Materials and Structures最新文献

This study determines how untreated recycled concrete aggregates (URA), thermally treated recycled concrete aggregates (TRA), and recycled concrete aggregates developed through an integrated thermomechanical treatment process (T_mRA) perform in concrete relative to each other. A concrete composed of 100% recycled aggregates (RCA) with Portland pozzolana cement has been successfully developed in the present study. The compressive strength, split tensile strength, flexural strength, fracture energy, and modulus of elasticity of T_mRC is observed higher than URC by 18.62%, 8.20%, 40.72%, 24.18%, and 54.99%, and those TRC by 7.54%, 28.57%, 29.78%, 24.12%, and 34.35%, respectively. The split tensile strength, flexural strength, fracture energy, and modulus of elasticity of these concretes are strongly correlated with their compressive strength. T_mRC material properties match NAC, standard requirements, and reported values closely. URC and TRC chloride-ion penetrations are around 3.51- and 2.42-times greater than T_mRC. Among these concretes, only T_mRC meets corrosion protection requirements like NAC. The abrasion resistance of T_mRC is observed 52.03% greater than URC and 43.07% greater than that of TRC. T_mRC has substantially lower sorptivity compared to URC and TRC and is close to NAC. T_mRC has around 32.65% and 16.67% less weight loss in drying than URC and TRC, respectively. URC and TRC have around 1.99- and 1.82-times less abrasion resistance than T_mRC. An optimal reduced adhered-mortar volume, the minimized porosity and microcracks, dense and uniform surface texture, strengthened interfacial transition zones leads the performance of T_mRA superior to URA and TRA, and close to or superior to parent aggregates.

This paper presents an investigation on the seismic behavior of RC frames with masonry infills retrofitted by precast Ultra-Lightweight Insulated Cementitious Composites plates under cyclic loading. The objective was to provide an easy retrofit approach for concurrent seismic behavior and energy efficiency upgrading of existing RC frames. Three scaled RC frames were built including a control frame and two frames with different retrofit schemes. The experiments were conducted to investigate the effect of different retrofit schemes over the failure patterns, hysteretic curves, energy dissipation abilities, skeleton curves, and characteristic loads and displacements. The retrofitted RC frames provided higher carrying capacities, energy dissipation abilities, and displacement ductility. Retrofit schemes proposed can prevent severe damage of masonry infills, and alleviate shear failure of columns significantly. Based on the test results, ULICC plates influenced on the flexural moments of columns and beams, and base shear distribution were analyzed. Interactions between retrofitted infills and surrounding frames were discussed. A theoretical model based on equivalent strut was proposed to obtain initial lateral stiffness and carrying capacity of retrofitted RC frames. The experiments have demonstrated that precast ULICC plates retrofit strategy can enhance the seismic performances under low-frequency cyclic loading.

Rejuvenators are critical for restoring the performance of recycled asphalt pavement produced with a high dosage of reclaimed asphalt pavement (RAP) materials. In this study, a biomass-derived phenolic oil (BDPO) recycled from biomass pyrolysis was proposed as a novel rejuvenating agent. Its rejuvenation efficiency and mechanism on the asphalt binder aged with three laboratory-aging conditions, including the rolling thin-film oven (RTFO) aging, pressure aging vessel (PAV) aging, and ultraviolet (UV) radiation aging, were investigated systemically. The chemical components of BDPO were first identified through the Gas-Chromatography-Mass Spectrometry (GC–MS) analysis. The rejuvenation efficiency was subsequently evaluated on the laboratory-aged asphalt binders using typical physical-rheological properties tests and compared with two commercial rejuvenators. The rejuvenation mechanism of BDPO was finally revealed by the Fourier Transform Infrared Spectroscopy (FTIR) test. Results indicated that the BDPO can balance the unstable colloidal structure and restore the physical-rheological properties of aged asphalt binders, whose optimal dosages were determined as 1.5%, 3%, and 8% for the selected asphalt binder aged under RTFO, PAV, and UV aging conditions, respectively. Compared with commercial rejuvenating agents, the BDPO-rejuvenated asphalt exhibits performance properties similar to those of unaged asphalt in terms of high-temperature rutting resistance, fatigue cracking resistance, and low-temperature cracking resistance. FTIR spectra identified that the rejuvenation process of aged asphalt binders using BDPO involves complicated chemical reactions, which are beneficial to alleviate the aging degrees. These findings confirm the potential of BDPO as a promising rejuvenator for recycled asphalt pavements.

Basic oxygen furnace slag (BOFS) is a high-volume waste resulting from the production of steel from pig iron. Due to its high free lime content, BOFS is difficult to recycle and/or include into conventional cement systems. Alkali-activation technology offers a pathway to transform industrial wastes such as BOFS into low-carbon cements. Alternative precursors for cement systems are needed as the reliance on commonly used materials like ground granulated blast furnace slag (GGBFS) is becoming unsustainable due to decreasing availability. This study investigates alkali-activated cements incorporating 20 and 30 wt.% of naturally weathered BOFS as a replacement for GGBFS, in both sodium silicate- and sodium carbonate-activated systems. A fraction of BOFS subject to mechanical activation is compared against the untreated BOFS in the 20 wt.% systems. It is observed that in naturally weathered BOFS, a significant portion of the free-lime is found to convert to portlandite, which accelerates alkali-activation kinetics. In sodium silicate-activated systems, the high pH of the activator results in incomplete reaction of the portlandite present in BOFS. The sodium carbonate-activated system shows near complete conversion of portlandite, causing an acceleration in the kinetics of reaction, setting, and hardening. These findings confirm the viability of sodium carbonate activated GGBFS-based systems with only a minor loss in strength properties. BOFS can be utilised as a valuable cement additive for the production of sustainable alkali-activated cements utilising sodium carbonate as a less carbon-intensive activator solution than the more commonly used sodium silicate. Mechanical activation of BOFS offers further optimisation potential for alkali-activation.

This study addresses the imbibition kinetics of finite water amounts in kaolinite plasters. Using an X-ray tomograph with in-situ liquid addition, 2D radiograph images precisely measure the water imbibition and distribution. Two distinct regimes are observed in the presence of a limited water reservoir. Following a classical penetration scaling with the square root of time, the progression continues slowly. The addition of sand minimally impacts these kinetics, only modifying the porosity volume. Imbibition front kinetics is described by analyzing unsaturated flow under limited water conditions, particularly in scenarios where water availability is restricted. The study underscores the importance of investigating imbibition under finite water amounts, a common degradation scenario. The physical understanding aims to contribute to the enhanced design of earthen plaster.

Understanding the stiffness of a concrete structure is crucial to analyze it, particularly for statically indeterminate structures. Stiffness degradation – commonly referred to as damage – occurs with the onset of cracking or large compressive strains. For most conventional and specialized types of concrete, damage studies and models for predicting damage development are available. However, more information is needed about the damage behavior for the most common steel fiber reinforced concrete in Europe with strength class C30/37 and modern end-anchored high-strength fibers in dosages of 20–40 kg/m³. Therefore, in this study, these common steel fiber concretes were subjected to multiple load cycles in (1) uniaxial compression tests on cylinders and (2) direct tensile tests on bone specimens to investigate their damage behavior. The resulting damage was then compared to known damage laws, but none of the models predicted accurate damage results. Finally, an existing damage law for plain concrete was modified as a function of the residual flexural tensile strength—the relevant parameter for describing the performance of the steel fiber reinforced concrete. Hereby, we were able to decisively improve the agreement between experimental results and the theoretical prognosis by utilizing our modified damage law.

Compressive strength of grouted concrete masonry is an important parameter to design reinforced/grouted concrete masonry walls. The design standards stipulate two methods to determine the compressive strength of masonry (1) using tabulated unit strength and mortar type, and (2) testing representative masonry prisms. The compressive strength prediction of grouted concrete masonry is influenced by compressive strength values of hollow blocks, mortar and grout, and their geometries. Therefore, a multi-level approach was employed in this study to improve the existing unit strength correlations of the standards for more reliable prediction of compressive strengths of grouted concrete masonry. The existing methods to determine the compressive strength of grouted masonry were critically appraised and a database of compression tests of grouted concrete masonry prisms/wallettes was developed. This database was then used to evaluate the correlations between the compressive strengths of block, mortar, grout and masonry. The applicability of existing unit strength correlations from the design standards and literature were assessed and their relevancy and limitations are highlighted. Subsequently, updated sets of unit strength correlations are proposed in this study, through statistical reliability analyses of the predictions against the experimental results included in the database. The proposed unit strength correlations were classified according to the mortar type/strengths (≤ 10 MPa and > 10 MPa). It has been shown that the new correlations are more structurally reliable than the existing unit strength correlations through comparing the 95th percentile error values.

This article deals with the monitoring of strain on tuffeau, a soft and porous building limestone used in stonework in historical masonry. Previous studies have shown the limitations of using strain gauges for mechanical monitoring, due to the size and local nature of the measurement. The digital image correlation (DIC) technique has proved to be a significant, non-contact and non-destructive method for full-field strain measurements of various materials, including rocks which are natural and therefore heterogeneous. In this work, we studied the DIC parameters and calibration process to identify the best configuration for working with a porous limestone material subjected to mechanical loading. Because of its potential impact on the quality of strain measurement, we also explored the effect of geometry and rectification. While the results provide a set of optimized parameters to get the best out of DIC analysis, they also highlight the importance of rectification on the mechanical behavior of such soft, porous stones.