Assessment of Flowable Fill Strength in Pavement Construction

Abstract

Flowable fill is a self-compacted, cementitious material used primarily as a backfill in lieu of compacted fill. It generally consists of sand, portland cement, fly ash or slag, and water. It does not settle or require vibration or other means of compaction, it can be excavated, and it is safer than other forms of fill. One approach to predicting its ability to be excavated is to develop a correlation using early-age strength and long-term strength. Flowable fill mixture exhibiting strength less than 0.689 MPa (100 psi) is classified excavatable; mixtures with strengths higher than 0.689 MPa are difficult to excavate and are considered nonexcavatable. Because flowable fill is generally used for backfill and is placed underneath pavement, few studies have been undertaken evaluating moisture effects on long-term strength of flowable fill while underneath pavement. This paper presents the results of a laboratory study evaluating moisture effects on long-term strengths of flowable fill and assesses an accelerated method for predicting its 28-day strength. Samples were cast in limerock bearing ratio cylinders and rectangular wooden molds and were categorized as drained or undrained. Promising results were obtained on how moist environments affect the long-term strength of flowable fill mixtures. Results showed that for an early curing period, the undrained samples exhibited lower strength than drained samples. However, the strength of undrained samples increased with longer periods and to some extent exceeded the drained samples at a 28-day curing period. The accelerated samples had the potential to predict the 28-day strength using an accelerated method.