Environ. Sci. Technol. 2010, 44, 3181–3186
Sequestration of CO2 by Concrete Carbonation I S A B E L G A L A N , * ,† C A R M E N A N D R A D E , † PEDRO MORA,‡ AND MIGUEL A. SANJUAN§ Eduardo Torroja Institute IETcc-CSIC, Serrano Galvache 4, 28033 Madrid, Spain, Oficemen, Jose Abascal 53, Madrid 28003, Spain, and IECA, Jose Abascal 53. Madrid 28003, Spain
Received November 25, 2009. Revised manuscript received March 3, 2010. Accepted March 3, 2010.
Carbonation of reinforced concrete is one of the causes of corrosion, but it is also a way to sequester CO2. The characteristics of the concrete cover should ensure alkaline protection for the steel bars but should also be able to combine CO2 to a certain depth. This work attempts to advance the knowledge of the carbon footprint of cement. As it is one of the most commonly used materials worldwide, it is very important to assess its impact on the environment. In order to quantify the capacity of cement based materials to combine CO2 by means of the reaction with hydrated phases to produce calcium carbonate, Thermogravimetry and the phenolphthalein indicator have been used to characterize several cement pastes and concretes exposed to different environments. The combined effect of the main variables involved in this process is discussed. The moisture content of the concrete seems to be the most influential parameter.
Introduction One of the main problems related to climate change is the greenhouse effect produced by the partial absorption of infrared radiation emitted by the Earth by the so-called “greenhouse gases”, including CO2. The United Nations Framework Convention on Climate Change defines “sink” as “any process, activity or mechanism which removes a greenhouse gas, an aerosol or a precursor of a greenhouse gas from the atmosphere”. As part of the initiatives undertaken by the cement industry to reduce the greenhouse effect, this work studies the extent of the CO2 sink effect of concrete carbonation. Carbonation of concrete takes place when the CO2 from the atmosphere reacts with the alkaline components of concrete, mainly portlandite, and/or with the CsSsH (hydrated calcium silicate) gel, resulting in the formation of CaCO3. The reaction generally leads to a decrease in the pH of the aqueous phase of the concrete pores, from very alkaline values greater than 12 to values below 8. If the reaction reaches the steel reinforcement, its passive layer may disappear, exposing the steel surface to corrosion. Most of the publications related to carbonation are mainly focused on its relationship with rebar corrosion. Their main objective is to measure and predict the progress of the carbonation front and the evolution of corrosion due to the * Corresponding author phone: +34913020440; fax: +34 913020700; e-mail:
[email protected]. † Eduardo Torroja Institute IETcc-CSIC. ‡ Oficemen. § IECA. 10.1021/es903581d
2010 American Chemical Society
Published on Web 03/12/2010
steel depassivation. The phenolphthalein indicator technique is used to measure the carbonation front, which is actually a pH front that differentiates zones with pH below and above 8-9. Closest to the object of this publication, there are some studies which focus on the amount of CaCO3 formed during natural carbonation process. Leber and Blakey (1) used chemical analysis to estimate the carbonation degree in mortars and concretes, based on the assumption that all absorbed CO2 reacts with the lime to form calcium carbonate. Steinour (2) proposed a formula to calculate the amount of CO2 incorporated by carbonation based on the clinker composition. Thermogravimetry (TG) and differential thermal analysis (DTA) have been used for both qualitative and quantitative studies of the carbonation phenomenon by some authors (3-6). Houst and Wittmann (7) used an induction furnace and an IR analyzer to measure carbonation and concluded that there is no simple corelation between depth measurements and carbonates profiles. All these authors have contributed to better delimit the depth of carbonation, and also to provide information on the amounts of combined CO2. There are also some recent publications regarding the CO2 absorption capability of cement based materials from U.S. (8, 9), Norway (10) and UK (11). One of the most exhaustive studies was carried out by a consortium of research institutes and cement industries from Denmark, Sweden, Norway and Iceland (12-17). This work studies the CO2 absorption capacity of cement based products in these four countries throughout their service life and after a process of demolition and recycling, considering structures of 100 years of total life, with 70 of service life and 30 of secondary life. The percentages of CO2 absorption given by these authors vary depending on the assumptions taken, the experimental measurements on which the studies are based and the calculations used to obtain the results. As it is very complicated to extrapolate values and to generalize laboratory results, the comparison of the results obtained in the different studies is very difficult. The main objective of this study was to estimate the quantity of CO2 that is reabsorbed into cementitious materials due to the carbonation phenomenon, taking into account cements’ composition, environments, type of concrete, and time. The study was based on Spanish cement, concrete uses and applications, and the continental climate in Madrid.
Experimental Section The cements used to fabricate the specimens are given in Table 1. 10 × 10 × 60 mm prismatic paste specimens and 75 × 150 mm cylindrical concrete specimens were produced. Two water/cement ratios (w/c) were used for the mixtures: 0.6 and 0.45. For the specimens with w/c 0.6, cements numbered 1-12 were used. In addition to the 12 cements selected for the 0.6 w/c specimens three more were added for the 0.45 w/c specimens. This explains the ordering of the cements in Table 1, grouped by type of additions. For the specimens with w/c 0.45, all 15 cement types were used. The concrete mix with 0.6 w/c and 300 kg/m3 is considered representative of concrete used for building works, and the one with 0.45 w/c and 400 kg/m3 for civil works. The curing period was 48 h. The specimens were then dried inside for 26 days. After 28 days the specimens were placed in three different environmental conditions: outside exposed to the rain, outside sheltered from the rain, and inside, on the Eduardo Torroja Institute campus in Madrid. As the specimens were put on a grill, all surfaces were exposed to the VOL. 44, NO. 8, 2010 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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TABLE 1. Cements Selected for the Tests ref
cement
clinker %
additions
CaO %
producer
origin
1 2 14 3 4 5 6 7 9 10 13 8 15 11 12
CEM I 42,5R I 42,5R/ SR CEM II/A-L 42,5R CEM II/B-LL 32,5N CEM II/A-M (V-L) 42,5R CEM II/B-M (S-V) 42,5N CEM II/A-P 42,5R CEM II/B-P 32,5N CEM II/A-V 42,5R CEM II/B-V 32,5R CEM IV/B (V) 32,5N CEM II/A-S 52,5N III/A 42,5N/SR III/B 32,5N/SR III/C 32,5N/SR/BC
95-100 95-100 80-94 65-79 80-94 65-79 80-94 65-79 80-94 65-79 45-64 80-94 35-64 20-34 5-19
no additions no additions limestone limestone fly ash, limestone GBFS, fly ash pozzolan pozzolan fly ash fly ash fly ash GBFS GBFS GBFS GBFS
64 63 62 56 57 54 53 49 56 49 41 60 56 46 47
Lafarge-Asland Uniland Cosmos Cemex Portland-Valderrivas Holcim CEISA Cemex Lemona Cosmos Alfa Tudela Veguı´n Tudela Veguı´n Alfa Cemex
Toledo Barcelona Huelva Alicante Madrid Almerı´a Las Palmas Toledo Vizcaya Co´rdoba Santander Leo´n Oviedo Santander Tarragona
atmosphere. The specimens not sheltered from the rain (Figure 1) were never submerged in water, as rain always washed away. In addition to these specimens made specifically for the study, samples from old structures and specimens were taken and analyzed in order to evaluate the effect of time. Three types of concrete specimens made in 1991, 1999, and 2001 were selected. The specimens from 1991 were 7 × 7 × 28 cm prisms fabricated with 395 kg/m3 and six different experimental mixes: two without additions, two with fly ash, one with silica fume, and one with fly ash and silica fume. Plasticizers and superplasticizers were used for all mixes. The specimens were kept outside sheltered from the rain. The specimens from 1999 were 7.5 × 15 cm cylinders fabricated with 400 kg/m3 and microsilica and fly ash additions as well as superplasticizer. These specimens were kept inside. The specimens from 2001 were taken from concrete used to build a house. A standard mix for building works was assumed for making the calculations, cement without additions, 300 kg/m3 and 0.5 w/c. For the first four years these specimens were kept outside exposed to the rain and the rest of the time sheltered from the rain. Two reinforced concrete structures designed by Eduardo Torroja were chosen for taking old samples: the roof of the Zarzuela Hippodrome, built in 1935, and a column from the pergola built in 1951 in the gardens of the Eduardo Torroja Institute. From the documentation available about concrete in Spain before the seventies and from suggestions from experts in the field, it was assumed that, in both cases, cement
FIGURE 1. Specimens Outside Not Sheltered from the Rain. 3182
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without additions, 0.5 w/c and 300 kg/m3 were used. The thickness of the Hippodrome roof varies from 65 cm in the area of the columns to 6 cm at the edges. Samples, approximately 50 mm thick, were taken from both the upper and the lower part of the roof. The upper part is covered by an asphalt layer added after the construction of the structure. In the pergola, the thickness of the columns also varies from approximately 30 to 10 cm. The sample taken from the upper part of one of the columns was about 20 mm thick. All columns were painted some years after the construction and in 1993 some of them were repaired using different methods. The column chosen for the study was repaired with traditional mortar. After one year of exposure, the carbonation depth, that is, the depth at which the pH drops below 8-9, was measured in the new specimens by means of phenolphthalein coloration. From the uncoloured carbonated part a representative sample was taken to perform thermogravimetry (TG) and differential thermal analysis (DTA). These techniques allow the determination of the carbon dioxide present in the sample from the mass lost in the dissociation of calcium carbonate. The quantities of calcium carbonate formed in this “carbonated” front may change with depth; the surface may absorb more CO2 than the inner part. For this study the whole “carbonated” part was taken, that is, the average value of CO2 absorption in the zone with pH lower than 8-9 was considered. Also, the “noncarbonated” part may absorb CO2 even though the pH does not drop below 8, but this absorption is not taken into account. In this sense the “real” CO2 absorption might be underestimated. As the samples’ masses change with time and carbonation due to the uptake and release of water and the uptake of CO2, some calculations were done to obtain all values in percentages of CO2 per gram of cement instead of per gram of sample. For this, samples were also characterized at the age of 28 days, and the amount of cement in the sample (mass that remains after TG calcinations) and the initial CaCO3 content were taken as reference values. In order to express the results in CO2 absorbed per mol of CaO available for carbonation, the CaO content in the different cements was measured by chemical analysis (Table 1). For performing TG in the concrete samples, the “mortar” part was taken, that is, the coarse aggregates were removed from the samples and the fine aggregate/cement mix proportions were assumed to perform the corresponding calculations. The old specimens were also characterized by the same two techniques at their corresponding age. It was possible to determine the carbonation depth in the old specimens
FIGURE 2. Carbonation rates of concrete specimens 0.6 w/c.
FIGURE 3. Carbonation rates of concrete specimens 0.45 w/c. but not in the case of the old structures because the samples taken were not thick enough to perform the coloration test accurately. The characteristic parameters of environmental conditions were regularly measured both inside and outside.
Results Environmental Conditions. The relative humidity (RH) measured inside varied between 24 and 68% with an average value of 38%. Outside it varied between 27 and 97% being the average value 57%. The inside temperature was in the range of 13-25 °C, with an average value of 22 °C, and outside 0-31 °C, with an average value of 16 °C. The CO2 concentration measured inside varied between 500 and 850 ppm. Outside it was almost constant 500 ppm. This high value compared to the average atmospheric concentration is probably due to the highway which is close to the site where the specimens were placed. The daily precipitation varied between 0 and 40 mm. Carbonation Depths and Rates. A similar behavior in the carbonation depth with regard to the environment was found in the paste specimens made for the study. In general, specimens outside sheltered from the rain presented maximum depth after 1 year, appearing colorless throughout the tested area. Specimens kept inside also appeared fully carbonated throughout the cross section, but in this case with very soft pink color, indicating that the pH did not drop below 8. Finally, about half of the specimens kept outside exposed to the rain presented maximum depth colorless, and the other half partial depth with a pink core. In Figures 2 and 3, the rates of carbonation for the concrete specimens with 0.6 and 0.45 w/c in the three exposures are represented. The rate was calculated with the formula x ) k · t1/2. The specimens are grouped according to type of additions, with the reference numbers shown in Table 1.
The results clearly show a higher rate of carbonation in the concretes made with the mixes considered representative of building works (lower cement content) than in the ones made with the mixes representative of civil works. This difference is in some cases as much as double. In general, the specimens that were kept outside sheltered from the rain are the ones with the highest carbonation rates, while the ones that were kept inside present the lowest rate. In this regard, the 0.45 w/c specimens present a more homogeneous behavior than those with 0.6 w/c. It is worth highlighting the increase in carbonation depth with the percentage of addition within some of the groups of cement types; this effect is indicated by arrows in Figures 2 and 3. Concrete specimens 1 and 2 show very similar behavior in the carbonation rate of the front advance in each of the environments, with both w/c ratios. The fact that cement has low C3A and cement 1 has normal C3A content does not appear to have an effect on the carbonation rate. Regarding the old specimens, most of them presented rates lower than 3 mm/year1/2, with four of the 1991 specimens not reaching 1 mm/year1/2. The 1999 specimen is the one which presents the highest rate, close to 5 mm/ year1/2. The carbonation rates are not easily comparable to the data published by some of the authors that have studied the natural carbonation phenomenon from the point of view of calcium carbonate formation (4, 6, 7), as the environmental conditions and type of specimens are very different. However it should be noted that none of the rates published by theses authors exceeds 6.5 mm/year1/2. Quantities of Combined CO2. Figures 3 and 4 represent the molar percentages of CO2 absorbed per mol of CaO in the “carbonated zone” (indicated by the colorless phenolphthalein) after 1 year in the pastes made with 0.6 and 0.45 VOL. 44, NO. 8, 2010 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 4. CO2 quantities absorbed in paste specimens 0.6 w/c.
FIGURE 5. CO2 quantities absorbed in paste specimens 0.45 w/c. w/c, respectively. These values were measured with TG analysis, taking the values at 28 days as references. The behavior of the 0.6 w/c specimens (Figure 4) was very homogeneous with regard to the influence of the environment on their CO2 sequestration capacity. The specimens that absorbed less CO2 were those kept inside, not reaching values higher than 13%. On the contrary, the ones that absorbed more CO2 were those that were outside exposed to the rain reaching values of absorption of 33 mol of CO2 per 100 mols of CaO in the carbonated zone. The specimens that were kept outside sheltered from the rain absorbed between 12 and 23% of CO2 per mol of CaO. These results demonstrate the great importance of the sample moisture content in the combination of CO2. Regarding the 0.45 w/c specimens (Figure 5) the ones kept inside were also those that absorbed less CO2, with the exception of specimen 2 without additions and specimen 4 with fly ash and limestone. However, the specimens that absorbed more CO2 were in half of the cases those sheltered from the rain, and in the other half the ones that were exposed to the rain. The behavior of the two groups of concrete specimens, w/c 0.6 and 0.45, is similar to the paste specimens with 0.6 w/c with regard to the environment. In general, with few exceptions, the specimens of concrete made with w/c 0.45 absorb less CO2 than the specimens made with w/c 0.6, being the percentages of CO2 uptake quite similar to those found in the paste specimens. In the old specimens and structures, the quantities absorbed varied from zero to 36%. From the group of specimens produced in 1991 three of them did not practically absorb CO2 during the exposure time. The other three 17 years old specimens did absorb CO2 but did not reach 14% of absorption, being the specimens made with fly ash the ones that absorbed more CO2. The specimen made in 1999 absorbed less than 10% of CO2 per mol of CaO in nine years. The specimens made in 2001 with a building type of concrete absorbed between 27 and 36% CO2 in seven years. In the tested sample of the Pergola, a quantity of 33% of CO2 absorbed over about 57 years was measured. The two samples from the Hippodrome absorbed very different amounts of CO2: about 30% in the upper part and 3% in the lower part. The difference might be explained as a consequence of the 3184
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difference in humidity between the upper and lower parts of the roof. The humidity in the upper part might have been higher due to its likely exposure to the rain at some points in time. However, this is only a hypothesis. In general, it is very difficult to give an explanation as we do not know exactly about the repairs, alterations and paintings the old structures have undergone throughout their life. Figure 6 represents all the data of CO2 absorbed as a function of time collected in this study, both for specimens made for the study and for the old ones, as well as for the data collected from the literature. In some cases, as the data are expressed in different units, some calculations and estimations have been made to express the results in the same units as the rest of the results in the study. The two horizontal gray and black lines represent the maximum possible absorption according to the proposals of Steinour (2) and Pade and Guimarares (17), respectively. Since these are different samples and different conditions the values can not be directly compared, however, it can be said that in most of the cases absorptions above 50% per mol of CaO in the carbonated part are not reached.
Discussion Indicator Parameters and Characterization Techniques. The depth of carbonation x measured by means of the phenolphthalein indicator and the carbonation rate k are parameters of interest when studying the corrosion of steel reinforced concrete because they help to identify the pH change front and its evolution with time. However, they do not provide information on the amount of calcium carbonate formed since no general relationship between the depths of carbonation and the quantities of calcium carbonate formed was found. Trends in the relationship could only be seen within groups of samples. The amount of CO2 absorbed is also a key parameter not only to calculate the ability of cement based materials to reabsorb CO2, but also to model the progress of carbonation. Using Thermogravimetrical techniques the carbon dioxide absorbed and combined as calcium carbonate can be determined. Other techniques should be used to measure other possible minor contributions to CO2 absorption arising from other phases, and more research should be performed
FIGURE 6. Quantities of CO2 absorbed as a function of time 0-80 years. in the future in order to complement these data and to avoid the underestimation of the CO2 absorption. Influence of the Exposure Environments. Humidity is one of the most influential factors in the advancement of the carbonation front and in the amount of CO2 combined. In general terms, specimens made for the study that were kept outside sheltered from the rain presented higher carbonation depth after one year than those that were outside not sheltered. In contrast, the amounts of CO2 absorbed in this “carbonated” zone were greater in the specimens that were outside exposed to the rain than in the ones kept outside sheltered. These differences are attributed to the degree of water saturation of the pores resulting from the moisture changes that occur inside the concrete as a consequence of the rain-drying cycles. The amount of CO2 combined in the specimens and the carbonation depth reached during the first year of exposure were considerably lower in the internal environment than in the external environment. This result indicates that a higher concentration of CO2 in the interior does not imply a greater sequestration of CO2 in the range of CO2 concentrations considered. The other parameters involved, mainly the relative humidity, appear to have a greater influence. Type of Cement. There are significant differences in the resistance to carbonation (amount combined and carbonated depth) of the different specimens depending on the type of cement used, linked both to the type of additions and to the amount of clinker per m3 of concrete. In general, with increasing amount of clinker, the amount of CaO increases, that is, material subject to carbonate. When introducing additions to the cement, it is important to take into account that the water/clinker ratio will increase, but it is also very important to know the contribution of the additions to the CaO content. By increasing the amount of CaO, the amount of CO2 absorbed increases generally and the depth of carbonation decreases, being the relationship with depth much more clear than the relationship with the combined CO2. Both relationships become more evident when considering the groups of additions separately, and also when dividing them by environments. In any case, it is important to note the presence of exceptions. It can be stated that there is a combined dependence of the type of cement and the environmental conditions on the carbonation. Life Time. There are several models to predict the progress of the carbonation front, mostly based on the solution of Fick’s law. The effectiveness of these models has been experimentally tested on numerous occasions. However, it is important to be cautious when using them as the constants of proportionality depend on many factors.
Regarding CO2 combined there are very few models or proposals. The evolution of CO2 combination with time is not evident. Young samples may have greater uptake than older ones. In general, the ones studied here do not exceed 50% of CO2 absorption (per CaO mol) in the carbonated zone. Composition of Concrete. By increasing the amount of cement in the concrete, both the carbonation depth and the amount of CO2 absorbed decrease, being the main cause for that the decrease in porosity. The fact that the amount of CO2 decreases as the cement content increases indicates that a decrease in porosity has a higher influence than an increase of the amount of carbonatable material. Calculation of CO2 Absorbed. Based on the carbonation depth data, the CO2 absorbed in the carbonated zone, the exposed surface of the concrete, and the mix proportions, the amount of CO2 absorbed per m3 of concrete in a structure can be calculated. The corresponding CO2 absorbed in the carbonated concrete is determined by multiplying the CO2 absorbed per kg of cement in the carbonated zone by the amount of cement in the concrete. On the other hand, by multiplying the carbonation depth by the relationship between exposed surface and concrete volume, the relationship between carbonated concrete volume and total concrete volume is determined. Finally multiplying these two terms, the CO2 absorbed per total concrete volume is calculated. The results can also be expressed per ton of cement produced taking into account the relationship between cement produced and concrete consumed. To express the results per ton of CO2 emitted, the relationship between the amount of cement produced and the amount of CO2 emitted in their production should be considered. As there are not enough available data of surfaces exposed to carbonation and as the cement and concrete market is continuously changing, the calculations of the CO2 sequestration should be done very carefully. Considering the carbonated zone as the region where the pH is lower than 8-9 may underestimate the real CO2 absorption in the whole volume, because, as stated before, there might be absorption as well in the region with higher pH. To obtain more accurate calculations absorption profiles at all depths in the samples should be measured in the future, both in front and behind the pH front. From the data obtained in this study, it can be concluded that the carbonation depth is not a correct indicator of the amount of sequestered CO2. Regarding the parameters influencing the CO2 sequestration, higher water/cement ratio implies normally higher porosity which, in turn, leads to higher CO2 absorption. Within groups with the same type of VOL. 44, NO. 8, 2010 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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additions, the amount of CO2 bound increases with the CaO content. The big differences between exposure sheltered and not sheltered from the rain demonstrate that the moisture content of the concrete is a key parameter in the sequestration of CO2 by natural carbonation. In general, while the influence of the type of cement and the proportion of cement can help to predict the degree of carbonation, these are comparatively less important than the effect of humidity in the process of carbonation.
Acknowledgments This work was supported by the Spanish Ministry of Science and Technology, Oficemen, and CSIC to whom the authors are grateful.
Literature Cited (1) Leber, I.; Blakey, F. A. Some effects of carbon dioxide on mortars and concrete. J. Am. Concr. Inst. 1956, 53, 295–308. (2) Steinour, H. H. Some effects of carbon dioxide on mortars and concrete-discussion. J. Am. Concr. Inst. 1959, 30, 905–907. (3) Pihlajavaara, S. E.; Pihlman, E. Effect of carbonation on microstructural properties of cement stone. Cem. Concr. Res. 1974, 4, 149–154. (4) Parrott, L. J.; Killoh, D. C. Carbonation in a 36 year old, in situ concrete. Cem. Concr. Res. 1989, 19 (4), 649–656. (5) Gaztan ˜ aga, M. T. Influencia de la Carbonatacio´n en La Microestructura de Diferentes Pastas de Cemento Hidratadas. PhD. Universidad Complutense de Madrid, Spain, 1996. (6) Parrott, L. J. Carbonation, moisture and empty pores. Adv. Cem. Res. 1991/92, 4 (15), 111–118.
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(7) Houst, Y. F.; Wittmann, F. H. Depth profiles of carbonates formed during natural carbonation. Cem. Concr. Res. 2002, 32, 1923– 1930. (8) Gajda, J.; Miller F. M. Concrete as a Sink for Atmospheric Carbon Dioxide: a Literature Review and Estimation of CO2 Absorption by Portland Cement Concrete, R&D Serial no. 2255; PCA: Chicago, IL, 2000. (9) Gajda, J. Absorption of Atmospheric Carbon Dioxide by Portland Cement, Serial no. 2255a; PCA, R&D: Chicago, IL, 2001. (10) Jacobsen, S.; Jahren, P. Binding of CO2 by Carbonation of Norwegian OPC Concrete; CANMET/ACI International Conference on Sustainability and Concrete Technology: Lyon, 2002. (11) Clear, C. A.; de Saulles, T., BCA Recarbonation Scoping Study: British Cement Association: Camberly, UK, 2007. (12) Kjellsen K. O.; Guimaraes M., Nilsson A. The CO2 Balance of Concrete in a Life Cycle Perspective; Danish Technological Institute, DTI: Taastrup, Denmark, 2005; ISBN: 87-7756-758-7. (13) Pommer K.; Pade C.; Guidelinessuptake of Carbon Dioxide in the Life Cycle Inventory of Concrete; Danish Technological Institute: Taastrup, Denmark, 2005; ISBN: 87-7756-757-9. (14) Lagerblad, B. Carbon Dioxide Uptake During Concrete Life Cycle, State of the Art; Swedish Cement and Concrete Research Institute, CBI: Stockholm, 2005; ISBN 91-976070-0-2. (15) Jonsson, G. Information on the Use of Concrete in Denmark, Sweden, Norway and Iceland; Icelandic Building research Institute: Reykjavı´k, 2005; ISBN: 9979-9174-7-4. (16) Engelsen, C. J.; Mehus, J.; Pade, C., Carbon Dioxide Uptake in Demolished and Crushed Concrete, Norwegian Building Research Institute: Oslo, 2005; ISBN: 82-536-0900-0. (17) Pade, C.; Guimaraes, M. The CO2 uptake of concrete in a 100 year perspective. Cem. Concr. Res. 2007, 37, 1384–1356.
ES903581D
