Durability Problems Research Articles

A Review on Applications of Superhydrophobic Materials in Civil Engineering

Superhydrophobic (SHPB) materials have attracted a lot of attention in civil engineering due to their unique wettability in recent years. The SHPB characteristics pave up a new way for the applications of SHPB materials in civil engineering. In this review, the applications research progress of SHPB materials in various fields of civil engineering is summarized. The waterproofing, self‐cleaning, anticorrosion, anti‐icing, and antifogging applications of SHPB materials in architectural engineering are discussed. The applications of SHPB materials in road and bridge engineering such as anti‐icing and antiskidding are listed. The applications of SHPB materials in heating and ventilation engineering are ranged from anticondensation, antifrosting to dust removal. The anticorrosion and antibiofouling applications of SHPB materials in structural engineering in marine environment are presented. The key problem of insufficient mechanical and chemical durability of SHPB materials when applied in civil engineering is pointed out, and the application trend of SHPB materials in civil engineering is prospected. Finally, based on the detailed discussion of the applications of SHPB materials in civil engineering, a brief summary is proposed. It is expected that SHPB materials can be widely and systematically applied in civil engineering, making important contributions to multifunctional development of civil engineering in the future.

Bond Tests on Clay Bricks and Natural Stone Masonry Externally Bonded with FRP.

Nowadays, the solution of durability problems of existing buildings has a key role in civil engineering, in which there is an ever-increasing need for building restorations. Over the past 50 years, there is a growing interest in a new composite material, fibre-reinforced polymer (FRP), suitable for increasing the resistance and the stability of existing buildings and, consequently, for extending their service life. In this context, the effectiveness of the strengthening system is related to the bond behaviour that is influenced by several parameters such as bond length, the stiffness of the reinforcement, the mechanical properties of the substrate, environmental conditions, etc. This paper aims to analyse the main experimental results from shear tests performed on two kinds of masonry substrates and different types of FRP reinforcements. The purpose is to highlight the role played by many parameters to the bond behaviour of these systems: the mechanical properties of substrates; the stiffness of reinforcements; the type of supports (i.e., unit or masonry unit). The obtained experimental results underlined that the specimens realised with masonry unit show an increase in debonding load and different stress transfer mechanisms along the bonded length with respect to the specimens with a unit substrate. The analysis of the data revealed that the presence of mortar joints cannot be neglected because it influences the interface global performance.

Influence of Changes in the Shape of the Anode Channel in Polymer Electrolyte Fuel Cell on the Loss of Its Service Life.

The fuel cell operation is associated with significant current density and durability problems, among other anode collectors. We used a numerical model based on flows with chemical reactions in a porous medium to solve these problems. We tested four variants of the anode channels. In the shape of the anode channel, we introduced changes to improve the current density. We also examined the influence of the channel shape on the stress field and rheological processes in the casing material. We verified the numerical model on the experimental data. Furthermore, we corrected the amount of the hydrogen stream and the produced water in the whole range of the cell’s operation. The test results show that it is possible to increase the current density in all operating fields of the fuel cell while maintaining a low mechanical load on graphite elements and their safe operation time.

Effect of Carbon Particle Feeding as Radiant Absorbent for Enhanced Heat Transfer

Abstract Carbon particles can be used as catalyst in solar reactors where they serve as radiant absorbent and nucleation sites for the heterogeneous decomposition reaction. Unlike commonly used metal catalysts, carbon catalyst does not have durability problem and high cost. However, in order to achieve sustainable catalytic decomposition of feedstock over carbon catalysts at elevated temperatures, the surface area of the carbon particles must be maintained. A subsequent treatment of deactivated carbon samples with CO2 at about 1000 °C would increase the surface and would recover the original activity as catalyst. In a windowed solar reactor, carbon particles are directly exposed to the high flux irradiation providing efficient radiation heat transfer directly to the reaction site. Therefore, one of the key parameters to achieve higher conversion efficiencies in a solar reactor is the presence and transport of carbon particles. In this paper, a transient one-dimensional model is presented to describe the effect of carbon particle feeding on energy transport and temperature profile of a cavity-type solar receiver. The model was developed by dividing the receiver into several control volumes and formulating energy balance equations for gas phase, particles, and cavity walls within each control volume. Monte Carlo ray tracing method was used to determine the solar heat absorbed by particles and cavity walls, as well as the radiative exchange between particles and cavity walls. Model accuracy was verified by experimental work using a solar receiver where carbon particles were injected uniformly. Comparison of simulation results with the experimentally measured temperatures at three different locations on cavity receiver wall showed an average deviation of 3.81%. The model was then used to study the effect of carbon particle size and feeding rate on the heat transfer, temperature profile, and energy absorption of the solar receiver. Based on the simulation results, it was found that injection of carbon particles with a size bigger than 500 µm has no significant influence on heat transfer of the system. However, by reducing the particle size lower than 500 µm, temperature uniformity and energy absorption can be enhanced.

A review on the physical & chemical properties of sea sand to be used a replacement to fine aggregate in concrete

Sea sand is a widely available form of sand on comparing with the river sand. Sea sand is not used widely because it may contain chloride, sea shells in large numbers and other harmful chemicals like Fe2O3, V2O5, Cr2O3, Ga2O3, Br2O and Re2O7. The usage of sea- sand may either address the concrete’s existing problems in strength and durability or can be an excellent replacement material to river sand which is in great danger due to excessive excavation in almost all countries around the world. A large number of individual works have been done worldwide on sea sand as partial/full replacement of fine aggregates in concrete and this paper is aimed and compiling all the works and give an in depth understanding about how this material can be effectively utilized in concrete. The present work focuses on compiling and reporting various works on the general material properties of sea- sand, effect of chloride content in strength and workability, effect of rainfall on the chloride content, alkali – aggregate reaction. It also consists and understanding of the likely dangerous chemical components, effect of shell content on workability and strength, effect of size and uniformity of sea sand in concrete. Effect on compressive strength due to grading of the sea sand’s, curing with sea water and using washed the sea sand before use have also been reported. From the report it can be concluded that by understanding the material properties of sea- sand, it can be effectively utilized as fine aggregate in concrete.

Comparative Study on Degradability Characteristics of Evaporitic and Carbonate Rocks from Al Ain, United Arab Emirates

The slake durability index (SDI) test is a well know and extensively used to measure the degradability behaviour of rocks especially for weak rocks like mudstone, shale, evaporites, carbonates, etc. The degradability of rocks plays a critical role in engineering design process either on or in the rock mass for safe and sustainable structures. Evaporitic and carbonate rocks are vulnerable to physical, chemical and mechanical weathering, break down, as result of wetting-drying processes during the SDI test. Evaporites and carbonates are outcropped at the surface and subsurface of the Al Ain city, which is located on the south-eastern of Abu Dhabi, capital city of the United Arab Emirates (UAE) at various level, and it is one of the rapid growing cities in the UAE. However, the detailed comparative data on the slaking behaviour of evaporites and carbonates are not available presently in the study area. Therefore, this paper provides a comparative study on the degradability characteristics of evaporitic and carbonate rocks in the city of Al Ain as well as comprehensive data for the study area. 142 rock blocks (∼ 40×40×40 cm3 in size), which represent evaporitic (48 blocks) and carbonate (94 blocks) rocks were collected from various accessible either surfaces outcrops or excavated areas from the study area. 48 and 94 slake durability test samples of evaporites and carbonates were prepared and slake durability tests were performed according to the American Society for Testing and Materials (ASTM) standards. Furthermore, their compositional and textural characteristics were examined using polarized-light microscope, X-ray diffractometry (XRD), X-ray fluorescence (XRF) and scanning electron microscope (SEM). The degradability data for evaporite and carbonate rocks designate medium to very low and extremely high to very high values based on the classification after multiple cycling, Id1 to Id4, processes, respectively. The weight loss values from the first to the fourth cycles (Id1–Id4) of evaporite and carbonate samples are approximately 24–95 and 0.68-4.22 wt%. Obviously, evaporites are highly vulnerable compare to carbonates because of their differences in chemical and mineralogical structures and their reactions to the slaking fluid of distilled water. Hydration-dehydration effects on the evaporitic rocks may occur within short time compare to the carbonate rocks due to their natural occurrences. Thus, this study provide comparable and details information for the degradability characteristics of evaporitic and carbonate rocks, and likely improve the understanding of the durability of both rock types in the study area and elsewhere. Especially, such a reliable and inclusive information will compromise a practical guideline for engineers and decision makers to overcome difficulties on durability problems associated with evaporites and carbonates in the study area and elsewhere.

Carbonation of High-Ca Fly Ashes under Flue Gas Conditions: Implications for Their Valorization in the Construction Industry

The utilization of high-calcium fly ashes (HCFA) from coal-fired power plants in the construction industry is problematic, since their high free lime contents can lead to durability problems. In this research, the carbonation of a high-CaO fly ash has been carried out using simulated flue gas and concentrated CO2, with the aim to assess the valorization potential of such materials in the construction industry. The results show that, at 7 bars total pressure, an up to 36% carbonation efficiency can be achieved in just 30 min when pure CO2 is used; a comparable result with flue gas requires about 4 h of reaction. On the other hand, experiments carried out at atmospheric pressure show significantly different carbonation efficiencies depending on the CO2 concentration of the gas used. All experiments resulted in a substantial reduction in the original free lime content, and after reaction times of 4 h (at atmospheric pressure) and pressures of 7 bars (for any reaction time >30 min), the final free lime values were low enough to comply with the requirements of European Standards for their utilization as additions in cement.

Enhancement of Photocatalytic Effect By Hydroxyapatite Coating on Titanium Dioxide Electrode

Titanium dioxide (TiO₂) electrodes are used as anode electrodes in dye-sensitized solar cells, and when hydroxyapatite was coated on the TiO₂ layer to facilitate the dye-sensitizing such as ruthenium on TiO₂ electrodes, HAp itself was found to act as a photocatalyst to improve the electrode properties of TiO₂ electrodes. It was found that HAp itself acts as a photocatalyst to improve the electrode properties of TiO2 Therefore, before dye-sensitizing, the photocatalytic effect of HAp was tested to find the optimal coating method, and as a result, the electrode property of TiO₂ electrode was improved.Type 329J4L stainless steel was used as the base metal for the electrode; before coating the TiO₂ layer, the surface was cleaned and passivation treated with HNO3. The passivated substrate was coated with TiO₂ paste in two steps by screen printing method. The first layer was coated on the electrodes by screen printing method and heat treated at 150°C for 60 minutes. The second layer was coated by the screen-printing method like the first layer and then heat-treated at 550°C for 30 min. The HAP layer was coated in the same way. The HAp layer is prepared by processing the powdered HAp powder into a slurry, coating it on the TiO₂ layer by the screen-printing method, and then heat-treating it.The photopotential characteristics of the electrode are measured and compared with the electrochemical characteristics of the TiO₂ electrode coated with HAp. The photopotential was measured using a potentiostat. Artificial seawater was used as the electrolyte and a saturated calomel electrode (SCE) was used as the reference electrode. The light used in the experiment was a xenon lamp (150W, wavelength range 250~800nm), generating a light intensity of 10.5mW/cm². The potential was measured for 2 hours. The measurements were carried out in the dark for the first 3 minutes, followed by light illumination conditions.The photopotential of the TiO₂ electrode coated with HAp was more active than that of the TiO₂ electrode not coated with HAp. However, there is a problem that HAP is peeled off from the electrode surface during a photopotential measurement experiment using a xenon lamp and potentiometer for 2 hours. This issue was caused by the way the HAp paste was made. Initially, carboxymethyl cellulose (CMC) was used to make HAp paste due to its advantages of physical dispersibility and moderate viscosity. It was a good material that could take on viscosity and dispersibility, but it had durability problems. This was because CMC has a good affinity for water, so it contained the water in the electrolyte solution, causing the HAp layer to peel off from the TiO₂ layer. To make it clear this matter, we used nitric acid, acetylacetone, and Triton X-100, which are commonly used for making titanium dioxide slurries. Nitric acid and acetylacetone were used to improve the dispersibility of the HAP, while Triton X-100 was used as a surfactant.As a result, we could fabricate titanium dioxide and HAp layers as an electrode that were sufficient to withstand two hours of photopotential measurements.In the photopotential measurement, the prepared HAp-coated titanium dioxide electrode showed an apparent improvement in photopotential characteristics compared to the electrode with only titanium dioxide. In order to verify this effect, photopotential measurements were carried out on an electrode coated only with HAp. The relationship between the heat treatment temperature of HAp and the photocatalytic effect will be investigated in the later experiment.The current titanium dioxide electrodes do not adsorb dyes and can only utilize the photon energy of ultraviolet region. In the future, we aim to improve the electrode properties by adsorbing ruthenium dyes on the titanium dioxide and HAp layers to make the electrode capable of utilizing energy in the visible light region. In the meeting, it will be considered for use as an electrode in dye-sensitized solar cells.

Durability of Platinum Overlayers formed By Self-Terminating Electrodeposition

In Proton Exchange Membrane Fuel Cell (PEMFC), the membrane electrode assembly (MEA), especially the electrode, is considered 'the heart' and is designed to accommodate the need for efficient transport of electrons, reactants, and heat as well as constraints imposed by the platinum cost. Advances in PEMFC electrode design over the years, which range from using Pt black films with a loading of 10 gpt/cm2 in the 1970s to present-day Pt/ PGM (Platinum Group Metal) nanoparticle coated carbon-black particles (Pt/C) that use about 0.3 mgpt/cm2, have led to significant cost-reduction and performance enhancement. However, durability problems associated with corrosion of carbon support and subsequent loss of active surface area during start-up or shut down cycles have led to renewed interest in carbon-free nanostructured electrodes that employ a thin coating of Platinum or PGM-based catalytic layer on mesostructured conductive support ((Debe 2012), (Liu et al. 2012)).In this context, we carried out systematic ex-situ investigations on the durability of platinum thin films comprising of atomic layers formed by Self-Terminating platinum electrodeposition (Liu et al. 2012). We characterized the sequential growth of platinum film using XPS and AFM measurements; and analyzed the electrocatalytic performance as a function of the number of self-terminating pulses. We found that eight pulses of electrodeposition, corresponding to ~10 nm thick platinum film, can meet stringent ex-situ durability targets set, by the Department of Energy (DOE), USA, for a potential electrocatalyst in Fuel Cell Vehicles (FCVs) application. Our results also show that platinum layers formed using four pulses (< 4 µg/cm2 loading) and even one pulse (< 1 µg/cm2 loading) are electrochemically active. For platinum samples formed using eight or more pulses, we observed ~ 20% loss in Electrochemically Active Surface Area (ECSA) during the first 3000 cycles and 10-15% ECSA loss in the remaining 27000 cycles, indicating stabilization of platinum activity over time. We will present the results of our studies on the minimum number of platinum pulses needed to form a complete overlayer of electrochemically active platinum and discuss the platinum loss during the ex-situ durability tests using ICP-OES and Cyclic Voltammetry measurements. These studies pave the way for an additive, roll-to-roll, and cost-effective manufacturing process of ultra-low platinum loaded MEAs for PEMFCs by building on our earlier results on printing silver nanostructures using a simple inkjet printer by Print-Expose-Develop technique (Parmar and Santhanam 2014) in conjunction with the ability to controllably form atomic layers of platinum on metallic substrates by Self-terminating electrodeposition. Figure 1

Controlling efflorescence in geopolymers: A new approach

Excessive efflorescence in geopolymers can reduce their durability due to reduced compressive and tensile strength, in addition to an aesthetic problem. In this work, a new approach focused on the compositional adjustment was used to preserve the mechanical properties without efflorescence development in the geopolymers based on metakaolin (MK-G), biomass ash (BA-G), and stone cutting waste (SW-G). In the MK-G samples, the efflorescence formation was controlled by decreasing the Na2O/Al2O3 molar ratio from 1.10 to 0.90, without compromising the compressive strength (~ 16 MPa in MK-G0.9). In the BA-G tested samples, an increase in the compressive strength was observed. Similarly, for the SW-G samples, the reduction of Na2O/Al2O3 ratio (1.4–1.0) also hindered efflorescence, as well as denoted a decrease in sodium and alkalinity values in the leached extract. In addition to compositional adjustments, processing changes with the submerged water cure have proved to be an efficient alternative to prevent efflorescence development. Understanding this phenomenon and strategies to reduce the efflorescence formation potential can avoid durability problems in the use of geopolymers in building construction.

Study on mechanical properties and air-void structure characteristics of hybrid fiber fly ash concrete under sulfate attack

Sulfate attack is one of the common durability problems of concrete. The concrete structure in saline soil is particularly susceptible to sulfate attack. The aim of this paper was to investigate the effect of fly ash on the mechanical properties and pore structure of fiber reinforced concrete under sulfate attack. The sulfate resistance of different content of fly ash (0%, 10%, 20%) at different sulfate attack ages (0 d, 30 d, 60 d, 90 d, 120 d, 150 d) was presented. By analyzing the variation of mass loss rate, ultrasonic wave velocity, relative compressive strength and relative splitting tensile strength, the mechanical properties of concrete under sulfate attack were studied. In addition, the air-void structure test was carried out to explore the pore structure characteristics of concrete. The test results suggested that the contribution of fly ash could improve the sulfate resistance of concrete. At the same sulfate attack age, compared with other contents, the hybrid fiber fly ash concrete with 10% fly ash could strong against sulfate attack. At the later stage of sulfate attack, the corrosion resistance of concrete weakened, the mass loss rate, wave velocity, relative compressive strength and relative splitting tensile strength were reduced, while the pore structure parameters showed that fly ash could fill large pores for reducing corrosion damage. Adding 10% fly ash refined pores and enhanced the strength of concrete. The generation of pores is main factor for the deterioration of concrete structure. The fractal dimension well expressed the changes of pores in concrete. Based on fractal dimension and fly ash content, the damage model was established, which could predict the damage deterioration of hybrid fiber fly ash concrete under sulfate attack.

Numerical Simulation of the Effect of Freeze–Thaw Cycles on the Durability of Concrete in a Salt Frost Environment

In order to improve the accuracy of the analysis of the impact of freeze–thaw cycle on concrete durability in a salt freezing environment, the numerical simulation of the impact of the freeze–thaw cycle on concrete durability in a salt freezing erosion environment is studied in this paper. Firstly, considering the influence of axial force and bending moment on the relationship between bending moment and curvature, a concrete fiber beam column model is established. Then, according to the joint influence of temperature field, stress field and seepage field on concrete in the process of freezing and thawing, the control differential equation of the freezing and thawing cycle is established. The freeze–thaw damage section is divided, the non-uniform distribution of freeze–thaw damage is determined, and the division of the freeze–thaw damage section is completed. According to the linear relationship between freeze–thaw damage degree, relative dynamic elastic modulus, freeze–thaw cycle times and position variables, the durability of concrete is numerically simulated, and the attenuation law of bond strength at different section depths after freeze–thaw is determined. The results show that the temperature curve simulated by the design method is consistent with the actually measured temperature curve, which can better reduce the temperature change of the inner core of the test block during freezing and thawing, and the relative dynamic elastic modulus is in good agreement with the actual value, which can prove that the method in this paper has certain practical application value. It is expected to provide some reference for solving the durability problem of concrete in a salt frost erosion environment and the optimal design of concrete structures.

ANALYSIS OF DIFFERENT ENVIRONMENTS INFLUENCE ON COPPER ALLOYS CORROSION RESISTANCE

Purpose of this work was to establish relationship between corrosion damages depending on chemical composition, as well as external factors affecting copper and copper alloys in different operating conditions corrosion. Methodology. Object of analysis was actual normative and technical database on standard and prospective copper-based alloys compositions for operation in aggressive environments (atmosphere, gases, salts and alkalis solutions, aqueous mediums). Comparative analysis method in order to substantiate the prospects of special bronzes implementation for manufacture of machines and mechanisms corrosion-resistant parts has been used. Results and discussion. Copper alloys behavior in different operating conditions has been analyzed and factors causing their destruction have been considered. Corrosion damaging relationships with chemical composition, as well as external factors affecting corrosion have been demonstrated. Information on copper alloys corrosion rate in different environments has been given. Issues of copper alloys rational uses in relation to parts and constructions peculiar working conditions have been presented. Relevant information on copper alloys products problem of reliability and durability increasing, one of which solving methods is purposeful choice of material for their manufacturing depending on operating conditions, has been given. Practical value. According to research results, effective practical using of technical copper, brasses, tin, silicon, aluminum, nickel bronzes have been substantiated in terms of their resistance to corrosion damages features. Conclusions. It has been established that copper alloys are characterized by high corrosion resistance in different environments. In marine and ocean environments aluminum bronzes corrosion resistance exceeds in some cases all other copper alloys resistance. It has been concluded that aluminum bronzes and copper-nickel alloys have the highest corrosion resistance among copper alloys.

Evaluation of the Durability of Slippery, Liquid-Infused Porous Surfaces in Different Aggressive Environments: Influence of the Chemical-Physical Properties of Lubricants

Liquid-repellent surfaces have been extensively investigated due to their potential application in several fields. Superhydrophobic surfaces achieve outstanding water repellence, however their limited durability in severe operational conditions hinders their large-scale application. The Slippery, Liquid-Infused Porous Surface (SLIPS) approach solves many of the durability problems shown by superhydrophobic surfaces due to the presence of an infused liquid layer. Moreover, SLIPS show enhanced repellence towards low surface tension liquids that superhydrophobic surfaces cannot repel. In this perspective, SLIPS assume significant potential for application in harsh environments; however, a systematic evaluation of their durability in different conditions is still lacking in the literature. In this work, we report the fabrication of SLIPS based on a ceramic porous layer infused with different lubricants, namely perfluoropolyethers with variable viscosity and n-hexadecane; we investigate the durability of these surfaces by monitoring the evolution of their wetting behavior after exposure to severe environmental conditions like UV irradiation, chemically aggressive solutions (acidic, alkaline, and saline), and abrasion. Chemical composition and viscosity of the infused liquids prove decisive in determining SLIPS durability; especially highly viscous infused liquids deliver enhanced resistance to abrasion stress and chemical attack, making them candidates for applicable, long-lasting liquid-repellent surfaces.

A short- and long-term prognostic associating with remaining useful life estimation for proton exchange membrane fuel cell

Proton exchange membrane fuel cell (PEMFC), as a promising power source, provides a feasible solution for clean and low-carbon energy systems. The durability problem restricts PEMFC application in some scenarios, which can be improved by the prognostic technology indirectly. This paper aims to develop a data-based method to implement the short-term and long-term prognostic simultaneously, and the developed long-term prognostic can be performed without future operation information. First, the short-term prognostics of five multi-step ahead forecasting strategies are proposed and compared based on a long short-term memory (LSTM) network. Results show that the multi-step input and multi-step output (MIMO) with LSTM strategy has a better performance in the short-term prognostics under the test conditions of the stationary and dynamic current. Then, the hyper-parameters of the prediction model are determined by an evolutionary algorithm. Furthermore, in the long-term prognostics regime, the variable-step long-term method is proposed and rectified by the short-term prognostics. Finally, the developed remaining useful life (RUL) prediction is compared with a model-based extended Kalman filter. The average root mean square error results for the short-term prognostics of two conditions are 0.00532 and 0.00538, respectively. The RUL estimations of two PEMFCs named FC1 and FC2 are given with 95% and 90% confidence intervals, respectively. Consequently, the proposed method can achieve acceptable accuracies in the short-term prognostic, the long-term prognostic, and the RUL prediction.

Bioinspired Multifunctional Glass Surfaces through Regenerative Secondary Mask Lithography.

Nature-inspired nanopatterning offers exciting multifunctionality spanning antireflectance and the ability to repel water/fog, oils, and bacteria; strongly dependent upon nanofeature size and morphology. However, such patterning in glass is notoriously difficult, paradoxically, due to the same outstanding chemical and thermal stability that make glass so attractive. Here, regenerative secondary mask lithography is introduced and exploited to enable customized glass nanopillars through dynamic nanoscale tunability of the side-wall profile and aspect ratio (>7). The method is simple and versatile, comprising just two steps. First, sub-wavelength scalable soft etch masks (55-350nm) are generated through an example of block copolymer micelles or nanoimprinted photoresist. Second, their inherent durability problem is addressed by an innovative cyclic etching, when the original mask becomes embedded within a protective secondary organic mask, which is tuned and regenerated, permitting dynamic nanofeature profiling with etching selectivity >1:32.It is envisioned that such structuring in glass will facilitate fundamental studies and be useful for numerous practical applications-from displays to architectural windows. To showcase the potential, glass features are tailored to achieve excellent broadband omnidirectional antireflectivity, self-cleaning, and unique antibacterial activity toward Staphylococcus aureus.

Ettringite hysteresis under sorption from molecular simulations

The response of ettringite under sorption is critical for the utilization of this mineral as an energy storage material and to understand the concrete durability problems associated with ettringite formation. We report molecular simulations directly sampling the osmotic ensemble to understand the sorption processes and structural changes in ettringite-metaettringite transition. Desorption branch and sorption-induced volume changes from simulations agree with the experiments. The structural changes at low relative humidity are analyzed, revealing for the first time details of metaettringite structure. The reversibility under sorption observed experimentally is captured by simulation in the ettringite domain. The reversibility in the conversion of metaettringite into ettringite is not captured by the direct simulations in the osmotic ensemble due to the large volume changes associated with ettringite desorption. Finally, we discuss the role of hydrogen bonds on the hysteresis in ettringite.

Improvement of ASTM A53 Steel Durability Using Agrowastes as Carburizing Agent

The importance of steel in manufacturing and construction over the past century cannot be over-emphasized and easy accessibility couple with excellent mechanical properties make it preferable over others. However, the problem of durability has posed a serious concern as majority of steel application are meant for long term use. Several attempts have been made to improve the durability of steel in the past and increase of carbon content in low carbon steel was found to be a suitable agent. Although getting carbon is not the challenge rather obtaining it from a sustainable source that has zero environment impact. This research identified two separate agrowaste that has high carbon content the issue of sustainability brought about the development of carburizing agent from agrowaste that are easily accessible namely palm kernel and eggshell which is employed in this research. The use of agrowaste was found to be effective as there was notable increase in grain structure of the carburized steel when compared to the control sample without carburized agent in it.

Electrochemical Study of Stainless Steel Anchor Bolt Corrosion Initiation in Corrosive Underground Water

Application of low-nickel stainless steel anchor was one of the economical and effective methods to solve the durability problem of slope engineering. At present, there are scarce reports about corrosion characteristics of low-nickel stainless steel in various underground waters. For investigating the corrosion initiation of stainless steel anchor bolt in corrosive underground water, the effect of SO42−, HCO3− and pH value on the corrosion behavior of 201 low-nickel stainless steel was studied via electrochemical methods. As the SO42− concentration, HCO3− concentration or pH value increase, the open circuit potential and polarization resistance increase, while the double-layer capacitance, donor density and passive current density decrease. The results indicate that corrosion is inhibited by SO42−, HCO3− and OH− in underground water. In addition, the inhibitive efficiency of SO42− and HCO3− increases with the SO42− and HCO3− concentration.

Evaluation of the Uniformity of Protective Coatings on Concrete Structure Surfaces Based on Cluster Analysis.

With the continuous development of urbanization and industrialization in the world, concrete is widely used in various engineering constructions as an engineering material. However, the consequent problem of durability of concrete structures is also becoming increasingly prominent. As an important additional measure, a protective coating can effectively improve the durability of concrete performance. Moreover, the uniformity of the concrete surface coating will directly affect its protective effect. Therefore, we propose a nondestructive inspection and evaluation method of coating uniformity based on infrared imaging and cluster analysis for concrete surface coating uniformity detection and evaluation. Based on the obtained infrared images, a series of processing and analysis of the images were carried out using MATLAB software to obtain the characteristics of the infrared images of the concrete surface. Finally, by extracting the temperature distribution data of the pixel points on the concrete surface, an evaluation method of concrete surface coating uniformity based on a combination of cluster analysis and hierarchical analysis was established. The evaluation results show that the determination results obtained by this method are consistent with the actual situation. This study has a positive contribution to the testing of concrete surface coating uniformity and its evaluation.