The relative effects of deformation and aging on sealant behavior

One-component polyurethane sealant specimens were cast between sections of aluminum substrate, cured at standard conditions for 21 days and then subjected to deformations ranging from 50% compression to 75% extension. Specimens were divided into three groups: one group remained at standard conditions, another group was mounted in a xenon arc weathering device and the remaining group was placed in a forced air oven. After 500 hours of exposure specimens were returned to standard conditions and then tested to failure. The sealant characteristics monitored were recovery from deformation, ultimate elongation, tensile strength, strain energy to break and the nature of the failure. Both elongation and strain energy were discriminating indicators of changes in the mechanical properties of the sealant The results indicate that prolonged compression markedly reduced the elongation capacity of the sealant, whereas prolonged extension produced specimens with higher elongation capacities. In most specimens, adhesive failure predominated; cohesive failure was evident in those specimens that had been extended and exposed to elevated temperatures. Five hundred hours of exposure were observed to be insufficient to cause significant chemical degradation of the sealant.Dr. Michael A. Lacasse: https://orcid.org/0000-0001-7640-3701Dr. Michael A. Lacasse: https://orcid.org/0000-0001-7640-3701Peer reviewed: YesNRC publication: Ye

Movement during cure of latex building joint sealants

Dr. Michael A. Lacasse: https://orcid.org/0000-0001-7640-3701Dr. Michael A. Lacasse: https://orcid.org/0000-0001-7640-3701Peer reviewed: YesNRC publication: Ye

Static and dynamic cut growth fatigue characteristics of silicone based elastomeric sealants

Dr. Michael A. Lacasse: https://orcid.org/0000-0001-7640-3701Dr. Michael A. Lacasse: https://orcid.org/0000-0001-7640-3701Peer reviewed: YesNRC publication: Ye

Laboratory cyclic fatigue test of silicone sealant mini- specimens

Dr. Michael A. Lacasse: https://orcid.org/0000-0001-7640-3701Dr. Michael A. Lacasse: https://orcid.org/0000-0001-7640-3701Peer reviewed: YesNRC publication: Ye

Evaluation of cyclic fatigue as a means of assessing the performance of construction joint sealants: silicone sealants

Corrosion characteristics of reinforcement in modified high-alumina cement (HAC) containing a conversion-preventing additive (CPA) was studied. An investigation was carried out using ordinary portland cement, high-alumina cement, and modified high-alumina cement. Results includingcompressive strength, bond strength, porosity, CT permeability, and extent of steel bar corrosion are presented. The effect of a deicing salt, calcium chloride, on formation of hydrogarnet and str\ue4tlingite in HAC and modified HAC mortars is also reported. This work indicates that HAC mortar, after conversion, is unable to protect the reinforcement from corrosion in an environment containing chloride ions. Conversion-inhibited high-alumina cement has the capability of protecting the reinforcement fromcorrosion under severe test conditions due to its effective resistance to the penetration of chloride ions.Dr. Michael A. Lacasse: https://orcid.org/0000-0001-7640-3701Dr. Michael A. Lacasse: https://orcid.org/0000-0001-7640-3701Peer reviewed: YesNRC publication: Ye

Evaluation of cyclic fatigue as a means of assessing the performance of construction joint sealants: polyurethane sealants

Dr. Michael A. Lacasse: https://orcid.org/0000-0001-7640-3701Dr. Michael A. Lacasse: https://orcid.org/0000-0001-7640-3701Peer reviewed: YesNRC publication: Ye

Cucurbit[n]urils (n = 5\u20138): a comprehensive solid state study

Cucurbit[n]urils (CB[n], n = 5\u20138) have been prepared, separated, and purified, and the structure of their solid state assemblies has been addressed. A number of general features were identified which are of interest to understand some peculiar properties of cucurbiturils (solubility, aggregation, assembly, transformation to porous crystals, influence of air humidity). CB[5], CB[6], and CB[8] were isolated as hydrate crystals whose structures were found to show a strong tendency of the macrocycles to interpenetrate. A self-closing effect was rationalized in terms of multiple weak CH\ub7\ub7\ub7O interactions between the macrocycles, the degree of which is discussed in detail. Solid state cross polarization magic angle spinning (CP-MAS) 13C NMR spectra obtained at 900 MHz were correlated with the crystal structures. An odd\u2013even effect in the crystallinity of thermally treated CB samples (CB[5] and CB[7] amorphous, CB[6] and CB[8] crystalline) was observed, which is reflected in differences in water solubility (CB[5] and CB[7] are water-soluble, whereas CB[6] and CB[8] are only very scarcely so). This may be explained by a less efficient self-association for CB[5] and CB[7] as compared with CB[6] and CB[8], which is reflected in the number of inter-cucurbituril CH\ub7\ub7\ub7O interactions per cucurbituril. This leads to a more favorable solvation for the CBs having an odd symmetry, whereas those with even symmetry prefer to self-associate in a manner ultimately leading to crystallization. We also propose an explanation for the presence of anions (Cl\u2013) inside some cucurbituril materials, whose cavity is often considered hydrophobic. Furthermore, it is demonstrated that large quantities of the very stable microporous CB[6] crystals (which have the R3\u305 channel structure) can be obtained very easily by a simple thermal treatment of the hexagonal crystals of CB[6] (P6/mmm structure) obtained directly from the initial reaction used to synthesize the various CB[n]. The micromorphology of the CB[n] powders was established using scanning electron microscopy (SEM), and the tendency of each material to absorb water from the atmosphere was demonstrated by thermogravimetric analyses (TGA).Peer reviewed: YesNRC publication: Ye

Photoluminescent quantum dot\u2013cucurbituril nanocomposites

The preparation of entrapped CdSe\u2013ZnS fluorescent quantum dots (QDs) in cucurbituril (CB) polymer capsules is reported.Peer reviewed: YesNRC publication: Ye