Asphalt pavement cold repair material is an emergency repair material without heating and normal temperature construction. It is widely used in repairing road pits, cracks, looseness, subsidence and other diseases by virtue of its advantages of convenient construction, no seasonal temperature restriction and rapid opening of traffic after repair. Compared with traditional hot-mix asphalt, the construction threshold of cold repair material is lower, but in order to realize smooth and dense pavement after repair, durable, non-falling and non-seepage, and avoid short-term secondary damage problem, it is necessary to master standardized and refined practical operation skills. Combined with the field construction experience, this paper comprehensively explains the core skills of cold repair material application from the aspects of preliminary pretreatment, filler paving, compaction forming, special construction conditions, maintenance acceptance and pit avoidance. 

Pretreatment in the early stage of construction: lay a good foundation and eliminate hidden diseases 

Pre-cleaning and base surface treatment are the key to determine the repair quality. Most of the problems of cold repair pavement damage, sanding and hollowing are caused by the substandard base surface treatment, so it is necessary to strictly follow the four-step skills of "trimming, bottom cleaning, drying and bottom sealing". 

Regular trimming, regular repair contour 

For potholes and irregular damaged areas on the road surface, it is prohibited to fill directly and randomly. It is necessary to cut regular rectangular or square cuts along the edge of the disease with a cutting machine. The cuts are vertical to the road surface and the edges are neat. The loose, aged and cracked old asphalt surface at the periphery shall be removed until the solid and stable base pavement is exposed. This can avoid cracks and nibbles at the junction of new and old pavement, and greatly improve the tightness and integrity of joints. 

Thoroughly clean impurities to ensure the cleanliness of the base surface 

After cutting, manually remove loose old materials, gravel and muck inside the pit groove, and then thoroughly clean the groove and surrounding gaps with blower and broom to ensure that there is no dust, mud, accumulated water, ice, weeds and other sundries. Especially wet, after rain construction, must wait for the groove completely dry before operation, wet base will lead to cold repair material and base bonding failure, later easy to appear overall fall off, seepage freezing damage problems. 

Apply priming oil as needed to strengthen adhesion 

For pits with depth greater than 3cm and dry and rough base surface, or old pavement repair scenes, a thin layer of emulsified asphalt prime coat oil can be sprayed evenly, and filler can be filled after the prime coat oil is initially set and does not stick to hands. The thin layer of permeable oil can fill the fine pores of the base surface, greatly improve the bonding strength between the cold repair material and the original pavement, and prevent delamination; this step can be omitted when the shallow pit groove and the base surface are flat and clean, so as to avoid excessive oil causing oil flooding and soft pavement. 
Cold repair paving is not simply filling compaction, thickness control, layered filling, surface shaping directly affect the compaction effect and pavement flatness, core skills focus on thickness, layering, shaping three points. 
1. overfill reserve settlement 
The filler shall follow the principle of "rather high than low", and the overall filler height shall be 1~1.5cm higher than the original pavement. Natural settlement will occur during the compaction of cold repair materials, and repeated rolling by vehicles in the later period will further compact. The reserved height can perfectly offset the settlement amount and avoid road surface depression and ponding after repair. Small shallow pits can be reserved for 1cm, and deep pits with a depth of more than 10cm can be appropriately increased to 1.5cm. 
2. Deep pit filling and compaction 
It is forbidden to exceed the standard for single paving thickness. The pit depth>6cm must be filled and compacted layer by layer, and the paving thickness of each layer shall be controlled within 3~5cm. It is forbidden to fill the deep pit at one time, otherwise there will be problems such as internal cavity, loose compaction of surface layer and loose compaction of lower layer, and pit recurrence and road settlement will easily occur in the later stage. After leveling and compacting each layer of filling, the next layer of filling shall be carried out, and the overall compactness shall be ensured by tamping layer by layer. 
3. Surface arc shaping 
After paving and leveling, the surface of the repaired area shall be trimmed into a slight arc with a slightly higher middle and a periphery conforming to the original pavement, so as to avoid surface flatness or depression in the middle. The arc structure can adapt to the rolling force of vehicles, quickly drain road water, reduce rainwater infiltration into joints, and prolong the service life of repaired roads. 

The core skills of compaction molding: adaptation equipment, global compaction 

Compaction is the core process of cold repair material construction. Insufficient compaction degree will lead to loose pavement, sanding and water seepage. Excessive compaction will cause oil flooding and cracking. Compaction equipment shall be matched according to repair area and scene, and standardized compaction skills shall be mastered. 

Select compaction equipment according to scene 

Community roads, sidewalks, scattered small pits and grooves: manual compaction plate and small handheld tamping machine shall be adopted to flexibly adapt to corner areas; municipal trunk roads and large-area continuous repair areas: small vibrating roller shall be selected, the rolling speed shall be controlled at 2~4km/h, and the rolling operation shall be carried out at a uniform speed to avoid material displacement and surface cracking caused by high-speed rolling. 

Control of rolling sequence and number of times 

Follow the sequence of "corner first, then middle, static pressure first, then vibration pressure", and focus on tamping the joints around the pit, which is the weak area most prone to loose water seepage. 3~4 times of rolling under normal working conditions, the first static pressure setting, subsequent vibration compaction, and the last static pressure polishing to ensure that the surface is flat without wheel traces and loose particles. 

Tips for improving quality 

After compaction is completed, a layer of fine sand or stone powder can be evenly spread on the repair surface to clean up the fine voids on the surface. It can not only absorb excess asphalt on the surface, prevent vehicles from sticking, but also improve the wear resistance and anti-skid performance of the road surface, so that the appearance and texture of the repaired area are highly unified with the original road surface. 

Special construction skills for different environments: adapting to working conditions and improving quality in all weather 

Cold repair materials can realize all-weather construction at minus low temperature, rain and snow, normal temperature and high temperature. Construction details need to be adjusted in different environments to adapt to environmental characteristics and ensure repair effect. 

Normal temperature conventional construction (5~30℃) 

The most suitable construction temperature range, no special pretreatment, according to the standard process construction can be. After compaction, light vehicles can be directly opened for passage. Within 3~7 days, cold repair materials will gradually precipitate asphalt under vehicle compaction, solidify and compact, and reach the best strength. During this period, it is necessary to avoid long-term parking of heavy-duty vehicles and sudden braking in place. 

Summer high temperature construction (>30℃) 

Under high temperature environment, the softening speed of cold patching is fast, and it is easy to appear oil flooding, softening and deformation problems. During construction, the amount of single filler can be appropriately reduced, and the paving and compaction speed can be accelerated to avoid long-term exposure of materials in the open air; fine sand shall be spread in time after compaction, and the speed shall be strictly controlled at the initial stage of opening traffic to prevent the road surface from moving and wrinkling. 

Winter low temperature construction (<5℃) 

Low temperature environment material fluidity, cohesiveness decline, easy to agglomerate, compaction difficult. Before construction, the cold patching material can be placed in a warm environment to defrost and break up the agglomerated materials to ensure that the materials are evenly loose; during construction, the frost in the groove shall be thoroughly cleaned, and the construction with ice shall be prohibited; after compaction, the standing time shall be appropriately extended. It is recommended to delay the opening of heavy vehicles for 1~2 hours to ensure the preliminary solidification of materials. 

rainy and wet construction 

Emergency repair can be carried out under the condition of light rain and no accumulated water after rain. The accumulated water in the groove must be completely drained before construction and the wet base surface must be dried. After construction, it shall be compacted and sealed in time to block rainwater infiltration. Construction is prohibited in heavy rain, which can dilute asphalt and wash away filler, resulting in complete failure of the repair. 

Open traffic and post-maintenance skills 

Traffic opening regulations 

Cold patching has the advantage of fast opening to traffic. Light vehicles can be opened after conventional compaction is completed; heavy vehicles shall be delayed in low temperature and wet weather. Within 12 hours after opening to traffic, the speed of the repair area shall be controlled within 30km/h. It is strictly prohibited to turn around, brake suddenly and park for a long time, so as to prevent deformation, peeling and loosening of the road surface that is not completely cured. 

Late self-inspection and maintenance 

Timely acceptance after completion of construction, the standard is that the road surface is smooth, no wheel track, no loose, tight joints without gaps, no ponding depression. 3~7 days after opening to traffic, the material is completely solidified and formed. If there is local fine looseness, a small amount of supplementary material can be compacted and repaired; the compactness and strength of the pavement can be continuously improved without special maintenance and natural rolling. 

Common construction mistakes and pit avoidance skills 

- Mistake 1: direct packing without trimming. The connection between the old and new pavement is loose and easy to seep and gnaw. Pit avoidance: must be regular trimming, remove all loose old material, ensure that the base solid. 
- Mistake 3: Insufficient filler height. After opening to traffic, the road surface caved in and accumulated water. Pit avoidance: uniformly reserve 1~1.5cm settlement height, rather slightly convex than low. 
- Mistake 5: construction with ponding and ice. Material bonding failure, overall shedding. Pit avoidance: the base surface must be dry and clean, and the construction under wet and icing conditions shall be avoided. 

Conclusion 

The construction of asphalt pavement cold repair material seems simple, but in fact the details determine the durability. The core construction logic is that the base surface is clean and solid, the layered filler thickness is controlled, the whole area is compacted in place, and the environment is fine tuned. Strictly follow the above practical operation skills, which can not only give full play to the construction advantages of quick emergency response of cold repair materials, but also effectively solve the problem of repeated damage of pavement, greatly improve the repair quality and service life of pavement, and adapt to the normal maintenance operation of various scenarios such as municipal roads, park pavements, factory roads, etc.