Pavement grouting technology; Cement concrete pavement; Maintenance/curing
Grouting treatment technology is a repair measure, which can ensure the uniform support of the bottom of the slab, make the bottom of the slab dense, avoid the void of the bottom of the slab and ensure the stress of the concrete pavement. Specifically, grouting treatment is carried out to enrich the cavity and make the bottom of the slab dense, which conforms to the stress design principle and improves the supporting effect. Because of the choice of grouting material, it has high strength, good fluidity and certain stability, which makes the slurry penetrate. Under the action of pressure, the base and subgrade are dense, which improves the water stability, increases the strength of subgrade and prolongs the service life of pavement.
1 grouting technology
Grouting technology for cement concrete pavement is a technical method to reinforce the bottom of the slab and enrich the foundation for the early diseases of cement concrete pavement by using the grouting filling principle in geotechnical engineering. The main mechanism is: drilling holes on the cement panel with small construction machinery and filling cement mortar under the panel. By applying high pressure, the loose base of the floor slab is filled tightly, and the gap between the base and the panel is closely connected, so as to achieve the purpose of uniform force transmission of the panel. The main construction procedures of grouting treatment are: plate fixing, hole arrangement, drilling, grouting, sealing and maintenance.
1. 1 fixing plate
When investigating the road surface, visually observe the looseness and fluctuation of the plate when heavy vehicles pass by; Measure and record the height difference of staggered plates; For the mud pumping board, it is best to observe the slurry leakage in the gap in time after the rain; The location of grouting holes is determined according to the subsidence of the corner of the crack plate. During the survey, paint should be prepared at the drilling position, and the detailed position and damage of each grouting plate should be recorded with the reference of100m pile, so as to observe the grouting effect in the future.
1.2 hole arrangement
According to the requirements of the tender documents, plum blossom holes are arranged, 8 holes are arranged in the roadway and 8 holes are arranged in the overtaking lane. For the plate with less cracks (such as the plate is broken into two pieces), the grouting holes are adjusted appropriately, and 1 ~ 2 holes are added on both sides of the cracks. Before drilling, technicians should select the hole position, which should be on the four sides of the plate, 50cm away from the edge of the plate, and generally avoid the hole position in the center of the plate. For cracked plates, consider arranging holes at the edge of cracks, and the distance between holes and cracks should be more than 30cm.
1.3 drilling
When drilling with a drilling machine, in order to ensure the continuity of construction, the hole should be drilled in advance according to the determined hole position, and the hole depth should run through the thickness of the plate. The diameter of the drill bit is 3cm, and the drilling hole should be vertical and circular, and its depth should pass through the original asphalt concrete and cement concrete slab and enter the untreated base. During this construction period, the total thickness of cement slab and asphalt pavement is about 3 1.5cm, and the drilling depth is controlled between 35cm and 40 cm, not less than 35 cm. A cavity is formed by blowing air to facilitate the initial distribution of mortar, and a 3 cm rubber tube is inserted into the orifice as a liner. The outer diameter of the rubber tube is consistent with the aperture, which is convenient for the grouting plug to be closely combined with the orifice to prevent slurry leakage. After drilling holes, mark the grouting sequence of each hole on the board with red paint. See attached figure 2 for grouting sequence.
1.4 Grouting
1.4. 1 preparation of mortar mixture
The mix proportion used in grouting construction is ordinary portland cement 42.5: fly ash: water: JK-24: aluminum powder =1:0.6: 0.7: 0.16: 0.001.
Put cement and fly ash into a mortar mixing drum in proportion, and stir for15s, then add JK-24 and aluminum powder, and stir for15s, and then add water to stir. Stir continuously during the feeding process until the slurry is uniform, and then send the slurry into a stirrer and pump it out.
1.4.2 Grouting under slab
Drive the grouting plug into the hole, pass through the asphalt composite layer and fix it on the cement board. The bottom of the plug is properly separated from the base, and the outlet of the hose is sleeved on the plug and fixed. If the connection part is not firm or the seal is not enough, slurry leakage, hole explosion and pressure difference will occur. After the anchorage is firm, plug the pump. After normal operation, start the grouting pump, and at the same time turn on the discharge switch at the bottom of the mixer, and continuously send the mortar into the pump until it is observed that the mortar flows from one hole to another. When it is observed that the plate starts to rise or the pressure in the mortar flow line rises rapidly, the pumping is stopped. When the grouting pressure is driven, it should be driven slowly and evenly. Generally, when the pressure reaches a certain value between 2.5 and 3 MPa, it should be kept in a stable state for more than 2 to 3 minutes, so that the slurry can fully flow and penetrate to the bottom of the plate, and the effect of compaction and enrichment can be achieved. Then, turn on the unloading switch, slowly reduce the pressure, and zero the pressure. According to the construction experience, the pressure during grouting is generally controlled at 1 ~ 4 MPa, in which the staggered sinker pressure is 2 ~ 4 MPa, generally empty plate1~ 3 MPa; The pressure of pumping mud and cracking plate is generally 2 ~ 3 MPa, which should be observed and controlled at any time during construction. During grouting, the grouting gap between adjacent holes (plates) should not stop pulping and stirring to keep the slurry uniform and not separate.
It is very important to determine the pressure during grouting. Too much pressure will easily cause the panel to arch and break, and too little pressure will not be full. However, due to different grouting models, the pressure reflected by the pressure gauge during grouting is also different, so the pressure gauge should be measured before grouting and calibrated at the construction site. Matters needing attention during grouting are as follows:
A) When cement slurry emerges from longitudinal and transverse cracks of concrete slab, continue grouting for 5 ~ 10 seconds, and stop grouting; Where there is water at the bottom of the plate, water will appear from the gap under mud pressure. At this time, it is necessary to continue grouting until the slurry appears for 5 ~ 10 seconds (the pressure in this case is 2 ~ 3 MPa).
B) If the pressure can't reach the specified value due to the mud bursting at the plate joint and the edge, the mud will first gush out freely along the plate joint. After the slurry is solidified, drill and grout again until the pressure reaches the above requirements.
1.4.3 After grouting, the mixing barrel must be washed with clean water. At this time, the hydraulic pump will work as usual, so that water is discharged from the high-pressure pipe through the pipeline and grouting pump, and the residual slurry of each component is completely removed and washed clean.
1.4.4 seal
After grouting, the grouting plug should be pulled out immediately, and the wooden plug should be inserted immediately, so as to have enough time to fully solidify the mortar. If the grouting in the hole drops, the grouting should be taken out from the concrete gap until the concrete surface becomes flat. Only when the pressure will not be restored and the mortar will not be squeezed out of the hole, can the cork be pulled out, and the hole will be permanently closed with quick-setting cement mortar and smoothed. Mortar left on the pavement after grouting should be cleaned up in time and washed with water to avoid mortar flowing into pavement cracks, prevent pavement pollution and affect the bonding of asphalt concrete in the future.
1.4.5 curing
Vehicles are prohibited from passing through the grouting area within 2 hours after grouting, and the general curing period is 3 days.
2 grouting construction quality control
2. 1 The on-site builder should make construction records carefully, mainly including the following aspects:
2. 1. 1 Record the specific position, staggered or sinking height and drilling position of each plate in detail.
2. 1.2 Fill in the grouting record carefully, and the project department will send special technicians to monitor each grouting machine. The mixture ratio of grouting materials must be accurate, and the number of holes, hole depth, pressure stabilization, maximum pressure, initial pressure time, final pressure time, pressure stabilization time and grouting quantity of each hole should be recorded in detail.
2.2 Grouting must be carried out in a certain order. Generally, the holes on both sides of the transverse joint are pressed first, then the other holes are pressed, and then they move forward in turn. When grouting, the pressure and time of each hole should be strictly controlled. If the pressure is not reached, it will not work. If it is unstable, the pressure stabilizing time will have a great influence on the grouting effect.
2.3 The site laboratory shall go deep into the site to conduct sampling inspection on the quality of grouting materials.
2.4 After curing for 3 days, the deflection of the grouting plate shall be tested, and the measured deflection shall not be greater than 14( 10-2mm). Unqualified shall instruct the original construction team to drill and grout again until it is qualified.
The application of grouting technology in urban road cement concrete pavement maintenance embodies the purpose of "prevention first, combining prevention with control" in the maintenance policy. Bringing the maintenance of concrete pavement into the scope of preventive work will play a positive role in prolonging the service life of concrete pavement and preventing the early and medium-term damage of concrete pavement. Under the condition of not destroying the concrete pavement slab, the grouting technology at the bottom of the slab has the advantages of low cost, high speed, good effect and fast opening to traffic. It can also avoid the environmental pollution caused by the removal of broken slab waste residue, which is a scientific maintenance technology to effectively prolong the service life of pavement. With the continuous popularization of pressure grouting technology, good economic and social benefits will be further achieved.