2, strictly control the dosage of cement. Too little cement can not guarantee the construction quality of cement stabilized soil; However, if the dosage is too large, it will not only be uneconomical, but also increase and widen the cracks at the base, thus causing corresponding reflection cracks on the asphalt surface. Therefore, we must strictly control the amount of cement, be economical and reasonable, and strive for perfection to ensure the quality of the project.
3. Water content control of mixture. At the scene of the factory-mixed mixture, full-time testers in the backcourt measure the water content of various aggregates every morning, noon and afternoon, and determine the water consumption when mixing the mixture according to the optimal water content index designed by the construction mixture ratio and the temperature, humidity and transportation distance of the day. Full-time front-field inspectors who are responsible for testing the degree of compaction also measure the water content of the mixture in time during the paving and molding of the mixture, instruct the roller to roll it in time, and try to roll it under the best water content condition to avoid the phenomenon of "bounce" and "wave" due to excessive water content, which will affect the density and strength of the mixture, increase the drying shrinkage of the mixture and make the structural layer prone to dry shrinkage cracks; Or because the water content is small, the mixture is easy to loosen and not easy to crush, which will also affect the density and strength that the mixture may reach. Therefore, only by strictly following the specifications and strengthening the quality control of each construction link can the construction quality be guaranteed.
4. The transportation of mixture should avoid the bumping of vehicles, so as to reduce the segregation of mixture. When the temperature is high and the transportation distance is long, cover it with felt cloth to prevent excessive water loss. When paving and rolling, the paving coefficient is between 1.3∽ 1.5 (at normal speed, Ingersoll Rand paver is 1.3, Xugong paver is 1.5, and the paving coefficient is also related to the speed of paver), so it is necessary to implement the principle of "Better high than low" in construction. After rolling, the compactness test shall be conducted immediately. If the test result is not up to standard, roll again.
5, mixture paving joint treatment. There are two kinds of seams: longitudinal seams and transverse seams. When the paver is wide enough, there is no longitudinal joint problem when paving the whole width. When the paving width of paver is insufficient, two pavers are used to spread the mixture in tandem and roll them together, which can also avoid longitudinal joints. Because there are many structures in this bid section, the general construction section is between two structures to avoid horizontal joints. If there are special circumstances, it is necessary to set transverse joints. The treatment method is to remove the uncompacted mixture near and below the paver, dig the compacted end whose elevation and flatness meet the requirements into a transverse and vertical downward section, return the paver to the end of the compacted layer, use a wooden mat to cushion it to the virtual paving height, and then pave a new mixture to continue the next construction.
6. Compaction of the mixture. After the mixture is paved and shaped by a paver, it can be rolled by a roller. The rolling length should be determined according to the actual situation of the construction site. If the measured water content of the mixture is higher than the optimum water content and the temperature is low, the rolling length can be appropriately extended. If the mixture is close to the optimum water content, the temperature is high and the evaporation is fast, the rolling length should be shortened to ensure the rolling under the optimum water content. In order to ensure the compactness of the base and shorten the delay time, a large-tonnage roller combination should be adopted, and the general combination form is:
Initial pressure: 1 vibratory roller (CA30 type), vibration before standstill 1 pass.
Re-compaction: 2∽3 vibratory rollers (YZJ- 18 type), with each vibration before and after 1 pass.
Final pressure: 2 sets of 30T rubber-tyred rollers, each with constant pressure 1 time.
Road sections without superelevation shall be rolled from the edge to the middle, and the lateral phase displacement of the mixture shall be prevented while ensuring the edge compaction. The rolling speed is generally1.8 ∽ 2.2 km ∕ h; Roller shift should be smooth, and it is forbidden to yank and shove the structural layer; Return by road. In the direction of the paver, the shift position should be staggered to form a tooth shape and return to the original road.
7. A healthy mixture. After the rolling is completed and the compaction degree is qualified, the maintenance shall be carried out immediately without delay. Curing can be carried out by covering impermeable plastic film or wet sand, or by using asphalt emulsion, or by immediately making a lower seal coat on the finished base, or by directly spraying water on the finished mixture. According to the technical specifications, the curing period should not be less than 7d. During the maintenance period, a special person shall be responsible for restricting the driving of vehicles. Heavy vehicles are absolutely forbidden to drive except sprinklers. This bid adopts two ways of keeping in good health, plastic film keeping in good health and watering keeping in good health.
Verb (abbreviation of verb) quality inspection
Test detection is an important link and means of engineering quality management, and objective, accurate and timely detection data is the scientific basis for guiding, controlling and recognizing engineering quality. In the construction of cement stabilized macadam base, because of the inherent characteristics of cement materials, quality inspection is particularly important. We must strengthen the concept of using data to guide production and do a good job in quality control.
1, raw material quality inspection of mixing station
Material name detection project detection purpose frequency quality standard cement physical properties determine whether cement is suitable for material source change or suspected unstable quality. Within the specified range, gravel particle analysis determines that the gradation meets the requirements of 2000m3.
2. The sample conforms to the gravel list.
Gradation requires that the liquid limit plasticity index is less than 0.6mm, and the liquid limit and plasticity index of particles are the same as above.
3, mixture detection
The frequency of inspection items should be measured by sampling and sieving the cement on the conveyor belt within the specified range once in the afternoon according to the remarks of the quality standard inspection method. The dosage of fly ash should be checked by EDTA titration every 2 hours, and the water content should be calculated by sampling and sieving the cement on the conveyor belt every day 1 time or every 2 hours 1 time if necessary within the specified range. The optimal water content is 2. The uniformity of standard water content should be observed at any time, and no color should be observed.
4, paving site detection
Description of inspection method for frequency quality standard of inspection items: measure the compaction degree at two places in each rolling section according to the standard sand filling method, and then quickly check the compressive strength of water content (alcohol combustion method). After standing in the morning and afternoon, it should form 1 group 3-5kpa. After soaking for 24 hours during curing, it should be randomly sampled and formed indoors before rolling.
5. Problems that should be paid attention to in detection.
(1) When measuring the cement dosage, the ammonium chloride used should be the solution prepared on the same day, and it should be used up on the same day, so as not to affect the test accuracy.
(2) In the compaction test of cement stabilized macadam, if there is no peak point, the highest point should be found as the maximum dry density value through encryption test.
(3) When the unconfined compressive strength is randomly sampled at the site, a compressive specimen shall be prepared from the mixture taken at each point, and the compressive specimen shall not be prepared after mixing the samples.
(4) After curing, the mass loss of the specimen should meet the requirements (not more than 10g), and the deviation coefficient CV(%) of several parallel tests should not be more than 20%, otherwise it will be invalid or treated as unqualified.
(5) In the compaction test, the density of standard sand should be checked frequently, and the water content test (warm bath burning loss method) should be carried out immediately after the mixture is controlled. Three methods can be adopted in advance, namely, drying method, warm bath burning loss method and iron pot method.
Discussion on several problems of water stability
1, strengthen construction management and improve the degree of mechanized construction.
Because the time required for water stabilization construction is urgent, and it is required to meet the quality standards at one time, otherwise the formed slab is not easy to repair. Therefore, it is necessary to strengthen construction management, improve the degree of mechanized construction, and form a large-scale and standardized operation mode, so as to easily meet the requirements of water-stable construction.
2. The water stability of fly ash is easy to reach high strength in the later stage of construction.
Judging from the usage of two kinds of aggregates (one containing fly ash and the other not), the effect of adding fly ash is better. This is because only the mixture of sand needs a lot of water, and the drying shrinkage is also large, so cracks are easy to appear in the construction under the conditions of high temperature and drought in summer, and the vibrating roller is easy to boil during the rolling process, which is not conducive to the operation of the roller. The fly ash mixture has obvious effect on improving its workability and reducing the temperature rise of hydration heat. Adding fly ash can improve the later strength of water temperature, the activity of fly ash and the smoothness of spherical particle surface, reduce the friction between aggregates in water stability, correspondingly reduce the water consumption of mixture, and improve the workability of water stability. Fly ash can stabilize water and generate some heat at the same time, but the amount is very small, thus reducing temperature cracks. In addition, adding a certain amount of fly ash to the water stabilizer can also inhibit the alkali-aggregate reaction. Mixing pulverized coal as subgrade not only treats the waste discharged from power plants, saves land resources, reduces environmental pollution, but also reduces the project cost, which is a good strategy for benefiting the country and the people.
3. Control of cement consumption and water consumption
When the mixing water is stable, the dosage of cement must be accurately controlled. If the dosage is too small, the gelation will be reduced. When the dosage is too large, the reaction temperature of hydration heat will increase, and cracks will easily occur. In addition, when the vibratory roller vibrates, it is easy to form a layer of cement slurry to cover the water-stable surface, which hinders the evaporation of hydration heat of water-stable, which is not conducive to the roller operation.
Seven. Concluding remarks
Through the construction of cement stabilized macadam in the southwest section of Xinyi line reconstruction project of 205 national highway, it is not difficult to find that the gradation of cement stabilized macadam is very important to its strength, and the gradation has an absolute control effect on the cement consumption. In addition, organizing and coordinating the quality of construction machinery is also an important means to ensure the quality of the project. At the same time, according to different regional differences, different gradations are determined according to local conditions, and different mixture ratios are adopted. Only by constantly summing up experience can we better control the technical indexes in the construction of cement stabilized macadam.