Temperature control of asphalt mixture runs through the whole process of production, storage, transportation and paving, among which storage temperature is the key link to ensure stable performance of mixture and avoid construction quality defects. Asphalt belongs to temperature-sensitive material. During the temporary storage period of mixture in storage bin, too high temperature will cause asphalt thermal aging, mixture flooding and stability decline; too low temperature will lead to poor aggregate cohesiveness and mixture segregation and agglomeration, which will directly cause substandard paving compaction, excessive pavement void ratio, cracking, loosening, pit and other diseases in the later stage. According to the Technical Specification for Highway Asphalt Pavement Construction (JTG F40-2004), this paper systematically combs the storage temperature standard, cooling control, storage time and field control points of various asphalt mixtures, providing a normative basis for engineering construction. 

Bituminous mixture storage core temperature criteria 

According to the national standard specification, all hot-mixed asphalt mixtures must follow the principle of temperature reduction range control during storage in the storage bin of the mixing station: the overall temperature reduction shall not exceed 10℃ during the process of mixture discharge to storage and standing. This is the general core standard for mixture storage. No matter base asphalt or modified asphalt mixture, excessive temperature difference cooling is regarded as performance failure and is strictly prohibited for pavement construction. At the same time, all hot-mixed mixtures are set with waste temperature threshold, and over-temperature aging mixtures must be directly discarded and prohibited from use. 

Storage temperature standards for different types of asphalt mixtures 

Common base asphalt mixture

Common road asphalt mixture has stable performance and low temperature sensitivity. It is a common mixture for municipal and common roads. The standard discharge temperature is controlled at 140~160℃, the storage temperature of the storage bin follows the discharge temperature, and the whole temperature is reduced to ≤10℃. The stable storage temperature range of the storage is 130~150℃. The highest discard temperature of mixture is 190℃, if the temperature exceeds this value during storage, the light components of asphalt will volatilize seriously, and the mixture will dry and age, so it must be discarded. The storage and discharge temperature shall not be lower than 130℃, so as to ensure that the subsequent paving and compaction temperature meet the standard. 

SBS modified asphalt mixture

SBS modified asphalt mixture is mostly used in expressway, heavy-load pavement and bridge deck engineering. The modifier is extremely sensitive to temperature, with fast cooling speed, fast performance attenuation and stricter control standard. The ex-factory discharging temperature is 170~185℃, the storage temperature shall be kept at 160~175℃, and the specification requirement that the temperature drop shall not exceed 10℃ shall be strictly implemented. the low critical storage temperature is not lower than 160 DEG C, and once that temperature is low than the minimum critical storage temperature, the activity of the modifier is invalid, and the rutting resistance and the cracking resistance of the mixture are greatly reduce. The maximum waste temperature of modified mixture is 195℃, and over-temperature aged mixture shall not be paved. 

Rubber asphalt mixture 

Rubber asphalt mixture is mostly used for stress absorbing layer and special pavement, and the construction temperature is on the high side as a whole. The discharging temperature of the mixture shall be 180~190℃, and the storage temperature of the storage bin shall be stably controlled at 175~185℃. The temperature fluctuation shall be strictly controlled during storage, and the maximum discarding temperature shall be 200℃. If the temperature is too high, the mixture must be discarded, so as to prevent the aged mixture from being put into use. 

Warm mix asphalt 

Warm mix asphalt mixture reduces construction temperature through warm mix agent, saves energy and protects environment, and adapts to low-temperature construction scene. Conventional storage temperature control in 130~150℃, different from the hot mix, warm mix mixture should not be stored for a long time, the specification requires that the storage time should not exceed 12 hours, to avoid the failure of warm mix agent, mixture bonding performance attenuation. 

Emulsify asphalt cold mix 

Cold mix emulsified asphalt mixture without high temperature storage, suitable for road surface repair, sporadic engineering. The storage shall be mainly protected at normal temperature, and the ambient temperature shall be controlled at 5~60℃. The key point of core management and control is not high temperature insulation, but sealed, waterproof and light-proof storage to prevent emulsion demulsification and delamination failure. There is no requirement for high temperature insulation. 

Third, storage time and temperature linkage control requirements 

Under the premise of stable temperature, the storage time directly determines the performance of the mixture, and the storage time limit of different graded mixtures is clearly distinguished to prevent long-term stacking and storage. 
1. Densified asphalt mixture: when the thermal insulation storage bin is closed and the thermal insulation performance is good, it can be stored continuously for a short time, and it is appropriate to mix and use at any time. The performance will not be affected by single-day storage. 
2. Open-graded, gap-graded mixture (SMA, OGFC): skeleton void structure heat dissipation fast, easy to separate, it is forbidden to store for a long time, the storage time should not exceed 2~3 hours, must be produced with the shop; 
3. All modified asphalt mixtures: in principle, they are mixed and used at any time. Overnight storage is prohibited. Long-term standing will lead to temperature stratification and modifier precipitation, resulting in color difference and uneven compactness of pavement construction. 

On-site storage temperature control measures 

1. Equipment insulation control: the storage bin of mixing station must be completely wrapped with insulation layer, seal the gap of bin body, reduce heat loss, ensure uniform temperature in bin, and avoid local low temperature agglomeration and local high temperature aging. 
2. Multi-point temperature measurement monitoring: regularly detect the temperature of the upper, middle and lower layers in the warehouse during storage to ensure uniform temperature difference in the warehouse, strictly control the overall temperature reduction range ≤10℃, and immediately check the equipment fault if the temperature difference exceeds the standard. 
3. Eliminate secondary heating: Mixtures with excessive low-temperature cooling and over-temperature aging mixtures are prohibited from being reused for secondary heating. Heating will aggravate asphalt aging and destroy the original properties of the mixture, and must be discarded directly. 
4. Classified and partitioned storage: mixed storage of asphalt mixtures of different grades and types is strictly prohibited to avoid construction quality problems caused by different temperature standards and mixed performance. 

Conclusion 

The core of asphalt mixture storage temperature control is to strictly follow the requirements of JTG F40-2004 specification, achieve classified temperature control, strict control of temperature reduction, time-limited storage, and ultra-waste use. The storage temperature and time limit standard of ordinary mixture, modified mixture, warm mixture and special rubber asphalt mixture are different, so the construction site shall be accurately distinguished and finely controlled. Stable and compliant storage temperature can retain the adhesive performance and road performance of asphalt mixture to the greatest extent, avoid early road diseases from the source, and effectively improve the construction quality and service life of asphalt pavement.