10.047 Prism Testing per 2007 CBC

Q My question is in 2007 CBC Chapter 21 Section 2105A. states as always a set of 5 prisms shall be built prior to construction to meet the Fm’ before CMU block is placed. But it does not specify age days of testing, nor does the ASTM referenced is the same section, which is ASTM C1314. Should we test all 5 prisms at 28 days? Sometimes a specific job specification may state prism age days to be tested testing but if not stated what is the correct age days of testing field fabricated prisms?

— Steve Marcki, Construction Inspection Manager at Youngdahl Consulting Group, Inc.

A 1/09 – Response prepared by Kurtis K. Siggard, Executive Director of the Concrete Masonry Association of California & Nevada (CMACN).

For pre-construction prisms we refer to Section 2105A. of the 2007 California Building Code which states that “Prior to start of construction, a prism test shall consist of five prisms constructed and tested in accordance with ASTM C 1314.”

We find the age that prisms should be tested in ASTM C1314 Section 7.1, which states “Test prisms at an age of 28 days or at the designated test ages. Test a set of prisms at each age.”

A set of prisms is defined in ASTM C1314 Section 3.1.1 as “a set consists of at least three prisms constructed of the same material and tested at the same age.”

If the project specification indicates a different number of prisms to be tested than indicated in the building code or ASTM, a different age for testing the prisms other than that found in the ASTM, or anything less than three prisms per set, a request for clarification should be forwarded to the design professional.

It is critical that the prisms be transported and handled with care in accordance with ASTM C1314 Section 6.1.

ASTM C1552 should be followed closely to properly cap each prism. Care should be taken to avoid voids between the capping material and prism. Only caps using gypsum cement or sulfur materials are authorized for capping prisms.

Reference Documents

ASTM C1314-07 Standard Test Method for Compressive Strength of Masonry Prisms

ASTM C1552-07 Standard Practice for Capping Concrete Masonry Units, Related Units and Masonry Prisms for Compression Testing