1 project overview
The total length of expressway Bid D is 12.6km, and semi-rigid cement stabilized macadam base is adopted, with a thickness of 30cm and a single width of11.05m. The base is constructed in two layers with a thickness of 15cm. It is required that the 7-day compressive strength of the base is greater than 3.0MPa, the cement content of the mixture is controlled at 4.5%-6.0%, the mixture is mixed centrally, and the subbase is made of natural graded macadam. The following will discuss and analyze the construction of cement stabilized gravel base with this engineering example.
2 Application of Cement Stabilized Gravel Base in expressway Construction
2. 1 construction preparation
Before the base construction, in order to promote the smooth progress of the construction and ensure the orderly completion of all work, it is necessary to conduct a comprehensive and detailed inspection on the elevation, width, flatness and compactness of the base, and thoroughly clean up the sundries and garbage on the surface of the base to ensure that the base is clean and tidy. Install and debug the cement stabilized soil mixing station to ensure that it can meet the requirements of mixture mixing. According to the construction needs, allocate an appropriate number of construction personnel, construction machinery and equipment and construction materials, make various arrangements, pay attention to the mixture ratio design, ensure that it meets the requirements of specifications, and create conditions for subsequent mixture mixing and construction. In strict accordance with the requirements of construction organization design and progress, an appropriate number of trucks, pavers, rollers and sprinklers shall be configured, and the performance test and debugging of various equipment shall be done well. And pay attention to daily maintenance and maintenance, so that the performance of all equipment is in the best state, laying the foundation for the smooth progress of subgrade construction.
2.2 process flow
After the preparatory work is completed, the subgrade construction stage is entered, and the construction process of cement stabilized gravel base is as follows: measurement lofting → mixture mixing → mixture transportation → mixture paving → mixture rolling. During the construction, the quality control of each link should be strengthened, and the construction should be carried out in strict accordance with the technological process to ensure the effect of subgrade construction. 2.2. 1 Measurement The single width of cement stabilized gravel base course in lofting subgrade engineering is 1 1.05m, which is relatively wide, while the lateral stiffness of paver screed is relatively low. If quality control is not strengthened in the construction process, deformation problems will easily occur, thus reducing the detection accuracy of the lateral slope sensor. In order to avoid this situation and ensure the construction accuracy, steel wire reference lines are set on both sides when measuring and setting out. Before construction, the shoulder and the central separation zone are accurately set out with total station, and the distance between straight reference lines is12.5m. In order to better control the construction accuracy, the distance between reference lines can be properly encrypted, and it is appropriate to take 5m when measuring and setting out curve sections. And drive a stake every 50 meters on both sides to create convenience for the upper-level laying construction. 2.2.2 Sand, cement, admixture and water are added to the mixture in strict accordance with the design requirements, and each material should be weighed with an electronic scale before adding, so as to ensure the accuracy of the added quality and create conditions for improving the mixing effect. Control the mixing temperature reasonably, make observation and records, avoid the segregation problem and uneven phenomenon of the mixture, and effectively control the mixing quality of the mixture. Strictly control the water content of the mixture. In order to improve the comprehensive performance of the mixture, the water content should be controlled at about 0.5% ~ 1.0% of the optimal water content, and should not be too large or too small. Too large is easy to rebound, and the degree of compaction is difficult to guarantee; Too small is not conducive to compaction, but also easy to loose or separate. Mixing should be carried out continuously and evenly, avoiding stopping halfway, so as to ensure the good workability of the mixture and prepare for the subsequent improvement of subgrade construction quality. 2.2.3 Transportation of mixture The mixture shall be transported to the construction site immediately after mixing, and the mixture shall be transported by dump trucks. Covering measures should be taken during transportation to prevent the temperature loss of the mixture from being too fast and avoid the phenomenon of water evaporation and segregation of the mixture. During transportation, it is not allowed to stop and unload at the construction site at any time. The load capacity of the mixture truck should match the construction capacity of the paving equipment, avoid stopping halfway and ensure continuous paving. 2.2.4 Before paving the mixture, the appropriate paving equipment type should be determined, and the screed should be perpendicular to the center line of the road, so as to do a good job of preheating, avoid mixture bonding and lay a foundation for smooth paving. The two sides, middle and lower bearing layers of the leveling layer are backed by wooden boards and thin steel plates, and the bearing layer thickness is increased by a certain amount of compression on the basis of loose laying thickness, and then leveled and determined. When the first truck is transported to the construction site, it should be as close as possible to the paver, but it should not be touched. During the whole unloading process, the unloading must be uniform. In the future, the truck will stop at a place 20 ~ 30cm away from the paver to unload, and when unloading, put it in neutral and brake slightly. In the whole paving process, we should strengthen the control of paving speed, and reasonably control the paving speed of mixture according to the mixing capacity of mixing equipment and the transportation capacity of vehicles. The paving of the mixture should be carried out evenly at low speed as far as possible, without stopping in the middle, so as to ensure the continuous paving construction. Avoid paving too fast or too slow to affect the construction effect, effectively prevent mixture segregation and surface cracks, effectively control subgrade smoothness, and ensure the paving construction quality to meet the construction requirements. In order to improve the paving effect, the transverse slope and elevation of the paving surface are generally measured after paving for about 3 ~ 5m. If it meets the requirements, the paving construction of subsequent sections will be carried out. If it fails to meet the requirements, it should be adjusted in time to promote the paving construction effect. 2.2.5 In the whole construction of cement stabilized gravel base, mixture rolling is the most critical process to ensure the quality of base, which directly affects the quality of subgrade construction. Generally, a road roller of 12t or more is used for rolling construction, and layered paving and rolling are adopted, and the thickness of each layer should be controlled at 20cm. If the requirements for rolling thickness of each layer are different, rollers with different tonnage can be selected, which can not only ensure the compaction construction effect, but also avoid the quality problems such as crushed stone base rolling. In addition, the rolling construction is carried out in sections, generally every 50m. The length of the operation section can be adjusted appropriately according to the water content and climate change, but it is best to control it within each section1200mm. The adjacent rolling sections overlap by 3 ~ 5m for rolling construction, so as to strengthen the rolling quality control of the connection parts and ensure the rolling construction effect of the whole section. The roller follows the paver for 5 ~ 10m to roll the subgrade. In addition, in order to improve the rolling construction effect, the water content of the mixture should be controlled reasonably. Usually, the rolling construction effect is the best when the water content is at or close to the optimal water content, and the compaction degree of this project is controlled above 98%. During the rolling construction, the width of roller marks between two adjacent rolling passes should overlap by 20 ~ 30cm, which is divided into three steps: initial rolling, secondary rolling and final rolling. The rolling speed should be controlled at 1.5 ~ 3.5 km/h ... At the same time, continuous and uniform rolling should be ensured to ensure the rolling construction effect. 2.2.6 After the subgrade curing and rolling construction is completed, grass-roots curing shall be carried out after passing the inspection, and the general curing time shall not be less than 7d. Adopt sprinkler maintenance to ensure that the base is in a wet state. If it is a base with layered construction method, the next layer can be constructed after rolling for 24 hours. When paving the upper layer, ensure that the lower layer is in a wet state, ensure that the two layers have a good bonding effect, and also play a health-preserving role for the lower layer. During the curing period, traffic control should also be strengthened, and pedestrians and vehicles are not allowed to pass. At the end of the curing period, it can only be opened to traffic after passing the inspection.
3 Application Effect of Cement Stabilized Gravel Base in expressway Construction
The above-mentioned expressway construction adopts cement stabilized gravel base and strictly follows the technological process, which not only successfully completes the construction task, but also achieves good construction results. The process flow is simple and the construction period is shortened. The process flow of cement stabilized gravel base is simple, including measuring lofting, mixture mixing, transportation, paving, rolling and other links, and the operation is convenient. At the same time, it can shorten the construction period, ensure that the construction period objectives meet the progress requirements, and reduce unnecessary losses. Improve the quality of subgrade engineering after the completion of construction, the quality of subgrade engineering passed the quality inspection at the grass-roots level, obtained relevant data, and passed the quality evaluation. The whole subgrade project has the characteristics of high quality, high strength and good integrity. At present, expressway has been in operation for two years, and the subgrade quality is in good condition, and there are no quality defects such as subsidence, which has created good conditions for the effective operation of expressway.
Cement stabilized gravel base can meet the needs of expressway construction, and its application in engineering construction has achieved good results. Expressway grass-roots construction is worth popularizing and applying. At the same time, we should master the technological process, pay attention to the quality control of each process, improve the quality of construction personnel and improve the construction management system, so as to ensure the construction quality of cement stabilized gravel base and create good conditions for the construction of expressway.
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