Talking about the technical points of SMA pavement construction?

The following is the related content of SMA pavement construction technical points brought by Zhong Da Consulting for your reference.

Expressway Project (hereinafter referred to as Zhensheng Expressway) of Huruiguo Road (Guizhou) from Xinzhai River to Shengjingguan is located in the southwest of Guizhou Province, surrounded by mountains. The construction is difficult, the working face is long and narrow, and the safety level is high. Combined with the past experience and existing problems in expressway, Guizhou Province, it is the first time for Zhensheng expressway to adopt SMA asphalt-coded hoof fat macadam as the surface material, which is also the first official large-scale SMA pavement construction in Guizhou Province.

SMA- 13 is adopted in the pavement structure design of Zhensheng expressway, with AC-20 on the upper layer, AC-25 on the middle layer and cement stabilized macadam subbase on the lower layer. The structural design thickness is 4-6-8-37- 15, with a total thickness of 70cm. SBS modified asphalt is used in the upper layer, and ordinary asphalt concrete is used in the middle and lower layers.

I. Composition of SMA Mixture

SMA is the abbreviation of asphalt mastic aggregate, which is an asphalt mixture composed of asphalt binder, a small amount of fiber stabilizer, fine aggregate and more fillers (mineral powder), and is filled in the gaps between discontinuous graded coarse aggregate skeletons.

Second, the technical performance of SMA mixture

It has the advantages of wear resistance, skid resistance, compactness, durability, fatigue resistance, high-temperature rutting resistance and low-temperature cracking reduction, and is suitable for the upper layer of high-grade road asphalt pavement.

1. Rutting resistance at high temperature. (1)SMA consists of coarse aggregate skeleton and asphalt mortar. (2) The coarse aggregate with particle size ≥4.75mm is as high as 70%~80%. The dosage of mineral powder is about 10%, and the fine aggregate is less, generally about10% ~ 20%; (3) Due to the embedding of skeleton, the mixture has strong resistance to load deformation and rutting at high temperature.

2. Low temperature deformation resistance. At low temperature, because there is a considerable amount of asphalt mastic in SMA mixture, when the temperature drops, asphalt mastic has high bonding ability, and its toughness and flexibility make the mixture have good low-temperature deformation ability.

3. Durability. In SMA mixture, the gaps of coarse aggregate skeleton are densely filled with asphalt-rich mucilage, aggregate particles are bonded together, and asphalt forms a thick asphalt film on the edges and surfaces of aggregate. In addition, SMA mixture has a small gap, and asphalt has little contact with water or air, so SMA mixture has better water stability, aging resistance and fatigue resistance than ordinary asphalt mixture. At the same time, because SMA mixture is basically impermeable, it has good protection and waterproof effect on middle, lower and base course, so that asphalt pavement maintains high overall strength and stability.

4. Surface uniqueness. On the one hand, SMA mixture requires the use of hard, rough and wear-resistant high-quality macadam, on the other hand, it requires the use of discontinuous graded mineral aggregate. After compaction, the depth of the structure formed on the surface is large, generally exceeding 1mm, and the friction coefficient can be more than 8BBM, which makes the asphalt pavement have good anti-sliding and wear resistance, reduces water splash and noise, and improves the road driving quality.

5. Control of 5.SMA mixture before construction. (1) Qualified raw materials are the first prerequisite for project quality. Based on a large number of investigations and sampling tests, considering the quality, output, transportation and other factors, the basalt sandstone material used in SMA pavement construction is preliminarily selected, and the processing, storage and transportation of raw materials are strictly controlled as required, so that its technical indicators can meet the quality requirements of coarse and fine aggregates in expressway pavement engineering. (2) Mix proportion design stage. A perfect mix design must be determined after repeated comparative tests and comprehensive consideration of various key technical indicators. After repeated tests and adjustments, the target mix design and construction mix design of SMA- 13 are finally completed. (3) Technical disclosure before construction is essential. There are many technical points in SMA mixture construction. Therefore, before the formal paving of SMA pavement, all technicians and mechanical operators are required to fully understand and master the construction technology and technical characteristics of SMA pavement and make technical disclosure.

6.SMA- 13 asphalt mastic macadam pavement construction. (1) Preparation before construction; (2) supply of sand and gravel: when the project officially starts, the storage bin is guaranteed to be 4000m? 3? The above materials are reserved to avoid the shortage of materials during construction, resulting in excessive temperature or shutdown of the mixture; Asphalt supply: fully consider the daily output and hourly output of asphalt mixing station, fill all asphalt storage tanks every day (according to the effective construction time of 20 hours) before construction, and equip with modified asphalt transport vehicles with more than 30 tons to avoid stopping to take materials due to abnormal operation of the transport vehicles; (4) Mineral powder supply: the mineral powder used in SMA is made of limestone, and 8- 10 transport vehicles must be organized to ensure the timely supply of mineral powder; (5) Before construction, diesel oil, heavy oil and fiber shall be fully prepared. Equipped with enough transport vehicles for mixture (clean the transport vehicles with cleaning solution before loading), so as to avoid the mixing building from stopping and waiting for the bus due to insufficient transport vehicles; (6) Preparation of mechanical equipment on the construction site: at least 2 pavers. Paving with a single frame and two machines to avoid segregation of asphalt mortar; At least 3 8- 12 ton all-steel rollers, 1 contactless balance beam and 1 flat rammer. Before construction, the performance of all construction machinery must be comprehensively checked to ensure that all construction machinery can work normally.

Fourth, SMA mixture construction control

(1) mixing of modified asphalt SMA- 13. To use advanced asphalt mixing equipment to mix the mixture, there must be a dust removal system, a temperature control system and a weighing system; (2) Paving of SMA-13 mixture. ① Due to the high viscosity of SMA asphalt horseshoe fat, more oil-water mixture must be applied to the bottom of the carriage of the material delivery vehicle; In order to prevent the surface mixture from crusting, the materials should be covered with tarpaulin when transported, and the number of materials transport vehicles should be appropriately increased. In order to ensure the flatness, it needs to be spread slowly, evenly and continuously. This is the most important measure to improve the smoothness of pavement. (2) The upper layer adopts non-contact balance beam device to control paving thickness and smoothness. ③ Adjust the paver to the best working condition, and debug the automatic material level devices at both ends of the auger to make the opening of the feed door, the speed of the chain feeder and the rotating speed of the auger match. The material quantity of the spiral distributor should be higher than the center of the spiral distributor, so that the mixture in front of the screed baffle is evenly distributed in the whole width range. The material quantity should be adjusted before construction every day, and then paving should be carried out to avoid segregation of the paving layer. (4) Paving should be carried out in the high temperature period of one day, and it is not suitable for paving when the pavement temperature is lower than 15℃. When paving encounters rain, stop construction immediately and remove uncompacted mixture. The mixture exposed to rain should be discarded, and shall not be unloaded into the paver for paving; (3)SMA- 13 mixture is rolled. Rolling is an extremely critical link in SMA pavement construction. Rolling technology, rolling times and rolling temperature directly affect the compactness, smoothness and water permeability of SMA pavement. (4) After the road surface is compacted for 24 hours, construction vehicles can pass; (5) Treatment of construction joints. Adopt a three-meter ruler along the longitudinal position, draw a ruler at the end of the paving section to make the ruler cantilever, determine the joint position at the contact point between the paving layer and the ruler, and cut and remove it with a sawing machine; When paving continues, the mortar left during sawing shall be scrubbed clean, coated with a small amount of adhesive modified asphalt, and the paver screed shall be paved from behind the seam; When rolling, the steel wheel roller is used for transverse compaction, and the new pavement layer is gradually removed from the completed pavement.

Five, SMA mixture quality management in the construction stage

1. Quality inspection of raw materials: including modified asphalt, coarse aggregate, fine aggregate, filler, wood flocculent fiber, etc.

2. Quality inspection of mixture: asphalt-aggregate ratio, mineral aggregate gradation, stability and porosity; Factory temperature, paving temperature, initial pressure temperature and final rolling temperature of the mixture.

3. Quality inspection of rolled sections: thickness and smoothness. Width, transverse slope, compactness and skewness; Uniformity of paving. At the same time, it is necessary to track and detect the structural depth and water seepage.

4. The inspection of construction compactness adopts drilling method, and the frequency of drilling inspection is twice per lane and kilometer.

5. The qualified rate of water seepage coefficient should be not less than 90%. When the qualified rate should be less than 90%, the frequency should be doubled. If the test result is still below 90%, the pavement should be treated.

Ending of intransitive verbs

Strictly speaking, the construction difficulty of SMA pavement is much greater than that of ordinary asphalt concrete. The success of highway SMA pavement largely depends on its material quality, equipment performance and construction technology. Every link is interlocking, and if any one of them is ignored, SMA pavement will be doomed to failure.

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