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Title: Comparison of Core and In-Place Compressive Strengths for Early-Age Concrete

Author(s): Agustin Spalvier, James A. Bittner, Kerry Hall, and John S. Popovics

Publication: Materials Journal

Volume: 116

Issue: 3

Appears on pages(s): 63-72

Keywords: core; correction factor; in-place cylinder; in-place strength; pavement

DOI: 10.14359/51715584

Date: 5/1/2019

Accurate determination of concrete in-place strength remains a challenge. Although drilled cores provide reasonable representation of in-place strength, core strength results are known to be affected by factors such as core aspect ratio, moisture condition, and internal damage caused by extraction. To account for these effects, previous research has developed correlations between cores and standard molded companion cylinders in mature concrete. In this investigation, the authors evaluate the effectiveness of compressive strength estimation for new pavement construction using cores for wet and air-dried sample conditions, and for the presence of embedded steel reinforcing bar. The effects of these conditions on in-place strength estimates for early-age concrete with “good” and “low” quality are studied using statistical analysis. The actual in-place strength is determined using castin-place cylinders. Based on the analysis, the optimal correction factors for core to in-place strengths for early-age concrete are 1.05, 1.20, and 1.08 for 1-day air-dried cores, 1-day wet cores, and 1-day air-dried cores containing steel reinforcing bar, respectively.