Materials and Structures最新文献

The application of basalt fibre reinforced concrete (BFRC) is crucial for reducing carbon emissions, enhancing structural performance, and extending service life. Electrical resistivity (ER), a non-destructive testing indicator, can be used to evaluate parameters such as compressive strength and chloride ion permeability of concrete. Therefore, this study examines BFRC-ER from three perspectives: the applicability of existing ER prediction models, hybrid machine learning modelling, and experimental validation. The findings indicate that the predicted values of the existing nine models have a poor correlation with actual values, limiting their practical application. The prairie dog–optimised XGBoost (PDO–XGBoost) model developed in this study exhibited closer alignment between predicted and actual values. It boasted smaller mean and standard deviation (μ = 0.0508 kΩ·cm, σ = 3.409) of model error distribution, along with superior performance evaluation metrics (MAE = 2.165, MAPE = 0.243, RMSE = 3.410 MSE = 11.625, and R² = 0.984). Analysing the contribution of each input feature to BFRC-ER revealed that saturation, age, and water–binder ratio are the three significant influencing factors. Moreover, this study developed a graphical user interface (GUI) for BFRC-ER, enabling the visualisation of BFRC-ER predictions. Subsequently, BFRC with varying mix proportions was prepared, and BFRC-ER was tested using the two-electrode method. The comparison between actual values and GUI predictions showed errors below 7.5%, highlighting the accuracy of the predictions. This research achieves high-accuracy predictions of BFRC-ER, laying the foundation for optimising BFRC mix proportions and evaluating concrete performance.

Macroscopic voids at the steel–concrete interface and their degree of saturation with an aqueous electrolyte are known to play an important role in the corrosion of steel in reinforced concrete. Irrespective of the exposure conditions and testing parameters, in the majority of studies corrosion products have been reported to consistently precipitate in a unique pattern within these macroscopic voids, preferentially along the void walls and growing inward. The underlying mechanisms governing corrosion product precipitation in macroscopic voids and their effects on long-term durability remain unclear. Through in-situ X-ray computed tomography observations, thermodynamic and kinetic considerations, and numerical modelling of water transport within macroscopic voids, here, we provide plausible hypotheses of the processes responsible for the precipitation of corrosion products along the walls of the voids. Understanding the mechanisms of corrosion product precipitation can offer insights into the development of stresses in and around the macroscopic interfacial void and the durability of reinforced concrete structures. This contribution also discusses opportunities for different avenues for research to elucidate several multiscale processes that influence the durability of reinforced concrete.

Supplementary cementitious materials (SCMs) can mitigate alkali-silica reaction by lowering the alkali metal concentration in the pore solution. This is a theoretical study on the applicability of a thermodynamic model (GEMS) and the empirical Taylor model to predict the required replacement level of portland cement (PC) by SCMs to achieve an alkali metal concentration below 300 mmol/L. The SCMs investigated are silica fume (SF), metakaolin (MK), fly ash (FA) and slag. The impact of the alkali content of the PC and the w/b ratio on the required replacement level is modelled and compared to experimental pore solution concentrations. Both models predict a similar impact of the SCM replacement level on the distribution of alkali between the pore solution, C–S–H and unreacted material. The thermodynamic model predicts little impact of the alkali content of PC and the w/b-ratio on the required replacement level, i.e., 20% SF, 20% MK, 40–50% FA and 60–70% slag. This is contrary to the Taylor model, which predicts that the replacement levels of FA and slag ranges from 7 to 58% when increasing the alkali content from 0.47 to 0.93% and from 80 to 10%, when increasing the w/b ratio from 0.3 to 0.9. The required replacement levels for SF and MK vary between 2 and 19% when increasing the alkali content from 0.47 to 0.93%, and from 40 to < 5% when increasing the w/b ratio from 0.3 to 0.9. The main difference between the two models is how they account for the uptake of alkali metals by the C–S–H.

This report presents a new proposal for conducting the water capillary absorption test of hemp concretes and establishing the parameters useful for analyzing the obtained results. Based on the standards of traditional materials such as concrete and mortar, a testing protocol was developed and executed by eight laboratories from RILEM TC 275-HDB through interlaboratory testing. Homogeneous cubic specimens of hemp concrete with an edge length of 150 mm were cast and distributed to the laboratories, where they were conditioned before undergoing test. By adopting the new testing procedure, consistent results were achieved after analyzing data in both square root of time and log-time regimes. For each regime, two pairs of parameters CA and k (square root of time regime), and IRA and K1 (log-time regime) were utilized to compare the data and successfully validate the interlaboratory testing.

Microsurfacings are widely recognized as a valid solution for reducing the consumption of energy and raw materials in the construction and maintenance of road surfaces. They require specifically formulated mixtures, designed to compensate for the variability of the substrate and to ensure a durable bond at the interface of the newly applied layer. In fact, the surface texture of the support has a strong effect on the bonding behaviour, as it influences the interlocking and adhesion at the interface. Insufficient interlayer bonding can lead to slippage and to partial or complete delamination of layers. This can impair the functionality of the pavement, as large cracks and potholes can occur. Although several methods for assessing the mechanical performance of microsurfacings are included in the main international standards, there is a lack of standardised guidelines for assessing their bond strength. This recommendation proposes a testing procedure to assess the interlayer bond strength of microsurfacing mixtures using a common shear testing device. In addition to the results of the shear strength, the surface of the substrate can be characterised with regard to its texture using a simple laboratory method.

In terms of sustainability and resource efficiency, concrete structures such as bridges and wind turbines should be used as long as possible and—in the case of new constructions (as a replacement)—the cross-sections should be as slender and thin-walled as possible using high-performance or ultra-high performance concrete. A further development of the fatigue design would be useful both for the verification of a possible longer remaining service life and for a safe, but also for economical and sustainable design of these engineering structures, which are particularly exposed to fatigue. The verifications of structural safety for non-static loading of concrete in the national and international design codes and standards provide for high safety margins, particularly for concretes with high strengths. These result, among other things, from the large scatter of the number of cycles to failure in experimental fatigue tests. In this article, current verifications of structural safety for non-static loading of concrete are presented, results of compressive tests on concrete specimens of different strengths, geometries and test boundary conditions are summarised in a database and the scatter of the experimentally determined number of cycles to failure is statistically evaluated. In addition, the compressive strength of concrete, which significantly influence the scatter of the numbers of cycles to failure, are statistically analysed for concretes of different ages. From this, a continuous description of the strength development and its scatter is derived. Finally, the compressive stress levels of the previously analysed fatigue tests are adjusted using a stochastic approach in order to take into account the scatter of the compressive strength of concrete as a function of the concrete age. By applying the time-dependent scatter of the compressive strength of concrete, a significant reduction in the scatter bandwidth of the analysed numbers of cycles to failure in the S–N curve is achieved.

Reactive magnesium oxide cement (RMC) is emerging as a sustainable binder in construction applications due to its ability to sequester CO₂ through carbonation, forming stable carbonates. However, the efficiency of RMC carbonation relies heavily on maintaining sufficient humidity and CO₂ concentration during curing. Various additives—including hydration agents, carbonate species, and seeds—have demonstrated effectiveness in enhancing both hydration and carbonation of RMC, thereby improving its mechanical performance. This study explores the use of biochar—a highly porous, carbon-based by-product of biomass pyrolysis—as a sustainable and cost-effective carbonation aid by evaluating its impact on the physical, rheological, mechanical, and microstructural properties of RMC composites. The results showed that the incorporation of 2 wt% biochar significantly improved early-age mechanical performance, with compressive strength increasing from 37.8 to 45.8 MPa at 7-days under CO₂ curing, and promoted the formation of hydrated magnesium carbonates (HMCs), raising total HMCs content from 5.4 to 13.9 wt% at 7-days under CO₂ curing. This improvement is attributed to biochar’s micro-filler effect, internal curing capability and its ability to facilitate CO₂ diffusion. Moreover, the inclusion of biochar effectively shortened the curing time, further enhancing the sustainability of CO₂ curing by reducing energy consumption. In conclusion, this study highlights the potential of biochar as a bio-renewable additive in RMC-based composites, enhancing brucite and HMCs formation, shortening CO₂-curing time and contributing to development of sustainable, carbon-efficient construction materials.

The inevitable snow accretion over pavement in winter is always troublesome for transportation systems. Many open questions on road icing and snowing remain, and there is significant demand to develop a green, reliable, efficient, and secure approach for ice and snow cleaning. This work fabrication of a mechanically tough, flexible, and highly conductive graphene-paper (GP). This novel material demonstrates a combination of mechanical robustness and high conductivity, making it suitable for self-heating applications. Based on the remarkable Joule heating effect of GPs, which served as efficient heating elements and was embedded into an emulsified asphalt pavement slab (APs) to construct a new type of self-heating system through a separately packaged and uniformly integrated procedure. Owning to the conductivity of the GPs reached up to 5300 S/m, thermal energy could be provided via clean energy (such as solar, wind, and tidal energy), contributing to the goal of carbon neutrality. Furthermore, the APs demonstrates ice melting under the extreme temperature condition of − 30°C without damaging the pavement structure. What’s more, the ability of anti-accretions of snow has resisted the extreme blizzard in unfavorable weather. Such self-heating pavement based on GPs has the advantages of high efficiency, good stability, and outstanding safety for both snow-melting and deicing.

Very-High-Performance Concrete (VHPC) are defined as concrete capable of reaching compressive strength higher than 80 MPa. These performances can be reached thanks to its compact and extremely dense microstructure, as a result of a proper mix. Together with their great durability properties, these concretes may lead to reduce cross sections of structural elements and thus save material and built volumes. The addition of synthetic fibers allows to significantly increase the toughness and crack opening resistance, beyond the tensile strength. These benefits can easily be traduced in an improved durability of the VHPC concrete. the aim of this research activity is to enlarge the experimental database of high-performances concrete reinforced with synthetic fibers having different size. In fact, contrary to the case of steel fibers, few works are report ed in literature regarding the types of fibers investigated herein. In the present work three Very High-Performance Fiber Reinforced Concrete (VHPFRC) mixes have been studied and characterized in laboratory. The mixes were realized with the same VHPC concrete matrix and different types of synthetic fibers: 10 mm straight polyvinyl alcohol (PVA) fibers; 30 mm waved polypropylene (PP) fibers; 40 mm waved polypropylene (PP) fibers. The first mix was realized using PVA fibers only, the second with 30 mm PP fibers and the last one was obtained by mixing PVA fibers and 40 mm PP fibers. A further VHPC mix with no fibers has been also realized and tested as reference material. Compression tests on both cylindrical and cubic specimens and modulus of elasticity tests have been performed for each mix. The VHPFRC toughness have been determined by means of three-points bending tests according to EN 14651. The bending parameters obtained from the experimental test have been compared between all the mixes and an analysis of the fracture energy has been performed. Moreover, each mix has been tested at bending with four-points setup in order to verify the efficiency of this test type for VHPC reinforced with synthetic fiber. The results provided in the paper highlight the different effects, in terms of mechanical response, caused by fibers of different size at different cracking stages of the tested materials.

Steel fiber reinforced self compacting concrete has high potential application in structural elements. The distribution and orientation of fibers in fiber reinforced self compacting concrete play a key role in defining the mechanical and durability behavior. Several factors such as casting method and rheological properties of concrete may influence the fiber distribution and orientation within structural elements. In this paper, due to the importance of vertical elements and high uncertainties regarding fiber distribution and orientation in these elements, steel fiber dispersion and alignment were investigated. In this study, five structural walls (7.0 × 2.5 × 0.2 m) with three distinctive casting procedures (single point, double points, and continuous casting) and two rheological properties [self compacting concrete (SCC) and vibrated compacted concrete] were constructed. Thereafter, by using the inductive test, fiber orientation and distribution were assessed. The results indicated that using two casting points resulted in a more uniform fiber distribution. A comparison between the two SCC mix designs revealed that large coarse aggregates significantly increased segregation and scattering in fiber distribution and orientation. Additionally, fiber orientation analysis demonstrated that continuous casting and vibration led to greater fiber alignment in the horizontal direction. Finally, the results showed that the rheological behavior of concrete mix plays a major role in the fiber distribution compared to the casting procedure. Therefore, to achieve higher uniformity, altering mix designs is recommended.