Evaluation of water sensitivity and the impact of thermal cycles on asphalt mixtures with different aggregates and hydrated lime as additive: Experimental study

This experimental study aims to assess the water sensitivity and fracture toughness of asphalt Mixtures subjected to thermal cycling, using different types of aggregates and incorporating hydrated lime as an additive. To achieve this, two types of aggregates were used: limestone and schist aggregates, each with distinct characteristics. These aggregates were mixed with pure grade 35-50 bitumen to create two asphalt Mixtures. In addition, 2% hydrated lime was added to both Mixtures as a filler to assess its impact on asphalt mixture properties. The water sensitivity of the asphalt Mixtures was assessed using the water resistance test, in accordance with NM EN 12697-12, method B. A total of 40 samples were tested, divided into "dry specimens" and "humid specimens". The former were kept under controlled conditions (temperature 18°C and 50% humidity) for 7 days, while the latter were subjected to a water saturation process beforehand, then kept immersed in water at a temperature of 18°C for the same period. Water resistance was calculated by comparing the compressive strength of the two types of specimens. To evaluate the specimens' fracture toughness, the Semi-Circular Bending (SCB) test was employed. Cracks were introduced into the center of each semicircular specimen to measure their resistance to crack propagation. This test was carried out after the samples had been subjected to a water-saturated degassing process and the application of thermal cycles. Thermal cycles were applied using temperatures based on Moroccan climatic conditions to simulate actual road conditions. Three conditioning methods were used: freeze-thaw cycles (-5 to 20°C), heating-cooling cycles (20 to 40°C) and a combination of both. SCB samples were tested at a temperature of 20°C after a number of thermal cycles, ranging from 15 to 120. A total of 160 SCB samples were tested for resistance to temperature-induced cracking. The results showed that asphalt Mixtures based on schist were generally more sensitive to thermal cycling than those based on limestone. However, the inclusion of hydrated lime as an additive has proved to be beneficial for both types of asphalt mixtures, particularly for those based on schist by attenuating the decrease in their strength and sensitivity to water. The primary goal is to enhance the durability of Moroccan roads while minimizing maintenance costs.