Carbonation

Handbook of Alkali-activated Cements, Mortars and Concretes. http://dx.doi.org/10.1533/9781782422884.3.319Copyright 2015 Elsevier Ltd. All rights reserved.

12The resistance of alkali-activated cement-based binders to carbonation S. A. BernalUniversity of Sheffield, Sheffield, UK

12.1 Introduction

The chemical reaction between a cement-based material and carbon dioxide (CO2) is referred to as carbonation, and is one of the most harmful degradation processes that can drastically affect the long-term durability of civil infrastructure (Hobbs, 2001; Glasser et al., 2008). A truly sustainable material must be durable, and therefore efforts have been focused in the past decade to understand the changes induced by carbonation in the microstructure of alkali-activated materials, and its consequent effects on permeability and mechanical strength, in order to predict service life performance (Bernal and Provis, 2014). Carbonation of ordinary Portland cements (OPC) takes place when CO2 from the atmosphere diffuses through the pore network of the material, and dissolves in the pore solution forming HCO3

. This anion is a weak acid, and reacts with the calcium-rich hydration products present in the matrix, mainly the portlandite (Ca(OH)2), calcium silicate hydrate (C-S-H), calcium aluminate hydrates (C-A-H) and ettringite (Johannesson and Utgenannt, 2001; Fernndez-Bertos et al., 2004), promoting the formation of calcium carbonate polymorphs through a decalcification process. This leads to the decay of the strength-giving phases and a drop in the internal pH of the system, which facilitates the development of corrosion of steel components in reinforced concrete materials (Poonguzhali et al., 2008). In alkali-activated materials, the mechanism of carbonation is not yet fully understood, but it has been demonstrated that it is fundamentally a chemically controlled mechanism that occurs in two steps: (1) carbonation of the pore solution leading to a reduction in pH and the eventual precipitation of Na-rich carbonates, followed by (2) the decalcification of Ca-rich phases (mainly C-S-H, as portlandite usually does not form in these systems) and carbonation of secondary reaction products present in the system (Bernal et al., 2012, 2013). These materials usually perform poorly when tested under accelerated carbonation conditions compared with Portland cement-based products; however, natural carbonation rates as low as 1 mm/year have been identified (Shi et al., 2006) in aged structures based on alkali-activated binders. This indicates that the accelerated carbonation testing methods applied to alkali-activated materials are not accurately replicating what is experienced under

Handbook of Alkali-activated Cements, Mortars and Concretes320

natural carbonation conditions, and raises the need for further examination of the testing methods themselves.

12.2 Testing methods used for determining carbonation resistance

The relatively low concentration of CO2 in the atmosphere (0.030.04%) makes carbonation a slow process in dense and chemically stable cementitious materials. This has led to the development of accelerated testing methods exposing the material to high CO2 concentrations to induce carbonation. This is usually achieved through the use of climatic chambers where the exposure conditions such as temperature, relative humidity (RH) and concentration of CO2 can be completely controlled. Table 12.1 shows a summary of the testing methods and protocols used for the assessment of the carbonation resistance of cementitious materials. It is important to note that carbonation resistance of alkali-activated materials has generally been tested using the same methods applied for Portland cement testing, but their applicability to these alternative binders still needs to be validated. The reproducibility and repeatability of the results obtained by following different accelerated carbonation testing protocols has been strongly questioned (Sanjun et al., 2003), and therefore comparison between carbonation results reported in different studies must be approached with care. It is evident that the accelerated carbonation conditions vary significantly depending on the protocol adopted, and in those cases where very high concentrations of CO2 are used, it is important to consider the disruption suffered by the material, and to question the real meaning of the results in giving a good representation of a natural carbonation process. Accelerated carbonation results need then to be understood as an indicator of the potential durability of materials with comparable chemistry, when tested under similar exposure conditions. The phenolphthalein method is widely used by the cement community to determine carbonation front; however, its applicability to the assessment of modern blended cements and alkali-activated materials is also questionable. This method is based on the changes in pH expected to occur in the specimens as a consequence of the CO2 exposure. Considering the chemical differences between Portland cements and alkali-activated materials (i.e., the lack of portlandite (Ca(OH)2) as a reaction product in most alkali-activated binders), changes in the pH of the pore solution can be easily registered using this method, instead of real decomposition via decalcification of the binding phases due to carbonation. The effect of the different solvents (distilled water/ethanol) and concentrations used for the preparation of the phenolphthalein indicator in each of the carbonation testing methods described in Table 12.1 is largely unknown, with regard to the actual pH changes in the material. It is possible that this leads to different results in terms of measured carbonation depths, especially in alkali-activated

The resistance of alkali-activated cement-based binders to carbonation 321

materials, as a water-rich solution might promote the redissolution of dried pore solution remaining in the material after carbonation exposure, and reveal a fully alkaline surface, even though some chemical reaction with CO2 has occurred. This is one limitation related to assessment of the susceptibility to carbonation of cementitious materials, especially alkali-activated binders, via accelerated carbonation testing. Consequently, the development and validation of testing protocols to estimate more accurately the long-term performance of these materials is required.

Table 12.1 Summary of accelerated test methods

Test Sample preconditioning required Indicator Exposure conditions

BS EN 13295:2004

Specimens covered with a plastic film for 24 h, then demoulded and sealed again with a plastic film for 48 h, followed by curing of the specimens under water at 21 2C for 27 days. Afterwards the samples should be brought to an even moisture content, which is achieved by storing the samples at 21 2C and 60 10 RH until constant weight, for a minimum of 14 days.

1 g of phenolphthalein dissolved in 70 mL of ethanol, diluted to 100 mL with distilled or deionised water

[CO2]: 1%, T : 21 2CRH: 60 10%

RILEM CPC-18

Not specified Solution of 1% phenolphthalein in 70% ethanol

[CO2]: Not specifiedT : 20CRH: 65%

Nordtest Method: NT Build 357

Specimens are stripped 1 day after casting, and cured in water at 20 2C for 14 days, then cured in air at 50 5% RH, 20 2C until reaching a total of 28 days of curing

1 g phenolphthalein dissolved in 500 mL of distilled/ion exchanged water, and 500 mL ethanol

[CO2]: 3%, T: Not specifiedRH: 5565%

Portuguese Standard LNEC E391

Samples cured submerged in water for 14 days at 20 2C, and stored in an enclosed environment at 50 5% RH and 20 2C until 28 days

0.1% of phenolphthalein in an alcoholic solution

[CO2]: 5 0.1% T: 23 3C RH: 5565%

French test method AFPC-AFREM (1997)

Specimens cured for 28 days are saturated with water prior to CO2 exposure, and then oven dried at 40C for 2 days.

0.1% of phenolphthalein in an alcoholic solution

[CO2]: 50%, T: 20CRH: 65%


12.3 Factors controlling carbonation of cementitious materials

Carbonation of cements is controlled by the diffusivity and reactivity of the CO2 within the bulk matrix (Fernndez-Bertos et al., 2004), which is strongly dependent on the transport properties of the material, as well as the chemistry of the binding phases. Diffusivity of gaseous CO2 is affected by the interconnectivity of the pore network and the carbonation exposure conditions, including CO2 concentration, relative humidity and temperature (Houst and Wittmann, 1994; Fernndez-Bertos et al., 2004). The reactivity of the CO2 will depend on the CO2 concentration, as well as the type of binder (Goi et al., 2002), the gel maturity and pore solution chemistry (Fernndez-Bertos et al., 2004), as this controls the nature and chemistry of the reaction products that will be present over the time of service, and consequently their susceptibility to react with CO2. In alkali-activated materials it could be expected that the diffusivity of CO2 is controlled by the same variables as identified in conventional Portland cements, as this is a physically controlled mechanism that is mostly driven by the permeability of the material. However, the reactivity of CO2 in these alternative binders strongly differs from what has been observed for Portland cements, as the chemistry and nature of reaction products forming is quite different, as will be discussed in the following sections.

12.4 Carbonation of alkali-activated materials

12.4.1 The role of exposure conditions

There are a limited number of published studies evaluating carbonation of alkali-activated materials, but there seems to be a general agreement that these materials are more susceptible to carbonation than conventional Portland cements, when tested under accelerated carbonation conditions, which is one of the major perceived limitations facing their adoption on an industrial scale. Byfors et al. (1989) published one of the first studies of carbonation of alkali-activated materials, and identified that higher relative humidities (80%) promoted lower carbonation rates than identified in specimens carbonated at 50% relative humidity, and carbonation in F-concretes (plasticised alkali silicate-activated granulated blast furnace slag) is more intense when compared with OPC samples formulated to achieve comparable compressive strengths. Similar results were obtained by Bakharev et al. (2001), who observed a higher susceptibility to carbonation (associated with higher carbonation depths measured through phenolphthalein method) in concretes based on alkali-activated slag than in Portland cement concretes exposed to carbonated water (0.35 m solution of NaHCO3). In a later study, Deja (2002) identified comparable carbonation depths in alkali-activated slag mortars and concretes, and in reference samples based on Portland


cement, with increased compressive strengths at longer times of exposure to CO2. These results were attributed to the refinement of the pore structure in both alkali-activated slag and Portland cement, associated with the precipitation of carbonates forming as the carbonation reaction progresses. It is important to note that the specimens were accelerated carbonated at a relative humidity of 90%, and in an atmosphere of 100% CO2, and therefore the results of this particular study need to be interpreted with care when compared with natural exposure conditions. At very high relative humidity it is expected that the pores are fully saturated with moisture, and therefore, even using high CO2 concentrations, the diffusivity of this gas through the pore network will be hindered, in both alkali-activated slag and Portland cement samples. This will reduce the likelihood of developing a carbonation process sufficiently representative to give a good indication of how these materials will perform under natural conditions during service. Carbonation of cementitious materials is generally faster at intermediate relative humidity (5070%), and decreases at higher and lower relative humidities (Papadakis et al., 1991; Houst, 1996; Galan et al., 2013). High humidity increases the fraction of pores filled with water, hindering the diffusion of gaseous CO2, while at low humidity the pore network will not be sufficiently moist to promote the solvation and hydration of the carbon dioxide to form carbonic acid (Houst and Wittmann, 1994). Under intermediate moisture conditions, both reaction kinetics and diffusion of CO2 are favoured, and therefore acceleration of the carbonation process is observed (Fernndez-Bertos et al., 2004; Galan et al., 2013). Bernal et al. (2014a) evaluated the effect of exposure conditions (relative humidity and CO2 concentration) on the progress of accelerated carbonation of alkali-activated slag/metakaolin blended concretes, showing that the progress of carbonation is slightly higher when the test was conducted at 65% relative humidity, compared with specimens carbonated at relative humidities of 50% or 80%, consistent with that identified in conventional Portland cement; however, after longer periods of carbonation testing, the effect of the relative humidity became less pronounced. It is noted that in these alternative binders, the role of the relative humidity during accelerated carbonation testing goes far beyond the effect it can have in the saturation of the pore network and diffusivity of CO2. This is related to a number of reasons, largely associated with the stability of the gel with respect to changes in humidity. Alkali-activated slag binders can be more susceptible to shrinkage-related processes than Portland cement (Palacios and Puertas, 2007; Collins and Sanjayan, 2000, 2001), especially at early times of curing (Chi et al., 2012), and the extent of shrinkage is strongly influenced by the nature and concentration of the alkaline activator (Melo Neto et al., 2008). Dry conditions promote desiccation of the reaction products, especially in alkali-activated slag, leading to structural changes (Ismail et al., 2013) and resulting in the superficial microcracking of the material, which facilitates the ingress of CO2. Consequently, during the pre-conditioning of the specimens prior to accelerated carbonation testing, as required by the available standards and protocols shown in Table 12.1, it is likely that severe changes in the superficial permeability of the material take place as a result of drying shrinkage.


This can provide misleading indications regarding the mechanism of carbonation, compared to what can be experienced under natural carbonation conditions. In both Portland cement (Castellote et al., 2009) and alkali-activated materials (Bernal et al., 2013), it has been identified that the concentration of CO2 during accelerated carbonation testing plays a key role in inducing different structural changes in the binding products, and therefore, in the mechanism of accelerated carbonation. Changes in the pore solution of Portland cement carbonated specimens carbonated under different CO2 concentrations and relative humidities have also been identified (Anstice et al., 2005). In alkali-activated cements, significant differences in the total porosity and capillary structure in these materials were observed as the CO2 concentration of exposure increased from 1% to 3% (Bernal et al., 2014a). A recent study (Bernal et al., 2012) has demonstrated that the CO2 concentration also affects the carbonation of the pore solution, as slight changes in temperature, relative humidity and CO2 concentration lead to modification of phase equilibria in the system Na2CO3NaHCO3-CO2-H2O that can describe the carbonated pore solution of alkali-activated materials (Figure 12.1). In alkali-activated binders it has been identified (Bernal et al., 2012, 2013) that under atmospheric CO2 concentrations the formation of natron (Na2CO310H2O) is favoured; however, under accelerated carbonation testing conditions (CO2 concentrations between 1% and 100%) the formation of nahcolite (NaHCO3) prevails. Natron has a higher molar volume than nahcolite, meaning that under accelerated carbonation conditions nahcolite will fill much less space, and thus provide a greatly reduced degree of pore blockage in an alkali-activated binder than what could be expected under natural carbonation conditions. This, along with the differences in cracking due to sample conditioning as discussed above, indicates that the permeability developed by the material under natural carbonation conditions will differ from what is promoted under accelerated carbonation testing. Modifications of the carbonate/bicarbonate phase equilibrium favouring formation of bicarbonates (Figure 12.1) will lead to a more notable decrease in pH upon carbonation than would be observed in natural CO2 environments, by as much as 2 pH units (Bernal et al., 2012). This will then render the pore solution environment in an accelerated test far more damaging to embedded steel reinforcing than is the case in actual service conditions.

12.4.2 The role of the binder composition

The mechanism of carbonation in alkali-activated materials is strongly dependent on the type of precursor used (slag or fly ash) (Bernal et al., 2013) and the nature and concentration of the activator used (Bernal et al., 2014c; Palacios and Puertas, 2006) as these parameters control the type of the reaction products formed. Puertas et al. (2006) observed higher accelerated carbonation depths in slag-based mortars activated with sodium silicate than in sodium hydroxide activated specimens. This was mainly attributed to the differences in the composition and structure of the C-S-H product forming in each system. In the case of the silicate-activated slags the


Content of species (mol/kg H

2

O)

Content of species (mol/kg H

2

O)

0.00

10.

001

0.01

0.01

0.1

0.1

11

1010

0.01

0.

1 1

10N

aOH

add

ed (

mol

/kg

H2O

)0.

01

0.1

1 10

NaO

H a

dded

(m

ol/k

g H

2O)

4% C

O2

Nah

colit

e

Nah

colit

eN

atro

n

Nat

ron

Mag

nesi

teM

agne

site

HC

O3 (

aq)

HC

O3 (

aq)

Na+

(aq

)

Na+

(aq

)

Hun

tite

Hun

tite

CaC

O3

CaC

O3

CO

32

(aq)

CO

32

(aq)

0.04

% C

O2

Fig

ure

12.1

Dif

fere

nces

in

phas

e as

sem

blag

es c

alcu

late

d fr

om t

herm

odyn

amic

sim

ulat

ions

of

carb

onat

ion

of N

aOH

sol

utio

ns,

as a

fun

ctio

n of

N

aOH

con

cent

ratio

n an

d C

O2

part

ial

pres

sure

. Dat

a fr

om B

erna

l et

al.

(201

2).


C-S-H had a lower Ca/Si ratio (~0.8) than those formed when NaOH was used (Ca/Si ratio ~1.2). The higher Ca/Si ratio, along with the reduced silicate chain length observed in NaOH-activated slags, might favour the formation and precipitation of an increased amount of carbonate products to fill pore spaces when compared to silicate-activated slag products, and this could influence the diffusivity of CO2 within the material. Natron and the calcium carbonate polymorphs calcite, vaterite and aragonite were identified as the main crystalline accelerated carbonation products of these silicate-activated slag binders (Palacios and Puertas, 2006). Bernal et al. (2010) also determined the carbonation products forming in accelerated carbonated silicate-activated slags, but in that study calcite was the only calcium carbonate polymorph identified, along with trona (Na3(CO3)(HCO3)2H2O). The differences in the carbonation products forming in these materials are mainly attributable to the exposure conditions used in each study. Specifically, the formation of trona will be favoured over natron with slight increments in the exposure temperature, independent of the CO2 concentration of exposure (Bernal et al., 2012). The Mg-Ca carbonate huntite (Mg3Ca(CO3)4) has also been observed as an accelerated carbonation product derived from the degradation of hydrotalcite (one of the secondary products in these binders) in the presence of high CO2 concentrations (Bernal et al., 2013). Most recently it was observed (Bernal et al., 2014b) that the MgO content of the slag influences the extension and the mechanism of carbonation of alkali-activated slags, so that an increased content of MgO in the slag promoted a significant reduction in the carbonation extent. This is associated with the formation of layered double hydroxides with a hydrotalcite-type structure as a secondary reaction product in systems with sufficient content of MgO (>5 wt.%) (Bernal et al., 2014b). Layered double hydroxides are materials that have the capacity to absorb CO2 (Leon et al., 2010), and therefore it could be expected that a larger formation of this particular phase in these systems significantly contributes to enhancing the performance of alkali-activated slag binders when exposed to high CO2 concentrations. Prior to accelerated carbonation, silicate-activated slag pastes present a very cohesive and homogeneous structure as shown in Figure 12.2(a). In contrast, the carbonated paste (Figure 12.2(b)) exhibits a highly heterogeneous and porous structure. The surface of the carbonated pastes usually shows crystalline-like particles with dimensions of a few micrometres, accompanied by more irregular-shaped particles, identified as calcite. Chemical analysis of these pastes (Figure 12.2(c)) shows that the carbonation of the paste leads to the decalcification of the C-A-S-H type gel, along with the formation of a sodium-rich aluminosilicate-type product. These structural changes lead to the increased porosity and the reduced mechanical strength usually identified in accelerated carbonated silicate-activated slags. Even though accelerated carbonation testing of alkali-activated slag materials is more damaging than is identified in Portland cement, it has been observed (Bernal et al., 2011) that an increased paste content in these concretes reduces the carbonation depth, so that the carbonation depths are comparable to those obtained in Portland cement concretes produced with similar mix designs. A similar trend has been identified in naturally carbonated silicate-activated slag concretes as shown


(a) (b)

(c) Non-carbonatedCarbonated

0.73 1.79 2.85 3.91 4.97Energy (keV)

Ca

Au

Al

Na

O Si

Figure 12.2 SEM images of silicate-activated slag binders before (a) and after (b) 1000 h exposure to 1% CO2, and corresponding EDX data (c).

400 500 400 500Binder content (kg/m3)

w/b ratio 0.48w/b ratio 0.42

7 ye

ars

natu

ral c

arbo

natio

n de

pth

(cm

)

2.5

2.0

1.5

1.0

0.5

0.0

Figure 12.3 Natural carbonation depths of aged silicate-activated slag concretes, as a function of mix design. Error bars correspond to the value of one standard deviation among 16 measurements. Data from Bernal et al. (2014c).


in Figure 12.3, and this effect seems to be more significant when the concretes are formulated with lower water/binder ratios (Bernal et al., 2014c). The carbonation depth is also strongly dependent on the activation conditions, specifically the concentration of the activator, as higher concentration of alkalis in the pore solution is likely to attract a higher concentration of CO2, favouring the formation of carbonic acid and carbonates, and therefore accelerating the carbonation reaction (Bernal et al., 2014c). This highlights that it is possible to tailor durability of alkali-activated materials to promote desired performance. Accelerated carbonation testing methods are designed and intended to develop a better understanding about what is likely to occur when the material is in service. The study of de Castro et al. (2004) found a square-root dependence of carbonation rate on CO2 concentration in Portland cement concretes when assuming diffusion control of carbonation, enabling comparison of the outcomes of the accelerated and natural carbonation testing for these concretes. Correlating accelerated and natural carbonation results of silicate-activated slag concretes using the de Castro equation, it has been demonstrated that the accelerated test is notably overpredicting the natural carbonation rate in these systems (Bernal et al., 2014c). The difference in the correlation between natural and accelerated carbonation between alkali-activated slag concretes and Portland cements has also been reported in Bernal et al. (2012), where a higher degree of aggressiveness of the accelerated test is observed in alkali-activated systems when the concentration of CO2 increases above the natural concentration, compared with Portland cement concretes exposed under the same carbonation environment. This suggests that under accelerated carbonation testing conditions, if an alkali-activated concrete shows similar carbonation depths to a Portland cement concrete, it is likely that the durability of the alkali-activated material under natural carbonation conditions (and thus the service life) would be considerably greater. Carbonation of alkali-activated fly ash, also referred to as fly ash geopolymers, has not been as broadly studied. Criado et al. (2005) identified the formation of nahcolite (sodium bicarbonate) in samples cured under atmospheric conditions, which was associated with the carbonation of the alkalis in the pore solution. This is consistent with a recent study (Bernal et al., 2013) assessing carbonation of fly ash geopolymers at different concentrations of CO2 (15%). Formation of sodium carbonate heptahydrate (Na2CO37H2O) has been observed in young fly ash geopolymer specimens (1 day of curing) carbonated at 5% CO2, which is an indication that carbonation in these systems promotes an internal CO2 concentration gradient, associated with a more rapid drop in the internal relative humidity in the early stage of the CO2 exposure, before a high CO2 concentration is able to diffuse through the pore network to the binder. Structural changes in the geopolymer gel in carbonated specimens were not detected via 29Si and 27Al MAS NMR spectroscopy; however, carbonated samples presented a marked reduction in mechanical strength. The partial substitution of slag for fly ash in alkali-activated binders promotes the formation of two distinctive binding products: a C-A-S-H gel formed through alkali silicate activation of slag, and an N-A-S-H gel (Puertas et al., 2000, Ismail et al., 2014). Under accelerated carbonation exposure, decalcification of the C-A-S-H


type gel is identified, the products of which coexist with an apparently unaltered N-A-S-H type gel resulting from the activation of fly ash, as well as various alkali and alkali-earth carbonate precipitates (Bernal et al., 2013).

12.5 Remarks about accelerated carbonation testing of alkali-activated materials

The need to develop a standard methodology to assess carbonation performance of alkali-activated materials is evident. The availability of such a method is essential to develop a better understanding of the factors governing the mechanism of degradation of these materials. The information reported in the open literature must be interpreted considering that this is an indicator of the performance of materials produced with similar formulations and evaluated under comparable environmental conditions, as accelerated carbonation results of alkali-activated materials are strongly dependent on the carbonation testing environment parameters such as relative humidity, temperature and CO2 concentration. It is not recommended to carry out accelerated carbonation testing of alkali-activated binders at CO2 concentrations higher than 1% CO2, and further work is required to determine accurate recommendations regarding other aspects of the testing procedure. The relatively low natural carbonation rates identified in alkali-activated concretes suggest that these materials have a good resistance to carbonation during their service life, and accelerated carbonation tests are not replicating what is likely to take place in the long term. Changes in the carbonation reaction equilibria take place under accelerated carbonation conditions, especially in the interaction between CO2 and pore solution, promoting poor performance results despite the low permeability and good mechanical strength identified in the specimens before accelerated carbonation testing. This highlights that further research in this area needs to be undertaken to determine how the testing conditions are affecting the outcomes of the tests conducted. Little attention has been given to those factors that can be strongly affecting the performance of alkali-activated materials when assessed through accelerated carbonation tests, such as the effect of pre-conditioning of the specimens inducing desiccation of the hydrated products, carbonation shrinkage induced by decalcification of the binding products, and the chemistry of the pore solution. These factors can strongly influence how the phenolphthalein indicator might work, modifying the outcomes of tests. This suggests that further research in developing methods for measuring the progress of the carbonation front in alkali-activated materials needs to be conducted. Efforts in this area are being led and coordinated through the RILEM technical committee TC 247-DTA (Durability testing of alkali-activated materials).


References

Anstice, D. J., Page, C. L. and Page, M. M. 2005. The pore solution phase of carbonated cement pastes. Cement and Concrete Research, 35, 377383.

Bakharev, T., Sanjayan, J. G. and Cheng, Y. B. 2001. Resistance of alkali-activated slag concrete to carbonation. Cement and Concrete Research, 31, 12771283.

Bernal, S. A. and Provis, J. L. 2014. Durability of alkali-activated materials: progress and perspectives. Journal of American Ceramic Society, 97, 9971008.

Bernal, S. A., Meja de Gutierrez, R., Rose, V. and Provis, J. L. 2010. Effect of silicate modulus and metakaolin incorporation on the carbonation of alkali silicate-activated slags. Cement and Concrete Research, 40, 898907.

Bernal, S. A., Meja de Gutierrez, R., Pedraza, A. L., Provis, J. L., Rodrguez, E. D. and Delvasto, S. 2011. Effect of binder content on the performance of alkali-activated slag concretes. Cement and Concrete Research, 41, 18.

Bernal, S. A., Provis, J. L., Brice, D. G., Kilcullen, A., Duxson, P. and Van Deventer, J. S. J. 2012. Accelerated carbonation testing of alkali-activated binders significantly underestimate the real service life: The role of the pore solution. Cement and Concrete Research, 42, 13171326.

Bernal, S. A., Provis, J. L., Walkley, B., San Nicolas, R., Gehman, J. D., Brice, D. G., Kilcullen, A., Duxson, P. and Van Deventer, J. S. J. 2013. Gel nanostructure in alkali-activated binders based on slag and fly ash, and effects of accelerated carbonation. Cement and Concrete Research, 53, 127144.

Bernal, S. A., Provis, J. L., Meja de Gutirrez, R. and Van Deventer, J. S. J. 2014a. Accelerated carbonation testing of alkali-activated slag/metakaolin blended concretes: effect of exposure conditions. Materials and Structures, in press, DOI: 10.1617/s11527-014-0289-4.

Bernal, S. A., San Nicolas, R., Myers, R. J., Meja de Gutirrez, R., Puertas, F., Van Deventer, J. S. J. and Provis, J. L. 2014b. MgO content of slag controls phase evolution and structural changes induced by accelerated carbonation in alkali-activated binders. Cement and Concrete Research, 57, 3343.

Bernal, S. A., San Nicolas, R., Provis, J. L., Meja de Gutirrez, R. and Van Deventer, J. S. J. 2014c. Natural carbonation of aged alkali-activated slag concretes. Materials and Structures, 47, 693707.

Byfors, K., Klingstedt, G., Lehtonen, H. P. and Romben, L. 1989. Durability of concrete made with alkali-activated slag. In: Malhotra, V. M. (ed.), 3rd International Conference on Fly Ash, Silica Fume, Slag and Natural Pozzolans in Concrete, ACI SP114. American Concrete Institute, 14291444.

Castellote, M., Fernandez, L., Andrade, C. and Alonso, C. 2009. Chemical changes and phase analysis of OPC pastes carbonated at different CO2 concentrations. Materials and Structures, 42, 515525.

Chi, M.-C., Chang, J.-J. and Huang, R. 2012. Strength and drying shrinkage of alkali-activated slag paste and mortar. Advances in Civil Engineering, 2012, 579732.

Collins, F. and Sanjayan, J. G. 2000. Cracking tendency of alkali-activated slag concrete subjected to restrained shrinkage. Cement and Concrete Research, 30, 791798.

Collins, F. and Sanjayan, J. G. 2001. Microcracking and strength development of alkali activated slag concrete. Cement and Concrete Composites, 23, 345352.

Criado, M., Palomo, A. and Fernndez-Jimnez, A. 2005. Alkali activation of fly ashes. Part 1: Effect of curing conditions on the carbonation of the reaction products. Fuel, 84, 20482054.


De Castro, A., Ferreira, R., Lopes, A. M., Cacudo, O. and Carasek, H. 2004. Relationship between results of accelerated and natural carbonation in various concretes. In: Vzquez, E., Hendriks, C. and Janssen, G. (eds), International RILEM Conference on the use of Recycled Materials in building and Structures, Barcelona. RILEM Publications, 988997.

Deja, J. 2002. Carbonation aspects of alkali activated slag mortars and concretes. Silicates Industriels, 67, 3742.

Fernndez-Bertos, M., Simons, S. J. R., Hills, C. D. and Carey, P. J. 2004. A review of accelerated carbonation technology in the treatment of cement-based materials and sequestration of CO2. Journal of Hazardous Materials, B112, 193205.

Galan, I., Andrade, C. and Castellote, M. 2013. Natural and accelerated CO2 binding kinetics in cement paste at different relative humidities. Cement and Concrete Research, 49, 2128.

Glasser, F. P., Marchand, J. and Samson, E. 2008. Durability of concrete degradation phenomena involving detrimental chemical reactions. Cement and Concrete Research, 38, 226246.

Goi, S., Gaztaaga, M. T. and Guerrero, A. 2002. Role of cement type on carbonation attack. Journal of Materials Research, 17, 18341842.

Hobbs, D. W. 2001. Concrete deterioration: causes, diagnosis, and minimising risk. International Materials Reviews, 46, 117144.

Houst, Y. F. 1996. The role of moisture in the carbonation of cementitious materials. Internationale Zeitschrift fr bauinstandsetzen, 2, 4966.

Houst, Y. F. and Wittmann, F. H. 1994. Influence of porosity and water content on the diffusivity of CO2 and O2 through hydrated cement paste. Cement and Concrete Research, 24, 11651176.

Ismail, I., Bernal, S. A., Provis, J. L., Hamdan, S. and Van Deventer, J. S. J. 2013. Drying-induced changes in the structure of alkali-activated pastes. Journal of Materials Science, 48, 35663577.

Ismail, I., Bernal, S. A., Provis, J. L., San Nicolas, R., Hamdan, S. and Van Deventer, J. S. J. 2014. Modification of phase evolution in alkali-activated blast furnace slag by the incorporation of fly ash. Cement and Concrete Composites, 45, 125135.

Johannesson, B. and Utgenannt, P. 2001. Microstructural changes caused by carbonation of cement mortar. Cement and Concrete Research, 31, 925931.

Leon, M., Daz, E., Bennici, S., Vega, A., Ordoez, S. and Auroux, A. 2010. Adsorption of CO2 on hydrotalcite-derived mixed oxides: sorption mechanisms and consequences for adsorption irreversibility. Industrial and Engineering Chemistry Research, 49, 36633671.

Melo Neto, A. A., Cincotto, M. A. and Repette, W. 2008. Drying and autogenous shrinkage of pastes and mortars with activated slag cement. Cement and Concrete Research, 38, 565574.

Palacios, M. and Puertas, F. 2006. Effect of carbonation on alkali-activated slag paste. Journal of the American Ceramic Society, 89, 32113221.

Palacios, M. and Puertas, F. 2007. Effect of shrinkage-reducing admixtures on the properties of alkali-activated slag mortars and pastes. Cement and Concrete Research, 37, 691702.

Papadakis, V. G., Vayenas, C. G. and Fardis, M. N. 1991. Experimental investigation and mathematical modeling of the concrete carbonation problem. Chemical Engineering Science, 46, 13331338.

Poonguzhali, A., Shaikh, H., Dayal, R. K. and Khatak, H. S. 2008. Degradation mechanism and life estimation of civil structures A review. Corrosion Reviews, 26, 215294.


Puertas, F., Martnez-Ramrez, S., Alonso, S. and Vzquez, E. 2000. Alkali-activated fly ash/slag cement: strength behaviour and hydration products. Cement and Concrete Research, 30, 16251632.

Puertas, F., Palacios, M. and Vzquez, T. 2006. Carbonation process of alkali-activated slag mortars. Journal of Materials Science, 41, 30713082.

Sanjun, M. A., Andrade, C. and Cheyrezy, M. 2003. Concrete carbonation test in natural and accelerated conditions. Advances in Cement Research, 15, 171180.

Shi, C., Krivenko, P. V. and Roy, D. M. 2006. Alkali-Activated Cements and Concretes, Abingdon, Taylor and Francis.

Carbonation

Documents

mechanism of carbonation

carbonation resistancethe

alkaliactivated materials

alkaliactivated binders

natural carbonation

activated cements

handbook of alkali

activated cementbased