Cold in-place recycling of asphalt pavement: A case study with laboratory and in-situ testing for a highway project in Southern Vietnam

This paper provides a comprehensive analysis of the implementation of Cold In-Place Recycling (CIR) for asphalt mixtures, covering on-site investigations, reclaimed asphalt materials, laboratory testing, structural design, and field evaluations. In the CIR process, foamed asphalt and Portland cement were used as additives. The foamed bitumen was produced by combining bitumen with 3% water at a flow rate of 10.8 m³/s, resulting in an expansion ratio of 8 and a minimum half-life of 6 seconds. CIR properties, such as indirect tensile strength under dry, wet, and equilibrium humidity conditions, were investigated. The results indicated that CIR with a foamed bitumen content of 1.9% met the relevant requirements set by current standards. Additionally, incorporating 1% cement into the foamed bitumen significantly enhanced the indirect tensile strength of the CIR by approximately 45.1%. The combination of 1.9% foamed bitumen and 1% cement notably improved the tensile strength ratio, thereby increasing durability compared to other mixtures. Field construction was conducted, and test results confirmed that the in-situ CIR samples met the key requirements of AASHTO MP31-22, demonstrating the method's suitability for sustainable road construction. • The CIR method demonstrated environmental benefits, including material reuse, energy savings, and reduced waste generation. • A detailed investigation of the existing pavement was conducted, including surface condition assessment and structural evaluation. • A foamed bitumen content of 1.9%, with and without 1% cement, met the required tensile strength and durability standards. • The proposed pavement structure - 20 cm CIR layer and 5 cm hot mix asphalt proved to be both cost-effective and durable.