Johan Blom

The influence of nanoclay on the durability properties of asphalt mixtures for top and base layers

To avoid traffic congestion, due to road works, a continuous research into asphalt pavement and especially its durability is of great importance. This research focuses on improving the mechanical performance and the durability of asphalt mixtures by nanoclay modified bitumen. This promising technique of introducing nanoclays or nano particles into bitumen could offer an significant improvement on the fatigue properties and rutting performance and thus the durability of the asphalt top layer.

Digital Image Correlation to Investigate Crack Propagation and Healing of Asphalt Concrete

Accurate determination of the mechanical properties of asphalt concrete is very important in Road Engineering. The traditional method to calculate these properties is to run experiments using a hydraulic/pneumatic actuator and strain gauges to apply stress and measure the strain. However, in the last decade optical measurement techniques have become popular for strain calculation on the surface of the specimen and detecting the cracks on the surface. In this study, digital image correlation is used to estimate the strain map on the surface of an asphalt specimen, predict the location of crack initiation, and investigate the healing phenomenon in asphalt concrete.

Visualization and Chemical Analysis of Bitumen Microstructures

Microstructures of bitumen were investigated using atomic force microscopy (AFM) and environmental scanning electron microscopy (ESEM), and a chemical characterization was successfully carried out using time-of-flight secondary ion mass spectrometry (TOF-SIMS). The bee structures were observed by AFM, for which a chemical explanation by wax was confirmed by the TOF-SIMS analysis. A tube pattern or worm structures were generated and visualized by ESEM on bitumen surfaces. Chemical differences between the structured and unstructured areas, as well as between different areas of the structure, were observed. A mechanism for the structure formation on bitumen surface during ESEM analysis is suggested.

Peat as an Example of a Natural Fiber in Bitumen

In this study, the suitability of a natural peat fiber, as a modifier for bitumen was investigated. Peat fibers were dried, ground, and fractionated into a fiber and a granular fraction. Rheological data on peat modified binders indicated that the granular fraction is acting as a filler mainly stiffening the bituminous binders whilst the fiber fraction mainly increases the elastic behavior, which became especially visible at higher service temperatures. It was observed that by changing the ratio of fibers versus granular particles, the rheological behavior can be regulated. In addition, drainage tests were carried out on stone mastic asphalt (SMA) mixes. The data indicated that peat fibers can effectively reduce drainage, and can be used as an alternative for the currently used cellulose fibers.

The use of a non-nuclear density gauge for monitoring the compaction process of asphalt pavement

The mechanical performance of an asphalt pavement affects its durability – thus carbon footprint. Many parameters contribute to the success of a durable asphalt mix, e.g. material selection, an accurate mix and even the road design in which the asphalt mix quality is quantified. The quality of the asphalt mix, by its mechanical properties, is also related to the compaction degree. However, and specifically for high volume rates, the laying process at the construction site needs an effective method to monitor and adjust immediately the compaction quality before cooling and without damaging the layer, which is now absent. In this paper the use of a non-nuclear density gauge (PQI – Pavement Quality Indicator) is evaluated, based on a site at Brussels Airport. Considering the outcome of the present research, this PQI is advised as a unique tool for continuous density measurements and allow immediate adjustments during compaction, and decreases the number of core drilling for quality control, and as a posteriori asphalt pavement density test where cores are prohibited. The use of PQI could be recommended to be a part of the standard quality control process in the Flemish region.

Fracture monitoring by acoustic emission: recent applications of parameter-based characterization

The present paper describes a collection of fracture monitoring cases in different materials. The cases examined include bending of textile reinforced cement (TRC), hybrid concrete-TRC lightweight beams, granite, additive manufacturing metal components, combined loading of human femur bone and pull-out in reinforced concrete. In all cases the basic role is played by acoustic emission (AE). It is shown that certain waveform parameters exhibit strong sensitivity to the rate of fracture as well as the dominant fracture mode. Parameters like frequency content and the duration of the signals supply real time trends that in the present cases are verified by optical techniques. It is concluded that AE supplies important information and allows the prediction of how the material will behave based on the initial AE recordings and before serious damage is inflicted. AE shows a very broad application range; however, the contribution of combination with other techniques is highlighted in order to increase the reliability of the interpretation of AE results.

Impact Study of Textile Reinforced Cementitious Materials: Test Method and Preliminary Results

In building engineering, impact loading and other accidental loads are mostly taken into consideration by measures on the structural level rather than on the material level, the latter one is even seldom explored. Textile reinforced Cements (TRCs) is a composite material group which is still in full development. Its potential to dissipate a significant amount of energy under low velocity impact loading was already indicated in a preliminary study. In the present study, the low velocity impact behaviour of TRC laminates is investigated more closely and this by means of an instrumented drop weight test. This study has shown the ability of the used test method to identify damage mechanisms underlying the energy absorption under low velocity impact loading in TRC composite laminates.