Erroneous strength estimates can occur if the in-place concrete is significantly different than the concrete used to develop the pre-established temperature-time-strength curve. Changes in materials, water and air contents, and batching accuracy can introduce strength estimation errors. ASTM C1074 recommends supplementary testing be performed to periodically verify the temperature-time-strength curve, especially when life-threatening construction activities are based on estimated in-place concrete strengths.
ACI306R-10 Guide to Cold Weather Concreting, American Concrete Institute, www.concrete.org, Mindness, S., Young, J.F, and Darwin, D., Concrete, 2nd Edition, Prentice Hall, 2003.
Kim Basham, PhD, P.E. FACI is president of KB Engineering LLC, which provides engineering and scientific services to the concrete industry. Basham also teaches seminars and workshops dealing with all aspects of concrete technology, construction and troubleshooting. He can be reached via email at KBasham@KBEngLLC.com.
Methods for Estimating In-place Concrete Strength
Here are several alternatives to field-cured test cyliners for estimating in-place concrete strength.
ASTM C31/C31M-12 Standard Practice for Making and Curing Concrete Test Specimens in the Field - Described in this article.
ASTM C873/C873M-10a Standard Test Method for Compressive Strength of Concrete Cylinders Cast in Place in Cylindrical Molds - Involves casting in-place test cylinders into slabs, only for with depths between 5 and 12 inches.
ASTM C803/C803M-03(2010) Standard Test Method for Penetration Resistance of Hardened Concrete - Involves shooting pins into the concrete with a power-actuated tool and measuring pin penetration.
ASTM C900-06 Standard Test Method for Pullout Strength of Hardened Concrete - Requires placing bolts into formwork before placing concrete.