Next Article in Journal
Effect of Surface Active Agent (SAA) on 50/70 Bitumen Foaming Characteristics
Next Article in Special Issue
Prediction of Electrical Conductivity of Fiber-Reinforced Cement-Based Composites by Deep Neural Networks
Previous Article in Journal
Influence of Cooling Methods on the Residual Mechanical Behavior of Fire-Exposed Concrete: An Experimental Study
Previous Article in Special Issue
Comparative Analysis of Static and Dynamic Mechanical Behavior for Dry and Saturated Cement Mortar
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Materials
Volume 12
Issue 21
10.3390/ma12213513
materials-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles thumb_up
...
Endorse textsms
...
Comment
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Effects of CO2 Curing on Alkali-Activated Slag Paste Cured in Different Curing Conditions

by
Yubin Jun
,
Seong Ho Han
,
Tae Yong Shin
and
Jae Hong Kim
*
Department of Civil and Environmental Engineering, Korea Advanced Institute of Science and Technology, Daejeon 34141, Korea
*
Author to whom correspondence should be addressed.
Materials 2019, 12(21), 3513; https://doi.org/10.3390/ma12213513
Submission received: 1 October 2019 / Revised: 21 October 2019 / Accepted: 24 October 2019 / Published: 26 October 2019
(This article belongs to the Special Issue Testing of Cement-Based Materials)
Browse Figures
Versions Notes

Abstract

:
The effect of CO2 curing on alkali-activated slag paste activated by a mixture of sodium hydroxide and sodium silicate solutions is reported in this paper. The paste samples after demolding were cured in three different curing environments as follows: (1) environmental chamber maintained at 85% relative humidity (RH) and 25 °C; (2) 3-bar CO2 pressure vessel; and (3) CO2 chamber maintained at 20% CO2 concentration, 70% RH and 25 °C. The hardened samples were then subjected to compressive strength measurement, X-ray diffraction analysis, and thermogravimetry. All curing conditions used in this study were beneficial for the strength development of the alkali-activated slag paste samples. Among the curing environments, the 20% CO2 chamber was the most effective on compressive strength development; this is attributed to the simultaneous supply of moisture and CO2 within the chamber. The results of X-ray diffraction and thermogravimetry show that the alkali-activated slag cured in the 20% CO2 chamber received a higher amount of calcium silicate hydrate (C-S-H), while calcite formed at an early age was consumed with time. C-S-H was formed by associating the calcite generated by CO2 curing with the silica gel dissolved from alkali-activated slag.

1. Introduction

Greenhouse gas emission, including CO2, is one of the causes of global warming, which increases the frequency and extent of natural disaster in the world. Cement clinker production for Portland cement contributes 4% of global CO2 emission according to the statistics of 2017 [1], which is taken seriously in the construction industry. As environmental problems of CO2 emission becomes serious worldwide, there have been considerable efforts to find a way to reduce the CO2 level in the atmosphere. The construction industry has also tried to reduce greenhouse gas emissions.
The use of CO2 for accelerated curing of cement-based materials is one of the active responses to decrease CO2 concentration in the atmosphere. Calcium silicates such as alite and belite in Portland cement are spontaneously carbonated, which mainly results in the formation of calcium carbonate (CaCO3). Cement-based materials subjected to CO2 curing at an early age show a rapid development of their strength because in the process of CO2 curing, CaCO3 precipitates in pores of cast mortar and concrete. Densifying the pore refines their microstructure, including the cement paste matrix and the interfacial transition zone, which results in a higher strength at a rather early age [2,3]. However, previous studies adopted a very low water-to-cement ratio (w/cm) ranging from 0.06 to 0.28 [4], 0.11 to 0.25 [2], and 0.125 [5] to 0.18 [3]. This limits the application of CO2 curing in practice [3].
On the other hand, the use of alternative cement replacing Portland cement expectedly contributes to the decrease in CO2 emission. Calcium sulfoaluminate cement has merit due to the low temperature requirement for its calcination process; an approximately 100–200 °C decrease in the calcination temperature compared to the calcination for Portland cement contributes to lower CO2 emissions [6,7]. In addition, alkali-activated binders, including geopolymers synthesized with industrial byproducts such as blast-furnace slag and fly ash, are one of the promising alternatives [8,9,10,11]. It had been reported that they possesses excellent durability [11]. The blast-furnace slag utilized as a raw material also contains a large amount of calcium silicates. It is susceptible to carbonation while its hydration is latent, requiring an alkaline activator. The alkaline activator enables calcium to dissolve from slag particles, and the calcium participates in the formation of calcium silicate hydrate (C-S-H) gels contributing to the development of strength [12,13]. In addition, it is expected that the dissolved calcium could participate in the formation of CaCO3 in the process of CO2 curing.
From the viewpoint of recycling industrial byproducts as well as a reduction in CO2 emission, this paper conducted research on CO2 curing for alkali-activated slag. The setting of a slag paste was obtained by the alkali activation, and the cast samples were subjected to CO2 curing. The CO2 curing was carried out in a pressure vessel of approximately 300 kPa of CO2 pressure or in a chamber maintained at a constant 20% CO2 concentration. The compressive strengths of the samples were studied according to the CO2 curing condition. X-ray diffraction (XRD) and thermogravimetric (TG) analyses on the samples quantitatively analyzed the quantity and crystallization of the reaction products.

2. Experiments

2.1. Materials

Ground-granulated blast-furnace slag (GGBFS) used in this study was produced by H Steel Company in Dangjin, Korea. Table 1 reports the chemical composition of GGBFS by X-ray fluorescence analysis. The GGBFS consists of lime and silica to a high extent. Figure 1 presents the XRD pattern of the GGBFS, which corresponds to the general pattern of blast-furnace slag [14,15,16]. Sodium hydroxide and sodium silicate were used as an alkaline activator. Sodium hydroxide pellets (NaOH; reagent grade higher than 98% purity) and liquid sodium silicate (Na2SiO3; reagent grade with a molar ratio of SiO2/Na2O of 2.8) were acquired from S company in Pyeongtaek, Korea.

2.2. Experimental Design and Sample Preparations

The mixture proportions of samples are shown in Table 2. In this study, alkali activators (i.e., activator type and activator concentration) were chosen to harden samples within 1 h for the given GGBFS. The alkaline activator was prepared by blending 5 M NaOH solution with liquid Na2SiO3. The blend ratio of the NaOH solution to the liquid Na2SiO3 was 1.0 by mass. The 5 M NaOH solution was prepared by dissolving NaOH pellets in deionized water. The weight ratio of the alkali activator (5M NaOH + Na2SiO3) to the binder (GGBFS) was 0.4.
After 4 min of mixing with a planetary mixer, the fresh paste was cast in 25 mm cube molds. Each sample was taken from a mold after 1 h of pre-curing in an environmental chamber at 85% relative humidity (RH) and 25 °C. Table 3 summarizes the designed curing conditions including the control of conventional humid curing (85% RH and 25 °C). The first set of samples (denoted with CO2P-##) was subjected to 99.9% purified CO2 in a pressure vessel, where the initial pressure was set between 3 and 4 bar. The demolded samples were placed in the pressure vessel and then the pressure vessel was vacuumed before injecting the CO2. The 3 bar CO2 curing continued for 3 h, 23 h or 167 h, and additional CO2 was injected in the middle of the 167 h curing. Pressure loss in the pressure vessel was monitored using a pressure digital gauge (PDR1000; Pressure Development of Korea Co., Daejeon, Korea). The sampling rate for the pressure measurement was 1 record per second. A total curing time of 4 h, 24 h, and 7 days (168 h) included 1 h of pre-curing. After the 3 bar CO2 curing, the samples were placed in the environmental chamber (85% RH and 25 °C) for further hydration. The samples cured for 3 h, 23 h, and 167 h in the 3 bar CO2 pressure vessel were labelled CO2P-T1, CO2P-T2, and CO2P-T3, respectively. The other sample, labeled CO2-HC, was cured in a CO2 chamber controlled at 20% CO2 concentration, 70% RH and 25 °C until its strength measurement.
The compressive strengths of the samples were measured at the age of 4 h, 24 h, 7 days, and 42 days after the mixing (Table 3), where an average of the strengths of four replicated specimens was reported. The strength development of alkali-activated slag paste was faster than normal cement concrete. Approximately 90% of the strength at 42 days was obtained even with a 7-day old sample. (see Table 4). This study therefore conducted a detailed investigation until 7 days for CO2 curing. After each measurement of compressive strength at the age of 4 h, 24 h, and 7 days, fractured specimens were finely powdered and then immersed in isopropanol to stop their hydration. The XRD and TG analyses were applied to the powdered samples after vacuum drying. The XRD and TG were performed for the phase analyses of the reaction products formed in samples. The XRD measurement was carried out using a high-power X-ray diffractometer (Rigaku Corp., Tokyo, Japan) with an incident beam of Cu Kα radiation for a 2θ scanning range of 5–60°. The XRD patterns of samples were analyzed with the International Center for Diffraction Data (ICDD) PDF-2 database [17] and the Inorganic Crystal Structure Database (ICSD) [18]. The TG measurement was performed in nitrogen gas at a heating rate of 10 °C/min from room temperature to 950 °C using an SDT Q600 thermal analyzer (TA Instruments, Inc., New Castle, Delaware, USA).

3. Results and Discussion

CO2 curing reportedly accelerates the strength development of Portland cement-based materials [5,19]. Alkali-activated slag pastes were cured in various CO2 curing environments, and Table 4 reports the effect on their compressive strength. Figure 2 directly compares the effect of CO2 curing at the moment when curing finished. The time shown in Figure 2 includes the 1 h pre-curing required to have acceptable demolding in common (Table 3). The effect of CO2 curing for 3 h was compared in Figure 2a: the sample cured in the 20% CO2 concentration chamber (CO2-HC) showed the highest strength, followed by the sample cured in the 3 bar CO2 pressure vessel (CO2P-T1). Both CO2 curing conditions provide a higher strength than the control curing environment. However, a longer period of CO2 curing had a negative effect on strength. As seen in Figure 2b, the samples cured in the 3 bar CO2 pressure vessel (CO2P-T2) for 23 h gave a lower compressive strength than the control sample. In contrast, the samples cured in the 20% CO2 concentration chamber still showed a higher strength than the control. The trend on the strengths at 168 h (CO2P-T3 for 167 h) was the same as CO2P-T2 for 23 h, as shown in Table 4.
Here it should be noted that CO2 was sufficiently supplied for CO2 curing. Figure 3 shows the measured pressure loss in the pressure vessel during CO2 curing. The CO2 pressure decreased over time while the initial pressure was controlled between 3 and 4 bar as previously described. This implies that the CO2 was consumed with time. About 24 h after injecting CO2, the CO2 pressure dropped to a level of approximately 0.3 bar. In this study, CO2 was reinjected so that the CO2 pressure did not drop to 0 bar during CO2 curing. For the CO2P-T3 case (CO2 curing for 167 h), CO2 was reinjected one time during the 167 h of CO2 curing (Figure 3).
A successive moisture curing after CO2 curing reportedly causes the hydration of calcium silicates, which results in further increases in the strength of Portland cement-based materials [2,20,21]. Figure 4 presents the compressive strength development of the samples taken after further moisture curing following CO2 curing. In the case of the CO2-HC samples, since they were cured in a 20% CO2 concentration chamber maintained at 70% RH, we can presume that the samples were subjected to moisture curing. It achieved the highest strength of 111.89 MPa at seven days while the control alkali-activated slag reached 85.77 MPa at seven days. Further hydration on the samples cured in the 3 bar CO2 pressure vessel (CO2P-T1) obviously provided strength development, but its increase was lower than the control. The strength of the control sample exceeded that of CO2P-T1 at 24 h and seven days while the 4 h strength of the control sample was lower than that right after CO2 curing.
It was again confirmed that the long period of CO2 curing (CO2P-T2 for 23 h and CO2P-T3 for 167 h) in the 3 bar CO2 pressure vessel was not effective. Their compressive strengths were lower than that of the control sample. The effect of further moisture curing on the CO2P-T2 sample was also not effective.
The XRD patterns of all samples are shown in Figure 5. Earlier studies have shown that calcite, C-S-H, hydrotalcite, and calcium alumina silicate hydrate (C-A-S-H) were present in NaOH/Na2SiO3-activated slag [12,22,23]. It was also reported that the reaction products of alkali-activated slag depend on the composition of slag and the activator. Nevertheless, C-S-H is the main reaction product in alkali-activated slag [12,13] regardless of the activator used. As shown in Figure 5a, the main reaction products of the control sample were calcite and C-S-H. Figure 5b shows the detailed XRD pattern, where the strongest peaks of calcite (29.395° 2θ) [18] and C-S-H (29.356° 2θ) [17] were overlapped at 29° to 30° 2θ. The formation of C-S-H(I), which is a more crystalline form of C-S-H [24], was additionally found at 24 h and seven days.
CO2 curing for the alkali-activated slag pastes (Figure 5c–f) also provided calcite and C-S-H as their main products. However, C-S-H(I) was not present in the CO2-cured samples until seven days. In addition, vaterite, a metastable allotropic form of CaCO3 [25,26,27], was found in the samples right after the 3 bar CO2 curing (CO2P-T2 at 24 h and CO2P-T3 at seven days). The vaterite was not found in CO2P-T1 (the 3 bar CO2 curing for 3 h) and CO2-HC (the continuous CO2 curing in the 20% CO2 chamber).
TG and derivative TG (DTG) curves of the alkali-activated slag pastes before and after CO2 curing are compared in Figure 6. The first weight loss below 200 °C, clearly identified in the DTG curves, represented the loss of the combined water due to dehydration of C-S-H (50–200 °C [28]) and C-S-H(I) (90–110 °C [13]). The weight loss in the range of 600–700 °C indicated the presence of calcite [29,30]. The amount of calcite in each sample could be roughly quantified on the basis of the weight loss from 600–700 °C [29]. The calcite concentrations at all ages of the samples are tabulated in Table 5.
The extent of C-S-H in the control sample obviously increased with conventional humidity curing (see Figure 6a). Although the weight loss of C-S-H and C-S-H(I) overlaps, it can be shown that C-S-H increased with curing time because the C-S-H(I) peak in the XRD result was almost the same between 24 h and 7 days. This observation can also be identified in Figure 5b. In addition, the DTG peak of calcite slightly increased with curing time. The calcite concentrations were evaluated at 1.33%, 1.51%, and 2.09% at 4 h, 24 h and 7 day, respectively. It was reported that C-S-H in alkali-activated slag paste is also carbonated even in conventional humidity curing [31]. As a result, the formation of C-S-H and C-S-H(I) contributes to the strength of alkali-activated binders [29,32], and the formed calcite is helpful in improving the early age strength even though the concentration is as low as 2.8–4.6% [29]. The strength development of the control sample, shown in Figure 4, also supports the correlation. Furthermore, C-S-H is considered as the major reaction product contributing to strength development because the peak intensity of C-S-H(I) in the XRD pattern was relatively small and the growth rate of calcite was low, as reported in Table 5.
Even when the samples were cured in the 3 bar CO2 pressure vessel, we still observed a small amount of calcite. The calcite concentrations right after CO2 curing were only 1.43% for 3 h, 3.64% for 23 h and 2.76% for 167 h (CO2P-T1, CO2P-T2 and CO2P-T3, respectively) as reported in Table 5. CO2 in the gaseous phase does not react, and its dissolution in pore water is required for the formation of CaCO3 [31,33]. Water starvation due to dry-out of the samples was reported to decrease the carbonation [5]. In the case of alkali-activated materials, the high pH of the alkali activator can hinder the CO2 dissolution and obtain a low degree of carbonation.
In regards to porosity, carbonation of the inside of a cast sample needs CO2 diffusion into the sample, which can be obtained with a higher extent of air pores. Therefore, a low w/cm was adopted and then the produced mixes were compacted in the previous study. For example, w/cm ranges from 0.06 to 0.28 [4], 0.11 to 0.25 [2], 0.125 [5] or 0.18 [3]. Pre-conditioning for effective CO2 curing sometimes included an additional process to evaporate free water in the compacted samples [34,35]. As a result, the low w/cm compact sample with a high efficiency on CO2 curing had a high air-filled porosity beyond 20%. The samples produced in this study had a high activator (liquid)-to-binder ratio, and they had a low volume of air pores compared to the compact samples. Among them, the CO2P-T3 sample was cured for a sufficiently long time (167 h) that CO2 diffusion was expected inside. Nevertheless, it gave a low calcite concentration (2.76%). Therefore, the CO2 diffusion related to air-filled porosity cannot be considered as a critical factor.
Successive hydration of the sample after CO2 curing contributed to a higher amount of calcite as shown in Figure 6b. The calcite concentrations in CO2P-T1 increased over time: 1.43%, 2.90%, and 4.07% as reported in Table 5. The sample had a relatively higher degree of carbonation than the control sample even though the calcite concentration was still low (less than 5%). However, as shown in Figure 4, the strength of the CO2P-T1 sample was less than that of the control sample at all ages. The small amount of calcite formation by CO2 curing was negative on the strength of alkali-activated slag.
The 20% CO2 concentration curing provided a different trend of calcite formulation as shown in Figure 6d and Table 5. First of all, calcite formation in the short period (3 h) of CO2 curing was substantial: 8.37% at 4 h. Compared with the other samples, the high level of calcite concentration is attributed to the simultaneous presence of moisture and CO2 in the chamber. The RH was also controlled at 70%. The CO2 dissolution is more active with the neutral moisture supplied in the CO2 chamber. The highest concentration of calcite was confirmed at 4 h and then it decreased with curing time. It is worth noting that C-S-H formation kept increasing with curing time. During the hydration of alkali-activated slag paste, Ca as well as Si dissolved first in an alkaline environment and then C-S-H, including the other products that entered a solid phase in the paste. Ca2+ dissolved from the blast-furnace slag is preferably consumed for the calcite formation at an early age. The calcite formation is suppressed when the Ca dissolution in an alkaline environment exceeds the CO2 dissolution in the limited amount of moisture. The calcite is then consumed to form C-S-H with silica gel released from the blast-furnace slag: SiO2∙xH2O + yCaCO3 + H2O ↔ yCaO∙SiO2∙xH2O + H2CO3, as reported in [31]. The major reaction product of C-S-H was dominated in the CO2-HC sample, which results in the highest strength among the samples considered in this study.
On the other hand, in the case of the CO2P-T2 and CO2P-T3 samples, weight loss in the range of 520–580 °C was identified and it was related to the decomposition of vaterite [27]. The difference in the strength development with time in the sample (Figure 4) seems to be due to the formation of vaterite (metastable CaCO3). Among the samples cured under CO2 pressure, the samples that were cured for 23 h or 167 h showed the presence of vaterite, except for the sample that was CO2-cured for 4 h. This probably indicates that the CO2 curing time affects the polymorphs of CaCO3. As shown in Figure 6c, further humidity curing decreased the DTG peak of vaterite at seven days and increased the peak of calcite. Vaterite can be easily recrystallized to calcite when exposed to water [27].
The CO2-HC sample at 24 h also showed the weight loss in the range of 450–550 °C. This weight loss is likely due to the decomposition of amorphous calcium carbonate (CaCO3∙xH2O [36]) rather than vaterite, which is because the peaks for vaterite was not detected in the XRD result as shown in Figure 5f. Amorphous CaCO3 was reportedly decomposed at temperatures between 245 °C and 645 °C [37].

4. Conclusions

CO2 curing for alkali-activated slag paste is promising in the view of reducing CO2 emission in the construction industry. In this study, blast-furnace slag is activated with 5 M NaOH solution and liquid Na2SiO3. The alkali-activated slag paste cured in a 20% CO2 concentration chamber (70% RH, and 25 °C) shows a higher compressive strength than the control samples cured at 85% RH and 25 °C. A higher amount of calcite was confirmed in the CO2 cured samples via XRD and TG analyses. The simultaneous supply of water vapor and CO2 in the chamber contributes to the CO2 dissolution, which results in the initial formation of substantial calcite (at 4 h). Continuous CO2 curing allows us to generate more C-S-H by the hydration of the calcite and silica gel dissolved from blast-furnace slag. As a result, the CO2-cured samples show a decrease in calcite concentration while the amount of C-S-H increases with curing time. However, the strengths of alkali-activated slag cured in a 3 bar CO2 pressure vessel were lower than the control samples. CO2 is hardly dissolved at the high pH of the pore solution of the alkali-activated slag, and a lower amount of calcite is formed even after CO2 curing in the pressure vessel. Limiting the supply of moisture in the pressure vessel prohibits the hydration of alkali-activated slag as well as CO2 dissolution. The strength development of the alkali-activated slag cured in the CO2 pressure vessel is therefore lower than the control samples cured in a conventional humid environment. This study finally concludes that CO2 curing at a constant CO2 concentration was more effective on alkali-activated slag paste than in a 3 bar-CO2 pressure vessel.

Author Contributions

Conceptualization, J.H.K.; Validation, S.H.H. and T.Y.S.; Formal Analysis, Y.J.; Investigation, S.H.H. and T.Y.S.; Data Curation, Y.J.; Writing – Original Draft Preparation, Y.J.; Writing – Review and Editing, J.H.K.; Visualization, Y.J.; Supervision, J.H.K.; Project Administration, J.H.K.; Funding Acquisition, J.H.K.

Funding

This work was supported by the Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant funded by the Korean government (MOTIE) (No. 20188550000580).

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Olivier, J.G.J.; Peters, J.A.H.W.; Schure, K.M. Trends in Global CO2 and Total Greenhouse Gas Emissions: 2018 Report; PBL Netherlands Environmental Assessment Agency: The Hague, The Netherlands, 2018. [Google Scholar]
  2. He, P.; Shi, C.; Tu, Z.; Poon, C.S.; Zhang, J. Effect of further water curing on compressive strength and microstructure of CO2-cured concrete. Cem. Concr. Compos. 2016, 72, 80–88. [Google Scholar] [CrossRef]
  3. Tu, Z.; Guo, M.-Z.; Poon, C.S.; Shi, C. Effects of limestone powder on CaCO3 precipitation in CO2 cured cement pastes. Cem. Concr. Compos. 2016, 72, 9–16. [Google Scholar] [CrossRef]
  4. Klemm, W.A.; Berger, R.L. Accelerated curing of cementitious systems by carbon dioxide: Part I. Portland cement. Cem. Concr. Res. 1972, 2, 567–576. [Google Scholar] [CrossRef]
  5. Young, J.F.; Berger, R.L.; Breese, J. Accelerated Curing of Compacted Calcium Silicate Mortars on Exposure to CO2. J. Am. Ceram. Soc. 1974, 57, 394–397. [Google Scholar] [CrossRef]
  6. Juenger, M.C.G.; Winnefeld, F.; Provis, J.L.; Ideker, J.H. Advances in alternative cementitious binders. Cem. Concr. Res. 2011, 41, 1232–1243. [Google Scholar] [CrossRef]
  7. Jun, Y.; Kim, H.J.; Kim, T. Hydration of Calcium Sulfoaluminate-Based Binder Incorporating Red Mud and Silica Fume. Appl. Sci. 2019, 9, 2270. [Google Scholar] [CrossRef]
  8. Palomo, A.; Grutzeck, M.W.; Blanco, M.T. Alkali-activated fly ashes: A cement for the future. Cem. Concr. Res. 1999, 29, 1323–1329. [Google Scholar] [CrossRef]
  9. Shi, C.; Jiménez, A.F.; Palomo, A. New cements for the 21st century: The pursuit of an alternative to Portland cement. Cem. Concr. Res. 2011, 41, 750–763. [Google Scholar] [CrossRef]
  10. Van Deventer, J.S.J.; Provis, J.L.; Duxson, P. Technical and commercial progress in the adoption of geopolymer cement. Miner. Eng. 2012, 29, 89–104. [Google Scholar] [CrossRef]
  11. Van Jaarsveld, J.G.S.; Van Deventer, J.S.J.; Lorenzen, L. The potential use of geopolymeric materials to immobilise toxic metals: Part I. Theory and applications. Miner. Eng. 1997, 10, 659–669. [Google Scholar] [CrossRef]
  12. Li, C.; Sun, H.; Li, L. A review: The comparison between alkali-activated slag (Si+Ca) and metakaolin (Si+Al) cements. Cem. Concr. Res. 2010, 40, 1341–1349. [Google Scholar] [CrossRef]
  13. Wang, S.-D.; Scrivener, K.L. Hydration products of alkali activated slag cement. Cem. Concr. Res. 1995, 25, 561–571. [Google Scholar] [CrossRef]
  14. Liu, H.; Lu, H.; Chen, D.; Wang, H.; Xu, H.; Zhang, R. Preparation and properties of glass–ceramics derived from blast-furnace slag by a ceramic-sintering process. Ceram. Int. 2009, 35, 3181–3184. [Google Scholar] [CrossRef]
  15. Park, S.M.; Jang, J.G.; Lee, N.K.; Lee, H.K. Physicochemical properties of binder gel in alkali-activated fly ash/slag exposed to high temperatures. Cem. Concr. Res. 2016, 89, 72–79. [Google Scholar] [CrossRef]
  16. Jun, Y.; Yoon, S.; Oh, E.J. A Comparison Study for Chloride-Binding Capacity between Alkali-Activated Fly Ash and Slag in the Use of Seawater. Appl. Sci. 2017, 7, 971. [Google Scholar] [CrossRef]
  17. Data ICDD. PDF-2 Database; Data ICDD: Newton Square, PA, USA, 2000. [Google Scholar]
  18. Allmann, R.; Hinek, R. The introduction of structrue types into the inorganic crystal structure database ICSD. Acta Crystallogr. A 2007, 63, 412–417. [Google Scholar] [CrossRef]
  19. Monkman, S.; Shao, Y. Assessing the Carbonation Behavior of Cementitious Materials. J. Mater. Civ. Eng. 2006, 18, 768–776. [Google Scholar] [CrossRef]
  20. Rostami, V.; Shao, Y.; Boyd, A.J.; He, Z. Microstructure of cement paste subject to early carbonation curing. Cem. Concr. Res. 2012, 42, 186–193. [Google Scholar] [CrossRef]
  21. Xuan, D.; Zhan, B.; Poon, C.S. A maturity approach to estimate compressive strength development of CO2-cured concrete blocks. Cem. Concr. Compos. 2018, 85, 153–160. [Google Scholar] [CrossRef]
  22. Sakulich, A.R.; Anderson, E.; Schauer, C.; Barsoum, M.W. Mechanical and microstructural characterization of an alkali-activated slag/limestone fine aggregate concrete. Constr. Build. Mater. 2009, 23, 2951–2957. [Google Scholar] [CrossRef]
  23. Puertas, F.; Palacios, M.; Manzano, H.; Dolado, J.S.; Rico, A.; Rodríguez, J. A model for the C-A-S-H gel formed in alkali-activated slag cements. J. Eur. Ceram. Soc. 2011, 31, 2043–2056. [Google Scholar] [CrossRef]
  24. Richardson, I.G.; Brough, A.R.; Groves, G.W.; Dobson, C.M. The characterization of hardened alkali-activated blast-furnace slag pastes and the nature of the calcium silicate hydrate (C-S-H) phase. Cem. Concr. Res. 1994, 24, 813–829. [Google Scholar] [CrossRef]
  25. Chang, R.; Choi, D.; Kim, M.H.; Park, Y. Tuning Crystal Polymorphisms and Structural Investigation of Precipitated Calcium Carbonates for CO2 Mineralization. ACS Sustain. Chem. Eng. 2017, 5, 1659–1667. [Google Scholar] [CrossRef]
  26. Kato, T. Polymer/Calcium carbonate layered thin-film composites. Adv. Mater. 2000, 12, 1543–1546. [Google Scholar] [CrossRef]
  27. Qiao, L.; Feng, Q.L.; Liu, Y. A novel bio-vaterite in freshwater pearls with high thermal stability and low dissolubility. Mater. Lett. 2008, 62, 1793–1796. [Google Scholar] [CrossRef]
  28. Ben Haha, M.; Le Saout, G.; Winnefeld, F.; Lothenbach, B. Influence of activator type on hydration kinetics, hydrate assemblage and microstructural development of alkali activated blast-furnace slags. Cem. Concr. Res. 2011, 41, 301–310. [Google Scholar] [CrossRef]
  29. Jeon, D.; Jun, Y.; Jeong, Y.; Oh, J.E. Microstructural and strength improvements through the use of Na2CO3 in a cementless Ca(OH)2-activated Class F fly ash system. Cem. Concr. Res. 2015, 67, 215–225. [Google Scholar] [CrossRef]
  30. Wang, K.; Shah, S.P.; Mishulovich, A. Effects of curing temperature and NaOH addition on hydration and strength development of clinker-free CKD-fly ash binders. Cem. Concr. Res. 2004, 34, 299–309. [Google Scholar] [CrossRef]
  31. Palacios, M.; Puertas, F. Effect of Carbonation on Alkali-Activated Slag Paste. J. Am. Ceram. Soc. 2006, 89, 3211–3221. [Google Scholar] [CrossRef]
  32. El-Didamony, H.; Amer, A.A.; Abd Ela-ziz, H. Properties and durability of alkali-activated slag pastes immersed in sea water. Ceram. Int. 2012, 38, 3773–3780. [Google Scholar] [CrossRef]
  33. Ashraf, W.; Olek, J. Carbonation activated binders from pure calcium silicates: Reaction kinetics and performance controlling factors. Cem. Concr. Compos. 2018, 93, 85–98. [Google Scholar] [CrossRef]
  34. Shi, C.; He, F.; Wu, Y. Effect of pre-conditioning on CO2 curing of lightweight concrete blocks mixtures. Constr. Build. Mater. 2012, 26, 257–267. [Google Scholar] [CrossRef]
  35. Shi, C.; Wu, Y. Studies on some factors affecting CO2 curing of lightweight concrete products. Resour. Conserv. Recycl. 2008, 52, 1087–1092. [Google Scholar] [CrossRef]
  36. Kojima, Y.; Kanai, M.; Nishimiya, N. Synthesis of novel amorphous calcium carbonate by sono atomization for reactive mixing. Ultrason. Sonochem. 2012, 19, 325–329. [Google Scholar] [CrossRef] [PubMed]
  37. Nedeljković, M.; Ghiassi, B.; Melzer, S.; Kooij, C.; van der Laan, S.; Ye, G. CO2 binding capacity of alkali-activated fly ash and slag pastes. Ceram. Int. 2018, 44, 19646–19660. [Google Scholar] [CrossRef]
Materials 12 03513 g001 550
Figure 1. X-ray diffraction (XRD) patterns of raw GGBFS.
Figure 1. X-ray diffraction (XRD) patterns of raw GGBFS.
Materials 12 03513 g001
Materials 12 03513 g002 550
Figure 2. Compressive strengths at 4 h (a) and 24 h (b).
Figure 2. Compressive strengths at 4 h (a) and 24 h (b).
Materials 12 03513 g002
Materials 12 03513 g003 550
Figure 3. Pressure loss in the pressure vessel during CO2 curing.
Figure 3. Pressure loss in the pressure vessel during CO2 curing.
Materials 12 03513 g003
Materials 12 03513 g004 550
Figure 4. Compressive strength developments of paste samples cured under different curing conditions with curing time.
Figure 4. Compressive strength developments of paste samples cured under different curing conditions with curing time.
Materials 12 03513 g004
Materials 12 03513 g005a 550Materials 12 03513 g005b 550
Figure 5. XRD patterns of samples with curing time. (a) Control; (b) detailed XRD figure of the control sample in the 29–30° 2θ range with reference patterns of calcite and calcium silicate hydrate (C-S-H); (c) CO2P-T1; (d) CO2P-T2; (e) CO2P-T3; (f) CO2-HC. 1: calcite (PDF 98-005-2151), 2: C-S-H (PDF 00-033-0306), 3: C-S-H(I) (PDF 00-029-0331), and 4: vaterite (PDF 98-018-1959).
Figure 5. XRD patterns of samples with curing time. (a) Control; (b) detailed XRD figure of the control sample in the 29–30° 2θ range with reference patterns of calcite and calcium silicate hydrate (C-S-H); (c) CO2P-T1; (d) CO2P-T2; (e) CO2P-T3; (f) CO2-HC. 1: calcite (PDF 98-005-2151), 2: C-S-H (PDF 00-033-0306), 3: C-S-H(I) (PDF 00-029-0331), and 4: vaterite (PDF 98-018-1959).
Materials 12 03513 g005aMaterials 12 03513 g005b
Materials 12 03513 g006 550
Figure 6. TG and derivative TG (DTG) curves of (a) control, (b) CO2P-T1, (c) CO2P-T2, and (d) CO2-HC samples with curing time.
Figure 6. TG and derivative TG (DTG) curves of (a) control, (b) CO2P-T1, (c) CO2P-T2, and (d) CO2-HC samples with curing time.
Materials 12 03513 g006
Table
Table 1. Chemical composition (oxides in wt.%) of ground-granulated blast-furnace slag (GGBFS).
Table 1. Chemical composition (oxides in wt.%) of ground-granulated blast-furnace slag (GGBFS).
CaOSiO2Al2O3Na2OK2OMgOMnOTiO2SO3P2O5Fe2O3Others
47.9730.7613.260.230.543.060.520.871.810.010.610.25
Note: Others include BaO, ZrO2, V2O5, SrO, and Y2O3.
Table
Table 2. Mix proportions of samples.
Table 2. Mix proportions of samples.
Binder (g)Activator (g)Activator/Binder
GGBFS5M NaOHLiquid Na2SiO3
24004804800.4
Table
Table 3. Curing conditions of samples.
Table 3. Curing conditions of samples.
Sample LabelCuring time
1 h3 h20 h6 Days35 Days
ControlChamber at 25 °C and 85% RHChamber at 25 °C and 85% RH
CO2P-T13-bar CO2 pressure vesselChamber at 25 °C and 85% RH
CO2P-T23-bar CO2 pressure vesselChamber at 25 °C and 85% RH
CO2P-T33-bar CO2 pressure vesselChamber at 25 °C and 85% RH
CO2-HC20%-concentration CO2 chamber at 25 °C and 70% RH
Note. Demolding after 1 h pre-curing; Strength, XRD, and TG tests at 4 h: Control, CO2P-T1, and CO2-HC samples; Strength, XRD, and TG tests at 24 h: Control, CO2P-T1, CO2P-T2, and CO2-HC samples; Strength, XRD, and TG tests at 7 days: Control, CO2P-T1, CO2P-T2, CO2P-T3, and CO2-HC samples; Strength test at 42 days: Control, CO2P-T1, CO2P-T2, CO2P-T3, and CO2-HC samples.
Table
Table 4. Compressive strengths of the paste samples.
Table 4. Compressive strengths of the paste samples.
Sample LabelCompressive Strength (Standard Deviation), MPa
4 h24 h7 Days42 Days
Control14.78 (1.33)65.56 (1.88)85.77 (0.88)108.83 (3.52)
CO2P-T118.27 (1.1)55.72 (1.14)80.62 (2.99)85.6 (1.62)
CO2P-T2-53.47 (2.09)69.11 (2.6)74.69 (1.9)
CO2P-T3--61.96 (0.48)73.87 (2.57)
CO2-HC24.81 (1.96)81.77 (2.86)111.89 (1.88)121.98 (1.43)
Table
Table 5. Calcite concentrations of the samples.
Table 5. Calcite concentrations of the samples.
Sample LabelCalcite Concentration
4 h24 h7 Days
Control1.33%1.51%2.09%
CO2P-T11.43%2.90%4.07%
CO2P-T2-3.64%3.93%
CO2P-T3--2.76%
CO2-HC8.37%6.96%2.27%

Share and Cite

MDPI and ACS Style

Jun, Y.; Han, S.H.; Shin, T.Y.; Kim, J.H. Effects of CO2 Curing on Alkali-Activated Slag Paste Cured in Different Curing Conditions. Materials 2019, 12, 3513. https://doi.org/10.3390/ma12213513

AMA Style

Jun Y, Han SH, Shin TY, Kim JH. Effects of CO2 Curing on Alkali-Activated Slag Paste Cured in Different Curing Conditions. Materials. 2019; 12(21):3513. https://doi.org/10.3390/ma12213513

Chicago/Turabian Style

Jun, Yubin, Seong Ho Han, Tae Yong Shin, and Jae Hong Kim. 2019. "Effects of CO2 Curing on Alkali-Activated Slag Paste Cured in Different Curing Conditions" Materials 12, no. 21: 3513. https://doi.org/10.3390/ma12213513

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop