Quality Control of Concrete Masonry Compressive Strength

Some of concrete masonry being built in the US has a compressive strength well below specified strength. Quality control test data were analyzed on 80 sets of three prisms each from eleven projects in eight states. Most sets had average compressive strengths well above specified strength. However, if those 240 prisms are representative of concrete masonry in general, 15% of structural concrete masonry probably has a compressive strength lower than the specified strength. Most building code requirements for masonry do not now provide for variability in compressive strength, although they have done so in the past. Structural engineers should carefully consider the effects on structures of masonry’s greater stiffness than assumed.