One、Background and significance

By 2022, the total mileage of highways in Sichuan will be 40.50,000㎞，Among them, the second-class and above highways 3.20,000㎞，National and provincial trunk highway 3.90,000㎞，The expressway mileage is 9179㎞。Asphalt pavement is the main type of highway pavement.，General design service life: 12 years，Highway 15 years。But in the service life，With the natural aging of asphalt、The volume of traffic is increasing，Asphalt pavement structure、Performance is subject to varying degrees of degradation and damage，Structural damage such as cracks、Rut、Potholes, etc，Performance index attenuation such as flatness、The attenuation of sliding resistance coefficient does not meet the requirements of the specification。From the maintenance experience in recent years，4~It has entered a period of high incidence of diseases in 6 years.，Local excavation and repair is required，Usually 8 years~It will enter a large-scale maintenance period around 2010.，Such as medium repair overlay or even overhaul。If the average maintenance cycle is calculated by 10 years，Only the national and provincial trunk roads have 3900㎞、There are more than 900 highwayskmMedium repair is required。At present, the maintenance method of asphalt pavement is mostly to mill the old pavement and pave the new asphalt pavement.（Milling and planing overlay）The way，Other new processes such as asphalt recycling, especially asphalt hot in-place recycling（In-situ reclaimed pavement）Only a small number of test sections are tried out.，It has not been applied on a large scale.。

1000 tons per kilometer of asphalt pavement maintenance according to national and provincial trunk roads、Calculation of 2000 tons of material per kilometer of expressway，Only Sichuan needs 6 million tons of asphalt mixture for pavement maintenance every year.，At the same time, 6 million tons of waste are produced.。The traditional milling and paving method not only wastes resources,，For areas where sand and gravel materials are in short supply or mining is difficult，Insufficient maintenance funds are also an important pressure.，But also that exploitation of sand and gravel material、Processing、Transport to the environment、Land protection causes greater pressure。So，Asphalt pavement maintenance technology needs to be changed urgently.，Explore and promote the application of a highly efficient、Environmental protection、Durable asphalt pavement maintenance technology is particularly important under the requirements of the central high-quality development policy.。

Hot in-place recycling technology of asphalt pavement was introduced from abroad in 2002.，In Jiangsu Province alone, a total of 1400 kilometers of lanes have been completed.，It will be included in the comprehensive promotion of maintenance technology in 2017.。Sichuan Province was introduced by Sichuan Chengyu Expressway Co., Ltd. in 2004.，By 2007, it has been successfully applied in Chengdu-Chongqing Expressway to complete the pavement maintenance of 340 lanes and kilometers of recycled pavement.。In 2019，Chengdu-Chongqing Company has also explored and improved the original hot in-place recycling and remixing recycling process.，Respectively for Chengdu-Chongqing Expressway 10kmIt has been used for 12 years、Chengya Expressway 16kmPavement that has been used for 9 years，Directly regenerating the upper surface layer of the original pavement in situ to be used as a pavement wearing layer，New technology without new pavement。4 have been used so far.5 years，The road surface is free from disease，Grass-roots technicians compared the road conditions of milling and paving pavement constructed in the same period.，The hot in-place recycling section has obvious advantages.，According to their analysis，The advantages will be more obvious in the next few years.。So，It is fast and safe、Resource conservation、Cost savings、Durable quality、Environmentally friendly and other advantages，It is worth popularizing and applying in asphalt pavement maintenance.。

Two、Characteristics and advantages of improved hot-in-place recycling technology for asphalt pavement

Hot in-place recycling technology softens the old asphalt pavement by heating.，After that, the regenerant and new aggregate are added according to the proportion requirements after being raked by a milling machine.，After stirring、Spreading、Compaction and other processes，Eliminate the disease of road surface，Restoring the serviceability of asphalt pavement。This technology can maximize the use of old pavement materials.，Reduce the consumption of new materials，Reduce waste generation，At the same time，Large amount of excavation and transportation is not required during construction.，Reduced impact on traffic and environment。

The improved hot in-place recycling technology is based on the original hot in-place recycling process.，The heating and thermal insulation performance of the original equipment and construction process is improved.，Using Intelligent Temperature Control System to Improve the Efficiency of Process Heat Energy Utilization，Ffectively ensure the mixing temperature of the recycled mixture、Paving temperature，And greatly improve that stability and uniformity of the regeneration quality.，It makes up for the unstable pavement quality caused by the unstable and uneven temperature of the original process.，So that that durability of the regenerate pavement is improved。

Compared with milling and paving, the improved hot in-place recycling technology has the following advantages：

1. Faster and safer construction，50% less than milling overlay%Road occupation maintenance time。To complete the 12.Take 50000 square meters of 5 lane kilometers as an example.，It only takes about 10 days to complete the improved hot in-place recycling process.，It takes at least 23 days to use the traditional process of milling and paving.。So，The technology allows construction without disrupting traffic.，The construction efficiency can be greatly improved.，Shorten the construction period，Reduce disruption to traffic。

2. Resource conservation：

①The land occupation is reduced：4cm50000 thickm2 Road surface 5000 tons about 2500m3，The milling and paving process needs to cover an area of 1000m2 Stacking，The hot in-place recycling process utilizes the asphalt mixture of the old pavement in situ.，There is no need to occupy additional land for stacking，This alone can reduce the area of Sichuan Province by 1800 mu per year.。4.8 million tons of sand and gravel material resources can be reduced, and the mining and processing area is about 1500 mu.。

Qing、Materials such as new asphalt mixture and regenerant，The material cost is relatively low.。The milling and paving process of asphalt pavement needs to produce new asphalt mixture.，And transport and laying，Its material cost is relatively high.。

②And that sand and stone resource are saved：The hot in-place recycling process only needs a small amount of new material to improve the gradation.，Can be reduced by 80%Sandstone material。Sichuan saves 4.8 million tons of sand and gravel resources by maintaining the pavement of national and provincial trunk roads and expressways throughout the year，In the case of the lack of pavement sand and gravel materials in Sichuan, especially basalt ore,，Saving resources is more important.。

③ Asphalt、Conservation of fossil resources such as diesel oil：6 million tons of asphalt mixture per year in Sichuan can save 70% of heavy traffic#360000 tons of asphalt，6000 tons of diesel oil for mixture transportation。

④Maintenance cost savings：Milling Overlay 4cmThe average direct cost of asphalt pavement is 75 yuan./mAbout 2，The direct cost of hot in-place recycling process is about 60 yuan./m2 ，Save 20%。Because the thermal recycling does not need to deal with the diseases such as crack sealing of the middle layer of the original pavement.，The actual savings will be more，Sichuan Province can save at least 8% of the direct cost of maintenance every year.500 million yuan，Plus indirect costs can reach more than 1 billion.。

Along with that popularization and application of the improve hot in-place recycling proces,，Amortization of equipment、Energy consumption and efficiency will be further optimized，The construction period can be further shortened，Further reduce the project cost。In contrast，Milling and paving need to consume a large amount of sand and gravel materials, which will further increase the cost with the depletion of resources.。

3. The quality is more durable

Jiangsu Highway Maintenance Technology Company concluded from the large-scale application of hot in-place recycling technology in 2005 that，At present, the remaining sections in operation are mainly concentrated in 2009.~Ningjing Salt constructed in 2015、Ningsuxu, Suhuaiyan and other expressways are about 300 kilometers.，Satisfaction with the questionnaire survey of front-line technicians was basically 88%，Maximum service life of 14 years，Shortest 2~3 years，After improving the process in 2009, it has been widely used for more than 10 years.。In that original hot in-place recycle process, the mix uniformity of the materials,、Heating temperature control depends on workers' experience.、Manual operation，The heating temperature fluctuates from high to low，Or the materials are not mixed evenly，Affect the quality of recycled pavement。

2019，Sichuan Tiesen Road Maintenance Technology Company has improved the level of process intelligent management and control on the basis of Jiangsu experience.，It has been used in pavement maintenance of Chengdu-Chongqing Expressway and Chengdu-Ya'an Expressway..No disease for 5 years，It shows that the improved hot in-place recycling process can solve the problem of unstable quality.，Especially when the temperature of Chengya Expressway is as low as 10℃Time for construction，It can still ensure stable and reliable quality.，Judging from the front-line technical personnel，The estimated service life can reach 8 years.，More than 10 years from Jiangsu's experience，Compared with the milling and paving pavement constructed in the same period, the disease is much less.，It is possible to reach or even exceed the service life of milling pavement.。

Investigate the reason，The inherent defects of milling and paving are solved by improving the regeneration process.：

①Connection problem between pavement layers

The improved regeneration process can fully realize the effective thermal connection between the regenerated layer and the original middle layer，Form a solid whole and improve the shear resistance by two times。

②Horizontal、Longitudinal seam hot joint is more compact，Better water sealing effect，Improve the ability of road surface to resist water damage。

③Thermal regeneration also heats the original mid-course mix during the heating process.，The road roller shall be rolled together with the middle layer.，Thereby closing the reflection cracks of the original pavement.。So at 3~5 year post occupancy comparison，Hot in-place recycling pavement solves the problem of reflective cracks in milling and paving pavement.，Thereby avoiding early water damage and premature aging of the asphalt.。

④In terms of quality control，Temperature Segregation in Quality Control of Improved Regeneration with Milling Overlay Ratio、Cold joint、Reflection crack is a difficult problem that can not be solved at this stage.，Pecially pavement maintenance dispersion，Quality control is more difficult.。

4. Environmentally friendly：Hot in-place recycling 100%Use of old pavement materials，Resource conservation，There is no need to transport waste materials and prepare waste material storage yard.，Can effectively reduce environmental pollution such as noise pollution and dust pollution。

Substantial reduction in energy consumption and carbon emissions：After research and calculation，1 ton bituminous mixture，Hot in-place recycling process requires 2.8kgStandard coal and 4.65kg CO2 Emissions，The milling and paving process requires 9.6kgAnd 18.73kg CO2 Emissions，71% reduction in energy consumption and%And 75%。Sichuan Province will reduce energy consumption by 40,000 tons of standard coal and carbon emissions by 8% per year for highway pavement maintenance alone.450,000 tons。

So，From an environmental point of view，The improved hot in-place recycling process has lower energy consumption than milling and paving process of asphalt pavement.、Carbon emissions and environmental pollution，At the same time, it does not produce construction waste.，The recycling of resources is better realized.。

Three、Recommendations for large scale applications

To sum up，Hot in-place recycling technology of asphalt pavement has significant environmental protection compared with milling and paving technology.、Economic benefits、Pavement quality、Advantages of construction efficiency and less traffic interference。So，In the major and medium repair projects of high-grade highways and urban roads,，This technology has good economic value.、Social value and ecological environmental protection value。Especially the national and provincial trunk roads、The effect is more obvious in the maintenance and widening reconstruction of the expressway.。

Hot in-place recycling of asphalt pavement is a new type of pavement maintenance method.，Although it has been used in Sichuan for 20 years.，The improved hot in-place recycling process has been successfully applied for more than 4 years.，However, the industry is worried about the traditional habits and the quality defects of the original technology.，At present, there are still some difficulties in promotion.。

It is suggested that relevant departments at the provincial level should organize investigation and research to incorporate the technology into the comprehensive promotion and application of maintenance technology.，And strengthen technological research and development and innovation、Formulate unified technical standards and specifications、Strengthen personnel training and technology promotion、Improve the policy support and incentive mechanism，As well as measures to strengthen cooperation and exchanges between industry, University and research institutes.，Driving Core Technologies in Large-Scale Applications、Rapid upgrading and iteration of equipment，Road construction for our country、Maintenance and development to provide more efficient、Greener Solutions。Author：Zeng Lingjun，Sichuan Taisen Road Maintenance Co., Ltd.