Service Life Assessment Research Articles

Experimental Determination of Material Characteristics of New Type of Plaster

New type of commercial plaster which is not well known in the market is investigated in this paper. It is a new product delivered from Turkey, contains 80% of perlit, the binder is unknown and according to the producer it is some type of polymer. According to the producer’s data, the open porosity is 80% and the main advantages are good thermal and mechanical properties. The data in the technical data sheet are not complete, some important information is missing, therefore the basic physical, mechanical, thermal and hygric properties were studied in this paper. Moisture diffusivity, thermal conductivity and specific heat capacity are determined as a function of moisture content. Obtained data were compared with ordinary lime-cement plaster. The results can be further utilized in the computer simulation for service life assessment studies.

Service-Life Assessment of Existing Precast Concrete Structure Exposed to Severe Marine Conditions

The overall performance of a concrete structure is considered to be a key issue when determining its service life. The widespread use of precast concrete and consideration of durability as a design parameter in most of the international codes have the goal of achieving concrete structures with better durability. Nevertheless, the early deterioration of concrete is still common in a large number of concrete structures, which reduces the service life. This paper presents a case study of an existing precast concrete cooling tower for a thermal power station subjected to severe marine exposure conditions, which showed symptoms of serious deterioration after operating for three years. The main goal of this study was to clarify the origin of the accelerated deterioration of the structure. Wetting-drying cycles were identified as the main cause of the early deterioration of the structure. Furthermore, estimations on its remaining service life were made considering the accelerating effect of the wetting-drying cycles. Finally, the variation in the safety factor of the main structural elements was evaluated.

The effect of pitting corrosion on the safe-life prediction of the Royal Australian Air Force P-3C Orion aircraft

This paper investigates if corrosion pitting invalidates the fatigue lifeing method used by the Royal Australian Air Force to manage the structural integrity of its P-3C Orion aircraft. Fatigue life predictions made using the P-3C Service Life Assessment Program method were compared with those from an Equivalent Crack Size model for pitting corrosion. The data for this comparison came from a program of variable amplitude fatigue tests of high-kt specimens of 7075-T6. This testing was performed using two stress levels on both corroded and uncorroded specimens. Analysis of the results showed that the safe-life estimates made using the P-3 life assessment method were conservative in the presence of corrosion as they were above the 99.9th percentile of fatigue life predicted by the equivalent crack size method.

Wood coating failures against natural and accelerated climates

Monitoring, assessment and prediction of service life of materials are a serious challenge for the building and construction sector. According to ISO 15686 (2008), laboratory testing must be performed alongside field testing to evaluate different degradation outcomes. Coated wooden specimens, used for building façades, were exposed to different ageing conditions in (a) a vertical climate simulator, (b) a horizontal Atlas solar simulator and (c) against natural outdoor exposure conditions. Wood specimens were from Norway spruce grown at two locations in southern Norway. Wooden boards were surface finished by a primer and red acrylate paint. Ageing cycles in the laboratory include exposure to ultraviolet and infrared radiation, water spray, freezing and thawing. Non-destructive surface evaluation techniques were used to monitor and verify the effect of ageing stresses on coatings. Before and after exposure, the coated surfaces were graded visually. Short- and long-term exposures are observed to cause physical degradation such as flaking, cracking and blistering. Blistering on the knots occurs during initial phases of exposure. Different correlations are observed between the CIELab/CIE 1976 coating total colour difference and partial colour difference for artificially aged coated surfaces, naturally aged coated surfaces, and artificially aged uncoated surfaces. Fourier transform infrared spectra suggest possible degradation of wood or coatings during the ageing cycles and a higher content of carbonyl groups in aged acrylate coating. Arrhenius temperature and humidity acceleration factor shows higher rate of deterioration of cellulose, lignin and acrylate in humid conditions.

Assessment and prediction for service life of water resources and hydropower engineering

There are a large number of in-service water resources and hydropower engineering in the aging stage. It is an urgent problem how to assess and predict service life of water resources and hydropower engineering. The related theory and method need to be proposed to improve the safety management level and make the reinforcing, removing or downgrading decisions. The current achievements in the research are reviewed. The assessment criteria and system are analyzed. The methodological progress for assessment and prediction of service life is summarized. The future development direction is stated. The key problems and their approaches are related and analyzed. It is shown that the assessment and prediction for service life of water resources and hydropower engineering is a comprehensive research topic. To solve the problems in above field, it is necessary to integrate many theories, methods and techniques in other fields such as water resources and hydropower engineering, geotechnical engineering, construction materials, environmental engineering, cybernetics and computer engineering.

VIP service life assessment: Interactions between barrier laminates and core material, and significance of silica core ageing

As a result of temperature and humidity vacuum insulation panels (VIP) age: their thermal resistance decreases due to the combined effect of internal pressure and solid conduction increase. For given conditions this depends on the duration of the exposure and on the permeance of the envelope, as well as on the hygric and thermal behaviour of the core material. This paper begins by assessing the severity of the various building applications with regard to the VIP. It then presents the main behaviours and models needed and explains the life evaluation approach under stationary conditions. Furthermore particular attention is paid to the ageing of silica core material. It concludes that for a realistic estimation of the service life one needs to take into account both the thermal and hygric behaviour of the core material, the permeance of air and water vapour through the envelope, the temperature and humidity service conditions, and the thickness of the panel.

Assessment of Safe Service Life of Materials Based on Corrosion Conditions

The effect of stress concentration, arising from formation of pitting corrosion holes, on the strength and service life of a material is discussed. Formulas are derived for calculating the stress concentration factor in a plate containing a shallow round corrosion hole. A case study is presented showing the effect of the corrosion hole depth on the stress concentration factor and the burst pressure.

Service life assessment and moisture influence on bio-based composites

A race towards a more sustainable society is going on worldwide, and decreasing dependence on fossil resources in energy and transport sectors are main goals. One path to decreased oil usage is development of lightweight materials from renewable resources like bio-based composites. However, these new bio-based materials not only have to compete in mechanical performance but also have to restrain environmental loads like moisture and temperature over time. In this study, two bio-based composites have been compared to an oil-based composite in terms of long-term properties and water absorption behaviour. The long-term behaviour is determined by dynamic mechanical thermal analysis, DMTA and time temperature superposition, TTSP. The water uptake is determined by submersion of specimens into water and tracking their weight change over time. The moisture influence is characterised in form of water uptake and change in the master curves created by TTSP procedure. The results show that there is a significant difference in long-term performance between the bio-based and oil-based composites. It is realised that the bio-based composites can be a good alternative for some applications especially when taking their eco-friendly nature into account.

Practical Application of Structural Repair Fatigue Life Determination on the AP-3C Orion Platform

The AP-3C Orion aircraft is the oldest aircraft in the Royal Australian Air Force (RAAF) inventory. The planned fleet withdrawal has been extended far beyond the original design service objective. Continued safe and effective operation has required the development of a robust ageing aircraft management approach. A fundamental aspect was supplementing the structural certification basis with appropriate standards in the form of fatigue management requirements from Federal Aviation Regulations (FAR) 25.571 and Federal Aviation Administration Advisory Circular (FAA AC) 120-93. To develop and underpin the ageing aircraft management plan and transition to the supplementary fatigue management standards, the RAAF collaborated with the Original Equipment Manufacturer, Lockheed Martin Aeronautics Company, the United States Navy (USN) and other operators to form the P-3C Service Life Assessment Program (SLAP). This program provided Full Scale Fatigue Test (FSFT) data, associated analyses and analysis tools to support management in accordance with FAR 25.571. An important element of the ageing aircraft management plan included the introduction of a rigorous Safety By Inspection (SBI) maintenance regime to assure structural airworthiness. FAA AC 120-93 requires assessment of structural repairs to determine revised fatigue management and inspection requirements. Often, this information is derived using tailored analysis tools and detailed models on a case-by-case basis. This approach is specialized, expensive and usually occurs after the repair has been designed and installed. To avoid these limitations, the AP-3C Repair Assessment Manual (RAM) was developed to provide the repair designer with a design handbook approach to fatigue analysis. In conjunction with some simple Finite Element (FE) models, the RAM supports complete repair analysis prior to an aircraft leaving the maintenance venue. This paper will present the history of the SBI program, the genesis of the RAM and actual examples of assessing structural repairs on the P-3 platform using the RAM.

Service life assessment and moisture influence on bio-based thermosetting resins

In this study, three different types of bio-based resins are compared to a conventional oil-based epoxy in terms of moisture uptake, long-term properties and its influence of moisture and glass transition temperature, Tg. Moisture uptake is determined by means of gravimetric method, time temperature superposition (TTSP), and Tg data obtained in dynamic mechanical thermal analysis (DMTA). Moisture uptake show Fickian diffuison behavour for all resins, saturation level and diffusion coefficient however differ. The long-term properties is characterised by creep compliance master curves created by means of TTSP. The examined bio-based resins are compatible to the reference epoxy in term of stability up to 3–10 years. Comparison between master curves for virgin, wet, and dried material show that moisture present in the specimen increases creep rate, and that some of this increase remains after drying of samples. Tg measurements show that moisture inside the specimen decreases Tg; this is anticipated because of the plasticizing effect of water. The overall conclusions are that the bio-based resins of polyester, and epoxy type are comparable in performance with oil-based epoxy, LY556 and they can be used to develop high-performance composites.

Approaches for Modelling the Residual Service Life of Marine Concrete Structures

This paper deals with the service life design of existing reinforced concrete structures in a marine environment. The general procedure of condition assessment for estimating the residual service life of structures before a repair measure is illustrated. For assessment of the residual service life of structures which have undergone a repair measure a simplified mathematical model of chloride diffusion in a 2-layer system is presented. Preliminary probabilistic calculations demonstrate the effect of various conditions on the residual service life. First studies of the chloride diffusion in a 2-layer system have been conducted using the finite element method. Results of a long-term exposure test are presented to illustrate the performance of two different repair materials. The distribution of residual chlorides after application of a repair material is being studied in laboratory investigations. The residual chlorides migrate from the concrete layer into the new layer immediately after the repair material has been applied to the concrete member. The content and gradient of residual chlorides, along with the thickness and the chloride ingress resistance of both the remaining and the new layer of cover, will determine the residual service life of the repaired structures.

Case Study of Remaining Service Life Assessment of a Cooling Water Intake Concrete Structure in Indonesia

This paper deals with the assessment of remaining service life of a cooling water intake concrete structure (CWICS) subjected to corrosion due to chloride attacks. Field and laboratory tests were performed to determine the current existing condition of the structure. Both destructive and nondestructive tests were employed to obtain the parameter needed for the assessment. Based on the current condition and test results, structural analysis was carried out and the remaining safety factor of CWICS was determined. From the analysis, it was found that most concrete elements of CWICS had safety factor greater than unity and might fulfil its intended service life up to the year 2033. However, fewer elements require immediate strengthening to extend their service life.

Service life assessment of historical building envelopes constructed using different types of sandstone: a computational analysis based on experimental input data.

Service life assessment of three historical building envelopes constructed using different types of sandstone is presented. At first, experimental measurements of material parameters of sandstones are performed to provide the necessary input data for a subsequent computational analysis. In the second step, the moisture and temperature fields across the studied envelopes are calculated for a representative period of time. The computations are performed using dynamic climatic data as the boundary conditions on the exterior side of building envelope. The climatic data for three characteristic localities are experimentally determined by the Czech Hydrometeorological Institute and contain hourly values of temperature, relative humidity, rainfalls, wind velocity and direction, and sun radiation. Using the measured durability properties of the analyzed sandstones and the calculated numbers of freeze/thaw cycles under different climatic conditions, the service life of the investigated building envelopes is assessed. The obtained results show that the climatic conditions can play a very significant role in the service life assessment of historical buildings, even in the conditions of such a small country as the Czech Republic. In addition, the investigations reveal the importance of the material characteristics of sandstones, in particular the hygric properties, on their service life in a structure.

Service Life Assessment of the Cam Mechanisms

Currently, there are higher requirements on the cam mechanisms. Part of the design is a determination of the service life of a cam surface. This paper deals with wear mechanisms at cam mechanisms in its first part, then describes factors affecting the life and the last part deals with a methodology of durability testing. Hertz's contact theory is the basis for the pressure determination in the contact patch. By means of its value we get the relationship between surface hardness and required lifetime of the cam surface. This information is heading to determination of the materials suitable for the cam mechanisms production, and it is necessary taking into account the working conditions.

Influence of the carbon dioxide concentration on the resistance to carbonation of concrete

Carbonation of concrete at ambient CO2 concentration is a slow process. This makes the testing of the resistance of concrete against carbonation often too slow to be applicable for service life assessments of new structures. Raising the CO2-concentration will accelerate the test but the validity of an increase CO2-level is debated. If not valid, the service life can be seriously underestimated. In this paper, the effects of accelerating on the carbonation process are discussed.It is shown that a change in CO2 concentration will not change the carbonation process. Since carbonation occurs instantly, a zero CO2 concentration at the carbonation front is maintained. Moreover, it has been concluded that all hydrated and unhydrated cement ultimately carbonates. This implies that the amount of material that can carbonate can be determined on the basis of the amount of calcium in the unreacted cement.

Effect of coupled deterioration by freeze–thaw, carbonation and chlorides on concrete service life

Concrete performance is traditionally based on assessing the effect of a single degradation mechanism. In the field, however, concrete is simultaneously affected by degradation mechanisms, possibly with a synergetic effect on deterioration. This paper presents the results of a Finnish research project assessing coupled deterioration mechanisms including frost attack, carbonation and chloride penetration.Research was composed of an extensive laboratory testing regime, in parallel to the exposure of several concrete specimens at field stations. Testing took into account the effects of ageing and repeated exposure cycles to different conditions. More than 60 concrete mixtures were evaluated with varying binder types and air contents. Testing results together with local weather data serve as a basis for modelling and development of service life assessment tools.The results show the synergetic effect on concrete deterioration of coupled deterioration and quantitatively support that a holistic approach should be adopted for predicting deterioration.

Experimental Study on the Capillary Absorption of Cement-Based Materials and Analysis of Influencing Factors

Capillary absorption effect is very important to the research of concrete durability. Initial surface absorption test (ISAT) method has been employed to investigate the effect of W/C, age, aggregate volume percent and concentration of NaCl solution as a transmission medium of the capillary absorption of the cement-based materials. Experiment results indicate that, the capillary absorption coefficient increases with the increasing of W/C, but decreases with the increasing of age and aggregate volume percent. Within a certain range of low concentration, the capillary absorption coefficient increases with the increasing of the concentration of NaCl solution, however when the concentration is too high, the transmission rate will be lower than pure water. This investigation provides an experimental foundation for the durability design and service life assessment of concrete structures.

Systematic condition assessment of concrete facades and balconies exposed to outdoor climate

Determining the condition of a concrete building or structure through periodic assessments during its lifespan is an essential part of proper maintenance. The repair methods of concrete facades and balconies are selected primarily on the basis of their technical condition. The information on the deterioration level of structures provided by a condition assessment assists in the selection of appropriate repair methods and assessment of related risks and service life of the repair. The content of a condition assessment is to be such that set goals are achieved. Usually the aim is to determine the repair or maintenance need and safety of structures. To achieve that, the deterioration and performance defects of structures need to be established. Concrete facades and balconies can be subject to several types of deterioration. Thus, the existence, scope, location, degree, impacts and future progress of deterioration need to be determined in each case. The wide variation in the level of deterioration between dif...

Advanced Integrated Design Method for Fatigue Assessment of Large Elastic Ship Structures

This paper is focused on an advanced method for ship structures fatigue assessment. The ships classification societies standard rules for fatigue analysis are based on simplified procedures, with wave induced loads obtained by linear oscillation analysis (low frequency, around 0.1 Hz), or equivalent statistical wave loads. In the case of large elastic ship structures, with hull length over 150 m, the global wave induced vibration response (high frequency, around 1 Hz) becomes significant. The developed integrated method for large ships fatigue assessment includes three interlinked analyses, as follows: the hot-spot stresses evaluation by 3D finite element models, wave induced loads by short term linear and non-linear hydroelastic dynamic analysis, ship service life and fatigue assessment by damage cumulative ratio method. As testing ship, it is considered a double hull LPG Liquefied Petroleum Gas carrier, with total length 239 m, for a set of structural details with stress hot-spots. Based on the non-linear hydroelastic wave loads, the integrated method of fatigue assessment becomes more accurate, predicting for the amidships structure 14 years of ship service life, instead of over 20 years according to the rules standard approach, so that the confidence on ship structure fatigue evaluation can be increased in the design process.

Reliability-based service life assessment for deteriorating reinforced concrete buildings considering the effect of cumulative damage

Most engineering systems used in maintenance strategies must consider deterioration and seismic structural damage. To identify the effects of deterioration and earthquakes simultaneously on structural performance, this study applies an integral simulation method. Compared with that of previous studies, the feature of the proposed method is its analysis of the time-dependent structural capacity of a deteriorating reinforced concrete (RC) building and the simulation of life-cycle earthquake events within a specified service period, while considering cumulative damage induced by deterioration and earthquakes. In addition, the proposed assessment method is applied to derive the reliability-based service life of a deteriorating RC building located in a region with high seismic hazard. Briefly, for deteriorating RC buildings, the proposed reliability-based service life assessment method provides useful information related to maintenance based on both serviceability and safety.