Loss Of Durability Research Articles

Durability performance of self-compacting concrete

The methodological shift in the thinking about concrete from a strength-based concept to a durability-based design has led to the development of self-compacting concrete (SCC). This paper presents a systematic experimental programme on durability studies conducted, covering three grades of SCC from low strength (M20 grade) to high strength (M70 grade). The durability studies include acid attack, corrosion, sorptivity and thermal studies. The main objective of this investigation is to develop SCC mixes that are resistant to acid attack and suitable for Indian temperature conditions compared with vibrated normal concrete. Other durability factors such as capillary absorption and corrosion resistance of three such grades of SCC mixes have also been investigated. It was noted from the durability studies that in almost all cases the loss in durability is reduced with increase in grade of concrete. Furthermore, a comparison of SCC and normal concrete mixes has shown a good performance of SCC specimens as against normal concrete specimens.

Qualitative and quantitative analysis and identification of flaws in the microstructure of fly ash and metakaolin blended high performance concrete after exposure to elevated temperatures

The extensive use of eco-friendly materials in concrete has led to the demand to fully understand the effect of fire on concrete. This research was carried out to evaluate high performance concrete (HPC) made with fly ash and metakaolin with replacement level of 20 percent by weight of cement after elevated temperatures exposure (200°C, 400°C, 600°C and 800°C). The mechanical performance was assessed from compressive strength while the durability was assessed from chloride permeability and water sorptivity test. Qualitative analysis of the microstructure of heated and unheated concrete was performed by SEM while quantitative analysis was performed on SEM images using Image Pro-plus software. Based on the qualitative and quantitative analysis of SEM images, the distribution of the number, type and surface area fraction of flaws were identified and changes in the structure of Interfacial Transition Zone (ITZ) were classified into different temperature ranges.Test results show that for all mixes post-elevated temperature compressive strength decreased while charge passed and sorptivity values increased with the increase in temperature from 27°C to 800°C. For all mixes, major strength and durability loss occurred after 400°C. Therefore, 400°C can be considered as critical temperature from the standpoint of strength and durability loss. From the qualitative and quantitative analysis, different types of flaws were identified. These were texture flaws (T), orientation flaws (O) collectively called as textured and orientation flaws (TO) and local flaws (L). The post-elevated temperature surface area fraction of TO and local flaws in the ITZ of each concrete mix continuously increased with the increase of elevated temperature. The increase in surface area fraction of flaws resulted in gradual loss in the mechanical and durability properties of concrete. Major increase in surface area fraction occurred in between 400 and 600°C, resulting in major strength loss and sharp increase in charged passed and sorptivity values through concrete specimens. Therefore, 400°C can be regarded as critical for change in the properties of concrete. No specific relationship between the number of TO flaws and the type of binding material in concrete and the temperature was found. However for local flaws, in general, the number increased with the increase of temperature. Also, the changes in the structure of ITZ were classified into three temperature ranges namely; the low range temperatures (27–200°C), the medium range temperatures (200–400°C) and the high range temperatures (400–800°C). The physical character of ITZ in HPC changes gradually from a discrete or discontinuous flaw zone at normal or mildly elevated temperature to a continuous and highly porous flaw zone at elevated temperatures. Thus, the classification signifies the effect of the texture of coarse aggregate and the orientation of fine aggregate in concrete matrix coupled with the effect of elevated temperatures on ITZ of HPC.

Mechanical performance, durability, qualitative and quantitative analysis of microstructure of fly ash and Metakaolin mortar at elevated temperatures

An experimental investigation was carried out to evaluate the performance of Fly Ash (FA) and Metakaolin (MK) mortar at elevated temperatures. Variables of the test program include partial replacement of cement with MK from 5% to 20%, FA from 20% to 60% and temperatures from 27°C to 800°C. The mechanical performance was assessed from compressive strength while the durability was assessed from chloride permeability test. Qualitative analysis of the microstructure of heated and unheated mortar was performed by Scanning Electron Microscope (SEM) while quantitative analysis was performed on SEM images using Image Pro-plus software.Test results show that for all mixes compressive strength decreased while charge passed increased with the increase in temperature from 27°C to 800°C. For all mixes, major strength and durability loss occurred after 400°C. Therefore, 400°C can be considered as critical temperature from the standpoint of strength and durability loss. Qualitative and quantitative analysis of SEM were found to be consistent with the results of strength and durability loss. The observation of SEM images and image analysis of area fractions of hardened cement paste (hcp) of different mortar mixes indicated that with the increase in temperature the pore area fraction increased while hydrated paste area fraction decreased. These factors resulted in the degradation of microstructure and affected the strength and durability of mortar. Major drop in hydrated paste area and rise in pore area fraction occurred at 400°C. Therefore, 400°C could be regarded as the critical temperature for change in the properties of mortar. In general, fly ash mix (FA20) showed better performance in all aspects.

Moisture Sensitivity of Bituminous Mixtures with Compound Fly Ash Modifier

Bitumen pavement suffers from moisture damage mainly due to loss of durability and stability in a short span of service life. Filler is known to be capable of increasing the stiffness of bitumen binder, contributing to improvement of moisture sensitivity of bitumen mixture. In this paper a new type of filler named 'Compound Fly Ash Modifier' (CFAM) was introduced in order to enhance the bond strength between acidic aggregate with bitumen. The primary object is to determine the effect of CFAM on the moisture sensitivity of bitumen mixtures prepared by gneiss and granite respectively, which are termed acidic aggregate. Modified Lottman test and fatigue test were conducted. The results show that CFAM improves the resistance of mixes to moisture damage in the increase in indirect tensile strength and the extension of fatigue life. Finally the mechanism of modified effects for CFAM is discussed.

Influence of using nonmaterial to reduce the moisture susceptibility of hot mix asphalt

Moisture damage in an asphalt mixture can be defined as the loss of strength, stiffness and durability due to the presence of moisture leading to adhesive failure at the binder–aggregate interface and/or cohesive failure within the binder or binder–filler mastic. In order to improve adhesion and reduce moisture sensitivity in asphalt mixtures, two different approaches have become apparent. One approach suggests that the aggregate surface be coated by a suitable agent that will reverse the predominant electrical charges at the surface and thus reduce the surface energy of the aggregate. In this study, the effects of nanomaterial, namely Zycosoil, on the moisture damage of asphalt mixtures were studied. Two types of aggregates that represent a considerable range in mineralogy, limestone and granite, were evaluated during the course of this study. To assess the impact of Zycosoil on moisture damage of hot mix Asphalt, control mixes (without Zycosoil) and mixes containing Zycosoil in dry and wet conditions were tested using indirect tensile-strength (ITS) and indirect tensile fatigue (ITF) tests. The results showed that limestone has less moisture damage potential compared to granite. The ratio of wet/dry values of ITST and ITFT for mixes containing Zycosoil was higher than the control mix for two types of aggregate. However, in mixtures made of granite aggregate, using Zycosoil is more effective. As the density of silanol groups is more in its surface, these groups are hydrophilic, and Zycosoil migrates to the polar water-loving surface, reacts with the silanol groups and forms siloxane bond, the strongest bond in nature, and creates a molecular level hydrophobic zone.

Comparative Study of Corrosion Characteristics of MCS and KS7 SS in Selected Acid Media

<b> </b>The challenges of corrosion in manufacturing industries and domestic sectors are enormous and have caused product loss, product contaminations, plants shutdown, loss of customer confidence and non durability of machineries. The objective of this study is to investigate and compare the corrosion resistance of medium Carbon steel (MCS) and KS7 stainless steel in selected acid media. The MCS and KS7 SS were exposed to 0.5M of H<SUB>2</SUB>SO<SUB>4</SUB><SUB>,</SUB> HCl and HNO<SUB>3</SUB><SUB> </SUB>environment for 36 days. The weight loss was taken every 3 days in order to evaluate CPR. The results obtained showed that KS7 SS generally offers a better corrosion resistance than the MCS in the selected acids media. The conclusion that can be drawn from this study is that while MCS is found to be unsuitable alloy in sulphuric, nitric and hydrochloric acid environments, KS7 SS is a reliable choice material for fabrication of engineering machines and tools meant for utility in these media.

Transport Modeling of Chlorides with Binding in Concrete

Chloride-induced corrosion is one of the most revealing cause of deterioration leading to premature durability loss by structural concrete. Among mechanisms governing penetration of chloride ions into the concrete, ingress by simple diffusion is the most decisive one for concentration-driven transport. The use of Fick’s law of diffusion of the second type does in general permit a modest preliminary analysis of the diffusive transport subject to certain constraints, primarily associated with stationary chloride diffusion coefficient hypothesis. A realistic critique to such analysis based on constant chloride diffusivity is however its total disregard of intrinsic chloride-binding capacity evidently exhibited by cement-based materials constituent to the concrete. Given that the chlorides are also partly free and partly bound in concrete, the significance of chloride binding for a more accurate service life analysis of the concrete is of practical concern. Moreover, the challenge raised by chloride binding against the invariant diffusivity assumption cannot also be ignored, because only free chlorides diffuse into and through the bulk concrete to thereafter directly pose corrosion risk. Since chloride transport in cementitious material such as concrete based on one or another chloride-binding mechanism may also be quite different, careful choice of chloride-binding model, consistent with the underlying phenomenological behavior, is critical for its implication to service life predictions. The aim of this study is therefore to examine the effect of chloride binding in terms of their isotherm formulations on time to corrosion activation resulting from transport of chloride ions in saturated concrete. Numerical analysis employing nonlinear finite element modeling techniques is used to account for null, linear and nonlinear chloride-binding formulations, including Langmuir and Freundlich representations for the nonlinear types, on the chloride transport problem. Results of the analysis, in view of experimental chloride-binding and penetration profile data mined from the literature, are presented to quantifiably underscore the effects that various binding parameters significantly have on onset of chloride-induced corrosion in relation to specific durability requirements.

Mechanism Research on Water Damage of Asphalt Mixture Based on Chemical Thermodynamics

Moisture can be defined as the early loss of strength and durability caused by moisture penetrating through the asphalt-aggregate mixture. This failure can be adhesive occurring at the asphalt-aggregate interface or cohesive occurring within the matrix (asphalt binder plus mineral filler). Therefore, the knowledge of chemical thermodynamics theory will help a great deal in understanding the adhesive properties of the asphalt mixture within the water. Water damage model of asphalt mixture are presented based on surface and interface theory. Two types of aggreates, a limestone and sandstone, two asphalt binder of base asphalt and SBS modified asphalt are used to produce four different mixutres of HMA in the paper. The four mixtures are subsequently tested using the method and ranked. According analysis of results, the methods based on chemical thermodynamics theory offers viable alternative to the assessment of water susceptibility of HMA. This method is simple, quicker and equipment utilized can easily and cheaply be assembled.

Mechanism Research on Water Damage of Asphalt Mixture Based on Chemical Thermodynamics

Moisture can be defined as the early loss of strength and durability caused by moisture penetrating through the asphalt-aggregate mixture. This failure can be adhesive occurring at the asphalt-aggregate interface or cohesive occurring within the matrix (asphalt binder plus mineral filler). Therefore, the knowledge of chemical thermodynamics theory will help a great deal in understanding the adhesive properties of the asphalt mixture within the water. Water damage model of asphalt mixture are presented based on surface and interface theory. Two types of aggreates, a limestone and sandstone, two asphalt binder of base asphalt and SBS modified asphalt are used to produce four different mixutres of HMA in the paper. The four mixtures are subsequently tested using the method and ranked. According analysis of results, the methods based on chemical thermodynamics theory offers viable alternative to the assessment of water susceptibility of HMA. This method is simple, quicker and equipment utilized can easily and cheaply be assembled.

Influence of pigment on biodeterioration of acrylic paint films in Southern Brazil

Biodeterioration of paint films leads to loss of durability and increased repainting costs. The influence of pigments on the biodeterioration of architectural paint films in the city of Florianopolis, Brazil, was evaluated using ten differently colored acrylic paint films exposed to the environment for 34 months. Fouling (biofilm formation) on the surfaces was assessed macroscopically, using British Standard BS 3900/1989 G6, and microscopically. After 20 months, major colonizers were bacteria and fungi, with some cyanobacteria and few algae; north-facing suede and peach and south-facing ice colors showed 100% cover at this time. The least affected color at all times was blue, with a maximum of 30% cover on south-facing panels after 34 months. North-facing panels were generally more fouled than South-facing. Blue, red, and ceramic colors always performed best. Resistance to fouling may have been due to copper in blue and acidity from sulfur oxides in ceramic pigments. Pigments may prolong paint film life and reduce the need for biocides.

Behandlungsstrategie bei karpometakarpalen Luxationsfrakturen

Carpometacarpal (CMC) fracture dislocations of the 2nd through 5th ray are rare injuries whose extent is regularly underestimated in the initial radiographic evaluation of the hand. Obtaining a computed tomography scan is imperative due to the radiographic underrepresentation of the full bone and joint injury. Restoration of bone and joint anatomy of the affected region is of paramount import to prevent joint deterioration and loss of hand durability and dexterity. Early surgical intervention can lead to good functional results. Different operative treatment strategies exist with a common approach being Kirschner wire, screw or plate fixation after closed or open fracture reduction and joint relocation.

Physicochemical properties of Cs borosilicate glasses containing CaO

A series of Cs-borosilicate glasses of general formula (mol%): 17.5Na 2O–2.5Cs 2O–45SiO 2–(35- x)B 2O 3– xCaO, where x varies from 0 to 10, were prepared by conventional melt quenching technique. Physicochemical properties like glass transition temperature, extent of volatilization loss of Cs and chemical durability of these glasses have been investigated in detail. Based on the T g values obtained from DSC studies, it is confirmed that the glass network remains unaffected with increase in CaO content in the glass at the expense of B 2O 3. Cs loss as function of duration of heating revealed that the Cs evaporation follows diffusion controlled mechanism and the extent of loss increases with the increase of CaO incorporation in glass. Chemical durability of the glasses has been found to improve significantly with in the increase of CaO content in glass and this has been attributed to the formation of Ca and Si rich layer at the outer surface of the glass, as inferred from SEM with EDX analysis.

“Detecting the Most Suitable Materials for Certain Applications”. The Practice of Substitute Metals Research in the Phases of German Autarky during the 20th century

The focus of this essay is on substitute materials, particularly the research on substitute metals. The two periods of autarky in Germany were of primary influence on this field. Engineers and construction engineers proved most important in this context despite inter-institutional cooperation between the disciplines of metals research, materials testing, and technical mechanics. Engineers had to solve construction problems respecting the materials used and to analyse components in terms of economic efficiency. However, the research on substitute metals not only meant the substitution of one substance for another. It also implied economizing and recycling scarce materials. These activities required tacit knowledge. Engineers succeeded to some degree but the German war economy paid a high price for it. Each technical system demanded a case-specific approach. Typically a loss of effectiveness, reliability and durability of the products containing substitutes had to be taken into account.

Fiber-matrix interactions in cement mortar composites reinforced with cellulosic fibers

With the aim of gaining a better understanding of the phenomena responsible of the loss of durability of cement mortar composites reinforced with vegetable fibers, this paper focuses on the analysis of the fiber-matrix interactions. More specifically we analyze the effects of the vegetable fibers on the cementitious matrix after their mixture for different periods of time and vice versa. Three kinds of cellulosic fibers with differences on its physic-chemical properties were studied: bamboo fibers, kraft pulp and cotton linters. The results show that the cellulosic fibers modify the total amount of heat released during the hydration process in the cement paste, this effect differing depending on the purity of the fibers. The high alkalinity of the cementitious matrix causes the partial dissolution of chemical components of the fibers and a harmful precipitate of the inorganic particles on its surface and/or lumen, damaging the fibers and hence decreasing its reinforcement capacity.

Design of Permanent Magnet Hybrid Magnetic Bearing with Minimum Salient Poles

In order to reduce greenhouse gas emissions, the generation of renewable energy is required. Therefore, this paper focused on a small-sized hydraulic generator, since small scale hydropower has a large potential for power generation. Standard mechanical bearings are installed in conventional small-sized hydraulic generators to support the rotating shaft. However, mechanical ball bearings cause rotational loss, noise and limitation of device durability. In order to upgrade the performance of a hydraulic generator, a new type of permanent magnet hybrid type magnetic bearing is proposed in this study. The stator is designed by finite element method magnetic field analysis. According to the analytical result, by making the root of stator salient pole wider and eliminating magnetic saturation, stronger bearing power was obtained. The analytical attractive force and negative spring force characteristics were then verified under static operation conditions with a simple experimental setup. Moreover, in order to confirm dynamic performance in the time domain, the impulse response was measured with the result showing good performance. In addition, by using the measured coefficient of attractive force and negative spring force, a numerical simulation was carried out to check the dynamic performance in the frequency domain and compared with an experimental result. The result of the frequency response showed good control performance in frequency domain.

Micro-Raman study of stable and metastable phases in metakaolin/Ca(OH)2 system cured at 60 °C

The kinetics of hydration reactions between MK and Ca(OH)2 depends directly on the cementing matrix and curing temperature. For example, as the temperature increases in the metakaolin (MK)/calcium hydroxide system causes formation of the metastable hexagonal phases (C2ASH8 and C4AH13) that evolve into a thermodynamically stable cubic phase belonging to the hydrogarnet family (C3ASH6). This transformation will reduce the volume (approx. 9%) and a loss of durability of these cementing matrices. Although it is known that there are hydrated phases involved in the reaction, there is still an important scientific gap which occurs during the intermediate steps. For this reason, the micro-Raman spectroscopy is used for the first time as a suitable technique in order to study the conversion reaction in the MK/Ca(OH)2 system cured at 60°C. The results show that at short curing periods C–S–H gel as well as metastable phases with different AlO45− environments are present; this is the first time that these metastable phases have been observed by Raman spectroscopy. As hydration proceed C–S–H gel decreases, with a total disappearance at 30h. After longer hydration stages the metastable phases transform to stable hydrogarnets identified by two broad bands in the OH and AlO4 vibration region respectively (3670–3650cm−1 and 520–540cm−1) with no C–S–H gel formation.

Problems of the reliability and durability of dynamically loaded structures from physically nonlinear material

One aspect of the problem of providing safety assurance when designing structures for the implementation of technical applications of high-energy matter states related to the durable functioning of loaded components is considered. The regularities of the stress-strain state of structures made from a material with nonlinear properties exposed to a mobile heat source are examined. It is demonstrated that the plastic deformation is intensified when the amplitude of the temperature variations increases insignificantly, leading to a durability loss in the structure, according to the fracture criterion, of an order of magnitude.

РАзрАботкА методИкИ оценкИ тормозныХ сВойстВ автомобилЯ нА диагностическоЙ станцИИ

The article is devoted to the current problem concerning traffic accidents’ decrease, the reason of which is loss of durability by vehicles. Research method of front wheel drive vehicle’s brake characteristics on a rolling test bench of a movable diagnostic station is elaborated.

Thermodinamically stable phases in the CaO-SiO&lt;sub&gt;2&lt;/sub&gt;-Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;-CaSO&lt;sub&gt;4&lt;/sub&gt;-H&lt;sub&gt;2&lt;/sub&gt;O closed system at 25 ºC. Application to cementitious systems

One of the chief causes of cement and concrete deterioration is the loss of durability prompted by sulphate attack. The existing standards call for long test periods (2- 12 months). Thermodynamic modelling is a particularly appropriate technique for studying systems that only reach equilibrium in the long term. Used in the present study to establish the fields of thermodynamic stability for the phases in the CaO-SiO 2 -Al 2 O 3 -CaSO 4 -H 2 O system at 25 oC. According to the model, gypsum is stable at sulphate ion concentrations of 1.23e -2 mol/kg and over, while ettringite exhibits stability at concentrations ranging from 7.64e -6 to 1.54e -2 mol/kg. Ettringite is compatible with all system phases except SH and gypsum only with ettringite, the C-S-H gels, AH 3 and SH. None of the calcium aluminates or silicoaluminates in the system is compatible with gypsum: in its presence, they all decompose to cement deteriorating ettringite. Finally, the model revealed that the maximum sulphate concentration at which C-S-H gel is stable is slightly higher in systems with than without Al 2 O 3 .

Behavior of Chemically Bonded Molding Sands in Dry Air

This article presents the results of research on the elasticity and durability of chemically bonded molding sands, most notably those containing hydrophilic binders. This research concerns the top surface layer of a sand mold. The observed loss of durability in the top surface layer can be caused by excessive dehydration of the binder. The pace and range of the changes depends on the air temperature and moisture, grain size, and amount of binder. The developed ultrasound method allows for observation of the kinetics of these changes with the results having practical applications.