Title: Concrete Q & A: Cylinder Size and Strength Tests

Author(s): Nicholas Carino

Publication: Concrete International

Volume: 32

Issue: 6

Appears on pages(s): 75-76

Keywords:

DOI:

Date: 6/1/2010

Abstract:
I’m curious as to why ACI 318-08 Section 5.6.2.41 states that at least three test cylinders are required to define a strength test using 4 x 8 in. (100 x 200 mm) cylinders (4 x 8s) but only two test cylinders are required to define a strength test using 6 x 12 in. (150 x 300 mm) cylinders (6 x 12s). I work near Chicago, and we place a lot of concrete and fireproofing when the ambient temperature is between 0 and 20°F (–18 and –6°C). We just started using the smaller cylinders and have been having poor compressive strength results. Are there factors that could affect 4 x 8s more than 6 x 12s, or could the cold weather be affecting our results? I’ve read that smaller cylinders are supposed to provide higher test strength results (1 to 10% higher, with a 5% average increase), so I’m perplexed by our data.