Service life prediction of exterior cladding components under standard conditions

An empirical method was developed for the prediction of the service life of building components, based on an evaluation of their actual performance and on the identification of failure mechanisms affecting their durability. The service life of exterior components subjected to normal service conditions is predicted. Four types of exterior claddings are exemplified: cementitious mortar, synthetic rendering, ceramic mosaic, and wet‐fixing stone cladding. The proposed prediction models yield high degrees of fit to the data (R ² in the range of 0.86 to 0.93 at a 0.0001 level of significance). Life cycle costs (LCC) analysis – following service‐life prediction results – leads to the conclusion that maintenance and replacements costs account for 10–80% of initial capital costs. Synthetic rendering exhibited the highest LCC effectiveness, reflecting durability and low capital costs. The method can be used for planning preventive maintenance, evaluating economic implications of failures, and planning service life.     

Service life prediction and environmental exposure conditions of timber claddings in South Chile

ABSTRACT

In this research, a methodology for the service life prediction of external timber claddings is proposed and discussed. The proposed model is based on the visual assessment of 110 timber claddings, subjected to real exposure conditions. The claddings under analysis belong to 80 buildings, with and without heritage characteristics, located in Valdivia and Niebla, South Chile. Timber claddings are a relevant symbol of the local identity of this region, portraying a complexity of ideas and cultural values, inherited by Spanish and German colonizations. The main anomalies that can occur in these claddings are translated into a numerical index, which describes the overall degradation condition of a timber façade. This work also discusses the influence of the local climate and environmental exposure conditions, considering biotic factors (fungi, insects, moulds, algae and bacteria) and abiotic factors (water, solar radiation, amplitude of temperature, physical damage) in the evolution of the degradation condition of timber claddings. The scarcity of funds in Chile to maintain and preserve the constructions and its components needs a more rational approach to decision-making concerning inspection, maintenance and rehabilitation procedures. The expeditious tool proposed in this paper may help in providing the basis for rational decision-making by professionals in practice.     

Stochastic Petri-net models to predict the degradation of ceramic claddings

ABSTRACT

A stochastic Petri-net formalism is proposed to predict the degradation of ceramic claddings over time in order to understand how different environmental exposure conditions contribute to the overall degradation of these claddings. For that purpose, the degradation condition of 195 ceramic claddings located in Lisbon, Portugal, is evaluated through in situ visual inspections. In the first part of the study, a stochastic deterioration Petri-net model is proposed for the entire sample. In the second part, the original sample is divided according to the environmental exposure conditions, evaluating the influence of these conditions on the deterioration process of ceramic claddings. Four main degradation agents are analyzed: exposure to moisture; distance from the sea; orientation; and wind–rain action. The results reveal that Petri nets can accurately describe the deterioration process of ceramic claddings, providing relevant information regarding the performance of these claddings through their life cycle and according to the environmental exposure conditions to which they are subject. These results are extremely relevant for different practitioners: the approach allows the adoption of more sustainable and durable solutions at the design stage, as well as improving the durability of the ceramic claddings by performing optimized maintenance plans and strategies.     

Serviceability of facade claddings

In the present world economic situation, the resources directed to the maintenance of buildings are very limited. Therefore, an increasing concern arises for the planning and prioritization of necessary maintenance works during buildings’ life cycle. The planning of maintenance action is achieved by predicting the moment when construction elements reach degradation levels that exceed acceptable standards. To be able to make such forecasts, crucial developments must be made regarding the methods to predict the serviceability of building materials and components. In this study, 444 facades located in the cities of Lisbon and Almada and the Algarve region (Portugal) are analysed based on in situ visual inspections. The approach proposed can be employed in various scopes of service life prediction and maintenance of constructions. This paper develops a priority hierarchy of maintenance actions for the claddings under analysis. The expertise acquired in buildings’ serviceability is very useful to support decision-making in the development of proactive maintenance strategies. The results reveal accurate outcomes in the correlation with the functionality and degradation parameters of facade claddings. The serviceability of the most common types of facades claddings (render, ceramic and paints) applied in Portugal is analysed.     

Modelling the service life of rendered facades using fuzzy systems

The knowledge of the service life and durability of building components is paramount to sustainable analysis and decision making since it allows a more rational management of the maintenance of building and provides data for life cycle analysis procedures. Nevertheless, predicting the service life of a building or its components is a complex process with which a number of variables are associated. The main difficulties associated with service life prediction are related to the complexity of the degradation phenomena and to the lack of understanding of degradation factors and mechanisms. This paper aims at establishing a model for the service life prediction of rendered facades using a Takagi–Sugeno fuzzy model. The models proposed include the variables that influence the degradation of rendered facades (render age, render type, building height, facade orientation, exposure to damp, and facade protection level). In this study, the degradation condition of 100 case studies located in Portugal is analyzed based only on in situ visual inspections. The proposed models are able to describe appropriately the degradation of rendered facades and to predict the service life of the sample analyzed.     

Correlation between microstructural characteristics and weight loss of natural stones exposed to simulated acid rain

The correlation between stone microstructural characteristics and material degradation (in terms of weight loss), in given environmental conditions, was investigated. Seven lithotypes, having very different microstructural characteristics, were used. Four acidic aqueous solutions were prepared to simulate acid rain (two adding H₂SO₄ and two adding HNO₃ to deionized water, in order to reach, for each acid, pH values of 5.0 and 4.0), and deionized water at pH = 5.6 was used to simulate clean rain. Stone samples were then immersed in such aqueous solutions, the surface alteration being periodically inspected and the weight loss periodically measured. After 14 days of immersion, a good correlation was found between weight loss and the product of carbonate content and specific surface area in the starting materials. This was explained considering that this product accounts for the weight loss owing to the sample's fraction actually composed of calcite (the most soluble fraction) and the effective surface area exposed to dissolving solution (which depends on stone porosity and pore size distribution). Such correlation between stone microstructure and degradation may be useful for comparing the durability of different lithotypes, in given environmental conditions, and quantitatively predicting the weight loss of a lithotype, compared to another one. Hence, the correlation found in this study may be used to specifically tailor to various stone types, with different microstructural characteristics, some results that have been calculated in literature for specific stone types and then proposed as possibly representative for a broad category of stones with similar characteristics.     

Filtration performance of geotextile encasement to minimize the clogging of stone column during soil liquefaction

Stone columns, which are frequently employed to stabilize the liquefiable soil, are susceptible to accumulation of soil particles. The progressive accumulation of the soil particles causes clogging of the stone column which decreases its drainage capacity. The stone column can be encased with geotextile to sustain its long term drainage function. The encasement prevents the movement of the soil particles into the stone pores. In the present paper, a mathematical model is presented to assess the filtration performance of the geotextile encasement to prevent the clogging. The filtration capacity of the geotextile is related to its maximum pore size, porosity and soil characteristics. It is observed that the encased stone column dissipates the excess pore pressure at a faster rate compared to the stone column without encasement. The peak maximum excess pore water pressure (U_max) is not significantly affected due to selection of the opening size of the geotextiles for single earthquake. However, the opening size can significantly affect the peak U_max value for multiple earthquakes. Depending on the capture coefficient of the stone column, the clogging can be fully prevented for higher hydraulic gradient if geotextile with maximum opening size in between D₁₀ to D₅ is used as encasement.     

Effect of polyethylene on life of flexible pavements

The present study investigates the potential use of pyrolysis low density polyethylene (LDPE) as a modifier for asphalt paving materials. Five different blends including conventional mix were subjected to binder testing such as rheological tests, as well as to some other tests related to the homogeneity of the system. Further, its effect on the moisture sensitivity and low temperature performance of stone matrix asphalt (SMA) mixtures was studied. Research results indicate that modified binders showed higher softening point, keeping the values of ductility at minimum range of specification of (100⁺ cm), and caused a reduction in percentage loss of weight due to heat and air (i.e. increase durability of original asphalt). The results indicated that the inclusion of LDPE in SMA mixtures can satisfy the performance requirement of high-temperature, low temperature and much rain zone. In addition, the horizontal tensile strain at the bottom of asphalt concrete layer (Ε_t) and the vertical compressive strain at the top of subgrade layer (Ε_c) were calculated using multi-layer elastic analysis program, BISAR under 50KN set of dual tires with 106.5 mm contact radius. These responses were used for estimating the improvement in service life of the pavement or reduction in thickness of SMA and base layer for the same service life due to modification the SMA mixtures.     

A systematic approach for maintenance budgeting of buildings façades based on predictive and preventive strategies

Maintenance strategies are essential to control the first stages of degradation and prevent the failure of building elements. The selection of the most cost-effective and appropriate strategies can enable better budget allocation and can also minimize the decline in the performance of buildings during their whole life cycle. This paper characterizes a systematic methodology for selecting optimal maintenance strategies for façades based on different maintenance policies and interaction with the user. Life-cycle cost analysis is used to compare different maintenance scenarios using equivalent uniform annual cost (EUAC) for five façades’ claddings. These scenarios are compared through the simulation of performance–degradation models and characterization of several parameters: service life, performance, minimum level of quality, maintenance operations, frequency and costs. The results allow the comparison of preventive and predictive maintenance strategies. This methodology, the result of a two-year academic research program, is intended to help clients, users, practitioners and decision-makers in the choice of facades’ interventions (type, frequency and cost estimation) at buildings’ design and post-occupancy stages. Finally, the future drawbacks and benefits of this study are discussed.     

Modeling of some properties of the crushed tile concretes exposed to elevated temperatures

In this study, artificial neural network (ANN) and fuzzy logic (FL) models have been developed for predicting the compressive strength (f_c) and dynamic modulus of elasticity (E_d) of the crushed tile concretes (CTC) exposed to elevated temperatures. Some relationships are established between chosen inputs and outputs by developing and testing a multi-layered feed forward ANN and FL trained with the back-propagation algorithm. First of these relationships is established between the outputs as f_c of CTC after being exposed to elevated temperatures and the inputs as exposed temperature (T), crushed tile aggregate (CT) and crushed stone II (CSII) contents of concrete. The second one is the relationship between E_d of concretes and the same inputs. In this aim, concrete specimens are produced by CT replacing 16–31.5 mm coarse aggregate at the ratios of 0%, 10%, 25%, 50%, 75% and 100%. Concrete specimens are exposed to 20, 150, 300, 400, 600, 900 and 1200 °C high temperatures corresponding TS EN 1363-1 after an initial 28 day curing period. After heating, the specimens are slowly air-cooled to the room temperature and then E_d and f_c of concretes were determined. Experimental results are also predicted by constructing models in ANN and FL methods. In the models, the training and testing results have shown that ANN and FL methods have strong potential for predicting the f_c and E_d of crushed tile concretes exposed to elevated temperatures.     

Life-cycle cost analysis of highway noise barriers designed with photocatalytic cement

This study examines the environmental and economic feasibility of concrete noise barriers containing photocatalytic cement using a life-cycle cost analysis (LCCA). Photocatalytic concrete contains titanium dioxide (TiO₂) which allows for the oxidation of air pollutants to occur on the surface of the building material. Design variables studied include the cementing material type (general use (GU) cement, ground granulated blast furnace slag (GGBFS) used as cement replacement, and photocatalytic (PCAT) cement), and the thickness of a photocatalytic concrete cover. The LCCA accounts for the CO₂ and NO_x generated during manufacturing and the NO_x (NO, NO₂) oxidised during the life of barriers containing photocatalytic concrete. A key outcome from this study revealed that at a 40-year service life, assuming a 6 mg/h/m² NO_x degradation rate, a barrier designed with 100%GU cement and a 25 mm photocatalytic concrete cover has an annual cost that is 7%, 30%, and 36% greater than the 100%GU, 35% and 50%GGBFS barriers without a photocatalytic cover, respectively. Results of this analysis also indicated that the application of a 25 mm photocatalytic concrete cover to concrete containing 35 and 50%GGBFS is more economically feasible than 100%GU concrete, irrespective of the service life and pollution degradation rate.     

Quantifying environmental effects on cement-rendered facades: A comparison between different degradation indicators

The purpose of this research is to assess and quantify the environmental effects on cement-rendered facades in real-life service conditions. A holistic approach is proposed based on the assessment of the visual impact of the actual climatic environment that affects the aesthetic performance and durability of 19 cement-rendered facades located in Lisbon, Portugal. Different degradation indicators are presented and a deterioration path is identified, which points out to the possibility of modeling the overall degradation of facades in similar building and environmental conditions. Although the proposed method reflects the Portuguese building context, it can be easily adapted to other countries and expanded to include various cladding solutions, so that their remaining service life can be integrated in the existing commercial methodologies for service life prediction and asset management.     

A strain criterion for pull-through failures in crest-fixed steel claddings

Crest-fixed steel claddings made of thin, high strength steel often suffer from local pull-through failures at their screw connections during high wind events such as storms and hurricanes. Adequate design provisions are not available for these cladding systems except for the expensive testing provisions. Since the local pull-through failures in the less ductile steel claddings are initiated by transverse splitting at the fastener holes, numerical studies have not been able to determine the pull-through failure loads. Numerical studies could be used if a reliable splitting criterion is available. Therefore, a series of two-span cladding and small scale tests was conducted on a range of crest-fixed steel cladding systems under simulated wind uplift loads. The strains in the sheeting around the critical central support screw fastener holes were measured until the pull-through failure occurred. This paper presents the details of the experimental investigation and the results including a strain criterion for the local pull-through failures in crest-fixed steel claddings.     

BuildingsLife: a building management system

The financial resources available for infrastructure maintenance and rehabilitation are always limited, which creates a need for efficient resources' management and for the ability to predict maintenance actions throughout the infrastructure's service life. In the context of bridges, management systems have been developed and are already implemented around the world. A much larger variety of maintenance problems and a reduced number of buildings per owner mean that building management systems (BdMSs) are still quite rare. Actually, efficient methods for the service life prediction of building materials still need to be developed. This paper discusses the service life prediction methods used in building components based on deterministic, stochastic or engineering methods. The architecture of a recently developed BdMS – BuildingsLife – is presented, where the service life analysis of components is based on an initial statistical analysis of anomalies obtained from the inspection of in-use buildings. This method analyses the corresponding degradation through the use of deterministic and stochastic models.     

Design and analyses of floating stone columns

Two-dimensional (2D) finite element analyses were performed on floating stone columns using the unit cell concept to investigate the settlement and the consolidation characteristics of an improved foundation system. Undrained analyses, followed by consolidation analyses, were conducted throughout the study. The computed values for settlement and excess pore pressure distribution over time are compared for different area replacement ratios. Based on these coupled consolidation analyses, a simple approximate method is developed to predict the degree of consolidation for floating stone columns. In addition, a simple method to calculate the settlement improvement factor for floating columns is proposed. The proposed method may provide more realistic answers than other design methods in view of the yielding characteristics and the influence of key parameters that are considered in the analyses. The key parameters relevant to the design of floating stone columns include the area replacement ratio, the friction angle of the column material, the loading intensity, and the post-installation earth pressure. Closer agreements are obtained with the proposed method than with the established Priebe׳s method or α–β method.     

Mechanical performance of BStIV grade steel bars with regard to the long-term material degradation due to corrosion damage

The mechanical performance of BStIV grade reinforcing steel bars from four different manufacturers was experimentally investigated and evaluated by exploiting the performance indices concept. The experiments included tensile tests, carried out on uncorroded and pre-corroded steel specimens. To corrode the specimens, accelerated laboratory corrosion tests were involved. The later tests were made to assess the expected degradation of the materials mechanical performance with accumulating corrosion damage during the life of a reinforced structure. For the evaluation of the mechanical performance, index Q_D has been introduced. The index Q_D considers the combination of tensile strength and tensile ductility in a single quantity by accounting also for scatter in material’s mechanical properties. Index Q_D can be applied to assess the materials mechanical performance both in the undamaged and in the corroded conditions. In both cases, the materials were ranked based on the outcome of the evaluation of their mechanical performance. Subjective choice is needed in order to consider the effect of corrosion damage on the material’s mechanical performance.     

Applicability of infrared thermography to the study of the behaviour of stone panels as building envelopes

Thin stone wall cladding systems used on exterior building envelopes typically consist of stone panels made of granite. There is a risk of detachment if the cement used to stack the panels is defective. There is a wide range of destructive techniques to evaluate the state of the facades, but they are scarcely practical. Infrared thermography (IRT) offers a cost-effective alternative to traditional evaluation. The sizes and shapes of the defects detected by this methodology in the cement holding the panels are presented in order to evaluate the capacity of the aforementioned technique.     

Effect of air and noise pollution on species diversity and population density of forest birds at Lalpahari, West Bengal, India

The Rajmahal-type quality stones for building purposes are found abundantly in Birbhum district, West Bengal, India, where stone mining and crushing have become the main industrial activity. Although crusher dust is injurious to health, demand for crushed stone is ever-increasing as a result of rapid infrastructural growth in the country. Most of the crusher units at Rampurhat are situated along the roadways adjacent to forest under Tumboni Beat of Rampurhat Range of Birbhum Forest Division. Excessive load of air pollution in this area has led to degradation of this forest. The status of the ambient air and noise level was evaluated. The effect of air and noise pollution on abundance and variability of birds in this forest have been compared to an almost non-polluted forest of the same bio-geographic zone. Both species diversity and population density of birds were found to decrease in the polluted forest, especially in the areas adjacent to crushers. For comparing the pollution status of two different forest sites and for establishing whether the density of birds have any correlation between the sites, the Student's t-test and the chi-square test were applied respectively. Most of the results proved to be significant.     

Proliferation of antibiotic resistance genes in microbial consortia of sequencing batch reactors (SBRs) upon exposure to trace erythromycin or erythromycin-H2O

A variety of antibiotics and their metabolites at sub-inhibitory level concentrations are suspected to expand resistance genes in the environment. However, knowledge is limited on the causal correlation of trace antibiotics or their metabolites with resistance proliferation. In this study, erythromycin (ERY) resistance genes were screened on microbial consortia of sequencing batch reactors (SBRs) after one year acclimation to ERY (100 μg/L) or dehydrated erythromycin (ERY-H₂O, 50 μg/L). The identified esterase gene ereA explains that ERY could be degraded to six products by microbes acclimated to ERY (100 μg/L). However, ERY could not be degraded by microbes acclimated to ERY-H₂O (50 μg/L), which may be due to the less proliferated ereA gene. Biodegradation of ERY required the presence of exogenous carbon source (e.g., glucose) and nutrients (e.g., nitrogen, phosphorus) for assimilation, but overdosed ammonium-N (>40 mg/L) inhibited degradation of ERY. Zoogloea, a kind of biofilm formation bacteria, became predominant in the ERY degradation consortia, suggesting that the input of ERY could induce biofilm resistance to antibiotics. Our study highlights that lower μg/L level of ERY or ERY-H₂O in the environment encourages expansion of resistance genes in microbes.