Condition % Reduction Effect at 10,000 psi
Rough ends before capping 27 7300
Reuse of plastic molds 22 7800
Use of cardboard molds 21 7900
Convex end, capped 12 8800
Eccentric loading 12 8800
Out-of-round diameter 10 9000
Ends not perpendicular to axis 8 9200
Thick cap 6 9400
Sloped end leveled by cap 5 9500
Chipped cap 4 9600
Rebar rodding 2 9800
1 day at 100°F/27 in lab cure 11 8900
3 days at 100°F/24 in lab cure 22 7800
7 days at 100°F/21 in lab cure 26 7400
1 day air/27 days moist 8 9200
3 days air/24 days moist 11 8900
7 days air/21 days moist 18 8200

*NRMCA Publication No. 179

Various improper testing practices can cause strength reductions in test cylinders as demonstrated in this National Ready Mix Concrete Association table. Assuming a 10,000-psi mix strength, the reduction in compressive strength is shown for numerous situations where cylinders where not properly cast, stored, or prepared for testing.

Return to concrete testing