Influence of wet-dry cycles on the withdrawal capacity and corrosion of zinc electroplated self-tapping screws in CCA-treated and untreated Southern pine

Abstract

Fastener products are commonly exported to different continents, and it is important to understand their performance in local timber species and construction practices. This paper investigates the effects of cyclic moisture changes on the withdrawal performance of yellow-zinc and nickel-zinc coated European screws in Australian copper chrome arsenate (CCA) treated Southern Pine, up to a maximum of 24 cycles. A 68–78% loss of the initial withdrawal strength was observed after three cycles, but this was recovered after twelve cycles. Overall, screws lost at least 50% of their initial strength after 24 cycles, regardless of the treatment or fastener coating. The corrosion resistance of nickel-zinc screws in CCA-treated timber was superior to that of yellow-zinc screws in the first three cycles, but the difference disappeared as the moisture cycle number increased. In CCA-treated timber, the corrosion rates of yellow-zinc screws were 40% higher than those in untreated timber. Although nickel-zinc screws were relatively more corrosion-resistant than yellow-zinc screws, the strength loss caused by corrosion confirms that the selected screws are best suited for indoor use. Finally, following a comparative analysis of test results, some recommendations were made in this paper for future research.