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1、ACI 229R-99 became effective April 26, 1999. Copyright 1999, American Concrete Institute. All rights reserved including rights of reproduction and use in any form or by any means, including the making of copies by any photo process, or by electronic or mechanical device, printed, written, or oral, o
2、r recording for sound or visual reproduc- tion or for use in any knowledge or retrieval system or device, unless permission in writing is obtained from the copyright proprietors. 229R-1 ACI Committee Reports, Guides, Standard Practices, and Commentaries are intended for guidance in planning, designi
3、ng, executing, and inspecting construction. This document is intended for the use of individuals who are competent to evaluate the significance and limitations of its content and recommendations and who will accept re- sponsibility for the application of the material it contains. The American Concre
4、te Institute disclaims any and all re- sponsibility for the stated principles. The Institute shall not be liable for any loss or damage arising therefrom. Reference to this document shall not be made in con- tract documents. If items found in this document are de- sired by the Architect/Engineer to
5、be a part of the contract documents, they shall be restated in mandatory language for incorporation by the Architect/Engineer. Controlled Low-Strength Materials ACI 229R-99 (Reapproved 2005) Reported by ACI Committee 229 Bruce W. Ramme Chairman Wayne S. AdaskaMorris HuffmanFrances A. McNealCharles F
6、. Scholer Richard L. BooneBradley M. KluteDonald E. MilksGlenn O. Schumacher Christopher CrouchHenry J. KolbeckNarasimhan RajendranVictor Smith Kurt R. GrabowRonald L. LarsenKenneth B. RearRichard Sullivan Daniel J. GreenLeo A. LegatskiPaul E. ReinhartSamuel S. Tyson Richard R. HalversonWilliam MacD
7、onaldHarry C. RoofHarold Umansky William HookOscar ManzEdward H. RubinOrville R. Werner Controlled low-strength material (CLSM) is a self-compacted, cementi- tious material used primarily as a backfill in place of compacted fill. Many terms are currently used to describe this material, including flo
8、wable fill, unshrinkable fill, controlled density fill, flowable mortar, flowable fly ash, fly ash slurry, plastic soil-cement, soil-cement slurry and other various names. This report contains information on applications, material proper- ties, mix proportioning, construction, and quality-control pr
9、ocedures. The intent of this report is to provide basic information on CLSM technology, with emphasis on CLSM material characteristics and advantages over con- ventional compacted fill. Keywords: aggregates; backfill; compacted fill; controlled density fill; controlled low-strength material; flowabl
10、e fill; flowable mortar; fly ash; foundation stabilization; low-density material; pipe bedding; plastic soil- cement; preformed foam; soil-cement slurry; trench backfill; unshrinkable fill; void filling. CONTENTS Chapter 1Introduction, p. 229R-2 Chapter 2Applications, p. 229R-2 2.1General 2.2Backfil
11、ls 2.3Structural fills 2.4Insulating and isolation fills 2.5Pavement bases 2.6Conduit bedding 2.7Erosion control 2.8Void filling 2.9Nuclear facilities 2.10Bridge reclamation Chapter 3Materials, p. 229R-5 3.1General 3.2Cement 3.3Fly ash 3.4Admixtures 3.5Other additives 3.6Water 3.7Aggregates 3.8Nonst
12、andard materials 3.9Ponded ash or basin ash Chapter 4Properties, p. 229R-6 4.1Introduction 229R-2ACI COMMITTEE REPORT 4.2Plastic properties 4.3In-service properties Chapter 5Mixture proportioning, p. 229R-9 Chapter 6Mixing, transporting, and placing, p. 229R-9 6.1General 6.2Mixing 6.3Transporting 6.
13、4Placing 6.5Cautions Chapter 7Quality control, p. 229R-11 7.1General 7.2Sampling 7.3Consistency and unit weight 7.4Strength tests Chapter 8Low-density CLSM using preformed foam, p. 229R-12 8.1General 8.2Applications 8.3Materials 8.4Properties 8.5Proportioning 8.6Construction Chapter 9References, p.
14、229R-14 9.1Specified references 9.2Cited references CHAPTER 1INTRODUCTION Controlled low-strength material (CLSM) is a self-com- pacted, cementitious material used primarily as a backfill as an alternative to compacted fill. Several terms are currently used to describe this material, including flowa
15、ble fill, un- shrinkable fill, controlled density fill, flowable mortar, plas- tic soil-cement, soil-cement slurry, and other various names. Controlled low-strength materials are defined by ACI 116R as materials that result in a compressive strength of 8.3 MPa (1200 psi) or less. Most current CLSM a
16、pplications re- quire unconfined compressive strengths of 2.1 MPa (300 psi) or less. This lower-strength requirement is necessary to allow for future excavation of CLSM. The term CLSM can be used to describe a family of mix- tures for a variety of applications. For example, the upper limit of 8.3 MP
17、a (1200 psi) allows use of this material for ap- plications where future excavation is unlikely, such as struc- tural fill under buildings. Chapter 8 of this report describes low-density (LD) CLSM produced using preformed foam as part of the mixture proportioning. The use of preformed foam in LD-CLS
18、M mixtures allow these materials to be produced having unit weights lower than those of typical CLSM. The distinctive properties and mixing procedures for LD-CLSM are discussed in the chapter. Future CLSM mixtures can be developed as anticorrosion fills, thermal fills, and durable pavement bases. CL
19、SM should not be considered as a type of low-strength concrete, but rather a self-compacted backfill material that is used in place of compacted fill. Generally, CLSM mixtures are not designed to resist freezing and thawing, abrasive or erosive forces, or aggressive chemicals. Nonstandard materi- al
20、s can be used to produce CLSM as long as the materials have been tested and found to satisfy the intended application. Also, CLSM should not be confused with compacted soil- cement, as reported in ACI 230.IR. CLSM typically requires no compaction (consolidation) or curing to achieve the de- sired st
21、rength. Long-term compressive strengths for com- pacted soil-cement often exceed the 8.3 MPa (1200 psi) maximum limit established for CLSM. Long-term compressive strengths of 0.3 to 2.1 MPa (50 to 300 psi) are low when compared with concrete. In terms of allowable bearing pressure, however, which is
22、 a common criterion for measuring the capacity of a soil to support a load, 0.3 to 0.7 MPa (50 to 100 psi) strength is equivalent to a well-compacted fill. Although CLSM generally costs more per yd3 than most soil or granular backfill materials, its many advantages often result in lower in-place cos
23、ts. In fact, for some applications, CLSM is the only reasonable backfill method available.1-3 Table 1 lists a number of advantages to using CLSM.4 CHAPTER 2APPLICATIONS 2.1General As stated earlier, the primary application of CLSM is as a structural fill or backfill in lieu of compacted soil. Becaus
24、e CLSM needs no compaction and can be designed to be fluid, it is ideal for use in tight or restricted-access areas where placing and compacting fill is difficult. If future excavation is anticipated, the maximum long-term compressive strength should generally not exceed 2.1 MPa (300 psi). The follo
25、w- ing applications are intended to present a range of uses for CLSM.5 2.2Backfills CLSM can be readily placed into a trench, hole or other cavity (Fig. 2.1 and 2.2). Compaction is not required; hence, the trench width or size of excavation can be reduced. Gran- ular or site-excavated backfill, even
26、 if compacted properly in the required layer thickness, can not achieve the uniformity and density of CLSM.5 When backfilling against retaining walls, consideration should be given to the lateral pressures exerted on the wall by flowable CLSM. Where the lateral fluid pressure is a con- cern, CLSM ca
27、n be placed in layers, allowing each layer to harden prior to placing the next layer. Following severe settlement problems of soil backfill in utility trenches, the city of Peoria, Ill., in 1988, tried CLSM as an alternative backfill material. The CLSM was placed in trenches up to 2.7 m (9 ft) deep.
28、 Although fluid at time of placement, the CLSM hardened to the extent that a persons weight could be supported within 2 to 3 hr. Very few shrink- age cracks were observed. Further tests were conducted on patching the overlying pavement within 3 to 4 hr. In one test, a pavement patch was successfully
29、 placed over a sewer trench 229R-3CONTROLLED LOW-STRENGTH MATERIALS immediately after backfilling with CLSM. As a result of these initial tests, the city of Peoria has changed its backfilling pro- cedure to require the use of CLSM on all street openings.4 Some agencies backfill with a CLSM that has
30、a setting time of 20 to 35 min. (after which time a person can walk on it). After approximately 1 hr, the wearing surface con- sisting of either a rapid-setting concrete or asphalt pave- ment is placed, resulting in a total traffic-bearing repair in about 4 hr.6 2.3Structural fills Depending upon th
31、e strength requirements, CLSM can be used for foundation support. Compressive strengths can vary from 0.7 to 8.3 MPa (100 to 1200 psi) depending upon appli- cation. In the case of weak soils, it can distribute the structures load over a greater area. For uneven or nonuniform subgrades under foundati
32、on footings and slabs, CLSM can provide a uni- form and level surface. Compressive strengths will vary de- pending upon project requirements. Because of its strength, CLSM may reduce the required thickness or strength require- ments of the slab. Near Boone, Iowa, 2141 m3 (2800 yd3) of CLSM was used
33、to provide proper bearing capacity for the footing of a grain elevator.7 2.4Insulating and isolation fills LD-CLSM material is generally used for these applica- tions. Chapter 8 addresses LD-CLSM material using pre- formed foam. 2.5Pavement bases CLSM mixtures can be used for pavement bases, sub- ba
34、ses, and subgrades. The mixture would be placed directly from the mixer onto the subgrade between existing curbs. For base course design under flexible pavements, structural coefficients differ depending upon the strength of the CLSM. Based on structural coefficient values for cement-treated bases d
35、erived from data obtained in several states, the struc- tural coefficient of a CLSM layer can be estimated to range from 0.16 to 0.28 for compressive strengths from 2.8 to 8.3 MPa (400 to 1200 psi).8 Good drainage, including curb and gutter, storm sewers, and proper pavement grades, is required when
36、 using CLSM mixtures in pavement construction. Freezing and thawing damage could result in poor durability if the base material is frozen when saturated with water. A wearing surface is required over CLSM because it has rel- atively poor wear-resistance properties. Further information regarding pave
37、ment base materials is found in ACI 325.3R. Table 1Cited advantages of controlled low-strength materials4 Readily available Using locally available materials, ready-mixed concrete suppliers can produce CLSM to meet most project specifications. Easy to deliver Truck mixers can deliver specified quant
38、ities of CLSM to job site whenever material is needed. Easy to place Depending on type and location of void to be filled, CLSM can be placed by chute, con- veyor, pump, or bucket. Because CLSM is self-leveling, it needs little or no spreading or compacting. This speeds construction and reduces labor
39、 requirements. Versatile CLSM mixtures can be adjusted to meet specific fill requirements. Mixes can be adjusted to improve flowability. More cement or fly ash can be added to increase strength. Admix- tures can be added to adjust setting times and other performance characteristics. Adding foaming a
40、gents to CLSM produces lightweight, insulating fill. Strong and durable Load-carrying capacities of CLSM are typically higher than those of compacted soil or granular fill. CLSM is also less permeable, thus more resistant to erosion. For use as per- manent structural fill, CLSM can be designed to ac
41、hieve 28-day compressive strength as high as 8.3 MPa (1200 psi). Allows fast return to traffic Because many CLSMs can be placed quickly and support traffic loads within several hours, downtime for pavement repairs is minimal. Will not settle CLSM does not form voids during placement and will not set
42、tle or rut under loading. This advantage is especially significant if backfill is to be covered by pavement patch. Soil or granular fill, if not consolidated properly, may settle after a pavement patch is placed and forms cracks or dips in the road. Reduces excavation costs CLSM allows narrower tren
43、ches because it eliminates having to widen trenches to accom- modate compaction equipment. Improves worker safety Workers can place CLSM in a trench without entering the trench, reducing their exposure to possible cave-ins. Allows all-weather construction CLSM will typically displace any standing wa
44、ter left in a trench from rain or melting snow, reducing need for dewatering pumps. To place CLSM in cold weather, materials can be heated using same methods for heating ready-mixed concrete. Can be excavated CLSM having compressive strengths of 0.3 to 0.7 MPa (50 to 100 psi) is easily excavated wit
45、h conventional digging equipment, yet is strong enough for most backfilling needs. Requires less inspection During placement, soil backfill must be tested after each lift for sufficient compaction. CLSM self-compacts consistently and does not need this extensive field testing. Reduces equipment need
46、s Unlike soil or granular backfill, CLSM can be placed without loaders, rollers, or tampers. Requires no storage Because ready-mixed concrete trucks deliver CLSM to job site in quantities needed, stor- ing fill materials on site is unnecessary. Also, there is no leftover fill to haul away. Makes use
47、 of coal combustion product Fly ash is by-product produced by power plants that burn coal to generate electricity. CLSM containing fly ash benefits environment by making use of this industrial product material. 229R-4ACI COMMITTEE REPORT 2.6Conduit bedding CLSM provides an excellent bedding material
48、 for pipe, electrical, telephone, and other types of conduits. The flow- able characteristic of the material allows the CLSM to fill voids beneath the conduit and provide a uniform support. The U.S. Bureau of Reclamation (USBR) began using CLSM in 1964 as a bedding material for 380 to 2400 mm (15 to
49、 96 in.) diameter concrete pipe along the entire Canadian River Aqueduct Project, which stretches 518 km (322 miles) from Amarillo to Lubbock, Tex. Soil-cement slurry pipe bed- ding, as referred to by the USBR, was produced in central portable batching plants that were moved every 16 km (10 miles) along the route. Ready-mixed concrete trucks then de- livered the soil-cement slurry to the placement site. The soil was obtained from local blow sand deposits. It was estimated that the soil-cement slurry reduced bedding costs 40%. P
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