A Procedure for Testing Concrete Masonry Unit (CMU) Mixes

Abstract

Abstract A laboratory method for the evaluation of concrete masonry unit (CMU) mix designs is proposed. The zero slump requirement and the unique method of molding CMU using simultaneous vibration and compression on an automated assembly line basis make CMU mix design a unique subset of concrete mix design. The compression and vibration of a block machine is simulated by the use of a drop hammer to compact the test specimens. The different compaction methods are equated by modifying the height of the hammer drop or the number of drops to obtain the same density as that obtained from the production block machine. The volumetric fill method of a production machine is replaced with weighing the mix placed in each mold prior to compaction to provide a uniform amount of material. Numerous batches can be made quickly in a laboratory using small amounts of material on a cost-effective basis. Two-inch (50-mm) cubes for strength testing based upon modified ASTM C 109 (Test Method for Compressive Strength of Hydraulic Cement Mortars (Using 2-in. or 50-mm Cube Specimens)) procedures, and 1-in. (25-mm) square bars for change of length testing based upon modified ASTM C 157 (Test Method for Length Change of Hardened Hydraulic-Cement Mortars and Concrete) procedures can both be made using standard molds and testing equipment.