Mia Schou Møller Lund

Frost susceptibility of sub-base gravel used in Pearl-Chain Bridges: an experimental investigation

Abstract This study investigates frost susceptibility of sub-base gravel determined by the ASTM D5918-13 standard as a conservative estimate of the frost heave risk of fill in overfilled arch bridges, particularly in Pearl-Chain Bridges. Frost heave of granular materials has been of great research interest from the end of the 1920s until the present day. Most new literature relates to empirical results that are several decades old. This is also the case for Danish tender specifications according to which the frost susceptibility of a sub-base gravel is solely assessed from its fines content. However, no actual frost tests have been carried out to verify this assumption. In the present study, the frost susceptibility of four different Danish gravel materials is categorised from their heave rate. We test two Danish sub-base gravel materials, with particle size distributions of 0–8 mm and 0–31.5 mm, respectively, and also two modified sub-base gravel materials with increased and reduced fines contents. The fines content of the gravel materials is analysed by laser diffraction, and compared with two common frost susceptibility criteria, Casagrande’s and Schaible’s, and with Danish tender specifications. Even though the two sub-base gravel materials are expected to be frost safe, 0–31.5 mm sub-base gravel shows medium frost susceptibility, whereas 0–8 mm sub-base gravel shows negligible frost susceptibility. The gravel materials with increased and reduced fines content are categorised as having low to medium frost susceptibility and low frost susceptibility, respectively. The permeability of the gravel materials is determined, and the permeability coefficient of 0–31.5 mm sub-base gravel is five times greater than that of 0–8 mm sub-base gravel. The results suggest that the criterion used to classify the frost susceptibility of Danish sub-base gravel materials based solely on their fines content is insufficient, and that the permeability coefficient should also be considered.

Self-Compacting Pervious Concrete Mix Design for Permeable Concrete Soakaway Rings

Permeable concrete soakaways store surface rainwater and let it seep slowly into the soil. This minimizes the risk of flooding, which is an increasingly larger problem because of climate change causing heavier and heavier rainfalls. In the present study, a self-compacting pervious concrete mix design is developed to use for permeable soakaway rings. A self-compacting mix design ensures a more uniform void distribution throughout the soakaway ring compared to the use of a conventional stiff pervious concrete mix design. The study is divided into two main parts: laboratory testing, in which the influence of the casting height on the void distribution is also considered, and full-scale casting of a 2.25-m-high pervious concrete soakaway ring. The overall conclusion is that a successful self-compacting pervious concrete mix design was developed by carefully balancing the use of a superplasticizer and stabilizer. Thereby, it was also possible to perform a successful full-scale casting.