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Construction methods for repairing damaged concrete pavement

1 Causes of damage to cement concrete pavement

1.1 Water is the direct external cause of cement concrete pavement disease. Water control must be done before building roads. Water is the first necessity in highway engineering and highway maintenance work. One of the main problems that has been solved is a direct external cause of early disease of cement concrete pavement. Every spring and winter, due to the infiltration of surface water and the rise of underground water levels, the humidity of the roadbed is directly changed, which reduces the strength of the road and the bearing capacity of the roadbed, thus leading to the occurrence of road diseases, such as a heavy rain and several consecutive rainstorms. After the rain, the road surface begins to crack in small areas, and then large areas of loosening, muddying, potholes and other phenomena appear.

1.2 Over-limit and overloaded vehicles are potential external causes of early disease on cement concrete pavement. Over-limit and overloading of road transport vehicles is another major external cause of early disease on highway cement concrete pavement.

According to relevant statistics: the increase in the vehicle's overload weight and its damage to the road surface increase geometrically. A truck that is 10% over the limit will cause 40% more damage to the road, and a truck that is overloaded is 2 times more likely to cause damage to the road. When a vehicle travels once, the damage to the road is equivalent to that of a non-overloaded vehicle driving 16 times. The damage to the road caused by a 36-ton overloaded vehicle is equivalent to the damage caused by 9,600 1.8-ton vehicles. The damage caused by overloaded vehicles to the road structure The damage causes cracks, deformation, loosening, subsidence and potholes in the road network.

1.3 Unreasonable and non-standard pavement design, construction and non-standard pavement design, unreasonable and non-standard construction are the internal causes of early disease of cement concrete pavement. First, the pavement structure design is unreasonable, the asphalt surface structure is improperly selected, and the mixture type is unreasonable. Second, the improper design of the reinforcement thickness of the pavement base (subbase) leads to early diseases of the asphalt surface layer, such as cracks, looseness, and local subsidence. Third, the pavement construction is not standardized, the materials are not strictly controlled, and the construction equipment is outdated and unmatched. As a result, the mix ratio design, mixing uniformity, compaction, and flatness of the asphalt mixture do not meet the standard requirements, resulting in loose and loose surface layers. Cracks and other diseases.

1.4 Improper and timely initial maintenance of the pavement. Timely and appropriate initial maintenance of the cement concrete pavement surface will extend the service life of the cement concrete pavement, otherwise it will shorten its service life. Due to insufficient maintenance funds or an unclear management and maintenance system, there has been a phenomenon of under-reconstruction and maintenance. In some places, especially the current cement concrete pavements in Tongxiang and Tongcun, no one has ever repaired some roads a year after they were repaired, and even more Not to mention initial maintenance.

2 Repair method of damaged cement concrete pavement

Renovation of cement concrete pavement is simple and easy to repair damaged concrete pavement, but it requires a large amount of crushing of old pavement, vibrating roadbed, Re-laying the base and surface layers requires a lot of work, and it is difficult to maintain traffic during the construction period. Moreover, some areas have been renovated before, but the results were not ideal. Therefore, the ideal repair plan is as follows:

First, calculate the thickness of the overlay layer based on the ordinary concrete overlay layer: the steel fiber concrete overlay layer should be 0.55 to 0.65 times the thickness of the ordinary concrete overlay layer; continuously reinforced concrete The overlay layer shall be 0.9 times the thickness of the ordinary concrete overlay layer, and the thickness shall also meet the minimum thickness requirements of the overlay layer. To determine the thickness h of the ordinary concrete overlay layer, the principle of equal stiffness is adopted. According to the bonding conditions of the separated overlay layer, the double-layer concrete slab is converted into an equivalent single-layer concrete slab to calculate its load stress and temperature stress, and then the old concrete is calculated Stress on the underside of slab and overlay. When the stress of the old concrete pavement and the stress of the overlay layer both meet the specification requirements, the thickness h of the overlay layer is determined, otherwise it is recalculated. Assume that a 24-hour traffic volume survey is conducted on this road section. The vehicle axle load is converted into the number of times under standard axle load Ns=125n/d. The design service life is 20 years. The average annual growth rate of traffic volume is 14%. The old cement concrete The flexural and tensile strength of the pavement panel fem=4.3MPa, the flexural and tensile elastic modulus Ee=28×103MPa, and the equivalent resilience modulus of the top surface of the base layer Et=87.83MPa. After calculation, the thickness of the ordinary concrete overlay layer is h=17cm, so it is continuous The thickness of the reinforced concrete overlay layer ha′=0.9×h=16cm; the thickness of the steel fiber concrete overlay layer ha=0.6×h=11cm.

Secondly, analyze the properties and functions of steel fiber concrete.

Steel fiber concrete is a composite material mixed with a certain amount of low carbon steel or steel fibers in cement concrete. It is a composite material that is a mixture of fiber type and particle type. It becomes one through the interface between the two. In the process, the two materials each exerted their own strengths and significantly improved various performance indicators of concrete. Moreover, steel fiber concrete pavement can also be laid, vibrated and smoothed using the construction methods of general concrete pavement. No special machinery is required and the construction is simple. Comprehensive comparison, the use of steel fiber concrete overlay is the best solution.

3 Construction Points of Steel Fiber Concrete Overlay

The quality of concrete pavement slabs depends to a large extent on the construction quality. When constructing steel fiber concrete pavement, in addition to meeting the general requirements for ordinary concrete pavement construction, attention should also be paid to:

3.1 Inspection and renovation of old pavement For slabs that are severely broken and cracks continue to develop in the old pavement, Crush, clear, and re-concrete. In order to prevent the cracks of the old cement concrete slab from reflecting upward, clean the old road surface first, then apply a layer of asphalt according to the standard of 1.0~1.5kg/㎡, and add a layer of oil felt with a uniform thickness as an isolation layer.

3.2 Material test and concrete mix ratio The mix ratio should ensure that the steel fiber concrete has a large flexural strength to meet the requirements of compressive strength and flexural strength of the structural design and the ease of construction. In order to ensure that the mixture has a uniform texture and does not segregate during construction, the aggregates should be continuously graded, and the maximum particle size of coarse aggregates should not be greater than 20mm. The length of steel fiber should be 25-60mm, the diameter 0.4-0.7mm, and the optimal ratio of length to diameter is 50-70. The volume ratio of steel fibers in the mix ratio of steel fiber concrete is 1.0% to 1.2%, and the sand ratio is slightly higher than that of ordinary concrete.

3.3 Construction of concrete slabs

3.3.1 During the concrete mixing process, in order to ensure the uniform distribution of steel fibers, gravel, steel fibers, sand, and cement should be added in the order. After dry mixing for 2 minutes, add water and wet mixing for 1 minute.

3.3.2 Due to the high cement content in steel fiber concrete, the short initial setting time and the rapid slump loss, it is required that the time from discharging to completion of pouring should not exceed 30 minutes.

3.3.3 In order to ensure the two-dimensional distribution of steel fibers, it is advisable to use a flat vibrator for vibration forming.

3.3.4 Construction should be carried out in the morning and at night when the temperature is lower as much as possible. When the temperature is higher than 30℃ and the temperature of the mixture is 30-35℃, it is advisable to stop the work to prevent the moisture of the mixture from evaporating and causing shrinkage and cracking.

3.3.5 It is best to use a forced mixer, because the self-falling mixer has a slow discharging speed and the steel fibers can easily form agglomerates when rolling.

3.3.6 Steel fiber concrete has small shrinkage and good crack resistance. Longitudinal joints are not required. When the steel fiber concrete is poured and cured to reach 50% of the design strength, a shrinkage joint can be cut every 15m.

3.4 Plastering and anti-slip steel fiber concrete has the characteristics of fine coarse aggregate, high sand rate, and random fiber distribution. It is advisable to use vacuum water absorption technology and mechanical smoothing to prevent fiber exposure. When plastering, the steel fibers emerging from the concrete surface need to be pulled out, and the embossing process using an embossing machine can avoid the exposure caused by plucking.

3.5 The moisture curing method is used for curing and caulking. After the concrete surface is renovated, curing should be carried out immediately, and the concrete surface should be covered with 20 to 30mm thick wet sand. Sprinkle water evenly several times a day. The curing time is determined by testing and is based on when the concrete reaches more than 80% of the 28d strength. After the curing period has expired, modified asphalt can be used to seal the joints. When filling joints, keep the joints clean and dry. The joint filling material should adhere tightly to the joint wall and be impermeable to water. The filling height is generally about 2mm lower than the board surface.