QA / QC

Concrete Core Test

Q: When is a core test required?

When cube tests fail the IS 456 acceptance criteria, cubes are missing or doubtful, or the in-situ strength of an old, distressed or fire-affected structure must be established.

Q: Does one failed cube mean the concrete must be demolished?

No. IS 456 Cl. 17 directs a structural assessment — typically core tests plus NDT. The member is accepted if the cores meet the ≥0.85 fck mean / ≥0.75 fck individual criteria.

Drilled cylindrical core tested for in-situ concrete strength when cubes are in doubt

Also calledcore testconcrete corecore cutting testdrilled core strengthin situ strength test

Related on InfraLens

CODES

IS 516 IS 456

Definition

The concrete core test extracts a cylindrical core (typically 100 mm or 150 mm diameter) from the hardened structure with a diamond core drill, then tests it in compression to assess the actual in-situ strength. IS 516 Part 4 (and the historic IS 1199) governs cutting, preparation (capping/grinding ends, length-to-diameter correction) and testing.

It is the definitive investigation invoked under IS 456 Cl. 17 when cube results fail the acceptance criteria, when cubes are missing/doubtful, or when assessing old/distressed/fire-damaged structures. A length/diameter ratio correction and a conversion factor (in-situ core strength is typically taken as ~equivalent to 0.8 × the potential cube strength) are applied. Acceptance per IS 456 Cl. 17: the structure is generally acceptable if the average equivalent cube strength of cores ≥ 0.85 fck and no individual core < 0.75 fck — so a cube failure does not automatically condemn the work.

Where used

IS 456 Cl. 17 investigation after cube-test failure
Strength of old / heritage / distressed structures
Fire-damage + accident structural assessment
Verifying suspected under-strength members before demolition
Calibrating NDT (rebound/UPV) against true strength

Acceptance / threshold

Per IS 456 Cl. 17: concrete acceptable if mean equivalent cube strength of cores ≥ 0.85 fck and no individual core < 0.75 fck (after L/D + capping corrections per IS 516 Part 4).

Frequently asked

When is a core test required?

When cube tests fail the IS 456 acceptance criteria, cubes are missing or doubtful, or the in-situ strength of an old, distressed or fire-affected structure must be established.

Does one failed cube mean the concrete must be demolished?

No. IS 456 Cl. 17 directs a structural assessment — typically core tests plus NDT. The member is accepted if the cores meet the ≥0.85 fck mean / ≥0.75 fck individual criteria.

Tensile strength in bending from a beam test; governs pavement slab design

Early Age Strength of Concrete

Strength gain at 1, 3, 7, 14 days — typically 16%, 40%, 65%, 90% of 28-day strength for OPC.

Carbonation Depth & Carbonation of Concrete

Depth from concrete surface to which atmospheric CO₂ has neutralized the alkalinity of the cement paste — drives rebar corrosion timeline once it reaches the cover.

Split Tensile Strength

Indirect tensile strength of concrete from diametral splitting of a cylinder

QA/QC Inspection

Quality assurance and control checklists/templates

IS 516 — Concrete Testing

Methods of test for strength of concrete

Cube Test (Compressive Strength)