Masonry Magazine August 2000 Page. 10
FIELD TESTING
By Robert L. Nelson, Robert L. Nelson & Associates, Inc.
The American Society for Testing and Materials (ASTM) has developed two distinct standards for testing masonry mortars. ASTM C 270 is a mortar specification which outlines procedures for testing mortar prepared in the laboratory. The purpose of the testing is to determine whether a mortar mixed with construction materials to specified proportions conforms with physical property requirements listed within the standard.
ASTM C 780 is a field test method which defines standard procedures for sampling and testing mortars before and during their use in construction. Mortars can be tested to determine composition or to obtain their plastic and harden properties. Test methods and procedures within this standard can be used to evaluate masonry mortars prepared in the laboratory prior to construction or to evaluate masonry mortars mixed at the job site. Field testing and sampling of mortar is used to verify consistency of materials and procedures, not mortar strength. Test results of masonry mortar obtained through field testing conducted in accordance with ASTM C 780 are not required to meet the minimum compressive strength values listed in the property specification of ASTM C 270.
Compressive strength values obtained from field testing of mortar can be expected to be lower and less consistent than values obtained in the laboratory. Laboratory prepared mortars are mixed with a quantity of water to produce a flow of 110 ± 5 percent. This quantity of water is not sufficient to produce mortar with a workable consistency suitable for laying masonry units in the field. Mortar for use in the field must be mixed with the maximum amount of water, consistent with workability, in order to provide sufficient water to satisfy the suction of the masonry units. The properties of laboratory prepared mortar with a required flow rate of 1105 percent are intended to approximate the flow and properties of field prepared mortar after it has been placed in contact with masonry units.
WHEN TO REQUIRE FIELD TESTING
Field testing of mortars is not a mandatory MSJC Code requirement, but is an option left to the discretion of the specifier. Specifying ASTM C 780 field testing to determine whether the physical properties of a mortar are in compliance with those listed in ASTM C 270 is not appropriate. Also, it would not be appropriate to require field testing to verify structural performance of mortar or of a masonry assemblage.
Field testing of mortar according to ASTM C-780 can be used to establish a quality control program for mortar produced during construction at the job site. The program should consist of both preconstruction and construction site evaluation. Preconstruction testing should be conducted to establish baseline values that can be expected during construction for the approved mortar mix design.
Preconstruction testing and evaluation of mortar allotys for comparisons of mortar produced in the laboratory to those mixed at the job site. Preconstruction evaluation establishes compatibility of individual constituents in the mortar and general physical characteristics of the mixture.
Construction site testing procedures establish a mortar's conformance to proportion specifications and monitors the consistency of mortar production. On-site testing makes evaluation of masonry mortars possible by sampling.
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10 MASONRY JULY/AUGUST, 2000
Photo (above): Ed Bochat, Project Foreman for Thorleif L