J H GREENWALD(1) and J FARNY(2)
(1) P.E., National Concrete Masonry Association;
(2) Portland Cement Association
Quality control and quality assurance for field mortar is often misunderstood and, therefore, the provisions of ASTM C 780, Standard Test Method for Preconstruction and Construction Evaluation of Mortars for Plain and Reinforced Unit Masonry are often misapplied. The mortar-aggregate (M-A) ratio test of Annex A4 determines the ratio of cementitious materials to aggregate and this ratio can be used to verify the mortar proportions determined to prequalify the mortar under a laboratory evaluation, such as ASTM C 270. The M-A test determines the amounts of cement and aggregate by introducing alcohol into a mortar sample to stop the hydration process. The report presents the results of testing to investigate the sensitivity of mortar testing time and mortar sampling time on the testing procedure. These parameters were varied over a reasonable range and the resulting M-A ratio calculated. During masonry construction, an inspector may not know the actual time the mortar was mixed and therefore the age of the mortar sample may be unknown. Further, the actual test may not be conducted immediately after sampling. Both of these variables may affect the M-A results and before recommendations can be brought forward to ASTM, they needed to be investigated.