Research on the Influence of Rainfall Infiltration on the Stability of Urban Road Base Mixtures

Every paved road is a layered structure, but the surface we drive on is only the beginning. Beneath the smooth asphalt lies a complex mixture of stone, sand, and a sticky black binder that holds it all together. This foundation is designed to bear the weight of traffic, yet it faces a constant, invisible enemy: rain. When water seeps into the tiny gaps between stones or finds its way through small cracks, it does more than just wet the surface. It changes the internal pressure of the road, weakening the bond between the stones and the binder. Over time, as vehicles pass over these waterlogged layers, the force of the tires pushes the water around, creating a dynamic pressure that can eventually rip the mixture apart. This leads to common failures like potholes, loose gravel, and deep grooves worn into the pavement. Understanding exactly how water damages these roads is critical for building streets that last longer and stay safer for drivers.

Researchers at Xinyang University set out to investigate this specific problem, focusing on how rainfall infiltration affects the stability of urban road bases. They compared two different types of asphalt mixtures: a traditional hot-mix asphalt, which is heated to high temperatures before being laid down, and a newer warm-mix foamed asphalt. The warm-mix version uses a special process where hot asphalt is mixed with water and high-pressure air to create a foam, allowing the material to be produced and laid at temperatures roughly 30 degrees Celsius lower than the traditional method. The team wanted to see if this lower-temperature alternative could withstand water damage as well as the conventional material, or if the difference in how they were made made them more vulnerable to the elements.

To find the answers, the scientists took samples of both mixtures and subjected them to a series of rigorous tests that simulated the harsh conditions a road might face. They placed the samples in water at a temperature of 60 degrees Celsius for different lengths of time, ranging from a short 40-minute soak to a prolonged 48-hour immersion. Some samples were even placed under a vacuum to force water deep into their pores, mimicking the saturation that happens after heavy, persistent rain. Once soaked, they measured how much weight each sample could support before breaking and how much it deformed under that weight. They also performed freeze-thaw tests, which simulate the cycle of water freezing and expanding inside the road, then melting, to see how this repeated stress affected the materials.

The results revealed a clear picture of how water interacts with these road structures. The study found that when rainwater infiltrates the mixture, it reduces the internal forces that hold the stones together, leading to a loss of strength and an increase in deformation. As the water damage accumulates, the stability of the road mixture declines. When comparing the two types, the traditional hot-mix asphalt showed a higher initial strength and could support a heavier load before failing. However, once submerged, the traditional mix suffered a greater reduction in strength compared to the warm-mix foamed asphalt. Despite this difference in how much they weakened, both mixtures performed well enough to meet the required safety standards for road construction. The warm-mix material retained a high percentage of its original stability even after soaking, and the residual stability and freeze-thaw splitting strength ratios for both types met the specification requirements.

These findings suggest that while traditional hot-mix asphalt starts out stronger, the newer warm-mix foamed asphalt is remarkably resilient when faced with water. The research indicates that the lower-temperature production method does not compromise the material's ability to resist water damage in a way that would cause premature failure. Both mixtures demonstrated the ability to hold up under the combined stress of water erosion and internal pressure, meeting the necessary specifications for use in urban road bases. This work provides a solid reference for engineers and builders, offering evidence that warm-mix foamed asphalt is a viable and durable option for constructing roads that must withstand the constant cycle of rain and traffic.