In order to effectively evaluate the condition of cement pavement and implement maintenance countermeasures, it is necessary to understand the types and causes of diseases of cement pavement. The main types of cement concrete pavement damage are divided into structural damage and surface damage according to the damage forms. The main forms of structural failure are longitudinal cracking, transverse and oblique cracking, broken slab, staggered slab and boiling. The main forms of surface damage are: fragmentation and spalling, surface wear and so on. We must fully investigate and find out the reasons so as to take targeted governance measures. Based on the analysis of several typical diseases of cement concrete pavement, this paper puts forward maintenance countermeasures.
Several typical diseases of cement concrete pavement
1, crack
When the load stress and additional stress caused by repeated traffic load and temperature and humidity changes exceed the strength of concrete, the slab will break, and various cracks will appear, including longitudinal, transverse and oblique cracks, and the corner fracture of the slab will even develop into slab damage. The reason for the crack is that the thickness of the plate is too thin or the vehicle is seriously overloaded. Insufficient strength of foundation, especially uneven strength, and plastic deformation caused by rainwater infiltration into the base, which makes the bottom of slab empty; The plane size of the plate is large, which causes excessive shrinkage stress and temperature warping stress; The joint is damaged, and the load transfer capacity is lost; Poor quality of concrete due to poor quality of materials used or poor construction quality, and excessive shrinkage stress of concrete due to improper maintenance or untimely sawing. In addition, fatigue cracks will form a series of network cracks composed of polygonal small pieces. The initial shape is that one or more parallel longitudinal seams appear along the wheel track belt, and then transverse and oblique connecting seams appear between the longitudinal seams, forming a network crack.
2. The bonding material is damaged
The joints of cement concrete pavement are divided into longitudinal joints and transverse joints, and the transverse joints include expansion joints and contraction joints. When the performance of expansion joint material is poor, the joint filler is squeezed out when the temperature rises, and it cannot be recovered when the temperature drops, resulting in the formation of cracks at the joints. Mud, sand, stone chips and other debris fall into the cracks and become obstacles to re-expansion and extension. In addition, rain, snow and water penetrate into the cracks of the joints, causing damage to the base and cushion, which leads to deformation and damage of the joints of pavement plates during driving. The shrinkage joint has little change, but after repeated freezing shrinkage, the fake joint can be broken into a real joint, or it can be as damaged as the expansion joint due to the aging of the joint filler itself. Irregular construction and maintenance, untimely joint cutting or failure to reach the specified depth are also one of the reasons for joint damage.
3, corner fragmentation
Corner fragmentation refers to the pavement slab fragmentation within the width of 60cm or the angle of 15cm on both sides of the joint. The reasons are analyzed and summarized as follows: hard objects fall into the joint, the plate is stressed too much during expansion and contraction, the edge is crushed by hard objects, overloaded vehicles repeatedly act, and improper design or construction of dowel bar structure hinders the free expansion and contraction of the plate end; The concrete strength at the joint is insufficient or overlapped.
4. Wrong channel
Staggered platform refers to the vertical height difference between adjacent plates at the joint. When pouring concrete slab, the caulking plate of expansion joint is not fixed firmly, and the joint wall is inclined due to vibration during vibration, or the caulking plate at the upper part of the joint is not aligned, which leads to the dislocation of the two plates during expansion and extrusion. When there is no dowel bar at the joint, the load transfer capacity is insufficient, or the rain seeps into the base through the joint to produce pumping mud, which makes the joint plate sink unevenly and the joint of the plate warps due to the temperature and humidity gradient.
Second, the maintenance of cement concrete pavement diseases
1, crack repair
The main causes of cracks are: empty drum at the grass-roots level, insufficient strength of soil foundation and grass-roots, improper construction operation and poor maintenance of joints. In view of the influence of different cracks on pavement performance, different materials are used to repair them. Fine cracks with a crack width of less than 3 mm are classified as minor cracks. The operation method of concrete curing is to seal the joint with adhesive tape, use emulsified asphalt as potting material, and pour low-viscosity latex into the joint with pressure grouting machine. There is moderate or severe fracture at the edge, and the cracks with staggered height less than 13mm and joint width less than 25mm are moderate cracks, and the strip covering method is mainly used to repair the moderate cracks. Cracks with a stagger of more than 13 mm or a joint width of more than 25mm are classified as serious cracks. For the repair of serious cracks, the full-depth repair treatment method is mainly adopted, and the position of the repaired concrete pavement is marked parallel to the cracks, and the full-depth cutting is carried out along the marked position. Chisel the vertical surface of full-depth slit concrete into a rough surface. After the grass-roots treatment is qualified, repair and install dowel bars and pull rods, lay concrete with bending and tensile strength meeting the requirements, and vibrate and compact it. Curing agent should be used for repair, and caulking material should be filled in the shrinkage joint. After the concrete reaches the opening strength, the traffic can be opened.
2. Repair of plate angle fracture
Corner fracture is a crack that runs vertically through the bottom and intersects the seams on both sides of the corner. The failure reason is usually due to the sustained load at the corner of the slab, foundation void or insufficient support strength, which leads to the concrete slab breaking from the corner. Maintenance adopts conventional repair and polymer modified self-compacting concrete repair. The repair method of polymer modified self-compacting concrete is to clean the pavement first, draw the treatment area with chalk and determine the cutting range. According to the scribing, cut into grooves more than 5cm deep with a cutting machine, and mix the concrete with a drum mixer. When mixing, accurately control the dosage of expansion agent and early strength agent. Soak the cleaned concrete surface in water for 30 minutes, then clean the interface water, then brush a layer of cement slurry on the interface, wipe the edge with a rag, evenly brush the resin glue brush on the waterstop and the edge of the old concrete, and stick the glue strip on the concrete kerf according to the principle that the upper surface is the same height as the concrete surface. Pouring concrete, vibrating with a vibrating rod, covering with plastic film for curing, and opening to traffic in three days.
3, corner peeling repair
Corner peeling refers to the damage within 60cm width on both sides of the joint or within 15cm board angle. The causes of peeling at corners are hard sundries falling into joints, repeated traffic loads, improper design or construction of dowel bars, and low concrete strength at joints. The maintenance method of corner peeling is to clean the peeling surface when the corner peeling slightly, chisel it into a regular vertical surface and repair it with joint materials. The repair method of severe angular spalling adopts polymer modified self-compacting concrete to repair. The repair method of corner deep fracture adopts the methods of serious crack and plate angle fracture.
4. Repair of errors
Staggered platform refers to the vertical height difference between adjacent panels at the joint. The reasons are the effect of vehicle load, the influence of temperature and humidity, the absence of dowel bars at transverse joints, improper construction operation and other factors. Slight dislocation is mainly smoothed by grinder. The specific operation steps are as follows: from the highest point, the longitudinal slope is controlled within 65438 0%, and the transverse width is determined according to the dislocation width until two adjacent plates are flush. Sprinkle water at the same time when grinding, and carve patterns after grinding. Remove the sundries in the connector, blow off the dust and refill the connector.
3. Conclusion
The maintenance of cement concrete pavement is also very important in practical use. In order to reduce the cost of highway maintenance and improve the economic benefits of highways, many countries are vigorously developing new repair technologies. In the period of large-scale construction of cement concrete, it is particularly critical to maintain the existing road network in time for maintaining the road integrity rate and controlling the maintenance cost. Vehicles, especially freight vehicles, are generally overloaded all over China, which undoubtedly increases the bearing burden of the existing pavement and leads to premature damage of the pavement. Both new roads and old roads need necessary maintenance, which is very necessary to prolong service life and improve service quality.
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