Durability Problems Research Articles

Carbon footprint and water use of alkali-activated and hybrid cement mortars

Cement industry consumes large amounts of water, energy and it is one of the main sources of anthropogenic greenhouse gas emissions. Hence, addressing these environmental constraints leads to a search for alternative mortars to ordinary Portland cement (OPC) replacing the clinker by industrial by-products, such as blast furnace slag and/or fly ash.In this context, alkaline activated materials (AAM) show good mechanical properties comparable to OPC. However, AAM present durability problems against leaching phenomena, and workability problems because of the use of alkaline solutions. Therefore, other alternatives as the hybrid materials (HM) are receiving greater attention.In order to determine if the mechanical properties of hybrid and alkali-activated mortars are indeed comparable to those from Ordinary Portland Cements (OPC), this paper first examines the compressive strength and porosity of an AAM case study from slag and two HM systems, both from slag and fly ash. Moreover, since very little is known about their environmental impacts in terms on water use and carbon footprint they were calculated through the Life Cycle Assessment methodology and compared to those of OPC.Results revealed that the assessed AAM and two HM case studies obtained mechanical properties comparable to those for OPC.The AAM obtained −406.02 kg CO2/m3 while for the hybrids the carbon footprints were −253.26 kg CO2/m3 (HM from slag) and −253.27 kg CO2/m3 (HM from fly ash), proving that partial or total substitution of cement by waste in mortars reduces the carbon footprint of OPC more than 100%. In terms on water footprint, more than a 40% reduction in water use is obtained if HM are used instead of OPC supporting the idea that HM achieve good balance between carbon footprint and water use reductions.

Mechanical Robust Flexible Single-Component Organic Solar Cells.

Owing to the advantages of being lightweight and compatible with surfaces with different deformations, flexible organic solar cells (OSCs) have broad scopes of applications, including wearable electronics and portable devices. Most flexible OSCs focus on the two-component bulk-heterojunction (BHJ) photo-active layers, but they usually suffer from degradation problems both in efficiency and mechanical durability derived from the limited phase stability under mechanical and thermal stress. Whereas, single-component organic solar cells (SCOSCs) based on the double-cable conjugated polymer are supposed to possess excellent mechanical robustness and long-term stability. Here, the first flexible SCOSCs based on a double-cable polymer are fabricated on a transparent silver nanowires (AgNWs) electrode on a plastic foil. Impressively, the obtained flexible SCOSCs exhibited a power conversion efficiency (PCE) of 7.21%. The flexible SCOSCs are further demonstrated to possess superior mechanical robustness (>95% retention after 1000 bending cycles) and storage stability (>97% retention after 430 h in nitrogen atmosphere) compared to several BHJ-type flexible OSCs. The pseudo-free-standing tensile test and morphology investigation are conducted to reveal the distinction in mechanical durability of the single-component polymer film and the BHJ-type films. Besides, ultraflexible SCOSCs are also fabricated, indicating the application prospect and superiority in flexible devices and wearable electronic products.

Development of Folded Expanded Metal Mesh with Sound Absorption Performance

Reverberation time (RT) is an important factor affecting the quality of indoor acoustics. Using sound-absorbing materials is one method for quickly and effectively controlling RT, and installation in the ceiling is a common location. Sound-absorbing ceilings come in many forms, with light steel joist ceilings commonly used in office spaces, classrooms, and discussion rooms. Light steel joist ceilings are often matched with sound-absorbing materials such as gypsum board, mineral fiberboard, rock wool, and coated glass wool, but such materials may have durability and exfoliation problems. Therefore, considering performance and health, in this research, we aimed to design an expanded metal mesh (EMM) structure specimen for sound-absorption material, namely folded expanded metal mesh (FEMM). The results show that the FEMM can significantly improve the sound-absorption performance of the expanded metal mesh. The Math output errorαw of single panel is 0.05–0.35, and the Math output errorαw of FEMM is 0.65–0.85. On the other hand, the sound-absorption performance of the full frequency band has been significantly improved. Furthermore, the field validation result shows that RT decreased from 1.05–0.56 s at 500 Hz, meanwhile, the sound pressure level (SPL) is still evenly distributed, and speech clarity (C50) is increased by 5.6–6.5.

Concrete protection by combined hygroscopic and hydrophilic crystallization waterproofing applied to fresh concrete

Crystallization-based waterproofing is a multi-functional technology which combines hygroscopic and hydrophilic crystallization pore blocking with hydrophobic pore lining. This paper presents experimental findings of investigating dual-crystallization waterproofing engineered treatment (DCE) onto fresh concrete. The DCE has the potential to provide an effective solution to various concrete durability problems associated with all water phases of vapor, liquid and solid. The characteristics of treated and untreated concrete specimens have been investigated experimentally according to ASTM procedures. The DCE system is able to reduce moisture penetration through concrete thus enhances concrete durability. The DCE is able to increase concrete resistance against chloride ion penetration and to reduce damages from freezing and thawing cycles, scaling and ASR. Additionally, the application of DCE technology improves water retention for better cement hydration leading to an enhancement of surface characteristics (adhesion strength and surface smoothness).

A Study on the Energy-Harvesting Device with a Magnetic Spring for Improved Durability in High-Speed Trains.

Durability is a critical issue concerning energy-harvesting devices. Despite the energy-harvesting device’s excellent performance, moving components, such as the metal spring, can be damaged during operation. To solve the durability problem of the metal spring in a vibration-energy-harvesting (VEH) device, this study applied a non-contact magnetic spring to a VEH device using the repulsive force of permanent magnets. A laboratory experiment was conducted to determine the potential energy-harvesting power using the magnetic spring VEH device. In addition, the characteristics of the generated power were studied using the magnetic spring VEH device in a high-speed train traveling at 300 km/h. Through the high-speed train experiment, the power generated by both the metal spring VEH device and magnetic spring VEH device was measured, and the performance characteristics required for a power source for wireless sensor nodes in high-speed trains are discussed.

A superhydrophobic and flame-retardant cotton fabric fabricated by an eco-friendly assembling method

A novel eco-friendly and durable superhydrophobic and flame-retardant cotton fabric with fluorine-free, halogen-free was prepared via step-by-step dip-coating and spraying technology. At first, common cotton fabric was impregnated in the flame-retardant ethoxysilane-terminated phosphate polyurethane. Afterwards, methanol mixture containing silica nanoparticles, methyl triethoxysilane, and dihydroxy-terminated polydimethylsiloxane was sprayed on the surface of the cotton fabric. Finally, a flame-retardant cotton fabric with micro-nano rough surface and low surface energy was formed. The resulting superhydrophobic and flame-retardant cotton fabric exhibited superamphiphobicity with the contact angle and sliding angle of 160° and 6°, respectively, while flame retardancy with limited oxygen index of 28.1%. and flame self-extinguishing. Furthermore, this superhydrophobic and flame-retardant cotton fabric showed robust superhydrophobicity and flame-retardancy after undergoing 1000 cycles of abrasion, 60 min of ultrasonic washing and 50 standard machine washing cycles, in sequence, indicating its potential as a multifunctional protective textile fabric. Additionally, the method proposed in this study can effectively solve durability and environmental problems currently faced by the coated fabric with superhydrophobicity and flame-retardancy.

State of the Art Review on Prescriptive & Performance Based Approaches for Concrete Durability

Durability has become one of the most important requirements for the concrete structures across the globe. A durable concrete not only leads to the sustainability but serve for longer period without much repair and maintenances for the concrete members. The Concrete in various exposures such as mild, moderate, severe, very severe and extreme conditions was studied by researchers but no significance attention is given for the performance of the concrete in service. In the last few decades, many researchers investigated the causes of structures deterioration and suggested various solutions to tackle the durability issues which are mainly adopting of performance-based specifications rather than prescriptive. In this paper, the previous findings on concrete durability are reviewed. The studies on the durability problems are highlighted along with prescriptive and performance-based approaches and test methods. The effects on service life of the structures along with the solution are reviewed.

Behavior of highly ductile fiber–reinforced concrete columns under eccentric loading

Highly ductile fiber–reinforced concrete (HDC) is characterized by a tensile strain–hardening behavior and high compressive toughness, which is expected to alleviate the cracking and durability problems induced by the brittleness of high–strength concrete (HSC). In this study, HSC was substituted with HDC to construct columns. Six reinforced HDC (R/HDC) columns and two reinforced HSC (R/HSC) columns were constructed and tested under compressive loads with different eccentricities. The crack patterns, failure modes, lateral deflection curves, load–displacement curves, and strains of concrete and rebars were investigated. The test results revealed that the R/HDC column has a better failure mode and cracking pattern compared to the HSC column. A good synergy work performance between HDC and rebars significantly improved the utilization of the longitudinal rebars. A calculation method for the bearing capacity of the R/HDC column was proposed. The calculated results were in good agreement with the experimental results. The load–moment interaction curves (N–M curves) of the R/HDC column were calculated and plotted. Subsequently, the effects of HDC compressive strength, HDC tensile strength, the reinforcement strength, and longitudinal reinforcement ratio on the bearing capacity of the R/HDC column were studied using parametric analysis. The results indicate that a high tensile strain can guarantee the efficient utilization of the tensile strength of HDC.

Cyclic Plasticity and Low Cycle Fatigue of an AISI 316L Stainless Steel: Experimental Evaluation of Material Parameters for Durability Design.

AISI 316L stainless steels are widely employed in applications where durability is crucial. For this reason, an accurate prediction of its behaviour is of paramount importance. In this work, the spotlight is on the cyclic response and low-cycle fatigue performance of this material, at room temperature. Particularly, the first aim of this work is to experimentally test this material and use the results as input to calibrate the parameters involved in a kinematic and isotropic nonlinear plasticity model (Chaboche and Voce). This procedure is conducted through a newly developed calibration procedure to minimise the parameter estimates errors. Experimental data are eventually used also to estimate the strain–life curve, namely the Manson–Coffin curve representing the 50% failure probability and, afterwards, the design strain–life curves (at 5% failure probability) obtained by four statistical methods (i.e., deterministic, “Equivalent Prediction Interval”, univariate tolerance interval, Owen’s tolerance interval for regression). Besides the characterisation of the AISI 316L stainless steel, the statistical methodology presented in this work appears to be an efficient tool for engineers dealing with durability problems as it allows one to select fatigue strength curves at various failure probabilities depending on the sought safety level.

Hydration and Microwave Curing Temperature Interactions of Repair Mortars

Microwave curing of repair patches provides an energy efficient technique for rapid concrete repair. It has serious economic potential due to time and energy saving especially for repairs in cold weather which can cause work stoppages. However, the high temperatures resulting from the combination of microwave exposure and accelerated hydration of cementitious repair materials need to be investigated to prevent potential durability problems in concrete patch repairs. This paper investigates the time and magnitude of the peak hydration temperature during microwave curing (MC) of six cement based concrete repair materials and a CEM II mortar. Repair material specimens were microwave cured to a surface temperature of 40-45 °C while their internal and surface temperatures were monitored. Their internal temperature was further monitored up to 24 hours in order to determine the effect of microwave curing on the heat of hydration. The results show that a short period of early age microwave curing increases the hydration temperature and brings forward the peak heat of hydration time relative to the control specimens which are continuously exposed to ambient conditions (20 °C, 60% RH). The peak heat of hydration of normal density, rapid hardening Portland cement based repair materials with either pfa or polymer addition almost merges with the end of microwave curing period. Similarly, lightweight polymer modified repair materials also develop heat of hydration rapidly which almost merges with the end of microwave curing period. The peak heat of hydration of normal density ordinary Portland cement based repair materials, with and without polymer addition, occurs during the post microwave curing period. The sum of the microwave curing and heat of hydration temperatures can easily exceed the limit of about 70 °C in some materials at very early age, which can cause durability problems.

EXPERIMENTAL RESULTS OF DAMAGED RC BEAMS

This article presents the results of an experimental study of damaged reinforced concrete beams. Corrosion of reinforcement in concrete is one of the main problems of durability faced in practice by civil engineers. Particular attention should be paid to the action of an aggressive environment as one of the most common causes of the introduction of elements into an emergency. The aim of the work is to determine the strength and deformability of reinforced concrete structures without damaging the reinforcement and in case of damage. According to the research program 4 beams were tested. Among them were undamaged control samples with single reinforcement of ∅20 mm diameter and samples with ∅20 mm reinforcement with damages about 40%. The reinforcement was damaged before concreting the samples. The test specimens were tested for bending under short-term load. At the result impact of damage to reinforcement in RC beams reduces the load-bearing capacity. The results are given in the article.

Properties of cement mortar containing recycled glass and rice husk ash

Using recycled glass (RG) to replace river sand in the production of cement-based materials saves the increasingly depleting natural sand resources. Previous studies have shown that the smooth surface and reactive silica of RG adversely affected its bonding with the cement paste and thereby caused a potential alkali-silica-reaction (ASR). This study used rice husk ash (RHA) as an eco-friendly mineral admixture to ameliorate the properties of the RG incorporated mortar. A fixed replacement of 50% RG was used to replace sand, while varying proportions (10%, 20% and 30%) of RHA were adopted to replace cement. For comparison, a mixture containing only sand and cement was used as the reference sample. The flexural and compressive strength, water absorption, ASR expansion, and rapid chloride mitigation (RCM) of the hardened samples were evaluated. In addition, SEM, XRD, and TG analysis were employed to analyze the microstructures and chemical compositions of different samples. The results showed that incorporating RG as a river sand replacement in cement mortar reduced flexural and compressive strength and increased water absorption and chloride ion penetration. Moreover, the ASR expansion value (0.34%) was beyond the permissible limit (0.1) indicated by the ASTM C1260. The addition of RHA improved the mechanical properties and durability of the cement mortar at a later curing age as a result of the RHA-induced pozzolanic reaction and micro-filler effect. By converting portlandite (CH) derived from cement hydration into secondary C-S-H, the use of RHA greatly reduced the porosity (augmenting the compressive and flexural strength) and concurrently suppressed the RG-induced ASR expansion. The results of XRD, SEM and TG analysis corresponded well with the macro-property analysis and helped to elucidate the underlying mechanisms of the RHA-induced beneficial effects. Findings from this study provide new insights into the potential use of eco-friendly RHA in addressing the mechanical and durability problems associated with the use of RG as aggregate in cementitious materials.

Design Service Life of RC Structures with Self-Healing Behaviour to Increase Infrastructure Carbon Savings.

Corrosion of reinforced concrete (RC) structures costs the UK GBP 23b annually and is one of the main durability problems contributing to the development of rust, spalling, cracking, delamination, and structural deterioration. This paper intends to demonstrate the benefit of using tailored self-healing bacteria-based concrete for RC corrosion minimisation and service life increase. The purpose was to evaluate the enhancement in the lifespan of the structure exposed to a harsh marine microenvironment by utilising a probabilistic performance-based method. Comparison is made with the performance of a commercially available solution and in terms of embodied carbon impact. Three different concretes, using CEM I 52.5N, CEM II/A-D, and CEM III/A, were tested with and without an iron-respiring bioproduct (BIO) and an added admixture corrosion inhibitor (AACI). Results show that bioproduct significantly contributes to service life increase of RC structures with CEMIII/A. The repair solution with self-healing behaviour not only increases RC service life, but also enables us to decrease the required cover thickness from 60 mm to 50 mm in an XS2 chloride environment. In both XS2 and XS3 environments, a comparison of CEMIII/A+BIO and CEMII/A-D+AACI concrete shows the benefit of using bioproduct in corrosion inhibition context, besides contributing to an embodied carbon reduction of more than 20%.

Automated Vision-Based Crack Detection on Concrete Surfaces Using Deep Learning

Cracking in concrete structures affects performance and is a major durability problem. Cracks must be detected and repaired in time in order to maintain the reliability and performance of the structure. This study focuses on vision-based crack detection algorithms, based on deep convolutional neural networks that detect and classify cracks with higher classification rates by using transfer learning. The image dataset, consisting of two subsequent image classes (no-cracks and cracks), was trained by the AlexNet model. Transfer learning was applied to the AlexNet, including fine-tuning the weights of the architecture, replacing the classification layer for two output classes (no-cracks and cracks), and augmenting image datasets with random rotation angles. The fine-tuned AlexNet model was trained by stochastic gradient descent with momentum optimizer. The precision, recall, accuracy, and F1 metrics were used to evaluate the performance of the trained AlexNet model. The accuracy and loss obtained through the training process were 99.9% and 0.1% at the learning rate of 0.0001 and 6 epochs. The trained AlexNet model accurately predicted 1998/2000 and 3998/4000 validation and test images, which demonstrated the prediction accuracy of 99.9%. The trained model also achieved precision, recall, accuracy, and F1 scores of 0.99, respectively.

Mechanical Behavior of the Novel Gradient Concrete Tower of a Cable-Stayed Bridge

In this paper, the novel gradient concrete is innovatively applied to the bridge towers of Chizhou Yangtze River Bridge to solve the cracking and insufficient durability problems of concrete towers. Fiber-reinforced concrete is used in the outer functional area of the bridge tower, to significantly improve its crack resistance during construction and service. Moreover, the integrated design of anti-cracking and mechanical properties of tower materials is achieved. To study the performance of the novel functional gradient concrete (FGC) tower, the mechanical properties of the FGC tower material are tested, and the overall finite element stress is analyzed. Based on the material properties, the mechanical behavior of the cable-stayed bridge tower is studied. The temperature and stress of the FGC tower during the generation of the hydration heat are compared with that of the ordinary concrete tower. The crack resistance of the FGC tower is analyzed by the finite element method. The results show that the FGC tower has good mechanical properties and durability for the cable-stayed bridge towers.

Study on the Crack Resistance Properties of Manufactured Sand Concrete

In order to solve the problem of workability and durability of concrete caused by poor particle shape and morphology of manufactured sand and high content of stone powder, which leads to crack problems of concrete, the tensile strength, elastic modulus, shrinkage performance and adiabatic temperature rise performance of manufactured sand concrete were studied in this paper. And the cracking risk factor (the reciprocal of the anti cracking safety factor) of the concrete with the special admixtures and the crack resistant functional materials was calculated by according to GB 50496-2018. The experimental results show that the elastic modulus and tensile strength at the age of 28 d of the test concrete are increased from 31.0 GPa to 34.6 GPA and 2.91 MPa to 4.23 MPa, respectively. The shrinkage performance and adiabatic temperature rise of the concrete are reduced from 98 με to 65 με and 38.9°C to 38.4°C, respectively. The risk factors of surface and center crack resistance of mass concrete floor are 0.52 and 0.75, so the concrete under inspection will not crack.

Compressive behavior and modelling of engineered cementitious composite (ECC) confined with LRS FRP and conventional FRP

A combination of core engineered cementitious composite (ECC) and external fiber-reinforced polymer (FRP) composites can solve the problems of insufficient ductility and durability of normal concrete (NC) in adverse environments and improve bearing capacity. However, existing studies on the performance of ECC strengthened by FRP are very limited—particularly the research on large rupture strain (LRS) FRP-confined ECC. In this study, an experimental investigation of LRS FRP and conventional glass FRP-confined ECC cylinders with different confinement levels under axial compression is presented. It is found that the application of external FRP jackets leads to a significant improvement in the compressive strength and deformation of the core ECC. LRS FRP-confined ECC exhibits a higher ultimate deformation than conventional FRP-confined ECC. The dilation behavior, axial stress–strain behavior, and energy dissipation capacity between FRP-confined ECC and FRP-confined NC under the same confinement level are compared, and the former exhibits a significantly larger ductility and energy dissipation capacity than the latter. The results also indicate that most existing models are unable to accurately predict the compressive behavior of FRP-confined ECC. To address this, a dilation model and an axial stress–strain model of FRP-confined NC are modified to extend their application to FRP-confined ECC.

Slaking behavior of evaporitic rocks from Abu Dhabi area, United Arab Emirates

Slaking behavior of rocks is an essential indicator of their ability to resist degradation and is commonly assessed via the second cycle of slake durability index (Id2, SDI) test. In Abu Dhabi area, the evaporitic rocks commonly extend from the near surface to several meters depth, so that they lie at the foundation level of buildings and other infrastructures. Evaporites pose significant challenges for the construction sectors due to the easily degradable nature of these rocks. This study presents new and definitive data for evaporites that provides essential information for the construction businesses, engineers, and decision makers. Eighty-six rock blocks from eleven locations were collected. A representative sample of each block was extracted for slake durability testing. Samples were prepared and tested according to ASTM standards. Before and after the slaking process, the mineralogical composition and characteristic textures of the samples were examined in petrographic thin section and via XRD (X-ray diffraction), XRF (X-ray fluorescence), and SEM (scanning electron microscopy) analyses. Based on multiple cycling, Id1 to Id4, the slake test data for evaporitic rocks from Abu Dhabi indicate high to very low values. The weight loss values from the first to the fourth cycle (Id1–Id4) of all samples lie in the range 40 to 93 wt%. This is attributed to chemical and mineralogical properties of the evaporites, which allow rapid development of hydration-dehydration effects. The evaluation of the slaking behavior of evaporitic rocks provides explanations for durability problems associated with these rocks in the study area and elsewhere.

Life Prediction Model of Nano-CaCO3 Modified Concrete in Sulfate Environment

In the saline soil environment, the salts corrode the ordinary cement concrete seriously, and concrete structures deteriorate gradually until it fails, which impedes the practical application of ordinary Portland cement concrete in this area. Aiming at the durability problems of concrete in a harsh environment, this paper selects the coefficient of compressive strength, coefficient of flexural strength, relative dynamic elastic modulus, and relative mass to jointly evaluate the resistance of nano-CaCO3 modified concrete to sulfate corrosion. More importantly, the Wiener process for modeling the degradation process of concrete specimens was used to obtain the remaining life’s reliability function. The results indicated that adding 1% nano-CaCO3 (Nano Calcium Carbonate) can enhance the resistance of concrete to sulfate corrosion, and the service life of concrete will increase significantly. The Random Wiener process can effectively predict the durability deterioration process of concrete specimens. By integrating the deterioration process’s life data, this method’s reliability function may directly reflect the concrete’s life.

Insight into degradation mechanism of Pd nanoparticles on NCNTs catalyst for ethanol electrooxidation: A combined identical-location transmission electron microscopy and X-ray photoelectron spectroscopy study

Herein, we report a facile method to prepare palladium nanoparticles (Pd NPs) anchored on nitrogen-doped carbon nanotubes (Pd/NCNTs) with particle size distribution uniformed. The Pd/NCNTs exhibits excellent ethanol oxidation reaction (EOR) mass activity of 2,489 A g−1, which is 5.1 times higher than commercial Pd/C. However, the anodic reaction of EOR suffers from poor efficiency and low durability. In order to solve the problem of low durability and have better understanding of the degradation mechanism of anodic catalysts, identical-location transmission electron microscopy (IL-TEM), X-ray photoelectron spectroscopy (XPS), and electrochemical measurements were carried out. These were applied to Pd/NCNTs catalyst under EOR in alkaline media. The results showed that the leaching of Pd NPs and the reduction of surface metallic Pd0 were the main reasons for the decreased EOR activity. These findings provide practical guidance for the development of catalysts with higher activity and stability for energy conversion.