In winter, the temperature is low, the temperature difference between day and night is large, frost and snow frequently occur, the construction difficulty of asphalt and cement pavement is greatly increased, the mixture is easy to cool and solidify rapidly, and the pavement is easy to freeze. Once the construction control is not in place, it is easy to cause quality diseases such as loosening, cracking, insufficient strength and early damage.Combined with the winter construction characteristics of alpine mountains and Central Asia, the key control points of road construction in winter are sorted out from five dimensions: raw material control, mixing production, transportation and paving, rolling maintenance and safety management.

Before construction: environment and scheme pre-control

Strictly control the construction environment temperature bottom line

Hot-mix asphalt mixture construction: ambient temperature shall not be lower than 5℃; the lower limit of construction temperature of modified asphalt and SMA mixture shall be raised to 10℃, and paving operation shall be stopped directly in strong wind, frost and rain and snow weather.
Cold-mixed emulsified asphalt construction: construction can only be carried out when the temperature is higher than 0℃ and there is no ice or frost. It is forbidden to start construction when the temperature is below zero at night.
Cement stabilized base and concrete pavement: winter low-temperature construction mode shall be entered when the average temperature is lower than 5℃ for 5 consecutive days, and pouring is prohibited when the temperature is lower than-5 ℃.

Check weather conditions in advance

24 hours before construction, continuously monitor the temperature, wind and snow forecast, avoid cold wave, strong wind and rain and snow periods; give priority to centralized paving in high temperature section at noon in daytime, and shorten the open-air exposure time of mixture.

Perfect winter special construction scheme

Plan thermal insulation, antifreeze and emergency snow removal measures in advance; reserve snow-melting agent, thermal insulation tarpaulin and heating equipment for mountainous projects; specify the ex-factory temperature of mixture at low temperature, time limit for completion of rolling and thermal insulation maintenance process.

Key points of winter storage and pretreatment of raw materials

Bitumen and emulsified bitumen raw materials

Base asphalt, modified asphalt tank thickening insulation layer, supporting heat transfer oil continuous constant temperature heating, to prevent asphalt solidification caking; pipeline heat preservation throughout the heat tracing, to avoid transmission blockage.
The emulsified asphalt emulsion storage tank is equipped with heat preservation facilities to prevent emulsion emulsion breaking and layering at low temperature. The emulsion produced on the same day is used up on the same day and is not stored overnight in large quantities.

Sand aggregate

Set up enclosed material shed for sand and gravel, cover with thermal insulation tarpaulin, prohibit aggregate with ice, snow and caking into drying cylinder; timely clean snow and frozen blocks on the surface of material pile in ice and snow days.
The aggregate moisture content shall be strictly controlled. The increase of aggregate moisture content after melting of ice and snow will greatly increase the fuel consumption of mixing station, and will also cause insufficient mixture temperature and pavement water damage.

Cement, mineral powder and admixtures

Cement and mineral powder shall be stored in closed thermal insulation warehouse to prevent moisture and icing; early strength cement shall be selected for cement stabilization layer in winter construction, and antifreezing and retarding admixture shall be matched to improve low temperature molding strength.

Winter production control of asphalt mixing station 

Increase mixture delivery temperature 

The delivery temperature of ordinary hot-mix asphalt mixture shall be increased by 10~20℃; the delivery temperature of modified asphalt and SMA mixture shall be controlled at 180~190℃, and the temperature loss during transportation and paving shall be reserved. 

Equipment overall insulation antifreeze 

Drying drum, hot bin, weighing hopper and mixing pan wrap insulation cotton; preheat the whole equipment in advance before starting work every day to avoid too fast temperature drop of mixture caused by cold machine production. 
Shorten mixing cycle time 
Properly extend the dry mixing and wet mixing time to ensure that the aggregate and asphalt are fully coated under low temperature environment to prevent white materials and segregation; if the mixture is found to be agglomerated and the temperature is insufficient, it will be discarded directly. 

equipment shutdown freeze protection 

Drain water pipes, dust removal waterways and additive pipelines after work every day to prevent freezing and cracking of pipelines; do anti-freezing maintenance for burners and air compressors, and keep them intermittently at night. 

Heat preservation measures for mixture transportation 

The bottom and both sides of all material transport carriages are equipped with insulation interlayer, the top surface is fully covered with double-layer thickened insulation tarpaulin, and the gaps are compacted and sealed to reduce heat loss on the way. 
Plan the shortest transportation route to reduce the waiting time for unloading; there should not be too many vehicles on site to avoid long-term outdoor cooling. 
The temperature of the mixture on site is measured one by one. Paving is strictly prohibited if the temperature is lower than the lower limit of the specification. It is directly transported back to the mixing station for processing, and low-temperature materials are prohibited from paving the road. 

Key requirements for site paving and rolling 

base layer defrosting and deicing in advance 

Before paving, thoroughly clean the snow, thin ice and frost on the lower bearing layer; the frozen base layer shall be baked by hot air, and it is forbidden to directly pave asphalt mixture to prevent interlayer adhesion failure and later peeling. 

Continuous and uninterrupted paving operation 

The paver shall be constructed at a constant speed without interruption, so as to reduce the waiting time; immediately follow the compaction after paving, and strictly control the "bottom line of final pressure temperature": the final pressure of ordinary asphalt shall not be lower than 70℃, and that of modified asphalt shall not be lower than 90℃. 

Optimization of rolling construction procedure 

Shorten the interval between initial compaction, re-compaction and final compaction to achieve the goal of "pressing with paving"; give priority to using heavy steel wheel roller for rapid compaction in low temperature environment, so as to avoid the mixture from being unable to compact after cooling and hardening, and the void ratio exceeding the standard. 

Segmented short-width construction 

In winter, it is not suitable for long-distance one-time paving, sectional construction, sectional molding, reducing the exposed area of the mixture, and quickly completing the closed rolling. 

Pavement maintenance and finished pavement frost protection 

Cement base/concrete pavement anti-freezing maintenance 

After pouring, immediately cover with thermal insulation quilt and geotextile, and set up thermal insulation windproof shed if necessary; change watering maintenance to spray moisturizing during low temperature period, and prohibit large-area watering and freezing; open traffic after reaching design strength. 

asphalt pavement forming protection 

It is forbidden to open traffic before the hot asphalt pavement just rolled is completely cooled; water spraying and snow-melting agent spraying shall be avoided at the initial stage of molding, and snow-melting salt will corrode the asphalt pavement and shorten the service life of the road. 

Rain and snow emergency protection 

If snow falls suddenly in the middle of construction, immediately stop paving, quickly cover the insulation tarpaulin to protect the uncooled mixture; remove all the paved and uncompacted sections, and restart construction when the temperature rises. 
Winter construction site safety precautions 

anti-freezing and anti-skid protection 

Anti-skid mat shall be laid on the operation platform of construction access road, paver and roller; the working personnel shall be equipped with winter clothes and anti-skid protective shoes to prevent frostbite, slipping and falling injury. 
Fire and scald prevention management 
The high temperature area of heat transfer oil and asphalt storage tank in mixing station shall be kept away from flammable insulation materials; the insulation heating equipment shall be used in a standardized manner, and it is strictly prohibited to bake tarpaulin and oil in close range with open fire to prevent fire. 
Mechanical winter safety operation and maintenance 
Change winter antifreeze engine oil and antifreeze for construction machinery; preheat engine before starting every day to avoid damage to equipment at low temperature and cold start; empty water tank and water pipe to prevent freezing crack after finishing work. 

traffic diversion safety 

In winter, the visibility is low in foggy and snowy days. Reflective warning signs and warning lights shall be added in the construction section, and special personnel shall be arranged to guide the traffic flow to prevent traffic accidents caused by vehicle slippage. 
Supplement: Special requirements for cold mixed emulsified asphalt construction in winter 
If emulsified asphalt cold regeneration, slurry seal layer winter curing construction: 
Construction will only be carried out at noon when the temperature is stable above 0℃, and work will be suspended during freezing periods in the morning and evening; 
Appropriate addition of special low-temperature modifier to improve molding speed; 
After construction, the closed traffic time shall be extended, and the traffic shall be opened after the emulsion is completely demulsified and formed, and the moisture is volatilized, so as to prevent the surface layer from loosening. 

sum up 

The core control logic of road construction in winter: temperature protection, ice and snow removal, fast construction, strict insulation and strong protection. From raw materials, mixing, transportation, paving to maintenance, heat preservation and antifreezing shall be done well in the whole process, temperature index shall be strictly controlled, construction in extreme low temperature rainy and snowy weather shall be avoided, and fire safety management of personnel, machinery and traffic shall be implemented at the same time, so as to effectively avoid quality diseases such as pavement cracking, loosening and delamination, and ensure the construction quality and safety of road engineering in winter.