M. A. Lacasse

Towards Standardization of Service Life Prediction of Roofing Membranes

A service life prediction approach for roofing membranes and systems is proposed based on a probabilistic modeling of the time-dependent performance. The membrane performance is modeled using a discrete Markov chain that evaluates the change of performance over time as a result of deterioration or repair. This stochastic model will be developed using in-field performance data collected during roof inspections, considering the roofing system type, membrane type, age group, exposure conditions, and maintenance level. The use of in-field performance data captures the interaction between roofing components, as well as the synergism of the various degradation factors. The probabilistic modeling accounts for the uncertainty and variability of material properties, degradation factors, and quality of workmanship and maintenance. The service life is determined considering both the technical and economical performances, in addition to the risk of failure; this constitutes the first step towards the standardization of service life prediction of roofing membranes and systems.

Water Penetration of Cladding Components—Results from Laboratory Tests on Simulated Sealed Vertical and Horizontal Joints of Wall Cladding

Considerable work has focused on the deterioration of jointing compounds used to seal building joints; less emphasis has been placed on understanding the consequences of seal failure, particularly in respect to watertightness. Jointing products are subjected to different climate effects; some induce aging in the sealant that in time leads to deficiencies. Deficiencies may also come about from design faults or improper installation. Water entry at deficiencies may lead to a number of different deteriorating effects on the building fabric that may induce failure of other envelope components or premature failure of the joint sealant. Joints are also subjected to substantial wind driven rain loads, in particular atop multi-story buildings. The approach taken in this study focuses on determining the fault tolerance of joint systems of a simulated wall panel when subjected to watertightness tests that emulate heightened wind-driven rain loads. Vertical and horizontal joints of 20 mm width and sealed with a one-component polyurethane product were subjected to water spray rates ranging between 1.6 and 6 L/(min-m2) and pressures of up to 2 kPa. Faults introduced to the sealed joint and representative of deficiencies through which water could penetrate consisted of cracks of 2 to 16 mm long introduced along the sealant to substrate interface. For specific crack lengths, the crack size related to the degree of joint extension, the extension reaching a maximum of 10 % of joint width. Rates of water entry across the joint were determined for cracks of different lengths and size and the nature of water entry at deficient joints in which cracks were introduced was also examined. Results on vertical joints indicated that water readily enters open cracks in relation to the crack size, quantity of water present at the crack, and pressure across the opening. Water may also penetrate cracks of nonextended “closed” joints.

Experimental assessment of hygrothermal properties of wood-frame wall assemblies - moisture content calibration curve for OSB using moisture pins.

As part of a research program to establish the hygrothermal response of wood-frame wall assemblies to varying climate conditions, a series of drying experiments was performed in a programmable environmental chamber used to replicate exterior climatic conditions. In these experiments, bulk moisture content of the assembly was measured using a weighing system, and as well, measurements of local moisture content of oriented strand board (OSB) sheathing were taken with the use of electrical resistance moisture pin pairs. The local moisture content of the OSB was based on the relationship between moisture content and electrical resistance determined from a series of controlled laboratory experiments on OSB specimens of the same type and thickness. This paper reports on the results from experimental tests on seven small-size OSB specimens to establish the correlation between electrical resistance and the moisture content of the OSB. The process required the installation of several moisture pin pairs at different locations on and depths in the OSB. The weights of specimens together with resistance measurements taken across each pair of moisture pins were continuously monitored and results captured on a data acquisition unit. Details are provided in regard to electrical resistance measurements, the data acquisition unit, and method of weighing specimens. The results of the tests provided a simple equation to correlate moisture content of OSB to electrical resistance measurements using moisture pins pairs and as well correlation to moisture measurements using commercially available moisture metre. Given that moisture reading results obtained from commercially available moisture metres typically correlate to a specific wood species, the work completed in these experimental tests can be used to determine moisture contents in OSB from moisture metre readings.

Condensation risk assessment on box windows: the effect of the window-wall interface

Windows generally have the lowest temperature index in current building types, and will consequently be the primary location for interior surface condensation. Surface temperatures can easily be calculated using thermal finite-element models, but these generally omit the effect of convection in the windows and the window–wall interface. Hence, there is a need to determine if specific interface details provide potential for condensation on the window components in which air leakage paths may be prominent. The article reports on a laboratory evaluation of condensation risk assessment in a hotbox with varying pressure differences and the introduction of deficiencies. It was concluded that the effect of the type of insulation in the window–wall interface was very low for isobaric boundary conditions, whereas it has a significant effect when pressure differences are applied.

Evaluation of Sealed Joint Performance for the Selection of Sealants Suitable for Use in Autoclaved Lightweight Concrete Panels

The strength of autoclaved lightweight concrete (ALC) is evidently lower than that of normal concrete. Therefore, when movement occurs at a sealed joint between ALC panels, the sealant is required to deform and remain intact without damaging the ALC substrate. However, there is currently not sufficient information to permit evaluation of the expected performance of sealants applied to ALC substrates. In this study, static and dynamic tests were carried out in order to obtain an index that could be used to select the modulus of a sealant that can be expected to provide long-term performance when applied to an ALC substrate. To develop this index, an initial study was carried out in order to clarify actual joint movement between ALC panels of buildings; the expansion and contraction at the joint were measured, and shear joint movement was calculated based on the expected story-to-story drift of an external wall due to earthquake loads. Thereafter, in a subsequent stage of the study, five types of two-component polyurethane sealant products, of different elastic modulus, were subjected to tensile and shear tests from which the relationship between stress and the type of joint fracture was determined. The results from these tests revealed that when the stress is greater than 0.6 to 0.7 N/mm2, the ALC substrate is more easily fractured than the sealant. In a final stage of the study, the cyclic fatigue resistance of the same two-component sealants was evaluated using tensile and shear fatigue tests. Results from the fatigue tests indicated that the high modulus sealants lost adhesion from the ALC substrate at an early stage in the test. As well, the fatigue resistance of test specimens with joints having three-sided adhesion was lower than that of specimens having normally configured joints with adhesion on two sides of the sealant. Therefore, on the basis of results derived from all the studies, it was determined that a suitable sealant for use on ALC substrates is a sealant having a low modulus that is applied in the normal fashion as a two-sided joint.

Developing a Performance-Based Joint Sealant Specification for Airport PCC Pavements

Despite recent progress to develop a performance-based specification for bituminous sealants applied to asphalt concrete (AC) roadways and runways, a performance-based specification for cold-applied joint sealants for Portland cement concrete (PCC) aprons, taxiways, and parking areas has yet to be mapped and developed. Unique in-service conditions exist on these PCC pavements, where sealants are not only exposed to climatic effects and heavy traffic loads, but also to jet fuel and de-icing fluids. Installation and maintenance conditions are also unique in that it is often necessary to install or replace joint sealants at night or in a very short time so that aircraft traffic disruption is avoided. Hence, special consideration must be provided to ascertain that joint sealants are effective and durable. Recent studies on joint and crack sealants used on airport pavements that experience cold climates indicate that current specifications do not necessarily allow for the selection of durable sealants, and therefore sealant failure can be rapid. To address the issue of premature failure and to extend joint sealant service life, the elements of a performance-based specification for cold-applied joint sealants for PCC airport pavements is reviewed. The benefits of such a specification include the selection of joint sealants for specific local needs, reduced airport pavement maintenance costs, and extended airport PCC pavement service life.

A systematic methodology for design of retrofit actions with longevity

This article presents a method for the design of retrofit actions with focus on energy savings that permits a systematic and thorough assessment of potential failures, anticipated maintenance and the expected durability of the retrofit actions. The proposed method combines the use of failure mode and effect analysis (FMEA) to permit identifying likely failure modes from which maintenance actions could be planned and the limit states (LS) method to assess the durability of the given retrofit action. One case study was completed to illustrate the application of: (1) the FMEA and LS method and (2) the proposed method for a retrofit action of an internal insulated solid wall of masonry bonded with lightweight aggregate concrete and floor division of concrete. It was evident that FMEA is useful regarding failure-mode identification and maintenance planning, and the LS method has its strength in durability assessment. Combining the use of both the FMEA and LS methods allowed improved design of new energy-saving retrofit actions, given that a thorough risk assessment was possible that included a decision-making process on maintenance planning, durability assessment and decision on potential redesign of retrofit actions.

Drying response of wood-frame construction: laboratory and modeling.

Recent research in the assessment of hygrothermal response of building enclosures focuses on both laboratory experimentation and modeling in which the results from both processes are compared. Evidently such type of studies can potentially offer useful information regarding the benchmarking of models and related methods to assess hygrothermal performance of wall assemblies. This paper reports on experimental results and the use of an advanced hygrothermal computer model called hygIRC to assess the hygrothermal response of various components in wood-frame wall assemblies when subjected to nominally steady-state environmental conditions. There was interest in obtaining information on the drying rates of wall components, in particular, oriented strand board (OSB), featuring several different types of membrane in contact with OSB given that such results could provide direct evidence of the degree to which membranes may retain moisture and affect moisture migration. On this basis, the drying responses of mid-scale specimens of approximately (0.8×1 m2) and full-scale specimens (2.44×2.44 m2) were assessed in a series of experiments undertaken in a controlled laboratory setting. The results were subsequently used to help benchmark simulation results obtained from hygIRC in which a comparison is made between experimental and simulation results.