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8 Table 2.1. Typical CLSM materials and proportions. CLSM Fly Ash Sand Cement Water Air Mixture Types (kg/m3) (kg/m3) (kg/m3) (kg/m3) (%) Range 119 - 297 1483 - 1780 30 - 119 198 - 494 0.5 - 4.0 Aa Typical 178 1542 59 297 a Range 949 - 1542 None 47 - 74 222 - 371 1-5 B Typical 1234 None 62 247 Range C Typical 275 1500 165 1 Range 1200 - 1500 30 - 60 130 - 300 15 - 30 D Typical a After FHWA (1997) Unconfined compressive strength of CLSM is always an im- the plant, thereby reducing the mixture volume in the truck portant design parameter, and the vast majorities of applica- en route to the site. Some CLSM mixtures are produced using tions are designed for future excavatability and typically have volumetric, mobile-type mixers. Rapid-setting CLSM mix- strengths of 1.0 MPa or less. For these mixtures, low cement tures, which typically contain highcalcium oxide (CaO) fly ash contents are used (e.g., 30 to 60 kg/m3), with or without fly ash. as the only binder, are almost always produced on site using In general, fluidity is achieved by high water contents (and low volumetric mixers because of the short handling time of such cement contents), and segregation is addressed through the use mixtures before setting. of AEAs and high fines contents (from fly ash, sand, etc.). Table 2.1 summarizes four of the more common CLSM Properties of CLSM mixture types that have been widely used. Note that this table does not implicitly include CLSM modified with a foaming This section provides information on the properties of CLSM agent/gun, but any of the mixtures can be treated by this that most affect its performance in key applications. The most process to increase air content. The mixture types are referred important fresh, hardened, and durability-related properties to herein as Groups A through D, with the mixtures described are briefly described next. in Groups A and B adopted from FHWA (1997). The ma- terials typically used in any of these CLSM mixture designs are Fresh CLSM Properties portland cement, sand, fly ash, water, and AEA, but the spec- trum of mixtures used in the field can be highlighted by con- Flowability sidering that some mixtures have no portland cement (Group C: only fly ash as binder in rapid-setting CLSM, typically pro- One of the most important attributes of CLSM is its ability duced in volumetric mixer on site), and some have no aggre- to flow easily into confined areas, without the need for conven- gates (Group B: a paste composed of about 95 percent fly ash tional placing and compacting equipment. The self-leveling and 5 percent portland cement, with water added as needed properties of CLSM significantly reduce labor and increase for fluidity). Mixtures in Group A typically include relatively construction speed. Because the enhanced flow properties of small amounts of portland cement and moderate levels of fly CLSM are critical to successful placement and performance, ash, combined with sand and water. Lastly, Group D is a typ- flowability is measured routinely and is an important quality ical mixture that relies upon portland cement as the only control parameter. binder, with AEAs used to generate air contents in the 15 to ASTM D 6103, "Flow Consistency of Controlled Low 30 percent range. Strength Material," has gained some acceptance since its adop- tion by ASTM. The test method uses a 75 150 mm cylinder, which is lifted, allowing the CLSM to slump and increase in Batching, Mixing, and Transporting diameter. The final diameter is typically used to differentiate CLSM is typically batched, mixed, and transported in sim- between various degrees of flowability. A final diameter of ilar fashions as concrete. Most flowable fill is batched at ready- 200 mm or higher is typical of a highly flowable mixture. mixed plants and mixed in truck mixers. The high fluidity of ASTM C 939, "Flow of Grout for Preplaced-Aggregate Con- CLSM may create difficulties in transporting full or near-full crete," measures the efflux time of CLSM as it passes through loads in ready mixed trucks. To address this potential prob- a flow cone. Several state DOTs have, over the years, specified lem, some producers hold back part of their mixing water this test method for CLSM, and the Florida and Indiana DOTs for on-site addition, and many will add liquid AEAs (or use required or require an efflux time of 30 seconds 5 seconds pneumatic guns to generate air) at the job site, rather than at (ACI Committee 229 1999).