt Pavement Construction (JTG F40-2004), micro-surfacing is mainly used for preventive maintenance of expressways and first-class highways, as well as filling light ruts, and is also suitable for anti-sliding wear layers of newly-built highways. Slurry seal coat is generally used for the preventive maintenance of secondary and below roads, and is also suitable for the lower seal coat of new roads. At present, many expressways in China have early diseases, which affect the quality and service life of asphalt pavement. One of the most important reasons is that the grass roots are invaded by water. The problem is that the lower sealing layer does not really play the role of waterproof, water sealing and connection. Therefore, the lower seal coat technology constructed by traditional methods has aroused more and more people's doubts, and the slurry seal coat construction technology has been paid more and more attention, and it has been more and more recognized as the lower seal coat of pavement structure in expressway construction and applied in practice.
2. The main function of asphalt pavement under seal coat
(1) waterproof and watertight, to protect the base from water.
(2) The upper and lower bonding makes the base layer and the surface layer well bonded together to form a continuous whole, so as to avoid increasing the tensile stress at the bottom of the surface layer due to poor interlayer bonding.
(3) Close the base in time to effectively prevent the shrinkage strain of the base due to too long exposure time.
(4) Preventive maintenance of the completed base can be used as a temporary driveway for asphalt pavement construction.
The construction example can prove that the lower seal coat constructed by slurry seal coat is completely superior to the lower seal coat constructed by traditional layer laying method in the above four functions. 3 slurry seal design 3. 1 raw materials
3. 1. 1 asphalt
Slurry seal coat is paved with slow-cracking mixed emulsified asphalt (BC- 1). The matrix asphalt is heavy cross-linked asphalt (AH-70) and the modifier is styrene-butadiene latex (SBR). In order not to soften the slurry layer at high temperature in summer, the softening point of emulsified asphalt is required to be greater than 55℃. According to the test report, the SBR content is not less than 2%, the emulsifier is XTL2000- 1, and the content is 1.8%. In addition, 0.3% ammonium chloride was added as stabilizer.
According to the Technical Specification for Highway Asphalt Pavement Construction and the climatic conditions in Jiangsu, the main technical requirements of emulsified asphalt with slurry seal coat are shown in the following table 1.
Table 1 Main technical requirements of emulsified asphalt with slurry seal coat
Emulsified asphalt is suitable for alkaline stone. The demulsification speed and viscosity of emulsified asphalt should be selected according to the purpose and construction method. In order to strengthen the adhesion between asphalt and stone and shorten the demulsification time of emulsified asphalt, ordinary portland cement can be added.
Emulsified asphalt should be stored in a vertical tank with proper stirring, and the storage period should not be separated, frozen or emulsified. 3. 1.2 Total
Aggregates should be made of hard, rough, wear-resistant, clean, weathered and impurity-free stones by crushing. Mineral aggregate shall not contain oversize particles exceeding the thickness of seal coat. Due to the moderate selection of gradation, coarse may lead to large porosity and poor waterproof effect, while fine may lead to thin layer, insufficient strength and softness.
Table 2 Mineral aggregate grading table (1 and 2 standards recommended by ISSA)
Mineral aggregate gradation can be selected according to the design thickness of slurry seal. 3.2 Mix proportion design
The mix design of slurry seal coat can be carried out according to the following steps:
(1) According to the selected gradation type, determine the gradation range of mineral aggregate, calculate the proportion of various aggregates, and make the synthetic gradation within the required range.
(2) According to the experience, the dosage of emulsified asphalt, filler, water and additives is selected, and the mixing test and adhesion test are carried out. The test temperature of mixing time should consider the highest construction temperature, and the test temperature of cohesive force should consider the lowest temperature that may be encountered in construction. (3) According to the above test results and the appearance of slurry mixture, select 1-3 qualified mixture formula, and compare it with the technical requirements (mixture ratio design index) of slurry seal coat and micro-surfacing mixture in Table 3 below. If it does not meet the requirements, adjust the mixture ratio of various materials appropriately, and then test again until it meets the requirements.
Note: The width change rate of the roller compaction test (LWT) is applicable to the situation that the rut needs to be repaired.
(4) According to the experience and the test results of mix design, the formula is determined comprehensively on the basis of fully considering the climate and traffic characteristics. The general experience is that in terms of water consumption, it is necessary to ensure that the construction has good workability and will not lead to slurry flow because of excessive water consumption. Asphalt dosage should be strictly controlled according to the requirements of mix design. If the amount of asphalt is too small, the slurry seal structure will be loose. Too much, after the completion of construction, under the repeated action of driving load, may cause flooding, and then form a parcel passage.
(5) The composition ratio of various materials is usually determined as follows: mineral aggregate (stone chips): asphalt: water: cement =100: 8:16:1(weight ratio), in which mineral aggregate is dry stone chips, asphalt is the weight without emulsion, and water should include stone chips and modification.
4. Construction technical requirements and quality control 4. 1 Slurry seal construction technology
4.2 Sealing layer construction
(1) Before construction, use powerful cleaning machinery to remove all dirt, sundries and loose particles on the top surface of the base. If large oil stains are found, they should be removed with detergent. The smoothness and cleanliness of the base surface will affect the quality of the seal coat, directly reduce the adhesion between the seal coat and the base, and cause quality problems such as peeling and peeling.
(2) Construction raw materials (modified emulsified asphalt, mineral aggregate, water, etc.). ) inspection qualified rear can use. Mineral materials must be screened to remove oversize particles, so as to avoid the influence of large-size stones on mixing and paving.
(3) Before paving, it is necessary to conduct a comprehensive inspection and debugging of mechanical equipment, calibrate the paving thickness at the same time, check the mixture metering system and production ratio, and formally start construction after it is confirmed to be completely normal. If the pavement is too dry, too much water absorption will affect the consistency control of the mixture, making it difficult to spread. At this time, the water spray in front of the mixing box can be used for water mist pre-wetting.
(4) When paving, adjust the paving trough and turn on the control switch to make the mixed slurry flow into the trough. When it flows to 2/3 of the volume of the paving box and the consistency of the mixture is moderate, the storage in the box is evenly distributed, so that the chassis can be started, and it can move forward at a constant speed of 2~4 m/min, and it is always guaranteed.
The amount of slurry spread is basically the same as that of mixing.
(5) If the slurry mixture is uneven when paving, it should be leveled manually with a rubber rake immediately. The key parts of leveling are: starting point, ending point, vertical and horizontal joints and grooves caused by oversized particles.
(6) The joint shall be smooth, and there shall be no local leakage or excessive thickness. Longitudinal seams should be minimized. For longitudinal joints, if the paving mixture is partially solidified, it should be pre-wetted in time before the construction of the next vehicle. For transverse joints, it is advisable to retreat from the end of the previous driving to 5~ 10 cm to start the construction of the next driving, so as to ensure that the mechanical operation line is consistent with the previous driving.
(7) In the process of mixing and paving, the mixture shall not have too much moisture and segregation. In any case, water shall not be directly injected into the paving box when paving. The mixture in the paving box should basically maintain the required viscosity and stability. If it is too thick, it is easy to cause early demulsification and affect the thickness and smoothness of paving. If it is too thin, the mixture will segregate, and the asphalt will float, which will lead to the decrease of adhesion with the base. Therefore, the water content should be carefully adjusted on site, and appropriate adjustments should be made according to the actual factors such as environmental temperature, humidity, wind power, water absorption rate of pavement, etc., to ensure the proper paving consistency of the mixture. Control the construction thickness, the slurry seal is too thin to achieve waterproof effect; If it is too thick, a weak interlayer may be formed due to insufficient strength.
(8) The construction temperature of slurry seal coat shall not be lower than 108℃, and construction is prohibited in case of rain during construction and maintenance. After the rain, the top surface of the base can't be constructed before the water is wet.
(9) Pay attention to early maintenance. Once the emulsifier has just been demulsified, it should be repeatedly rolled with a small tire roller for 3~4 times, which is beneficial to improve the compactness, early strength, flatness and waterproof performance. 4.3 construction matters needing attention
(1) The equipment must be calibrated before use.
(2) The stirred mixture must be verified on site. (3) Control the consistency of the mixture. (4) Control the paving thickness. (5) controlling demulsification time and timely crushing. (6) Do a good job in combination therapy.
(7) It is forbidden to rob the shop before and after the rain. 4.4 Quality inspection
4.4. 1 The quality inspection method of slurry seal is shown in Table 4.
Table 4 Quality inspection method of slurry seal coat
4.4.2 Appearance inspection
(1) The surface is smooth and dense, without looseness, wheel tracks and pollution, and the appearance color is consistent. (2) Longitudinal and transverse joints shall be connected with other structures smoothly and neatly. (3) No slurry flows out when paving, and the surface is rough and flat. Application effect of slurry seal coat
5. The results of1test and field test show that the slurry seal coat has high tensile strength and water seepage resistance, which can effectively ensure the continuity between layers. These characteristics are beneficial to prevent the early cracks of semi-rigid pavement from being damaged by water, thus improving the long-term service performance of asphalt pavement.
5.2 The permeability test shows that the water permeability coefficient of slurry seal can basically be below 10 ml/min, which can be considered as basically impermeable and has good waterproof and water sealing functions.
5.3 The comparative analysis of pull-out test shows that the failure surface of slurry seal coat is usually between seal coat and top surface of base course, which is closely combined and has strong pull-out resistance, which is generally 3~5 times that of hot asphalt. The failure surface of hot asphalt seal coat is usually between the seal coat and the underlying layer. The main reason for the failure is that the stone chips on the surface of hot asphalt are not well combined with hot asphalt, and the pull-out resistance is reduced.
Table 5 Comparison Table of Drawing Tests
Continuous function. At the same time, although the core sample was soaked for 24 hours before the pull-out test, the interface of the core sample remained basically dry when it was taken out. The hot asphalt in the hot asphalt seal coat can be well connected with the base, but its pull-out resistance is obviously not as good as that of the slurry seal coat, because the stone chips spread on its surface can not be closely bonded with the hot asphalt. At the same time, after the core sample is soaked, the surface of most stone chips is wet, which further reduces the interlayer continuity.
5.5 Slurry seal coat can be well applied to the situation that construction vehicles need to pass temporarily, and it will not cause construction pollution due to threshing, flying and dust.
5.6 Slurry seal can promote and protect the health of the base, whether it can effectively prevent or reduce the premature shrinkage stress on the surface of the base and form transverse shrinkage cracks needs further verification; And whether its good interlayer continuity can absorb the stress at the bottom of asphalt pavement, reduce the bending stress inside the pavement without causing premature structural cracks on the asphalt pavement, and truly realize the construction efficiency of "strong foundation and thin surface" of asphalt pavement, which is also a subject worth studying.
The problems affecting the quality of slurry seal mainly depend on the construction technology level. With the accumulation and improvement of construction technology and the improvement of technical level, the construction quality of slurry seal can be guaranteed.
refer to
JTG F40-2004。 Technical specification for construction of highway asphalt pavement [S]. Beijing: People Communications Publishing House, 2004. [2] Technical Guidance for Pavement Construction of Shanghai-Nanjing Expressway Extension Project [S].2004.
, Qiu, Wang Hui. Application of Slurry Seal in Kaiyang Expressway [J]. Highway, 2003(8), 8:80-83.