Lead: Cement stabilized macadam takes graded macadam as aggregate, fills the gap of aggregate with a certain amount of cementing material and sufficient mortar volume, and spreads and compacts it according to the principle of embedding and squeezing. Let's briefly talk about the requirements and control of cement stabilized macadam base. Welcome to read the reference!
This paper briefly introduces the technical index, raw material requirements, construction sequence and matters needing attention of cement stabilized macadam, which can be used as a reference for relevant personnel engaged in municipal and highway design and construction.
Key words: cement stabilized macadam; Unconfined strength; Cement dosage; Pave the road; Here we go.
Cement stabilized macadam and lime-fly ash macadam are usually used in traffic and urban road base, among which cement stabilized macadam has been widely used in traffic road base in Jiangsu Province in recent years, and gradually adopted in urban roads, breaking the original pattern of lime-fly ash macadam.
Cement stabilized macadam base: a mixture formed by adding a certain amount of cement to macadam or gravel aggregate with a certain gradation, paving and rolling. This kind of base has the advantages of simple construction technology, convenient material source, high strength, good water stability, good slab and so on, and is especially suitable for areas lacking fly ash or other industrial waste residue. The main difference between its performance and lime-fly ash macadam lies in its high strength, rapid strength development, easy strength adjustment and short construction period.
As one of the main forms of road base, the construction quality of cement stabilized macadam will directly affect the overall quality of road, which must be strictly required and controlled from all related links.
First, the technical indicators of cement stabilized macadam
The aggregate gradation of cement stabilized macadam adopts anti-crack gradation. When bearing heavy traffic, the dosage of cement should be 5.0%, and it should be 4.0% for medium and light traffic. The actual construction needs to be determined by tests, but it should not exceed 6%. Its 7d unconfined compressive strength is specified as follows:
The compactness of cement stabilized macadam is not less than 96%.
Second, the raw material requirements of cement stabilized macadam
1, ordinary portland cement or slag portland cement with initial setting time longer than 3h and final setting time longer (preferably longer than 6h) shall be used as the cement, and the label shall be 42.5. Fast-hardening cement, early-strength cement and cement deteriorated by moisture should not be used.
2. Crushing value of crushed stone is not more than 35%, needle flake content is not more than 20%, liquid limit is less than 28%, plasticity index is less than 6, organic matter content is not more than 2%, and sulfate content is not more than 0.25%. See the table below for aggregate gradation requirements.
Third, the construction sequence of cement stabilized macadam
The main construction sequence of cement stabilized macadam is: mixing, transportation, paving, rolling and curing.
Four, cement stabilized macadam construction matters needing attention
1, mixed
Cement stabilized macadam should be mixed by centralized factory mixing method and forced concrete mixer; When mixing, the dosage of cement should be strictly controlled. Considering the influence of various construction factors and equipment metering control, the dosage of cement should be 0.3% ~ 0.5% larger than that of laboratory, but the total amount should not be greater than 6%. At the same time, according to the site construction conditions such as air temperature and water loss, the water content of the mixture should be higher than the ratio test value 1.5% ~ 2.5%.
Step 2 transport
During transportation, tarpaulins should be covered to reduce water loss; The paving time of the mixture from unloading shall not exceed 2 hours, and it shall not be used beyond the time limit.
3. Block stone pavement
Before paving, the lower bearing layer should be properly watered and wetted; Appropriate USES special paver mechanical paving, conditional should use full width paving at the same time; The compaction coefficient should be determined through the test section, and the general mechanical paving should be 1.25~ 1.35, and the manual paving should be appropriately enlarged to1.35 ~1.5; When paving, each layer should be paved once according to the virtual thickness, the particle distribution should be uniform and the thickness should be consistent, and multiple repairs are not allowed.
4. Rolling
Rolling should be carried out according to the principle of light before heavy, low before high, stable before vibration. It is advisable to stabilize the pressure with a light two-wheel roller immediately after the paver, and then compact it with a heavy vibrating roller, a three-wheel roller or a tire roller; When rolling, the staggered wheels should overlap by half, and the joints of two adjacent operation sections should be rolled by 45-degree stepped staggered wheels. The static pressure speed should be controlled at 25m/min, and the vibration rolling speed should be controlled at 30m/min. It is forbidden for the roller to suddenly brake or turn around on the cement stabilized macadam that has been completed or is being rolled. When stabilizing the voltage, if the mixture is separated or the surface is uneven, the separated mixture should be replaced manually or repaired.
When rolling, attention should be paid to the moisturizing and joint treatment of paving joints; When longitudinal joints cannot be avoided, they must be connected vertically, and oblique joints are prohibited. See Technical Specification for Construction of Highway Pavement Base for specific requirements of longitudinal joints. When paving, special personnel shall be assigned to eliminate the segregation of coarse aggregate, and the local "nest" of coarse aggregate during paving shall be carved out at the root in time and filled with fresh mixture; It is not recommended to interrupt the paving process. If the interruption time exceeds 2h for any reason, transverse joints shall be set according to Technical Specifications for Construction of Highway Pavement Base.
The rolling effect should be dense, stable and solid, the surface should be smooth, the raceway should be less than 5mm, and the degree of compaction should meet the design requirements.
5. Health
After the mixture is rolled, it should be watered in time for health preservation and covered with sacks or permeable geotextiles. When using uncovered water for curing, the watering frequency shall not be less than 1 time/hour, and the curing period shall not be less than 7d; During the maintenance period, except for sprinklers, traffic should be closed to control the passage of construction vehicles. After the maintenance period, traffic can be gradually opened, but the driving speed must be strictly controlled. It is forbidden for construction vehicles to suddenly brake and turn around.
Conclusion:
As one of the main forms of road base, the construction quality of cement stabilized macadam will directly affect the overall quality of road. In practice, we should strictly demand and control the design technical indicators, raw materials and specific construction operations to ensure the quality of cement stabilized macadam base and play a strong support for ensuring the overall quality of roads.
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