Background

By the end of 2022, the total road mileage in China has exceeded 5.3 million kilometers, which considerably challenges the process of highway pavement maintenance. The maintenance work for arterial highways would generate 160 million tons of waste asphalt pavement materials per year, and less than 30% of waste could be recycled which is far below the rate of 90% in developed countries. Traditional hot in-place recycling technology, which heats the original pavement at a high temperature, leads to excessive energy consumption, carbon emissions, smoke pollution and secondary aging of asphalt mix. There is an urgent need for the improvement of hot in-place recycling technology. Thus, the application of warm mix asphalt technology in hot in-place recycling process was sugested by Research Institute of Highway Ministry of Transport to minimize the problems.

Key properties of demonstration

After adding additives (naphthenic aromatics regenerant and silane warm mixing), the project team researched on the properties of in-place recycled asphalt mixture applying the warm-mixed technology, including high/low-temperature crack resistance, and water damage resistance. The results satisfied the requirements of the current Technical Specification for Construction of Highway Asphalt Pavement (JTG F40).

Construction of recycled asphalt pavement

The project team conducted hot in-place recycling of waste asphalt pavement on Nanyang section of Shanghai-Shaanxi expressway, with the length of 4.8 km and width of 4.1 meters. During the construction, the compaction of the pavement was monitored and the temperature reduction was in control at the same time. It turned out that the paving temperature, initial compaction temperature, and final compaction temperature were reduced by 14.9-18.1°C, while the compaction of warm mixed asphalt pavement was increased by 0.4% and the water seepage coefficient was less than that of the hot in-place recycled asphalt pavement.

Benefits Expected

This achievement could fully recycle the materials of the original pavement, which cuts the transport costs and saves energy. Meanwhile, this technology lowers the construction temperature, reducing carbon dioxide emissions by 60%, nitrogen oxide emissions by 70%, and asphalt smoke emissions by 90%. Besides, it can efficiently repair the original pavement and guarantee the public transport. The project is expected to promote the popularization and application of hydrocarbon-based products as well as the development of hot-in-place regeneration technology positively. Moreover, this achievement also realized the "high performance, high value, high efficiency" in-place regeneration of the aged pavement.