Julius J Komba

Aggregate Surface Areas Quantified through Laser Measurements for South African Asphalt Mixtures

For several decades, efforts have been made by engineers and researchers in road and airfield pavements and railroads to develop methods/procedures for accurate quantification of aggregate shape and packing properties. The difficult part of the process has been the fact that aggregate particles have irregular and nonideal shapes. New research capabilities, including laser-based technology, can effectively address the difficulties associated with aggregate shape measurements to optimize asphalt mix design. This paper introduces the use of a three-dimensional (3D) laser scanning method to directly measure the surface area of aggregates used in road pavements in South Africa. As an application of the laser-based measurements, the asphalt film thicknesses of five typical South African mixtures were calculated and compared with the film thicknesses calculated from traditional methods. Based on the laser scanning method, new surface area factors were developed for coarse aggregates used in the asphalt mixtures. Overall, the study demonstrated applicability of 3D laser scanning method to characterize coarse aggregates.

Analytical and Laser Scanning Techniques to Determine Shape Properties of Aggregates

The fundamental shape attributes of aggregates used in pavements (i.e., form, angularity, and surface texture) have not been accurately quantified historically because of their irregular and nonideal shapes. This paper presents selected results from the use of a laser-based scanning technique to determine the form of aggregates employed in construction of pavements in South Africa. A three-dimensional (3-D) laser scanning system was used to examine aggregate materials from various sources, and the data were processed to reconstruct 3-D models of the aggregate particles. The models were further analyzed to determine the properties of the forms. Two analysis approaches based on physical properties of the aggregate and spherical harmonic analysis were employed to determine the form indices, and the results were compared. The indices based on the physical properties included (a) sphericity computed from the surface area and volume, (b) sphericity computed from three orthogonal dimensions, and (c) the flat-and-elongated ratio computed from the longest and shortest dimensions of an aggregate particle. Good correlations were observed between the form indices from the aggregate physical properties and the spherical harmonic form index. One conclusion of the research is that the laser scanning technique can be employed to quantify better the form properties of aggregate materials used in pavements.

Evaluation of selected effects of pavement riding quality on logistics costs in South Africa

The efficient operation of a countrys economy depends, among other things, on an efficient logistical system to ensure that goods can be transported efficiently between producers and users. The costs of logistics include aspects such as transport, storage, inventory, and management. Of these, the transport costs are directly influenced by the condition of the transport infrastructure. The effects of road riding quality on the costs of logistics were evaluated through analysis of data on actual truck costs (specifically, vehicle damage and maintenance) obtained from a logistics service provider as well as data on road riding quality for the routes used by the company. Analysis of the data indicated that the vehicle operating costs increased with decreasing riding quality (as would be expected). Spending adequate resources on the maintenance of routes in a country decreased vehicle fleet operating costs and ultimately the logistics costs of the country. It is recommended that the study be broadened to incorporate a larger sample of vehicles and road conditions.

Long-Term Pavement Performance Monitoring and the Revision of Performance Criteria for High Modulus Asphalt in South Africa

Enrobe a Module Eleve (EME) technology, a High Modulus Asphalt (HiMA), was originally developed in France. The technology is primarily suitable for construction of heavily trafficked routes, airports and container terminals. The key performance characteristics of EME are high stiffness, high resistance to permanent deformation and fatigue cracking. EME is also designed to offer good moisture resistance and good workability. The EME technology has been successfully introduced to South Africa. The development of EME design guidelines in South Africa started in 2006. A major outcome was the publication of Sabita Manual 33: “Interim design procedure for high modulus asphalt in South Africa.” The performance criteria/specifications stipulated in Manual 33 were based on limited data. Based on further work against French mix design and analysis of data collected in South Africa, a revised fatigue and stiffness specifications were adopted in July 2015. Implementation of EME technology in South Africa started in 2011, when a trial section consisting of an EME base layer was constructed on the heavily trafficked South Coast Road in Durban. The section is a major entry route for heavy vehicles travelling to the Durban harbour. Several attempts to rehabilitate the section using conventional asphalt mixes had failed as a result of premature rutting due to the heavy traffic volumes entering the Durban harbour. The heavy traffic volumes at the section offered an ideal setting for an experiment in Accelerated Pavement Testing (APT) without the use of a Heavy Vehicle Simulator (HVS), which enabled the accelerated validation of the South African EME design procedure. The objective of this paper is to present the outcomes of the Long-Term Pavement Performance (LTPP) monitoring programme that was undertaken to assess the field performance of EME, and discuss the development of the newly adopted South African EME performance specifications.

Traffic Data Characterization for Road Rehabilitation: A Case Study of the Korogwe-Mombo Road Section in Tanzania

Traffic loading is one of the key inputs for the structural design of pavements. For pavement design purposes, heavy vehicles are mostly used for the estimation of the traffic load spectra, as they cause the most structural damage to pavements. As part of the pavement design process, heavy vehicle volume and axle load surveys are typically carried out to assist with the accurate estimation of the cumulative traffic loading over a pavement design period. However, traffic volumes, axle loads and, ultimately, the cumulative traffic loading are often not uniform due to factors, such as varying motorist population and economic activities along the length of road. In this paper, a comparative assessment of traffic loading estimated during the rehabilitation design in 2005 and the actual measured site-specific traffic loading in 2015, as well as the projected future traffic loading were conducted for the Korogwe-Mombo road section along the T2 trunk road that connects Tanzania’s business hub of Dar es Salaam with the northern regional cities. The T2 trunk road is also used by heavy vehicles travelling to and from the neighbouring countries of Kenya and Uganda. This study found inter alia that the cumulative traffic loading based on the 2015 measured site-specific traffic data is approximately 2.8 times higher than the design traffic loading based on the 2005 traffic data, which illustrates the importance of using the latest, most accurate and reliable traffic data during rehabilitation design. To improve the accurate determination of traffic loading, traffic studies should ideally be conducted over a long period (typically over one year), but this is not practical and cost effective when traditional manual methods are used. Hence, road agencies should consider installing portable or permanent automated traffic and Weigh-In-Motion (WIM) monitoring systems.

Investigation of the Effects of the Type of Crusher on Coarse Aggregate Shape Properties Using the Three-Dimensional Laser Scanning Technique

Geo-China 2016: Material, Design, Construction, Maintenance, and Testing of Pavement, Shandong, China, July 25-27, 2016.

Correlations Between Aggregate Particle Shape Parameters and Size Based on Images Captured Using a 3-D Laser Scanning Device

Abstract Three dimensional (3-D) laser scanning has recently proved to be an ideal technique for quantifying aggregate particle shape parameters. This is because 3-D laser scanners measure fine details and capture free-form shapes. This paper presents some results of an on-going study, which utilises 3-D laser scanning technology to quantify aggregate shape parameters. Specific correlations and shape parameters have been considered. The results have shown that meaningful correlations exist between 3-D sphericity and aspect ratio as well as between specific surface area and the particle diameter as defined in this paper. The results of the current study are consistent with generally accepted relationships between shape parameters and particle size, further validating the application of the 3-D laser scanning technology