Masonry Magazine February 1994 Page. 41
Portland Cement Association
pca
TROWEL TIPS
# an aid to the masonry industry
Field Testing Masonry Mortar
With the exception of masonry constructed in seismic zones, field testing of masonry has generally been limited to an occasional evaluation of masonry mortar. More frequently than not, even this testing is done improperly and interpreted incorrectly, resulting in needless controversy and waste. As ACI 530-88/ASCE 6-88 (Building code Requirements for Masonry Structures) and ACI 530.1-88/ ASCE 6-88 (Specifications for Masonry Structures) requirements for quality assurance are implemented into construction documents, field testing of masonry components and assemblies will become more commonplace. Specifiers, contractors, and project inspectors need to be familiar with the testing procedures and understand the meaning of laboratory and field results.
Field testing of mortar is included in project specifications as a quality control measure. Properly conducted, it must involve preparation prior to construction. The contractor selects the ingredients and the mix design in accordance with the project specifications. A preconstruction evaluation of mortar is conducted to develop data that serves as a benchmark for future evaluation of mortar produced during construction. The testing is to be conducted in accordance with the Standard Test Method for Preconstruction and Construction Evaluation of Mortars for Plain and Reinforced Unit Masonry (ASTM C780) and should be performed by an accredited laboratory conforming to the Standard Practice for the Accreditation of Testing Agencies for Unit Masonry (ASTM C1093). As stated in Section 2.1.3 of the Commentary on Specifications for Masonry Structures (ACI 530.1-88/ASCE 6-88) "ASTM C270 specifies mortar testing under laboratory conditions only for acceptance of mortar mixes under the property specification. Field sampling and testing of mortar is conducted under ASTM C780 and is used to verify consistency of materials and procedures, not mortar strength."
Unfortunately, the preconstruction evaluation is often omitted and many times laboratory field technicians do not use ASTM C780 testing procedures properly. These deficiencies, compounded by misunderstanding of the significance of mortar test results by project inspectors and engineers, often produce needless and costly construction delays. Sometimes unwarranted "corrective measures" are taken that further escalate costs. These problems can be avoided if all involved understand the following basic concepts with respect to the performance of masonry:
Compressive strength of mortar is only one of several important mortar properties.
* Compressive strength is only one of several important mortar properties. Workability and water retentivity often have a greater impact on the quality of the masonry constructed. Other properties such as shrinkage characteristics and resistance to freeze-thaw deterioration can also affect the long term performance of the masonry.
* Field test results of compressive strength of mortar do not represent laboratory mortar strengths and are not required or expected to meet ASTM C270 property specification limits.
* Performance requirements for masonry mortar cannot be equated to those for concrete.
* Field test results of compressive strength of mortar are not representative either of in-place compressive strength of the mortar or iri-place compressive strength of the masonry.
* Field test results of compressive strength of mortar are dependent on several variables. These include test procedures and test conditions in addition to proportions and properties of mortar materials.