There are two common diseases in cement concrete pavement, one is the damage of cement concrete slab, and the other is the damage of joints.

Causes of damage of cement concrete slab;

1, longitudinal crack

Longitudinal cracks usually occur in high fill, half-filled and half-excavated sections, filling-excavation joints and soft soil foundation sections, which are mainly caused by uneven lateral settlement of subgrade or uneven support under slab, especially when embankment passes through local depression, if there is no effective drainage on both sides of embankment, water will be generated on both sides of facilities and embankment, which will not only penetrate into foundation, but also into the lower part of embankment. In the marginal soil layer, the soil layer on the upper edge of the embankment becomes wet gradually by capillary action. Because the soil density at the edge of the embankment is worse than that at the middle part, once the soil at the edge becomes wet, the soil at the edge will be consolidated and deformed, and the lateral settlement of the embankment will be uneven. Under the action of traffic load, over time, longitudinal cracks will appear on the pavement, and the subgrade in the half-filled and half-dug section will not be treated well, which will also lead to longitudinal cracks in the middle road. In addition, in some expressway, the overtaking lane and the main lane are filled first, half of the subgrade is filled to keep the route passing, and then the rest are filled. When paving with large slip-form machinery, due to the high speed, the vibrating rod can not be fully vibrated, and longitudinal cracks will also occur.

2. Transverse oblique cracks

Transverse and oblique cracks of pavement usually occur in ① filling and excavation intersection, ② crossing between new and old subgrade, ③ different density parts of soil foundation, ④ joint between bridge and culvert and subgrade, ⑤ soft foundation, ⑤ subsidence loess and other special sections. The reason is that the strength of soil foundation is insufficient or uneven, and after concrete pouring. Because the friction coefficient of each section at the bottom of the slab is different, it is likely that the mixed slab will shrink before the slotting, and the tensile stress and temperature stress will be concentrated, which will exceed the tensile stress of concrete at that time. (3) the temperature difference is large, and the temperature difference between day and night of concrete pavement constructed in spring and autumn is large, generally at 7-8℃, and the highest temperature can reach 12℃. The sensitivity of the upper surface and the lower surface of the concrete slab to the external temperature is also quite different, which is generally around 10℃, resulting in a large warping stress due to the influence of temperature. ④ The cement used in cement concrete pavement is based on the building index, but so far there is no cement with road index, and only additives can be used for retarding, and the material index is unstable. (5) in the process of artificial construction, vibrating rod should be inserted in plum blossom shape. Too much insertion in the first section, too much slurry in this section, and the aggregate is concentrated in layers, which makes the sinking aggregate concentrated, with less slurry content, small shrinkage value, less slurry in the upper layer and large shrinkage value. This part breaks easily. ⑥ Unreasonable vacuum water absorption lap joint treatment leads to uneven distribution of water content in the concrete slab, the middle part has reached the plastic strength, and the edge is still in an elastic and soft state, which makes the lap joint easy to break, ⑥ maintenance is not timely, or there is a maintenance blank section on the longitudinal slope of the pavement, which reduces the strength and may lead to cracks. ⑧ Due to continuous construction and half-width construction, when the concrete is poured with plastic strength, cracks may appear in the concrete slab due to the vibration caused by the driving of heavy vehicles next to it. Pet-name ruby construction, when two cars meet without special attention, vibration is not dense, honeycomb, thus forming a weak section, prone to cracks on the section. Attending when the longitudinal slope of the route exceeds 20%, the upper slope should be taken as the construction direction as far as possible, and the downhill construction will also cause cracks due to slump. ⑾ Due to untimely maintenance during construction, shrinkage cracks appear, which are narrow, short and shallow. Although it will not affect the normal use of pavement, it will reduce the wear resistance and corrosion resistance of pavement, aggravate the weathering of concrete and affect the service life.

3. Corner falling

Due to expansion and contraction or improper selection of joint filler, or failure of joint filler, the surface water of pavement does not leak along the joint, especially the drainage of the base under the slab is not smooth, or there are too many fine materials in the base material, and the erosion resistance of the base material is poor. Under the repeated action of vehicle load, vacuum suction will produce mud at the corner, scour the bottom of the slab, cause the stress concentration at the corner of the slab, lead to the corner of the pavement slab, and the joint force transmission ability of the pavement slab is poor. In order to make the edges and corners easy to vibrate, and the bee surface is less, some concrete with less coarse aggregate is specially used, and the vibrating time is longer, resulting in too much cement slurry on the surface, concentrated delamination and segregation of aggregate, which reduces its flexural strength. On the other hand, due to the low vibration density, there are honeycomb pits on the corners. In both cases, the wheels are easy to fall off.

4. Cross cracks and broken plates

Cross cracks and broken slabs are serious damage forms of cement concrete pavement, which have great influence on the safety and comfort of driving. Serious road transportation overload, insufficient thickness or low strength of pavement slab, loose or insufficient strength of slab subbase, uneven settlement of soil foundation, high groundwater level and liquefaction of subgrade may all lead to cross cracks or broken slabs on pavement slab. In addition, when various cracks such as longitudinal, transverse and oblique cracks appear on the pavement, if the maintenance is not timely, the pavement water will enter the base or subgrade along the cracks, resulting in the base and subgrade being soaked and softened. Under the repeated action of heavy load, the cracks will further expand, and so on. Over time, the pavement will produce cross cracks and even fractures.

5, holes

Cracks and holes appear on the surface of concrete pavement, which are mainly caused by poor construction quality, or the inclusion of dead wood paper and mud leaves in concrete materials, and the inclusion of ice cubes in water during spring construction.

6. The wear layer falls off locally

Part of the wear layer falls off, resulting in exposed pits. The reasons are as follows: ① The metal hard wheels of some vehicles and machinery running on the road collide with hard stones and rub the road surface, causing damage; ② During construction, the setting time exceeds the initial setting time due to unreasonable retarder gradation or unstable index, resulting in loss of surface strength. (3) During construction, the concrete slab after vibrating is not thick enough. In order to save trouble, only mix mortar for leveling, or push and roll to form a layer of mortar. This place not only causes uneven surface water-cement ratio, but also causes cracks, even peeling and exposure under the repeated action of wheels. If the stability of cement is poor, it is easy to have pits.

Causes of joint damage:

Joint is the weak link of cement concrete pavement, and there are many kinds of diseases. The forms and influence scope of joint diseases and damages mainly include: joint extrusion, bulging, mud pumping and slab bottom void, staggered platform, joint filler loss and falling off. And other diseases.

1, joint crushed

Joint crushing means that cracks or concrete fragments do not extend to the entire thickness of the board within a width range of about 50CM near the joint or crack. The joint crush is mainly due to improper joint construction (including the joint plate is not vertical, and the dowel bar and pull rod are improperly arranged), or the joint is blocked by hard stones due to joint filler, peeling, extrusion and aging. When concrete expands, the upper part of concrete slab produces concentrated compressive strength, which exceeds the resistance of concrete. The slab was crushed by shear, and the strength of concrete at both ends of the joint was inconsistent. Due to the action of dowel bar, concrete slab will also break. However, this kind of situation is generally rare in ordinary road sections, and it mostly occurs at the joint of structures. In addition, the vibrating density of the concrete at the edge of the slab is low, and the strength is reduced, or the base and subgrade are weak and muddy after the joint seepage, which leads to the slab bottom falling off in a small range along the joint edge. Under the repeated action of traffic load,

2. Arch

The expansion joint spacing of concrete slab is long, and the expansion of concrete slab is not obvious before 1 ~ 2 years. When shrinkage occurs, the joint will fall into the soil or stone due to the failure of the joint filler. In addition, if the maintenance is not cleaned in time, the slab joints will expand year after year due to thermal expansion and cold contraction, resulting in the pressure generated when the concrete slab expands greater than the friction between the base and the concrete slab. However, when the compressive strength of concrete is not exceeded, due to the elongation of the slab, it will be adjacent to the real joint, and the two slabs will arch upward. Some expansion joints arch, and after falling, the plates break, reaching as much as 17 cm after overlapping. According to incomplete investigation, when the temperature is low in spring and autumn, the concrete pavement is more prone to arching because of its large expansion. The arch disease of concrete pavement in our city has been used for six years.

3, pumping mud and plate bottom gap

The diseases of boiling and void at the bottom of the board refer to the cracks in the joint or the fine base material under the edge of the board is infiltrated, and the pressure water stuck to the bottom of the board is pumped out from the joint or the edge, resulting in local void between the bottom of the board and the top of the board. The main reasons for pumping mud are the failure of joint sealant, poor joint load transfer ability and repeated action of heavy load. When the highway drainage system is not perfect, such as improper setting of road cross slope or poor drainage of subgrade. When the roadbed and pavement are soaked in water, the pavement will also have the phenomenon of boiling, and then the bottom of the slab will be empty; In addition, due to the local looseness of base material, uneven compaction of subgrade soil or uneven settlement of base will also lead to the void of base plate.

4. Wrong channel

There are many reasons for this. For example, ① When the lower joint plate of expansion joint is not aligned with the upper joint, or the joint is not vertical, the two plates next to the joint will move up and down in the process of telescopic extrusion, resulting in dislocation. ② Because of the infiltration of water, the grass-roots will become soft. ③ Unreasonable arrangement of dowel bars reduces the force transfer effect, leading to wrong platform. (4) when the traffic volume or bearing capacity of the base surface is unevenly distributed in each transverse frame, the settlement of each transverse frame is inconsistent, or the soil of subgrade filler is uneven, the groundwater level is high and the rolling is uneven.

5. Loss and loss of filler materials

Under the action of joint filler failure and wheel vibration, the joint filler will be squeezed out and taken away by the wheel.