Monolithic Behavior Research Articles

Exploring the Photophysical and Mechanical Behavior of Fluorescent Metal-Organic Framework Monoliths.

Luminescent metal-organic frameworks exhibit great potential as materials for nanophotonic applications because of their programmable properties and tunable structures. In particular, luminescent guests (LG) can be hosted by metal-organic frameworks due to their porosity and guest confinement capacity, forming LG@MOF composite systems. However, such guest-host systems are mainly produced as loose powders, preventing their widespread use in practical devices and technological applications that require implementation of a stable continuum solid. In this regard, using monolithic MOF hosts might be a workable option to solve this challenge. Herein, we reported the facile synthesis and fabrication of novel prototypical sol-gel monolithic systems, designated as LG@monoMOF. Red (rhodamine B), blue (7-methoxycoumarin), and yellow (fluorescein) emitting dyes were encapsulated in a robust UiO-66 monolithic host, resulting in the red, blue, and yellow light-emitting luminescent monoliths. The mechanical and photophysical characterization of the three LG@monoMOF systems was systematically carried out in order to unravel the role of guest-host interactions in the mechanical and optical response of the bespoke LG@monoMOF composites.

Effect of steel fibers on the interfacial shear strength of flyash and GGBS based geopolymer concrete activated with water glass

Concrete, a fundamental construction material, heavily relies on cement, manufacturing process of cement results in significant CO2 emissions, posing environmental concerns. Hence, exploring substitutes for cement becomes imperative to mitigate CO2 emissions. Geopolymer materials emerge as promising alternatives capable of entirely replacing Ordinary Portland Cement (OPC). However, these materials necessitate activators to initiate the polymerization reaction. While Na2SiO3 and NaOH are commonly utilized as activators, their cost-effectiveness is questionable. Moreover, when Ground Granulated Blast Furnace Slag (GGBS) reacts rapidly with these activators. To address these issues and streamline concrete production, “water glass” is employed as an activator, offering a solution to avoid rapid setting and economize the production process. In other hand the production of mass concrete structures, interfaces and joints critical points where cracks may develop. To ensure monolithic behavior, shear ties were advised at the interface in order to establish strong bond strength. However, the efficiency of construction could be decreased by adding more shear ties. The purpose of this study is to evaluate the interfacial shear strength of Geopolymer concrete (GPC), With the addition of different percentages of steel fibers 0.5, 1%,and 1.5%, with shear ties at the interface of push-off specimens. The findings reveal that it is viable to replace two shear ties with one 8 mm-2L shear tie and 1% crimped steel fibers of 30 mm length.

Experimental response of semi-rigid reinforced concrete beam-column joints with bolted angle dissipating connections

Accelerated building construction is a challenge and opportunity for modern construction techniques such as prefabricated building. However, insufficient connection detail for precast structures resulted in serious damages (even collapse) in past earthquake, which significantly hit the further development of prefabricated building. With satisfactory seismic performance and minimal residual displacement, self-centering joint is an excellent alternative with respect to traditional prefabricated joint. In self-centering system, bolted connections are sufficiently utilized as energy dissipation system. However, the information about connection details is quite limited. Thus, a comprehensive experimental study was conducted to characterize the seismic behavior of semi-rigid reinforced concrete (RC) beam-column joints with bolted angle dissipating connections, namely, semi-rigid joints. Ten full-scale semi-rigid joints were tested under cyclic loading, taking the connection detail as variable. The main configurations of semi-rigid joints based on Eurocode 3 were angle thickness, angle stiffener, bolt diameter, column bolt gauge, rows of beam bolts, and grouting of beam bolts. The test results showed that, by adopting the ductile connection concept, it was possible to produce high ductility and abundant energy dissipation, control damages within the connection zone, and even achieve equivalent monolithic behavior through mobilizing a sufficient rigidity. Feasibility of replacing the damaged connection with a new one with the identical or higher capacity thus obtaining the equivalent or better performance with respect to the original tested joint is also evaluated. Finally, a theoretical model was proposed to evaluate the initial stiffness and bearing capacity of the joints. A good correlation was achieved as comparing to the test results. This research provides significant insight into the performance of precast semi-rigid joints and offers essential data for further investigation of developing design-oriented procedures.

Experimental study of GFRP stiffened plates with and without large opening under combined axial and pressure loading

GFRP stiffened panels forms the basic component of ship hulls, decks, submarines, offshore oil platforms etc., GFRP stiffened panels used in ship hulls and decks are subjected to axial loading due to buoyancy and pressure loading due to cargo. GFRP stiffened plate dimensions considered in this study are the scaled down dimensions of a cargo ship. Aluminium moulds with and without opening are fabricated for casting GFRP stiffened panels. GFRP stiffened panels with integral stiffeners are manufactured using hand lay-up process. A unique lay-up pattern was adopted to achieve the monolithic behaviour of stiffeners and plate. Fabrication of GFRP stiffened panels by manual hand layup process leads to formation of indentations. These imperfections are determined using the LVDTs attached to imperfection measurement setup. The measured imperfections are compared with the allowable imperfection values available for steel in BS 5400, because limiting imperfection values are not available for FRP. Openings are necessary for access and maintenance in ship hulls, decks etc. The presence of openings can lead to loss in strength and stiffness of the GFRP stiffened panels. In this study, GFRP stiffened panels with and without opening are tested for different combinations of axial and pressure loading. Axial loads are applied using two hydraulic jacks and measured using two load cells which are fabricated to prevent eccentricity while applying axial load. Pressure loads are applied using inflatable air balloons with and without opening fabricated for this study. Load capacity, failure strain, failure patterns of GFRP stiffened panels under different load combinations are presented. Failure locations of GFRP stiffened panels with and without opening various load combinations are discussed. Reduction in load capacity, span to deflection ratio and loss in stiffness due to opening is calculated.

Nanostructure-dependent indentation fracture toughness of metal-organic framework monoliths

Monolithic metal-organic frameworks (MOFs) represent a promising solution for the industrial implementation of this emerging class of multifunctional materials, due to their structural stability. When compared to MOF powders, monoliths exhibit other intriguing properties like hierarchical porosity, that significantly improves volumetric adsorption capacity. The mechanical characterization of MOF monoliths plays a pivotal role in their industrial expansion, but so far, several key aspects remain unclear. In particular, the fracture behavior of MOF monoliths has not been explored. In this work, we studied the initiation and propagation of cracks in four prototypical MOF monoliths, namely ZIF-8, HKUST-1, MIL-68 and MOF-808. We observed that shear faults inside the contact area represent the main failure mechanism of MOF monoliths and are the source of radial cracks. MIL-68 and MOF-808 showed a remarkably high resistance to cracking, which can be ascribed to their consolidated nanostructure.

Experimental Seismic Structural Performance Evaluations of RC Columns Strengthened by Stiff-Type Polyurea

Recently, strong earthquakes are continuously occurring all over the world regarding, repair and strengthening of non-seismically designed structures. Presently, fiber-reinforced polymer (FRP) surface-bonding method is used as a quick and easy way to retrofit and strengthen damaged columns and walls. However, the inherent problems of the FRP surface-bonding method of bond degradation are adhesive interfaces and FRP sheet aging during service-life still. In order to overcome these problems, it is necessary to develop new materials and techniques that can induce monolithic behavior between the structural member and retrofit material by eliminating the bonding interface. One solution is to use repair and strengthening using stiff-type polyurea (STPU) developed as a seismic retrofitting material which can be applied by spraying method. In order to investigate the retrofitting effect of STPU, pseudo-dynamic push–pull test and dynamic shaking table tests are performed. The novelty of the study is that the RC columns strengthened with a newly developed STPU are tested for pseudo-dynamic (i.e., also represents the static behavior) and dynamic behavior. From the test results, overall strengthening effect of the STPU for both static and dynamic loading conditions can be understood, which can be used for retrofitting of concrete structures all over the world. The study results are discussed in detail in the paper.

Automatic strength assessment of the virtually modelled concrete interfaces based on shadow-light images

The interface between concrete layers cast at different ages is present both in new construction, e.g., precast beams with cast in place decks, and in rehabilitation, e.g., jacketing of existing beams and columns. The interface strength ensures the element’s monolithic behaviour. This strength is mainly determined by the interface surface roughness. Unlike other material parameters, the interface strength is accessed with deterministic parameters (cohesion and friction) making design dependent on their correct assessment. Within this framework, the research study herein described aims to find non-deterministic parameters of the interface strength and an automatic method for their evaluation. The proposed parameters are derived from best-fit geostatistical models for roughness. These parameters are neither deterministic nor used for roughness and strength evaluation but they describe natural phenomena well. The automatisation is obtained via the deep learning process of the interface texture and strength. Since this process requires huge and not available data, real sources of data (i.e. surfaces) are substituted with the virtual Gaussian models generated with the geostatistical parameters obtained from the real surfaces. A similar process can be applied to the strength data if available in sufficient numbers. For short, the paper presents the application of the geostatistical parameters to the evaluation of both surface texture and strength of concrete to concrete interface, which have not been used before. It is shown that these parameters can be used to ‘store’ surface data in a compact form and subsequently texture or strength virtual reproduction is possible making deep learning and automatisation possible to perform.

Boron-dependent self-healing behavior and mechanical properties of polymer-derived amorphous SiBCN monoliths

The pyrolysis characteristics of precursors, mechanical and anti-oxidation properties of the resulting amorphous SiBCN monoliths with different boron contents were investigated. An increase of boron content results in the decrease of ceramic yields, bulk densities, open porosities and mechanical properties of SiBCN monoliths. The boron-lean SiBCN monolith has the highest hardness and elastic modulus of 13.85 GPa and 142.65 GPa, respectively, due to the presence of more high-energy Si–N and Si–O bonds, and the promoted structural rigidity of the network with more C–B and B–N bonds. The boron-moderate and boron-rich SiBCN monoliths show a better self-healing performance at 1350 °C oxidation in spite of porous oxide scales. The oxide scales exhibit a parabolic growth law with rate constants of 0.22, 6.40 and 10.65 μm 2 /h for boron-lean, boron-moderate and boron-rich SiBCN monoliths, respectively.

Influence of Steel Fibers on the Interfacial Shear Strength of Ternary Blend Geopolymer Concrete Composite

Sustainable development is a major issue confronting society today. Cement, a major constituent of concrete, is a key component of any infrastructure development. The major drawback of cement production is that it involves the emission of CO2, the predominant greenhouse gas causing global warming. The development of geopolymers has resulted in a decrease in cement production, as well as a reduction in CO2 emissions. During mass concrete production in the construction of very large structures, interfaces/joints are formed, which are potential failure sites of crack formation. Concrete may interface with other concrete of different strengths, or other construction materials, such as steel. To ensure the monolithic behavior of composite concrete structures, bond strength at the interface should be established. The monolithic behavior can be ensured by the usage of shear ties across the interface. However, an increase in the number of shear ties at the interface may reduce the construction efficiency. The present study aims to determine the interfacial shear strength of geopolymer concrete as a substrate, and high-strength concrete as an overlay, by adding 0.50%, 0.75%, and 1% crimped steel fibers, and two and three shear ties, at the interface of push-off specimens. It was found that three shear ties at the interface can be replaced by two shear ties and 0.75% crimped steel fibers. In addition, a method was proposed to predict the interface shear strength of the concrete composite, which was found to be comparable to the test results.

Experimental testing correlation of the different aged concrete bond strength involving the new tilted cube test (TCT)

The bonding behavior of concrete repairs is highly dependent on the type of applied stresses. The slant shear test is mutually applied in the bonding investigations for its roughness sensitivity and for being a compression shear test indicating the actual members’ state. Cohesive failures are recommended to ensure monolithic behavior; however, adhesive failures are needed for bonding investigations. To better compare the test results, a modified slant shear test was previously developed with an enforced adhesive failure using larger reinforced prisms. This paper presents an application of a newly developed compression shear test with an enforced adhesive failure of unreinforced normal size tilted cubes. The bonding behavior was investigated under different bonding agents, substrate moisture conditions, interface surface roughness, and testing types. A testing correlation was presented between the tilted cube, slant shear, bi-surface shear, and pull-off tests. Since the ACI acceptance criterion for the slant shear test was found more suitable for the concrete repairs of higher than 45 MPa compressive strength, an improved acceptance criterion was presented and classified according to the concrete grade. Moreover, the previously developed pull-off bond strength qualification was extended using the obtained testing correlation of this study to include all the applied testing types. Citing the relevant studies; the obtained test results validated the tilted cube test for investigating the bonding behavior, where the test specimens of SSD, epoxy adhesive, and wire-brushed interfaces presented higher bond strength results.

Efficiency of Strengthening Interventions on Stone Masonry Panels through Grout Injection and FRCM

Fiber Reinforced Cementitious Matrices (FRCM) represent a very efficient strengthening solution for the retrofitting of masonry structures. When dealing with stone masonry walls, the use of these composite materials is usually combined with grout injection, which can be crucial to ensure a monolithic behavior of the structural element. The objective of this research was the study of the shear behavior of stone masonry samples subject to grout injection and strengthened by two different FRCM systems. Nevertheless, on few samples, grout injection only was performed. Before the execution of the diagonal compression tests, sonic tests were conducted with the objective of evaluating the quality of the grout injection. The Digital Image Correlation technique was also adopted to accurately measure the thickness of the FRCM layers, which can be variable according to the irregular surface of the stone masonry. The results of the experimental campaign showed that the correct execution of the grout injection is crucial for the strengthening solution to be effective since the efficiency of the FRCM system can be reduced if a monolithic behavior of the stone masonry panels is not ensured. The application of the FRCM strengthening system could influence the failure mode, further enhancing the capacity of the samples. Comparisons between the experimental results are presented in the paper.

Evaluating the Seismic Capacity of an Existing Maillart-Arch-Type Bridge: Case Study of Viadotto Olivieri

This paper deals with the seismic assessment of an existing Maillart-arch-type bridge. The evaluations concern a still-in-use deck-stiffened concrete arch bridge, the Viadotto Olivieri (Salerno, South Italy): it’s an r.c. deck-arch bridge having a permanent-to-live loads ratio of 6:1. The seismic characterization has been supported by various FEM models. Multiple accurate analyses have been necessary to exploit effectively the potentials of this structural scheme before evaluating any possible retrofit strategies. With this aim, different schemes were checked, changing deck configurations and restraints at the base. The bridge has been modeled in a realistic way, using shells and beams. A preliminary linear analysis has been performed that consisted of applying a total horizontal force equal to 10% of the bridge’s permanent loads in both plan directions. This displayed the most vulnerable elements, which were later also confirmed by modal outputs. The response spectrum analysis, assuming the seismic parameters of the site, showed that the highest effects occur for translational local modes in which only a few macro-elements are involved (monolithic behavior). The results also demonstrate the good performance of the Maillart-arch scheme in counteracting seismic loads.

Application of neuro-fuzzy estimation in prediction of shear bond strength between concrete layers through the efficient laser roughness analyzer

To ensure the monolithic behavior of reinforced concrete composite parts, the bond strength at the interface between concrete layers cast at various ages must be high. Reinforced concrete composite members include precast beams with cast-in-place slabs, bridge decks strengthened by adding a new concrete layer, and repair and strengthening of existing concrete structural members by adding a new concrete layer. in this study, the shear bond strength (SBS) of reinforcing steel on Portland cement and a hybrid cement including slag and Portland cement activated with sodium carbonate is investigated. The pull-out test was used to determine SBS; also a subsequent test data is evaluated using ANFIS, as well as surface classification utilizing a laser roughness analyzer designed particularly to assess the roughness of the concrete substrate. As a result, this research tried to create an in situ non-destructive approach for assessment of concrete surfaces and its influence on shear bond strength measurement of the concrete layers. All test data is analyzed using an adaptive neural fuzzy inference system (ANFIS) to classify the different input variables for determining the shear bond strength between concrete layers using the mean and maximum surface roughness (SR) height parameters Ra and Rt in X and Y direction. ANFIS was used to optimize the process based on five processing parameters. Skillful prediction could play a pivotal role in the optimal conditions during laser cutting process. Based on results, laser speed is the most influential on the Ra in X and Y direction (RMSE: 0.3255, RMSE: 0.6869, respectively). The most influential parameter on the Rt in X direction is laser power (RMSE: 1.5611), while the most influential parameter on the Rt in Y direction is laser speed (RMSE: 2.0781), resulting that the roughness of the substrate surface highly affects the shear bond strength of concrete interfaces.

A method for considering the influence of distinct casting stages in the flexural design of prestressed concrete cross sections

ABSTRACT Composite elements are structures of concrete, or other materials, constructed in different casting stages that act jointly under external loads. These elements are used when it is intended to combine the constructive advantages of precast structures with the monolithic behavior of cast-in-place structures. In regular civil engineering applications, such as the construction of a bridge or viaduct, the precast section is used as shoring before casting the slab in place. This process leads to imposed deformations prior to the ultimate limit state and a discontinuity in the specific strain of the composite cross section. This work proposes a methodology to design composite cross sections, built in two casting stages, evaluating the specific strain provided the construction process that can be easily implemented in precise computational routines. From applying the methodology on study-case numerical example, it is observed that the beam casted in two stages presents a factored moment resistance smaller than an identical beam casted in a single stage. However, further investigations should be conducted to assess the extent of this difference.

Hysteresis behavior of precast concrete composite shear walls with improved vertical connections

Precast concrete composite shear walls (PCCSWs) is a new type of precast shear wall with single- or double-layer precast panels and a cast-in-place (CIP) concrete layer (i.e., precast single wall, PSW, or precast double wall, PDW). PCCSWs could form a solid concrete structure with a shorter superstructure construction time. Therefore, these walls have become a promising precast concrete structural system for high-rise buildings worldwide. The objective of this study was to investigate the hysteresis behavior of PDWs and PSWs with improved vertical connections from the perspectives of efficiency in load transfer and simplicity in construction for applications in seismic zones. Low-reversed cyclic testing was conducted for six full-scale PCCSWs with two different axial load ratios (0.09 and 0.23). The six walls included four PDWs with two types of vertical connections (double-row spiral-confined lap connection and single-row protruding rebar lap connection) and two PSWs with a spiral-confined lap connection. The results revealed that the specimens exhibited monolithic behavior and flexural-shear failure, as expected. The difference in load capacity between the PCCSWs and CIP walls was less than 10%. All the walls had plump hysteresis loops and adequate energy dissipation performance. PDWs with the double-row spiral-confined lap connection had the highest ductility ratio (4.57 for the low axial ratio, 3.50 for the high axial ratio). The single-row protruding rebar lap connection enabled the PDWs to demonstrate relatively good ductile behavior (3.85 for the low axial ratio and 3.39 for the high axial ratio) and simple on-site construction. Although the PSWs had the lowest ductility, the ductility was comparable to that of the CIP wall with low and high axial ratios. All the specimens had a similar tendency in terms of the backbone curves and stiffness degradation. Accordingly, a trilinear degraded restoring force model was developed for different PCCSWs by regression.

A comparative study on high temperature oxidation behavior of SiC, SiC-BN and SiBCN monoliths

In this study, the oxidation behavior and mechanism of SiBCN monoliths were compared with SiC and SiC-BN monoliths. At 1100–1300 °C, the oxide layers of SiC and SiBCN monoliths were relatively smooth and dense, while that of SiC-BN monoliths were destroyed by many bubbles. Further oxidized at 1500 °C, some cracks and bubbles appeared on the surfaces and interfaces of SiC-BN monoliths. The oxidation of SiC phases was thermodynamically unstable than that of C and BN, but the oxidation of BN and/or C occurred preferentially after considering the kinetic factors. BN(C) phase has a positive role on SiBCN oxidation resistance. Data availabilityThe raw/processed data required to reproduce these findings cannot be shared at this time due to legal or ethical reasons.

Preliminary Investigation of the Mechanical and Physical Properties of Natural Hydraulic Lime Grouts with Nano-Silica

Natural hydraulic lime-based grouts are often used in the structural consolidation of old stone masonry walls, mainly to re-establish the monolithic behaviour of masonry constructions. To ensure an adequate grouting operation, it is essential to have good fresh and hardened grout properties. The motivation of the present study was to examine the fresh and hardened properties of natural hydraulic lime grouts with nano-silica (NS) and silica fume (SF). The contribution of these materials and the dosage of a high range water reducer admixture (HRWR) were investigated on the rheological properties, water capillarity, open porosity and mechanical strength of injection grouts. The effects on rheology were analysed through plastic viscosity and yield stress. The results indicated that, even for reduced NS content, an increase in plastic viscosity and yield stress occurred, which required a higher HRWR content in order to not compromise the grout’s rheological performance. The results also showed that, when NS and SF were combined, a beneficial joint effect occurred, resulting in a substantial and positive change on the mechanical strength and microstructure of the hardened injection grouts. Taguchi’s method was used to optimize the grout’s formulation and to fulfil the required performance concerning the fresh and hardened state.

Cyclic behavior of beams rehabilitated by reinforced concrete layers

AbstractOne of the well‐known methods for rehabilitation of insufficient or damaged reinforced concrete (RC) beams is to add a new RC layer. Although RC beams strengthened or repaired in this way have proved themselves under monotonic and repeated loads, the behavior under cyclic loads has not been adequately investigated yet. In this experimental research, beams were strengthened, repaired, or revived (repaired after heavy damage) using familiar RC layer adding methods and tested under reversal cyclic loading. Ten half‐scaled specimens, composed of columns and a beam, were prepared and 18 tests were conducted on these specimens. The obtained results showed that the strengthened and repaired beams mostly could achieve the monolithic behavior. However, sufficient ductility could not be maintained for the revived ones.

Simple Moment Analysis for a Kinetic Study of the Chromatographic Behavior of Spherical Particles and Silica Monoliths.

A simple procedure of moment analysis was proposed for a kinetic study of the rate processes in the columns packed with full-porous spherical particles and silica monoliths. Previous chromatographic data measured in reversed-phase HPLC systems using Mightysil and Chromolith columns were analyzed by a simple moment analysis. The surface of the packing materials is chemically modified with octadecyl alkyl ligands. A mixture of methanol and water (80/20, v/v) and alkylbenzene homologous series (C6H5CnH2n+1, n = 0 - 7) were used as the mobile-phase solvent and sample probes, respectively. More detailed information about the experimental conditions is provided in Supporting Information. The values of the intra-stationary phase diffusivity (De) and the surface diffusion coefficient (Ds), derived by the simple moment analysis, were almost the same as those by the conventional moment analysis. The simple moment analysis is effective for quantitative studies of mass transfer in chromatographic systems. The previous chromatographic data were also analyzed by assuming external porosity (εe) as typical values, i.e., 0.40 for spherical particles and 0.70 for silica monoliths. The resulting values of De and Ds were of the same order of magnitude as those derived by using εe experimentally measured. Even if εe is assumed to be typical values, the simple moment analysis is effective for preliminary studies of the mass-transfer kinetics in the columns.

WITHDRAWN: Portrayal of contact and consolidation grouting surrounding HRT lining: A study

Abstract Construction of tunnels through naturally fragile, weak and sheared rock masses is a challenging task for engineers, planners, designers and geologists. The presence of discontinuities like folds, faults, voids, number of shear zones, highly changing geological conditions with thick vegetative cover and over burden pose threat to construction activities in frail and fragile rock mass. These discontinuities get further separated and more widened as the excavation of tunnels involve drilling and blasting operations and do not allow the rock mass to behave monolithically. Proper grouting of the surrounding rock mass around the opening ensures the monolithic behavior of the rock mass. Contact grouting or back fill is required for filling of spaces between concrete lining or steel lining and shattered surface of the parent rock. Consolidation grouting in tunnels is essential to reduce the co-efficient of permeability and for strengthening the rock mass by filling up the open joint cracks. This paper deals with the proper grouting of the surrounding shattered, sheared and fragile rock mass around the power tunnel lining to ensure its monolithic behavior.