The causes of early cracking and broken plate
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The raw material is not qualified
- The stability of cement is poor and the strength is insufficient. Free calcium oxide in cement hydrates very slowly during the setting process, and the cement continues to play a hydration role after setting and hardening, when the free calcium oxide exceeds a certain limit, it will destroy the cement stone that has hardened or make the tensile strength drop. Insufficient cement strength will also affect the initial strength of concrete, so that the chances of cracking and breaking the plate greatly increased. High heat of hydration of cement, shrinkage is also prone to cracking.
- Aggregate (sand, gravel, etc.) mud content and organic matter content exceeds the standard. Cement concrete with poor bonding of the interface between cement stone and aggregate is often the weak part of the initial cracking. Aggregate mud content and organic matter more than the specification requirements, will certainly cause interface defects, easy to crack. In addition, some data show that under the same water-cement ratio conditions, limestone, quartzite and other hydrophilic aggregates and cement stone interface bonding, granite and other poorly hydrophilic aggregates are the opposite.
Concrete with improper ratio
- Unit cement dosage is large. Concrete caused by shrinkage of the main cement stone part, too much cement dosage will inevitably lead to larger shrinkage.
- The water-cement ratio is large. Cement fully hydrated minimum water-cement ratio of about 0.26 to 0.29, the construction of a higher water-cement ratio in order to meet the need for ease of construction. However, the large water-cement ratio increases the thickness of the water film on the surface of the aggregate at the early stage of hydration, which affects the strength of the concrete.
Improper construction process
- Insufficient or excessive mixing, pounding is not dense, forming insufficient strength of concrete, or uneven, easily lead to early cracking or broken plate. Vibrating time is not easy to be too long, otherwise it will cause layering, coarse aggregates sink into the bottom layer, fine aggregates stay in the upper layer, uneven strength, and increased surface shrinkage cracks.
- Not timely maintenance or improper maintenance. Especially high temperature, low humidity, high wind speed, it will make the concrete surface moisture evaporates too fast, thus forming dry shrinkage cracks.
- Untimely cutting, due to machine failure or operator’s inaccurate grasp of cutting time or insufficient cutting depth, resulting in the concentration of stress within the concrete and the formation of irregular penetration cracks at the weak points of the concrete slab.
Reasons for cracked and broken slabs during use
Improper design
- Pavement thickness is thin. If the design of the traffic volume is not allowed, the modulus of the roadbed, grass-roots level, sub-base and material parameters are not properly selected and the pavement thickness is thin, it will shorten the life of the pavement and prematurely cracked and broken plate;.
- Improper slab plane size.
- Improper concrete raw material ratio, concrete produces alkali-aggregate reaction or poor freeze-thaw resistance and other durability problems.
Uneven settlement of roadbed
Uneven settlement of the roadbed mainly occurs in
- Filling and digging intersecting sections, half-filling and half-digging combination, the intersection of the old and new roadbeds, different parts of the soil base density.
- Weak foundations, wet sink loess and special sections such as mining areas and traps.
- Insufficient compaction. Compaction uneven road sections, in the long-term use of the pavement, due to changes in water temperature conditions and the role of traffic load, the roadbed produces uneven settlement, resulting in different settlement of the combined surface to produce misalignment, the panel due to the role of load leading to fracture.
Base layer instability
- Poor quality of grass-roots construction, uneven or low strength, the use of grass-roots loose or under the action of water seepage, the material is sucked to one side, the surface layer off the air, when the bending tension is greater than the strength of the concrete plate, the panel is fracture.
- Surface layer joint filler failure, plate bending and sinking so that the gap within the water, erosion wash grass-roots level, and along the seam gap spray, that is, to produce chirping mud. If the phenomenon of mud is constantly generated, the edge part of the panel will lose support, and produce fracture under the load.
Cement concrete pavement broken plate preventive measures
Prevention of early cracking and fracture
Qualified raw materials are the necessary condition to ensure the quality of concrete
- For poor safety, free calcium oxide exceeds the standard and insufficient strength of the cement is prohibited; different manufacturers, different types, different batches of cement is strictly prohibited to mix. Try to use silicate road cement or ordinary silicate cement with less heat generation and shrinkage.
- The mud content and organic matter content of the aggregate shall not exceed the standard, and the grading shall meet the requirements of the ratio.
Strictly control the concrete ratio
- Accurate ingredients according to the test concrete ratio, the unit cement dosage should be accurate, and the error value should be controlled within 1%.
- The water content of the aggregate should be taken in time for the test, control the suitable water consumption, keep the water-cement ratio accurate, in order to reduce the water consumption and improve the compatibility, use suitable external admixture, the error of water consumption should not exceed 1%, and the admixture should be controlled within 2%.
Control of construction process
- The concrete mixing time should be accurately grasped according to the mechanical properties, and the longest mixing time should not exceed 3 times of the shortest mixing time, and the vibrating should be even and dense to avoid the phenomenon of leakage or over-vibration.
- Strengthen the concrete panel regeneration. The use of cover regeneration, to ensure that the surface of the concrete panel wet.
- Timely cutting joints. According to the construction site temperature and cement variety test to determine the earliest cutting time, generally should use more than one cutting machine to operate at the same time to ensure timely cutting. The depth of cutting joints is 1/3~1/4 of the concrete slab thickness, and it is not advisable to cut joints too shallow (less than 1/4) or too deep (more than 1/3), and the remaining section part can absorb the internal stress due to high temperature.
Control of boundary influence
- To cut the joints of the post-poured panels in time.
- There is a central divider, curb and other structures construction, should be in contact with the concrete panel coated with asphalt, so that both sides free expansion.
- After the end of grass-roots regeneration, timely pouring cement concrete pavement, in order to prevent the grass-roots level due to long exposure time and dry shrinkage cracks. If cracks appear in the grass-roots level, closed crack treatment should be taken to prevent the reflection of cracks due to the grass-roots level to the panel.
Prevention of cracked and broken panels during service life
Design considerations
- Due to the rapid development of transportation industry, some large transport vehicles appear, which requires the design to fully consider the thickness of concrete pavement, plane size and concrete grade. Normal use within the design service life should be ensured.
- Choose raw materials suitable for local environmental conditions, and pay attention to freeze-thaw and durability.
Roadbed quality control
- Roadbed compaction quality requirements to achieve the specified compaction value and bending value, especially bridges and culverts and other structures must ensure the back of the platform compaction, to ensure that the roadbed has sufficient uniform strength.
- For the roadbed is not stable special weak soil base, wet sink loess, mining areas, traps, landslides and other sections, should avoid the use of cement concrete pavement, other special roadbed should be special treatment before the construction of cement concrete pavement.
Quality control of road base layer
The subgrade should have great stability and uniformity
- The grass-roots level should be cement-stabilized as far as possible, and the fines should be strictly controlled to increase the water stability of the grass-roots level and to prevent chirping mud.
- Strict control of the thickness of the base layer to ensure uniformity of strength.
- Use plant mix method to mix the grass-roots material to ensure uniform mixing and accurate batching.
- According to the design requirements, to ensure the compactness of the grass-roots level.
The causes of concrete pavement broken plate as described above, the construction and production of only one by one implementation of the control, in order to effectively prevent the emergence of broken plate. At the same time, timely measures should be taken to seal and fill micro-cracks, such as filling epoxy resin, and to strengthen maintenance work, and to deal with the problems found in the drainage system in time to avoid causing larger diseases. Bridge and culvert construction process, should be combined with the bridge deck pavement, seriously deal with the combination of road and bridge parts to prevent uneven settlement. In addition, the road should also be done in accordance with the law, strict control of overload, overweight, over-limit vehicle traffic.
