Materials and Structures最新文献

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.

Physical hardening (PH) is an important factor affecting the low-temperature performance of bitumen. At present, most PH characterizations are performed by the bending beam rheometer. To present an alternative method based on the Dynamic Shear Rheometer (DSR) equipment, this paper explores the possibilities of the 4 mm plate-plate test to investigate PH in bitumen. A variety of binders was selected, differing in their content of natural waxes, in crude origin, and production procedure. An aged sample was also included. The results show that a 20 min equilibrium period is sufficient to stabilize the sample temperature. To evaluate the PH, a time follow-up of 4 h was selected, as after 4 h the change in slope of complex modulus versus time drops below 1%. Further conclusions show that the physical hardening index (PHI) of bitumen is temperature- and frequency-dependent. This PHI is largest at 0 °C and increases when tested at lower frequencies. The non-waxy binder had almost no hardening, while the waxy binders showed evident hardening. Although the presence of wax is an important factor, the PHI of these binders is not directly related to the total wax content, which was determined by differential scanning calorimetry. In conclusion, the findings show that 4 mm DSR tests provide an effective approach to characterize PH of bitumen.

Graphical abstract

Ferrochrome slag (FS) having favourable mechanical properties) may be gainfully utilised as concrete aggregate. The concrete specimens with FS, natural stones (NS) and NS concrete mixed with 2% chromium nitrate salt (CR) as coarse aggregate were prepared. The samples were cured in aggressive curing solution like sulphuric acid solution at pH 2 and 10% magnesium sulphate in order to examine its degradation aspects in terms of possible loss of strength, reduction of mass and the surface damage. The deterioration effects are assessed after 28, 56, and 90 days of curing. The results indicate that FS concrete has the minimum reduction of strength, least reduction of mass and less surface deterioration in comparison to concrete with NS and CR. FS has appreciable amount of environmentally deleterious residual chromium but almost all of these chromium contents are inherently immobilized in the slag matrix as evidenced in microstructure study. The concrete specimens using FS as coarse aggregate with its immobile chromium acting as passivation agent may provide better corrosion resistance and along with the usage of slag-based cement as binder furnish some protection measures against the corrosion effect under aggressive acid and sulphate action. This is the principal research significance of this work and it will provide a suitable platform for global research to explore the further work on the corrosion resistance of concrete bound FS exposed to different aggressive curing environment.

This study aimed to investigate the influence of the internal friction angle on the mechanical properties and resistance to permanent deformation of asphalt mixtures. Permanent deformation, resulting from vehicular loads, can occur due to densification, use, and flow of the mixture. Considering that the asphalt mixture behaves as a solid material at service temperatures of 40 °C to 60 °C, the Mohr–Coulomb criterion, commonly used to describe shear characteristics of solid materials, was employed to determine the internal friction angle and cohesive intercept of the mixture. An experimental program was devised to assess the mechanical properties associated with the internal friction angle of asphalt mixtures with asphalt binders of the types Petroleum Asphalt Cement with a penetration grade of 50/70 (PAC 50/70) and Petroleum Asphalt Cement modified with styrene–butadiene–styrene (SBS) polymer (E-55/75). Laboratory analyses were conducted to determine shear rupture parameters, using the Mohr–Coulomb theory. It was observed that an increase of 5% in coarse particles resulted in an average gain of 1° in the internal friction angle for each studied gradation range, up to the limit of 30–35% of coarse particles for each mixture. The results indicated that shear rupture parameters, especially the internal friction angle and cohesive intercept, play a crucial role in the resistance to permanent deformation of asphalt mixtures. It was concluded that an increase in the internal friction angle contributes to greater resistance to permanent deformation, providing valuable insights for optimizing the composition of asphalt mixtures in terms of mechanical performance.

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.

This paper re-examines common notions and conventions regarding the compressive strength of concrete in general and of the uniaxial compressive strength of concrete in particular. A distinction is introduced between the strength of the specimen and the strength of the concrete as a material, and the commonly measured and adopted strength is shown to be the specimen’s strength, wrongly interpreted as the material’s strength. the two major damage modes of concrete specimens (with the formation of either longitudinal cracks or shear bands) are discussed. Such failure modes are wrongly considered as features of concrete behavior in uniaxial compression, but this is not the case. Longitudinal cracking is due to lateral expansion (Poisson’s effect) and occurs at a relatively low applied load in absence of friction at specimen’s top and bottom boundaries. Shear failure (accompanied by the formation of an inclined shear band) is related to the shear envelope parameters that are related to the concrete mixture, but the applied ultimate pressure is not the concrete uniaxial compressive strength. Hence, though caused by applied compressive loading, these failure modes are little/hardly related to the concrete material intended as the ultimate uniaxial stress (strength) corresponding to a maximum value of the uniaxial compressive strain. Using the shear envelope parameters has been proven to yield a very good prediction of the applied compressive loading of the specimen in the limit state, as a demonstration that the applied pressure at specimen’s failure resulting from the formation of inclined fracture bands is the specimen’s failure strength, and not the material’s compressive strength! Reasons are given against the existence of a uniaxial compressive strength failure for concrete, and a piece of evidence in this direction is provided by concrete specimens subjected to pure hydrostatic compression, that do not fail at all. The entire issue requires, therefore, a deep revisiting and re-thinking, to provide correct measures for representing concrete response under compression in analysis and design.

Ultra-high-performance fiber-reinforced concrete (UHPFRC) is applied to joint nodes with its excellent mechanical properties, which helps to improve the force transfer performance of UHPFRC structures. The strength of the connections is dependent on the adhesion and friction between the connected materials in the bridge design procedure. This research aims to identify the adhesion performance between UHPFRC and UHPFRC under different interfacial roughening methods. To this end, the maximum tensile stress and the load–displacement curves of UHPFRC wet joints treated by high-pressure water jet roughening, uniform plastic formwork roughening, embedded wire mesh roughening, manual mechanical roughening, and epoxy resin were obtained via direct tension tests. The test results indicate that the bond strength of UHPFRC wet joints can reach 22.36%-68.06% of the tensile strength after different interfacial treatments, among which the roughening methods using high-pressure water jet significantly improve the bond performance of UHPFRC wet joints, followed by the roughing method of uniform plastic formwork and embedded steel wire mesh. Physical roughening treatment has less effect on the stiffness of UHPFRC wet joints and exhibits a typical brittle failure mode. A tensile constitutive model in the elastic phase of the UHPFRC wet joint interface and the simplified interfacial tensile stress-relative displacement model were proposed. Finally, the performance of the interfacial adhesion parameters was appraised by finite element modeling. The finite element analysis showed a good agreement with the experimental results.

The setting behavior of ultra-high performance concrete (UHPC) is demonstrably different from that of conventional concrete; thus, tools and guidance extending beyond common test methods such as Vicat and penetration are needed. While UHPC is known for its enhanced mechanical and durability properties, due to the low water and high cementitious contents, UHPC-class materials are prone to early-age autogenous shrinkage. Recognizing that UHPCs are commonly supplied to construction sites as prebagged, proprietary mixes with unknown constituents, and that accurate determination of setting time is crucial in determining the early-age autogenous shrinkage of UHPC-class materials as well as for scheduling construction operations and quality control actions, this study explores alternate test methods such as isothermal calorimetry (ASTM C1679), semi-adiabatic calorimetry (ASTM C1753), autogenous shrinkage (ASTM C1698), chemical shrinkage (ASTM C1608), and dual ring test (American Association of State Highway and Transportation Officials (AASHTO T 363) to evaluate the setting behavior of UHPCs. Setting times obtained using the alternate test methods aligned well with each other and were found to be different than the setting times indicated through standard test methods. Discussion and guidance on the applicability and the use of alternate test methods to determine the setting time of UHPCs for various laboratory and field applications are provided.

This paper investigates the durability performance of mortars with varying replacement levels of dolostone or limestone filler (0–30% by mass) and the stability of mortars with dolostone filler for 2 years. Compressive strength, total porosity, capillary water absorption, and chloride migration coefficients were determined. Results show that compressive strength decreases and the total porosity increases with increasing filler content due to a dilution effect, regardless of the filler composition. The capillary water absorption and the chloride migration coefficients rise significantly for mortars with 20–30% filler. However, the dolostone filler cements have lower chloride coefficients than those with limestone blended cement. Volumetric stability assessments reveal no significant expansion, and XRD and FT-IR analyses suggest the formation of hydrotalcite-like phases.