214.4R-10 Guide for Obtaining Cores and Interpreting Compressive Strength Results (Reapproved 2016)

214.4R-10 Guide for Obtaining Cores and Interpreting Compressive Strength Results (Reapproved 2016)

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Core testing is the most direct method to determine the compressive strength of concrete in a structure. Generally, cores may be obtained to assess whether concrete in a new structure complies with strength-based acceptance criteria or to evaluate the structural capacity of an existing structure based on the in-place concrete strength. In either case, the process of obtaining core specimens and interpreting strength test results is often confounded by various factors affecting in-place concrete strength or measured strength of test specimens. The scatter in strength test data, which is unavoidable given the inherent randomness of in-place concrete strengths and the uncertainty attributable to preparation and testing of the specimens, may further complicate compliance and evaluation decisions.

This guide summarizes practices for obtaining cores and interpreting core compressive strength test results. Factors that affect in-place concrete strength are reviewed so sampling locations that are consistent with objectives of the investigation can be selected. Strength correction factors are presented for converting the measured strength of non-standard core-test specimens to the strength of equivalent specimens with standard diameters, length-to-diameter ratios, and moisture conditioning. This guide provides direction for checking strength compliance of concrete in a structure under construction and methods for determining equivalent specified strength to assess capacity of an existing structure. The materials, processes, quality control measures, and inspections described in this document should be tested, monitored, or performed as applicable only by individuals holding the appropriate ACI Certifications or equivalent.

Keywords: compressive strength; core; hardened concrete; sampling; test.

Document Details

Author: ACI Committee 214

Publication Year: 2010

Pages: 17.00

ISBN: 9780870314926

Categories: Testing

Formats: PDF

Table of Contents

Chapter 1—Introduction




Chapter 2—Notation and definitions



Chapter 3—Variation of in-place concrete strength in structures





3.5—Overall variability of in-place strengths

Chapter 4—Planning the testing program

4.1—Investigating concrete in a new structure using strength-based acceptance criteria

4.2—Evaluating existing structure capacity using in-place strengths

Chapter 5—Obtaining test specimens

Chapter 6—Core testing

Chapter 7—Analyzing strength test data

7.1—ASTM C42/C42M precision statements

7.2—Review of core strength correction factors

7.3—Statistical analysis techniques

Chapter 8—Investigation of low-strength test results in new construction using ACI 318

Chapter 9—Determining an equivalent fc′ value for evaluating structural capacity of an existing structure

9.1—Conversion of core strengths to equivalent in-place strengths

9.2—Uncertainty of estimated in-place strengths

9.3—Percentage of in-place strengths less than fc′

9.4—Methods to estimate the equivalent specified strength

Chapter 10—References

10.1—Referenced standards and reports

10.2—Cited references

Appendix—Example calculations

A.1—Outlier identification in accordance with ASTM E178 criteria

A.2—Student’s t test for significance of difference

between observed average values

A.3—Equivalent specified strength by tolerance factor approach

A.4—Equivalent specified strength by alternate approach


Any applicable errata are included with individual documents at the time of purchase. Errata are not included for collections or sets of documents such as the Manual of Concrete Practice (MCP). For a listing of and access to all product errata, visit the Errata page.

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