Joint Sealants Research Articles

Adhesion Development of Organic and Silicone Sealants on Wet and Dry Concrete

Abstract Reliability of a sealed joint is directly related to the durability of its adhesion to the substrate. The presence of moisture on the surface of porous substrates caused by changing weather conditions prior to the application of sealants, such as the wetting of concrete by rainfall, can lead to poor sealed joint durability due to adhesion loss. In an attempt to better understand this mechanism, a method of testing adhesion of sealants on wet concrete has been developed and the effect of changes in surface conditions on sealant adhesion has been evaluated during the various drying phases identified for concrete. In the first 2 h of drying, a significant reduction of the pH at the surface is observed, which is mirrored with a reduction of the surface humidity. Both of these properties seem to have reached their plateau value within that timeframe, but in the following hours of the drying process the concrete continues to lose weight through water evaporation. Sealants based on different chemistries have been applied at various stages of the drying process (t = 0, 0.33, 2, 8, 24, 56 h) showing that the critical time period affecting the development of adhesion is within the first 2 h of concrete drying. This indicates that the alkalinity, surface moisture, on both, are the major factors responsible for the poor adhesion obtained on wet porous substrates and this is also the same for adhesion development of a primer on the substrate. The different sealant technologies evaluated in this program were silicones, urethanes, acrylics, silyl-terminated polyether, and silyl-terminated polyurethanes. In terms of adhesion development on wet concrete, the results highlight that the differences are more related to formulation within a sealant family than to the binder chemistry itself.

Substrate Durability Guidelines Used in Silicone Structural Attachment

Abstract This paper sets forth a procedure for evaluating substrates for durability for use in conjunction with structural silicone glazing (SSG). Lap shear and peel adhesion specimens are evaluated after exposures to various conditions using a modified ASTM C794-06, “Standard Test Method for Adhesion-In-Peel of Elastomeric Joint Sealants,” and ASTM C961-06, “Standard Test Method for Lap Shear Strength of Sealants.” Conditions of exposure include water, sodium hypochlorite (bleach), acetic acid (vinegar), salt fog, UV florescent accelerated weathering device (UVFl), ultraviolet light (UV) exposure, and heat. Evaluation of substrates and the interfaces are completed after tensile testing and visual surface analysis. The silicone structural glazing adhesive used in this evaluation is a high modulus high strength material intended to place the maximum load at the interface. Substrates evaluated include steel, anodized aluminum, galvanized steel, extruded rigid polyvinyl chloride (PVC), glass reinforced thermoplastic resin (fiberglass), and polyvinylidene fluoride (PVDF) painted aluminum. These evaluated substrates are tested to this procedure to show differences in performance and suggest a minimum time frame required for testing. The results and guidelines set forth in this paper provide the foundation for a practice and or a substrate specification for use in conjunction with structural silicone attachment methods.

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

Abstract 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.

The role of Ni buffer layer on high yield low temperature hermetic wafer bonding using In/Sn/Cu metallization

Low temperature hermetic wafer bonding using In/Sn interlayer and Au/Ni/Cu metallization as the high-melting-point (HMP) components was reported, wherein the thin Ni layer was introduced as a buffer layer to prevent solder consumption after their deposition. 8 in. wafer to wafer bonding was achieved at 180 °C for 20 min under 5.5 Mpa. Voids free seal joints composed of high temperature intermetallic compounds were obtained with good hermeticity. Present results show that the buffer layer is the key to ensure high yield hermetic wafer bonding when the low-melting-point solder was deposited directly on the HMP component.

Thermo-mechanical phenomena in PEM fuel cells

The experimental and theoretical studying of mechanical effects in running fuel cell is provided. It is shown that under optimized operating conditions it is possible to obtain the electrical performances of fuel cells at about 1 W cm−2. The further improvements can be achieved by means of mechanical effects. In particular, the influence of mechanical properties of seal joints and clamping bolt torques on the electrical performance is studied experimentally. It is demonstrated that rigid seal joints improve the electrical performance in comparison with the soft seal joints. Concerning the influence of the bolt torques, a certain optimal value is found for different types of MEA. The numerical modelling of mechanical stresses in running fuel cell is made. The developed model includes the main components of a real fuel cell (the membrane, the gas diffusion layers, the graphite plates, and the seal joints) and the clamping elements (the steel plates, the bolts, and the nuts). The operating conditions have been taken into account by imposing heat sources and humidity field. The results of modelling illustrate the main mechanical effects arising in the entire fuel cell. Copyright © 2009 John Wiley & Sons, Ltd.

Evaluation of D-Cracking Preventive Measures in Ohio Test Pavement

A test pavement located on part of State Route 2 near Vermilion, Ohio, was built in 1975 with sections designed to investigate the role of pavement design and material variables that included aggregate source and size, subbase drainage systems, pavement joint design, subbase materials, joint sealants, cement, type of cure, and joint spacing on D-cracking. In 1998 the current study was initiated to understand better the concrete durability of the different composition variables of the pavement sections after 23 years of performance. The study established a methodology to analyze the pavement sections, gathered data, and analyzed the data with SAS statistical software. Significant findings on the variables affecting the performance of pavement sections were obtained. Key findings show the impact of aggregate source and size, joint sealants, and vapor barriers on pavement D-cracking performance and overall pavement performance. On the basis of the findings from this research, the requirement to use larger-size aggregate in concrete pavement was incorporated into the Ohio Department of Transportation (ODOT) 2002 Construction and Material Specifications. Also, the 2009 ODOT specifications will eliminate the requirement for joint sealing in new concrete pavement in part because of the findings of this study.

Sound-insulating glazing with thermoviscous losses

An acoustic insulating glazing unit including at least two substrate sheets, joined together around their periphery using a device that forms a sealed joint and a spacer frame, which device, with the two substrate sheets, defines a flat cavity filled with a gas. At least one microcavity is formed over at least part of the periphery of the cavity, constituting a zone of thermoviscous losses from the cavity along at least one of internal walls of the two substrate sheets by which the cavity is bounded. Dimensions of the at least one microcavity are chosen to promote propagation of some of the acoustic waves from the cavity into the microcavity, generating thermoviscous losses and thus reducing acoustic energy of the cavity. A mechanism is provided to contain the acoustic waves escaping from the microcavity.

Designing demountable sealed joints for low-temperature systems

Design calculations are presented for demountable sealed joints working at cryogenic temperatures. Basic working formulas are given. Recommendations are made on using sealing elements to provide sealing in joints at low temperatures. Two forms of self-sealing are considered (radial and axial).

Track joint seal system

Track joint seal system

One component mould growth inhibiting sanitary joint sealant

One component mould growth inhibiting sanitary joint sealant

Recommendation of RILEM TC 190-SBJ: service-life prediction of sealed building and construction joints

Recommendation of RILEM TC 190-SBJ: service-life prediction of sealed building and construction joints

RILEM TC190-SBJ: development of recommendations on novel durability test methods for wet-applied curtain-wall sealants

The paper discusses the work carried out over the past 7 years within RILEM Technical Committee 190-SBJ Service Life Prediction of Sealed Building and Construction Joints towards the development of RILEM Technical Recommendations (RTR) on durability test methods for wet-applied (gun-grade) curtain-wall sealants. This paper is published along with the two draft RTR methods to provide some insight into the discussions within the committee during the development and early evaluation of both methods. The two draft RTR methods define test and evaluation protocols for accelerated artificial weathering and natural outdoor weathering. Both draft RTR methods are based on a novel test specimen configuration that allows simultaneous exposure of the sealant to compression and extension during movement cycles. Because of the special test joint configuration, the sealant is exposed to variable extension and compression amplitudes along the joint axis, allowing an evaluation of the effect of different movement amplitudes on the sealant when taking weatherability considerations into account. The results of the initial evaluations indicate that the test methods are capable of differentiating between products with regard to their resistance to accelerated or outdoor weathering and mechanical cycling. The type of failure and the changes in surface appearance observed during the test regimes are similar to those observed in actual service conditions. It is hoped that exposure studies based on these two new RTR methods will provide the underpinnings for the development of future ISO and ASTM durability test standards for building sealants.

Recommendation of RILEM TC 190-SBJ: service-life prediction of sealed building and construction joints

Recommendation of RILEM TC 190-SBJ: service-life prediction of sealed building and construction joints

Effects of Water Immersion on Building and Civil Engineering Joints and the Use of the Arrhenius Method in Predicting Adhesion Lifetime of Water-Immersed Joints

Abstract Moisture in the form of humidity, condensation, rain, or water immersion is the most commonly encountered element of the service environment and must be considered a critical factor in determining the long-term reliability of sealed or bonded joints. Moreover, the effects of moisture are exacerbated by elevated temperature. For many polymeric systems, warm, moist environments can considerably weaken the bulk or interfacial performance properties of the jointing materials formulated with these polymers. The majority of joint failures in service environments that comprise water exposure occur by degradation of the interface(s) between sealant or adhesive, primer, and substrate. Therefore, predicting the interfacial degradation in an actual service environment is of utmost importance. This paper provides information on the current understanding of the role of water in the failures of adhesive and sealant joints and discusses the usefulness of the Arrhenius’ relation in predicting the lifetime of sealed or bonded joints based on data generated at elevated temperatures. Finally, the paper suggests some guidelines aimed at improving the reliability of accelerated test and prediction procedures used in the evaluation of the durability performance of sealed or adhered joints in immersed environments.

Fluxless Hermetic Lid Sealing Using Electroplated Sn-Rich Solder

A new fluxless hermetic sealing technique using electroplated Sn-rich soft solder is reported. Specific glass (SCG72) is chosen as lid material to seal alumina packages. It has nominal coefficient of thermal expansion of 7 ppm/deg C, close to that of alumina. Alternatively, sapphire can also be used as the lid material. A thick Sn layer is plated over the Cr/Au patterned glass wafer, followed immediately by thin Au layer. This outer Au layer prevents the inner Sn from oxidation. In bonding, the glass lid is placed over the package rim which has a metallization structure of W/Ni/Au. The fluxless sealing process is performed in vacuum (50 millitorrs) to suppress tin oxidation. Compared to bonding in air, the oxygen content is reduced by a factor of 15 200. Fluxless bonding is valuable in many hermetic sealing applications such as microelectromechanical systems (MEMS), sensors, photonic devices, and imaging devices. Nearly void-free sealed joints are achieved with Sn-rich composition. Helium leakage tests are performed to evaluate hermetic quality. Scanning electron microscope (SEM) with energy dispersive X-ray spectroscopy (EDX) is used to evaluate the composition and microstructure of the sealing joints. The results show how the Sn-rich solder reacts with the W/Ni/Au on the package. This new sealing process can be applied to nearly all devices and packages that require hermetic sealing.

Performance Evaluation of Joint and Crack Sealants in Cold Climates Using DSR and BBR Tests

Joint sealants are used widely in Canada to protect pavements from infiltration of water and incompressible materials. Sealants are typically selected based on field studies, which are commonly repeated on a 10-year cycle. This paper examines a laboratory evaluation method based on two laboratory tests that are commonly used for testing asphalt binders: dynamic shear rheometer (DSR) and bending beam rheometer (BBR). Creep stiffness, rate of change in creep stiffness, and rate of change in complex shear modulus with temperature were used to evaluate sealant performance in cold climates. A sealant ranking system was proposed based on the calculation of a sealant index, which combines the proposed evaluation criteria. This method can potentially provide a cost-effective and rapid alternative to field studies. Eight hot-pour sealants were evaluated using this method. Results were verified from an ongoing field study that started in 2004. A good correlation was found between the proposed simplified evaluation method and the existing method.

Joint seal

Joint seal

Stress and plastic deformation of MEA in fuel cells: Stresses generated during cell assembly

A linear elastic–plastic 2D model of fuel cell with hardening is developed for analysis of mechanical stresses in MEA arising in cell assembly procedure. The model includes the main components of real fuel cell (membrane, gas diffusion layers, graphite plates, and seal joints) and clamping elements (steel plates, bolts, nuts). The stress and plastic deformation in MEA are simulated with ABAQUS code taking into account the realistic clamping conditions. The stress distributions are obtained on the local and the global scales. The first one corresponds to the single tooth/channel structure. The global scale deals with features of the entire cell (the seal joint and the bolts). Experimental measurements of the residual membrane deformations have been provided at different bolts torques. The experimental data are in a good agreement with numerical predictions concerning the beginning of the plastic deformation.

Performance Prediction and Life Cycle Costs at the Ohio Route 50 Test Pavement

ABSTRACT Application of mechanistic-based pavement performance prediction equations and life cycle costing to the Ohio Route 50 joint sealant experiment is presented. As-constructed pavement system characteristics are used as inputs, along with observed distress data for calibration of the predictive models. The relative cost effectiveness of the joint sealants on the project is determined. It is found that predicting the performance of a pavement using observations spanning over a small fraction of its design life and a set of purely empirical/statistical algorithms poses significant engineering interpretation challenges. Nonetheless, the test pavement may be expected to fail in transverse cracking long before it exhibits objectionable extents of spalling, or even before its riding quality deteriorates below a tolerable level. Neither the existence nor the type of sealant treatment used is likely to influence the progression of cracking. These findings are consistent with previous mechanistic analyses, which attributed rapid distress development to excessive slab length, an unexpected flood, and various construction issues.

Sealed flange joint for high pressure and high purity gas channels

Sealed flange joint for high pressure and high purity gas channels