Carbonation

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Rate of carbonation in cement
modified base course material
Reza Gholilou September 2018

Carbonation
1
• pH drop from 12.0 to around 8.3
• Forming thin loose powdery layer
• Spalling
• Transverse cracking
• Rutting
• Pumping of fine soils
• Loss of strength
Ca(OH)2+CO2 = CaCO3+H2O
(3CaO.2SiO2.3H2O)+3CO2 = (3CaCO3.2SiO2.3H2O)
SEM images of Calcite rhombohedral
crystals(Massi et al., 2012)
SEM images of cement paste and its constituents (Stutzman, 2000)

Carbonation records in literature
2
 State Highway 36 in Houston, after three years being in service from 1990.
Base course with 5% cement and 150 mm thickness.
 Hundreds of roads section with 800 m to 20 km length in South Africa.
In 15 cases, despite loss of strength and carbonation of base course
material there was no sign of distress on the surface. Paige-Green et al.(1990)

Carbonation records in WA
3
Reid Highway trial section
Section
Modified
Base
Course
Material
Depth (mm)
1 2% HCTCRB 100
2 2% Bitumen
Stabilised
Limestone
100
3 Crushed Rock
Base
100
4 Crushed Rock
Base
200
5 1% HCTCRB 200
6 2% HCTCRB 200
7 0.75%
Cement CRB
200
8 2% Cement
Stabilised
Limestone
200
9 LIMUD 200
Butkus, F. (2004). Reid Highway Basecourse Test Sections Construction Details And Performance to
November 2003 (94/15 M).
Harris, D., & Lockwood, N. (2009). Reid Highway Basecourse Test Sections Construction Details And
Performance to December 2008 (94/15 M). Retrieved from Western Australia:

Carbonation records in WA
4
Reid Highway trial section
Sections 1 5 6 7
Base course Description
2% cement
HCTCRB
1% cement HCTCRB 2% cement HCTCRB
0.75% GGBFS
Stabilised CRB
Thickness (mm) 123 210 211 231
Sample Chainage 11570
116
00
10520 10550 10430 10460 10330 10360
Test
Section
Phenolphthalein N N Y N Y Y N N
Phenol red N N - N - - N N
HCl acid Y Y Y Y Y Y Y Y
Carbonation Result FC FC Not FC FC Not FC Not FC FC FC
Taxiway D at the Broome Airport
Included 150 mm pindan base course stabilised with 1.5% cement, over 150mm compacted
pindan as a subbase
Emery, S. J., Masterson, S., & Caplehorn, M. W. (2003). SAND-CLAY PINDAN MATERIAL IN PAVEMENTS AS A STRUCTURAL LAYER. Paper presented at the
Proceedings of the 21st ARRB and 11th REAAA Conference. Transport. Our Highway to a Sustainable Future, Cairns, Australia

Doubtful cases in WA
5
 Orrong Rd, between McDowell St and west of Felspar Road in 2001
 Graham Farmer Freeway tunnel
Some hypothesis for WA
carbonation failures are rare because (Cocks, G. et al, 2015)
 Presence of Fe2O3 and Al2O3 in natural gravels
 Early curing by primer seals within a few days
 Rare evidences in flood ways with harsh environment
 Quality base course material

Carbonation identification
6Curtin University 22/09/2018
I. 0.4% Phenol red, yellow at pH<6.8, red at pH≥ 8.4
II. 0.5% Phenolphthalein, colourless at pH≤8.3, red pH≥10
III. Dilute HCL (5N), effervesces in presence of CaCo3

Cement modification of CRB material
7
Water susceptibility:
High surface deflections due to poor drainage and water intrusion
 Kwinana Freeway (1994)
South Street to Armadale Road,
CRB thickness of 125 mm to 160 mm
 Welshpool Rd
Lesmurdie.
Butkus, F., & Lee Goh, A. (1997). A Review Of Repeated Load Triaxial Test Results. (97-4 Vol 1).

Carbonation models for concrete
8
𝑥 =
𝑤𝑜 − 0.3
0.3(1 + 3𝑤𝑜)
𝑡
Uchida and Hamada (1930)
where w0 is water/cement ratio, x is the carbonation depth (mm) and t is the
time (year)

Carbonation models for concrete
9
𝑥 𝑐 𝑡 = 2. 𝑘 𝑒 . 𝑘 𝑐 . (𝑘 𝑡 . 𝑅 𝐴𝐶𝐶,𝑂
−1
+ 𝜀𝑡). 𝐶𝑠. 𝑡 . W(t)
FIB Bulletin 34 model (International Federation for Structural
Concrete) adopted by CIA.
where w0 is water/cement ratio, x is the carbonation depth (mm) and t is the
time (year)

Carbonation models Papadakis et al. (1991)
10
Based on mass conservation of carbon dioxide and Fick's first law for gas
diffusion
One dimensional diffusion of CO2 ,(Richardson, 2004)
𝑑𝑛 = 𝐷𝐴
𝑟𝑥 − 𝑟
𝑥
𝑑𝑡
𝑑𝑛 = 𝑐. 𝐴. 𝑑𝑥
n is the quantity of CO2 (kg),
D is the diffusion rate (m2/s),
A is area (m2),
t is time (s),
r and rx are the concentration of CO2 (kg/m3)
c is alkaline in a unit volume of material (kg/m3).
𝑥. 𝑑𝑥 = 𝐷
𝑟𝑥 − 𝑟
𝑐
𝑑𝑡
𝑥 =
2𝐷𝑟𝑡
𝑐

Carbonation models Papadakis et al. (1991)
11
𝑥 =
2 𝐶𝑂2 . 𝐷𝑒.𝐶𝑂2
𝐶𝑎(𝑂𝐻)2 + 3 𝐶˗𝑆˗𝐻
𝑡
[CO2] is the molar concentration of carbon dioxide (mol/𝑚3),
[Ca(OH)2] is the molar concentration of calcium hydroxide (mol/𝑚3),
[C˗S˗H] is the molar concentration of calcium silicate hydrate (mol/𝑚3),
De.CO2 is the effective diffusivity of carbon dioxide (𝑚2/s) and
Kc is the carbonation coefficient (m/𝑠0.5).
𝑥 = 𝐾𝑐 𝑡

Hydration reactions
2C3S+6H C3S2H3+3CH
2C2S+4H C3S2H+CH
C4AF+2CH+2CŜH2+18H C8AFŜ2H24
C3A+CŜH2+10H C4AŜH12
12
where notations stand for :
C: CaO, S: SiO2, A: Al2O3, F: Fe2O3, H: H2O, Ŝ: SO3, C3S: 3CaO.SiO2, CH: Ca(OH)2, C3S2H3 or C-S-H: 3CaO.2SiO2.3H2O
C+H CH
2S+3CH C3S2H3
A+4CH+9H C4AH13
A+F+8CH+18H C8AFH26
A+CŜH2+3CH+7H C4AŜH12
Cement
Pozzolans

Stoichiometry relations
13
PC-S-H =PC-S-H.C+PC-S-H.P
The capital letters P denote the weight of each constituent. The small indices .C or .P represent cement and the
pozzolan, respectively.
Key assumptions
 hydrothermal equilibrium (determination of water distribution in pores from ambient relative humidity and temperature)
 complete cement hydration and pozzolanic activities in mixture.
)𝐶𝑎(𝑂𝐻 2 + 3 𝐶𝑆𝐻 =
33000
1 +
𝑤
𝑐
𝜌𝑐
𝜌 𝑤
+
𝑎
𝑐
𝜌𝑐
𝜌 𝑎
Richardson (2004)
w/c and a/c are water/cement and aggregate/cement ratios, respectively. The symbols 𝜌𝑐, 𝜌 𝑤, and
𝜌 𝑎 represent density of cement, water and aggregates, respectively

Diffusivity
Measured with Wicke-Kallenbach type of apparatus (Papadakis et al., 1990)
14
𝐷𝑒.𝐶𝑂2 = (1.64 × 10 −6)𝜀 𝑝
1.8 1 −
𝑅𝐻
100
2.2
𝜀 𝑝 =
𝜌𝑐
𝜌 𝑤
𝑤
𝑐
− 0.3
1 +
𝑤
𝑐
𝜌𝑐
𝜌 𝑤
[CO2] =42 YCO2
YCO2 is the ambient volumetric carbon dioxide content (0.03-0.05%)
In molar concentration (mol/m3)
gas porosity of hardened cement paste

Experimental Works
 Stages of lab works
15
Stage One:
Parent material
Material Tests
Particle Size Distribution
(PSD)
Plasticity Indexes: LL, PL
Compaction
CRB material
Permeability
Stage Two:
Fly ash replacement
Material Tests
Compaction
ICC, TST
UCS , MR
Wet/Dry Cycles
S2: C=0.7% , F=1.3%
S3: C=0.9% , F=1.1%
S4: C=1.1% , F=0.9%
S5: C=1.3% , F=0.7%
S6: C=1.5% , F=0.5%
S1: C=0.5% , F=1.5%

Experimental Works
 Stages of lab works
16
Stage Three:
Nano silica incorporation
Material Tests
Shrinkage
UCS , MR
Wet/Dry Cycles
S2N3: C=0.7% (N=0.6%)
, F=1.3%
S2N4: C=0.7% (N=0.9%) ,
F=1.3%
S3N2: C=0.9% (N=0.3%) ,
F=1.1%
S3N3: C=0.9% (N=0.6%)
, F=1.1%
S3N4: C=0.9% (N=0.9%)
, F=1.1%
S2N2: C=0.7% (N=0.3%)
, F=1.3%
Material Tests
UCS , MR
SEM Imaging
S2N3: C=0.7% (N=0.6%)
, F=1.3%
S2N4: C=0.7% (N=0.9%) ,
F=1.3%
S3N2: C=0.9% (N=0.3%) ,
F=1.1%
S3N3: C=0.9% (N=0.6%)
, F=1.1%
S3N4: C=0.9% (N=0.9%)
, F=1.1%
S2N2: C=0.7% (N=0.3%)
, F=1.3%
Stage Four:
Accelerated Carbonation

Experimental Works
 Particle Size Distribution & Plasticity Indexes
17
Test type Results
Specification
Limits
Test Method
Liquid limit, LL 20.2% 25 % AS 1289.3.1.2
Plastic limit, PL 18.3% -- AS 1289.3.2.1
Plasticity Index, PI 1.9% --- AS 1289.3.3.1
Linear shrinkage, LS 1.7% 0.4% - 2% AS 1289.3.4.1
0
10
20
30
40
50
60
70
80
90
100
110
0.1 1 10 100 1000
Passing(%) Particle Size (µm)
Cement
Fly ash
Particle size of fly ash and cement
(Laser diffraction method)

Laboratory works
 Initial Consumption of Cement (ICC)
According to BS 1924: part 2 (BSI, 1990)
18
Cement
(%)
pH
0.5 12.54
0.7 12.70
0.9 12.74
1.1 12.82
1.3 12.84
1.5 12.88
pH versus cement content in CRB material
Initial Cement Consumption (ICC) tests

Laboratory works
 Unconfined Compression Strength (UCS)
According to standard test method AS 1141.51-1996
19
UCS tests results
Batch
7 days 28 days
Elasticity
Modulus
(MPa)
UCS
(kPa)
Elasticity
Modulus
(MPa)
UCS
(kPa)
S1 174 606 220 746
S2 191 628 230 874
S3 200 711 240 1009
S4 266 1002 350 1419
S5 316 1059 400 1465
S6 406 1349 404 1759

Laboratory works
 Accelerated carbonation condition facilitate
According to NTbuild 357 test method (Nordtest, 1989)
suggests using CO2 concentration of 3% and
a RH of 50% for accelerated carbonation experiments
20
Cylindrical specimens in accelerated carbonation chamber
A typical accelerated carbonation set-up (Atis, 2003)

Laboratory works
 Inclusion of nanosilica
Shrinkage is caused by pores with a size range from micropores to mesopores (i.e. between 2.5 ηm and
30 ηm in size)
21
Suction vs. pore size distributions in cement paste of CRB
mixtures Chakrabarti, S. (2004)
Relation of shrinkage to (A) Total porosity and
(B) Volume of pores ≤0.03 μm (Bentur, 1980)

Laboratory works
 Carbonation depth
According to NTbuild 357 test method (Nordtest, 1989)
suggests using CO2 concentration of 3% and
a RH of 50% for accelerated carbonation experiments
22
Phenolphthalein spraying at 7 days, 3% CO2, specimens of S2 (left) and
S2N3 (right)
Carbonation at 3 days (left) and 14 days (right) at 3% CO2, S3N4

Laboratory works
 Carbonation depth estimation
23
Batch
Cement
Content
(%)
OMC (%)
Dry Unit Weight
(Kg/m3)
Aggregate
Weight
(Kg), a
Cement
Weight
(Kg), c
Water
Weight
(Kg), w
a/c w/c
S1 0.5 7.2 2300.0 2288.5 11.5 167.0 200.0 14.4
S2 0.7 6.8 2310.0 2293.8 16.2 157.8 142.9 9.7
S3 0.9 6.8 2318.0 2297.1 20.9 157.8 111.1 7.6
S4 1.1 6.6 2325.0 2299.4 25.6 153.1 90.9 6.0
S5 1.3 6.5 2330.0 2299.7 30.3 150.8 76.9 5.0
S6 1.5 6.3 2345.0 2309.8 35.2 146.2 66.7 4.2
Details of different batches constituents in stage one

Results
 Carbonation depth records
24
Measured depth of ambient carbonation vs. square root of time at RH=50% (Set of
Batch S2)
Measured depth of ambient carbonation vs. square root of time at RH=50% (Set of
Batch S3)

Results
 Carbonation depth records
25
Measured carbonation constant for different S2 batches, 𝐾𝑐(mm/day^0.5)
S2
(N=0.0%)
S2N2
(N=0.3%)
S2N3
(N=0.6%)
S2N4
(N=0.9%)
7.47 7.12 6.70 6.32
S3
(N=0.0%)
S3N2
(N=0.3%)
S3N3
(N=0.6%)
S3N4
(N=0.9%)
7.17 6.86 6.56 6.06
Kc
(mm/day0.5)
Measured carbonation constant for different S3 batches, 𝐾𝑐 (mm/day^0.5)

Results
 Carbonation depth records (Comparisons)
26
Kc
(mm/day0.5)

Other Findings (UCS)
27

Other Findings (Mr)
28
Mr results for carbonated samples in stage two, θ=205 kPa Mr results for carbonated samples in stage two, θ=400 kPa

Other Findings (Mr)
29
ln 𝑀𝑟𝑐 = 𝑖. 𝑇 + 𝑗. 𝐶 + 𝑘. 𝑁 + 𝑙
ln
𝑀𝑟𝑐
𝑈𝐶𝑆28𝑑𝑎𝑦𝑠
= 𝑖. 𝑇 + 𝑗. 𝐶 + 𝑘. 𝑁 + 𝑙
ln
𝑀𝑟𝑐
𝑈𝐶𝑆𝐶28𝑑𝑎𝑦𝑠
= 𝑖. 𝑇 + 𝑗. 𝐶 + 𝑘. 𝑁 + 𝑙
Where θ is bulk stress (kPa), C is cement content (%), N is nano content (%) and T is the age of a sample
during curing (day). UCSC of a carbonated specimen and I,j,k,l are constants
ln
𝑀𝑟𝑐
𝑈𝐶𝑆7𝑑𝑎𝑦𝑠
= 𝑖. 𝑇 + 𝑗. 𝐶 + 𝑘. 𝑁 + 𝑙

Other Findings (Wet/Dry cycles)
30
Wet/dry cycle tests for batch S2 with added nano silica Wet/dry cycle tests for batch S3 with added nano silica

Other Findings (Shrinkage)
31
Horizontal comparator (Cat. No. 55-C0115/9.Con)
The underlying idea is to have multiple narrow cracks rather than limited wide cracks. Nanosilica added material have
less than 310 micro strain for coarse material which is suggested by George (2002) upon records by PCA

Conclusions
 Carbonation progress is predictable for soil cement materials in
general
 Analytical carbonation model displays a high potential for
reasonable estimations.
 This model has capacity for improvement by inclusion of details
for soil and other supplementary products.
 Analytical carbonation model underestimate carbonation rates
32

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