Controlled Low-Strength Materials (CLSM)

Controlled Low Strength Materials SpecificationSpecification For:
Controlled Low-Strength Materials (CLSM)Scope:

This Work consists of furnishing and placing controlled low strength materials (CLSM) in accordance with the Contract Documents, Jackson County permit requirements, or as directed by the Engineer. All products shall be pre-approved by the County Engineer in accordance to this specification.


CLSM - A highly flowable lean concrete mix consisting of a mixture of cement, fly ash, densely graded mineral aggregates, water, and admixtures. CLSM shall be capable of freely flowing to fill all voids in trenches or other areas without compaction or other additional effort, shall be of uniform density, shall be of low permeability to prevent migration of adjacent fines into the set mix, and shall excavate easily at any later time with minimal risk of damage to buried services.

Fine Aggregate CLSM - A CLSM containing a maximum size aggregate of 3/8-inch.


All material specifications shall conform to the latest version of the Oregon Standard Specifications for Construction that Jackson County Roads has issued Supplemental Standard Specifications for. Furnish Materials meeting the following requirements from the Oregon Standard Specifications for Construction and/or modified in the Jackson County Supplemental Standards or Special Provisions:

  • Admixtures               02040
  • Fly Ash                        02030.10
  • Portland Cement   02010.10
  • Water                           02020
Aggregates shall be a densely graded virgin rock or appropriate recycled material which produces a mix meeting all requirements within this Specification. A minimum of 50 percent of the total aggregate weight shall pass a #8 sieve and no more that 5 percent of the total aggregate by weight may pass a #200 sieve. The maximum size aggregate for fine aggregate CLSM shall pass a 3/8-inch sieve.

Performance Specification:

CLSM shall meet the following requirements:

  • Flowability - The mix shall have a slump of between 6 and 8 inches as per AASHTO Designation T 119-82 or ASTM Designation C 143
  • Compressive strength - The mix shall have a 28-day compressive strength of between 50 and 150 psi, per AASHTO Designation T 22-90 or ASTM Designation C 39
Mix Design and Testing:

Vendors who purpose to supply CLSM for work within Jackson County right-of-way shall submit a mix design and test results to Jackson County Roads for approval. Jackson County will maintain an approved products list on the Jackson County Roads website. The mix submittal shall include the following information:

  • Company Name and Address
  • Company Contact Information
  • Identifying name and/or number for the mix design
  • Mix Design (including aggregate type and gradation)
  • Certified test results for flowability, and compressive strength
Submittals which do not contain all required information shall not be considered.

Products that are rejected in the field may be removed from the approved list at the discretion of the County Engineer.

Mixing and Placement:

CLSM shall be mixed accordance with subsection Sections 00756.20 or 00756.21; delivered in a truck mixer conforming to 00756.22; and conveyed in accordance with 00540.22.

Contractor shall provide and maintain steel jump plates with locks as required for traffic and safety. In paved areas open to the public, the top of the trench shall be patched with Asphalt Concrete Pavement not sooner than the CLSM is adequately set (generally 48 hours), nor longer than 10 calendar days following placement of the CLSM.

When CLSM is delivered to the job site, delivery tags shall be collected from the delivery driver and provided to the Jackson County Inspector or Engineer. The delivery tag shall contain the supplier name and the mix identifying name and/or number as identified in the supplier’s submitted mix design.

The Jackson County Inspector or Engineer may reject any mix that does not appear to meet the requirements of this Specification (for example: segregation, insufficient slump, or open graded aggregates). The Jackson County Inspector or Engineer may require removal of any mix that has been placed but doesn’t perform as specified.

Only fine aggregate CLSM will be allowed in pipe zones or trenches of less than 1-foot width.

In the event of extremely cold or wet conditions, and with the approval of the Jackson County Inspector or Engineer prior to use, an approved fine aggregate CLSM may have up to 94 additional pounds of cement per cubic yard added to the design mix to facilitate setting.

CLSM Approved Products ListStandard CLSM

Southern Oregon Ready Mix
Vance McGonagle
Approved Product: CLSM 

LTM, Inc., dba Knife River Materials
Mike Milhoan
Approved Product: 16LJACOSTD

Crater Sand and Gravel
Allen Savage
Approved Product: 1" Standard CLSM

Fine Aggregate CLSM

Crater Sand and Gravel/Savage Redi-Mix
Approved Product: Sand Slurry

LTM, Inc, dba Knife River Materials
Mike Milhoan
Approved Product: 16LJACOFINE & 16LCLSM2

Johnny Cat Inc.
Mark Biencourt
Approved Product: 1-Sack CLSM
Approved Product: 2-Sack CLSM