Design of Flowable Fill: Waste Foundry Sand as a Fine Aggregate

Abstract

Flowable fill is generally a mixture of sand, fly ash, a small amount of cement, and water. Sand is the major component of most flowable fill mixes; consequently, using a waste material as a substitute for natural sand results in the beneficial use of the waste material. Waste foundry sand (WFS) was used as a fine aggregate in this study. Three green sands from ferrous foundries and two Class F fly ashes were used. A natural river sand was used for comparison. The flow behavior, hardening characteristics, and ultimate strength behavior of flowable fill were investigated. The penetration resistance necessary to sustain walkability as the fresh flowable fill hardens was determined, and the time necessary to achieve this penetration resistance was defined as “walkable time.” The unconfined compressive strength at 28 days appeared to correlate well with the water-to-cement ratio. The 90-day compressive strength test results indicate that a maximum rise of 25 to 30 percent in long-term strength with respect to 28-day strength can be expected. The permeability of hardened flowable fill was found to be low (around 10−6cm/sec). The pH of pore solution of hardened flowable fill indicated that the potential for corrosivity is low. The toxicity tests indicated that some WFSs are environmentally safe. The concepts explained are not necessarily restricted to flowable fill containing WFS; they can be generalized as being applicable to all flowable fills.