Affinity between Bitumen and Aggregate in Hot Mix Asphalt by Hyperspectral Imaging and Digital Picture Analysis

Abstract

This study investigated the viability of quantifying the affinity between aggregate and bitumen by means of different imaging techniques. Experiments were arranged in accordance with the rolling-bottle test, as indicated in UNI EN 12697-11, “Test methods for hot bituminous conglomerates—Part 11”. Digital image processing (DIP) techniques have only recently been used for such quantification. The data gathered with a multi-sensor optical platform equipped with VIS–NIR and SWIR spectrometers were compared with DIP outcomes. Data were processed using the unsupervised ISODATA and the supervised parallelepiped algorithms. The exposed aggregate index (EAI) and the bitumen index (BIT) were calculated to retrieve the bitumen percentage coverage of different mixtures. The comparison with the results obtained employing the traditional 6, 24, 48 and 72 testing hours reveals the possibility to implement a standardized analysis methodology combining digital and hyperspectral imagery to highlight potential inaccuracies deriving from the visual interpretation.

A Study of Adhesion in Foamed WMA Binder-Aggregate Systems Using Boiling Water Stripping Tests

“…A number of technical observations were made based on the present research, previous trials, and the experiences of other researchers [ 51 , 52 , 53 , 54 , 55 , 56 , 57 ]: Repeatable lighting conditions with uniform lighting and mitigation of shadows are recommended; Careful selection and preparation of the workplace is required to mitigate color contaminated light reflections (e.g., blue color from the sky, other colors from clothes, furniture, etc. ); Precise arrangement of the aggregate particles without visible gaps is highly recommended for reliable classification of the reflective surfaces of asphalt binder; when gaps are present, the background reflects off the asphalt binder, which makes it difficult to distinguish from the binder, regardless of the background color; When artificial lighting is used and color analysis is made, use of lighting with high color reproduction index (CRI) is advised.…”

“…Based on previous trials and the experiences of other researchers [ 51 , 52 , 53 , 54 , 55 , 56 , 57 ], a methodology for acquiring high-quality photographic data was developed, main principles of which included: Image acquisition under repeatable, controlled, artificial lighting using a ring light; Use of a distinct background color for ease of its removal in post-processing, should it be necessary; Placing the sample aggregates without gaps for mitigating the background reflections; Each sample was photographed once, then it was flipped, and its underside was photographed again to obtain more data per sample; this also would decrease any potential bias of the initial sample arrangement. …”

“…All mentioned tests exhibit disadvantages, e.g., strong mechanical action in the rolling bottle method, long testing time, and weak differentiation of static tests, while the boiling water methods are troublesome and may be inaccurate due to the use of calibration curves and chemical reagents [ 50 ]. A number of authors have used digital image analysis for assessing the results of these tests with great accuracy and confidence [ 51 , 52 , 53 , 54 , 55 , 56 , 57 ].…”

The Influence of the Affinity between Aggregate and Bitumen on the Mechanical Performance Properties of Asphalt Mixtures

“…It can be observed that the difference in the coating of the granitic aggregate after 6 h was residual in both tests, while a significant variation was found after 24 h. As mentioned before, the difference in coating percentage after 6 h was only 1%. The uncertainty present in the subjective assessment of this value could be minimized using, for example, a hyperspectral imaging and digital picture analysis, as recently pointed out by Mei et al [30].…”

“…Many advanced tests and simulations can be performed to evaluate the quality of the binder-aggregate bonding, such as X-ray photoelectron spectroscopy (XPS) [19,25]; energy dispersive X-ray (EDX) [25]; active adhesion evaluation method (AAEM) [10]; atomic force microscopy (AFM) [26,27]; binder bond strength (BBS) [28]; scanning electron microscopy (SEM) with energy disperse spectroscopy (EDS) [17]; infrared spectroscopy (IR) [13]; optical microscopy (OM) [29], hyperspectral imaging/digital image processing (DIP) [30] and molecular dynamics simulation (MDS) [16,21,24]; in addition to other test methods described by Mehrara et al [2].…”