1 Process principle of shot blasting technology
The process construction of the shot blasting technology is to spray a certain diameter of steel sand, steel balls and other hard particles on the surface of the working surface to be treated at a relatively fast speed and a corresponding angle through a road shot blasting machine, so that the particle material impacts the surface of the working surface at a high speed (This article refers to the working surface of the lower bearing layer of the asphalt concrete panel), forming a hammering effect to clean up the debris and attachments on the working surface, forming a uniform and rough surface effect, and then realizing the lower bearing panel and subsequent processes The project is better bonded, has better integrity, and achieves higher quality effects.
2 Significance of shot blasting technology for asphalt concrete composite pavement
At present, domestic highway pavement design mostly adopts asphalt concrete composite pavement form, especially for the pavement in bridges and tunnels. In order to ensure the driving comfort of the pavement and the performance of the pavement, the cement concrete structure layer is mostly used as the underlying layer in the pavement design. On this basis, the asphalt concrete surface layer is added; then how to effectively connect the asphalt surface layer with the concrete structure layer and increase the service life of the road surface is a practical problem to be overcome in the highway design and construction stage. Before laying the asphalt surface layer on the cement concrete panel, in order to make the two materials better bond, the design often adopts a modified asphalt bonding layer between them, and how can the bonding layer better with the concrete? Effective surface bonding is a topic currently discussed in this article. In the past construction, the original construction quality of the original concrete panel is often used to solve this bonding problem, such as roughing; if the overall flatness of the concrete panel is poor, the milling machine is used. Or grinder for further processing, through the above form to achieve better bonding of each process engineering. After years of summarizing the existence of diseases in composite pavement, the main reason is that the effect of concrete surface treatment cannot meet the effective bonding between the bonding layer and the effective bonding strength or insufficient bonding strength, which leads to early cracks and voids in the asphalt surface. In order to better solve the above diseases In recent years, through technological innovation, shot blasting of concrete panels has been used to achieve effective bonding between the bonding layer and concrete panels. Through the shot blasting construction on the surface of concrete panels, the surface scum, debris and exposed hard aggregates are effectively removed. Provide a clean and uniform rough surface; at the same time, it can fully open the surface pores and exposed cracks of the concrete, so that the waterproof adhesive layer can effectively penetrate into the pores and small cracks on the concrete surface (large cracks require special treatment), which improves the waterproof adhesive layer The construction quality also guarantees the surface bonding quality of the asphalt concrete surface layer and the waterproof adhesive layer.
3 Construction technology
The milling and planing construction of concrete slab shot blasting technology is mostly applied to the surface of composite pavement concrete underlayers in highway bridges and tunnels. Next, the construction technology of highway bridge concrete underlayer shot blasting technology will be briefly introduced.
3.1.1 The selection of shot blasting equipment, according to the size of the construction workload and the cross-sectional size of the working surface, select the corresponding type of shot blasting equipment. For example, for working surfaces with long working sections and a certain width, large-scale vehicle-mounted driving shot blasting equipment can be used, and small self-moving shot blasting equipment (cleaning shot blasting at corners); for less workload, operation Small-scale self-propelled shot blasting equipment is used for projects with a small area; at present, the domestically advanced large-scale vehicle-driven shot blasting equipment 2-4800DHBLASTRAC has a shot blasting width of 1.22m and a walking speed of 0~113m/min. The efficiency reaches 1200~3000m2/h; the small automatic shot blasting equipment 2-30DS has a width of 0.8m for self-moving shot blasting, a walking speed of 0~29m/min, and a work efficiency of >400m2/h.
3.1.2 Before shot blasting of concrete panels, in order to effectively improve the quality and efficiency of shot blasting, the debris, scattered slurry and metal waste of the original bridge should be removed in time. Secondly, for heavily polluted bridge decks that cannot be directly removed, they should be manually scrubbed with soapy water. After the working surface is cleaned or rained, the shot blasting effect will be affected because the surface is wet. At the same time, the pill and the slag can not be effectively separated and the construction cannot be carried out normally. Therefore, the shot blasting construction must be carried out after the work is dry.
3.1.3 Before the shot blasting construction, prepare equipment or packaging bags for recycling shot blasting slag for centralized and unified processing.
3.1.4 For the expansion joint slots of the bridge deck, qualified materials should be used to fill in advance to facilitate the passage of shot blasting equipment and improve work efficiency.
3.2 Shot blasting construction
3.2.1 After the equipment is selected according to the workload, the shot blasting construction is carried out in sequence along the bridge. In order to ensure that the shot blasting covers the entire working surface, the width of adjacent operation routes should overlap by about 10cm to ensure that there is no missed blasting.
3.2.2 According to the design requirements of the structure depth of the shot blasting and the achieved effect, adjust the walking speed of the equipment, the particle size of the shot beads and control the flow rate of the shot blasting to achieve. For the working face that requires a large structure depth or the original bridge deck is relatively rough, reduce the equipment walking speed, change the shot blasting particle size to increase the shot blasting speed, or repeat the shot blasting several times to achieve the goal. Before normal construction Process tests are required to determine various parameters.
3.2.3 The waste slag hit by shot blasting is recovered in the storage tank behind the equipment by the automatic back-blowing cleaning vacuum cleaner of the equipment, and after the storage tank is full, it is manually bagged for centralized collection and processing.
3.2.4 In the case that the large machinery at the corners cannot be in place, use small supporting shot blasting equipment for supplementary polishing.
3.2.5 After shot blasting, perform the next process as soon as possible to prevent secondary pollution.
4 Factors affecting the effect of shot blasting
a. The impact speed, flow rate and diameter of the shot blasting;
b. The power, walking speed and incident angle of the equipment;
c. The material structure and hardness of the surface to be treated;
d. Cleanliness of the surface to be treated.
5 Advantages of shot blasting technology over ordinary milling technology
5.1 After the concrete bridge surface is treated by shot blasting technology, it effectively removes surface scum, debris, and exposed hard aggregate without causing damage to the concrete aggregate itself and the structure of the aggregate, and provides a clean, uniform and rough surface; The size of the beads, the flow rate, and the walking speed of the equipment can be shot blasting on the cement concrete panel at a time and the cleaning depth can reach 0.2~1.0cm. However, the ordinary milling process is used because the working principle is to use a milling cutter to hard mill the surface of the surface to be processed to the next layer, so it is easy to damage the original structure of the working surface—that is, the concrete panel structure, which disturbs the coarse aggregate inside the concrete to a certain extent. In addition, if the concrete underlayer is a reinforced concrete structure, the thickness of the steel protection layer is not uniformly controlled, which can easily damage the steel bars or the equipment itself, increase the cost of damage such as milling cutters, and the beads can be recycled and used at low cost.
5.2 The shot blasting construction is convenient, efficient and uniform (the coverage rate of the surface to be cleaned is high-it can reach more than 90%); compared with ordinary milling machines, there will be no untreated comb-shaped strips on the surface treated; the remaining width of the corners Smaller, you can use supporting small equipment to complete all cleaning tasks, effectively improving environmental adaptability.
5.3 Shot blasting technology is more economical than ordinary milling. Shot blasting technology handles 7 yuan/m2, while ordinary milling is 8 yuan/m2.
5.4 The technology of shot blasting technology is scientific, the equipment is advanced and environmentally friendly, and it will not pollute the surrounding environment; firstly, when the ordinary milling machine mills the concrete panel, the high temperature generated by the high-speed operation of the planer needs to be cooled with clean water, and the water is not available. Recycling causes environmental pollution, and the shot blasting technology construction does not require water to cool down, and is completed in a dry condition; secondly, because the shot blasting room and the bridge deck form a sealed space during the shot blasting technology operation, the generated slag body is connected to the blasting The slag suction pipe in the pill room sucks the slag and the pellets into the separation tank, and separates the pellets and the waste slag and recycles them separately. There will be no dust and leftover slag at the construction site, and no manual secondary cleaning or dust removal is required, which improves Work efficiency and protect the air environment; while the miller will have some dust during the construction process; in addition, after the shot blasting technology, the surface of the working face is clean without floating and sinking, and scum does not need to be cleaned twice, which improves the efficiency, and remains after milling. The floating and sinking scum on the side or inside of the working face needs to be further purged, causing pollution.
5.5 The working surface treated by shot blasting technology will not form convex and concave appearances, so that the spraying thickness of the waterproof adhesive layer material is more uniform than that of the working surface processed by the ordinary milling process, which improves the quality of the waterproof adhesive layer, and effectively and reasonably controls The amount of waterproof material per unit area.
6 The cause of the early disease of the asphalt pavement on the bridge deck and the necessity of shot blasting
Shedding, potholes, and shifting of the asphalt concrete surface of the bridge deck are common early failure forms of the bridge deck pavement. A considerable part of the cause of such diseases is that the bridge deck waterproof bonding layer and the cement concrete underlayer and the waterproof bonding layer and the asphalt concrete surface are not effectively bonded, resulting in insufficient interlayer adhesion and insufficient shear resistance. It is caused by the requirements of the specification. Of course, other reasons can also cause-such as poor flatness of the bridge deck, excessive permeability of the asphalt concrete, etc., causing water in the bridge area, and early damage to the surface layer through prolonged rutting. The following mainly analyzes the factors that affect the early damage of the bridge deck related to the shot blasting technology:
6.1 In the composite pavement, due to the poor construction quality of the cement concrete lower bearing layer and the thick cement laitance on the surface, the strength of a certain thickness range of the surface is insufficient, which affects the bonding effect of the waterproof adhesive layer.
6.2 The roughness of the concrete underlayer is the key control point for the service life of the composite pavement, and its roughness affects the bonding effect of the waterproof adhesive layer. A reasonable structure depth is beneficial to enhance the shear resistance between layers, but if the structure has a large height difference between the convex and concave layers, it will also affect the overall quality of the waterproof adhesive layer. There will be uneven thickness of the waterproof material and uneven shear resistance. Affect the service life of the bonding layer. By removing scum and pollutants on the surface of the cement concrete underlayer of the composite pavement, the surface of the cement concrete is exposed to fresh and dense aggregates, which further improves the surface roughness and improves the adhesion between the concrete surface and the waterproof adhesive layer , Increase the shear resistance of the waterproof bonding layer and the underlayer of hydraulic concrete and the asphalt surface layer, effectively reduce the formation of composite pavement diseases, make the pavement durable, and produce greater economic and social benefits. Through engineering practice-shot blasting technology can better remove the cement concrete surface scum layer and impurities, and at the same time can roughen the cement concrete surface to form a uniform and rough surface, which effectively improves the performance of waterproof bonding, thereby It has a positive effect on the overall service life of the composite pavement.
There are many reasons for the diseases existing in the asphalt concrete composite pavement, including the original underlying layer-concrete panel.