Experimental Study of Thermal and Mechanical Properties of Hydrated Lime Asphalt Concrete and Numerical Modelling of Constructed Pavement Performance

Alashaibi, Azedin

Abstract

The flexible pavement suffers primarily from three types of distress: fatigue cracking, thermal cracking, and permanent deformation. Thermal effects from climate are a significant in distress and early aging of pavements, and particularly in extreme weather contexts. To facilitate durable pavement design and construction, a deep understanding of the temperature profile within pavement structures becomes essential in order to assess internal stress and strain conditions together with mechanical loading from traffic. Two major fields of research are important in evaluating thermal effects on pavement structures. One relates to asphalt concrete material properties, thermal and mechanical, and their interactions. The other concerns service conditions like weather and climatic variation, which affect energy exchange at the surface. Obtaining complete and accurate material property values and characteristics for variation under coupled thermo-mechanical loading is a primary task in asphalt materials research.

Using mineral additions to improve asphalt concrete properties has been widely adopted as an effective approach. Among the mineral fillers used, hydrated lime [Ca (OH)2] has been shown to offer outstanding benefits in terms of both effectiveness and cost. Earlier research at the University of Salford has revealed that replacing limestone dust, a conventional mineral filler, with hydrated lime at 2.5% of total aggregate weight optimised mechanical properties at three different temperatures. In addition to this, it is also widely reported that using hydrated lime as a partial mineral filler helps in improvement of asphalt concrete’s capacity to resist the three typical distresses of constructed pavements.
To date, most research on hydrated lime modified asphalt concrete has primarily focused on improvement in mechanical properties, aiming to optimize the quantity of additive used.. There is little research involving experimental tests for thermal properties and measurements of mechanical properties under more complex conditions and under both thermal and mechanical loadings. In addition, little research has been found in literature to analyse the stress and strain condition of pavement structures constructed using hydrated lime modified concrete, and particularly, using a numerical modelling approach to understand the practical meaning and evaluate the benefits of using hydrated lime concrete under service conditions, taking account of climatic influences and weather.
In light of this background and existing deficiencies in research so far, this research project aims to conduct further experimental tests to fill gaps still to be addressed for a complete material database for hydrated lime modified concretes. Three experiment tests have been conducted and compared for two asphalt concrete mixes: one has no use of hydrated lime, the other one uses hydrated lime to replace the conventional limestone dust mineral filler at 2.5% of the total aggregate weight. The three tests are: 1) thermal property measurement; 2) fatigue testing at three temperatures; and 3) triaxial testing at three temperatures. Mathematical models have been proposed for each of the test results to characterise the measurements. These models are later implemented in finite element modelling to analyse the performance of the pavement structures constructed. Following the experimental study, to contribute a deep understanding the stress-stain conditions of the pavement which uses hydrated lime modified concrete, and the corresponding impacts on the distress resistance of the pavement’s structure, mathematical modelling and numerical simulation are performed for real world service conditions using climatic weather survey data. Three modelling case studies are performed. They are: 1) use of the measured thermal properties to evaluate the temperature profile within the pavement structure under simple temperature boundary conditions; 2) use of the fatigue test results to evaluate and compare the fatigue life of the constructed pavement with and without hydrated lime modified concrete, in which a complex climatic boundary condition is introduced to simulate real-world service conditions; and 3) use of triaxial test results to predict and compare rutting deformation for the constructed pavement with and without use of hydrated lime modified concretes. The boundary conditions adopted are the same as those of the preceding case.
The research findings indicate that incorporating hydrated lime in the mineral filler of asphalt concrete improves its thermal properties. Thermal conductivity was increased by 27%, 7% and 17% for wearing, levelling and base courses respectively, while the specific heat was increased by 25%, 6% and 16% for the same courses. This led to enhanced heat transfer to the sublayer, although it had minimal impact on localized temperature profiles within the pavement structure. The hydrated lime pavement experiences approximately 1.5% less deformation and 39% lower stress levels under traffic loads alone. However, during winter, the thermal effect increases the maximum total internal tensile stress in the hydrated lime pavement by 26%. Modelling analysis reveals that the surface region of the hydrated lime pavement is primarily affected by local maximum tensile stress. Both experimental and modelling results confirm that the use of 2.5% hydrated lime in hot mix asphalt concrete significantly enhances pavement deformation resistance and fatigue life, thereby reinforcing the overall benefits of hydrated lime -modified asphalt concrete in practical applications.

Citation

Alashaibi, A. (2023). Experimental Study of Thermal and Mechanical Properties of Hydrated Lime Asphalt Concrete and Numerical Modelling of Constructed Pavement Performance. (Thesis). University of Salford

• Thesis Type: Thesis
• Deposit Date: Jul 21, 2023
• Publicly Available Date: Oct 30, 2023
• Award Date: Sep 29, 2023