🧱 Chloride content in concrete

Construction PN-EN 14629

Overview

STATUS (as of 06.11.2026). PN-EN 14629:2008 — Polish version, published on 30.12.2008, implements EN 14629:2007 [IDT]; it replaced PN-EN 14629:2007 (English version), withdrawn on the same day. The PKN card has no withdrawal note — the standard is current; EN 14629:2007 (SIST EN 14629:2007) is published in the iTeh catalogue.

SCOPE (clause 1). The standard describes two methods for determining the total (free and bound) acid-soluble chloride content of hardened concrete or mortar. The result is intended for use in estimating the risk of chloride-induced corrosion of the steel reinforcement. Powder obtained by drilling, from cores or fragments removed from structures, and other appropriate laboratory specimens can be tested. The standard belongs to the series on products and systems for the protection and repair of concrete structures.

WHY (introduction of the standard). Steel reinforcement may be at risk of corrosion if the concrete is contaminated by chlorides; EN 1504-10 requires the chloride concentration to be considered when decisions about the removal of concrete are made. To assess whether the chloride content exceeds the critical threshold value, it is determined within the cover, especially at the surface of the reinforcement. Rapid field methods are not covered; Volhard's method and potentiometric titration are the reference methods. The result is expressed as a percentage of chloride by mass of cement or of concrete; the content by mass of cement is derived from an assumed or determined cement content or from construction records. The standard does not give the threshold value.

SAMPLING (4.1). According to a plan prepared by a suitably qualified person, taking account of the load-bearing capacity and reinforcement of the element, the aggregate size and the exposure conditions; the plan specifies the number, location and depth of samples and the depth increments — typically not exceeding 25 mm, and the surface layer is usually discarded. Drilled powder is collected separately for each depth increment; at least about 1 g is required. According to a note in the standard, a 20 mm drill and two holes normally give 1 g of powder per millimetre of increment, and a sample of at least 20 g is normally collected so that it represents all concrete constituents. Cores are usually 30 mm to 50 mm in diameter (depending on the aggregate); for a chloride profile versus distance from the surface they are cut into slices without cooling fluid or ground in increments. Sampling holes are repaired or protected immediately.

PREPARATION AND DIGESTION (4.2–4.3). A sample to be ground is dried to constant weight at (105 ± 5) °C, cooled (e.g. in a desiccator) and ground to pass a 1.18 mm sieve or smaller, then homogenised. Masses are given to the nearest 0.001 g and volumes to 0.05 ml. Between 1 g and 5 g of powder is wetted with 50 ml of water, 10 ml of 5 mol/l nitric acid and 50 ml of hot water are added, and the mixture is heated to boiling and boiled for at least 3 min with continuous stirring; if necessary it is filtered immediately through medium-textured paper, washing the beaker, stirrer and residue (filtration is not necessary for potentiometric titration). A blank is run in parallel without concrete. Approximately one sample in every 20 (or one per batch of fewer than 20) is an interlaboratory standard concrete dust of known chloride content, and occasional duplicate analyses are carried out.

DETERMINATION (4.3.4). Volhard's method (method A) starts by adding 5 ml of silver nitrate solution by pipette and stirring vigorously to precipitate the chloride; the excess silver is back-titrated with ammonium thiocyanate solution against an ammonium ferric sulfate indicator. The second method is potentiometric titration with an Ag/AgCl or similar electrode.

SECOND SOURCE — ASTM C1152/C1152M-20. In most cement systems, acid-soluble chloride equals the total chloride. Sulfides — e.g. from blast-furnace slag aggregates and cements — interfere with the determination and give erroneously high results (they are eliminated with hydrogen peroxide); some aggregates contain chloride that is not available for corrosion, which this method also detects.

WHAT WE DO NOT GIVE HERE. Further details of the titration, calculation formulae and the content of the test report — the end of 4.3.4 and clause 5 are not in the available text. The critical chloride content for corrosion of reinforcement — the standard does not give it. Permissible chloride contents in the composition of concrete according to concrete standards — a different requirement from the corrosion risk assessment of an existing structure.

Method principle

Concrete or mortar powder (from drilling, cores or fragments), dried and finely ground, is digested in a boiling nitric acid solution, which brings free and bound acid-soluble chlorides into solution. Chloride is determined by Volhard's method — precipitation with silver nitrate and back-titration of the excess silver with ammonium thiocyanate against an ammonium ferric salt — or by potentiometric titration. The result is expressed as a percentage of chloride by mass of concrete or cement; before digestion the powder is dried at (105 ± 5) °C and ground to pass a 1.18 mm sieve.

Applications

• Estimating the risk of chloride-induced corrosion of steel reinforcement in existing structures (clause 1)
• Decisions on the removal of contaminated concrete in repairs according to EN 1504-10 (introduction of the standard)
• Chloride profiles versus distance from the surface — cores cut into slices or ground in increments (4.1.3)
• Structures under chloride exposure, e.g. in salt water splash zones — taken into account in the sampling plan (4.1.1)
• Hardened concrete and mortar — drilled powder, cores, fragments or other laboratory specimens (clause 1)

Key parameters

Standard

Standard number

PN-EN 14629:2008

Title (PL)

Wyroby i systemy do ochrony i napraw konstrukcji betonowych — Metody badań — Oznaczanie zawartości chlorków w betonie

Title (EN)

Products and systems for the protection and repair of concrete structures — Test methods — Determination of chloride content in hardened concrete

Step-by-step procedure

1. Sampling plan

   Prepare a plan: number, location and depth of samples, depth increments (typically up to 25 mm, the surface layer usually discarded); check the position of the reinforcement so as not to damage it (4.1.1).

2. Collecting powder or cores

   Drill separately for each increment — at least about 1 g of powder (at least 20 g is normally collected); or take 30–50 mm cores marked for location and orientation (4.1.2–4.1.3). Repair or protect the holes immediately.

3. Drying and grinding

   Dry to constant weight at (105 ± 5) °C, cool, grind to pass a 1.18 mm sieve or smaller and homogenise (4.2).

   🌡 Temperature: (105 ± 5) °C

4. Digestion

   Weigh 1–5 g of powder into a 250 ml beaker, wet with 50 ml of water, add 10 ml of 5 mol/l HNO₃ and 50 ml of hot water, heat to boiling and boil for at least 3 min with stirring (4.3.2).

5. Filtration

   If necessary, filter immediately through medium-textured paper, washing the beaker, stirrer and residue; filtration is not needed for potentiometric titration (4.3.2).

6. Blank

   Carry out the same procedure without concrete (4.3.3).

7. Volhard's method (method A)

   Add 5 ml of silver nitrate solution by pipette and stir vigorously to precipitate the chloride; back-titrate the excess silver with ammonium thiocyanate solution against the ammonium ferric indicator (4.3.4.1; reagents 3.1).

8. Potentiometric determination

   Alternatively, titrate potentiometrically with an Ag/AgCl or similar electrode, with additional reagents as specified by the electrode manufacturer (3.1 note, 3.2).

9. Quality control and result

   About every 20th sample — standard concrete dust of known chloride content, occasional duplicates; result in % chloride by mass of concrete or cement (4.3.1, introduction).

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• Nitric acid — harmonised CLP classification: H272, H314, H331 (concentration up to 70 %); digest the boiling solution under a fume hood wearing goggles and gloves
• Silver nitrate — harmonised CLP classification: H272, H314, H400, H410; collect silver waste separately
• Sampling from structures — taking account of the load-bearing capacity and reinforcement of the element; repair or protect holes immediately (4.1.1)

Frequently asked questions