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Pavement design is essentially and usually a structural long-term evaluation process which is needed to ensure that traffic loads are efficiently distributed at all levels of the total road structure. Furthermore, to get a complete analysis of its durability behavior, long-term monitoring should be facilitated, not only from the top by falling weight deflectometer (FWD) or core drilling but preferably from inside the structure and at exactly the same positions during a long-time interval. Considering that it is very hard to devise an efficient method to determine realistic in-situ mechanical properties of pavements, the determination of strain at the bottom of asphalt pavement layers through non-destructive tests is of a great interest. As it is known, fiber Bragg grating (FBG) sensors are the most promising candidates to effectively replace conventional strain gauges for a long-term monitoring application in a harsh environment. The main goals of this paper are to compile an overview of the recent developments worldwide in the application of fiber optics sensors (FOS) in asphalt pavement monitoring systems; to find out if those systems provide repeatable and suitable results for a long-term monitoring; if there are certain solutions to validate an inverse modelling approach based on the results of FWD and FOS.

In the present study, a new approach to the installation of fiber Bragg grating (FBG) sensors in three asphalt pavement layers (the surface layer and both base layers) was implemented for the first time in Belgium. Fiber Bragg grating sensors (FBGs) are diagnostic tools that accurately and efficiently monitor in situ structural behavior. However, nowadays, this technology is not commonly used in asphalt due to its application restrictions under installation and service conditions. FBGs are fragile and break easily under loading. Therefore, there is a need for suitable protection of FBG sensors if they are to be installed during the rough construction process and exposed to heavy-duty loading afterwards. The main objective of the present study is to show the FBG results only for the initial construction process, and, if successful, to continue studying this FBG monitoring system and to plan the next research step by adjusting the system for its application in heavy-duty pavements. Two approaches to FBG installation in three asphalt layers (placed at the bottom of each layer) were tested in the present study: (1) installation of FBGs in prefabricated asphalt specimens in the base layer, directly on the base, and (2) installation of FBGs on the surface of the previously constructed asphalt layer. Both innovative approaches allow the implementation of FBGs without sawing the whole layer into two parts. The obtained results proved a survival rate of 100% for the FBGs. It can be concluded that these new described methods of FBG installation-using a cross-section configuration to carry out strain measurements in two directions (transverse and longitudinal)-can be applied for the monitoring of heavy-duty pavements, while providing the possibility to further re-evaluate current pavement design methods used in Flanders (Belgium).

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The negative environmental impacts associated with the usage of Portland cement (PC) in concrete induced intensive research into finding sustainable alternative concrete mixes to obtain “green concrete”. Since the principal aim of developing such mixes is to reduce the environmental impact, it is imperative to conduct a comprehensive life cycle assessment (LCA). This paper examines three different types of sustainable concrete mixes, viz., alkali-activated concrete (AAC) with natural coarse aggregates, AAC with recycled coarse aggregates (RCA), and bacterial concrete (BC). A detailed environmental impact assessment of AAC with natural coarse aggregates, AAC with RCA, and BC is performed through a cradle-to-gate LCA using openLCA v.1.10.3 and compared versus PC concrete (PCC) of equivalent strength. The results show that transportation and sodium silicate in AAC mixes and PC in BC mixes contribute the most to the environmental impact. The global warming potential (GWP) of PCC is 1.4–2 times higher than other mixes. Bacterial concrete without nutrients had the lowest environmental impact of all the evaluated mixes on all damage categories, both at the midpoint (except GWP) and endpoint assessment levels. AAC and BC mixes are more expensive than PCC by 98.8–159.1% and 21.8–54.3%, respectively.