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Key points of quality control of graded macadam construction technology and lime-fly ash macadam quality control
Combined with the construction practice of lime-fly-ash macadam, the construction technology and control points of lime-fly-ash macadam are discussed for reference by peers. Key words: quality control of lime-fly ash macadam construction technology, China picture classification number: O2 13. 1 document identification number: A document number:

First, prepare the lower bearing layer.

Before laying lime-fly ash macadam base, rutting, looseness and parts that do not meet the specified requirements on the lower bearing layer should be loosened and removed, and similar mixture should be used for filling, shaping and rolling, and the compactness requirements should be met. At the same time, all floating soil and sundries on the lower bearing layer should be removed, and the surface should be kept clean and tidy, watered and wet. Sprinkling water must make the surface of the lower bearing layer wet, because in the process of spreading lime-fly ash macadam by paver, a part of large-particle macadam under the front retaining plate freely rolls down to the bottom of lime-fly ash macadam, resulting in segregation of the cross section of lime-fly ash macadam (more fine materials above the cross section and more large-particle materials at the bottom), and the lower part is difficult to harden. If the surface of the lower bearing layer cannot reach the wet state, the water at the bottom of the lime-fly ash macadam will be absorbed, which makes the lower part of the lime-fly ash macadam more difficult to harden due to insufficient water content.

Second, the construction lofting

1. Measurement and calculation: the method of hanging datum steel wire is used for elevation control, and the middle pile is restored every 10 meter, and the elevation of the middle pile (datum point) is measured to calculate the height difference between the datum line and datum point.

Height difference between datum line and datum point = design elevation-datum point elevation+base thickness * loose paving coefficient+constant, and the constant is a fixed value, which is convenient for detecting loose paving elevation, that is, steel wire is higher than lime-fly ash macadam loose pavement. When testing, stretch both sides of the rope perpendicular to the road centerline (preferably fishing line with small deflection) on the reference line (the rope touches the reference line horizontally and cannot be pressed down), and stretch it left and right in the paving section with a steel ruler.

2. Baseline erection:

Generally, the length of each section of steel wire rope is 100- 120m, and 10m at both ends is the ground anchor and tightener, with the middle effective length of 80- 100m. The steel wire should not be too short or too long. If it is too short, it is not easy to tighten. If the middle deflection is too large, it will affect the paving elevation and smoothness, and it will easily break and cause danger. If it is too short, it should be replaced frequently, which is labor-intensive and easy to make mistakes.

The wire diameter of steel wire is 3-3.5 mm, and the thin steel wire has small bearing capacity, which is easy to be pulled off for a long time and is dangerous, fast in fatigue, short in service life and uneconomical; If the steel wire is too thick, the weight will be very heavy, and it is not easy to tighten, wind and reverse the steel wire, which is not conducive to erection and increases the construction difficulty.

During the discharging process of mixer, it is forbidden to open the door of finished product warehouse or cancel the continuous discharging of finished product warehouse. When the finished product warehouse is almost full, the door is closed and then the warehouse is intermittently discharged, which can improve the segregation caused by the large particle stone rolling down to both sides of the carriage. When picking up materials, pick up the front and rear parts of the car first, and then pick up materials indirectly, so that the front and rear parts can move back and forth (in order, the front part is full, and the middle and rear parts are actually composed of several piles, and each pile has segregation. Moving picking up materials means dividing a car into many small piles, and each pile can offset some segregation), which can improve the segregation of large and small materials produced in the process of collecting materials, and can fully solve the segregation produced in the process of collecting materials through secondary stirring in the paving process.

Fourth, pave the way.

1, go

At the beginning of the paving section on the same day, stow wood (the size of stow wood should be 25cm*50cm, the thickness of each board should be determined according to the thickness of each structural layer, and the initial total thickness of stow wood should be the thickness of the designed structural layer plus the virtual paving value), then put the paver in place, and the driver will adjust the elevation angle according to experience, and turn on various instruments to prepare for paving.

Sensitivity adjustment is very important when using various automatic levelers. If the sensitivity setting is too small, the hydraulic cylinder of the paver reacts too slowly in the adjustment process, resulting in a "long wave" on the surface of the molding structure layer, which can be obviously felt as a wavy bump when driving fast; If the sensitivity setting is too large, it will cause the paver to adjust the elevation frequently, and the "short wave" roller will feel undulating during rolling. Under normal circumstances, the sensitivity setting of all kinds of ordinary level meters does not exceed 2/3 of their effective scale, and the effect is good.

2. Block stone pavement

When paving, the speed, amplitude and frequency of the paver should be consistent. Every change and pause of the paver's speed, rammer and vibration frequency will have an impact on the lateral flatness, especially when it pauses, it will obviously produce lateral marks at the pause position. The frequency of the rammer should be adjusted to the appropriate frequency according to experience, and the speed should be adjusted synchronously when it changes. If the frequency of rammer is too high, the surface of structural layer will be rammed into "hard skin", which will affect the compaction of roller. If the frequency is too small, not only the preload fails, but also many cracks are easily opened on the surface of the structural layer.

Scraping, distributing and paving of paver are also the main processes of segregation, and the segregation caused by paver paving is mainly manifested in two aspects. (1) Due to the material resistance of the spreader, the large-grained stones thrown by the spreader from the inside to the outside and the large-grained stones in the middle part of the screed of the paver flow from the distributors on both sides to the middle because there is no paver, and the regular segregation parallel to the route direction is called longitudinal segregation. At present, there is no fundamental solution to this vertical segregation, but it can be improved by refitting small blades on the side of distributor and installing reverse blades at the root of hanger. The specific installation adjustment method should be determined according to the actual situation and construction experience. (2) When the hopper is lifted by the skip, the large-particle aggregate on the box plates on both sides of the skip and the large-particle aggregate falling freely at the top of the carriage or the segregation on both sides of the hopper are scattered in a certain section, resulting in horizontal segregation or nesting segregation of large material piles on a certain section. On the one hand, this segregation phenomenon can be improved by not closing the hopper of the paver. Generally, the hopper is only closed once at the end of the construction on the same day, and all the remaining materials are spread on the stubble, and finally removed when digging stubble; On the other hand, when the truck is unloading, the bucket should be lifted quickly so that the mixture can pour down. In the pouring process, the materials in the upper, lower, left and right parts of the car can be mixed and poured downwards, and then the segregation situation can be significantly improved through the secondary stirring when the paver scrapes and distributes materials. Originally, during the construction process, I slowly noticed the skip. In fact, it just happened that a layer of large particles on the hopper freely rolled into the hopper of the paver, resulting in nested segregation.

3. Repair

For the paved mixture surface, if there is segregation and washboard, especially the lack of cloth and segregation at the longitudinal seam, not only a layer of fine material should be sprinkled, which is a temporary solution, but also a special person should be arranged to dig out the segregation material and fill it with new material.

Verb (abbreviation for verb) rotates.

The rolling direction should be parallel to the center line of the route, and the order is as follows: the straight section is continuously and evenly rolled from the edge to the middle, and the ultra-high section is rolled from the inside out. When rolling, the wheel width should overlap 1/3, and the rolling speed and vibration frequency should be adjusted to the best matching state, so that the compactness and smoothness can achieve better results. The specific speed and frequency cannot be adjusted according to the paving material, gradation, water content and the performance of the roller. At present, the lime-fly ash macadam can meet the requirements by rolling it for 3-5 times with a vibratory roller with a steel wheel of more than 20 tons. The problem is that the thickness of lime-fly ash macadam paving layer is generally about 20cm, and the loose paving is relatively thick, and the weight of the roller is relatively large. Sometimes the speed of the roller does not match the vibration frequency, which has a great influence on the flatness.

Sixth, medical care.

No matter using water spraying or covering for curing, it is necessary to ensure that the surface of lime-fly ash macadam structure layer is in a wet state within 7 days of curing age. Because the strength of lime-fly ash macadam increases slowly, the curing period should be extended as much as possible to ensure that a complete core sample can be taken out by the age of 28. When the water truck is used to spray water for health preservation, it is forbidden for the water truck to stay in the process of spraying water, and the nozzle cannot directly face the surface of lime-fly ash gravel, which may easily cause the lime-fly ash covered on the face stone to be washed away. Another health preserving method is to spray Bufeng asphalt immediately after lime-fly ash macadam construction, which not only saves the cost, but also ensures the quality, which is beneficial to the bonding between the seal coat and the base. At present, this method has been applied to many high-grade highways with satisfactory results.

Conclusion: This method is adopted for subbase construction in expressway. Due to the good quality of raw materials, reasonable mixture ratio and good performance of paver, the combination of compaction machinery is optimized and the overall paving quality is good. After self-inspection and inspection by the quality inspection department, all technical indicators have reached or exceeded the quality standards stipulated in the specification, and the quality of the sub-projects has been evaluated as excellent, which has been well received by the owners.

References:

Wang Cuiping. Discussion on control technology of lime-fly ash technology in expressway pavement. 36860.8886888866 1

[2] Li Ranhong. Construction scheme of lime-fly ash macadam for municipal engineering .2008.06

[3] Wang Pan. Discussion on construction technology of lime-fly ash macadam .2006.08