Showing papers by "Nick Thom published in 2019"

Probabilistic prediction of asphalt pavement performance

Abstract: Variability of pavement design parameters has always been a concern to pavement designers and highway agencies. A robust pavement design should take into account the variability of the design input...

Sustainable Road Design: Promoting Recycling and Non-Conventional Materials

Abstract: Many factors impact on the sustainability of road maintenance, including the organization of road authorities, contract forms used, financing structure and, unfortunately, political interference and corruption. However, this paper reviews the opportunities to increase sustainability by utilizing less environmentally damaging material sources, and also the associated challenges. It is a field that has seen advances in recent decades, for example in the effectiveness of cold-mix asphalt binders. Nevertheless, the opportunities are not being taken up in many countries, and this reflects uncertainty in predicting performance. This paper reviews the different design methods available, developed in both temperate and tropical climates, and highlights the lack of agreement with regard to non-conventional materials. The different sources of uncertainty and risk are then discussed, together with ways of limiting them. It is found that, while advances in performance prediction are highly desirable, the key to encouraging recycling and the use of inexpensive but non-conventional materials lies in development of the right contractual arrangements, specifically partnering and risk/reward sharing. The paper concludes with a discussion on approaches to partnering in the construction industry and the prerequisite climate of trust without which innovation is almost inevitably stifled.

Data Compression Approach for Long-Term Monitoring of Pavement Structures

Abstract: Pavement structures are designed to withstand continuous damage during their design life. Damage starts as soon as the pavement is open to traffic and increases with time. If maintenance activities are not considered in the initial design or considered but not applied during the service life, damage will grow to a point where rehabilitation may be the only and most expensive option left. In order to monitor the evolution of damage and its severity in pavement structures, a novel data compression approach based on cumulative measurements from a piezoelectric sensor is presented in this paper. Specifically, the piezoelectric sensor uses a thin film of polyvinylidene fluoride to sense the energy produced by the micro deformation generated due to the application of traffic loads. Epoxy solution has been used to encapsulate the membrane providing hardness and flexibility to withstand the high-loads and the high-temperatures during construction of the asphalt layer. The piezoelectric sensors have been exposed to three months of loading (approximately 1.0 million loads of 65 kN) at the French Institute of Science and Technology for Transport, Development and Networks (IFSTTAR) fatigue carrousel. Notably, the sensors survived the construction and testing. Reference measurements were made with a commercial conventional strain gauge specifically designed for measurements in hot mix asphalt layers. Results from the carrousel successfully demonstrate that the novel approach can be considered as a good indicator of damage progression, thus alleviating the need to measure strains in pavement for the purpose of damage tracking.

Load Transfer Stiffness of Two-layer Roller Compacted Concrete for Pavements

Abstract: Roller compacted concrete (RCC) is a form of plain concrete pavement (JPCP). RCC is a zero-slump concrete consisting of well-graded aggregate, cement and water. RCC has many advantages over other pavement types, particularly cost and speed of construction. Recently, RCC has undergone many developments mostly directed towards improving quality, including smoothness and durability. RCC now has the potential to combine the performance of concrete with the low cost of asphalt installation. A two-layer system of RCC with different aggregate types and sizes was utilized in this study. This paper presents the determination of load transfer stiffness across induced joints in a two-layer RCC system based on a cyclic shear test. The test was carried out for three different upper layer placement cases with different crack widths and load magnitudes. From the test results, an approximate equation was formulated to predict joint deterioration. It is suggested that this equation provides a useful tool to assist in the design of two-layer RCC pavement and, potentially for other concrete pavement types.

Strategies for Reduced Cooling Time of Asphalt for Airfield Pavement Overlay

Abstract: Reducing the cooling period of newly laid asphalt overlays could help airport authorities to quickly open remediated pavements to traffic. This paper reviews four strategies for a reduced cooling period, prior to trafficking, of newly-placed asphalt overlays: (1) Defining and selecting the warmest permissible asphalt temperature at opening to traffic, (2) Reducing the cooling time by using warm mix asphalt (WMA), (3) Increasing the cooling rate of asphalt by using high thermal conductivity material, and (4) Decreasing the pavement temperature by spraying water onto the freshly paved asphalt. A one-dimensional (1D) heat-transfer model using a finite element (FE) solution is developed as a function of weather conditions to simulate the effect of each strategy on asphalt cooling time. The analysis shows that each strategy significantly contributes to the rapid cooling of newly laid asphalt. However, there are some concerns over the performance of the pavements when some strategies are adopted.

Developing the multiple stress–strain creep recovery (MS-SCR) test

Abstract: While most published work from Europe has been concerned with evaluating binders’ resistance to rutting based on their stiffness (deformation resistance), work originating in the US has mainly been concerned with ranking binders based on their recoverability in a multiple stress form. This paper details the design of a new modified multiple stress–strain creep recovery (MS-SCR) test. The test is designed to evaluate binders’ rutting resistance based on two rutting resistance mechanisms: stiffness and recoverability. A preliminary investigation is presented in this paper followed by details of the design of the new modified test. A 40/60 penetration grade bitumen and bitumen-filler mastics prepared with three filler concentrations (35%, 50%, and 65% filler content by mass of mastic) were tested. In addition, two polymer modified bitumens (PMBs) using the same base bitumen type were examined for validation. Two parameters are introduced to characterise the short and long recovery in the new test. In terms of stiffness, the test allows the behaviour of binders at different stress levels and loading cycles to be studied and produces a new parameter that can quantify the degree of modification. Finally, a relationship between nonlinearity and normal force in the test was investigated.