🏗️ Cores taken from structures — taking, examining and testing in compression

Construction PN-EN 12504-1

Overview

The standard PN-EN 12504-1 specifies a method of taking cores from hardened concrete, of examining them, of preparing them for testing and of determining their compressive strength. It gives no guidance on the decision to drill or on the places of drilling and contains no procedures for the interpretation of the results — the assessment of the strength of concrete in structures and precast units is covered by PN-EN 13791. The 2019 edition introduced the measurement of the dimensions of the cores, testing in the in-situ or in the wet state and procedures for the preparation of the specimens before the test.

The size of the aggregate has a significant effect on the strength measured when the ratio of the diameter of the core to the upper aggregate size is less than about 3 (the informative Annex A). Cores for compression must not contain reinforcing bars in the direction of the longitudinal axis or in its vicinity — such a core is rejected and a replacement is taken. The preferred ratios of length to diameter after preparation: 2.0 for comparison with the cylinder strength and 1.0 for comparison with the cube strength.

Strength tests on cores from a structure are the reference method for assessing the strength of the concrete in the structure, but they do not replace the testing of concrete according to PN-EN 206. The way the end surfaces are prepared has a large effect on the result: studies at the Wrocław University of Science and Technology showed that unprepared cores give a very high coefficient of variation (24 %) and a significantly lower strength, while a layer of high-alumina cement mortar and sand caps are the most reliable way of preparation (a variation of about 5 %).

Method principle

Cores cut with a core drill are examined closely, prepared by grinding or capping and tested in compression by standard procedures. The cores are drilled perpendicular to the surface with the drill rigidly fixed, avoiding the reinforcement; after drilling each core is marked permanently, its position and orientation are recorded, its surface is dried and it is placed in an airtight container (for example a polyethylene bag), so as to avoid any exchange of moisture with the surroundings. The compression test is carried out according to PN-EN 12390-3 in a machine conforming to PN-EN 12390-4.

Applications

• Assessment of the compressive strength of concrete in existing structures and precast units (together with PN-EN 13791)
• Control of pavements of cement concrete (cores; the WWiORB technical specifications of GDDKiA refer to PN-EN 12504-1 and PN-EN 12390-3)
• Building expert opinions where there are doubts about the quality of the concrete or where standard specimens are lacking
• Determination of the density of the concrete in the structure (a core before capping, according to PN-EN 12390-7)
• Preparation of cores for the splitting test (PN-EN 12390-6, Ø ≥ 75 mm)

Key parameters

Standard

Standard number

PN-EN 12504-1:2019-08

Title (PL)

Badania betonu w konstrukcjach — Część 1: Próbki rdzeniowe — Pobieranie, ocena i badanie wytrzymałości na ściskanie

Title (EN)

Testing concrete in structures — Part 1: Cored specimens — Taking, examining and testing in compression

Step-by-step procedure

1. Location and drilling

   Before drilling, consider the structural consequences. Take the cores away from joints and edges of the member, where there is little reinforcement. Drill perpendicular to the surface, without damaging the core, with the drill rigidly fixed; avoid drilling through reinforcement, and record any transverse reinforcement encountered (diameter and position in mm).

2. Marking and protection

   Immediately after drilling, mark the core permanently and record its position and orientation in the member (where it is cut into several specimens, mark the position of each). Dry the surface with a dry cloth or a paper towel and place it in an airtight container.

3. Examination and measurement

   Examine the core for irregularities; if need be, estimate any excess of voids by comparison with reference documentation or with a reference concrete. Measure the diameter (6 measurements, to 1 mm), the length of the core as received (to 5 mm) and, after the preparation of the ends, the length as the mean of 3 measurements about 120° apart (to 1 mm); measure the reinforcement. Determine the density of the core, if required, before capping.

4. Storage and saturation

   Keep the core in the airtight container until it is trimmed or capped. If testing in the saturated state is specified, place it in water at (20 ± 2) °C for at least 48 h.

   🌡 Temperature: 20 ± 2 °C

5. Preparation of the ends

   Prepare the core to the dimensions and tolerances of clauses 8.2 and 8.3 in accordance with Annex A of PN-EN 12390-3:2019. Capping with sulfur or sand: take it out of the container or the water, wipe it, leave it in air for 16–24 h, carry out the capping and test within 24 h of the exposure. Grinding or capping with high-alumina cement: take it out, wipe it, grind or cap it and test within 16–24 h of the exposure (if need be return it to the container or the water until the test).

6. Check of the tolerances

   Check the classification of L/d (2:1 → 1.95–2.05; 1:1 → 0.90–1.10), the flatness and perpendicularity of the ends according to PN-EN 12390-1 and the straightness of the generatrix (3 % of the mean diameter). For cores of a smaller diameter, narrow the tolerances in proportion to 100 mm.

7. Compression test

   Record the conditions of storage (container or water). Test according to PN-EN 12390-3 in a machine conforming to PN-EN 12390-4. Do not test cores with a cracked, hollow or loose capping layer; remove any loose sand from the surface and, when testing wet, wipe off the surface water.

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• Drilling of cores: check the run of the reinforcement and of the services and assess the structural consequences; protection of the hearing, the eyes and the respiratory tract, cooling with water
• Capping with sulfur: hot sulfur and its fumes — a fume hood, heat-resistant gloves, goggles
• Compression testing: the guard, goggles, the hands outside the loading zone

Frequently asked questions