Masonry Magazine January 1976 Page.22
FIG.8
E 518 Specimen-Cross Section
Face Shell Bedded Hollow Unit
Note: The crosshatched area represents the mortar bedded area of the specimen.
Materials
General. In addition to other quality control testing, it is desirable to periodically check the materials for compliance with job specifications. In some cases materials testing may be the only quality assurance testing done.
Brick. Brick should be tested in accordance with ASTM C 67 as outlined in Technical Notes 39. In addition to compressive strength of the units, it would be desirable to also run absorption and initial rate of absorption investigations.
Mortar. Jobsite mortar quality can be assessed periodically by the test methods of C 91 and C 109 as described in Technical Notes 39.
In addition to the above methods of test, a recently adopted ASTM standard, C 780, provides more test methods for mortar. ASTM C 780 contains five methods of test for mortar in the plastic state and two for mortar in the hardened state.
These test methods are listed in the ASTM C 780 Annexes and provide test procedures for the following:
A1. Consistency by Cone Penetration Test Method
A2. Consistency Retention of Mortars for Unit Masonry
A3. Mortar Aggregate Ratio Test Method
A4. Mortar Water Content Test Method
A5. Mortar Air Content Test Method
A6. Compressive Strength of Molded Masonry Mortar Cylinders
A7. Splitting Tensile Strength of Molded Masonry Mortar Cylinders
Until such time as performance levels and/or requirements for C 780 test methods are established, BIA does not recommend that these methods be used as the only tests on mortar. These test methods should be used only in addition to C 91 and/or C 109 tests.
EVALUATION OF TEST RESULTS
General
In most cases the level of strengths will have been established during testing for determination of design stresses or by the selection of design stresses used. Evaluation then becomes a simple matter of comparing the results of the quality control tests with the desired strength levels.
Unsatisfactory Test Results
Examination of Procedures. There are several things that can be done if the test results fall below the required level. If backup specimens have been prepared, these can be tested. Quite often the contractor will prepare extra prisms for just this situation. If backup specimens are not available for testing, then close examination should be made of the method of building the prism, the handling of the specimens during transportation and storage, and of the laboratory facilities and test procedures. The actual stresses in the masonry at the location of the questionable masonry should be checked to determine if the lower strength will provide structural stability. After the above observations and calculations are made, then some judgments should be made.
Answers to the following questions should be forthcoming from these judgments:
1. Did mortar proportions or properties change?
2. Were there unusual curing conditions?
3. Was specimen damaged during transit or storage?
4. Was the specimen properly constructed?
5. Were test procedures used properly?
From these and other questions, the possible cause of low test results may be determined.
Test Procedure. If no immediate solution is evident and the reduced strengths of the test results reduce the safety factor below an acceptable level, prisms may be cut from the wall and tested. These prisms should be cut from the affected area and should be of the same size as described earlier in each test method.
After the specimen is cut from the wall, it should be transported to the lab for testing. If the specimen was cut from the wall by a water cooled saw, it should be allowed to dry prior to testing.
Exercise of Judgment. If the test results are still low, then a judgment must be made. If the field cut prism test results give strengths which lower the factor of safety below a tolerable level, then removal of the masonry in the questionable area must be considered. Obviously, this is the last resort after all other possibilities have been closely examined.
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