Theoretical backgrounds of durability analysis by normalized equivalent stress functionals

Generalized durability diagrams and their properties are considered for a material under a multiaxial loading given by an arbitrary function of time. Material strength and durability under such loading are described in terms of durability, safety factor and normalized equivalent stress. Relations between these functionals are analysed. We discuss some material properties including time and load stability, self-degradation (ageing), and monotonic damaging. Phenomenological strength conditions are presented in terms of the normalized equivalent stress. It is shown that the damage based durability analysis is reduced to a particular case of such strength conditions. Examples of the reduction are presented for some known durability models. The approach is applicable to the strength and durability description at creep and impact loading and their combination

Nirs tools for prediction of main extractives compounds of teak (Tectona grandis L.) heartwood

Biochemical and physiological process which occurred during heartwood formation have consequences on wood properties such as colour, natural durability and some mechanical properties. However, it is very time-consuming to take measurements of extractives contents. Teak has been reported to contain 1-hydroxy- 2-methyl-anthraquinone, 2-hydroxy-methyl-anthraquinone, 2-methyl- anthraquinone, lapachol, 1,4-naphthoquinone for the main compounds. In teak, natural durability is ascribed to extractives. Consequently, it's possible to estimate natural durability by measurement of extractives indirectly. For the purposes of selection for the production of improved varieties, the number of samples to be measured rapidly exceeds the capacity of a traditional laboratory. Near-infrared spectroscopy approach, based on spectral data and reference data, is a tool enabling many of the chemical properties of wood to be predicted and the number of laboratory measurements to be reduced exponentially. The issue here is a question of checking the effectiveness of NIRS tool to build models and predict the main extractive compounds of teak wood from Ivory Coast. We try to calibrate these chemical properties with Nirs spectral information measured on grounded wood. The results show the possible use of NIRS to predict total phenol content and some main extractive compounds of teak heartwood as tectoquinone, 2-hydroxymethylanthraquinone,Consequently, after verification on other sets of teak samples, which may or may not be included in the prediction model, NIRS can be used to predict extractive compounds accurately for a large number of samples, making it possible to estimate natural durability indirectly and to include these characteristics in the selection criteria for classifying wood and high throughput phenotyping. (Résumé d'auteur

Tree crown architecture: a tool for decay resistance evaluation

The variability of natural durability contributes to the bad perception of some wood end-users. In our search, we need to adjust our methods and strategies to estimate natural durability and extract higher value from wood resources. Architectural analysis is essentially a detailed, multilevel, comprehensive and dynamic approach to plant development. Numerous biological process which impact some wood properties like durability are linked with tree development. A better understanding of the interelationship between tree physiology through tree achitecture analysis and natural durability could be an approach to predict this property. This study explore the relation between the crown architecture, decay resistance and wood extractives in Dicorynia guianensis in order to propose tree crown architecture as an evalution decay resistance tool. (Résumé d'auteur

A reverse chemical ecology approach to explore wood natural durability

The natural durability of wood species, defined as their inherent resistance to wood‐destroying agents, is a complex phenomenon depending on many biotic and abiotic factors. Besides the presence of recalcitrant polymers, the presence of compounds with antimicrobial properties is known to be important to explain wood durability. Based on the advancement in our understanding of fungal detoxification systems, a reverse chemical ecology approach was proposed to explore wood natural durability using fungal glutathione transferases. A set of six glutathione transferases from the white‐rot Trametes versicolor were used as targets to test wood extracts from seventeen French Guiana neotropical species. Fluorescent thermal shift assays quantified interactions between fungal glutathione transferases and these extracts. From these data, a model combining this approach and wood density significantly predicts the wood natural durability of the species tested previously using long‐term soil bed tests. Overall, our findings confirm that detoxification systems could be used to explore the chemical environment encountered by wood‐decaying fungi and also wood natural durability

Strength and flexibility properties of advanced ceramic fabrics

The mechanical properties of four advanced ceramic fabrics are measured at a temperature range of 23 C to 1200 C. The fabrics evaluated are silica, high-and low-boria content aluminoborosilicate, and silicon carbide. Properties studied include fabric break strengths from room temperature to 1200 C, and bending durability after temperature conditioning at 1200 C and 1400 C. The interaction of the fabric and ceramic insulation is also studied for shrinkage, appearance, bend resistance, and fabric-to-insulation bonding. Based on these tests, the low-boria content aluminoborosilicate fabric retains more strength and fabric durability than the other fabrics studied at high temperature

On the Growth and Stability Effects of Habit Formation and Durability in Consumption

This paper shows that a unique balanced growth monetary equilibrium exists in a transactions-based monetary endogenous growth model with habit formation or durability in consumption. An increase in the nominal money growth rate reduces the long-run output growth rate, wherein habit formation enforces the effectiveness of monetary policy while durability in consumption reduces it. We also show that while habit formation destabilizes the macroeconomy by making the balanced growth equilibrium exhibit local indeterminacy, durability in consumption maintains saddle-path stability of the balanced growth equilibrium. We find that the mechanism through which habit formation and durability impose different effects on both the growth-effect of money and the macroeconomic stabilizing properties is such that habit formation and durability influence the elasticity of intertemporal substitution in consumption in opposite directions.Habit formation, Durability, Superneutrality, Indeterminacy

Influence of concrete composition on chloride ingress and carbonation : analysis by means of an extended data-set

In 2015 an IWT-TETRA project, called DurOBet, was initiated focusing on service life design assessment according to different chloride diffusion and carbonation models applied on Belgian concrete mixtures. The main purpose of this research project is to develop a quantitative method for a service-life based design of concrete structures, more particular applicable for the Belgian concrete industry. In this way an improvement of the deemed-to-satisfy approach of the EN206-1 code can be established which is more reliable with regards to service life predictions of concrete structures. In the framework of this DurOBet project it was decided to develop an extensive database incorporating concrete related results on i) fresh properties, ii) hardened properties and iii) durability related properties such as porosity, permeability and more specifically on chloride ingress and carbonation. The data originate from numerous journal articles and conference papers, doctoral research projects and master thesis studies. At this time more than 100 papers or studies were investigated, reported between 1992 and 2016, generating a dataset of over a thousand unique concrete recipes, geographically spread but with focus on the concrete mixes applicable for the Belgian industry. Both traditional and self-compacting concrete mixes are incorporated into the database. This database is being used for the analysis of the durability related properties, such as the chloride diffusion and carbonation coefficient, and their relation with mix proportioning parameters of the concrete mixtures (cement or binder content, type of binder, water-to-binder ratio,…). The main focus of this paper is to highlight the framework of the database: the mix proportioning of the concrete mixes is being discussed and the origin of the concrete data (country, reference info, etc.). By means of data mining and some known relations with respect to the durability related properties, e.g. correlation between w/b-ratio and chloride diffusion coefficient, are being evaluated

Monitoring the reduction in shrinkage cracking of mortars containing superabsorbent polymers

Ultra-high performance concrete (UHPC) is characterized by a low water-to-cement ratio, leading to improved durability and mechanical properties. However, the risk for autogenous shrinkage and cracking due to restrained shrinkage increases, which may affect the durability of UHPC as cracks form pathways for ingress of aggressive liquids and gases. These negative features can be prevented by the use of superabsorbent polymers (SAPs) in the mixture. SAPs reduce autogenous shrinkage by means of internal curing: they will absorb water during the hydration process and release it again to the cementitious matrix when water shortage arises. In this way, hydration can continue and shrinkage is diminished