Search

The drying shrinkage of alkali-activated concrete (AAC) is a very complex process, and it warrants long-term testing. The present study was focused on the development of drying shrinkage prediction models for ambient-cured AAC. AAC with four distinct precursor combinations for experimental validation and investigation of the influence of mix proportions were used. The applied fly ash (FA) to ground granulated blast-furnace slag (GGBFS) ratio was varied as 100:0, 70:30, 60:40, and 50:50. Drying shrinkage strains were determined for hardened paste, mortar, and concrete specimens. The observed drying shrinkage behavior was correlated with the mineralogical, chemical, and morphological characteristics of corresponding paste specimens of alkali-activated binder (AAB). These characteristics were evaluated using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDS), respectively. The results showed that the drying shrinkage of hardened AAB paste and AAB mortar increases by 26%–32% and 13%–28% with GGBFS content, respectively. The qualitative and quantitative microstructural analysis suggested that this behavior could be ascribed to the formation of a calcium aluminosilicate hydrate matrix. Moreover, FA-based AAC exhibited maximum shrinkage, probably due to its comparatively high overall porosity with the addition of both coarse and fine aggregates. Using the experimental data, stepwise linear and multivariate nonlinear regression models were developed by modifying existing portland cement concrete (PCC) models to predict the drying shrinkage strains of AAC. Recommended linear and nonlinear regression models were selected based on the least deviation from the experimental value. The modified GL2000 model was found to be the best fit for shrinkage predictions in AAC because of its simplicity and comparable precision to experimental findings.

Funding Information: The authors would like to acknowledge the contributions of the active members of the RILEM technical committee TC 264-RAP in terms of experimental results, data analysis and proofreading. The authors would also like to thank Nynas AB, Kraton Chemical BV and Technical University of Braunschweig for supporting the interlaboratory activity by providing bituminous materials, ARA and RA binder. Publisher Copyright: © 2022, The Author(s). This recommendation is based on the results of an inter-laboratory study organised by the RILEM technical committee TC 264-RAP "Asphalt Pavement Recycling"—Task Group 3 (TG3) focusing on Asphalt Binder for Recycled Asphalt Mixture. The TG3 aimed to evaluate the effect of a specific family of materials known as asphalt recycling agent (ARA) on the aged binder under different configurations. Even though ageing is an irreversible phenomenon, effective ARA must have the capability to improve the flexibility of the bituminous materials and their resistance against cracking susceptibility with no adverse effect on the rutting resistance of pavements containing reclaimed asphalt. A total of 17 participating laboratories analysed the properties of binder blends composed of aged binder from reclaimed asphalt in three different contents (60, 80, 100%), ARA and virgin binder. The physical properties of the blends were thoroughly evaluated through traditional and rheological binder testing. This recommendation proposes to restore the original material properties at low and intermediate temperatures (i.e. cracking resistance) while balancing the high-temperature characteristics (i.e. rutting susceptibility) with durable impact throughout the progression of ageing phenomena. Therefore, useing of the Dynamic Shear Rheometer is foreseen as a more suitable and sustainable means to evaluate binder blends containing an asphalt recycling agent. Compared with conventional testing, the proposed approach requires fewer materials while resulting in a faster experimental procedure with one single test.

Nowadays, a vast number of concrete structures are approaching the end of their expected service life. The need for maintenance and repair is high due to the continued deterioration of the existing building inventory and infrastructure, resulting in a large need for concrete repair in the near future. Reinforcement corrosion is the most important deterioration mechanism, causing (i) severe concrete damage (cracking along reinforcement and the spalling of the cover concrete) and (ii) loss in steel section. Therefore, appropriate repair techniques for corrosion damage are the main focus of this review paper. With the European transition towards a circular economy and with sustainable development goals in mind, it is also important to consider the environmental impact along with the technical requirements and life cycle cost. In order to improve the sustainability of concrete structures and repairs over their life cycle, life cycle assessment (LCA) and life cycle cost analysis (LCCA) should be applied. However, more research efforts are needed in this field for further development and refinement. This literature review tries to adress this need by compiling existing knowledge and gaps in the state-of-the-art. A comprehensive literature survey about concrete repair assessment through LCA and LCCA is performed and showed a high potential for further investigation. Additionally, it was noticed that many differences are present between the studies considering LCA and/or LCCA, namely, the considered (i) structures, (ii) damage causes, (iii) repair techniques, (iv) estimated and expected life spans, (v) LCCA methods, (vi) life cycle impact assessment (LCIA) methods, etc. Therefore, due to the case specificity, mutual comparison is challenging.

Cold recycling of reclaimed asphalt (RA) is a promising technique to build or to maintain roads, combining performance and environmental advantages. Although this technique has been extensively used worldwide, there is no unique and internationally-shared method to characterize cold recycled mixtures. The previous work of the RILEM TC 237-SIB TG6 successfully attempted to characterize different RA sources with both traditional parameters (gradation, bitumen content and geometrical properties) and non-conventional properties (fragmentation and strength testing). The current RILEM TC 264-RAP TG1 mainly focuses on the influence of different RA sources on physical and mechanical characteristics of cement-bitumen treated materials (CBTM) using foam or emulsified bitumen, taking into consideration compaction and curing methods. This paper presents results from the first step of the inter-laboratory project in which foamed bitumen and cement were used as binders. The influence of two RA sources, one from Alabama (USA) and one from San Marino, were investigated through the collaboration of several laboratories. Specimens were manufactured with the same diameter by means of both Marshall and gyratory compactors and then cured following two procedures: free surface drying (FSD) and partially-surface drying (PSD). A preliminary study allowed obtaining specimens with similar volumetric properties. Along with compactability and water loss, the indirect tensile stiffness modulus was measured and analyzed. The results have shown that the RA source and curing procedure influence the CBTM mechanical properties.

The use of rejuvenators has seen a consistent increase over the years in the asphalt pavement industry. This is due to the need for maximizing the demand for incorporating a higher amount of Reclaimed Asphalt (RA) in the pavement asphalt mixtures. In order to tackle this challenge, the Task Group 3, focusing on asphalt binders and additives, of the RILEM TC RAP conducted an interlaboratory activity to evaluate the effect of aging on blends of virgin and rejuvenated RA binders. A set of conventional tests including penetration value at 25 °C, softening point temperature and rheological measurements by means of Dynamic Shear Rheometer (DSR) were selected to involve a large number of participants. A binder, recovered from field RA, was treated with a bio-based rejuvenator and blended with a virgin binder to simulate recycling at three different percentages 60, 80, and 100%. These blends, as well as the pure virgin binder, were next short and long term aged and tested to evaluate the changes in the corresponding properties. Relatively consistent results were obtained for the entire set of blends. The aging of combined rejuvenated RA and virgin binders was comparable to that experienced for the pure virgin binder. DSR data provided a more precise evolution of the impact of aging on the materials.

Bitumen is one of the most important materials used in roads. During asphalt pavement construction, workers can be affected by emissions, such as volatile organic compounds (VOCs), when bitumen is heated. Therefore, it is crucial to correctly identify and measure VOCs. This paper presents a novel, promising method to determine VOC emissions. The proposed method offers a way to standardize routine measurements on a lab scale, enabling reliable comparison across bitumen types and their modifications or additives. A proton-transfer reaction time-of-flight mass spectrometer (PTR-TOF-MS) was used to monitor VOC emissions from commercial unmodified bitumen and crumb rubber modified bitumen (CRMB) with heating of up to 180 °C. Results confirmed that the temperature range of 160–180 °C is a highly influential factor for VOC emissions from heated commercial bitumen and particularly CRMB. A significant increase in alkane and aromatic emission was detected when the binders were heated to 180 °C. Sulfur-containing VOCs were almost nonexistent for the base bitumen fumes, while a significant increase was detected in the fumes when two different types of CR were added to the bitumen, even at 120 °C. The additional CR in the bituminous binder contributed to the potentially harmful VOC emission of benzothiazole, which belongs to the class of sulfur-containing compounds. The concentration of benzothiazole was 65%, 38%, and 35% higher for CR1 in comparison to CR2 at 140, 160, and 180 °C, respectively. It is clear from the results that this method allows different bitumen sources or modifications to be quickly analyzed and their VOC emissions cross-compared. If adopted and confirmed further, the method could offer the asphalt industry a viable solution to monitor VOC emissions by analyzing samples in real time at different steps of the production process.

The authors wish to make the following corrections to this paper [...]

This Special Issue “Recent Advances and Future Trends in Pavement Engineering” has been proposed and organized to present recent developments in the field of innovative pavement materials and engineering. For this reason, the articles and state-of-the-art reviews highlighted in this editorial relate to different aspects of pavement engineering, from recycled asphalt pavements to alkali-activated materials, from hot mix asphalt concrete to porous asphalt concrete, from interface bonding to modal analysis, from destructive testing to non-destructive pavement monitoring by using fiber optics sensors.

For rehabilitation of existing concrete structures, strength and durability related properties of the reinforced element are of high importance. Assessment of these properties of existing structures can be performed by (i) destructive testing of drilled cores and testing the extracted samples in lab environment and (ii) indirect methods by using non- or semi-destructive techniques on site. The use of core-drilling is a time-consuming and labour-intensive method that weakens the existing concrete structure, leaving a lasting impression on it. As an alternative, many different non and semi-destructive techniques are available for the in-situ determination of compressive strength and durability related properties. An experimental program is conducted on concrete slabs of different strength classes intended for various exposure classes (according to EN206), based on a limestone aggregate matrix, which is typically used for Belgian applications. The plates have an age of approximately 5 years, which were also characterized at younger stage (in 2014). Besides destructive core drilling and testing (compressive strength tests, chloride migration testing, and determination of carbonation rate), several non-destructive techniques were selected for this study: the rebound hammer, the ultrasonic pulse velocity tester, the Wenner probe for concrete resistivity and the air permeability tester. Best fit correlations between the output of these different techniques were established. The effect of age (e.g. carbonation) on the established predictive models is being evaluated.

In the present study ultra-fine fly ash as a novel by-product obtained by a dry and closed separation process was investigated as cement replacement in concrete. The impact of ultra-fine fly ash on material properties was investigated following an upscaling as an approach considering paste, mortar and concrete properties. Two types of cement, Portland cement (CEMI) and slag cement (CEMIII), two types of ultra-fly ashes, one with particle size d90< 9.3lm (FA1) and second with d90< 4.6lm (FA2) were used.At paste- and mortar- level, cement was replaced at 0%, 15%, 25%, 35% and 50% with FA1 and FA2. At concrete- level, cement was replaced at 0%, 15% and 25% with different ratios of FA1 and FA2. The results at paste- and mortar- level showed that an increased fineness of the fly ash (FA2) contributes to better workability of the mix. For CEMI, the compressive strength of concrete with FA2 at 25% cement replacement was already equal to the reference 0% replacement concrete at the age of 28 days. For CEMIII, the compressive strength of concrete mix with FA1 with 15% and FA2 with 25% cement replacements reached the reference concrete value at the age of 91 days. Regarding the durability, replacing cement with ultra-fine fly ash (FA2) had a positive influence on the resistivity, chloride migration coefficient and alkali-silica reaction (ASR), and a negative influence on the carbonation resistance.

In this study, the feasibility of a natural peat fiber and finely ground peat powder as a modifier for bitumen was investigated. Initially, the as-received peat material was characterized in detail: the material was ground to various degrees, separated into fiber and powder fractions, and the gradation of the powder fraction as well as the size of the fibers were determined. A possible solubility in bitumen, the moisture content, and the density of both fractions were evaluated, and a limited chemical characterization of the fibers was conducted. Secondly, the rheological behavior of the powder and the fibers when blended with bitumen was evaluated. Additionally, a limited asphalt study was conducted. The rheological data showed the stiffening effects of the powder fraction and the presence of a fiber network, which were obvious as a plateau modulus towards lower frequencies. The fiber network was strain-dependent and showed elastic effects. This was further confirmed by the multiple stress creep recovery (MSCRT) tests. These tests also indicated that the fibers should improve the rutting resistance, although it was not possible to confirm this in asphalt rutting tests. Asphalt drainage tests demonstrated that adding dry peat, whether this is ground or not, is effective in reducing the binder drainage. However, the data also revealed that the amount of added peat fibers and powder should be limited to avoid difficulties in the compaction of these asphalt mixes.

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 2015, the ROADJT project initiated the development and demonstration of an integrated and coherent IT process control system for the Flemish asphalt sector in order to modernize existing asphalt paving technologies and to obtain real-time data to monitor pavement behavior. One of the demonstration test tracks is CyPaTs, the construction of a bicycle path built in September 2017, using innovative technologies (www.uantwerpen.be/cypats). Five technologies are described in this contribution. An asphalt solar collector (PSC) with a piping system was installed directly in the asphalt. Cold water during summer season and hot water in winter season running through the pipes, keep the asphalt structure in a better temperature interval, avoiding rutting and cracking. Other advantages of this system are: energy gain, the prevention of damage to asphalt and the enhancement of traffic safety. The expected energy gain per year varies between 0.5 and 0.8 GJ/m(2). About 20% of this energy is used for the operation of the asphalt collector itself. The remaining 80% can be used in nearby buildings. Fiber Bragg Grating (FBG) monitoring system was integrated in all three asphalt layers for the first time in Belgium. Two novel approaches of FBGs installation in asphalt layers were elaborated in this bicycle path: installation of FBGs in prefabricated asphalt specimens at the bottom of base layer and installation of FBGs in a saw cut of approx. 2mm in the previously constructed asphalt layer. The results proved a survival rate of the FBGs of 100%. The obtained strain and temperature data from FBG monitoring system has proved to be an excellent approach to establish and reflect the real condition of the asphalt pavement behaviour in time at different temperatures. The temperatures of the asphalt pavement during construction were followed up by the infrared thermography measurement techniques: a thermographic line-scanner (PAVE-IR by Moba AG) which was mounted at the back of the finisher and a hand-held IR camera (FLIR T640) was used for taking pictures every 2 meters. A real-time temperature contour plot of the pavement during construction was created to monitor asphalt pavement temperatures for quality inspection during the paving process or for later assessment. Two other non-destructive technologies for quality assessment were applied during this project. At first, the thickness was measured using aluminium plates and the MIT-SCAN T3. The obtained values were compared with topographic height measurements. Secondly, the density was measured with the PQI-380 non-nuclear density meter at several spots. The objective here is to check the density of the bicycle path, as well as the accuracy and investigate different parameters that influence the variations of the results, in particular the temperature dependency.

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.

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&mdash, using a cross-section configuration to carry out strain measurements in two directions (transverse and longitudinal)&mdash, 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).

The scope of the paper is to report an investigation on durability of infrastructure concrete for roads and bridges by creating a size and shape-designed pore systems in concrete in order to improve it, especially in terms of freezethaw resistance. By means of this experimental laboratory study, an alternative for usage of air entrainment agents (AEA) in concrete infrastructures was found in the way of using superabsorbent polymer materials (SAPs). The effect of the addition of SAPs of different amounts and different types into fresh concrete mix was investigated, including: compressive strength tests, weight loss measurements, visual and microscopic inspections and scanning electron microscopy (SEM) analysis. The detrimental strength reduction effect was not observed. The freezethaw procedure was varied, using different types of de-icing salts and heating/cooling regimes. It can be concluded that an improvement of the freezethaw resistance of concrete infrastructure depends on the particle size and optimal amount of SAPs added into concrete mix. The addition of 0.26 wt % of dry SAPs into the fresh concrete reference mix led to the significant decrease of scaling up to 43% after 28 freezethaw cycles. Both dosage and particle size of the SAPs had a significant impact on the obtained results and the freezethaw resistance in this experimental laboratory study. Engels irua-catalogus ispartof: Infrastructures vol:3 issue:1 pages:1-14 status: published

Currently the majority of industrial companies in the world develop and implements clean production technologies where manufacturing wastes are recycled and are used for new building materials production. Due glass debris sorting and recycling are practiced at minimum level in Latvia, there should be found alternative ways how to reduce the accumulated glass wastes. The worldwide application of waste glass in concrete was quite limited due to alkali-silica reactivity (ASR) for almost forty years, but this supplementary cementitious material gained again interest in its alternative use in concrete industry in the last decade. It was found that the ground glass particles (

In the present study the performance characteristics (workability, compressive strength, frost resistance, permeability and temperature of hydration) of the ecological self compacting concrete with reduced cement content and with the next generation recycled concrete aggregates which are obtained from crashed concrete specimens with cement substitution at level of 30% with waste glass powder were investigated. Waste glass as powder ground to certain fineness accelerates beneficial chemical reactions in concrete offers desired chemical composition and reactivity for enhancing the chemical stability and durability of concrete.

The grinding of glass waste chips in a wet environment for 120 minutes gives possibility to obtain particles finer in size in comparison to glass waste chips ground in dry environment. The particle distribution analysis showed that borosilicate glass lamp waste slurry has particle size in the range of 0.713 μm to 8.088 μm, fluorescent lamp glass waste slurry - from 2.473 μm to 20.088 μm, amber glass cullet slurry - from 1.435 μm to 21.118 μm, green glass cullet slurry - from 0.903 μm to 23.125 μm, flint glass cullet slurry - from 1.511 μm to 8.932 μm. The obtained waste glass slurries show pozzolanic characteristics and using of them as a cement component in concrete might be a solution for CO2 and accumulated landfilled glass wastes reduction. Application of waste glass slurries in concrete has a positive effect on workability of concrete mixtures and improves considerably mechanical properties of concrete at early ages. The alkali-silica reactivity (ASR) tests results indicate that the presence of finely ground waste glass in wet environment has a relatively small influence on ASR expansion.

Buildings are large consumers of energy in all countries. The proper use of thermal insulation in buildings does not only contribute in reducing the required air-conditioning or heating size, reducing the thickness of walls but also in reducing the annual energy cost. As the heat flows through the building envelope (walls, roofs, floors) in the way of radiation, conduction and convection, there are buildings in which the radiation is the dominant method of heat transmission. Reflective Insulation System is formed by a combination of low emittance surfaces and air spaces that provide reflective cavities which have low levels of radiant energy transmission. In this research insulation panels with multilayer, low-emissivity aluminum-polyethylene sheets were prepared and investigated with a thermal box. The investigation includes the analysis of the effects of changing the number of reflecting layers, ranging from zero to seven, as well as the number and thickness of air spaces, within the same total insulation thickness (40 mm). This study showed that surface emissivity and convection have important influence on heat flow. The aluminum-polyethylene sheets were effective in reflecting heat and reducing heat transfer by radiation.

Heavy-duty pavements have met new challenges over the past decades. Many pavements were not designed for servicing today's traffic frequency and axle loads, which impose loads much greater than those initially considered. Both factors result in an accelerated deterioration of the pavement structure. The accurate measurement of the strain and stress distributions in pavement is critical for understanding pavement behavior and modeling failures of pavements. With the development of information technology and digitization, traditional pavement monitoring systems have been integrated with other monitoring systems, including bridge monitoring, Weigh-in-Motion (WIM), traffic classification etc. In the present study, a fiber Bragg grating monitoring system for heavy-duty pavement health monitoring is introduced. The concept was designed by University of Antwerp and first installed together with Com&Sens in a test track demonstration project CyPaTs (Cycle Pavement Technologies) in September 2017. The same advanced system is installed in a larger scale project in a test track in the Port of Antwerp in June 2019. Numerous sensors (strain and temperature) installed between three asphalt layers allow better descriptions of the behavior of asphalt layers under heavy loading during real-time monitoring. This technology can provide strain data for the service life of the asphalt layers during a subsequent monitoring campaign under actual moving vehicular load. Since the accuracy is very high, this technology is appropriate for monitoring the deformation of the asphalt layers over time, considering aging, fatigue and rutting. The real-time monitoring data from the FBG sensors embedded in geogrid and three asphalt layers will be discussed in this study.