Andreas Thomas Franz Wolf

Preliminary Evaluation of the Mechanical Properties and Durability of Transparent Structural Silicone Adhesive (TSSA) for Point Fixing in Glazing

The paper reports on the preliminary evaluation of a transparent structural silicone adhesive (TSSA) developed for point fixing in glazing, which combines high transparency, strong adhesion performance, thermal stability, and excellent weatherability. The transparent film adhesive is a heat curing one-part material that shows strong bonding to glass, metals, ceramics, and even plastics typically without primer. The paper presents information on the durability and physical properties of the new material and suggests a methodology for deriving static and dynamic design strength values for the new material based on creep rupture experiments as well as nondestructive dynamic load experiments using the stress whitening phenomenon observed with this material as the limit state. The paper further discusses material characterization and hyperelastic modeling used in the finite element analysis based on finite strain theory.

Studies into the life-expectancy of insulating glass units

Abstract Insulating glass units are exposed to a variety of environmental factors, such as temperature and atmospheric pressure fluctuations, wind loads, working loads, sunlight, water and water vapour. The service life of a sealed insulating glass unit critically depends on the perfect functioning of the edge seal under these environmental influences. The water vapour permeability of the secondary insulating glass sealant plays only a subordinate role in the life expectancy of a dual-seal insulating glass unit, since the resistance of the edge seal to water vapour diffusion is determined almost exclusively by the low water vapour permeability of the PIB primary seal. On the other hand, great importance must be attached to the viscoelastic properties of the secondary insulating glass sealants, particularly to their tensile stress behaviour and their elastic recovery, as these properties affect the ability of the primary seal to function. In the case of gas-filled insulating glass units, the gas permeability of the secondary seal exerts a great influence on the gas leakage rate, since the gas permeabilities of organic primary and secondary sealants are approximately equal. When silicone sealants are used for the production of gas-filled insulating glass units, additional measures must be taken to ensure a gas-tight edge seal.

Mould fungus growth on sanitary sealants

Abstract The last 10 years have seen an almost explosive development in the market for sanitary sealants. There are several reasons for this: Firstly, there has been a fundamental increase in the use of sealants per cubic meter of interior space, due to increased numbers of joints resulting from modular designs. Typical examples of this are shower walls or bases which need a watertight joint between glazing and frame as well as between the frame and bathtub or shower basin and wall. Furthermore, there is a greater awareness of quality in todays consumer. While in the Sixties mortar was accepted as state-of-the-art in joint sealing, the present-day user is no longer prepared to accept crumbling joint fillings.

Evaluation of Silicone Sealants at High Movement Rates Relevant to Bomb Mitigating Window and Curtainwall Design

Silicone sealants have a long history of successful use in high performance windows and curtainwalls, such as structural glazing systems. With the recent threat of terrorist attacks, there has been an increased use of windows designed to mitigate the impact of bomb blasts. Due to the high strength and durability characteristics of silicone sealants, structural silicone sealants have been utilized in new bomb blast mitigating window designs. Effective bomb blast mitigating window designs allow the window system to withstand a moderate bomb blast without causing significant injury to building occupants from the blast itself or flying glass shards. The occupants are protected because laminated or filmed glass, which can withstand the blast, is attached in the framing with a silicone sealant. Silicone sealants provide unique benefits to these window designs due to their strength properties and their ability to anchor the laminated glass in the framing during a blast situation. In this paper, three commercially available high strength structural silicone sealants are evaluated at applied load velocities (movement rates) up to 5.0 m/s. These elevated load velocities are intended to simulate loads encountered during a bomb blast. Sealant joints are fabricated to evaluate the sealant in tension, shear, and combined tension and shear loads. Sealants joints are also exposed to accelerated weathering (heat, water, and artificial light through glass). Results show that the sealant strength values increase substantially at elevated rates of applied load. The paper discusses the effect of joint configuration, load velocities, and accelerating weathering on the performance and durability of the silicone sealants tested.

Factors governing the life expectancy of dual-sealed insulating glass units

Abstract The water-vapour permeability of the secondary insulating glass sealant plays only a subordinate role in the life expectancy of a dual-sealed insulating glass unit, since the resistance of the edge seal to water-vapour diffusion is determined almost exclusively by the low water-vapour permeability of the polyisobutene ( pib ) primary seal. On the other hand, great importance must be attached to the viscoelastic properties of the secondary insulating glass sealants, particularly to their tensile stress behaviour and their elastic recovery, as these properties affect the ability of the primary seal to function.

Use of Optical Imaging/Image Analysis System for the Quantitative Analysis of Surface Changes Induced by Outdoor Weathering on Sealants

Six sealant samples that had been weathered outdoors for 6.8 years in Japan were evaluated using an Optical Imaging/Image Analysis System, Atlas VIEEW™. The specimens were first visually evaluated with aesthetic ratings assigned. These ratings were then used as the reference for the optical image analysis. Image analysis was carried out on sealant images taken under optimized diffuse illumination at a constant illuminance. Two sets of images were captured per specimen, first the weathered surface for deterioration evaluation, and second the unweathered surface as a control (reference) image. Four distinct surface defects are quantifiable in the samples. These are cracking (crazing), visual color change, spatial uniformity of deterioration (due to dirt pick-up and uneven color change, or both), and overall surface texture. Chalking and dirt pick up, as rated visually prior to this evaluation, could not be accurately assessed with the digital imaging technique. The analysis shows that surface cracking and crazing generally can be well characterized using the automated VIEEW™ system. Judging color changes visually is problematic, since cracking and crazing interferes with color judgment. Further investigations are needed to develop an automated surface characterization method for sealants.

Studies of the ageing behaviour of gun-grade building joint sealants— the state of the art

Abstract In the mid-1970s the first studies, in the form of inspections of building joints, were conducted in England and Germany into the failure rate of sealants. As a consequence of these studies, the ageing behaviour of sealants was investigated with the aid of artificial accelerated ageing methods and by storing sealants outdoors for several years in moderate or tropical climates. The results acquired with these ageing methods can only be interpreted on the basis of a comprehensive understanding of the environmental factors responsible for ageing and the synergism of such factors. In this context, particular attention must be paid to the cyclic mechanical strain upon sealants which occurs in a building joint due to expansion, compression and shearing. By comparing the results acquired using different ageing methods it is possible to demonstrate the faults of the accelerated ageing methods currently in use and to submit recommendations for the future development of standardized methods.

Characterization of Adhesive Joints for Hybrid Steel-Glass Beams by Means of Simplified Small Scale Tests

In the recent past there have been calls for transparent and filigree structures in the building industry. Therefore, glass plays an increasing role not only in a classic way, as a space enclosing element, but also more and more in terms of offering load carrying functions. Glass beams for facade elements or floor girders, glass columns, or bracing facade elements are examples of this. To realize such architecturally attractive structures, bonded hybrid steel-glass elements have been developed in which each material is used in an optimized way according to its material properties. Promising examples for such bonded structures are I-beams in which steel flanges and glass webs are connected by linear adhesive bonds. The shear force is carried by the glass web, whereas the bending capacity of the hybrid beam is significantly increased by slender steel flanges compared to the pure glass pane. The shear forces between steel and glass are sustained only by the adhesive between them. In order to maximize the exploitation of both steel and glass, the adhesive on the one hand has to ensure an adequate stiffness but on the other hand has to be flexible enough to allow for a reduction or redistribution of local stress peaks, as well as other constraints such as thermal dilatation. However, the load-bearing capacity of such beams is governed, besides by the mechanical and geometrical characteristics of the adhesive joint, by aging, temperature, and creeping. In this contribution, an approach is shown for characterizing the adhesive joints for hybrid steel-glass beams by means of simplified small-scale tests. Standardized specimens (block shear and tension bulk specimens) and small-scale push-out tests are used to derive adequate mechanical values for analytical and numerical calculations, allowing one to draw conclusions regarding the general load carrying behavior of large-scale hybrid steel-glass beams. The results show that full-scale hybrid steel-glass beams, especially those with butt splice bonded and U-bonded geometries, are feasible using new structural adhesives, predominantly elasto-plastics such as polyurethanes or epoxy resins.

Material Properties for Use in FEA Modeling: Sealant Behavior with Ambient Laboratory Climate Aging

Stress relaxation uniaxial testing is used to define the behavior of elastomeric materials in their functional range. The stress-strain data obtained by this method are used in finite element analysis (FEA) to model the behavior of the material in a given application. The objective of this study is to determine the effect of aging on the uniaxial stress-strain properties of silicone sealants. This paper examines the material behavior changes that occur as these sealants continue to cure at ambient laboratory conditions. The study is intended as a first step toward developing simple working models that account for the effects of sealant aging in FEA modeling. Uniaxial stress relaxation testing was conducted on six commercially available silicone structural glazing, insulating glazing, and weatherproofing sealants in tension and in compression at temperatures of −20°C, 22°C, and 80°C. Testing was carried out immediately after cure, i.e., after three days for two-part and after 30 days for one-part sealants, and after an additional one-year storage period at ambient laboratory conditions. The test specimens were pre-loaded prior to testing in order to eliminate the Mullins effect. Testing was carried out over a strain range of −45–90%. The specimen was loaded to the desired strain level and then allowed to relax. The load at the end of the relaxation period was used to calculate the engineering stress. Coefficient of variance (CoV) was used to determine the significance of material property changes with continued sealant cure. No significant changes in engineering properties were observed for two sealants. For two further sealants, half or more of the test results were within CoV, and no clear trends in property drift could be derived. The changes in material properties of the final two sealants were well outside the CoV limit, and moderate to strong stiffening was observed.

Effects of anodized aluminium surface parameters on the long-term adhesion of silicone structural glazing sealants

Abstract The quality of silicone sealant adhesion to anodized aluminium varies widely. Key parameters that affect adhesion are the degree of surface sealing, the pigmentation of the anodization layer, the nature of the cleaner, and the time period allowed between cleaning the substrate and sealant application. While the cleaners display different effectiveness in removing organic contamination from the anodized aluminium surface, this effectiveness does not correlate with adhesion quality. It is hypothesized that by absorbing on the anodized aluminium substrate the cleaning solvents ‘condition’ the surface for improved silicone sealant adhesion. This conditioning effect diminishes, as the cleaning solvents desorb over time. For a given cleaning solvent, optimum adhesion is observed for a certain degree of surface sealing. Adhesion to unpigmented anodized aluminium substrates can be predicted by measuring the degree of surface sealing according to the ISO 2143 acid etch method. For pigmented anodized aluminium substrates, electrical phase shift measurements, made in accordance with the ISO 2931 test standard, can be used to predict adhesion quality. A quality control method for anodized aluminium surfaces is proposed that allows successful correlation of the electrical impedance measured at various frequencies with the long-term adhesion of silicone sealants to this surface.