Selection of raw materials
1, cement.
Generally choose ordinary cement or slag silicate cement as the construction material for cement concrete pavement of rural roads. Before the material is delivered to the construction site, it should ensure that its quality meets the construction requirements, such as having a product certificate or lab report, etc. The quality of the material does not meet the relevant provisions, can not be delivered to the construction site. After the cement material enters the construction site, the form of overhead stacking must be chosen and different grades of cement should be sorted and stacked. In the process of transportation and storage, moisture-proof and rain-proof measures should be taken to avoid damage to the quality of cement, such as cement material caking and other phenomena, it will not be used for construction.
2、Fine aggregate.
In the fine aggregate selection should ensure that its gradation, particle size, etc. in line with the relevant design provisions, with tough wear-resistant clean and other characteristics, and has a low content of harmful impurities. Such as coarse and medium sand can not be selected, must use the ratio test for construction, fine sand within the content of soil impurities must be controlled at 3% or less.
3、Coarse aggregates.
Choose hard, clean, graded with the relevant design requirements of coarse aggregate, generally divided into gravel, crushed pebbles, etc. 19 mm for the maximum size of pebbles; 26.5 mm for the maximum size of crushed pebbles; 31.5 mm for the maximum size of gravel. Rural road technical indicators should meet the needs of Class III, not to choose too much needle or flake material.
4, water.
General drinking water can be used as a source of water for rural road cement concrete pavement construction, should ensure that it contains fewer impurities.
5, admixture.
Under specific conditions, in order to achieve good construction results, must choose the appropriate admixture, such as water reducing agent or early strength agent, the application of these admixtures, the quality of concrete can be effectively improved, and can be effectively enhanced mix strength, durability.
Application of cement concrete pavement construction technology for rural roads
1、Matching ratio setting
Follow the laboratory benchmark ratio, verify the test section, meet the test mix and test paving, compressive strength and other needs, to ensure that its ratio meets the construction requirements. Rainy season, must follow the weather conditions, analysis of the specific moisture content of sand and gravel materials, while fine adjustment of sand and gravel material weighing, can not change other mix ratio parameters. Through the reasonable setting of the mix ratio, improve the quality of the project.
2、Mixing and transportation
The raw material preparation work is responsible by the site laboratory, following the relevant test principles and combined with the site test section for the determination of the total amount of the mixture. Generally classified piles of coarse and fine aggregates, and sampling testing of various materials. Cement mixes must be mixed and constructed at the mixing site to ensure the uniformity of its mixing, and problems should be corrected in time if found. By the mixer will be mixed into the material delivery vehicle, should be balanced loading, as far as possible to avoid quality problems in the process of transporting the mixture. Generally choose the larger tonnage of the vehicle as transport machinery, in order to achieve the purpose of insulation, rain, etc., can be covered with canvas to the carriage. At the same time, assign a person to check the quality of materials in the process of transporting materials to ensure that its quality meets the construction requirements.
3、Installation of template
Before the pavement mixture laying work, the pavement template should be installed first. Before the application of the formwork should be regularly tested and corrected, such as bending, deformation and other conditions, can not be used, should ensure that the formwork and concrete have consistency. When installing the formwork, the position should be put on the line, and the formwork should be placed on the base, followed by drilling into the base with a brazier on its outer side and fixing the formwork. In the process of concrete paving and pounding, it should ensure that the formwork is always in a fixed state and realize the reasonableness of the formwork elevation and plane position. Before laying the concrete pavement must be withdrawn from the brazier to ensure the solidity of the formwork and to avoid misalignment and other phenomena. Use the mixture to fully fill the gap under the formwork to avoid settlement, leakage and other phenomena in the process of pounding concrete.
4、Fabric and paving
After the mixture is transported to the construction site, it is usually dumped directly to the side mold installed in the road groove, and by manual means, the leveling construction, such as the more serious phenomenon of segregation, should be uniformly mixed again. Rural cement concrete pavement paving construction in general first leveling operation of the mixture, the tools include shovel, scraper, etc.. When paving around the formwork, the buckle shovel method can be used for construction, and pounding construction, pounding out the mortar, should avoid the appearance of hollow honeycomb and other situations.
Paving process of loose concrete should be 10% higher than the design height of the top surface of the formwork. Vibrating rod insertion depth should be between 3 to 5 cm distance from the grass-roots level, 50 cm for the range of mobile spacing to ensure that bubbles, cement paste will not appear on the surface of the concrete, only then can choose the flat vibrator for construction.
5、Vibrating and leveling
Plate vibrator pounding construction, in the concrete surface to the total width of the plate 2/3 spacing for repeated pounding, vibration leveling selected vibrating beam for construction, followed by the use of roller for 2 to 3 times compaction, so as to lift the slurry leveling concrete surface. If cement paste, air bubbles, sand eyes and other conditions appear in the concrete pavement, the springboard should be laid to the concrete pavement, the choice of mud clip smear the way the way to construction.
6、Embossing
After the initial set of concrete, in the concrete surface with finger light pressure, such as finger prints and embossing depth consistent, can be embossed printing construction. The best time for embossing is that the dent depth is 2mm under finger pressure.
7、Demoulding
Demoulding is carried out after 12 hours of pavement forming, first remove the formwork support, brazier, etc., and then insert the flat-headed shovel stick between the formwork and concrete, and then gradually warp outward, and no concrete slab edge damage, etc. The formwork should be cleaned immediately after demolition to avoid deformation and other situations.
8、Joint construction
Transverse construction joint processing through flat joints, first use 3 meters length of straightedge to test its flatness, such as greater than 3 mm must be excised excess end to form a vertical surface, and then clean up the road and joint position. Choose flat joints plus transmission rods as the main way of construction of transverse construction joints shrinkage, should ensure the consistency of transverse shrinkage spacing, can not choose the construction of oblique joints, and can not adjust the length of the plate, to ensure that 6 meters is the maximum plate length.
9、Conditioning
After the completion of joint construction, watering operation should be carried out to ensure that the maintenance time is more than 7 days, and the whole period should always be in a wet state, closed to traffic to avoid serious harm to the road surface caused by vehicle traffic.
Conclusion
To sum up, as an important infrastructure for national economic and social development, rural roads have also been developed greatly after the reform and opening up. Cement concrete pavement construction as an important part of rural highway engineering construction, the level of its technical level will directly affect the overall quality of highway engineering, and even affect the sustainable development of the highway business.
For this reason, relevant departments and construction units in rural highway engineering construction must pay attention to cement pavement construction, make good preparation for construction, take scientific and effective measures to effectively improve construction quality and realize the social and economic benefits of rural highway construction.