Matériaux et constructions

Gas and water vapour transport properties are of main concern in evaluating the suitability of a polymeric material to be used as a protective for monuments. In this work, oxygen, carbon dioxide and water vapour transport properties have been investigated for a new class of polymers, fluorinated polyurethanes, which have been recently proposed as a protective material for stone monuments. They consist of block copolymers made of hydrophilic polyurethane and hydrophobic perfluoropolyether blocks. The properties of these copolymers are expected to be strongly related to the relative amounts of these two blocks. In this investigation, three different types of fluorinated polyurethane copolymers were considered in order to assess the effect of chemical composition and physical morphology on mass transport properties. In particular, sorption and permeation experiments were performed at 30°C to evaluate permeabilities, diffusivities and solubilities. In fact, the analysis of the effect of chemical composition on transport properties can give useful selection criteria to tailor the material to be used as a protective.

Microbial activity can have an important impact on the durability of building materials. It is important to understand this activity in order to select appropriate treatment strategies for the repair and restoration of buildings and monuments. This paper describes the microorganisms which can modify the properties of building materials such as concrete, mortars, composites, timber, gypsum, etc., as well as the mechanisms responsible for deterioration of these materials. The information provided by the members of TC 183-MIB via a questionnaire is discussed. Techniques currently utilised and areas requiring further study are identified. In addition to the references, a list of publications for further reading completes this article.

The goal of this study was to analyze behavior of the cross-laminated timber (CLT) panel subjected to torsion and develop an efficient procedure for quick verification of numerical model of CLT that subsequently may be used for virtual prototyping of non-standard CLT products. Study used both experiments based on optical measurement using digital image correlation (DIC) and numerical modeling by means of finite element method (FEM). A physical torsion test of the CLT panel was first analyzed in terms of a displacement field that was computed on its surface. The FE simulation of the torsion test followed real boundary conditions and was carried out with use of 2 geometrically different FE models of the CLT. The first FE model did not take into account edge-bonding of the lamellas, the second one demonstrated alternative manufacturing option by considering the lamellas’ edge-bonding. The experiment and FE simulations were mutually compared based on displacement paths created on the panel surface. Results showed that the presented procedure offers relatively easy way of verification of FE analyses of CLT. FE model with edge-bonding of lamellas exhibited higher stiffness and higher relative error to DIC measurement than FE model without edge-bonding. Edge-bonding of lamellas introduces influential factor in FE modeling of CLT and should be omitted for accurate and realistic FE analyses of their behavior. Study also showed that lack of orthotropic properties of Oregon hybrid poplar can be in FEA sufficiently substituted by using cottonwood properties. Combining the DIC measurement and FEM in the analysis of the CLT is favorable since it offers an full-field validation of numerical models, which can be subsequently used for virtual prototyping.

In this study, the enhancement mechanism of steel fiber reinforced cement-based composite was investigated by quantitative analysis of the fiber-matrix interfacial transition zone (ITZ) and the corresponding fiber pull-out behavior. Silica fume was selected as a typical mineral admixture with modification effects. The fiber-matrix ITZ microstructure was innovatively characterized by backscattered-electron image analysis, EDS map scanning mode combined with image analysis, and micro-hardness test. Pull-out tests were performed to determine the bond strength and pull-out energy, and the anchorage force and normalized slip-hardening shear stress during fiber pull-out were calculated. The macro mechanical performances were also analyzed and discussed. The results showed that although the improvement effect of silica fume was less significant in the ITZ than in the bulk paste, the gaps, defects, and aggregated calcium hydroxide around the fiber were improved effectively. The increased calcium silicate hydrate and contact area strengthened the bonding established between fiber and matrix, and the denser microstructure and harder matrix resulted in the enhanced anchorage force and slip-hardening effect. The flexural performance was improved by strengthening interfacial bond properties by silica fume, whereas silica fume increased the compressive strength through improving matrix microstructure.

The paper gives a short description of the different types of test series on creep and shrinkage of concrete, which are under work at the Cement and Concrete Research Institute at the Technical University of Norway. Some results are given concerning creep and shrinkage of concrete under periodic changes in moisture content. It is found that a very short time of immersion in water— 6 hours weekly— will reduce the creep permanently. This holds also if the concrete later on is exposed to rather hard drying conditions. A study of concrete under periodically varying stresses showed that a characteristic stress, σB, applied as a constant stress equalized the periodically varying stresses within reasonable limits for the creep development. A rough estimation for the characteristic stress is given. Creep under decreasing and under increasing stresses as well as creep and shrinkage of concrete with low prehardening values are studied in special test series.