Field Laboratory Testing Of Fly Ash Based Flowable Fill

摘要

This investigation was undertaken to explore the suitability of a fly ash based flowable fill for use in the bedding of buried pipes. A fly ash based flowable fill represents a cost effective alternative to conventional cement based fill materials commonly in use. The study attempted to characterize the fill properties initially in a laboratory environment and then based on these findings, test a fly ash based fill in field conditions. The laboratory portion of this study involved the investigation of basic physical characteristics such as compressive and tensile strengths of pure type "F" fly ash mixes with variable water contents. Based on these tests, 30 - 35% water content was found to be most applicable for field testing. In addition to basic strength testing, additional lab tests were conducted to measure potential hydration activity during the set process, shrinkage characteristics, and material behavior under triaxial loading conditions. The field testing portion of the investigation involved the installation of 12" diameter HDPE (high density polyethylene) SDR 32.5 sewer line in 24" deep by 30" wide test trenches excavated in clay soil above the water table. Three installations were made and all were capped with compacted sand above the bedding material. The three installations were made as follows: with the first pipe bedded in fly ash flowable fill to spring line, the second with fly ash bedding to the pipe crown and the third bedded entirely with compacted sand. Each installation was subjected to a vehicle load under successive reductions of cover thickness. Fill performance was measured indirectly with dial gauges within the pipe measuring pipe deflection. The results of this study indicate that a fly ash flowable fill reduces the minimum cover requirement for a buried pipe up to 3 fold compared to a pure compacted sand pipe bedding, In addition, flowability and ease of installation with a fly ash flowable fill were confirmed. Due to the small scale of these tests, 2000 lb. loads with shallow pipe burial, additional investigation(s) of this type of fill are recommended.