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5 CHAPTER 2 State of the Art and Current Practice Introduction Clem et al. 1995; Buss 1989), encapsulation of contaminated soils (Gardner 1998), soil stabilization (Green et al. 1998), Research performed under this project included a com- and erosion control (Larsen 1988, 1993). prehensive literature review and a survey of state Department Over the past 40 years, various terms have been used to de- of Transportation (DOT) practice regarding CLSM use for scribe what is currently known as CLSM, including flowable backfill, utility bedding, void fill, and bridge approaches. A fill, unshrinkable fill, controlled density fill, flowable mortar, more detailed review of literature and information related plastic soil-cement, soil-cement slurry, and K-Krete. In 1984, to CLSM was included in the Phase I Interim Report for ACI Committee 229 was formed, and the ACI-approved term NCHRP Project 24-12 (Folliard et al. 1999); only a brief syn- "controlled low-strength material or CLSM" was adopted. In thesis is provided in this chapter. its 1999 committee report, ACI Committee 229 defined CLSM The remainder of this chapter presents a brief summary of as a self-compacted, cementitious material used primarily as information gathered on CLSM, focusing mainly on labora- a backfill alternative to compacted fill (ACI Committee 229 tory and field research projects. It is based on a comprehensive 1999). Today, CLSM has been used throughout the United literature search and interactions with various state DOTs, States for a wide range of applications, using a spectrum of the American Concrete Institute (ACI), the Portland Cement different materials. Association (PCA), the National Ready Mixed Concrete As- sociation (NRMCA), the American Public Works Association (APWA), and other agencies and organizations. Much of the Materials information on current state DOT practice was obtained This section describes the most common constituent ma- through the use of a written survey distributed in 1998 as part terials used in CLSM, including portland cement, fly ash, ag- of the aforementioned Phase I Interim Report for NCHRP gregates (including foundry sand), chemical admixtures, and Project 24-12. other by-product materials. A significant benefit of CLSM is the ability to use a wide range of local materials, including by- Historical Background product materials. Because of the relatively high material cost of CLSM (compared to compacted fill), the ability to specify The development of CLSM can be viewed as a natural evo- and use by-products such as fly ash and foundry sand will be lution of plastic soil-cement, with the main improvements re- critical to the continued growth of CLSM usage. lated to increased flowability and improved quality control. One of the earliest records of the use of CLSM was in 1964 by Portland Cement the U.S. Bureau of Reclamation as the bedding of a 515-km long pipeline in the Canadian River Aqueduct Project (Adaska Although any type of portland cement can be used in CLSM, 1997). Since then, CLSM has been used on many projects for ASTM C 150 Type I is the most commonly used. The prevail- backfill (Brewer 1992; Sullivan 1997), utility and pipe bedding ing criteria are the local availability and cost of cement, and as (Adaska and Krell 1992; Larsen 1993), void fill (Gray et al. 1998; such, Type II or Type I/II cements may be more common in Hook and Clem 1998), and bridge approach applications some regions of the United States. Because of the compara- (Snethen and Bensen 1998). Other applications include tively low cement contents found in CLSM, common concrete using CLSM for structural fill (ACI Committee 229 1999; durability problems, such as alkali-aggregate reaction and