Title: Durability of Two-Stage (Pre-Placed Aggregate) Concrete to Sulfate Attack
Author(s): M. F. Najjar, A. M. Soliman, T. M. Azabi and M. L. Nehdi
Publication: Symposium Paper
Appears on pages(s): 1-16
Keywords: chemical; ettringite; physical; sodium sulfate; sulfate attack; supplementary cementitious materials; thaumasite; two-stage concrete.
Sulfate attack is one of the aggressive damage mechanisms that can jeopardize the durability of concrete structures. Several research studies have investigated the positive influence imparted by supplementary cementitious materials (SCMs) regarding the resistance of conventional concrete to sulfate exposure. However, the effects of SCMs on the sulfate resistance of two-stage concrete (TSC) has not been duly explored. In this paper, the durability of TSC mixtures incorporating different SCMs, including fly ash (FA), silica fume (SF) and metakaolin (MK), as partial replacement for ordinary portland cement (OPC) was investigated. Two different sodium sulfate exposure regimes were simulated: full immersion (conducive to chemical sulfate attack) and partial immersion combined with cyclic temperature and relative humidity (conducive to physical salt attack). Results show that TSC specimens incorporating FA achieved acceptable resistance to chemical sulfate attack, while incurring severe surface scaling
under physical salt attack. Moreover, TSC specimens made with MK exhibited adequate resistance to both chemical and physical attacks. Surprisingly, TSC specimens incorporating SF deteriorated significantly due to abundant thaumasite formation. An attempt is made herein to delineate the mechanisms that result in deterioration.