Forensic Investigation of Ultra-Thin Whitetopping Failures in Taiwan

Abstract

This paper addresses the causes of the premature failures observed on newly constructed ultra-thin whitetopping (UTW) sections. The key factors contributing to premature failure were high pouring temperature and an insufficient underlying asphalt layer. Severe cracking and deep rutting were observed on sections placed during the daytime when the weather was hot and dry. Pouring temperature was even more critical when river gravel aggregate was used because it has a high thermal coefficient of expansion. Also, a low water-cement ratio magnified the effect of thermal cracking at high pouring temperature. On the basis of field results, it was found that the use of high-strength concrete should be discouraged when the pour temperature is high, since high shrinkage and premature cracking can result. It was concluded that the deep rutting was caused by the pumping of fines from the underlying base layer, in locations where there was no erosion-resistant asphalt layer. Sections poured at temperatures below