With the rapid development of China's economy, the volume of highway traffic has increased, and the proportion of heavy-duty transport vehicles has become larger. This imposes higher requirements on the structural strength and service performance of highway pavements, while cement concrete pavements have high strength. Good stability, good water resistance, long service life, low maintenance cost, etc. Therefore, cement concrete pavement has occupied a place in high-grade highways in recent years, and new material and new technologies have been continuously promoted and applied in the construction of cement concrete pavement.
Subgrade settlement observations In the vast majority of cases, early stage slab failures on the cement concrete pavement of expressways were caused by unstable subgrade and excessive settlement. In order to prevent this phenomenon, we should first make observations on the entire highway highway cement concrete pavement subsidence, and carry out a detailed reinforcement design for the construction of the road section with large settlement, and calculate the unevenness of the permanent cement concrete pavement. Settlement limits, which effectively guarantee the quality and stability of highway cement concrete pavement subgrade, and prolong the service life of cement concrete pavement.
New technology for stabilizing the mud-concrete roadbed According to the characteristics that the cement concrete pavement is more sensitive to the stability of the roadbed than the asphalt pavement, it is required that the subgrade filling of the high-grade highway cement concrete road surface be increased to a level of compaction standard. For compacted soils and sandy soils with a particle size below the loam, heavy-duty road rollers are used for compaction; for clayey soils with a high plasticity index, roadbed lime is used to improve soil stabilization technology.
Adopting compaction standards and compaction measures for heavy-duty compactors on multi-segment highways, and using roadbed lime to improve soil stabilization technology, it has strongly ensured the quality and stability of expressway cement concrete pavement subgrade or grass-roots level, and greatly extended cement. The service life of concrete pavement. Subgrade improvement technology is a technology adopted for high-plastic clay, soft soil or roadbed frequent excavation sections where the degree of compaction cannot meet the requirements. On the one hand, the strength, load-bearing capacity and stability of the soft soil subgrade are improved; on the other hand, the road The improvement of soil in bed is equivalent to adding a solid foundation layer, which will play a significant role in improving the service life of cement concrete pavement.
The lean concrete base layer slipform paving technology uses the lean concrete base layer slipform paving technology, and puts forward clear technical requirements for the raw materials, mix ratio, paving and quality acceptance of the poor concrete base layer, and expands the domestic and foreign think The new type of grass-roots that resists water erosion, has the highest strength and longest service life, and its construction technology and quality acceptance control standards. Its significance will be gradually displayed in the construction and maintenance of expressways in the future in China. We hope that in the future the highway base in China will be able to use for more than 50 years without renovating and only renovating the surface layer.
The main advantages of the new technology of the sliding closed layer using the asphalt surface at the surface of the upper base or the sliding sealing layer of the slurry is that it is beneficial to prevent the breakage; it is beneficial to prevent the long-term water erosion damage of the semi-rigid base; it is conducive to the health of the base; it is beneficial to prevent During the construction period, the wheels of the transport vehicle will crush or crush the surface of the base layer; this will help the protection of the grass through the winter. However, in order to prevent the expansion joint from swelling after using the bitumen sliding sealing layer, the width of the expansion joint plate should be increased by 5mm.
High-flexural-tensile-strength pavement-sliding-molded concrete uses high-shear tensile strength cement concrete pavement slipform paving technology, mainly using high-performance road concrete admixture admixtures and fly ash “double-blending technology†for ultra-heavy-duty traffic reduction. The thickness of the thin plate increases the resistance of the panel to breakage and increases the safety reserve of the road surface for damage to the overweight axis. At present, the average bending strength of pavements for slipform paving using high-performance road concrete technology in China is between 6.5 and 7.5 MPa. This is the high bending strength that we have not seen in the international literature so far. Leading level.
High-Precision Slipform Paving Technology for Cement Pavements At present, the smoothness of a static 3m ruler for slipform paving cement concrete pavements of highways and first-class highways in China is generally not less than 3mm, which is more than 90%; the overall dynamic flatness is basically δ. At around 1.0, the best cement concrete pavement has reached a mark of δ ≤ 0.76, and the best 6 km single-pass road has reached δ ≤ 0.45, which is much smaller than the δ ≤ 1.5 specified in the acceptance standard. These data show that China's high-level cement concrete pavement has reached the international advanced level; at the same time, it shows that there is potential for further improvement in the smoothness of China's slipform paving cement concrete pavement; in the end, China's slipform paving cement concrete pavement The flatness will be comparable to asphalt pavement.
Crack Control Technology for Cement Concrete Pavement Further mastered the crack control technology of slipform paving cement concrete pavement. The first is to prevent plastic shrinkage cracks during construction; the second is to use the initial temperature difference, wet differential cracks and broken plates; more importantly, the construction technology and control indexes to eliminate longitudinal cracks are proposed. It should be said that it is a long way to prevent the cracking of cement concrete pavement. At present, there are not many people who really master the technology. If the actual work is not careful, there will still be cracking and broken plates. The main technical measures to solve cracking and breaking are: in the windy days, to prevent plastic shrinkage and cracking, to use crack-resistant concrete mix ratio, and to spray health-care agents in advance to strengthen the health measures; to use asphalt to slide the closed layer to reduce the surface of the upper baseboard The annual temperature difference, season wet shrinkage cracks and breakage plates; deepen the kerf depth (1/3.1/4)h of all joints between the push rod and the force transmission rod, and advance the slitting time to prevent longitudinal fracture.
Research on freeze-thaw and salt-frost resistance of cement concrete pavement is the first time in China to study and use anti-freezing and salt-freezing slipform paving technology for cement concrete pavement (Heilongjiang and Jilin, 1998). The air content and air bubble spacing of concrete pavement are clearly stated. The testing methods and standards provide effective technical measures to solve the freezing and salt-freezing delamination of the surface of cement concrete pavement in northern China, and demonstrate that non-delaminated high-quality cement concrete pavements can also be constructed in northern China.
At present, this content still needs to directly adopt the EU's anti-salt freezing test method in Heilongjiang and other provinces, and formulate it as a standard test method in China through research. In addition, it is urgent to study the mechanism of salt-freezing and the prevention and control measures for cement concrete pavement.
Subgrade settlement observations In the vast majority of cases, early stage slab failures on the cement concrete pavement of expressways were caused by unstable subgrade and excessive settlement. In order to prevent this phenomenon, we should first make observations on the entire highway highway cement concrete pavement subsidence, and carry out a detailed reinforcement design for the construction of the road section with large settlement, and calculate the unevenness of the permanent cement concrete pavement. Settlement limits, which effectively guarantee the quality and stability of highway cement concrete pavement subgrade, and prolong the service life of cement concrete pavement.
New technology for stabilizing the mud-concrete roadbed According to the characteristics that the cement concrete pavement is more sensitive to the stability of the roadbed than the asphalt pavement, it is required that the subgrade filling of the high-grade highway cement concrete road surface be increased to a level of compaction standard. For compacted soils and sandy soils with a particle size below the loam, heavy-duty road rollers are used for compaction; for clayey soils with a high plasticity index, roadbed lime is used to improve soil stabilization technology.
Adopting compaction standards and compaction measures for heavy-duty compactors on multi-segment highways, and using roadbed lime to improve soil stabilization technology, it has strongly ensured the quality and stability of expressway cement concrete pavement subgrade or grass-roots level, and greatly extended cement. The service life of concrete pavement. Subgrade improvement technology is a technology adopted for high-plastic clay, soft soil or roadbed frequent excavation sections where the degree of compaction cannot meet the requirements. On the one hand, the strength, load-bearing capacity and stability of the soft soil subgrade are improved; on the other hand, the road The improvement of soil in bed is equivalent to adding a solid foundation layer, which will play a significant role in improving the service life of cement concrete pavement.
The lean concrete base layer slipform paving technology uses the lean concrete base layer slipform paving technology, and puts forward clear technical requirements for the raw materials, mix ratio, paving and quality acceptance of the poor concrete base layer, and expands the domestic and foreign think The new type of grass-roots that resists water erosion, has the highest strength and longest service life, and its construction technology and quality acceptance control standards. Its significance will be gradually displayed in the construction and maintenance of expressways in the future in China. We hope that in the future the highway base in China will be able to use for more than 50 years without renovating and only renovating the surface layer.
The main advantages of the new technology of the sliding closed layer using the asphalt surface at the surface of the upper base or the sliding sealing layer of the slurry is that it is beneficial to prevent the breakage; it is beneficial to prevent the long-term water erosion damage of the semi-rigid base; it is conducive to the health of the base; it is beneficial to prevent During the construction period, the wheels of the transport vehicle will crush or crush the surface of the base layer; this will help the protection of the grass through the winter. However, in order to prevent the expansion joint from swelling after using the bitumen sliding sealing layer, the width of the expansion joint plate should be increased by 5mm.
High-flexural-tensile-strength pavement-sliding-molded concrete uses high-shear tensile strength cement concrete pavement slipform paving technology, mainly using high-performance road concrete admixture admixtures and fly ash “double-blending technology†for ultra-heavy-duty traffic reduction. The thickness of the thin plate increases the resistance of the panel to breakage and increases the safety reserve of the road surface for damage to the overweight axis. At present, the average bending strength of pavements for slipform paving using high-performance road concrete technology in China is between 6.5 and 7.5 MPa. This is the high bending strength that we have not seen in the international literature so far. Leading level.
High-Precision Slipform Paving Technology for Cement Pavements At present, the smoothness of a static 3m ruler for slipform paving cement concrete pavements of highways and first-class highways in China is generally not less than 3mm, which is more than 90%; the overall dynamic flatness is basically δ. At around 1.0, the best cement concrete pavement has reached a mark of δ ≤ 0.76, and the best 6 km single-pass road has reached δ ≤ 0.45, which is much smaller than the δ ≤ 1.5 specified in the acceptance standard. These data show that China's high-level cement concrete pavement has reached the international advanced level; at the same time, it shows that there is potential for further improvement in the smoothness of China's slipform paving cement concrete pavement; in the end, China's slipform paving cement concrete pavement The flatness will be comparable to asphalt pavement.
Crack Control Technology for Cement Concrete Pavement Further mastered the crack control technology of slipform paving cement concrete pavement. The first is to prevent plastic shrinkage cracks during construction; the second is to use the initial temperature difference, wet differential cracks and broken plates; more importantly, the construction technology and control indexes to eliminate longitudinal cracks are proposed. It should be said that it is a long way to prevent the cracking of cement concrete pavement. At present, there are not many people who really master the technology. If the actual work is not careful, there will still be cracking and broken plates. The main technical measures to solve cracking and breaking are: in the windy days, to prevent plastic shrinkage and cracking, to use crack-resistant concrete mix ratio, and to spray health-care agents in advance to strengthen the health measures; to use asphalt to slide the closed layer to reduce the surface of the upper baseboard The annual temperature difference, season wet shrinkage cracks and breakage plates; deepen the kerf depth (1/3.1/4)h of all joints between the push rod and the force transmission rod, and advance the slitting time to prevent longitudinal fracture.
Research on freeze-thaw and salt-frost resistance of cement concrete pavement is the first time in China to study and use anti-freezing and salt-freezing slipform paving technology for cement concrete pavement (Heilongjiang and Jilin, 1998). The air content and air bubble spacing of concrete pavement are clearly stated. The testing methods and standards provide effective technical measures to solve the freezing and salt-freezing delamination of the surface of cement concrete pavement in northern China, and demonstrate that non-delaminated high-quality cement concrete pavements can also be constructed in northern China.
At present, this content still needs to directly adopt the EU's anti-salt freezing test method in Heilongjiang and other provinces, and formulate it as a standard test method in China through research. In addition, it is urgent to study the mechanism of salt-freezing and the prevention and control measures for cement concrete pavement.
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