First, the origin of the crushed stone transformation technology: The original crushed stone is to facilitate the demolition of cement concrete pavement and the separation of steel bars in the pavement. 1986 completed the first hma pavement rolling project in new york, USA. By 200 1, this technology has been used in 35 States in the United States, with more than 300 projects and a mileage of more than 900 kilometers,1280,000 square meters. In addition, the American Asphalt Association and some states have included this technology in their specifications.
Second, the concept of gravel transformation technology The so-called gravel technology is to break the cement concrete pavement into concrete blocks which are generally less than 38 cm, so as to limit the reflection cracks on the newly paved hma overlay and produce a uniform base for the hma overlay.
3. Several characteristics of the fragmentation technology: (1) The fragmentation technology is the most effective method to solve the reflection cracks at present. (2) Roller compacted concrete pavement is closely combined with roller compacted concrete blocks, and the high-density material layer provides higher structural strength for asphalt overlay. (3) Simple construction, short renovation period and low comprehensive cost. (4) In-situ recycling is environmentally friendly and pollution-free, and the damaged pavement can be directly used as the base or subbase, adding a new surface layer, which is an ideal way to renovate the old cement pavement. (5) It is an ideal method to use the broken concrete slab directly as the base or subbase and then lay a new surface layer. The biggest advantage of this crushing technology is that it doesn't need to crush the damaged cement board away, which saves subgrade materials and transportation costs, improves the project progress and greatly reduces the total project cost. At the same time, it also solves the environmental protection problem of discarding cement fragments. (6) It has little impact on traffic, so it is not necessary to completely close the traffic during construction.
Four. Basis and scope of construction scheme compilation (1) Compilation basis (1) Damage condition of cement concrete pavement in the road section to be rebuilt (2) Technical data of cement concrete pavement rolling in the United States (3) Current specifications and standards of the Ministry of Communications (4) Summary of implementation experience of domestic cement concrete pavement rolling project.
5. Overview Crushing refers to a final treatment method for old cement concrete slabs to solve the problem of reflection cracks in common pavement methods when the old cement concrete pavement loses its overall bearing capacity due to large-area damage, and its use function can no longer be restored by local excavation, grouting and other treatment methods, or the structural strength requirements can no longer be met. Generally, this method is to crush the old cement concrete slab into smaller particle size (no more than 37.5cm at the bottom, no more than 22.5cm in the middle and no more than 7.5cm at the surface) with special construction machinery (such as multi-hammer cement pavement crusher) after treating the partially damaged base, and then roll it into a new pavement structure, base or subbase, and then pave a new pavement structure. Deputy Director Wang Songgen, a researcher of Shandong Highway Bureau, elaborated the characteristics and application of gravel technology in the book Application and Research of Highway Maintenance Technology in Shandong Province. Let's briefly summarize the construction scheme of gravel transformation.
6. Equipment used in crushing technology 1. Multi-hammer cement pavement crusher Multi-hammer cement pavement crusher is a self-propelled crushing equipment produced by Shandong Highway Machinery Factory. The back of the equipment is equipped with two pairs of hammers on average, so that it can be continuously crushed within the full width of the equipment, and the lifting height of hammers can be independently adjusted within the range of cylinder stroke. This crusher can crush a 4-meter-long driveway at a time. 2 Special vibratory roller yz 18a The Z-wheel vibratory roller produced by Shandong Highway Machinery Factory carries specially processed steel hoops and is bolted to the surface of the vibratory steel wheel. Used for supplementary crushing of the surface layer of cement concrete pavement after crushing.
Seven. Preparation before crushing 1. Removal of old asphalt pavement Before crushing, asphalt patching materials on cement concrete pavement should be removed, because the existence of these materials will affect the crushing effect. 2. Investigation and marking of concealed structures Before fracture, investigate concealed structures, such as buried culverts and underground pipelines, in combination with design drawings and information provided by the owner to determine whether the fracture will cause damage to these structures. Generally, the buried depth of structures below 1 m will not be crushed. If the above conditions are not met, the hammer height can be reduced to roll the cement pavement, or other schemes deemed feasible by the supervision engineer can be adopted. 3. The pavement connected with the bridge should indicate the fracture position. According to the actual situation, it can be broken to the back end of bridge end transition slab, or to the position designated by the supervisor according to the elevation of the pavement design line. The complete pavement should be rolled to the extent that asphalt overlay with the same thickness can be laid. 4. Traffic control Because the roller compacted pavement is not allowed to open to traffic in principle before paving asphalt concrete surface on the beach, the requirements for traffic control are strict, and it is recommended to completely close the construction section at one time if conditions permit; If conditions do not permit, at least semi-closed construction should be carried out. 5. Other requirements: Any road widening or shoulder repair unrelated to traffic maintenance during construction should also be restored to the elevation of concrete pavement before construction.
Eight. Before the crushing procedure of cement pavement crusher is approved, the contractor shall complete the test section and obtain the approval of the supervision engineer. The test section is the position determined by the supervision engineer within the scope of the project. The lane is full width and the length is 100-200m. The contractor shall record the setting of cement pavement crusher corresponding to different crushing conditions, such as hammer height and ground running speed. In order to ensure that the road surface is broken to the specified size, the contractor shall dig trial pits according to the instructions of the supervisor. The test pit should not be selected at the position with transverse joints or working joints, and the broken particle size of the pavement should be detected within the full depth range. The test pit shall be backfilled with dense graded macadam material and compacted to meet the requirements. After crushing in the experimental section, the crushing settings that meet the requirements should be recorded for future reference. The crusher scheme determined in the test section will be used in this project. The contractor shall continuously monitor the crushing operation and make adjustments during the construction process to ensure that the results meet the requirements (construction site of expressway Longquan section in Chengdu-Chongqing).
Nine. Construction control and requirements of rolling 1, and 75% of the concrete pavement required by pavement rolling should be rolled into a particle size of no more than 7.5cm in surface, no more than 22.5cm in middle and no more than 37.5cm in bottom. 2. Remove the original joint filler. Before paving the asphalt surface, all loose joint filler, joint expansion material or other similar materials should be removed. 3. Concave backfill should not trim the broken concrete pavement or try to level the pavement to improve the alignment, which will destroy the effect of the concrete pavement after rolling. The 5cm concave land found before compaction shall be backfilled with dense graded macadam and compacted to the requirements. When rolling, it is best to roll from the high part of the concrete pavement to the low part, so as not to affect the drainage after asphalt concrete paving. 4. Connection with adjacent lanes In the process of rolling a lane, the actual rolling width should exceed one lane and overlap with adjacent lanes, and the width should be at least 15cm. 5. Spreading emulsified asphalt priming oil In order to make loose granular materials have certain cohesive force and water resistance, it is suggested to spread emulsified asphalt priming oil on the broken and compacted surface, and to spread 50% slow-cracking emulsified asphalt according to the dosage of 2.5 ~ 3.5 kg/㎡. 6. The disturbance to the concrete pavement before paving should minimize the traffic times and load of construction vehicles. If the surface of the crushed concrete pavement has been partially or completely damaged by trucks, it should be compacted again. 7. The minimum thickness of gravel cover for surface construction is 15cm. And is preferably a dense hierarchical structure. 10. Construction progress and construction period of old cement concrete pavement reconstruction. The construction period mainly depends on the weather and the cooperation of all parties. Without interference from external conditions, the daily workload of each equipment is about 3000-3500 m2. In order to ensure the construction period, the intact rate of equipment is the decisive factor. We have enough accessories and professional maintenance technicians to maintain the equipment at any time to ensure that the daily workload is completed as required, thus ensuring the total construction period.