Durability Problems Research Articles

Release of Interface Confined Water Significantly Improves Dentin Bonding

Water residue and replacement difficulty cause insufficient adhesive infiltration in demineralized dentin matrix (DDM), which produces a defective hybrid layer and thus a bonding durability problem, severely plaguing adhesive dentistry for decades. In this study, we propose that the unique properties of a highly hydrated interface of the porous DDM can give rise to 1 new type of interface, confined liquid water, which accounts for most of the residue water and may be the main cause of insufficient infiltration. To prove our hypothesis, 3 metal ions with increasing binding affinity and complex stability (Na+, Ca2+, and Cu2+) were introduced respectively to coordinate negatively charged groups such as -PO43−, -COO− abundant in the DDM interface. Strong chelation of Ca2+ and Cu2+ rapidly released the confined water, significantly improving penetration of hydrophobic adhesive monomers, while Na+ had little effect. A significant decrease of defects in the hybrid layer and a much decreased modulus gap between the hybrid layer and the adhesive layer greatly optimized the microstructure and micromechanical properties of the tooth–resin bonding interface, thus improving the effectiveness and durability of dentin bonding substantially. This study paves the way for a solution to the core scientific issue of contemporary adhesive dentistry: water residue and replacement in dentin bonding, both theoretically and practically.

Exploring Exact Effects of Various Factors on Chloride Diffusion in Cracked Concrete: ABAQUS-Based Mesoscale Simulations

Chloride ion attack is a major cause of concrete durability problems, and existing studies have rarely addressed the effects of damage zones. In this paper, an improved mesoscale model including five phases was constructed using the finite element software ABAQUS to study the diffusivity of chloride ions in cracked concrete. It was found that the damage zone is negligible when the crack width is less than 50 μm, while the width and depth of the damage zone are about 15 times the crack width and 15% of the crack depth when the crack is greater than 50 μm. The results show that the diffusion of chloride is greatly influenced by the crack width, while it is little-influenced by the crack shape. Low water-cement ratio and adequate hydration of the concrete are also key factors affecting chloride diffusion. In contrast, regular rounded aggregates have a positive effect on reducing chloride diffusion compared to irregularly shaped aggregates, and this effect becomes weaker with increasing service time. In addition, the protective layer can effectively prevent the diffusion of chloride in concrete. Therefore, when designing marine concrete, efforts should be made to ensure that the concrete has a low water-cement ratio, adequate hydration, less cracking and a protective layer.

Hygrothermal performance optimization of lightweight steel-framed wall assemblies in hot–humid regions using orthogonal experimental design and a validated simulation model

As a layered construction, lightweight steel-framed (LSF) wall assemblies are applicable to different climates and used worldwide. Due to ill-informed construction and material designs, moisture-related durability problems occur, especially in hot–humid areas. Here, a hygrothermal simulation model of typical LSF wall assemblies was validated, and the influences of six construction layers (each with three sets of parameters) on the overall properties and performance were investigated via orthogonal experimental design (OED). Each layer exhibited various impact trends and contribution ratios at different positions. To reduce moisture risks, LSF wall assemblies should generally prevent the infiltration of outdoor moisture as much as possible while strengthening the inward drying capacity. The optimal configuration should comprise multiple water and vapour barriers with a ventilated layer, external insulation, permeable cavity insulation and interior sheathing board with a finish. Finally, this optimization method comprising the hygrothermal simulation and OED techniques could be applied to the hygrothermal performance of LSF wall assemblies under certain climatic conditions.

Characteristic of solid-ferrofluid triboelectric nanogenerator for ultra-low-frequency vibration energy harvesting

Durability problems caused by friction loss have restricted the development of a solid-solid triboelectric nanogenerator, which has provided an opportunity for the solid-liquid triboelectric nanogenerator. Ferrofluid has been used in the solid-liquid triboelectric nanogenerators due to its liquid and magnetization properties. In this study, we propose a solid-ferrofluid triboelectric nanogenerator (SF-TENG) for ultra-low-frequency vibration energy harvesting. This SF-TENG can harvest swing vibrations using friction electrification between the polytetrafluoroethylene shell and ferrofluid. To increase the moving speeds of charges, we applied a magnetic field to the SF-TENG to raise the flow velocity of the ferrofluid. The volume of ferrofluid and the magnetic field intensity applied were optimized to enhance the performance of the SF-TENG. We then characterized the SF-TENG by applying frequency swing vibrations of 0.1–0.5 Hz. When the frequency of the input swing was 0.5 Hz, the peak-to-peak value of the open-circuit voltages was 0.98 V, and the maximum instantaneous current was 1.05 nA. In addition, the output power was approximately 1.03 nW, and the power density was 0.0426 mW/m3. The peak output power of the SF-TENG parallel array reached 18.2 nW at the 700 MΩ load resistance. And the capacitor with capacity of 1 μF can be charged to 1.5 V in 150 s.

Effects of using autoclaved aerated concrete block debris as lightweight aggregate on internal curing of concrete

This investigation was carried out to evaluate the effects of using autoclaved aerated concrete (AAC) block debris as lightweight aggregate (LWA) on internal curing of concrete. The volumetric changes during the early period of curing leads to early shrinkage before to the concrete hardening. The formation of internal cracks due to the shrinkage had evidenced the strength and durability problems in concrete during later stage. The higher absorption capacity of LWA has been acted as internal water stored reservoir in concrete and facilitate the supply of water for internal curing to promote the additional hydration. The internal curing effect of pre-wetted AAC debris as LWA on mechanical properties and absorption behaviour of concrete was deliberated as novelty and the investigation was carried out using three different cement contents such as 340 kg/m3, 380 kg/m3 and 420 kg/m3. The granite coarse aggregate was replaced by 10%, 20% and 40% using AAC block debris of the same size by volume. The density reduction of concrete was determined after the addition of LWC. It was found that the AAC block debris can help in increasing the slump value of concrete and enhancing the mechanical properties and the absorption behaviour of concrete on par with control concrete.

Effect of spent bleaching earth ash on sulphate attack resistance of concrete

One of the severe durability problems of concrete is sulphate attack. Sulphate attack can cause expansion of concrete due to the formation of gypsum and ettringite. Recently, spent bleaching earth ash (SBEA) is being used as a partial cement replacement in concrete. In this study, the effects of unground SBEA (USBEA) and ground SBEA (GSBEA) on sulphate attack resistance on concrete in terms of expansion of mortar bar and loss in compressive strength of concrete exposed to 5% sodium sulphate solution were determined. The SBEA was ground in a planetary grinding ball mill for 30 min to obtain a finer particle size. The expansion of mortar bars exposed to sulphate conditions containing USBEA and GSBEA was evaluated for 6 months according to ASTM C1012. Meanwhile, the compressive strength of concrete containing USBEA and GSBEA against sulphate attack was determined at 28 and 90 days. It was found that the expansion of mortar bars containing GSBEA was the lowest (0.01%) among the specimens. The strength deterioration factor of concrete containing GSBEA against sulphate attack was the lowest, with 1.31% at 90 days. The findings showed that ground SBEA could be used to enhance the sulphate attack resistance of concrete.

Nonlinear finite element modeling of bridge piers under the combined effect of corrosion, freeze–thaw cycles, and service load

AbstractCorrosion of reinforcing steel in reinforced concrete (RC) infrastructure is one of the most concerning durability problems affecting its serviceability and ultimate capacity in North America. The rise of greenhouse emissions in recent decades and the use of de‐icing salts during the winter increase the potential risk of corrosion. Furthermore, global warming could lead to higher freeze–thaw cycles (FTC) frequency in cold regions. The combined effects of corrosion and frost damage tend to affect aging RC infrastructure's structural performance and service life. The present study adopts comprehensive reinforcement corrosion and frost damage models from the literature and proposes a stage‐based damage analysis scenario. Three‐dimensional nonlinear finite element analyses using the commercially available finite element program DIANA are conducted to evaluate the structural performance of RC bridge piers under the synergetic effects of FTCs, corrosion, and service load during their service life. The proposed methodology for each damage mechanism is assessed by comparison with available experimental data from the literature. The synergetic effects cannot be validated because there is no data, but the methodology highlights the deterioration rate at which several mechanisms acting at the same time can affect the structural performance of these members.

A Study on Development of New Type Rubber Boot for Sleeper Floating Track System (STEDEF): Materials and Shapes

Urban railway sleeper floating track (STEDEF) reduces the block vibration transmitted to the subgrade structure by structurally separating the sleeper and the concrete bed, using a rubber boot and a resilient pad. Recently, the replacement of rubber boot material (SBR) after long-term wear and tear has become of utmost importance because of durability problems such as deformation, tearing, and abrasion. This study investigates rubber boots—a component of the urban railway sleeper floating track—to resolve these concerns and proposes the material and shape of a novel rubber boot. The proposed rubber boot reduces the maximum displacement and strain by more than 83% and 90%, respectively, compared with the existing rubber boots. In addition, the results of numerical analysis and indoor tests show that type 3 rubber boots can prevent displacement and stress generation in rubber boots.

Ultrathin positively charged electrode skin for durable anion-intercalation battery chemistries

The anion-intercalation chemistries of graphite have the potential to construct batteries with promising energy and power breakthroughs. Here, we report the use of an ultrathin, positively charged two-dimensional poly(pyridinium salt) membrane (C2DP) as the graphite electrode skin to overcome the critical durability problem. Large-area C2DP enables the conformal coating on the graphite electrode, remarkably alleviating the electrolyte. Meanwhile, the dense face-on oriented single crystals with ultrathin thickness and cationic backbones allow C2DP with high anion-transport capability and selectivity. Such desirable anion-transport properties of C2DP prevent the cation/solvent co-intercalation into the graphite electrode and suppress the consequent structure collapse. An impressive PF6−-intercalation durability is demonstrated for the C2DP-covered graphite electrode, with capacity retention of 92.8% after 1000 cycles at 1 C and Coulombic efficiencies of > 99%. The feasibility of constructing artificial ion-regulating electrode skins with precisely customized two-dimensional polymers offers viable means to promote problematic battery chemistries.

NV-SQL: Boosting OLTP Performance with Non-Volatile DIMMs

When running OLTP workloads, relational DBMSs with flash SSDs still suffer from the durability overhead. Heavy writes to SSD not only limit the performance but also shorten the storage lifespan. To mitigate the durability overhead, this paper proposes a new database architecture, NV-SQL. NV-SQL aims at absorbing a large fraction of writes written from DRAM to SSD by introducing NVDIMM into the memory hierarchy as a durable write cache. On the new architecture, NV-SQL makes two technical contributions. First, it proposes the re-update interval-based admission policy that determines which write-hot pages qualify for being cached in NVDIMM. It is novel in that the page hotness is based solely on pages' LSN. Second, this study finds that NVDIMM-resident pages can violate the page action consistency upon crash and proposes how to detect inconsistent pages using per-page in-update flag and how to rectify them using the redo log. NV-SQL demonstrates how the ARIES-like logging and recovery techniques can be elegantly extended to support the caching and recovery for NVDIMM data. Additionally, by placing write-intensive redo buffer and DWB in NVDIMM, NV-SQL eliminates the log-force-at-commit and WAL protocols and further halves the writes to the storage. Our NV-SQL prototype running with a real NVDIMM device outperforms the same-priced vanilla MySQL with larger DRAM by several folds in terms of transaction throughput for write-intensive OLTP benchmarks. This confirms that NV-SQL is a cost-performance efficient solution to the durability problem.

Effect of Expanded Perlite Aggregate Plaster on the Behavior of High-Temperature Reinforced Concrete Structures

Polyurethane-based materials, which are widely used in exterior cladding, pose a great risk for buildings because they can easily catch fire at temperatures as low as 50–65 °C. Thus, different materials are needed to ensure that structures exposed to high temperatures do not have any stability problems. In this study, expanded perlite aggregate plaster (EPAP) was produced to eliminate the negative effects that may occur in buildings exposed to high temperatures. High temperature tests were carried out on test plates of different thicknesses to determine the effect of plaster thickness under high temperatures. In order to compare the effects of high temperatures, a test sample of normal aggregate plaster (NAP), which is widely used in buildings, was prepared. In the high temperature test, the temperature values on the back surfaces of the EPAP (≈115 °C) test plates were approximately 3 times lower than the temperature values of the NAP (≈350 °C) test plate. It can be said that structural stability loss and durability problems may occur in structures covered with NAP in a high-temperature environment, and that no negative effect will occur in terms of structural stability and durability problems in structures covered with EPAP in high temperature environments.

Sulfate resistance of class C/class F fly ash geopolymers

Sulfate attack is one of the significant durability problems for the geopolymer applied for various severe conditions. In this study, the effects of the water-to-fly ash ratio (W/FA), class C fly ash (CF) content, and alkaline content on the setting times and compressive strength of geopolymer pastes were investigated. According to the results, geopolymer samples of three different strength grades (low, medium, and high) were exposed to a 10% magnesium sulfate (MgSO₄) solution at 80 °C. The weight changes, ultrasonic flight-times, and compressive strengths of the specimens were measured to evaluate their sulfate resistances. Control samples were exposed to water at the same temperature. Finally, microstructural analyses using Fourier-transform infrared spectroscopy, X-ray diffraction, and mercury intrusion porosimetry were performed to investigate the corrosion mechanism. The results indicated that higher CF contents led to shorter initial and final setting times and a higher compressive strength regardless of the W/FA and alkaline content. In addition, there was a small weight change for all the geopolymer with different strength grades after they were exposed to an MgSO4 solution. The low strength geopolymer exhibited a better sulfate resistance because of the sustainable increase in the compressive strength and reduction in the ultrasonic flight-time. Moreover, there was a close relationship between the corrosion resistance and the inner structure of the geopolymer mortars. This research provides a theoretical foundation for the application of geopolymers—particularly in coastal and saline areas, which are often subject to sulfate attack.

Research on Performance Deterioration of Internally Cured Pavement Concrete under the Coupling Effect of Salt Freeze-Thaw.

This paper aims at solving the material durability problem caused by spraying deicing salt on pavement concrete in the northern winter. Super absorbent polymer (SAP) was adopted as an internal curing agent to enhance the durability of pavement concrete. Curing parameters including particle size and dosage of SAP and curing condition were optimized based on mortar tests by means of the grey target decision method. The deterioration rule of durability and mechanical properties of pavement concrete internally cured by different SAP dosages after salt freeze-thaw cycles were explored through rapid freeze-thaw test. Combined with the characteristics of pore structure, hydration and microstructure, the influence mechanism of SAP on the salt freeze-thaw resistance of pavement concrete was revealed. The experimental results showed that: (i) The reduction in mass loss rate and relative dynamic modulus was significantly improved by SAP internal curing with moderate dosage; (ii) The more freeze-thaw cycles the specimen underwent, the greater the increase in strength; (iii) After 75 cycles, the chloride ion erosion depth could be decreased by approximately 23.18%. Moreover, the addition of SAP could refine the pore size, inhibit the generation of shrinkage microcracks, and promote the degree of cement hydration in the late stage, which improved the internal density of the cement concrete structure. Therefore, the deterioration of pavement under the coupling effect of salt freeze-thaw was reduced.

Microstructures evolution and chloride migration characteristics of concrete under ultra-deep underground environment

Understanding the microstructures evolution and chloride migration characteristics of concrete is essential to solve the durability problem of reinforced concrete structures in ultra-deep buried rail transit projects (40 m–100 m). Herein, we developed a novel experimental system that can simulate the corrosion process under high hydraulic pressure and stray current coexistence environment. The changes in microstructures, phases, elements, minerals, and the Ca-leaching were comprehensively investigated. Further, the mechanisms of pores and cracks propagation, and migration characteristics of chloride ions were revealed. The results showed that stray current and hydraulic pressure significantly altered the microstructures of concrete, both of which led to the increase of specific surface area, porosity, pore diameter and more ink-bottle-shaped pores. The development of dominant microfractures and three types of crack propagation patterns caused by hydraulic pressure were found, and the mechanical framework for “local fracturing” was established. Migration characteristics in micro-nano scale showed chloride ions were mainly transported along the pores, and the decrease of adsorption sites was the main reason.

Estimation of safe cover thickness to steel reinforcement in coastal structures addressing several tidal stations

Corrosion of steel in reinforced and prestressed concrete members exposed to a marine tidal zone is a serious durability problem. This study presents a methodology for rationally estimating the safe cover thickness for steel in concrete structures exposed to the tidal zone. The proposed methodology was implemented for the case of six Indian coastal stations using 100-year-long simulations of chloride transport in concrete. Real-time meteorological and tidal height data were used for simulating the model boundary conditions. Using simulated results of chloride threshold depths (CTDs), safe cover thickness to steel was assessed. Estimated safe cover thicknesses to steel across coastal stations differed significantly (25–30 mm), indicating a need for corrosion vulnerability zonation of coastlines. Conventionally used tide models were improved by superimposing with an annual component of astronomical tides, which expanded the range of wet-dry regimes simulated by the tide models. The study also compared the chloride ingress predictions from the modified tide models with those from real tides. The superimposed tide model was found to be a better approximation of real tides than the diurnal tide model. The modified tide models very well simulated chloride ingress around the critical sections in the tidal zone.

Исследование влияния качества поверхности при изготовлении комбинированных теплообменных элементов технологических реакторов путем склеивания

As is known, the problem of durability is directly related to the technological processes of manufacturing reactor elements, including elements in contact with the internal reactor environment – the reaction zone. Based on this, it is important to develop new, as well as modernize old technologies for manufacturing reactor equipment elements in order to improve their technical and operational characteristics. The technology developed by the authors of this manuscript can act as a technology for manufacturing and assembling elements of reactor equipment. This technology consists of several main stages. One of these stages is the process of roughness formation on the contacting surfaces before gluing them. However, it is necessary to understand that different values of roughness indicators lead to a change in the strength characteristics of adhesive joints. In view of this, the purpose of this study is to determine the strength characteristics of the adhesive joint at various Ra values and adhesive temperature. The article presents an analysis of the most popular thermochemical reactors at the present time, as well as an analysis of the main types of malfunctions leading to the failure of reactor equipment. The developed manufacturing technology of the most wear-prone parts of the reactor (heat pipes, shells) is described. A feature of this technology is the possibility of forming a thermal contact surface on the manufactured parts, which acts as an intensifier of heat exchange, increasing the efficiency of the unit. The practice of using high-strength and high-temperature adhesives is analyzed. Studies have been carried out to determine the strength of adhesive compounds under various conditions. Heat–resistant epoxy adhesives of K-800 and CMK-Vt brands were used as adhesive compositions. The influence of the Ra index in the range from 1 to 6 microns and the influence of temperature in the range from 200 to 600°C on the strength of the adhesive seam is shown.

STRENGTHENING OF RC BEAM USING CARBON FIBER REINFORCED POLYMER LAMINATES

Numerous factors, including I the need to upgrade existing structures as a result of infrastructure development, (ii) excessive deflection, cracking, and insufficient ultimate strength, (iii) the need to carry higher permissible loads, (iv) design flaws, (v) subpar building techniques, (vi) poor durability, etc., have made structural strengthening of reinforced concrete (RC) structural elements necessary. Structures or components may occasionally be overloaded, which results in increased cracking and decreased stiffness/strength. The repair and retrofitting of RC structural components can be handled using a number of well-liked procedures, including externally bonded steel plates, concrete jacketing, fiber-reinforced laminates or sheets, external pre-stressing, and external bar reinforcement techniques. Because to a significant mismatch in the tensile strength and stiffness of that material, strengthening employing CFRP has recently been found to be susceptible to unfavourable brittle failures. These restrictions are essential for selecting the right technology and material for strengthening. Each method or retrofit material has advantages and disadvantages of its own. Low strength to weight ratios, compatibility challenges between the parent and repair materials, corrosion and durability problems, and failure modes are the main drawbacks of these techniques.

Optimised technology for repair of vertical surface of concrete bridge elements

Abstract A large number of concrete bridges need to be repaired due to durability problems. This research focuses on evaluating the bond quality of the repair material, which has the highest influence on the durability of the repair. Onsite experimental research is performed on the vertical surfaces of the column of the Klara Jug bridge, which is located in the southern part of the Zagreb. Since the experimental research is carried out in parallel with the ongoing repair works on other bridge elements, the experimental conditions correspond to the real construction site conditions. Simulation of the actual site rehabilitation process was carried out on the test fields, which included removal of the damaged concrete by hydrodemolition at a depth of 1.5–2 cm, washing of the concrete by roto nozzle and wet spraying of the repair mortar. The results of the pull-off tensile bond strength show that there is an optimum period for spraying of repair mortar after washing the concrete surface. Optimal time for application of mortar is 90 min after completion of washing of the vertical concrete surface by the roto nozzle. In other weather conditions, the application time depends on the expected evaporation of water from the surface. The tensile strength of the bond between concrete and the repair mortar is 62% lower if the concrete is not washed by the roto nozzle prior to the application of the repair mortar. This investigation can serve as a practical guide for the repair of vertical surface of concrete elements of bridges, overpasses and viaducts.

Evaluation of Self-Healing Efficiency of Microcapsule-Based Self-Healing Cementitious Composites Based on Acoustic Emission

Microcapsule self-healing technology is one of the effective methods to solve the durability problem of cement-based composites. The evaluation method of the self-healing efficiency of microcapsule self-healing cement-based composites is one of the difficulties that limits the self-healing technology. This paper attempts to characterize the self-healing efficiency of microcapsule self-healing cement-based composites by acoustic emission (AE) parameters, which provides a reference for the evaluation of microcapsule self-healing technology. Firstly, a kind of self-healing microcapsules were prepared, and the microcapsules were added into the cement-based composites to prepare the compression samples. Then, the specimen with certain pre damage was obtained by compression test. Secondly, the damaged samples were divided into two groups. One group was directly used for compression tests to obtain the damage failure process. The other group was put into water for healing for 30 days, and then compression tests were carried out to study the influence of self-healing on the compression failure process. During the experiments, the AE signals were collected and the AE characteristics were extracted for the evaluation of self-healing efficiency. The results show that the compression pre damage test can trigger the microcapsule, and the compression strength of the self-healing sample is improved. The failure mechanism of microcapsule self-healing cement-based composites can be revealed by the AE parameters during compression, and the self-healing efficiency can be quantitatively characterized by AE hits. The research results of this paper provide experimental reference and technical support for the mechanical property test and healing efficiency evaluation of microcapsule self-healing cement-based composites.

Influence of hoop restraint on microstructure and phase composite of cement paste filled steel tube under external sulfate attack

The deterioration of cement-based material caused by external sulfate attack (ESA) is a major durability problem affecting concrete structures. This study aims to investigate the effect of hoop restraint of steel tube on microstructure and phase composition of cement pastes prepared with ordinary Portland cement (OPC) and high sulfate-resistance Portland cement (SRPC) under ESA for 540 days. The effects of hoop restraint on the change in micromorphology, phase composition and microstructure of cement hydration products under ESA were investigated by SEM-EDS, XRD, 29Si and 27Al MAS NMR spectroscopy and low-field NMR. Moreover, the effects of hoop restraint on local mechanical properties of the cement pastes under ESA were evaluated by micro-hardness measurement. Results indicate that hoop restraint significantly inhibits the formation of micro-cracking and limits the permeation rate of sulfate ions, leading to a reduction in the amount of ettringite and gypsum crystals. 27Al NMR analysis shows that the hoop restraint has significant “delay effect” on the transfer of Al phase transition from monosulfoaluminate (AFm) and third aluminate hydrate (THA) to ettringite. 29Si NMR test reveals that hoop restraint can significantly slow down decalcification and dealuminization of C-(A)-SH gel, leading to a slow reduction in Al[4]/Si ratio of C-(A)-SH, together with the lower mean chain length (MCL) of the silicate chain. The MCL reduces by 34.7 % and 9.0 %, and Al[4]/Si ratio increases by 41.9 % and 8.3 % for OPC and SRPC pastes with steel tube compared to the equivalent free ones, respectively. Additionally, hoop restraint results in better quality pore structure of cement pastes with steel tube than the equivalent free ones.