Durability of Acrylic Sealants Applied to Joints of Autoclaved Lightweight Concrete Walls: Evaluation of Exposure Testing

ABSTRACT: In Japan acrylic sealants are traditionally the sealant products of choice when specified for use between autoclaved lightweight concrete (ALC) panels. Although, in general terms, the mechanisms of the deteriora­tion of acrylic sealants are well known its long-term durability to outdoor ex­posure has not, however, been fully investigated. The research described in this paper focuses on the change in the properties and deterioration of acrylic sealant products when exposed to outdoor testing. The two stage project consisted of (i) on-site investigations of deteriorated acrylic sealants that had been placed in external joints of ALC-clad buildings; and (ii) outdoor expo­sure testing of different types of acrylic sealant in three climate regions located in Japan. The results of the work from the first stage of the study revealed the following. Two-sided adhesion joint configurations installed in deep panel ALC cladding were more reliable than three-sided adhesion joints used for thin panel ALC cladding from the viewpoint of the durability of the

sealed joint installed in actual buildings. Most fractures of the sealed joint could be characterized as failure in peel (or thin layer cohesive failures), in which the sealant ruptured at the interface with the ALC substrate to which it was applied. Additionally, in 47 of 62 locations surveyed, surface cracks were apparent on the coating that had been applied to protect the sealant. The second stage of the project focused on the degree of deterioration of coated and non-coated acrylic sealants subjected to outdoor exposure testing in a cold, a warm, and a subtropical climate. Results from this stage showed that aging of the sealant, as determined by the degree of surface cracking, expectedly depended on the local temperature and the respective degree of exposure to solar radiation. It was determined that the longer the exposure period, the lower the tensile performance of the acrylic sealants. The elonga­tion of three-sided adhesive joint configurations after 5 years exposure test­ing decreased remarkably and their maximum elongation was less than 50 %. A significant number of sealed joints after 5 years ofexposure had ALC substrate failure.

KEYWORDS: Sealant, autoclaved lightweight concrete, wall panel, durabil­ity, exposure testing

Introduction

The “Housing Quality Assurance Act" [1] was established in 2000 in Japan and, as a consequence, a ten year warranty period was imposed on industries pro­ducing and installing waterproofing systems. Sealed joints installed in buildings form part of a building facade’s waterproofing system and thus require long­term performance and it is therefore necessary to verify the durability of cur­rently available sealed joint systems. In Japan when considering performance standards and specifications for sealed joint systems, the performance of seal­ants is regulated by two test methods: (i) “Sealants for Sealing and Glazing in Buildings" (JIS A 5758) [2], and (ii) “Testing Methods of Sealants for Sealing and Glazing in Buildings"(JIS A 1439) [3].

The primary specification and guideline documents that respectively pro­vide for the material, design, and construction of sealed joints include: “Public Construction Standard Specifications" [4] and “The Construction Work Super­vision Guideline" [5]; both of these documents are regulated by the Ministry of Land, Infrastructure, Transport and Tourism of Japan. The Architectural Insti­tute of Japan also provides the “Recommendation for Design of Joints and Jointing for Control of Water and Air Penetration in External Walls" [6]. The performance regulations for the design and installation of sealed joints in build­ing and constructed works have been established to improve the long-term per­formance of such products used both in government building assets and those of the private sector.

Sealed joint systems designed for use in ALC (autoclaved lightweight aer­ated concrete) panels have, for a considerable time, followed construction prac­tices as provided for external walls of industrial buildings. Likewise, acrylic sealant products have been used in Japan for ALC panel joints for a significant

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time, and perhaps elsewhere around the globe, because: (i) coatings can readily be applied to these products (thus prolonging their aesthetic performance);

(ii) their initial tensile strength is low thus offering a reduced risk to premature tensile failure of the ALC panel substrate; and (iii) this sealant type can be in­stalled in conditions where the substrate may be moist or, indeed, wet. How­ever, a systematic verification concerning the long term performance of acrylic sealants used in ALC panel structures which have been exposed to up to 30 years of aging has not yet been done. Consequently, a study was undertaken to inves­tigate the condition of deteriorated sealed joints of buildings clad with ALC pan­els such that some basic information on the actual condition and degree of deterioration of aged sealed joints could be obtained. Following the information gained from this study, a subsequent work was initiated that focused on the ex­posure of acrylic sealed joints that were tested to evaluate their mode of degra­dation and the likelihood of achieving long-term performance.