The diffusion potentials can cause significant errors in corrosion-related investigations of reinforced concrete structures (half-cell potential mapping, potentiometric sensors). Therefore, an improved understanding of the diffusion potentials in cement-based materials is needed. This study investigates the permselective behavior and its implication for the arising diffusion potentials. A diffusion cell is used to study the diffusion potentials in hardened cement pastes with imposed NaCl gradients. The cement pastes consist of ordinary Portland cement (OPC) and blast furnace cement (BFC) with water-cement ratios of 0.30–0.70. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is used to determine the concentration profiles of Cl, Na, K and Ca in the cement pastes with a high spatial resolution (100 µm). For the BFC pastes, considerable differences in the Cl− and Na+ mobilities are found, indicating their permselective behavior. Despite the permselective behavior, the measured diffusion potentials are small (− 6 to + 3 mV) for all investigated cement pastes due to the high pH levels (13–14) in the pore solutions. However, when using the diffusion cell, the pH differences interfere with the measured diffusion potentials. The interfering pH differences need to be considered for an accurate measurement of the diffusion potentials in cement pastes.
A new impact-absorbing material is being developed to protect vulnerable road users in urban areas and has been produced and tested, mechanically and environmentally in the laboratory. The main constituent of this innovative material is the rubber recycled from end-of-life tyres to foster a circular use of resources and exploit rubber’s elastic properties. The study aims to provide a complete Uniaxial Compression Test (UCT) and leaching analysis of the material to propose and optimise a mix that is mechanically sound, durable, and respectful of the environment, in view of in-situ applications. Therefore, the UCT and Dynamic Surface Leaching Test (DSLT) were carried out on rubberised asphalt specimens with different mix designs. The 64 days cumulative concentrations of leached heavy metals and trace elements from unit surface of specimens were calculated and quantified, according to the CEN/TS 16637 standard. In parallel, thanks to a specific mechanical characterisation, compressive stress–strain curves were obtained, and the relaxation and elastic modulus were evaluated. The results from the compression tests showed that the A-mixes have the best elastic and absorbing behaviour, especially those made with an SBS-modified bituminous emulsion (A4). The results from DSLT showed that the cumulative concentration of released elements, per unit surface of specimens were lower than the Dutch Soil Quality Decree (SQD) thresholds, taken as a reference. The low and early release of leachant observed for the mixtures, especially A4 as the most promising one, leave the possibility to handle the leaching with several solutions, including rubber coating treatment or water washing before their incorporation into the mix to limit and prevent their leaching while permitting very high injury reduction performances.
Cellulose ethers are often used to improve the properties of cement-based ceramic adhesives during their setting and hardening stages. The chemical and structural characteristics of a cellulose ether significantly improve some properties like the rheological and water retention characteristics as well as the mechanical properties of the adhesives. Since the effects of cement type are seldom studied in literature, this study aims to examine how the interaction of different cellulose ether-cement combinations will affect the properties of ceramic adhesives. In the experimental program, five different cement types and four different cellulose ethers based on hydroxyethyl methyl cellulose (HEMC) were utilized to obtain 20 ceramic adhesives. The performance of the adhesives was determined using the readily available standards. It was found out that in addition to HEMC type, the cement type has an effect on the properties of ceramic adhesives. As a result, it was shown that the cement fineness is also a parameter that contributes to the physical jamming effect of the cellulose ether molecules, thus affecting the water retention properties of the ceramic adhesives.
Early-age carbonation curing of concrete is receiving more interest in terms of performance improvement and emission reduction. However, the volume change of cement-based products subject to carbonation curing may become a concern because of the potential carbonation shrinkage and its related shrinkage cracking. The purpose of this study was to investigate the dimensional stability of cement paste and concrete subject to the early-age carbonation curing. It was found that the carbonation curing introduced first an initial shrinkage due to water evaporation upon gas injection and then generated an expansion due to CO 2 uptake and carbonate precipitation. As carbonation proceeded, the deformation was switched to a secondary shrinkage after expansion. The residual deformation due to carbonation curing was shrinkage in cement paste samples and expansion in concrete samples. This was because the relative expansion due to carbonate precipitation in paste was not large enough to compensate for the shrinkage caused by water loss. However, for concrete samples, the introduction of aggregates reduced the pore spaces in concrete, leading to an expansion owing to the limited precipitation. The results of carbon dioxide uptake, XRD, and SEM analysis confirmed that calcium carbonate formation played a critical role in the relative expansion. The study also showed that cement-based products were more resistant to weathering carbonation after the early-age carbonation curing. After 61-day weathering carbonation exposure, both paste and concrete samples exhibited carbonation shrinkage as a result of carbonation of hydration products. However, the magnitude of shrinkage was much smaller in carbonation curing than in weathering carbonation because of the short period of exposure. Both carbonations did not significantly affect the compressive strength of carbonated products. Carbonation curing likely makes concrete products more dimensionally stable in the long-term service.
This study aims at investigating the mechanical and electromagnetic interference (EMI) shielding properties of cementitious composites with combined utilization of recycled carbon fiber (rCF) and steel slag. Different dosage of raw steel slag (SS) and wet-grinding steel slag (WSS) as replacement of cement were introduced to the cementitious composites with rCF. Wet-grinding can enhance hydration activity of SS, and also can improve the dispersibility of rCF in cement matrix thus optimizing the mechanical properties. The electrical resistivity of the composites decreases with increased WSS dosage, the conductive phase in WSS not only form new conductive pathways, but also act as bridges to connect rCFs, the WSS is more effective in lowering the electrical resistivity. The shielding effectiveness (SE) of the rCF-WSS cementitious composites increases with increased WSS dosage, which is higher than that of SS due to the higher conductivity and scattering effect of reduced particle fineness. The absorption loss SE A dominates the SE T , which is mainly attributed to increasing electrical conductivity, the dielectric loss and magnetic loss also contribute to absorption loss. The synergistic effect of rCF and steel slag on electrically conductive and EMI shielding properties was demonstrated, wet-grinding process can promote the synergistic effect.
Ultra-high performance mortar (UHPM) has been proposed to replace conventional mortar (CM) as it can improve the compressive performance of stone masonry structure. To investigate performance features such as failure modes, load-versus deformation and ultimate compressive strength, eighteen UHPM and CM stone masonry specimens were tested under axial loading with mortar type, fiber type, mortar thickness and stone block surface condition as the main parameters. The test results indicate that for UHPM specimens, the primary cause of failure is the cracking of stone blocks rather than the mortar joints. And the cracking and ultimate compressive strength is 182.1% and 245.3% higher respectively compared with that of the CM ones. mechanism possible explanation is that stone blocks in stone masonry with UHPM are in a tri-axial compression due to the confinement effect of UHPM material which possesses high elastic modulus and low Poisson's ratio. UHPC without fibers recommended for stone masonry structures as the theoretically positive effects of steel and PVA fibers on UHPC did not show up in this experiment. The artificial sand blasting treatment on stone surface exerts little effect on the compressive performance of UHPC stone masonry. Based on the test results, a new formula of EC6 is recalculated and the ratio between recalculated and test values is 0.97 with a variance of 0.07. However, for the equation used to predict the compressive strength of UHPM stone masonry is still need to improvement.
This study aims to explore the effects of different Ca(OH)2 contents on the mechanical performance and corrosion behaviors of steel in Calcium sulfoaluminate (CSA) cement, where compressive strength, corrosion potentials of reinforcements, corrosion current density, pH of pore solution as well as mortar resistivity of CSA/Ca(OH)2 mortar were researched, and the corrosion behaviors were further interpreted by the clarification of hydration phases through microstructural analyses. The initial results highlighted the positive effects of using adequate Ca(OH)2 ( 6
To understand the general coupled chemo-thermo-hydro-mechanical (CTHM) behavior of CSRE, this work reviews the cement hydration process in CSRE and its influence on the thermo-hydro-mechanical (THM) behaviors of CSRE materials. It has been observed that the unconfined compressive strength of CSRE increases with material dry density. Compared to other factors such as grain size distribution, dry density, and water content, the effect of cement hydration on the variations of the soil water retention curve (saturation-suction scale) and thermal conductivity is not significant. The free water consumed in the hydration process exists in the form of chemically reacted water and gel water. Moreover, cement hydration increases the mechanical resistance of CSRE over time and is influenced by the curing conditions. The characteristics of CSRE vary considerably among different experimental works reported in the literature. The combined effect of initial water content, initial dry density, initial grain size distribution, initial cement content, curing conditions and curing time needs to be considered together from the design stage of CSRE material. The lack of a global view of all types of CSRE materials poses great difficulties in making a worldwide acceptable standard for CSRE materials. Consequently, based on the experimental results from literature review, a finite element numerical framework is proposed to reproduce a typical CSRE material as well as to globally explain the complex coupled CTHM properties of CSRE from the design stage.
Foam concrete stands out among special concrete for presenting a porous structure by incorporating foam into the cement matrix. The tendency for bubbles to coalesce and collapse during preparation poses some challenges in production and control over the properties of cell structures. This research aims to evaluate the behavior of cellular concrete using ultra-lightweight expanded polystyrene aggregate (EPS) as a source for reducing specific mass. Since, there are few publications investigating the integration of EPS pearls in foam concrete. For comparison, samples were made with Portland cement and quartz aggregate using the dosage method proposed by Ferreira (1987) for foamed concrete. In these concretes, properties in the plastic state were evaluated, compressive strength and ultrasonic wave propagation velocity tests were carried out at 3, 7, and 28 days and, in addition to these tests, at 28 days, the absorption, thermogravimetric analysis, and X-ray diffraction were carried out, under three water/binder factors: 0.38, 0.42 and 0.46. The results showed an apparent specific mass below 750 kg/m(3) and mechanical strength of up to 1 MPa. The replacement of expanded polystyrene promoted an average reduction in mass over the volume of around 30%. Making the technology more commercial for the use of thermal and acoustic insulators requires further studies to improve the product. In general, EPS aggregate is a viable and advantageous alternative when applied to cellular concrete from the point of view of the civil construction industry.
In the near future, the world of civil and building engineering will be dominated by the advent of bio-materials. Even the road paving sector is involved in the transition towards more sustainable solutions, promoting at the same time environmental benefits and economic savings. Currently, one of the main goals is to ensure that bio-binders offer good performance, at least comparable with that offered by conventional materials. In the last decades, the exponential increase in traffic volumes has led to various types of asphalt pavement distresses, among which fatigue cracking is one of the most common. Within this context, this study presents the characterization of a bio-based asphalt mixture obtained by replacing 30% of bitumen with lignin, which was compared with a reference asphalt mixture containing a plain bitumen characterised by the same penetration grade. Laboratory produced and compacted specimens were subjected to complex modulus and cyclic fatigue tests with the Asphalt Mixture Performance Tester (AMPT). Both unaged and long-term aging conditions were investigated. The tests and the subsequent analyses were based on the simplified viscoelastic continuum damage (S-VECD) approach. Overall, the results showed that the presence of lignin led to a lower aging susceptibility, but also caused a slight reduction in fatigue life due to an increase in the material stiffness. Furthermore, the obtained results confirmed previous findings deriving from the study of the two binders and from the conventional characterization of the same asphalt mixtures as well.
The curing process in bituminous mixes plays a vital role during the early-stage strength development of cold in-place recycling technology. Curing temperature and curing period (collectively termed as curing regime) are the critical factors governing the curing process. Inadequate curing of cold recycled (CR) bituminous mixes can result in distresses as well as premature failure. The present study evaluated the influence of the curing regime on the mechanical characteristics of CR-Bituminous mixes stabilized with foam and emulsion bitumen (CR-Foam and CR-Emulsion) respectively. The moisture loss pattern in both CR-Foam and CR-Emulsion mixes was monitored over a curing period of 14 days and at three temperatures of 25, 40 and 60 °C. Results of the research showed that moisture loss was rapid during the 24 h and then the rate of moisture loss decreased eventually becoming constant approximately after 7 to 10 days. An increase in curing temperature accelerated the moisture loss in the initial days of curing resulting in better mechanical characteristics whereas the increase in humidity delayed the strength development process even after a prolonged curing period of 7 days. Both the CR-Mixes were found to have similar resilient modulus values for the same residual moisture content indicating the impact of curing temperature. In terms of performance, CR-Emulsion mixes showed superior cracking resistance than CR-Foam mixes as indicated by the Cracking Tolerance Index.
Recent rapid improvements in laminated timber technology have led to the increased use of wood in both mid- and high-rise construction, generally posed as a more carbon-friendly alternative to concrete. However, wood is significantly more sensitive to changes in relative humidity than concrete, which may impact the sustainability and durability of mass timber buildings. Moisture cycling in particular affects not only shrinkage and swelling but also strongly influences wood creep. This sensitivity is of high concern for engineered wood used in mass timber buildings. At the same time, wood, considered as an orthotropic material, exhibits varying diffusivity in all three directions, complicating efforts to characterize its behavior. In this work, an orthotropic hygroscopic model was developed for use in laminated timber. A species database for wood sorption isotherm was created and an existing model was used to fit species-based parameters. Diffusion behavior which considers the sorption isotherm was modeled through numerical simulations, and species-dependent orthotropic diffusion parameters were identified. A database of permeability in all directions for various species was created. The resulting model is able to predict diffusion behavior in glulam and cross-laminated timber (CLT) for multiple species of the lab tests. The model also predicts the moisture ranges for a CLT panel under environmental change with parameters from these sorption isotherm and diffusion databases.
The lower bond strength of FRP bars to concrete compared to steel bars has remained an unsolved barrier to the widespread use of FRP-reinforced concrete under extreme loading. Additionally, the degradation of the bond between FRP reinforcement and concretes in aggressive environments adds to the existing concern. In this study, an innovative anchorage system comprised of polypropylene pipe was used to strengthen the bond between seawater concrete and GFRP bars after 250 days of exposure to offshore environmental conditions. As material factors, two types of GFRP bars (sand-coated and ribbed) and two types of concrete (normal and seawater concrete) were evaluated. Four distinct environmental conditions were used to assess the samples: (i) ambient environment (control), (ii) tap water, (iii) seawater, and (iv) wet-dry cycles in seawater. According to the findings of the direct pull-out tests, the suggested anchor system strengthens the bond and shifts the failure mode from bond failure to bar rupture. Additionally, after exposure to 250 days of seawater wet-dry cycles, GFRP-reinforced seawater concrete lost 5% of its maximum bond strength (developed bar tensile stress). All other samples exposed to different environmental conditions either increased or decreased in bond strength by less than 5% after 250 days, compared to the control samples.
This research determines an adequate alkali-activated material (AAM) for the incorporation of huge amounts (20 or 40% vol) of low viscosity organic liquids (LVOL), e.g. for waste stabilization/solidification. The selected AAM are either based on high-Ca content blast furnace slag, or on low Ca-content metakaolin, i.e. on a geopolymer matrix. First, the selection of the AAM is performed to ensure no LVOL leakage and a sufficient compressive strength f c (> 8 MPa). Surfactants are compulsory to allow incorporation. After 90 days curing, for slag pastes, f c ranges between 10 and 20 MPa at 20% vol LVOL, but it is zero at 40% LVOL, whatever the surfactant. For geopolymer pastes, the AAM-LVOL composites have an average f c of 25 MPa at 20% vol LVOL, and of 15 MPa at 40% LVOL. With surfactant, the AAM solid pore structure of slag pastes is denser (with smaller specific surface area and micropore amount); it is unchanged for geopolymer pastes. Whatever the surfactant, air entrained bubbles are present. Their proportion is maximal with Glucopon. Together with LVOL presence, this generally contributes to decreasing f c . The emulsion (entrained air + LVOL droplets) is characterized in hardened AAM by combining 2D Scanning Electron Microscopy and 3D X Ray micro-computed tomography. Surfactants significantly decrease the emulsion droplet size distribution. For geopolymer pastes up to 40% vol LVOL, the most adequate surfactants are Brij O10 and CTAB; for slag paste up to 20% vol LVOL, it is CTAB. Moreover, the setting reactions are not impacted by LVOL or surfactants, and neither are the reaction products. It is concluded that the decrease in mechanical performance of AAM-LVOL composites is only due to physical reasons, particularly the decrease in AAM proportion, the emulsion quality (coalescence, droplet size and shape) and air entrained bubbles.
In this study, the fresh state and hydration properties of 0–60% lithium slag blended cement pastes were investigated at water-binder ratio of 0.47. The workability of the fresh pastes was evaluated by measuring the air content, marsh cone flow, mini-slump flow, setting times, and through rheology tests. A 40% lithium slag cement could produce 91% strength activity index at 28 days; mini-slump pat diameter of 70.54 mm; marsh cone flow efflux time of 145 s; air content 0.6%; hydration heat of 300 J/g (at 72 h). At replacement levels above 40%, the strength activity index, air content, mini-slump flow, hydration heat, and fluidity were significantly reduced. Experimental investigations confirm that the mini-slump test provides the best correlation coefficients ( R 2 = 0.96) with the maximum shear viscosity of lithium slag cement pastes than the marsh cone flow efflux time and air content. The classical slump and rheological models were used to characterise the mini-slump, yield stress, and plastic viscosity of low to high volume lithium slag cement pastes. The present study recommends that a 40% lithium slag cement paste is a viable option to produce green concrete for optimum fresh, hydration, rheological, and hardened properties.
In the composite system of asphalt mixtures, asphalt mastic, which is composed of fillers and bitumen, plays a key role. To achieve precise control and prediction of the performance of asphalt mastics, the effects of filler characteristics and bitumen components on the performance of mastics were investigated in this study. Five bitumen sources and five filler types were selected to prepare twenty-five kinds of asphalt mastics, and the macro and micro tests were conducted on the mastics. The grey relational analysis was applied to quantify the relationship between raw material characteristics and mastic performances. The results indicate that the properties of asphalt mastics exhibit a high correlation with the raw material characteristics. The resin content of bitumen is suggested to be one of the most influential properties for the fatigue performance of asphalt mastics. The penetrations, resins and aromatics contents of bitumen exhibit a specific contribution to the low-temperature performance of mastics. Among all filler characteristics, D10 (the particle diameter when the pass rate of the filler is 10%) and P20 (the content of fillers with a diameter of less than 0.02 mm) are recommended as two critical indicators for selecting fillers because these two parameters exhibit a higher correlation than other similar parameters. The filler characteristics such as particle size and specific surface area significantly affect the fatigue performance of asphalt mastics because the effect of fillers on the fatigue performance of mastics is the competitive mechanism between physical hardening and particle-filling enhancement. This study provides a reference for achieving the better performance of asphalt mastics by controlling bitumen sources and filler characteristics.
