Evaluation of crack sealant adhesion properties under complex service ambient conditions based on the weak boundary layer (WBL) theory

The use of crack sealant is an effective, simple, and extensive maintenance approach to repairing cracks. However, the extended exposure of sealants to complex ambient conditions have negative impacts on sealant properties, causing gradual degradation of sealant performance and even more seriously, premature failure during their service. According to fracture modes of the failure interface, a weak boundary layer reportedly exists and results in adhesion failure of crack sealants. This work studied three environmental factors, namely, temperature, water, and impurities, to determine the effects of hostile ambient exposure on different crack sealants commonly used in hot and moderate climates. Tensile test was the main evaluation method, and the weak boundary layer (WBL) theory was introduced to illustrate the adhesion failure between sealant and crack wall. Analysis of experimental results showed that the lower temperature, the longer soaking time and the impurities would precipitate the eventual formation of a WBL. Sealants reached a glassy state and were likely to acquire brittle fracture at the interface at −30 °C. When soaked, sealants gradually hardened and water penetrated into the pores on the adhesive surface of the crack wall. Impurities at the interface hindered adhesion and reduced the contact area between sealant and crack wall. Consequently, the adhesion ability between interfaces dropped sharply and thus caused adhesion failure.