IS 516:2022 Part 6 is the Indian Standard (BIS) for methods of tests for strength of concrete - part 6: core testing of hardened concrete. This code specifies the procedures for extracting, preparing, and testing cylindrical cores from hardened concrete to determine compressive strength. Engineers use this standard to assess the actual in-situ strength of concrete in existing structures, especially when standard cube test results fail to meet requirements or during structural audits.
Specifies procedures for drilling, preparation, and compressive strength testing of concrete cores from structures.
Quick Reference — IS 516 Part 6:2022 Cores from Existing Structures
Core diameter, L/D correction, soaking, acceptance per IS 456 Cl. 17.4 for forensic strength assessment.
| Reference | Value | Clause |
|---|
| Scope | Cores from existing structures — strength assessment | Cl. 1 |
| Min core diameter | 100 mm preferred; 75 mm acceptable | Cl. 4.1 |
| Core diameter — relation to aggregate | ≥ 3 × max nominal aggregate size | Cl. 4.1 |
| Length-to-diameter (L/D) — desirable | 1.0–2.0 (correction applied) | Cl. 4.2 |
| L/D correction — 2.00 | 1.00 | Cl. 5.2 (Table 1) |
| L/D correction — 1.75 / 1.50 / 1.25 / 1.00 | 0.98 / 0.96 / 0.93 / 0.87 | Cl. 5.2 (Table 1) |
| Soaking — before crushing | 40 hours in water (or equilibrium with field conditions) | Cl. 5.1 |
| Capping | Sulphur or high-alumina mortar; ends planed/ground | Cl. 4.3 |
| Reinforcement in core — correction | Avoid; if present apply Concrete Society correction | Cl. 5.4 |
| Number of cores per zone — IS 456 reference | ≥ 3 (location of doubtful concrete) | IS 456 Cl. 17.4.3 |
| Cube-equivalent strength | fc(cube) = (5/4) · fc(core) · LD correction | Cl. 5.5 |
| Acceptance — mean of 3 cores | ≥ 0.85 fck | IS 456 Cl. 17.4.3 |
| Acceptance — individual core | ≥ 0.75 fck | IS 456 Cl. 17.4.3 |
| Coring direction — preferred | Horizontal in vertical members; vertical in slabs | Cl. 4.5 |
| Hole reinstatement | Repair with non-shrink grout / micro-concrete | Cl. 4.6 |
⚠ Acceptance limits cross-link to IS 456 Cl. 17.4.3. Where strict assessment is required, also reference Concrete Society TR 11.
Overview
- Status
- Current
- Usage level
- Frequently Used
- Domain
- Materials Science — Testing Methods and Quality Control
- Type
- Testing Method
Also on InfraLens for IS 516
Practical Notes
! Always scan the concrete using a rebar locator or GPR before drilling to avoid cutting through reinforcing steel, which weakens the structure and severely skews test results.
! Ensure core ends are properly ground or capped perfectly perpendicular to the longitudinal axis; irregular ends cause stress concentrations and premature failure.
! Cores containing embedded reinforcement should be avoided for compressive strength testing as they yield lower and less reliable results.
Frequently referenced clauses
concretehardened concrete
International Equivalents
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We're adding equivalent international standards for this code.
Key Values5
Quick Reference Values
Minimum core diameter>= 3 times nominal maximum aggregate size
Standard core diameters100 mm or 150 mm
Preferred Length/Diameter (L/D) ratio1.0 to 2.0
Tolerance on perpendicularity of prepared ends0.05 mm
Rate of loading during compression0.2 to 0.4 N/mm²/s
Key Formulas
f_core = P / A — Compressive strength of core (P = max load, A = cross-sectional area)
Tables & Referenced Sections
Key Clauses
Clause 5 - Apparatus and Equipment
Clause 6 - Drilling of Cores
Clause 7 - Preparation of Cores
Clause 8 - Testing Procedure
Frequently Asked Questions3
What is the minimum recommended diameter for a concrete core?+
It should be at least three times the nominal maximum size of the coarse aggregate used in the concrete.
Can cores containing reinforcing bars be tested for compressive strength?+
It is highly discouraged. If unavoidable, the reinforcement should be perpendicular to the direction of loading, and specific correction factors must be applied.
What should be the length-to-diameter (L/D) ratio of the test core?+
The preferred L/D ratio for testing is between 1.0 and 2.0. Ratios outside this range require correction factors.
QA/QC Inspection Templates
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QA/QC templates coming soon for this code.