The following is the relevant content about cement concrete pavement construction brought to you by Zhongda Consulting for your reference.
In order to meet the requirements of fast, stable, comfortable and long service life of highways, the state requires the use of large-scale paver for highway concrete pavement construction. However, because a large-scale paver generally costs 7 million Therefore, it is a relatively large capital investment for a Chinese road industry that is still in the development stage. In order to ensure the quality of concrete pavement projects and reduce cost investment. Nowadays, some highway cement concrete pavement pouring uses "three-roller paving and leveling machine" (hereinafter referred to as "three-axis leveling machine") for construction.
The introduction of "three-axis screed machine" construction and pavement notching technology into highway concrete pavement construction was first introduced in Guangxi in 1994. After years of continuous exploration and improvement, the current construction technology has Quite mature.
I was fortunate enough to participate in the concrete pavement construction work of the "Guangzhou North Second Ring Expressway". Now I would like to talk about my experience in the construction of a complete set of technical equipment for the expressway with the "three-axis leveler".
The main complete set of mechanical equipment of the "three-axis leveling machine" includes: large mixing plant, bulk cement tank, admixture tank, loader, dump truck, sprinkler truck, self-draining vibrator and Longitudinal tie rod installation machine, three-axis paving and slurry leveling machine, troweling board, three-meter and four-meter scraper, ordinary seam cutting machine, rigid notching machine, blade grinder, etc. The core processes of the complete set of three-axis leveling machine technology are row vibration, three-axis slurry lifting and leveling, and three-meter scraper precision leveling processes. Among them, row vibration ensures the density of cement concrete, and three-axis slurry lifting and leveling It lays the foundation for fine leveling, and the flatness finally reaches the standard through the three-meter scraper fine leveling. But to achieve better internal quality and smoothing effect, every process in the construction is equally important, and even a small detail may affect the quality.
The concrete pavement construction of the North Second Ring Road in Guangzhou uses large-scale cement concrete mixing plants, generally equipped with 1-2 forced mixers, and the actual concrete productivity is not less than 70-100M3/h to meet the needs of cement concrete Workability and on-site paving construction speed needs. The forced mixing of large-scale mixing plants avoids problems such as the use of small self-falling mixers, difficulty in controlling concrete slump, and uneven cement concrete mixture, thus ensuring the quality of concrete. At the same time, the mixing plants are equipped with automatic metering equipment, and the mixing water consumption is basically controlled by gravimetric method, making the input materials more accurate. In terms of raw materials for the project, the cement uses high-strength, dry-shrunk 52.5 grade cement, and the gravel is graded from 5 to 30 mm (2-4 stones are not suitable). The quality and specifications of the gravel are strictly controlled from beginning to end to ensure that the cement Concrete strength and pavement smoothness are important. In addition, before each work shift starts, the moisture content of sand and stone must be measured and the construction mix ratio adjusted to ensure the accuracy of the ingredients.
The vibration and leveling of cement concrete are mainly completed by self-discharging vibrators and three-axis pulp leveling machines. The row vibrators are mainly composed of a row with a spacing of 40 cm and a power of 1.1 It is composed of KW vibrating rod (which can be lifted and lowered mechanically) and moves forward automatically by machinery. Because it is mechanically operated automatically, it avoids the influence of human factors such as vibration leakage and under-vibration in cement concrete construction in the past, so that the vibration effect is effectively improved and guaranteed. During vibrating, the remaining material should be manually processed or replenished according to the situation to ensure that the cement concrete surface after vibrating is flat and slightly higher than the top of the formwork. Since the width of the construction slab is generally 7.5m or 8.5m, longitudinal tie rods must be installed according to the design. In this case, a tie rod installation machine is installed on the row vibrator truss corresponding to the longitudinal joint position, so that the longitudinal tie rods can be accurately buried while the row vibrator is traveling.
After vibrating, there is a three-axis leveling machine to lift and level the pulp. The three-axis leveling machine has equipment such as the vibrating beam and the manually dragged drum-type pulp lifting stick that are equipped with previous manual construction. It is mainly composed of three axes. The first axis is the vibration axis, which performs rolling, vibrating and pulp lifting. The latter two axes mainly play the role of rolling and leveling. Its paving speed is 15-30m per hour, and it can generally pave about 200m per day. During the specific operation, the three-axis leveling machine should roll back and forth 3-4 times. During this period, the original pulp is manually shoveled to make up the level, and then the three-axis leveling is performed. Judging from on-site use, the effect of pulp lifting and leveling is relatively good.
However, only leveling by a three-axis leveling machine cannot meet the flatness requirements stipulated in the specification. It only creates a better basic condition for the fine leveling process. After that, a large trowel board (usually a wide-body curved aluminum alloy plate) is used to wipe the surface multiple times until the cement concrete surface is water-free, and then a three-meter and four-meter scraper is used for 2-3 back and forth smoothing. After the meter ruler is leveled, the surface should be wiped manually with a plastic board immediately to remove pores, floating sand, scratch marks, etc. on the surface. A certain roughness should be wiped out as required, and the large surface should be flat to avoid protruding sharp edges. Finally, manual slurrying and plastering can be carried out appropriately. When manually plastering and inspecting with a 3m ruler, no one can step on the cement concrete surface, but should stand on the movable working bridge to avoid affecting the flatness and appearance. After this treatment, the flatness measured using a Dianpo instrument is generally around 1 mm, and the pass rate of cement concrete pavement flatness is basically above 90%-95%.
The curing of concrete is now carried out by spraying curing agent to prevent early shrinkage and cracking. The initial curing is carried out after cutting the joints. The curing agent must be sprayed evenly and in place, and no less or missed sprays are allowed. The cutting time of concrete must be carefully controlled. Cutting too early will cause the coarse aggregate in the cement concrete to fall off, and cutting too late will cause early cracks or even broken panels. Therefore, the time of cutting should be controlled appropriately. Generally, the control starts when the product of construction temperature and post-construction time reaches 300-400℃h, and is determined after trial cutting. When cutting seams, stakes should be placed every 5 meters first, and then the line should be used for setting out, and an directional frame should be used to guide the cutting machine to move to make the seams straight.
The engraving uses a rigid groove method, which solves the problem that in the past, the embossing was often too shallow and the texture depth could not meet the requirements. On the other hand, it avoids the problem of embossing before and after the initial setting of cement concrete, which affects the flatness. Generally, the slot spacing is 15-20mm, the slot width is 3-5mm, and the depth is 3-5mm. This is guaranteed during construction. To ensure that the slots are straight and smooth, a guide wheel can be added in front of the engraving machine.
Judging from the grooves on the cement concrete pavement of the North Second Ring Expressway in Guangzhou, the effect is relatively ideal. Grouting materials include polyvinyl chloride cement, etc. To clean the seam wall, first cut the seam again, then use a high-pressure water gun to clean it, and then use an air compressor to blow it out and dry it. The purpose is to clean up the blockage in the seam and ensure that the inside of the seam and the seam wall are clean and dry. , is crucial to ensure the quality of grouting.
The construction technology of the three-axis screed machine for the cement concrete pavement of the North Second Ring Road in Guangzhou has the following obvious advantages:
1. Large cement concrete mandatory mixing equipment is used. Due to the concentrated site , the raw materials are easy to monitor, the finished concrete has good workability and the quality is guaranteed.
2. The row vibrator and longitudinal tie rod installation machine effectively solve the artificial impact of easy slurry leakage, lack of vibration and uneven installation of tie rods that are difficult to control due to manual vibration of concrete.
3. Three-axis grout lifting and leveling effectively ensures the uniformity of the concrete surface, greatly improves the flatness of the cement concrete surface, and avoids the disadvantages of manual roller grout lifting in the past.
4. The "fine smoothing" process uses three-meter and four-meter scrapers to scrape the surface repeatedly, which greatly improves the flatness.
5. The use of rigid grooves effectively solves the problems of uneven embossing texture, insufficient depth and interference to cement concrete during embossing, which affects the flatness.
6. Spraying curing agent is used to avoid the shortcomings of insufficient artificial watering and curing that affected the depth growth in the past. And it plays the role of steam curing to a certain extent.
In the construction process using a three-axis leveling machine, although the three-roller paving and slurry leveling machine has many of the above advantages, there are also some problems, such as a partial lack of lateral joints between the old and new concrete slabs. Smooth, with slight height differences. Although the row vibrator solves some of the vibration problems in the middle of the concrete slab, there is still a local honeycomb phenomenon caused by lack of vibration on the sides of the slab, but these can be improved. The complete set of three-axis leveling machine technology has withstood the test in practical work, so its application on highways is relatively successful.
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