Showing papers on "Durability published in 2010"

Laundering Durability of Superhydrophobic Cotton Fabric

Abstract: www.MaterialsViews.com C O M Laundering Durability of Superhydrophobic Cotton Fabric M U N I By Bo Deng , Ren Cai , Yang Yu , Haiqing Jiang , Chunlei Wang , Jiang Li , Linfan Li , Ming Yu , Jingye Li ,* Leidong Xie , Qing Huang , and Chunhai Fan C A IO N A superhydrophobic surface, displaying a contact angle (CA) of water greater than 150 ° , [ 1 ] is a fascinating phenomenon in nature, which attracts not only academic but also industrial interest. It is well known that a superhydrophobic surface generally has a low surface energy chemical structure combined with a particular micro-structural roughness. [ 2 ] Using this principle, numerous superhydrophobic surfaces have been developed based on different materials using various methods and techniques, which have been reviewed recently. [ 3 ] There are many potential applications for artifi cial superhydrophobic surfaces in our daily life, among which waterproof textile is considered to be one of the most promising ones. [ 4 ] In this work, we report a convenient radiation-induced graft polymerization method to prepare an extremely stable, superhydrophobic cotton fabric, which is chemically stable over the entire pH range (0–14), and durable for more than 250 commercial or domestic launderings. Cotton fabric is widely used in daily life, it is a hydrophilic woven textile with numerous holes in its woven structure that make cotton fabric-based clothes comfortable. It is expected that a cotton fabric that is endowed with superhydrophobic properties, a so-called “superhydrophobic cotton fabric” (SCF), simultaneously possesses the properties of being waterproof as well as being air-breathing, which would lead to comfortable waterproof clothes. [ 5 ] In addition, because of the existence of air layers, its surface may not be wetted even upon full immersion in water, which makes it a good candidate for life vests. Because of the above-mentioned merits, many publications have been reported on the study of SCFs, which were mainly fabricated by doping of the cotton fabric with low surface energy nanoparticles. [ 6 ] However, the laundering durability, which is one of the most important characteristics for a fabric, has been largely ignored in these previous studies. Forming covalent bonds between cotton fi bers and low surface energy compounds is a critical point to enhance the stability of the SCF, and, as a consequence, should be the way to improve the laundering durability. [ 7 ] It is mainly the strength

Effect of rice-husk ash on durability of cementitious materials

Abstract: In this paper the effects of partial replacements of Portland cement by rice-husk ash (RHA) on the durability of conventional and high performance cementitious materials are investigated Different percentages of RHA replacement levels, two RHAs (amorphous and partially crystalline optimized by dry-milling) and several water–cementitious materials ratio are studied The following durability aspects were tested: air permeability, chloride ion penetration, alkali-silica expansion, sulfate and acid resistance The results were compared with those of cementitious materials without RHA It is concluded from the tested properties that the incorporation of both RHAs in concretes show different behaviors for air permeability and chloride ion penetration depending on the water/cementitious materials ratio used; in mortars, it reduces the mass loss of specimens exposed to hydrochloric acid solution and decreases the expansion due to sulfate attack and the alkali-silica reaction The results of durability aspects due to physical or pozzolanic effects after the addition of both RHAs, and its chemical composition, in general indicate an enhanced performance, proving the feasibility of its rational utilization as a supplementary cementing material

Temperature as an Accelerating Factor for Long-Term Durability Testing of FRPs: Should There Be Any Limitations?

Abstract: Fiber-reinforced polymer (FRP) composites are increasingly being used in civil engineering applications due to their numerous advantages. Moreover, some environmental conditions can potentially enhance their long-term durability. Therefore, the study of their long-term behavior is crucial to ensure their durability. To perform durability study in a reasonable time limit, accelerating factor, such as high temperature, is generally used. However, the use of very high temperature of conditioning could amplify the reduction of the properties leading to conservative prediction of long-term properties. The present paper attempts to clarify the effects of high temperatures on the mechanical and barrier properties (moisture absorption) of GFRP’s internal reinforcement, by presenting some experimental results and conclusions of laboratory accelerated studies.

Observation and quantification of water penetration into Strain Hardening Cement-based Composites (SHCC) with multiple cracks by means of neutron radiography

Abstract: Durability of reinforced concrete structures has become a crucial issue with respect to economy, ecology and sustainability. One major reason for durability problems of concrete structures is the limited strain capacity of cement-based materials under imposed tensile stress. By adding PVA fibers, a new material named Strain Hardening Cement-based Composites (SHCC) with high strain capacity can be produced. Due to the formation of multiple micro-cracks, wide cracks can be avoided in SHCC under an imposed strain. The high strain capacity, however, is beneficial with respect to durability only if the multi-crack formation in SHCC does not lead to significantly increased water penetration. If water and aggressive chemical compounds such as chlorides and sulfates dissolved in water penetrate into the cement-based matrix and reach the steel reinforcement service-life of reinforced concrete structures will be reduced significantly. In this project, neutron radiography was applied to observe and quantify the process of water penetration into uncracked SHCC and after the multi-crack formation. In addition, water penetration into integral water repellent cracked and uncracked SHCC, which has been produced by adding a silane-based water repellent agent to the fresh SHCC mortar has been investigated. Results will be discussed with respect to durability.

Durability of lightweight OPS concrete under different curing conditions

Abstract: The use of waste materials and by products from different industries for building construction has been gaining increased attention due to the rapid depletion of natural resources. It has been found that oil palm shell (OPS), which is a waste from the agricultural sector, can be used as coarse aggregate for the manufacture of structural lightweight concrete. However, for OPS concrete to be used in practical applications, its durability needs to be investigated. Therefore, this paper presents the durability performance of OPS concrete under four curing regimes. The durability properties investigated include the volume of permeable voids (VPVs), sorptivity, water permeability, chloride diffusion coefficient and time to corrosion initiation from the 90-day salt ponding test, and Rapid Chloride Penetrability Test (RCPT). Results showed that the durability properties of OPS concrete were comparable to that of other conventional lightweight concretes and proper curing is essential for OPS concrete to achieve better durability especially at the later ages.

Study on durability of natural fibre concrete composites using mechanical strength and microstructural properties

Abstract: Investigations to overcome the brittle response and limiting post-yield energy absorption of concrete led to the development of fibre reinforced concrete using discrete fibres within the concrete mass. Out of the commonly used fibres, easily available low cost natural fibres are renewable source materials. Though these fibres are ecologically advantageous, they have some limitations such as lower durability and lesser strength. But recent research provides several treatment processes to enhance the durability of natural fibres. In this paper, the durability of natural fibres such as coconut coir and sugarcane bagasse has been reported by conducting an experimental investigation. This investigation includes two parts. The first part focuses on the determination of mechanical strength properties such as compressive, tensile, modulus of rupture and flexural properties of natural fibre reinforced concrete specimens once every 3 months for a period for 2 years under alternate wetting and drying conditions. Gain or loss in strength of composite concrete at 9 intervals were computed and are reported here. The second part covers the microstructural properties of fresh natural fibres in as received condition and natural fibres reacted with concrete under accelerated curing conditions for two years. SEM and EDAC test results are discussed.

Fresh, Mechanical, and Durability Characteristics of Self-Consolidating Concrete Incorporating Volcanic Ash

Abstract: Self-consolidating concrete (SCC) is known for its excellent deformability, high resistance to segregation, and use in congested reinforced concrete structures characterized by difficult casting conditions without applying vibration. The use of known mineral admixtures such as fly ash and slag cement has proved very effective in the production of nonexpensive SCC with satisfactory fresh and hardened properties. However, the use of volcanic ash (VA) in SCC is new and can provide low cost SCC. This paper presents fresh, mechanical, and durability characteristics of VA based SCC mixtures (VA-SCCs). VA-SCCs are developed by varying water-to-binder ratio, percentages of VA as cement replacement, and dosages of superplasticizer (SP). Mix design parameters are optimized to achieve minimum use of SP and optimum use of VA. The fresh concrete properties are determined from slump flow, V-funnel flow time, bleeding, air content, and segregation tests. The mechanical properties and durability characteristics such as compressive strength, freezing-thawing resistance, rapid chloride permeability, surface scaling resistance, and drying shrinkage are determined to evaluate the performance of VA-SCCs. The study produces encouraging results and confirms the production of satisfactory VA based SCC mixtures with acceptable properties. VA-SCCs having a minimum strength of 15 MPa (requirement for some structural concrete applications) can be obtained by replacing up to 50% (by mass) of cement by VA. Development of nonexpensive and environmental friendly VA-SCC with acceptable strength and durability characteristics (as illustrated in this study) is extremely helpful for the sustainable development and rehabilitation of volcanic disaster areas around the world.

Harmonic and Random Vibration Durability of SAC305 and Sn37Pb Solder Alloys

Abstract: In this paper, durability tests were conducted on both SAC305 and Sn37Pb solder interconnects using both harmonic and random vibration. The test specimens consist of daisy-chained printed wiring boards (PWBs) with several different surface-mount component styles. Modal testing was first conducted on a test PWB to determine the natural frequencies and mode shapes. The PWB was then subjected to narrow-band excitation at its first natural frequency. Electrical continuity of the daisy-chain nets was monitored to measure the time-to-failure (and hence cycles-to-failure) of the interconnects. The response history of the PWB was recorded with strain gages located near the components of interest. Finite element analysis (FEA) was conducted for each component type, to estimate the transfer function between the flexural strain of the PWB and the strain in the critical solder joint. The predicted strain transfer function was then combined with the measured PWB strain response history to estimate the strain history in the critical solder joints. The solder strain history was used, in conjunction with the failure history, to estimate lower bounds for the fatigue durability (S-N curves) of the solder interconnects. In the first part of this paper, the results show that the SAC305 interconnects are marginally less durable than Sn37Pb interconnects for the harmonic excitation range used in this paper. The durability model constants are found to be very sensitive to the solder stress-strain curve assumed in the FEA. Since the stress-strain properties reported in the literature for these solder alloys vary significantly, the solder stress-strain curves were parametrically varied in the FEA, to assess the resulting effect on the estimated S-N curves. In the second part of this paper, random-vibration tests were conducted to assess durability under step-stress, broad-band excitation. Conventional cycle counting techniques were used to quantify the random excitation histories in terms of range distribution functions. Using the same time-domain vibration fatigue analysis used earlier for narrow-band excitation, the durability trend for the corresponding SAC305 and Sn37Pb solder interconnects under broad-band excitation was found to be similar to that found earlier under harmonic vibration excitation. Comparison between the durability prediction and test results provides a good understanding of the effect of stress-strain behavior on the fatigue constants of these solder materials. The best set of material properties was then used to verify the durability of leadless chip resistor interconnects under quasi-static mechanical cycling.

Physical, Mechanical, and Durability Characterization of Preloaded GFRP Reinforcing Bars

Abstract: This paper presents the physical, mechanical, and durability characterization of glass fiber-reinforced polymer (FRP) (GFRP) bars subjected to different tensile stress levels. FRP bars were first loaded at levels up to 20, 40, 60, and 80% of their ultimate tensile strength (UTS) which could create cracks and microcracks in the FRP bars and affect the long-term durability of the product. Microstructural observations were conducted on preloaded GFRP reinforcing bars to show the deterioration of fiber, matrix, and the fiber/matrix interface. Moisture absorption and tensile properties of loaded bars were also measured to estimate the potential effects of cracks and microcracks on durability-related properties and on short-term mechanical properties, respectively. Loaded bars were also embedded in a moist mortar at elevated temperature to perform accelerated aging. The measured tensile strengths of the loaded bars before and after exposure were considered as a measure of the durability performance of the speci...

Probabilistic Assessment of Concrete Structure Durability under Reinforcement Corrosion Attack

Abstract: In the context of performance-based approaches, sustainability and whole life costing, the concrete structure durability issue has recently gained considerable attention. The present paper deals with service life assessment using durability limit states specialized for concrete structures. Both initiation and propagation periods of reinforcement corrosion are considered and a comprehensive choice of limit states is provided. The approach is based on degradation modeling and probabilistic assessment, enabling the evaluation of service life and the relevant reliability level, serving thus to facilitate the effective decision making of designers and clients. For this purpose the selected analytical models for degradation assessment are randomized and appropriate software has been developed. Three numerical examples are presented: a comparison of modeled carbonation depth with in situ measurements on a cooling tower, and analyses of crack initiation due to corrosion and loss of reinforcement cross section.

Evaluation of durability of natural fibre reinforced cement mortar composite- a new approach

Abstract: ‘Toughness’ of a composite generally based on the ‘toughness indices’ evaluated by flexural tests as contemplated in several codes (ASTM, ACI, JCI-SF4/JSCE-SF4) may not be appropriate / realistic for natural fibre cement composites containing low modulus fibres like sisal, coir etc., due to several reasons. Further, durability of natural fibre cement composite can be evaluated on the basis of flexural toughness (FT) and it has a special significance. Toughness of a natural fibre composite can also be evaluated by impact tests, which helps in realistic assessment of ductility of the above composite. Evaluation of durability of a natural fibre composite by residual impact strength (Irs) and flexural toughness index (IT) and their comparison are presented and discussed. Irs values could be used to assess the durability of natural fibre composites, than, the conventional ‘toughness indices’ used for composites, in general.

Modeling of time to corrosion-induced cover cracking in reinforced concrete structures

Abstract: Concrete cover cracking induced by reinforcement corrosion is an important indication of durability limit state for reinforced concrete(RC) structures,and can be used to determine the structural service life.Based on the assumption of uniform corrosion of reinforcement,two models for predicting the time from corrosion initiation to cover cracking and its corresponding corrosion ratio of reinforcement were established according to the mechanics of elasticity and Faraday's Law.In the present models,the deformation property of corrosion products and the extent of corrosion products'ingress into expansive cracks were all taken into account.The main factors affecting the time to corrosion-induced cracking were analyzed.It is found that the increase of cover thickness,decrease of rebar diameter,improvement of concrete strength and reducing volume expansion of corrosion products are in favor of improving the durability of RC structure.The comparison of prediction results with experimental values obtained from accelerated and long-term tests shows that the proposed model is in good agreement with test results and can be applied in practical design.

Durability assessment of concrete structures: reinforcement depassivation due to carbonation

Abstract: This paper deals with durability design and comments on the assessment of reinforced concrete (RC) structures in relation to existing codes. Enhancement is provided by advanced approaches incorporating probabilistic simulations, mathematical models of the carbonation process in concretes made from CEM I through to CEM V, and the reliability issue. This paper presents practical software tools used for service life prediction, concrete cover evaluation and assessment of relevant reliability levels. A partial verification using test results is also presented.

Durability Estimates of Copper Plated Electrodes for Self-sensing CFRP Composites

Abstract: This study deals with the durability tests of a new copper plated electrode process for self-sensing or self-healing Carbon Fiber Reinforced Plastic (CFRP) composites. The self-sensing or self-healing CFRP composites adopt carbon fibers as sensors or actuators. The electrical contacts at the electrodes have a significant effect on the self-sensing or self-healing ability. This research proposes a new electric copper plated process for fabricating reliable electrodes. Using single-ply specimens, electrical contact resistances after cyclic loading are measured. The cyclic loading test is performed to investigate the long term durability of these new electrodes. The new copper plated electrode was found to have high durability after cyclic loading and is appropriate for the practical self-sensing or self-healing CFRP composites.

Characterization of electromagnetic properties for durability performance and saturation in hardened cement mortar

Abstract: Electromagnetic (EM) properties—dielectric constant and conductivity are changed with porosity and saturation in cement-based materials. In this paper, dielectric constant and conductivity are measured in cement mortar with 5 different mixture conditions considering saturation. For the same mixture proportions, durability tests including porosity, chloride diffusion, air permeability, sorptivity, and water diffusion are performed. Among the continuously measured EM properties within 5–20 GHz of frequency range for different saturation, results under 60% of saturation which shows stable results are selected and averaged as one value. The averaged measurements utilizing results under 60% of saturation are compared with those from durability tests. Through the normalization using the results of W/C 40% which shows best durability performances, changing ratios of durability characteristics are evaluated with normalized dielectric constant and conductivity. The behaviors of EM properties with different saturation and their relationships with durability performances are studied.

A column dependency-based approach for static and dynamic recovery of databases from malicious transactions

Abstract: Even state of the art database protection mechanisms often fail to prevent occurrence of malicious attacks. Since in a database environment, the modifications made by one transaction may affect the execution of some of the later transactions, it leads to spreading of the damage caused by malicious (bad) transactions. Following traditional log-based recovery schemes, one can rollback (undo) the effect of all the transactions, both malicious as well as non-malicious. In such a scenario, even the unaffected transactions are also rolled back. In this paper, we propose a column dependency-based approach to identify the affected transactions which need to be compensated along with the malicious transactions. To ensure durability, committed non-malicious transactions are then re-executed in a manner that retains database consistency. We present a static recovery algorithm as well as an on-line version of the same and prove their correctness. A detailed performance evaluation of the proposed scheme with TPC-C benchmark suite is also presented.

Durability design and specification for concrete structures––the way forward

Abstract: Much effort has been made in recent years to adopt suitable strategies for durability design of concrete. Most of this work has focused on the development of ‘performance specifications’ for concrete. However, there are many barriers and limitations to successful implementation of these strategies for early-age control of reinforced concrete durability. This article reviews some of the recent efforts in the implementation of such strategies. It describes the South African approach to durability design, which is based on performance specifications that are to be satisfied at the time of construction. Case studies are presented on approaches to reinforced concrete design and the corresponding application of a durability performance specification, to highlight the potential for adopting a probability-based methodology for durability design. Finally, the paper attempts to provide a way forward towards successful utilization of such approaches, with particular emphasis on the construction industry in India.

Use of pore solution analysis in design for concrete durability

Abstract: Pore solution analysis of hardened cement-based materials has been in increasing use over the last 30 years to determine the ionic composition of the pore fluid at various ages and after exposure to various temperature regimes. In addition, it has been used to evaluate the potential for results of chemical interaction with external solutions or with other concrete materials (such as alkali-reactive aggregates). Once related to physical durability test data, knowledge of the pore solution composition in combination with the nature of the solid phases present can be used to predict the potential for future durability-related chemical interactions. This paper discusses three areas where the usefulness of pore solution analysis has been instrumental in increasing the understanding of concrete durability issues related to: (a) alkali binding as it affects alkali–silica reaction (ASR), (b) chloride-binding as it affects reinforcement corrosion resistance, and (c) delayed ettringite formation (DEF).

Sol-gel thermal barrier coatings: Optimization of the manufacturing route and durability under cyclic oxidation

Abstract: A new promising and versatile process based on the sol–gel transformation has been developed to deposit yttria-stabilised thermal barrier coatings. The non-oriented microstructure with randomly structured pore network, resulting from the soft chemical process, is expected to show satisfactory thermo-mechanical behaviour when the TBC is cyclically oxidized. First stage of the research consists of optimizing the processing route to generate homogeneous microstructure and controlled surface roughness. The objective is to reduce, as much as possible, the size and depth of the surface cracks network inherent to the process. Indeed, the durability of the TBC when cyclically oxidized strongly depends on the sharpness of those cracks that concentrate thermo-mechanical stresses and generate detrimental propagation resulting in spallation. Cyclic oxidation tests are performed using a cyclic oxidation rig instrumented with CCD cameras to monitor in a real time basis the mechanism of crack propagation and spallation. The impact of various parameters either directly related to the processing route, e.g. the intimate microstructure of the TBC and the TBC thickness, or to the thermal loading, e.g. the oxidation temperature and the cumulated hot time, on the durability of the TBC is investigated

Self temperature regulating phase-change energy storage plate

Abstract: The invention belongs to the field of building materials and relates to a plate for buildings or decoration with the functions of storing energy, insulating heat and automatically regulating indoor temperature, in particular to a self temperature regulating phase-change energy storage plate. The self temperature regulating phase-change energy storage plate comprises a honeycomb plate, and the honeycomb plate comprises a bottom plate, a high-thermal-conductivity panel and a multiattribute honeycomb sandwich layer between the panel and the bottom plate, wherein the panel, the bottom plate and the honeycomb sandwich layer are sealed and bonded; a plurality of mutually and independently sealed phase-change units are formed in the honeycomb plate; and the phase-change units are filled with phase-change materials. The invention has the advantages that the self temperature regulating phase-change energy storage plate has various original advantages of the honeycomb plate, meanwhile, the phase-change materials can be effectively packaged so as to increase the durability of the phase-change materials; moreover, by using high thermal conductivity of the multiattribute honeycomb sandwich layer and the panel, the phase-change materials can be quickly carried out heat exchange with the external environment to improve the utilization efficiency of the phase-change heat; and the processing is simple and the cost is low.

On Durability of SHCC

Abstract: Strain-hardening cement-based composites (SHCC) resist increased tensile stress after first crack formation, over a significant range of tensile strain. This increased strength and strain capacity is achieved by effective crack bridging by fibres, across multiple cracks of widths in the micro-range. Whether the crack width limitation translates into increased durability through retardation of ingress of moisture, gas and other deleterious matter, is scrutinised in this paper. This is done by evaluation of recent test results from several laboratories internationally. The question whether these small crack widths are maintained under sustained, cyclic or other load paths is also addressed, concluding that the crack widths are not independent of the loading path. This contribution summarises the State-of-the-Art- Report prepared in the period 2005 to 2009 by RILEM TC 208-HFC, Subcommittee 2: Durability of SHCC. The potential of the comparatively new composite material becomes obvious, yet it is clearly outlined that further research is necessary before we fully understand the basic mechanisms underlying deterioration of SHCC. The JSCE Recommendation for design and construction of high performance fibre-reinforced composites with multiple fine cracks (HPFRCC) is a useful tool but it should be complemented by a similar recommendation on service life design in the future.