Quality control of asphalt concrete pavement construction?

Asphalt concrete pavement has the characteristics of firmness, durability, good skid resistance, smoothness and stability, and has been widely used in the construction of high-grade highways in China. In the construction of asphalt concrete pavement, quality control is the key. Through years of asphalt concrete pavement construction, I have accumulated some work experience. The following only talks about some views on the quality control of asphalt concrete pavement construction. 1 quality control in construction preparation stage 1. 1 quality control of raw materials In the construction preparation stage, the quality of raw materials is an important factor in the quality of asphalt concrete pavement, and unqualified raw materials are strictly prohibited from entering the construction site. (1) Asphalt is the most critical raw material. For asphalt entering the site, the shipment quantity, date of shipment and factory laboratory test sheet should be strictly checked, and sampling inspection should be carried out according to the standards and frequency specified in the specification. Bitumen from different sources and specifications shall be stored separately and shall not be mixed. The asphalt tank mouth should be tightly closed to prevent moisture from entering the asphalt. The storage time of asphalt should not be too long and the storage temperature should not be too high. The storage temperature during construction should be between 90℃ and 140℃. (2) Gravel is the skeleton and main supporting material of asphalt concrete pavement. The specification of crushed stone is determined by the type of asphalt concrete and the thickness of each surface, and all technical indexes should meet the requirements of the specification. Sand should be hard, clean, dry, weathering-free, impurity-free, high-quality natural sand or machine-made sand with proper gradation, and the silt content should be less than 3%. Mineral powder should be dry and clean. The material yard must be hardened as required. All kinds of materials should be neatly stacked with clear boundaries. 1.2 asphalt concrete composition design (1) Target mix design: First, calculate the dosage ratio of various materials and mix them into mineral aggregate meeting the grading range required by the specification. Then, according to the test regulations and the actual situation of simulated production, asphalt and mineral mixture are mixed with six different asphalt contents (interval of 0.5%) in the laboratory with a small asphalt mixture mixer to form test pieces. The indexes determined by Marshall test should meet the requirements of Technical Standard for Marshall Test of Hot Mix Asphalt to determine the best asphalt content. With mineral aggregate gradation and asphalt content as the target mixture ratio. This work is the embodiment of technology and experience. Skilled test engineers should operate it to ensure the correct test method and reliable results, and parallel tests should be conducted if necessary. (2) Design of production mix ratio: It is necessary to re-sample all the screened materials entering the mixer's cold and hot silos for screening test and adjustment, so that all the materials in production can meet the requirements of target mix ratio, so as to determine the material mix ratio of each hot silo for use in the mixer control room. At the same time, the cold bin and the feeding bin are repeatedly adjusted to achieve the feeding balance, and Marshall test is carried out to determine the optimal asphalt content of the production mixture ratio. (3) Verification of production mix ratio: The mixer adopts production mix ratio for trial mixing, paving the test section, and sampling for Marshall test. At the same time, core samples are drilled from the pavement, and the void ratio is observed, so as to determine the standard mixture ratio for production as the basis for production control and the standard for quality inspection. During the construction, it shall not be changed at will, so as to ensure that all indexes meet the requirements and the standard deviation is as small as possible. 1.3 Before preparing for the construction of the asphalt pavement of the lower bearing layer, the base should be carefully inspected, with emphasis on checking whether the elevation meets the requirements, whether the surface is loose, whether the flatness meets the requirements, and whether it does not meet the requirements of the specification. Ensure that the base surface is dry and clean, free of loose stones, dust and impurities. 2. Quality control in construction stage 2. 1 Mixing of asphalt mixture When mixing asphalt concrete, control its temperature, asphalt-aggregate ratio and material gradation. Aggregate, mineral powder and asphalt of various specifications must be mixed in the required proportion respectively. Asphalt materials should be heated by heat transfer oil, and the heating temperature should be within the range of 160℃- 170℃. The heating temperature of mineral aggregate is 170℃- 180℃. Adjust the heating temperature of asphalt and mineral aggregate so that the ex-factory temperature of mixed asphalt concrete is 150℃- 165℃, and the mixture exceeding 200℃ should be discarded, and the temperature transported to the site should not be lower than/kloc. The control of asphalt-aggregate ratio is to weigh various materials with electronic scales respectively. The hierarchical control mode is two-level control. First of all, the discharge hopper and belt speed of each raw material bin are initially controlled, and after mixing, they are sent to the vibrating screen by the conveyor belt and hoist, and then re-screened by the vibrating screen. The size selection of vibrating screen should be basically consistent with the size of sieve hole in the specification. The mixing equipment has a high degree of automation, and various data can be adjusted at any time through the instructions of the operation room. The site laboratory shall check the oil-stone ratio and mineral aggregate gradation from time to time. The mixed asphalt mixture shall be uniform, without ashing, caking or serious separation of coarse and fine materials. Unqualified mixture shall not leave the factory. 2.2 The asphalt mixture shall be transported by large-tonnage dump trucks as far as possible, and the number of transport vehicles shall be reasonably configured according to the comprehensive consideration of production capacity, vehicle speed and transportation distance. The truck must be cleaned before loading, and a thin layer of oil-water mixture should be coated on the bottom plate and inner wall of the truck to prevent the material from sticking. The loaded car should be covered with thermal insulation cloth to ensure the paving temperature. The transportation time generally does not exceed 0.5 hours. 2.3 When the asphalt mixture paving vehicle arrives at the paver operation surface, the paver should be adjusted to the initial state. The paving thickness and width shall be subject to the design. The elevation angle of screed of paver should be accurate, the walking speed should be stable, and the leveling device should work normally. When paving, the paver will advance at a uniform speed with the paving speed, vibration and vibration frequency determined by trial paving, and it is forbidden to change speed or stop halfway. Before the paved asphalt mixture is compacted, the construction personnel shall not trample it. Asphalt mixture shall not be paved in rainy days or when the construction temperature is lower than 10℃. 2.4 After the asphalt mixture is paved and leveled, the pavement shall be inspected immediately, and the unevenness shall be adjusted manually in time, and then fully and evenly compacted. The compaction of asphalt mixture is carried out according to the rolling combination and procedure determined in the test section, and the compaction is divided into three stages: initial compaction, secondary compaction and final compaction. (1) Initial compaction: After paving the mixture, use two light steel wheel rollers (≤8t) to stabilize it, and roll it at least twice at a rolling speed of 2 ㎞/h ~ 3 ㎞/h. After initial compaction, check the flatness and road arch, and trim it if necessary. (2) Re-compaction: Re-compaction shall be carried out after initial compaction, and shall be completed by vibratory roller and tire roller. Generally, a vibratory roller is used for rolling for 3-4 times, and then a tire roller is used for rolling for 4-6 times to achieve the specified degree of compaction. (3) Final pressure: the final pressure shall be rolled by double steel roller or vibratory roller, and the vibration shall be closed to eliminate wheel tracks (the final pressure temperature is higher than 80℃). (4) Initial pressing and vibration rolling should be carried out at low speed to avoid hot material pushing and cracking. After paving, it should be rolled at a higher temperature. In general, the initial pressure should not be lower than 130℃. The higher the temperature, the easier it is to improve the smoothness and compactness of pavement. (5) During rolling, the roller shall not stop, turn or brake. (6) The roller shall not stay on the compacted mixture with the temperature higher than 70℃. At the same time, effective measures should be taken to prevent oil, grease, gasoline or other organic impurities from spilling on the road surface during the operation or parking of the roller. (7) In the process of paving and rolling, special personnel shall be organized for quality inspection and control and defect repair. Where the roller can't reach, fully compact the mixture by hand or machine rammer. 2.5 Treatment of Joints (1) Automatic sewing machine shall be adopted for longitudinal joints to control the elevation between adjacent segments and realize reliable combination between adjacent segments. The longitudinal joints shall be hot joints, continuous and parallel, and the joints shall be vertical and form a straight line. The dislocation between the upper and lower layers of the longitudinal seam should be at least 15cm. (2) Transverse joints shall be perpendicular to the paving direction, and oblique joints are strictly prohibited. Transverse joints between adjacent horizontal planes and adjacent strokes shall be staggered at least1m. Transverse joints shall have vertical edges rolled into a good shape. Before the next paving, an appropriate amount of viscous asphalt should be painted at the end of the last trip, and the height of the whole board should be set to leave appropriate reserves for rolling. The construction control of asphalt concrete pavement is mainly a series of construction quality control. It includes not only the quality control of raw materials, but also the quality control of construction process. In addition, the construction quality of the base also directly affects the quality of the surface layer. In the process of construction, we should combine the actual situation, organize the construction scientifically and reasonably, pave high-quality and high-level asphalt concrete pavement, and create excellent projects.

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