With the state increasing investment in rural infrastructure construction, rural cement roads have gradually become popular, and the travel problems of farmers have been well solved, realizing village access and facilitating the travel of the masses. However, in individual areas, due to the substandard quality of roads, many village village roads have not been used for a long time, there are various problems, especially the problem of cracked road surface, which has caused a lot of trouble to farmers.
According to the national requirements of the village road, the minimum grade of the village road is the national standard grade 4 road. (1) Design speed: 20km/h. (2) Pavement width: 4.5m. (3) Pavement structure type: cement concrete pavement.
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Problems that often occur on rural roads
With the arrival of summer, the quality problems of rural roads become more and more prominent, especially the cracking problem. Fig. 1 and Fig. 2 show the common forms of cracks in the pavement.
Analysis of the causes of the main problems
- Concrete ratio design
In principle, road concrete should use flexural strength to control the quality and reduce the slump. However, it is common to apply ready-mixed concrete, which is controlled by compressive strength and has a large slump.
The result of this, first of all, the mortar is easy to float, coupled with the concrete itself is very poor crack resistance, maintenance is not in place is easy to crack.
Preventive measures: the requirements of the concrete ratio as far as possible to reduce the slump, while special attention should be paid to the aggregate gradation must be controlled to reduce the sand rate.
- Improper roadbed treatment
The roadbed should be paved smoothly, filled in layers, and rolled as required, and the moisture content of the material should be controlled before rolling, such as higher or lower than the best moisture content of 4%, to dry or sprinkling treatment. Rolling machine using vibratory roller, after rolling the surface of the mat should be smooth, dense to meet the design requirements. And the site of the road bed potholes, not according to the requirements of leveling treatment, layered filling, strict rolling.
- Maintenance is not timely
Road surface concrete belongs to large area concrete, large area concrete is most likely to have problems with the timing of maintenance and maintenance time problems. At the early stage of maintenance, in order to prevent the cement concrete from being exposed to sun and rain, pavement maintenance is appropriate to use plastic film maintenance method. Can also be used to cover can store water such as straw, straw curtain and other sprinkling maintenance method. In the hot weather in the summer, maintenance is not timely also easy to cause spring concrete, that is, the surface skin water loss slating, while the internal concrete is still in a plastic state, not conducive to close the surface and cracking.
- Late cutting joints
Cement concrete pavement in the hardening process, continuous shrinkage, will lead to cracking. In order to make the cracking controllable, cut joints in time, the significance of cutting joints is to make the later cracking mainly at the cut joints. The timing of cutting joints is very important, cutting joints early, cement concrete strength is not enough to reach the cutting strength requirements, easy to produce missing edges and corners damage phenomenon; cutting joints too late, the temperature stress can not be released in time, when the temperature stress exceeds the concrete flexural strength will occur when the broken plate, so the choice of the best time to cut joints mainly by the cement concrete strength growth law with time to determine.
Generally reach the design strength of 25% or more when cutting joints, in order not to damage the principle of concrete, the next day of the high temperature season can be cut. To not chipping, no cracks shall prevail, as far as possible to lean forward. Fig. 5 shows the cracks at the lower end of concrete cut joints caused by untimely cutting.
The general concrete pavement can be opened to traffic only when the design strength reaches about 80% to 90%, and the specific time can be estimated according to the strength of the test blocks left in the same condition.
In many villages and towns, cement concrete roadbeds are not treated according to the requirements, the compaction is not enough, the foundation bearing capacity is not enough, coupled with premature opening, it is easy to break the plate, see Figure 6 for details of the cracks due to premature opening of traffic.
Concrete project is a system project, can not be separated from the joint efforts of the mixing plant and the construction unit, all parties in accordance with the requirements of their respective duties, good cooperation is to ensure the quality of the project must be required.