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Publication Number: FHWA-HRT-07-021
Date: April 2007

Durability of Segmental Retaining Wall Blocks: Final Report


Designation: C 1372 - 01 a

Standard Specification for Segmental Retaining Wall Units1

This standard is issued under the fixed designation C 1372; the number immediately following the designation indicates the year of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscript epsilon (e) indicates an editorial change since the last revision or reapproval.



1. Scope*


1.1 This specification covers segmental retaining wall units of concrete, machine-made from portland cement, water, and suitable mineral aggregates with or without the inclusion of other materials. The units are intended for use in the construction of mortarless segmental retaining walls.

NOTE 1-When particular features are desired, such as weight classification, higher compressive strength, surface texture, finish, color, or other special features, such properties should be specified separately by the purchaser. Local suppliers should be consulted as to availability of units having the desired features.


1.2 The text of this standard references notes and footnotes which provide explanatory material. These notes and footnotes (excluding those in tables and figures) shall not be considered as requirements of the standard.


1.3 The values stated in inch-pound units are to be regarded as the standard. The values given in parentheses are for information only.


2. Referenced Documents


2.1 ASTM Standards:

C 33 Specification for Concrete Aggregates2

C 140 Test Methods for Sampling and Testing Concrete Masonry Units and Related Units 3

C 150 Specification for Portland Cement4

C 331 Specification for Lightweight Aggregates for Concrete Masonry Units2

C 595 Specification for Blended Hydraulic Cements4

C 618 Specification for Coal Fly Ash and Raw or Calcined Natural Pozzolan for Use as a Mineral Admixture in Concrete2

C 989 Specification for Ground Granulated Blast-Furnace Slag for Use in Concrete and Mortars2

C 1157 Performance Specification for Hydraulic Cement4

C 1209 Terminology of Concrete Masonry Units and Related Units3

C 1232 Terminology of Masonry 3

C 1262 Test Method for Evaluating the Freeze-Thaw Durability of Manufactured Concrete Masonry Units and Related Concrete Units3

C XXXX Test Method for Evaluating the Freeze-Thaw Durability of Segmental Retaining Wall (SRW) Units3

C 2.1 — A new version of the ASTM C 1262 may be on the horizon exclusively for testing SRW units.

3. Terminology


3.1 Terminology defined in Terminology C 1209 and Terminology C 1232 shall apply for this specification.


4. Materials


4.1 Cementitious Materials—Materials shall conform to the following applicable specifications:


4.1.1 Portland Cements—Specification C 150.


4.1.2 Modified Portland Cement—Portland cement conforming to Specification C 150, modified as follows: Limestone—Limestone, with a minimum 85 percent Calcium Carbonate (CaC03) content, shall be permitted to be added to the cement, provided these requirements of Specification C 150 as modified are met:

(1) Limitation on Insoluble Residue—1.5 percent

(2) Limitation on Air Content of Mortar—Volume percent, 22 percent max.

(3) Limitation on Loss of Ignition—7 percent.


4.1.3 Blended Hydraulic Cements—Specification C 595.


4.1.4 Hydraulic Cement—Specification C 1157.


4.1.5 Pozzolans—Specification C 618.


4.1.6 Blast Furnace Slag Cement—Specification C 989.


4.2 Aggregates—Aggregates shall conform to the following specifications, except that grading requirements shall not necessarily apply:


4.2.1 Normal Weight Aggregates—Specification C 33.


4.2.2 Lightweight Aggregates—Specification C 331.


4.3 Other Constituents—Air-entraining agents, coloring pigments, integral water repellents, finely ground silica, and other constituents shall be previously established as suitable for use in segmental retaining wall units and shall conform to applicable ASTM standards or shall be shown by test or experience to be not detrimental to the durability of the segmental retaining wall units or any material customarily used in segmental retaining wall construction.


5. Physical Requirements


5.1 At the time of delivery to the work site, the units shall conform to the physical requirements of Table 1 when tested in accordance with 8.2.

TABLE 1 Strength and Absorption Requirements
Minimum Required Net Average Compressive Strength, psi (MPa) Maximum Water Absorption Requirements lb/ft3 (kg/m3)
Weight Classification Oven-Dry Density of Concrete lb/ft3 (kg/m3)
Average of 3 Units Individual Unit Lightweight: Less than 105 (1682) Medium Weight: 105 (1682) to less than 125 (2002) Normal Weight: 125 (2002) or more
3000 (20.7) 2500 (17.2) 18 (288) 15 (240) 13 (208)

5.2 Freeze-Thaw Durability—In areas where repeated freezing and thawing under saturated conditions occur, freeze thaw durability shall be demonstrated by test or by proven field performance that the segmental retaining wall units have adequate durability for the intended use. When testing is required by the specifier to demonstrate freeze-thaw durability, the units shall be tested in accordance with 8.3.

C 5.2 — All SRW units tested in the FHWA study (obtained from major block plants and from a local plant) complied with compressive strength, water absorption and oven-dry density as per Table 1 in this standard. A number of these units did not, however, meet the freeze-thaw durability requirements of 5.2.1. This confirms that compliance with Table 1 requirements does not imply adequate freeze-thaw requirements. This issue is also pointed out in ASTM C 1262 (Note 3).

5.2.1 Specimens shall comply with either of the following: (1) the weight loss of each of five test specimens at the conclusion of 100 cycles shall not exceed 1 percent of its initial weight; or (2) the weight loss of each of four of the five test specimens at the conclusion of 150 cycles shall not exceed 1.5 percent of its initial weight. In either case, RDM shall not be less than 60 percent.

C 5.2.1a — While this specification standard concerns freeze-thaw durability in water, there is substantial evidence that saline conditions exacerbate freeze-thaw damage. In the NCMA study, it was also demonstrated that at 1 percent mass loss many specimens had already suffered loss internal damage as indicated by resonant frequency and pulse velocity measurements. Further field studies are required to determine appropriate specification values for mass loss and resonant frequency.

C 5.2.1b —RDM is more sensitive to specimen internal damage compared to mass loss (ref. NCMA study). The reference value of 60 percent employed here reflects values typically used for testing of ordinary concrete, as found in ASTM C 666 and C 260.

6. Permissible Variations in Dimensions


6.1 Overall dimensions for width, height, and length shall differ by not more than ± t/8 in. (3.2 mm) from the specified standard dimensions.

NOTE 2-The term "width" refers to the horizontal dimension of the unit measured perpendicular to the face of the wall from the exposed surface of the unit to the back of the unit. The term "height" refers to the vertical dimension of the unit as placed in the wall. The term "length" refers to the horizontal dimension of the unit measured parallel to the running length of the wall.


6.1.1 Dimensional tolerance requirements for width shall be waived for architectural surfaces.

NOTE 3-Split-faced surfaces are the most common surfaces used to provide an architectural appearance to segmental retaining walls. However, other means could be used to obtain similar architectural effects like tumbling, grinding, and slumping.


7. Finish and Appearance


7.1 All units shall be sound and free of cracks or other defects that interfere with the proper placement of the unit or significantly impair the strength or permanence of the construction. Minor cracks incidental to the usual method of manufacture or minor chipping resulting from customary methods of handling in shipment and delivery, are not grounds for rejection.


7.2 Where units are to be used in exposed wall construction, the face or faces that are to be exposed shall not show chips or cracks, not otherwise permitted, or other imperfections when viewed from a distance of not less than 20 ft (6.1 m) under diffused lighting.


7.2.1 Five percent of a shipment containing chips not larger than 1 in. (25.4 mm) in any dimension, or cracks not wider than 0.02 in. (0.5 mm) and not longer than 25 percent of the nominal height of the unit is permitted.


7.3 The color and texture of units shall be specified by the purchaser. The finished surface that will be exposed in place shall conform to an approved sample consisting of not less than four units, representing the range of texture and color permitted.


8. Sampling and Testing


8.1 The purchaser or authorized representative shall be accorded proper facilities to inspect and sample units at the place of manufacture from the lots ready for delivery.


8.2 Sample and test units for compressive strength, absorption, and dimensional tolerances in accordance with Test Methods C 140.


8.3 When required, sample and test five specimens for freeze-thaw durability in water in accordance with Test Method C 1262. Freeze-thaw durability shall be based on tests of units made with the same materials, concrete mix design, manufacturing process, and curing method, conducted not more than 24 months prior to delivery.


9. Compliance


9.1 If a sample fails to conform to the specified requirements, the manufacturer shall be permitted to remove units from the shipment. A new sample shall be selected by the purchaser from remaining units from the shipment with a similar 'configuration and dimension and tested at the expense of the manufacturer. If the second sample meets the specified requirements, the remaining portion of the shipment represented by the sample meets the specified requirements. If the second sample fails to meet the specified requirements, the remaining portion of the shipment represented by the sample fails to meet the specified requirements.

NOTE 4-Unless otherwise specified in the purchase order, the cost of tests is typically borne as follows: (1) if the results of the tests show that the units do not conform to the requirements of this specification, the cost is typically borne by the seller; (2) if the results of the tests show that the units conform to the specification requirements, the cost is typically home by the purchaser.


10. Keywords


10.1 absorption; aggregates; cementitious materials; compressive strength; concrete masonry units; dimensions; durability; weight classification

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