Attempt at Quantification of Surface Degradation and Evaluation of Relationship between Outdoor and Accelerated Exposure of Construction Sealants

ABSTRACT: The weatherability of construction sealants is a highly impor­tant performance criterion for the prediction of their service lives. Currently, the evaluation of a sealant’s surface weatherability is carried out mainly via qualitative visual judgment. One objective of this paper is to establish a quan­titative method for the assessment of surface degradation. A further objective is the evaluation of the relationship between outdoor and accelerated expo­sure with regard to surface degradation. The understanding of this relation­ship is important for the shortening of the development cycle and the prediction of a sealant’s service life. The paper presents information on the weatherability of construction sealants based on a recently developed test specimen design that allows simultaneous exposure of the sealant to forced compression and extension movement in a single specimen with cyclic move­ment and weathering carried out simultaneously. A quantitative method for the assessment of surface cracks is employed, and the relationship between outdoor and accelerated weathering exposure is evaluated by using metrics that indicate the degree of surface cracking as a new semi-quantitative crite­rion of surface degradation.

KEYWORDS: sealant, weatherability, durability, accelerated exposure, outdoor exposure, surface degradation

Introduction

The weatherability of construction sealant is evaluated by outdoor and/or accel­erated weathering exposure, and the accelerated exposure is applied in order to shorten the time periods required for the performance evaluation and the over­all development of products. Though the relationship between outdoor and accelerating exposure has been considered since the 1960s, the relationship between the two exposure types is not fully defined. Whereas the weatherability of a sealant is evaluated quantitatively, mainly by the changes occurring in its mechanical properties, changes in the appearance of the sealant surface as a result of the sealant’s degradation, such as changes in color and the appearance of surface cracks, are typically assessed only via qualitative methods. This paper presents a quantitative method for the assessment of surface cracks and dis­cusses the relationship between outdoor and accelerated weathering exposure by using metrics that indicate the degree of surface cracking as a new semi­quantitative criterion of surface degradation.

Experiment