Q: We recently supplied several split-face blocks for a large commercial project. The work continued for several months, and with about two weeks left, we started receiving complaints about the quality of the units from the mason contractor.
After several meetings, the quality issue narrowed to the architect's concern that he found some chips, dimension irregularities, and surface blemishes in the block that has been placed on the completed wall. The architect has delayed payment to the mason contractor until this issue is resolved.
What are the guidelines regarding the architect's quality concerns?
A: Most block manufacturers submit documentation to their customers, assuring that the material they provide will, at the very least, conform to the ASTMspecifications that outline the basic quality requirements. As a result, most architects specify that blocks must conform to ASTM C-90, the Standard Specification for Loadbearing Concrete Masonry Units. In section 8.2 of C-90, the specification calls for the block producer to conform to the testing procedures as outlined in ASTM C-140, Standard Test Methods for Sampling and Testing Concrete Masonry Units and Related Units.
C-140 outlines the testing procedures that occur at the plant during production. Section 5 states the producer must select units from the production lot that are representative in configuration and dimension of the final product.
Unless specified otherwise, six units shall be selected from each lot of 10,000 units, 12 units from each lot of more than 10,000 units and less than 100,000 units, and for lots of more than 100,000 units, six units shall be selected from each 50,000 units or fraction thereof.
Dimensional measurement is one of the four required quality tests on these sample units. The testing procedure and reporting requirements of the results for loadbearing block are outlined in Annex A of C-140. C-140 advises how to perform the dimensional requirements for loadbearing units detailed in C-90. So you should refer the architect to Section 6 of C-90, where the document outlines permissible variations in dimensions, and Table 1, which lists the minimum thickness of face, shells, and webs.
C-90 provides more guidance on your quality question. In article 7, the standard states that all units shall be sound and free of cracks or defects that interfere with the proper unit placement or significantly impair the strength or permanence of the construction. Your note indicates that the architect does not have concerns with this.
The specification states, "minor cracks, incidental to the usual method of manufacture or minor chipping resulting from customary methods of handling and delivery, are not grounds for rejection."
Masonry professionals realize that there are several causes of cracks and surface defects in block construction. C-90 outlines acceptable guidelines. An order lot is acceptable if less than 5% of a shipment has any chips no larger than 1-inch in any direction, or cracks wider than 0.02 inches and no longer than 25% of the unit's nominal height. These guidelines are the minimal requirements. Most block producers provide units at much higher quality.
The architect's concern about measurable quality of the finished wall is an important aspect of masonry construction. Most projects use mock-ups of finished walls as guidelines for visual acceptance. While this technique provides some guidance, finished quality continues to be discussed. The recently reformed Task Group on Finish and Appearance, ASTM C15.03.07, is trying to develop a standard that would outline a performance standard to address these quality issues.
We invite questions from readers on any aspect of concrete mix design, production, testing, or troubleshooting. To submit your questions, send an e-mail to email@example.com.
ASTM WK17659, New Precast Concrete Products Used for Stormwater Management, was developed by ASTM Subcommittee C27.70 last December. Its scope is to delineateand define terminology used in designing, describing, measuring, and validating precast concrete products that are used for stormwater management applications.
As a new subcommittee, C27.70 will develop standards for stormwater management products. A document defining the terminology used in these standards is needed to help establish common communication. The technical contact for this new subcommittee is Theodore Coons.
New Approved Standard
An important ASTM standard affecting concrete producers has been updated: C1227. Standard Specification for Precast Concrete Septic Tanks, has been revised to C1227-07c.
To view the document summary page on this and other standards, visit ASTM's Web site at www.astm.org. You can quickly access the information by entering the standard designation number in the search engine. Or contact ASTM's customer service by telephoning 610-832-9585, or by e-mailing . Related Article