1、Standard Practice for Coal Combustion Fly Ash for Embankments AASHTO Designation: PP 59-09 (2013)1 American Association of State Highway and Transportation Officials 444 North Capitol Street N.W., Suite 249 Washington, D.C. 20001 TS-1a PP 59-1 AASHTO Standard Practice for Coal Combustion Fly Ash for
2、 Embankments AASHTO Designation: PP 59-09 (2013)11. SCOPE 1.1. This practice covers the use of coal combustion fly ash (typically but not limited to non-self-hardening ash) as a fill material for the construction of embankments. 1.2. When properly processed, hauled, spread, and compacted on a prepar
3、ed grade to appropriate density standards, coal combustion fly ash used alone, or blended with traditional soil aggregate or other approved aggregate materials, can be expected to provide a lighter-than-normal weight fill material (85 to 100 pcf, 1360 to 1600 kg/m3) with adequate stability and load
4、support for use as road or highway embankment. 1.3. The technique described in this practice uses containment berms, cover fill material, and sometimes a liner and leachate system to isolate the fly ash and any resulting effluent. This is a conservative approach to the environmental issues raised by
5、 the use of fly ash as fill, and may not be required for all fly ashes or for all regulatory requirements. 1.4. This practice recognizes that since fly ash is a by-product of the burning of coal in electricity- and steam-generating facilities, various state, county, and local environmental laws and
6、regulations apply if fly ash is used as an alternative embankment material. Aspects of fly ash that are of environmental concern are identified. Therefore, this standard discusses elements such as impermeable layers and leachate collection, as they may be required according to the environmental regu
7、lations affecting the proposed installation. 1.5. More specific guidance for the detailed use of fly ash as embankment material may be found in ASTM E 2277. 1.6. The values stated in SI units are to be regarded as the standard. 2. REFERENCED DOCUMENTS 2.1. AASHTO Standards: M 146, Terms Relating to
8、Subgrade, Soil-Aggregate, and Fill Materials M 295, Coal Fly Ash and Raw or Calcined Natural Pozzolan for Use in Concrete T 2, Sampling of Aggregates T 27, Sieve Analysis of Fine and Coarse Aggregates T 99, Moisture-Density Relations of Soils Using a 2.5-kg (5.5-lb) Rammer and a 305-mm (12-in.) Drop
9、 T 180, Moisture-Density Relations of Soils Using a 4.54-kg (10-lb) Rammer and a 457-mm (18-in.) Drop T 272, Family of CurvesOne-Point Method 2014 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-1a PP 59-2
10、 AASHTO T 310, In-Place Density and Moisture Content of Soil and Soil-Aggregate by Nuclear Methods (Shallow Depth) 2.2. ASTM Standards: C 295/C 295M, Standard Guide for Petrographic Examination of Aggregates for Concrete C 311/C 311M, Standard Test Methods for Sampling and Testing Fly Ash or Natural
11、 Pozzolans for Use in Portland-Cement Concrete D 5918, Standard Test Methods for Frost Heave and Thaw Weakening Susceptibility of Soils E 2201, Standard Terminology for Coal Combustion Products E 2277, Standard Guide for Design and Construction of Coal Ash Structural Fills (Withdrawn 2012) 2.3. U.S.
12、 EPA Test Method: SW-846, Test Methods for Evaluating Solid Waste, Physical/Chemical Methods, 3rd Edition 3. GENERAL DESCRIPTION 3.1. Fly ash is the finely divided residue that results from the combustion of coal. Fly ash is the airborne residue that exits a coal combustion chamber with the flue gas
13、 and is removed from the flue gas by electrostatic precipitation, baghouses, or other particulate control devices prior to the introduction of scrubber reagents. It contains siliceous and aluminous materials. 3.2. For purposes of this practice, fly ash is divided into two types. One is self-hardenin
14、g and the other is non-self-hardening. Both types contain siliceous or siliceous and aluminous materials, which in the presence of lime or portland cement and water react to form a cementitious material. 3.2.1. Self-Hardening Fly Ash (Class C)For the purpose of this practice shall mean fly ash that
15、will form cementitious material in the presence of water alone. 3.2.2. Non-Self-Hardening Fly Ash (Class F)For the purpose of this practice shall mean fly ash that requires the presence of lime or portland cement and water to form a cementitious material. It is likely that fly ash used in accordance
16、 with this practice will commonly be the non-self-hardening type, as it is less desirable for other uses. 3.3. Additional definitions relative to fly ash and other coal combustion by-products are provided in ASTM E 2201. 3.4. The very fine-grained nature of fly ash, similar to that of natural silt-s
17、ized materials, makes it susceptible to vertical capillary water migration. Capillary water migration in embankments could lead to embankment saturation and instability under loading or frost heaving due to the development of ice lenses. As such, this practice recommends that a layer of open-graded
18、granular material be constructed at the base of the fly ash embankment, and a layer of cover material be constructed on top of the embankment to prevent frost penetration into the fly ash in frost-prone locations. 3.5. Aqueous solutions that percolate through fly ash or fly ash containing admixtures
19、 could exhibit pH values that fall outside the range of 5 to 9. The engineer is cautioned that aqueous solutions with pH values that fall outside this range could result in corrosive conditions detrimental to concrete or metal conduit structures. 3.6. For cases where applicable laws and regulations
20、raise concern regarding the quality of the leachate from the fly ash embankment, this practice includes a liner and leachate collection system. 2014 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-1a PP 59
21、-3 AASHTO 3.7. The definitions of fill material and other soil aggregate terms are provided in M 146. 4. FLY ASH ORDERING INFORMATION 4.1. The purchaser or specifier of coal fly ash shall include the following information in the purchase order or contract documents: 4.1.1. Reference to this standard
22、, including year; 4.1.2. Reference to the requirements of state, local, or both, environmental protection agencies; 4.1.3. Requirements for grading, blending, or both; 4.1.4. Type or types of fly ash specified (self-hardening fly ash is commonly referred to as Class C ash and non-self-hardening fly
23、ash is referred to as Class F); and 4.1.5. Exceptions or additions to this standard. 5. PHYSICAL AND CHEMICAL PARAMETERS 5.1. Fly Ash: 5.1.1. Fly ash shall meet the requirements set forth in the contract documents in regard to gradation, blending, and type of fly ash. 5.1.2. If not otherwise stated
24、in the contract documents, fly ash supplied as an embankment material shall have 100 percent of the material pass the 12.7-mm (1/2-in.) sieve. 5.1.3. The loss on ignition (LOI) of the fly ash should not exceed 20.0 percent when tested in accordance with ASTM C 311/C 311M. This guide limit on LOI has
25、 been established to allow fly ashes to be used for fill that have LOIs that are typically too high for use in concrete, without allowing such a high LOI that environmental impacts and buried energy issues become too large. 5.1.4. Fly ash may be combined with other approved embankment materials or a
26、dmixtures as approved by the engineer. Mixing shall be accomplished by the use of mechanical interlock systems (pug mills), conveyor belt blending, or by other methods approved by the engineer. The supplier shall maintain actual production blending of fly ash and other approved embankment material w
27、ithin a tolerance of 5 percent of the approved proportion. 5.1.5. Blends of fly ash and other approved embankment materials must be free of deleterious substances. Fly ash or blended products should be free of pyrites and other metal sulfides as determined by ASTM C 295/C 295M. In particular, the pr
28、esence of pyrites or other metal sulfides should be investigated when coal combustion bottom ash is added to a blended mix due to their potentially expansive nature. Other potentially expansive compounds, such as sulfur trioxide, could be present in certain coal combustion by-product sources. It is
29、recommended that the engineer investigate the source material and blended product to ensure that excessive expansion will not be a problem. 5.1.6. If chemical stabilization of the fly ash is specified, the contractor should submit a mix design to the engineer for approval. The materials should be mi
30、xed in a mechanical interlock system (pug mill) or other approved method. The use of certain stabilizing agents may elevate pH values of aqueous solutions that may contact the stabilized fly ash. The engineer is reminded that aqueous solutions that percolate through fly ash or admixtures containing
31、fly ash could exhibit pH values 2014 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-1a PP 59-4 AASHTO greater than 9 or less than 5, which could result in corrosive conditions detrimental to concrete or m
32、etal conduit structures. 5.2. Containment Berms: 5.2.1. Material used to construct the containment berms for the fly ash embankment shall meet the requirements of the specifying agency. Containment berm material should provide adequate strength to retain the fly ash fill during compaction. 5.3. Cove
33、r for Fly Ash Embankment: 5.3.1. Material used to construct the cover for the fly ash embankment shall meet the material requirements of the specifying agency. The cover material should be dense-graded so as to minimize infiltration of surface water and be placed at a thickness such that it will pre
34、vent freezing temperatures from reaching the fly ash fill. Fly ash materials, being very fine-grained, are naturally frost-susceptible and will likely heave if frozen. In some cases, it may even be desirable to specify a geomembrane over the top of the fill. 5.4. Liner and Leachate Collection System
35、: 5.4.1. Where specified, material used to construct a liner beneath the fly ash embankment shall meet the material requirements of the specifying agency. In areas where a liner is not specified, consideration should be given to the installation of a capillary break such as recommended in Section 3.
36、4 to prevent the rise of groundwater into the embankment. 5.4.2. Where specified, material for the components of a leachate collection system constructed beneath the fly ash embankment shall meet the material requirements of the specifying agency. 6. FIELD APPLICATIONS 6.1. Site Preparation: 6.1.1.
37、Clear and grub the existing site in accordance with the applicable specification. All unsuitable material shall be removed. Compact the ground surface as per the agencys specifications. 6.1.2. Place and compact a layer of open-graded granular material where necessary to meet lines and grades shown i
38、n the contract plans. 6.2. Liner and Leachate Collection System: 6.2.1. Where specified, construct the liner and leachate system in accordance with, and to the lines and grades shown in, the contract plans. 6.3. Containment Berms: 6.3.1. Before construction of fly ash embankments begins, construct c
39、ontainment berms having a trapezoidal cross section and side slopes of 2:1 or less and a width of at least 1.8 m (6 ft) at the top of each containment berm segment. The first containment berm segments should be located on the outside limits of the embankment footprint. As the embankment is construct
40、ed upward, containment berms should be placed on the outside of each new tier before placing fly ash. Note 1For narrow embankments, such as ramps, the engineer may consider narrower containment berms because smaller equipment will be required. 2014 by the American Association of State Highway and Tr
41、ansportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-1a PP 59-5 AASHTO 6.3.2. The material used to construct containment berms should be placed in loose lifts having a maximum thickness of 200 mm (8 in.). Each lift should be compacted as required by the specify
42、ing agency. 6.4. Fly Ash Placement: 6.4.1. The delivery, placement, spreading, and compaction of fly ash should be planned so the work can proceed from one step to the next without delay. 6.4.2. Non-self-hardening fly ash should be conditioned for dust control and to reduce the potential for erosion
43、 by the addition of 10 to 15 percent water by weight at the source site prior to delivery, and subsequent storage (stockpiling) of the fly ash for a period of 24 h or more until the water is evenly dispersed. If the supplier can demonstrate that water is evenly distributed throughout the fly ash, th
44、en stockpiling may not be required or the duration may be reduced. Self-hardening fly ash must be kept dry until placement to avoid hardening before compaction. 6.4.3. Delivery of fly ash must be in closed or covered trucks. 6.4.4. Large-scale storage of fly ash shall not be permitted at the project
45、 construction site. Small amounts of fly ash, such as a days supply for the project, may be stored for short periods of time to facilitate construction when stockpiling is done in accordance with the project sediment and erosion control plan. 6.4.5. Fly ash, delivered to the project site, should be
46、unloaded directly inside the contained embankment area where it will be used. 6.4.6. Fly ash material should be spread into loose lifts approximately 200 mm (8 in.) thick. The engineer may consider thicker lift dimensions if it can be satisfactorily demonstrated with a test section that adequate com
47、paction can be achieved over the full depth of the thicker lift. 6.4.7. If necessary for proper compaction, water should be added to the fly ash by the use of water distribution tank trucks. The water and fly ash should be mixed using a rototilling mixer or other approved method. At the time of comp
48、action, the fly ash should have a moisture content that will result in an after-compaction dry density that complies with the requirements of the project specifications. 6.4.8. The fly ash embankment should be compacted as required by the specifying agency. This will normally be to minimum density c
49、riteria. This material should be compacted much like a natural silt material. Note 2The first pass in the compaction process may be accomplished by the method known as tracking. This involves the use of a bulldozer track to accomplish initial compaction. The bulldozer is moved progressively across the fly ash embankment until the entire area is tracked. The fly ash embankment should then be compacted using pneumatic tired, vibratory, or other types of compaction equipment. Best results are often obtained when the equipment works from the edge of the
