ISO 1920-12:2015 download.Testing of concrete — Part 12: Determination of the carbonation resistance of concrete — Accelerated carbonation method.
1 Scope
This procedure Is a method for evaluating the carbonation resistance of concrete using an accelerated carbonation test. After a period of preconditioning, the test is carried out under controlled exposure conditions usingan increased level of carbon dioxide to which, the vertical sides of the specimen are exposed.
The test results are not designated to set performance requirements but to compare the carbonation resistance of different concretes of the same strength class, which are used in the same environmental conditions.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition ol the referenced document (including any amendments) applies.
ISO 1920-2, Testing of concrete — Part 2: Properties off resh concrete
ISO 1920-3, Testing of concrete — Part 3: Making and curing test specimens
ISO 1920-4, Testing of concrete — Part 4: Strength of hardened concrete
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
depth of carbonation
depth as measured using a phenolphthalein solution sprayed on a freshly-split concrete surface
3.2
single point carbonation depth
depth of carbonation measured at a single point on a specimen, dk1oInL
3.3
specimen face carbonation depth
mean depth of carbonation of a single exposed face of a single specimen, dk,face.
4 Principle
Two concrete cubes are cast and cured for 28 d in accordance with Iso 1920-3 (see also changes to the curing conditions in .2). The two concrete cubes are then conditioned in a laboratory air environment for 14 d prior to seating the top, bottom, and two opposite side faces. After sealing of all but two faces, the cubes are placed in a storage chamber meeting the conditions specified in £4 and having a carbon dioxide level of (3,0 ± 0,5) % for a period of 70 d. After 70 d of exposure, the cubes shall be split in half, perpendicular to the exposed faces, and the depth of carbonation measured in accordance with the procedure given in Ciauei.
The test under reference conditions takes therefore a minimum of 112 d, period that comprises a minimum age of the specimen of 28 d prior to conditioning, a minimum conditioning period of 14 d, and a minimum exposure to increased carbon dioxide levels of 70 d. In case where a higher range of additions such as pozzolanic materials, slag, and others are used, extended curing and drying times are allowed and the same should be reported.
If required, further cubic specimens may be casted and used for measurement of the depth of carbonation at exposure periods other than 70 d. Each cubic specimens shall be used for testing at one period of exposure only.
When the purpose of the test is to measure the depth of carbonation on the same specimen at more than one exposure period, concrete prisms shall be used.
In this case, two prisms are cast and cured for 28 d in accordance with ISO 1920-3 (see also amendments of the curing conditions in ). The prisms are conditioned in a laboratory air environment for 14 d prior to sealing the top, bottom, and two end faces. After sealing all but two longitudinal faces, the prisms are placed in a storage chamber, meeting the conditions specified in 5A and having a carbon dioxide level of (3,0 ± 0.5) % for the overall test period which should be 70 d. After each exposure period, a 50 mm slice is broken from each prism and tested for carbonation depth. After splitting off a slice, the split end faces of the prisms are sealed and the remainder of the prisms returned to the storage chamber.
The specimens, cubes, or prisms shall be positioned with their exposed faces in the vertical position.
The curing conditions may vary from one country to another in accordance with local provisions; however, these conditions shall be recorded and reported.
The carbonation depth of prisms shall be measured after the following exposure periods: 56 d, 63 d, and 70 d or as specified after placing in the storage chamber. The carbonation depth of cubes shall be measured at 70 d unless specified otherwise.
10 single point carbonation depths (dk,nJ are measured after each exposure period on each prism or cube and the depth of carbonation dk,Is expressed as the mean of the 20 readings.
A slice approximately 50 mm thick shall be broken off after each exposure period and the split surface on the remaining prism resealed to prevent longitudinal carbonation [see Figure±b)I. Where a single determination of the carbonation depth is made on a cube after 70 d of storage, the cube shall be split in half. The depths of carbonation on the freshly broken surface of the split slice shall be measured.
NOTE 1 Slicing by saw is not suitable.
Clear the broken surface immediately of dust and loose particles after breaking and then spray with a fine mist of indicator solution. Avoid the formation of flow channels on the test surface. If only a weak colouration or none at all appears on the treated surface, spray again after 30 s.
The measurements shall be conducted after the colour has stabilized.
NOTE 2 The measured depth of carbonation may be influenced by the time of measuring after application of
the indicator solution.
8 Determination of the carbonation depth
8.1 General
The carbonation depth shall be determined by the colour change in accordance with the method given below.
8.2 Measuring the depth of carbonation
The carbonation depth shall be measured at five points on each exposed face. To locate these points, the edge length shall be divided into six equal distances. The five central points shall be used. With the help of a ruler or a sliding gauge and a magnifier, the point carbonation depth (dk point) shall be determined perpendicular to the exposed surface of the prism with a precision of 0,5 mm per measured point.
The depth of the carbonation shall he measured on the one broken face on both prisms giving (normally) a total of at least 20 measurement noints.
8.5 Expression of the results
The mean depth of carbonation for each exposed face of a specimen dk, face) shall be calculated and recorded. The mean depth of carbonation for each specimen (dk, spec) shall be calculated and recorded. The arithmetical mean of the mean carbonation depth of two specimens (dk) at 70 d shall be reported as the carbonation depth of the concrete mix.
Where testing is undertaken on prisms at alternative exposure periods, these shall be expressed as the arithmetical mean of two specimens (d1J at the reported alternative exposure periods.
9 Test report
a) reference of the concrete under test;
b) date of casting of the specimens;
c) date of the start of the test;
d) all measured minimum and maximum carbonation depths of at least 20 points at the reference exposure period of 70 d or the specified exposure periods;
e) mean carbonation depth of specimen faces (dLfac.), each specimen the overall mean (dk);
f) ilany, the number of values of Mk,0t and their magnitude that were not included in the calculation of the mean value;
g) any deliberate deviation from the reference conditions or non-conformity with the test conditions, e.g. any failure to maintain the required carbon dioxide for an identified short period or changes to the preconditioning environment.
The test report may contain the following:
a) details of the concrete mixes;
b individual test results and relevant photographic records;
c) results of additional testing, e.g. compressive strength results at 28 d.