Effect of aggregate size on the spalling of high-strength wall panels exposed to hydrocarbon fire

摘要

Concrete spalling has been widely accepted as being caused by a thermomechanical process resulting from high thermal gradients, as well as a moisture-clog process attributable to the buildup of pore-water pressure. The effect of aggregate size on the influence of concrete spalling of tilt-up wall panels after exposure to a hydrocarbon fire is studied in this paper. Six reinforced high-strength concrete wall panels 3,360 × 3,880 × 200 mm in dimension, loaded by self-weight only and consisting of 7-, 14-, and 20-mm aggregate sizes were exposed to the hydrocarbon fire curve for a period of 120 min. The specimens were approximately 70 MPa at the test date and were instrumented with in situ thermocouples to predict steam pressures based on thermal diffusivity calculations. The degree of spalling was quantified by mass loss with both solid mass and water mass being independently calculated. The concept of nominal spalling depth was introduced as a new way of quantifying the degree of spalling. The results show that aggregate size is an influencing parameter in regard to concrete spalling, with the degree of spalling ranging from 13 to 33%, respectively. Spalling is more prominent for smaller-size aggregates because of the facture-zone process.