ASTM C805/C805M-18 PDF

Full title and description

ASTM C805/C805M-18 — Standard Test Method for Rebound Number of Hardened Concrete. This is a short, nondestructive field test method that uses a spring-driven steel hammer (rebound hammer) to obtain a dimensionless rebound number indicative of surface hardness and, with appropriate correlation, an estimate of in-place compressive strength.

Abstract

This test method defines the procedure for obtaining rebound numbers from hardened concrete surfaces using a spring-driven steel hammer, describes apparatus verification and test practice, notes factors that affect readings (surface moisture, finishing/form material, carbonation, instrument variation), and explains that strength estimates require site-specific correlation with cores. The method is concise (four pages) and intended for assessing in-place uniformity and relative strength, not for acceptance/rejection without correlation.

General information

• Status: Superseded (original 2018 edition; later revised and reissued as ASTM C805/C805M-25 — active 1 June 2025).
• Publication date: Current edition (C805/C805M-18) approved December 15, 2018 (published early 2019).
• Publisher: ASTM International (ASTM).
• ICS / categories: 91.100.30 — Concrete and concrete products.
• Edition / version: C805/C805M-18 (designation indicates 2018 revision).
• Number of pages: 4 pages (concise test method).

Scope

The standard covers determination of a rebound number of hardened concrete using a spring‑driven steel hammer; values are reported as a dimensionless rebound number. Both SI and inch‑pound unit systems are accommodated (to be used separately). The procedure is intended to assess in‑place uniformity and to provide relative indications of strength when a correlation with measured core strengths is established; it is not intended as a standalone acceptance test without proper correlation.

Key topics and requirements

• Apparatus: spring‑driven steel rebound hammer and plunger; instrument verification using a manufacturer‑specified verification anvil.
• Test procedure: take multiple rebound readings on prepared, clean surfaces; report mean rebound number and distribution.
• Correlation for strength: to estimate compressive strength, develop site‑specific correlations by testing cores (minimum replication and sampling across a range of rebound numbers are required).
• Influencing factors: surface moisture, finishing/form materials, depth of carbonation, orientation, and instrument differences — account for these when interpreting results.
• Limitations: provides an indirect estimate of strength; not suitable as sole basis for acceptance/rejection; instrument readings can vary 1–3 units between hammers of same design.

Typical use and users

Used by structural and geotechnical engineers, concrete testing laboratories, field inspectors, and contractors for rapid, nondestructive assessment of concrete surface hardness, uniformity, and for preliminary strength estimation when correlated with cores. Typical applications include condition surveys, locating areas of nonuniform concrete, and monitoring changes over time.

Related standards

Commonly used alongside ASTM standards for coring and core testing (ASTM C42/C42M) and terminology (ASTM C125), and referenced guidance such as ACI 228.1R and BS EN 13791 for in‑place strength estimation and correlation practices.

Keywords

rebound hammer; rebound number; hardened concrete; nondestructive testing; in‑place strength estimation; correlation; verification anvil; surface hardness.

FAQ

Q: What is this standard?

A: ASTM C805/C805M-18 is the 2018 edition of the Standard Test Method for Rebound Number of Hardened Concrete, describing the rebound‑hammer procedure to obtain a rebound number as an indicator of surface hardness and, with correlation, in‑place strength.

Q: What does it cover?

A: It covers the apparatus, verification, test procedure for obtaining rebound numbers, factors affecting readings, and guidance on developing correlations with core strength to estimate in‑place compressive strength. It notes limitations and that the method is not intended as the sole basis for acceptance.

Q: Who typically uses it?

A: Structural engineers, concrete testing labs, field inspectors, contractors, and researchers conducting nondestructive evaluation of concrete.

Q: Is it current or superseded?

A: The C805/C805M-18 edition (approved December 15, 2018) has been superseded; ASTM issued a subsequent revision designated C805/C805M-25 (effective/published 1 June 2025). Users should apply the 2025 edition where the latest requirements are required.

Q: Is it part of a series?

A: It is part of ASTM Committee C09 (Concrete and Concrete Aggregates) test methods and is related to other in‑place testing standards (for example, ASTM C42/C42M for cores, C803 for penetration resistance). Editions of C805 have earlier revisions (e.g., 2013, 2008) and are periodically updated.

Q: What are the key keywords?

A: Rebound number, rebound hammer, nondestructive testing (NDT), hardened concrete, in‑place strength, verification anvil, correlation.