Section III: structural characteristics of cement concrete pavement

Cement concrete pavement The structure consists of subgrade 、 Cushion 、 The basic level as well as Surface course .

1、 Structural characteristics

One 、 Cushion

In an environment with poor temperature and humidity , Cement concrete road shall be provided with cushion , To improve the pavement performance .
（1） stay Seasonally frozen areas , The total design thickness of the road structure is less than the minimum anti freezing thickness When required , according to Subgrade dry and wet type and Characteristics of subgrade filler Set cushion , The difference is the thickness of the cushion . Soil cutting with poor hydrogeological conditions , When the moisture of subgrade soil is high , Should be set Drainage cushion . The subgrade may cause uneven settlement or Uneven deformation when , It is advisable to add Semi rigid cushion .
（2） Width of cushion It should be the same as the subgrade width , Its minimum thickness is 150mm.
（3） Sand should be used for antifreeze cushion and drainage cushion 、 Granular materials such as gravel , Low dose cement should be used for semi-rigid cushion 、 Lime and other combined stable granular materials or soil materials .

Two 、 The basic level

（1） Function of cement concrete road base ： To prevent or mitigate from pumping As a result of The bottom of the board is hollow and Staggered platform And other diseases ; Together with the cushion , It can control or reduce the adverse effect of uneven frost heave or volume deformation of subgrade on concrete surface ; Provide a stable and solid foundation for the concrete surface , and Improve the load transfer capacity of joints .
（2） Selection principle of base course materials ： according to Road traffic grade and Anti scouring capacity of subgrade To select the base material . Lean concrete should be selected for special traffic 、 RCC or asphalt concrete ; Cement stabilized aggregate or asphalt stabilized macadam shall be selected for heavy traffic roads ; in 、 Cement or lime fly ash stabilized aggregate or graded aggregate shall be selected for light traffic roads . Humid and rainy areas , Drainage base course shall be adopted for heavy traffic sections .
（3） The width of base course shall be different according to the construction method of concrete surface course , At least... Wider than each side of the concrete surface course 300mm（ During the construction of small machines and tools ） or 500mm（ During the construction of rail mode paver ） or 650mm（ During the construction of sliding mode paver ）.
（5） To prevent the subgrade from being affected by water seepage , The drainage base course shall be provided with Cement stabilized aggregates or Dense granular material An impermeable subbase composed of , The top surface of subbase should be paved Asphalt seal coat or waterproof geotextile .
（6） RCC base course Joints corresponding to the concrete surface course shall be set .

3、 Surface course

（1） The surface concrete is usually divided into Ordinary （ plain ） concrete 、 reinforced concrete 、 Continuously graded concrete 、 Prestressed concrete etc. . At present, China mostly adopts Ordinary （ plain ） concrete . The cement concrete surface course shall have sufficient Strength 、 Durability （ Frost resistance ）、 Surface skid resistance 、 wear-resisting 、 smooth .
（2） The plate length of each rectangular plate is as follows Type of finish 、 The thickness of the And by the Stress calculation determine .
（3） Longitudinal joints are based on Pavement width and Construction paving width Set up . When the one-time paving width is less than the pavement visibility , Should be set With pull rod In the form of flat seams Longitudinal construction joints . The one-time paving width is greater than 4.5m when , Should be set With pull rod In the form of a false seam Longitudinal contraction joint , The longitudinal joint shall be parallel to the centerline of the line .
Transverse joints can be divided into Transverse contraction joint 、 Expansion joint and Transverse construction joint . The transverse construction joint shall be selected at the contraction joint or expansion joint as far as possible . Expressway 、 Dowel bar shall be added to the transverse expansion joint of the main road ; Near bridges or other fixed structures 、 Where the plate thickness changes 、 Small radius horizontal curve, etc , Expansion joints shall be provided .
（4） about Special traffic grade concrete pavement , Transverse expansion joint 、 Dowel bar shall be set for contraction joint . stay At the free edge , Expansion joint bearing heavy traffic 、 Construction joints , Less than 90° The corner of the surface layer , Under the municipal pipeline pavement , as well as Around rainwater inlets and underground inspection wells , Reinforcement shall be provided .
（5） Anti sliding structure — The concrete surface shall have a large roughness , That is, it has high anti sliding performance , To improve the safety of driving . In this way Grooving 、 Pressure groove 、 Broaching or Roughening And other methods to form a certain structural depth .

2、 Selection of main raw materials

（1） Roads with heavy traffic or above 、 Urban Expressway 、 The trunk road shall adopt 42.5 Portland cement for roads above grade 、 Ordinary portland cement ; Other roads can use the same slag cement , Its strength grade should not be lower than 32.5 level .
Cement with a factory life of more than three months or affected with moisture , must After testing , It can be used only after it is qualified .
（2） Coarse aggregate shall be hard 、 Durable 、 Clean gravel 、 Gravel 、 Crushed gravel , The technical indicators shall meet the specification requirements , Coarse aggregate should be used Artificial grading , Maximum nominal size of coarse aggregate , Crushed gravel shall not be greater than 26.5mm, The crushed stone shall not be greater than 31.5mm, Gravel should not be larger than 19.0mm.
（3） Silhouette of the appropriate place , The fineness modulus is 2.5 above , Clean coarse sand conforming to the grading requirements 、 Medium sand . Sea sand shall not be used directly on the concrete surface . Desalinated sea sand should not be used in urban expressways 、 The main road 、 Secondary road , Available for branch .
（4） Admixtures shall undergo mixing test .
（5） Reinforcement Varieties 、 specifications 、 composition , It shall comply with the design and current national standards , Having a manufacturer Brand 、 Heat number , Inspection Report and Certificate , And by Second interview （ Including witness sampling ） qualified . The reinforcement shall not be rusted 、 Crackle 、 Defects such as cuts and nicks . Dowel bar （ Pull rod ）、 Sliding sleeve material 、 The specifications shall comply with the regulations .
（6） The expansion joint plate should be thick 20mm, Good water stability , have A certain flexible sheet Make , And shall be approved by Antiseptic treatment . Caulking seasoning should be used Resin 、 Rubber 、 PVC mastic 、 Modified asphalt Caulking material , And should add Anti aging agent .