RILEM CPC 18 2 Carbonation

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RILEM RECOMMENDATIONS 
RECOMMANDATIONS DE LA RILEM 
TC56-MHM HYDROCARBON MATERIALS 
TC56-MHM MATt RIAUX HYDROCARBONt]S 
CPC-18 Measurement of hardened concrete 
carbonation depth 
CONTENTS 
1. Aim and scope 
2. Definition 
3. Test materials 
4. Laboratory tests 
4.1 Specimens: type, making, curing and storage 
1. AIM AND SCOPE 
The method of testing consists of determining the depth 
of the carbonated layer on the surface of hardened 
concrete by means of an indicator. This method can be 
carried out, using specimens made in the laboratory, on 
specimens taken from completed structures (site 
specimens), and be used for testing on site. 
Tests on laboratory specimens are generally used for 
comparing the rate of carbonation in concrete specimens 
with various mixes, under defined conditions. Tests on 
site or with site specimens are necessary, in general, to 
give information on the state of a structure or structural 
member at a certain moment in time, under the con- 
ditions on site. Because of possibly wide scattering of 
carbonation depths on site and because of the various 
controlling factors, site tests are not suitable for 
comparing various concretes but refer only to the part 
tested. 
In the case of tests using site specimens, the require- 
ments for accuracy of measurement are in general less 
severe than for laboratory specimens. Unless otherwise 
stated in the following pages, the suggestions given for 
laboratory tests should be interpreted accordingly. 
Carbonation affects various properties of hardened 
concrete. Primarily, the protection of the reinforcing steel 
against corrosion, which is originally guaranteed by the 
highly alkaline pore solution of the cement paste, becomes 
*This recommendation has been finalized by CCC, RILEM 
Coordinating Committee for Concrete Technology. It was first 
published as a draft in Material and Structures No. 102 (1984). 
0025-5432/88 �9 RILEM 
4.2 Testing 
4.3 Test results and test report 
5. Testing completed structures 
5.1 Specimens 
5.2 Testing 
5.3 Test results and test report 
lost. Climatic conditions leading to the highest rate of 
carbonation are not identical with those which accelerate 
corrosion of steel. Other concrete properties, like 
strength, permeability and resistance to some chemical 
and physical attacks, as well as shrinkage, are also 
affected by carbonation. 
This recommendation is aimed at improving the com- 
parability of carbonation tests. It is not aimed at laying 
down optimal test conditions for special testing problems. 
2. DEFINITION 
Carbon dioxide which penetrates the surface of concrete 
can react with alkaline components in the cement paste, 
mainly Ca(OH)2. This process (carbonation) leads to a 
reduction of the pH-value of the pore solution to less than 
9. The depth of the carbonated surface layer is called the 
depth of carbonation dk. 
The reduction of the pH-value can be made visible by 
the colour change of a suitable indicator.*' 
3. TEST MATERIALS 
A solution of 1% phenolphthalein in 70% ethyl alcohol is 
suitable for determining the depth of carbonation. 
Phenolphthalein turns non-carbonated concrete red, and 
remains colourless in carbonated concrete. 
*This indicator method does not make it possible, however, to 
determine whether the reduction of the pH-value may have 
resulted from influences other than the absorption of CO2 (e.g. 
SO2, HCI or other acidic gases). 
454 R ILEM Recommendat ion CPC- 18 
4. LABORATORY TESTS 
4.1 Specimens: type, making, curing and storage 
Concrete prisms with a cross-section of 100 mm x 100 mm 
that can be split into lengths of roughly 50mm, for each (a) 
date of testing, are suitable. For mortar, prisms 40 mm • 
40 mm x 160 mm are recommended from which a slice of 
roughly 20 mm is split off at each date of testing. In no 
case shall the shortest dimension of the prism be less than 
3 times maximum aggregate size. 
During specimen preparation, it is important to avoid 
any unwanted effects on the concrete surface which could 
impair measurement. For example, stripping agents shall 
be kept to a minimum. Normally the methods for making (bt 
and curing samples (RILEM Recommendation CPC-3) 
should be used. The kind of curing chosen (duration of 
water storage, extent of drying by air storage, accelerated 
hardening, etc.) must be precisely defined and followed 
during the tests. 
Climatic conditions of storage (relative humidity, 
amount of CO2 concentration, etc.) must be precisely 
defined. Specimens may be stored indoors or out of 
doors. For indoor storage roughly 0.03% CO2 concen- 
tration,* a temperature of 20~ and a relative humidity of (c) 
65% are recommended. Out of doors, storage under 
cover (protected against rain) or without cover must be 
differentiated. Air must be able to reach the test surfaces 
unhindered at all times. For this reason, leave a free space 
of at least 20 mm around the specimens. 
4.2 Testing 
The following dates of testing are recommended: 28, 90, 
180 days; 1, 2, 4, (8, 16 . . . ) years, after the first exposure 
to CO~. The longer testing periods should be chosen when 
a slow rate of carbonation is expected (e.g. storage out of 
doors without cover). In the case of more specialized 
investigation, additional dates may be necessary. 
In order to measure the depth of carbonation in 
laboratory specimens, a slice is broken off for each test. 
The slice must be thick enough to avoid any chance of 
carbon dioxide penetration from the end surface affecting 
the observed measurements from the side surfaces. 
Measure the depth of carbonation on the freshly broken 
surface. Saw-cuts are not always suitable. 
Clear the broken surface immediately of dust and loose 
particles after breaking, and then spray with indicator 
solution. If only a weak coloration or none at all appears 
on the treated surface, repeat the spray test after the 
surface has dried. Avoid the formation of flow channels 
on the test surface. In order to stabilize the coloration 
temporarily, a resin may be sprayed after drying. 
The measured depth of carbonation is influenced by the 
time of measuring after application of the indicator 
solution. Therefore, measurements within a series of tests 
Short tests may be carried out using higher CO2 concentrations. 
At present no universal agreement exists as to the value of short 
tests using considerably higher CO2 concentrations. 
Form cl 
Form b 
Form c 
Fig. 1(a-c) Definitions of the depth of carbonation. 
should always be made at the same time. Measuring about 
24 hours after spraying is recommended, when the margin 
between carbonated and non-carbonated concrete is 
often more clearly demonstrated than at earlier 
measuring times. The precision of the measurement must 
be to the nearest 0.5 mm. Carbonation depths less than 
0.5 mm are not differentiated. 
When the carbonation front runs as a straight line 
parallel to the surface, the depth of carbonation dk is 
determined as shown in Fig. la. 
When the carbonation front runs as shown in Fig. lb, a 
graphical average dk and the maximum depth dkm~ should 
be recorded. If the carbonation front runs parallel to the 
surface with isolated deeper carbonated areas, as in Fig. 
lc, then the maximum depth dk~ax of the carbonation 
must be given as well as the normal depth dk. In this case, 
no average is calculated. 
Ignore greater depths of carbonation in the corner 
areas of laboratory specimens, where carbon dioxide has 
penetrated from two sides at once. 
In the case of concretes with large-sized maximum 
aggregates, care must be taken to measure the carbon- 
ation only in the hardened cement paste. 
4.3 Test results and test report 
The average depth of carbonation is reported for each 
specimen. 
Materials and Structures455 
The average depth of carbonation for laboratory 
specimens includes values from all sides. If the depth of 
carbonation on the floated surface varies considerably 
from those on the other surfaces, this should be noted. 
Transition areas which have lost their colouring after 24 
hours are to be judged as carbonated. 
The test report must include 
(a) General data: 
(i) Concrete mix. 
(ii) Curing (type, duration). 
(iii) Climatic conditions (relative humidity, tempera- 
ture, wind speed, orientation and precipitation during 
storage outdoors, concentration of CO2. 
(b) Test data: 
(i) Age of concrete. 
(ii) Form and size of concrete surface tested. 
(rio Measuring apparatus, 
(iv) Length of time between spraying with indicator 
solution and measuring. 
{v) Average depth of carbonation d~ to the nearest 
0.5 mm with details of how the carbonation front runs, 
according to Fig. la: regularly; Fig. lb: irregularly dk and 
dkmax; Fig. lc: regularly dk and dkmax. 
(vi) Where relevant, record the depth of carbonation 
on the floated surface. 
(vii) Precision of measurement and/or tolerance. 
5. TESTING COMPLETED STRUCTURES 
5.1 Specimens 
The determination of the depth of carbonation may be 
carried out using drilled cores taken from completed 
structures and subsequently split. The diameter of such a 
drilled core should be at least 50 mm. If a rough estimate 
is required, e.g. only information as to whether the 
carbonation line has already reached reinforcing steel, 
then the concrete surface may be broken by chisel and the 
test carried out directly on site. 
5.2 Testing 
The determination of the depth of carbonation in drilled 
cores should be carried out immediately after drilling, 
using the procedure of Section 4.2. If a longer storage is 
unavoidable for special reasons, the specimens must be 
stored in CO2-free containers, until they can be 
measured. 
Measure the depth of carbonation on surfaces split 
from the samples at right-angles to the surface of a 
structural member. Measurements carried out on the 
outer surface of drilled cores are less accurate. 
5.3 Test results and test report 
The depth of carbonation shall be reported to the nearest 
1 mm. 
The test report must contain, in addition to the items 
given in Section 4.3, the following details: 
(i) Identification of the structure. 
(ii) Location of drilling and the orientation of the 
surface exposed to CO2 in the building (vertical or 
horizontal). 
(iii) Date of drilling and of test. 
(iv) General assessment of the concrete (structure of 
the concrete, aggregates, pores).