Saadoon, Tahseen Diwan
(2019)
Understanding and improving cold bituminous emulsion mixtures.
PhD thesis, University of Nottingham.
Abstract
Cold Asphalt Mixture (CAM) is a pavement material usually produced by mixing bitumen emulsion, aggregate, water, and cement at ambient temperature. CAM has many economic, environmental, energy-saving, and health and safety advantages compared to other types of mixtures used in roads, but it has weak mechanical performance as a structural layer, mainly due to containing trapped water. Consequently, studies attempting to increase the mechanical performance of CAM have attempted to dispose of its water content by promoting suction, absorption and consumption of water using cementitious and/or pozzolanic materials. Despite numerous attempts, CAM still has weak final performance, characterised by high porosity and slow development of performance in comparison to Hot Mix Asphalt (HMA). This is due to the lack of a deeper understanding of the dynamics of water evaporation, moisture and temperature profiles in CAM. Therefore, this research aims to investigate, understand and predict: the dynamics of water evaporation and the mechanical performance of CAM (with and without cement); and the affects of CAM components on performance (curing and strength).
Water evaporation dynamics are explored by comparing CAM with soil/granular materials without binder. Dynamic water evaporation and hydraulic conductivity test results were correlated to mechanical performance through a semi-empirical model. The pore size distribution index (n) for samples was estimated based on the hydraulic conductivity tests. Results indicate a reliable relationship between internal pore distribution and water dynamics during drying. In addition, bitumen emulsion was found to be the main component delaying the curing process of cold mix asphalt. The predictive model for CAM stability was accurate, fast and easy to use.
Prediction of cement’s mechanical performance during hydration reduces construction costs. A new model based on apparent activation energy (Ea), that fits the experimental data significantly, was obtained and can be used to predict the performance to different types of cement.
CAM samples with different contents and types of cement were tested by dynamic evaporation, hydraulic conductivity, hydration and Marshall stability test. The results show that cement does not significantly shorten the drying process, while bitumen emulsion delays cement hydration. Finally, a new predictive model with accurate fit was obtained to estimate the contribution of cement hydration products to the total stability of CAM.
Detailed investigation of the impact of aggregate on curing is explored, predicting the rate of water evaporation in unbound granular materials and cold asphalt layers, with and without cement. In addition, the thesis calculates the recommended time to open roads to traffic loads. The correlation between different properties related to material gradation, microstructure and hydraulic conductivity was investigated and their effect on the dynamics of water evaporation was analysed. Among other conclusions, it was found that porosity, surface area of voids, and mean size of aggregate particles of unbound materials significantly affect the time of full drying. In addition, a predictive model was obtained, able to significantly fit the rate of water evaporation in these materials, which enables estimation of the time necessary to open roads to traffic.
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