Cement concrete pavement is a kind of pavement structure with high rigidity, strong diffusion ability and good stability. With the increase of construction mileage, the accumulation of practical experience and the deepening of scientific research, the construction technology of cement concrete roads has been gradually improved and the quality has been continuously improved. In addition, cement concrete pavement has strong adaptability and disaster resistance, which can better meet the requirements of modern transportation; As far as materials are concerned, the gap of asphalt supply is large, the quality is not guaranteed, and the requirements for stone are high, while cement materials can be supplied nearby. Therefore, cement concrete pavement has developed rapidly. With the extensive popularization and application of cement concrete pavement, various diseases caused by related problems in the design, construction and use of cement concrete pavement are gradually exposed. If these diseases are not handled properly, they will seriously affect the speed, driving safety and driving comfort, increase fuel consumption and accelerate vehicle damage.
1, classification and cause analysis of cement concrete pavement diseases
1. 1 Panels are staggered, empty and muddy. The main causes of this disease are: (65,438+0) the subgrade construction density is not enough, repeated driving and natural factors lead to uneven settlement of subgrade; (2) The soil foundation or base with poor water stability is invaded by groundwater or surface water, causing subgrade settlement; (3) The foundation becomes soft and sinks, and the original ground of the embankment placed on the inclined plane is not properly treated during filling, resulting in uneven settlement of the new and old subgrade; (4) During subgrade construction, different filling materials are not filled in layers according to the specification requirements, resulting in uneven settlement of subgrade; (5) The strength of pavement base is uneven.
1.2 road slab is broken. The causes of pavement slab fracture can be divided into three categories: construction factors, small slump of concrete mixture, untimely maintenance after pouring and late joint cutting time; Vehicle overload, the vehicle load exceeds the design load; The hollow face slab and uneven settlement of the face slab foundation make the face slab hollow and greatly reduce the bending bearing capacity.
1.3 pavement surface diseases (potholes, exposed bones, net cracks, peeling, etc. ). The main causes of diseases are unqualified material quality, improper mixing ratio of cement concrete, poor construction quality or various impurities in aggregate, and inadequate maintenance. Secondly, the impact and friction of hard metal wheels of vehicles will also cause damage to cement concrete panels.
1.4 joint failure. The reason is that the joint plate and filler at the joint fall off and the driving chews the edge; When a hard object enters the seam, the edge of the plate will be crushed when it expands.
1.5 panel strength is not enough. Reasons: When mixing with 350 mixer, manual feeding generally exists improper control of cement concrete mixture ratio, and the transportation deviation of each mixture is large; Water or aggregate contains salt, which reacts with cement to reduce the strength or failure of cement concrete; Initial maintenance is not in place, watering is not timely, and the maintenance period is less than opening to traffic.
2, the construction quality control measures
2. 1 Strictly control the quality of pavement raw materials.
The structural layer of cement concrete pavement is formed by mixing, paving, compacting and curing with cement slurry synthesized by cement and water as binder, crushed (gravel) stone as aggregate and sand as filler. Because the pavement structure layer is subjected to the combined action of wheel load and natural factors, it is required that concrete materials must have high strength, wear resistance, frost resistance (cold area) and as low expansion coefficient and elastic modulus as possible. Therefore, some requirements should be put forward for pavement concrete and its constituent materials, and the appropriate proportion should be determined.
2. 1. 1 quality control of cement. Factors such as road grade, construction period, paving time, construction method and economy should be considered. In principle, cement with high flexural strength, fatigue resistance, dry shrinkage, wear resistance and frost resistance should be used. When cement enters the site, the test data (report form) of cement products of the manufacturer, its variety, label, packaging, quantity, production date, etc. shall be strictly checked. Should check whether it can meet all the road indicators; The fineness, setting time, volume stability and strength of cement are sampled on site, especially the safety indicators must be sampled; Cement for construction can only be used after re-inspection by qualified laboratories in the region; Cement with different labels, brands, varieties and production dates shall not be mixed and piled up, and mixed use is strictly prohibited; Cement that has been out of the factory for more than three months or is damp must be tested, and the normal use or deterioration can be decided according to the test results. Do not use caked and deteriorated cement; In the construction of concrete pavement, cement of the same grade produced by the same manufacturer should be selected as far as possible.
2. 1.2 aggregate quality control. During construction, the maximum particle size of cement concrete pavement should be determined according to specific construction requirements. When gravel is used, 30mm should be used. When gravel is used, 20mm should be used, and the content of needle-like particles should be strictly limited. The flaky and long-strip particles in coarse aggregate should be controlled within 15% (fine aggregate can be unlimited). The strength of aggregate should meet the quality requirements, the strength of coarse aggregate should be higher than 1.5 times the concrete grade, and its crushing value should not be greater than 20%; Strictly control the content of soil (stone powder) in aggregate; Gravel materials should be washed with high-pressure water, and stacking in the open air is not allowed. Like cement, gravel materials must be canned at the construction site without any pollution.
2.2 Optimize the mix proportion design of cement concrete
2.2. 1 Selection of water reducing agent. In order to prepare concrete with high flexural and tensile strength and good durability, the water-cement ratio of concrete is required to be small, so superplasticizer must be used to ensure good workability of concrete.
2.2.2 Composition principle of mineral aggregate gradation. Because of successful practical experience, the current theoretical and empirical data are relatively mature and easy to select. However, coarse aggregate is generally mixed with secondary aggregate. Because the current situation of coarse aggregate processing is not ideal, it is extremely important to determine a relatively reasonable mixing coefficient. According to the author's experience and consulting relevant data, the composition of coarse aggregate is the optimal curve, which is more conducive to the control of pavement smoothness and the improvement of flexural and tensile strength. In addition, the silt content of coarse aggregate is generally not more than 65438 0%, and the silt content of sand is not more than 2%, otherwise it will seriously affect the flexural strength of pavement and increase shrinkage deformation.
3.2.3 Road quality requirements for cement and fly ash. Before the mix design, the pavement performance of cement should be tested. If any problem is found, it should be discussed with the manufacturer in time to adjust the cement composition to ensure that the cement quality is completely qualified. Fly ash must reach Grade II or above, and the material of each vehicle must be tested before it can be put into the tank, otherwise fly ash above Grade III will do great harm to the pavement.
2.3 cement concrete pavement construction quality control
2.3. 1 Complete the test section carefully. The experimental section of paving cement concrete pavement is divided into two stages: trial mixing and trial paving. Through the test of the test section, the following objectives should be achieved. The experimental section is implemented under the same conditions as the construction conditions. By organizing construction, calculation and summary in designated sections, all necessary working parameters and construction experience are obtained to guide formal production.
2.3.2 Before paving the road, make all preparations. The first is to clean up and repair the grassroots. Repair the damaged base with high-grade cement mortar, clean up the cracks at the base, then pour asphalt, and paste a single-layer linoleum with a width not less than 1 m on the surface to prevent reflective cracks on the pavement. Second, prepare the baseline of the paver, ensure that the baseline is smooth and comfortable, check the thickness one by one, and fine-tune the baseline where the thickness is inappropriate; Thirdly, determine the position of expansion joints and steel bars in advance and put them in place in advance, so that the installation of steel bars will not affect the continuous operation of paver.
2.3.3 Before paving that day, the water content of materials, especially the water content of sand and small gravel, should be tested. Pay attention to control the mixing quality of concrete when mixing to ensure the uniformity of concrete slump.
2.3.4 According to weather conditions such as air temperature and wind speed, fine-tune the factory slump of concrete to ensure the uniformity of the mixture in front of the machine, and fine-tune the water reducer and water cement ratio according to the change of transportation distance to ensure the workability of concrete.
2.3.5 Before the paver starts construction, adjust the position of vibration support and trowel, and check the elevation and plane position of the paver. During construction, control the material level in the vibrating bin and in front of the machine, and control the walking speed, not too fast. If it is too fast, the trimming speed of the workers can't keep up, the insertion position of the pull rod is inaccurate, and the nursing before and after the manipulator is prone to defects. Generally, 1.0 ~ 1.5 m/min is appropriate. In addition, according to the road conditions after construction, adjust the vibration frequency of paver in time.
2.3.6 After pavement construction, curing agent shall be sprayed in time, and the spraying frequency and concentration of curing agent shall be determined according to weather conditions (temperature, wind speed, humidity, etc.). ). After the pavement is opened, it should be covered with moisturizing curing film or film for curing. After 28 days of health care, it was opened to traffic.
2.3.7 Construction of longitudinal and transverse joints of pavement. In general, the setting of expansion joints should be as few as possible. According to the local temperature difference and construction temperature, set the location of expansion joints. Must be located near the building.
3. Concluding remarks
For cement concrete pavement diseases, we should pay more attention to establishing the idea of prevention, and try our best to avoid and reduce them in design and construction. It is necessary to strengthen the management of pavement construction, adopt standardized and programmed construction and health preservation methods, cut joints in time, grasp the appropriate operation opportunity, and make different treatments according to the different conditions of temperature change.
For more information about project/service/procurement bidding, and to improve the winning rate, please click on the bottom of official website Customer Service for free consultation:/#/? source=bdzd