At the asphalt paving construction site of highway and municipal roads, it is often seen that sprinklers closely follow pavers and rollers to continuously sprinkle water to cool and moisturize the newly paved asphalt pavement. Many people mistakenly think that road watering is only a simple dust suppression operation, but in fact it is an indispensable key process of asphalt pavement construction, which directly determines the forming quality, service life, flatness and stability of the pavement. After paving asphalt pavement, watering is not a random operation, but a standardized operation based on the physical characteristics of asphalt materials, construction technology requirements and pavement forming rules. This paper analyzes in detail the core reason of asphalt pavement construction watering, watering effect in different stages and construction specification points. 

First, the core principle of asphalt pavement watering 

Asphalt is a typical temperature-sensitive polymer material, its hardness, viscosity and stability change completely with temperature: softening, viscosity and easy deformation at high temperature, hardening and setting at low temperature, strength enhancement. The paving temperature of ordinary hot mix asphalt mixture is as high as 140℃~160℃, and the pavement temperature is extremely high at the initial stage of rolling. If it is cooled naturally, it will have problems such as uneven cooling, shrinkage cracking and pavement deformation. 
The core principle of watering operation is to take advantage of the evaporation and heat absorption characteristics of water to quickly and evenly take away the surface and internal heat of asphalt pavement, accurately control the cooling speed of pavement, complete compaction, solidification and shaping of asphalt mixture within reasonable temperature range, avoid various pavement diseases caused by high temperature construction, and ensure that the pavement strength and compactness meet the standard. 

the main role of asphalt pavement construction watering 

Rapid and uniform cooling, standardize the pavement forming process 

The temperature of newly paved asphalt pavement is extremely high, and there are many disadvantages in natural cooling: the surface heat dissipation is fast, the internal heat dissipation is slow, the temperature difference between the inside and outside of the pavement is too large, which will produce uneven shrinkage stress, and cracks, net cracks and irregular cracks are easy to appear in the later stage. At the same time, the high temperature asphalt pavement molding speed is slow, in a soft state for a long time, easy to be crushed and deformed by construction vehicles and road rollers, rutting, potholes, flatness exceeding the standard and other problems. 
Sprinkling cooling can greatly reduce the temperature difference between the inside and outside of asphalt pavement, realize uniform cooling as a whole, accelerate the curing and shaping of asphalt mixture, shorten the pavement molding cycle, make the pavement quickly reach the design strength, and effectively eliminate the pavement quality problems caused by uneven cooling and slow molding. 

Auxiliary rolling construction to improve road compactness 

Roller compaction is the core process of asphalt pavement compaction. The asphalt mixture under high temperature is extremely viscous, so it is easy to adhere to the steel wheel of roller during compaction, resulting in sticking, peeling and galling, which not only damages the flatness of pavement surface, but also causes local mixture loss and insufficient compactness, leaving hidden dangers of pavement seepage and damage. 
Appropriate sprinkling of water on the road surface and roller wheel body during construction can form a very thin water film between the steel wheel and the asphalt road surface, which plays an isolation and lubrication role and completely avoids the problem of asphalt sticking to the wheel. At the same time, the asphalt mixture after moderate cooling is moderately soft and hard, which is easier to be compacted, which can effectively improve the overall compactness and flatness of the pavement, make the asphalt aggregate bite more tightly, and enhance the bearing capacity of the pavement. 

Prevent pavement cracking and extend road life 

Crack is the most common early disease of asphalt pavement. Besides temperature difference contraction, high temperature exposure, rapid cooling and stress concentration are the main causes. During construction at high temperature in summer, the surface temperature far exceeds the suitable molding temperature of asphalt pavement. The sun exposure will make the asphalt surface harden rapidly, and the interior is still in a high temperature softening state. A large number of shrinkage cracks will occur when the subsequent temperature drops. 
Continuous moderate watering can reduce the surface temperature of pavement, relieve the high temperature stress caused by sunlight exposure, balance the overall temperature field of pavement, reduce the shrinkage deformation of asphalt mixture, prevent the generation of temperature shrinkage cracks and dry shrinkage cracks from the root, avoid rainwater penetrating into the pavement base through cracks, prevent the occurrence of secondary diseases such as soaking water, settlement, pit and boiling of the base, and greatly prolong the service life of asphalt pavement. 

Dust suppression, noise reduction, optimization of construction site environment 

During asphalt paving and rolling operation, aggregate friction and equipment driving will produce a large amount of dust, which not only pollutes the construction site and surrounding environment, but also affects the sight of construction personnel and interferes with the construction operation accuracy. At the same time, the friction of dry aggregate will generate large construction noise. 
Sprinkling operation can effectively absorb road dust, inhibit dust diffusion, purify the air environment on the construction site, and meet the environmental protection requirements of municipal construction. At the same time, wet pavement can reduce aggregate frictional resistance, reduce construction noise, and optimize the overall construction environment. 

Maintain moisture, stabilize pavement structure performance 

Asphalt pavement is not stable immediately after forming, and it is still in the performance curing stage at the initial stage. For newly paved pavement just completed, moderate watering and moisturizing maintenance can avoid rapid air drying, hardening and embrittlement of pavement, fully complete stress release and structural stability of asphalt mixture, improve adhesion strength between asphalt and aggregate, enhance wear resistance, impermeability and aging resistance of pavement, and improve overall construction quality of road.

Requirements of watering specifications for different construction stages 

1. Rolling stage: a small amount of frequent sprinkling, mainly moistening 
The core purpose of this stage is to prevent sticking wheels and auxiliary rolling, and flood irrigation is strictly prohibited. Atomized watering method shall be adopted to keep the road surface and steel wheel wet without ponding, which will cause local asphalt temperature to drop sharply, causing problems such as peeling, loosening and color difference of road surface, which will affect the molding quality. 
2. Forming cooling stage: uniform watering, uniform cooling 
After rolling, the road surface is still in high temperature state, so it is necessary to continuously spray water to slowly cool down, control the cooling speed, and avoid sudden change of temperature difference. Until the temperature of the road surface drops below 50℃, the watering can be stopped and temporary traffic can be opened. 
3. Post-curing stage: moisture curing, intermittent watering 
After the road surface is completely cooled and formed, intermittent watering is still needed in a short period of time, especially in summer high temperature weather, which can effectively prevent the road surface from aging and cracking, and stabilize the road structure performance. 

Common mistakes and taboos in construction watering 

Many pavement quality problems stem from irregular watering operations, and three major mistakes need to be strictly avoided during construction: 
- It is forbidden to flood with water: a large amount of cold water directly washes the high temperature asphalt pavement, which will cause the local rapid contraction of the pavement, produce a large number of fine cracks, and at the same time lead to the decrease of asphalt adhesion, loose pavement and particle loss. 
- High temperature quenching and excessive temperature difference are prohibited: it is strictly prohibited to spray water in large quantities under ultra-high temperature condition of road surface, and the principle of slow and uniform cooling shall be followed to ensure stable road stress. 
- Prohibition of low temperature watering, excessive watering: when the road temperature is too low, there is no need to sprinkle water, excessive water will stay in the cracks of the road surface, long-term immersion will weaken the asphalt adhesion performance, reduce the durability of the road surface. 

Summary 

Asphalt pavement construction watering is not a simple dust reduction operation, but a core process link to ensure the quality of pavement molding. Its essence is to adapt the characteristics of asphalt temperature-sensitive materials through scientific watering, moisturizing and lubricating operations, standardize the pavement cooling and forming process, solve the construction problems such as wheel deformation, temperature difference cracking and insufficient compactness, avoid early road diseases from the source, and improve the flatness, compactness and durability of pavement. 
Standardized, moderate and uniform watering operation is an important embodiment of asphalt pavement construction standardization, and is also a key measure to ensure road quality, prolong road service life and improve driving comfort.