
==== Front
Environ Sci Pollut Res Int
Environ Sci Pollut Res Int
Environmental Science and Pollution Research International
0944-1344
1614-7499
Springer Berlin Heidelberg Berlin/Heidelberg

39115736
34582
10.1007/s11356-024-34582-2
Research Article
Effect of in situ CO2 mixing of cement paste on the leachability of hexavalent chromium (Cr(VI))
Cho Kian 1
Kim Won Kyung 1
Moon Juhyuk 1
Cha Daniel 2
http://orcid.org/0000-0003-4954-8010
Park Junboum junbpark@snu.ac.kr

1
1 https://ror.org/04h9pn542 grid.31501.36 0000 0004 0470 5905 Department of Civil and Environmental Engineering, Seoul National University, Seoul, South Korea 08826
2 https://ror.org/01sbq1a82 grid.33489.35 0000 0001 0454 4791 Department of Civil and Environmental Engineering, University of Delaware, Delaware, 19716 USA
Responsible Editor: Ioannis A. Katsoyiannis

8 8 2024
8 8 2024
2024
31 39 5158251592
9 5 2024
26 7 2024
© The Author(s) 2024
2024
https://creativecommons.org/licenses/by/4.0/ Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.
In situ CO2 mixing technology is a potential technology for permanently sequestering CO2 during concrete manufacturing processes. Although it has been approved as a promising carbon capture and utilisation (CCU) method, its effect on the leachability of heavy metals from cementitious compounds has not yet been studied. This study focuses on the effect of in situ CO2 mixing of cement paste on the leaching of hexavalent chromium (Cr(VI)). The tank leaching test of the CO2 mixing cement specimen resulted in a Cr(VI) cumulative leaching of 0.614 mg/m2 in 28 d, which is ten times lower than that of the control mixing specimens. The results in thermogravimetric analysis indicated that a relatively significant amount of CrO42− is immobilised as CaCrO4 during the CO2-mixing, and a higher Cr–O extension is observed in the Fourier transform infrared spectra. Furthermore, a portion of the monocarboaluminate is inferred from microstructural analyses to incorporate CrO42− ions. These results demonstrate that in situ CO2 mixing is beneficial not only in reducing CO2 emissions, but also in controlling the leaching of toxic substances.

Keywords

Carbon Capture and Utilisation (CCU) technology
Ordinary Portland cement
Leaching test
Hexavalent chromium
Monocarboaluminate
Chromate hydrate
Microstructural analysis
Seoul National UniversityOpen Access funding enabled and organized by Seoul National University.

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pmcIntroduction

Chromium is one of the 25 most widespread elements in the Earth’s crust (Emsley 2011). It exists in various forms, however hexavalent chromium (Cr(VI)) is significantly toxic and highly carcinogenic (Mondal et al. 2021; Saha et al. 2022). Since 1990, the International Agency for Research on Cancer (IARC 2012) has classified Cr(VI) as a group 1 carcinogen, indicating its confirmed ability to cause cancer in humans. Cr(VI) is used in various industrial processes, including medicine, catalysis, fuel production, leather tanning, electroplating, and pigment manufacturing (O'Neil 2013; Saha et al. 2011). Despite its utility, Cr(VI) poses severe health risks, such as damage to nasal epithelia, skin ulcers, known as 'chrome holes', and lung cancer when inhaled (Wu et al. 2020b). It can penetrate cells, causing DNA damage and oxidative stress, which contributes to its carcinogenic properties (Costa and Klein 2006). Environmentally, Cr(VI) contamination in water sources poses significant risks, necessitating strict regulatory control to mitigate exposure and protect both human health and the ecosystem. Recently chromium removal technologies highlighted a diverse range of effective methods (Mukherjee et al. 2013) including bioremediation (Costa and Klein 2006; Saha and Orvig 2010; Saha and Saha 2014), ion exchange (Rengaraj et al. 2001), membrane filtration (Ho and Poddar 2001), adsorption (Pakade et al. 2019), and electrochemical techniques (Liu et al. 2011).

Hexavalent chromium (Cr(VI)) has been widely recognised as a heavy metal that is eluted from cement-based materials (Eštoková et al. 2012; He et al. 2023). When Cr(VI) comes into direct contact with the human skin, it can trigger hypersensitivity reactions and allergic dermatitis, particularly for construction workers who work with cement or fresh concrete (Frías and Sánchez de Rojas 2002;Scrivener et al. 2016). Therefore, the presence of Cr(VI) compounds in cement-based materials may pose severe environmental and public health challenges owing to their solubility and potential leaching from cementitious materials, such as water tanks, pipes, or cementation of soils. The leaching of Cr(VI) from cementitious materials is caused by the dissolution of chromate (CrO42−) in the pore solution of the cement paste, which is an alkaline environment. Immobilisation of CrO42− is assumed to occur because of ion exchange in calcium aluminate hydrates (Perkins and Palmer 2000, 2001; Pöllmann and Auer 2012). The chromium compounds such as chromate-ettringite (Ca6·Al2·(OH)12·(CrO4)3·26H2O) or monochromate (Ca4·Al2· (OH)12·CrO4·6H2O) (Leisinger et al. 2012; Takahashi et al. 2003) can be generated by incorporating CrO42−.

The in situ CO2 mixing technology of cement paste is attracting global interest, as the cement industry accounts for a large portion of global CO2 emissions (United Nations Environment Programme 2020). The main idea of carbon capture and storage (CCS) or carbon capture and utilisation (CCU) technology is to collect CO2 at CO2-emitting processes, such as cement manufacturing, and inject and sequester it into stable sites or materials (Pacala and Socolow 2004; Sanna et al. 2014). CCS or CCU is feasible in the cement industry under favourable environmental conditions, such as abundant calcium ions (Ca2+) and high pH in the cement paste, as stated in Eq. 1 and 2.1 C3S+3H2O↔3Ca2++SiO2+6OH-

2 C2S+2H2O↔2Ca2++SiO2+4OH-,

where C3S is tricalcium silicate, and C2S is dicalcium silicate. In situ CO2 mixing technology or carbon curing of concrete is a mineral carbonation technique in which CO2 reacts with Ca2+ ions to deposit calcium carbonate (CaCO3) (Li et al. 2019). As CO2 gas dissolves in the cement slurry, it forms CO32−, and CaCO3 precipitates via the combination of Ca2+ and CO32−, as shown in Eq. 3.3 Ca2++CO32-↔CaCO3

The CO2 mixing that induces cement carbonation has been reported to have some impact on the mechanical and durability properties of cement (El-Hassan and Shao 2015; Li et al. 2019). However, its effect on the leachability of heavy metals has not yet been studied. Therefore, this study aims to evaluate the leachability of Cr(VI) from ordinary Portland cement (OPC) when the cement paste is partially carbonated via in situ CO2 mixing. The specimens mixed under laboratory conditions (i.e. air mixing) and high CO2 concentration conditions (i.e. CO2 mixing) are compared in terms of the leachability of Cr(VI) through a tank leaching test. To investigate the transformation of cement hydrates, the following microstructural analyses are applied: X-ray diffraction analysis (XRD), thermogravimetric analysis (TGA), and Fourier transform infrared (FTIR). For these microstructural analyses, a Cr(VI) solution was added instead of water to observe the effect of CO2 mixing on the Cr(VI) immobilisation mechanism in the cement paste.

Materials and methods

Specimen preparation

Commercial OPC (Hannil, South Korea) was used in this study. Table 1 presents the chemical composition of the OPC, as measured by the X-ray fluorescence (XRF) analysis. Table 2 lists detailed descriptions of each experimental condition. The cement paste was mixed in either a laboratory environment (air mixing) or a glove box filled with a high concentration of CO2 gas (CO2 mixing). The water-to-cement (w/c) ratio was 0.5, comprising 200 g of cement and 100 g of a water-or Cr(VI)-saturated mixing solution. The Cr(VI)-saturated mixing solution was prepared by dissolving 5 g of potassium dichromate (K2Cr2O7, DUKSAN Company, South Korea) in 100 mL of deionised water (i.e., 17.67 g/L of Cr(VI) solution). After mixing with cement under each experimental condition, the paste was moulded in a cylinder (2.5 cm I.D. × 2.5 cm H), sealed with plastic wrap, and tied with a rubber band. The specimens were cured in an environmental chamber at a constant temperature of 20 °C and humidity of 60%. Table 1 Chemical composition of OPC by XRF

Name	SiO2	Al2O3	TiO2	Fe2O3*	MgO	CaO	Na2O	K2O	MnO	P2O5	LOI**	Total	
%	19.93	4.61	0.21	3.12	2.74	63.21	0.09	0.93	0.09	0.21	3.02	98.2	
*Fe2O3: Total Fe, **LOI: Loss of ignition

Table 2 Material designs in the experiment

Name	Mixing	Cr(VI) addition (mg/L)	Water (g)	Cement (g)	
air_cr0	Air	0	100	200	
CO2_cr0	CO2	
air_cr5	Air	50	
CO2_cr5	CO2	

CO2 mixing of cement paste

To implement in situ CO2 mixing of the cement paste, a glove box was used to mix the cement paste under a specific CO2 concentration (Fig. 1). The beaker containing 100 mL of water or Cr(VI) solution, OPC, the mixer, and the CO2 sensor (SKY2000, Shenzhen YuanTe Technology Co., Ltd., Shenzhen, China) were placed inside the glove box. Subsequently, the glove box was filled with CO2 (Purity: 99.999%, KS Tech Co., Ltd., Anseong, South Korea) to a concentration of approximately 10 vol%. Moreover, the water and cement were mixed in the glove box for 30 min. The CO2 concentration in the glove box was recorded every 5 min. A condition without mixing was also tested to evaluate the CO2 reduction under unmixed conditions.Fig. 1 Schematic illustration of CO2-mixing method

Tank leaching test

Figure 2 illustrates the tank leaching test. The test was performed at an ambient temperature of 22 ± 1 °C and a relative humidity of ~ 60%. The ratio of the volume of the leachate to the surface area of the specimen (L/S ratio) was approximately 4.07 mL/cm2. The specimen was placed in a 200-mL beaker containing 100 mL of deionised water as leachate. To avoid evaporation of the leachate, the beaker was tightly sealed with plastic wrap. After specific leaching periods of 1, 2, 4, 8, 16, and 28 d, the leachate was stirred gently, and leachate samples were collected. The leaching tests were conducted on five samples for each mixing method. Subsequently, the leachate was discarded, and the beaker was refilled with deionised water.Fig. 2 Schematic illustration of the procedure in the tank leaching test

The collected leachate was analysed for Cr(VI) concentrations to quantify the Cr(VI) leaching from the cement specimens according to the European Standard method (EN196-10:2016 2016). Briefly, 1,5 di-phenyl-carbohydrazide (C13H14N4O) was used to form a 1,5 di-phenyl-carbohydrazide-Cr(VI) complex in a dilute acid solution (0.04 M HCl). The resulting Cr(VI) complexes were analysed using a UV–visible spectrometer (Cary 3500 UV–Vis Multicell, Agilent Technologies, Inc., USA) at a wavelength of 540 nm.

The Environmental Protection Agency (EPA1315 2013) proposed mass transfer rates of inorganic compounds in cement under diffusion-controlled release conditions as a function of leaching time. The observed diffusivity (Dobs) was determined by analysing the leaching test results, as shown in Eq. 4.4 Diobs=πMti2ρC0ti-ti-12

where Diobs is the observed diffusion coefficient for each interval (cm2/day), Mti is the mass released during the leaching interval, i (mg/m2), ti is the cumulative contact time at the end of the current leaching interval, i (s), ti-1 is the cumulative contact time at the end of the previous leaching interval, i-1 (s), ρ is the density of the material (g/cm3), and C0 is the initial leachable content, that is, the available release potential (mg/kg). The C0 of Cr(VI) from OPC was 3.495 mg/kg (EN196-10:2016 2016).

Microstructural analysis of cement paste

To prepare for microstructural analyses, a hydration stoppage was applied to preserve the samples and allow the analysis of various material properties at the same hydration stage (Snellings et al. 2018; Zhang and Scherer 2011). After pulverising, the specimens were soaked in a sufficient amount of isopropyl alcohol for 30 min to remove the free water trapped in the pores of the cement structure. The isopropyl alcohol was trimmed by vacuum pumping on filter paper (No. 2, with a pore size of 5μm). Subsequently, the sample was placed in a thermostatic oven maintained at 40 °C for approximately 5 min and soaked in ethyl ether for 30 min (i.e., expelling the isopropyl alcohol). Afterwards, the sample powder was trimmed again and dried in a thermostatic oven maintained at 40 °C for 40 min.

In this study, a TGA) was performed (SDT Q600, TA Instruments, USA). In the TGA, approximately 25–35 mg of the material was placed on the plate to avoid variations in the measurement. The ramps were 1.00 °C/min to 30 °C and 10.00 °C/min to 1000 °C. To observe the Cr(VI)-containing hydrates in the cement paste, additional measurements were performed with 1.00 °C/min to 20 °C and 10.00 °C/min to 1300 °C for 28-day cured samples. Moreover, an X-ray diffraction (XRD) analysis was performed (Bruker Co. Ltd., Germany). The initial setting of analysis was as follows: Cu-Kα line with a wavelength (λ) of 1.5418 Å, 2θ of 5–60°, the scanning rate of 2 min/°, and a step of 0.02°. FTIR spectroscopy was performed (TENSOR27, Bruker Co. Ltd., Germany). The spectral range was 400–4,000 cm−1, whereas the resolution was better than 0.4 cm−1 (apodised function), and the high-sensitivity DLATGS detector was used.

Results and discussion

Laboratory scale of in situ CO2 mixing

Figure 3 shows the concentrations of CO2 in the glove box during the mixing of 300 g of cement paste. The results showed that the experimental conditions of the glove box did not have a significant effect on the change in CO2 concentration because CO2 reduction was not observed in the unmixed beaker containing OPC, as implied in the blank test. Almost 0.6 vol% of CO2 decreased in the glove box for 30 min when the OPC paste was prepared with water (CO2_cr0). Moreover, approximately 1.1 vol% of CO2 concentration decreased more rapidly during the same mixing period with the Cr(VI) addition of 50 mg/L to the mixing solution (CO2_cr5). These results suggest that mixing the OPC cement paste under abundant CO2 conditions facilitates the absorption of CO2 by the cement paste. CO2 gas can react with Ca2+ dissolved in cement paste to form calcium carbonate (CaCO3) precipitates, according to Eq. 3. The greater absorption of CO2 during the mixing of the Cr(VI)-containing OPC paste may be attributed to the acidic pH of the CrO42− solution (O'Neil 2013). The dissolution of CO2 increased at a lower pH owing to the formation of carbonic acid (H2CO3).Fig. 3 Reduction of CO2 concentration in the glove box during the mixing of 200 g cement

Tank leaching test

A tank leaching test was conducted to compare Cr(VI) leaching from air and CO2 mixed specimens. Five specimens of each mixing condition were subjected to the leaching tests. Table 3 lists the mass and dimensions of the 28-day cured specimens at the start of the leaching test.

Figure 4a shows the cumulative amount of Cr(VI) in the leachate from the cured OPC specimens. The cumulative amount of Cr(VI) in the leachate was expressed as mg per m2 of the specimen surface area. In the air-mixed specimens, the cumulative amount of released Cr(VI) gradually increased to 6.41 mg/m2 in 28 d. However, the cumulative Cr(VI) leaching from the CO2-mixed specimens was ten times lower (0.614 mg/m2) at the end of the leaching test period. Moreover, on the 1st or 2nd day of the tank leaching test, the leachate of the CO2_cr0 samples was undetectable using a UV–visible spectrometer. Table 3 28-day cured specimens for tank leaching test

Name	No	Mass (g)	Height (cm)	
	1	21.95	2.30	
	2	22.16	2.35	
air_cr0	3	22.14	2.35	
	4	21.12	2.15	
	5	21.60	2.30	
	1	22.59	2.45	
	2	22.60	2.45	
CO2_cr0	3	22.78	2.45	
	4	21.18	2.25	
	5	22.66	2.40	

Fig. 4 Result of tank leaching test with 28-day cured specimens (a) Cumulative leaching amount of Cr(VI), (b) Observed diffusion coefficient, Diobs, and (c) Solidification rate

Figure 4b shows the logarithmic form of Dobs, expressed in cm2 per day. The Dobs was calculated as the mean cumulative amount of Cr(VI) released during the leaching test. Similar to the two experimental conditions, the Dobs were gently declined during the applied test period. The Dobs aligned at approximately 7.66 × 10–6 cm2/day in air-mixed specimens and 1.19 × 10–7 cm2/day in CO2-mixed specimens. Therefore, CO2 mixing suppressed the mobility of Cr(VI)-containing compounds in the specimens compared with air mixing.

The solidification rates s of Cr(VI) in the specimens were determined using Eq. 5.5 s=C0-CtC0×100,

where C0 is the initial leachable content of Cr(VI) in the OPC powder, and Ct is the total amount of Cr(VI) released during the test period. Figure 4c shows the solidification rate as a function of leaching time. Under the air-mixed condition, s dropped consistently over time immediately after the leaching test started and reached 72.04% at the end of the test period. In contrast, there was almost no significant decrease from the beginning of the leaching test under the CO2-mixed conditions, resulting in an s value of 97.22% at the end of the test period.

The mitigation of Cr(VI) release from the CO2-mixed samples can be attributed to the change in the cement hydrates or porosity of the cement specimens under CO2-mixing conditions. These results also indicate the transformation of Cr(VI)-containing cement hydrates after CO2 mixing.

XRD analysis

Figure 5 shows the XRD analysis results of air and CO2 mixing for the samples cured for 1, 3, 7, and 28 d. Figure 5a and 5b show the results for the cement paste specimens made of water, and Fig. 5c and 5d show the results for the Cr(VI) solution. In common with all the samples, the fundamental peaks were confirmed, such as alite (3CaO·SiO2), belite (2CaO·SiO2), calcite (CaCO3), ettringite, or portlandite (Ca(OH)2).Fig. 5 Result of XRD analysis for (a) air mixing with water, (b) CO2 mixing with water, (c) air mixing with Cr(VI) solution, and (d) CO2 mixing with Cr(VI) solution (1 = Alite (3CaO·SiO2), 2 = Belite (2CaO ·SiO2), 3 = Calcite (CaCO3), 4 = Ettringite (Ca6·Al2· (OH)12·(SO4)3·26H2O), 5 = Portlandite (Ca(OH)2), 6 = Monocarboaluminate (Ca4·Al2· (OH)12·CO3·5H2O))

The Ca(OH)2 peak at approximately 18° is shown in Fig. 6a. The peak increased as curing proceeded in air_cr0 and CO2_cr0. Meanwhile, the peaks for both air_cr5 and CO2_cr5 decreased from 7 to 28 d of curing. This might be because of the lowered pH of the cement pore solution owing to Cr(VI) addition (Cau Dit Coumes et al. 2006) or the contribution of Ca(OH)2 for the formation of chromate hydrate, such as CaCrO4·2H2O (Bakhshi et al. 2019; Wang and Vipulanandan 2000).Fig. 6 Enlarged graph of XRD analysis for (a) Ca(OH)2 at 17.5–18.5º, (b) CaCO3 at 28.0–18.5º, and (c) Monocarboaluminate at 11.0–12.5º and Ettringite at 9.0–9.5º

The CaCO3 peak at approximately 29.5° is shown in Fig. 6b. Clearly, the peak of CO2_cr5 was higher, which might be a consequence of the higher CO2 uptake, as shown in Fig. 3. In addition, both CO2_cr0 and CO2_cr5 exhibit slightly higher intensities than air_cr0 and air_cr5, implying that more CaCO3 is generated by CO2 mixing.

The monocarboaluminate (Mc, Ca4·Al2·(OH)12·CO3·5H2O) was observed at approximately 11.5° and ettringite was approximately 9.2° as magnified in Fig. 6c. In the case of air_cr0 and CO2_cr0, Mc peaks were observed after 7 d of curing; in particular, CO2_cr0 exhibited a more intense peak than air_cr0. For ettringite, CO2_cr0 exhibited a higher peak after 28 d of curing. In contrast, neither air_cr5 nor CO2_cr5 showed peaks of Mc. Furthermore, the ettringite peak did not change in CO2_cr5. Instead of generating Mc or ettringite, monochromate or chromate-ettringite was assumed to be generated (Leisinger et al. 2012; Rae et al. 2022).

TGA result

Figure 7 shows the TGA results for both the air and CO2 mixing samples with water and Cr(VI) solution. The weight reduction appeared at approximately 90–200 °C for the decomposition of H2O for cement hydrates such as calcium silicate hydrate (C-S–H), ettringite, or monosulfoaluminate hydrates (Ca4·Al2·(OH)12·SO4·6H2O, AFm), 350–550 °C for Ca(OH)2, and 550–1000 °C for CO2-bearing hydrate such as CaCO3 or Mc. It can be observed that weight reduction increased with the curing days under all experimental conditions. The weight reductions in air_cr0 and CO2_cr0 resulted in 23.55% and 27.89% in 28-day cured samples; however, air_cr5 and CO2_cr5 samples were 20.33% and 20.97%, respectively. CO2-mixing resulted in greater hydrate formation than air mixing. However, adding the Cr(VI) solution caused less hydrate generation than water mixing.Fig. 7 Result of TGA for (a) air mixing with water, (b) CO2 mixing with water, (c) air mixing with Cr(VI) solution, and (d) CO2 mixing with Cr(VI) solution (C-S–H = calcium silicate hydrate, Ett = ettringite, AFm = monosulfoaluminate hydrates, CBW = chemically bounded water, Mc = monocarboaluminate)

Subsequently, a differential thermogravimetric analysis (DTG) was performed, as shown in Fig. 8. Peaks for C-S–H, ettringite or AFm, Ca(OH)2, and CaCO3 were mainly observed. Figure 9 shows the peaks of the 28-day cured samples and compares the amounts of each hydrate. In Fig. 9a, there is a peak at approximately 130 °C in air_cr0 and CO2_cr0, which implies the decomposition of 5H2O in the interlayer of Mc and a comparatively small amount of 3H2O of AFm (Scrivener et al. 2016). The peak of CO2_cr0 was comparatively higher than that of air_cr0; therefore, CO2 mixing increased Mc production. Meanwhile, the peaks of 5H2O of Mc were neither confirmed in air_cr5 nor CO2_cr5, despite the peak at approximately 380 °C indicating the 6H2O of Mc regardless of the experimental conditions.Fig. 8 Result of DTG for (a) air mixing with water, (b) CO2 mixing with water, (c) air mixing with Cr(VI) solution, and (d) CO2 mixing with Cr(VI) solution (C-S–H = calcium silicate hydrate, Ett = ettringite, AFm = monosulfoaluminate hydrates, CBW = chemically bounded water, Mc = monocarboaluminate)

Fig. 9 Enlarged graph of DTG analysis for (a) 5H2O of Monocarboaluminate (b) CaCO3 and CO32− of Mc at 500–750 °C (c) Ca(OH)2 at 400–500 °C and (d) CaCrO4 at 1000–1300 °C

Figure 9b enlarged the neighbouring two peaks observed at approximately 500–750 °C. The peaks indicate the decomposition of CO32−. The peak at 700 °C represents CaCO3 as highly crystalline, whereas the peak at 650 °C indicates Mc defined as weakly crystalline (Scrivener et al. 2016). Interestingly, the peaks for CaCO3 and Mc were confirmed irrespective of the mixing method and the Cr(VI) addition, although the 5H2O in the interlayer of Mc at 160 °C was not.

Moreover, even though the absorption amount of CO2 was higher in the Cr(VI) added mixing (Fig. 3), the decomposition of CO32− was less in CO2_cr5 than that of CO2_cr0; the weight reductions of CO2_cr0 and CO2_cr5 were 6.40% and 4.76% respectively. This can be attributed to the partial replacement of CO32− in Mc or CaCO3 was partially replaced with CrO42− in the cement hydrates (Ohya et al. 2012). Furthermore, because the Mc peaks existed in the CO2_cr5 specimen at 650 °C, there is the possibility that the CO32− and CrO42− were not completely exchanged but coexisted in the cement structure. That is, a transformation of the Mc structure occurred (Ohya et al. 2012; Rae et al. 2022).

In addition, as shown in Fig. 9c, by enlarging the Ca(OH)2 peak, air_cr0 and CO2_cr0 showed an increase in the peak; however, air_cr5 and CO2_cr5 slightly decreased. This difference can be attributed to the consumption of Ca2+ ions during the generation of CaCrO4. This was also confirmed in the measurement of above 1000 °C as shown in Fig. 9d. Comparing the 28-day curing samples at 1000–1300 °C, the two peaks at approximately 1020 °C and 1200 °C were observed, representing the decomposition of CaCrO4 (Mao et al. 2015; Wu et al. 2020a). The water-soluble Cr(VI) is immobilised as CaCrO4 and deoxidised to Cr(III) above 1000 °C, as represented by Eq. 6.6 4CaCrO4→2CaCrO22+3O2+2CaO

The weight reductions between 1000–1300 °C were higher in CO2 mixing compared with air mixing; air_cr0, CO2_cr0, air_cr5, and CO2_cr5 decreased to 0.87%, 1.17%, 1.80%, and 2.40%, respectively. Accordingly, CO2 mixing appeared to affect the generation of cement hydrates, particularly Mc, CaCO3, Ca(OH)2, and CaCrO4. More Cr(VI) immobilisation was confirmed in CO2 mixing samples. The binding of Ca2+ and Cr(VI) or Cr(III) could be further evaluated by X-ray photoelectron spectroscopy (XPS) (Guo et al. 2024).

FTIR analysis

The results of the FTIR analysis are shown in Fig. 10. The bands at 920 cm−1 indicate the Si–O vibration of silicate, which were shifted to 950 cm−1 as the polymerisation and generation of C-S-Has hydration progressed (Zhang and Scherer 2011). The elongations at 1125 cm−1 and 1100 cm−1 were designated as S–O vibrations, which converged to 1120 cm−1 as the curing progressed. The bands between 3100–3700 cm−1 were the result of H2O molecules. The C-O vibration of CaCO3 appeared at 1420 cm−1. The bands at 874 cm−1 were inferred from the overlapping vibrations of Cr–O and Al–OH of the ettringite.Fig. 10 Result of FTIR for (a) air mixing with water, (b) CO2 mixing with water, (c) air mixing with Cr(VI) solution, and (d) CO2 mixing with Cr(VI) solution

Figure 11 is enlarged and compares the range 800–1600 cm−1. In Fig. 11a, curing for 0 d implies the hydration stoppage had been performed immediately after the mixing of cement paste. In the C-O bands, CO2 mixing samples stretched more than air mixing. At 28-day curing, shown in Fig. 11b, the CO2_cr5 had remained at almost the same transmission intensity as that in 0-day curing, whereas CO2_cr0 resulted in a decrease and aligned with air_cr0. Therefore, CO2_cr5 resulted in a significant amount of CO32− as the form of CaCO3. In addition, considering the outcomes of the XRD and TGA, it might be inferred that the reduced CO32− in CO2_cr0 had become Mc or Hemicarboaluminate, whose C-O band is known as possessing other vibration wavelengths (Horgnies et al. 2013).Fig. 11 FTIR result enlarged at 800–1600 cm−1 at (a) immediately after the mixing (i.e., 0-day curing) and (b) 28-day curing

Furthermore, the peak at 874 cm−1 was higher in air_cr5 and CO2_cr5 than in air_cr0 and CO2_cr0 samples in 0-day curing, which seemed to be due to the addition of Cr(VI). Later, the 28-day curing represented a higher peak in CO2_cr5 than in the other treatments. This inferred that CO2 mixing influenced the development of the immobilisation of CrO42− ions. Thus, CO2 mixing increased the Cr(VI) immobilisation capacity.

Assessing the effect of in situ CO2 mixing on the Cr(VI) release

Based on the tank leaching test results, in situ CO2 mixing reduced the amount of Cr(VI) leached from the cement specimens. The specimens with in situ CO2 mixing resulted in 0.614 mg/m2 of Cr(VI) leaching, which was almost ten times less than that in the control mixing (i.e. air mixing).

In accordance with the microstructural analysis, structural changes in the cement hydrates were confirmed in the CO2-mixed samples. Compared to air-mixed samples, CO2-mixed samples with 28-day curing exhibited the following features: (1) the total weight reduction in TGA was 27.89%, which was higher than 23.55% of air-mixed samples, indicating a lower porosity in CO2-mixed samples, and (2) more Mc and ettringite were observed in XRD, suggesting the possibility of the generation of more monochromate or chromate-ettringite. Therefore, the lower porosity and increment in Mc and ettringite generation possibly suppressed the mobility of Cr(VI), mitigating Dobs to 1.19 × 10–7 cm2/day and leading s to 97% after the applied test period.

Furthermore, this study found Cr(VI)-immobilised structures in CO2-mixed cement paste. In CO2-mixed samples, (1) a relatively large amount of CrO42− was immobilised as CaCrO4; this is because a larger amount of CaCrO4 was formed in the TGA at temperatures higher than 1000 ºC and a higher Cr–O extension was observed in the FTIR and (2) the partial disappearance of Mc and increment of CaCrO4 peak were detected in TGA, suggesting the incorporation of the CrO42− ion to the internal layer of Mc.

This finding indicates a potential contribution to both the challenges of the CO2 footprint and Cr(VI)-induced environmental problems in the cement industry. While this study was performed by use of OPC with comparatively small sized specimen. Therefore, mortar or concrete experiments near the field scale and environment should be performed to evaluate the actual CO2 absorption and pollutant immobilization performance. Further, the fresh cement paste should be elucidated in more detail in terms of pH changes and valance changes of chromium. These measurements can be beneficial for further discussion in Cr-immobilisation structures in cement. Moreover, considering the contamination of groundwater or the soil environment, further evaluation is desirable under the conditions examined in field environments, such as pH change owing to acid rain and structural changes owing to the potential mixing with industrial by-products (e.g. fly ash or ground granulated blast furnace slag). Combined with an experimental database of heavy metal leaching and the generation of cement hydrates, it is feasible to establish a monitoring system for underground heavy metal pollution.

Conclusion

This study evaluated the effect of a laboratory-scale in situ CO2 mixing method on the leachability of hexavalent chromium (Cr(VI)) from cement specimens. Tank leaching tests revealed that in situ CO2 mixing reduced Cr(VI) leaching from the cement specimens. The CO2-mixed samples showed only 0.614 mg/m2 of Cr(VI) leaching, almost ten times less than the air-mixed samples. Microstructural analysis confirmed structural changes in the CO2-mixed cement hydrates. These samples exhibited lower porosity, with a 27.89% weight reduction in thermogravimetric analysis (TGA) and higher monocarboaluminate and ettringite generation. These changes effectively lowered Cr(VI) mobility, reducing the observed diffusion coefficient (Dobs) to 1.19 × 10–7 cm2/day and achieving 97% of solidification rate (s) under the applied test period. This study also identified Cr(VI)-immobilised structures in the CO2-mixed cement, including CaCrO4 formation and CrO42− incorporation into Mc in the CO2-mixed samples. These findings demonstrate that CCUS technology, which has been the main focus of attention in recent years, is beneficial for reducing CO2 emissions and, from an environmental perspective, controlling the leaching of hazardous substances.

Author contributions

Conceptualization: Junboum Park & Kian Cho; Methodology: Won Kyung Kim & Kian Cho; Formal analysis and investigation: Won Kyung & Kian Cho; Writing—original draft preparation: Won Kyung & Kian Cho; Writing—review and editing: Juhyuk Moon & Daniel Cha & Junboum Park; Funding acquisition: Junboum Park & Juhyuk Moon; Supervision: Junboum Prak.

Funding

Open Access funding enabled and organized by Seoul National University. This work was supported by a Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant funded by the Korean government (MOTIE) (in situ carbonation technology development using CO2 emissions from the cement industry [grant number 20212010200080]); a Korea Institute for Advancement of Technology (KIAT) grant funded by MOTIE (Human Resource Development Program for Industrial Innovation [grant number P0017304]). The Institute of Engineering Research at Seoul National University provided research facilities for this study.

Data availability

The datasets are available from the corresponding author upon reasonable request.

Declarations

Ethics approval

This work does not contain any investigations with human participants or animals performed by any of the authors.

Consent to participate

Not applicable.

Consent to publish

Not applicable.

Competing interests

The authors declare no competing interests.

Publisher's Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
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References

Bakhshi N Sarrafi A Ramezanianpour AA Immobilization of hexavalent chromium in cement mortar: leaching properties and microstructures Environ Sci Pollut Res Int 2019 26 20829 20838 10.1007/s11356-019-05301-z 31111389
Bakhshi N, Sarrafi A, Ramezanianpour AA (2019) Immobilization of hexavalent chromium in cement mortar: leaching properties and microstructures. Environ Sci Pollut Res Int 26:20829–20838. 10.1007/s11356-019-05301-z31111389 10.1007/s11356-019-05301-z
Cau Dit Coumes C Courtois S Nectoux D Leclercq S Bourbon X Formulating a low-alkalinity, high-resistance and low-heat concrete for radioactive waste repositories Cem Concr Res 2006 36 2152 2163 10.1016/j.cemconres.2006.10.005
Cau Dit Coumes C, Courtois S, Nectoux D, Leclercq S, Bourbon X (2006) Formulating a low-alkalinity, high-resistance and low-heat concrete for radioactive waste repositories. Cem Concr Res 36:2152–2163. 10.1016/j.cemconres.2006.10.00510.1016/j.cemconres.2006.10.005
Costa M Klein CB Toxicity and Carcinogenicity of Chromium Compounds in Humans Crit Rev Toxicol 2006 36 155 163 10.1080/10408440500534032 16736941
Costa M, Klein CB (2006) Toxicity and Carcinogenicity of Chromium Compounds in Humans. Crit Rev Toxicol 36:155–163. 10.1080/1040844050053403216736941 10.1080/10408440500534032
El-Hassan H Shao Y Early carbonation curing of concrete masonry units with Portland limestone cement Cement Concr Compos 2015 62 168 177 10.1016/j.cemconcomp.2015.07.004
El-Hassan H, Shao Y (2015) Early carbonation curing of concrete masonry units with Portland limestone cement. Cement Concr Compos 62:168–177. 10.1016/j.cemconcomp.2015.07.00410.1016/j.cemconcomp.2015.07.004
Emsley J Nature's building blocks: an AZ guide to the elements 2011 USA Oxford University Press
Emsley J (2011) Nature’s building blocks: an AZ guide to the elements. Oxford University Press, USA
EN196–10:2016 (2016) Methods of testing cement - Part 10: Determination of the water soluble chromium (VI) content of cement. European Standard
EPA1315 (2013) Mass Transfer Rates of Constituents in Monolithic or Compacted Granular Materials Using a Semi-dynamic Tank Leaching Procedure. EPA
Eštoková A Palaščáková L Singovszká E Holub M Analysis of the Chromium Concentrations in Cement Materials Procedia Eng 2012 42 123 130 10.1016/j.proeng.2012.07.402
Eštoková A, Palaščáková L, Singovszká E, Holub M (2012) Analysis of the Chromium Concentrations in Cement Materials. Procedia Eng 42:123–130. 10.1016/j.proeng.2012.07.40210.1016/j.proeng.2012.07.402
Frías M, Sánchez de Rojas MI (2002) Total and soluble chromium, nickel and cobalt content in the main materials used in the manufacturing of Spanish commercial cements. Cem Concr Res 32, 435-440 10.1016/S0008-8846(01)00701-3
Guo X Ma H Zhou J Cheng W Ba M Stabilization mechanism of hexavalent chromium ions in portland cement-based materials Case Stud Constr Mater 2024 20 e03110 10.1016/j.cscm.2024.e03110
Guo X, Ma H, Zhou J, Cheng W, Ba M (2024) Stabilization mechanism of hexavalent chromium ions in portland cement-based materials. Case Stud Constr Mater 20:e03110. 10.1016/j.cscm.2024.e0311010.1016/j.cscm.2024.e03110
He C Yan B Li F Reactions of Chromium during the Calcination of Cement Clinker Produced Using Steel Slag. Journal of Wuhan University of Technology-Mater Sci Ed 2023 38 834 841 10.1007/s11595-023-2766-5
He C, Yan B, Li F (2023) Reactions of Chromium during the Calcination of Cement Clinker Produced Using Steel Slag. Journal of Wuhan University of Technology-Mater. Sci Ed 38:834–841. 10.1007/s11595-023-2766-510.1007/s11595-023-2766-5
Ho WSW Poddar TK New membrane technology for removal and recovery of chromium from waste waters Environ Prog 2001 20 44 52 10.1002/ep.670200115
Ho WSW, Poddar TK (2001) New membrane technology for removal and recovery of chromium from waste waters. Environ Prog 20:44–52. 10.1002/ep.67020011510.1002/ep.670200115
Horgnies M Chen JJ Bouillon C Overview about the use of Fourier transform infrared spectroscopy to study cementitious materials WIT Trans Eng Sci 2013 77 251 262 10.2495/MC130221
Horgnies M, Chen JJ, Bouillon C (2013) Overview about the use of Fourier transform infrared spectroscopy to study cementitious materials. WIT Trans Eng Sci 77:251–262. 10.2495/MC13022110.2495/MC130221
IARC (2012) Arsenic, metals, fibres, and dusts. In: Monographs on the evaluation of carcinogenic risks to humans, vol 100C. International Agency for Research on Cancer, Lyon (FR)
Leisinger SM Lothenbach B Le Saout G Johnson CA Thermodynamic modeling of solid solutions between monosulfate and monochromate 3CaO • Al2O3 • Ca[(CrO4)x(SO4)1–x] • nH2O Cem Concr Res 2012 42 158 165 10.1016/j.cemconres.2011.09.005
Leisinger SM, Lothenbach B, Le Saout G, Johnson CA (2012) Thermodynamic modeling of solid solutions between monosulfate and monochromate 3CaO • Al2O3 • Ca[(CrO4)x(SO4)1–x] • nH2O. Cem Concr Res 42:158–165. 10.1016/j.cemconres.2011.09.00510.1016/j.cemconres.2011.09.005
Li Z, He Z, Chen X (2019) The performance of carbonation-cured concrete. Materials (Basel) 12. 10.3390/ma12223729
Liu Y-X Yuan D-X Yan J-M Li Q-L Ouyang T Electrochemical removal of chromium from aqueous solutions using electrodes of stainless steel nets coated with single wall carbon nanotubes J Hazard Mater 2011 186 473 480 10.1016/j.jhazmat.2010.11.025 21122989
Liu Y-X, Yuan D-X, Yan J-M, Li Q-L, Ouyang T (2011) Electrochemical removal of chromium from aqueous solutions using electrodes of stainless steel nets coated with single wall carbon nanotubes. J Hazard Mater 186:473–480. 10.1016/j.jhazmat.2010.11.02521122989 10.1016/j.jhazmat.2010.11.025
Mao L Gao B Deng N Zhai J Zhao Y Li Q Cui H The role of temperature on Cr(VI) formation and reduction during heating of chromium-containing sludge in the presence of CaO Chemosphere 2015 138 197 204 10.1016/j.chemosphere.2015.05.097 26072117
Mao L, Gao B, Deng N, Zhai J, Zhao Y, Li Q, Cui H (2015) The role of temperature on Cr(VI) formation and reduction during heating of chromium-containing sludge in the presence of CaO. Chemosphere 138:197–204. 10.1016/j.chemosphere.2015.05.09726072117 10.1016/j.chemosphere.2015.05.097
Mondal MH Begum W Nasrollahzadeh M Ghorbannezhad F Antoniadis V Levizou E Saha B A comprehensive review on chromium chemistry along with detection, speciation, extraction and remediation of hexavalent chromium in contemporary science and technology Vietnam J Chem 2021 59 711 732 10.1002/vjch.202100048
Mondal MH, Begum W, Nasrollahzadeh M, Ghorbannezhad F, Antoniadis V, Levizou E, Saha B (2021) A comprehensive review on chromium chemistry along with detection, speciation, extraction and remediation of hexavalent chromium in contemporary science and technology. Vietnam J Chem 59:711–732. 10.1002/vjch.20210004810.1002/vjch.202100048
Mukherjee K Saha R Ghosh A Saha B Chromium removal technologies Res Chem Intermed 2013 39 2267 2286 10.1007/s11164-012-0779-3
Mukherjee K, Saha R, Ghosh A, Saha B (2013) Chromium removal technologies. Res Chem Intermed 39:2267–2286. 10.1007/s11164-012-0779-310.1007/s11164-012-0779-3
O'Neil MJ The Merck Index - An Encyclopedia of Chemicals, Drugs, and Biologicals 2013 Cambridge, UK Royal Society of Chemistry 1419
O’Neil MJ (2013) The Merck Index - An Encyclopedia of Chemicals, Drugs, and Biologicals. Royal Society of Chemistry, Cambridge, UK, p 1419
Ohya J, Atarashi D, Sango H, Sakai E (2012) Influence of calcium carbonate on immmobilization behavior of hexavalent chromium by AFm phase (in Japanese). Cement Sci Concrete Technol 66(1):15–21
Pacala S Socolow R Stabilization wedges: Solving the climate problem for the next 50 years with current technologies Science 2004 305 968 972 10.1126/science.1100103 15310891
Pacala S, Socolow R (2004) Stabilization wedges: Solving the climate problem for the next 50 years with current technologies. Science 305:968–972. 10.1126/science.110010315310891 10.1126/science.1100103
Pakade VE Tavengwa NT Madikizela LM Recent advances in hexavalent chromium removal from aqueous solutions by adsorptive methods RSC Adv 2019 9 26142 26164 10.1039/c9ra05188k 35531021
Pakade VE, Tavengwa NT, Madikizela LM (2019) Recent advances in hexavalent chromium removal from aqueous solutions by adsorptive methods. RSC Adv 9:26142–26164. 10.1039/c9ra05188k35531021 10.1039/c9ra05188k
Perkins RB Palmer CD Solubility of Ca6[Al(OH)6]2(CrO4)3·26H2O, the chromate analog of ettringite; 5–75°C Appl Geochem 2000 15 1203 1218 10.1016/S0883-2927(99)00109-2
Perkins RB, Palmer CD (2000) Solubility of Ca6[Al(OH)6]2(CrO4)3·26H2O, the chromate analog of ettringite; 5–75°C. Appl Geochem 15:1203–1218. 10.1016/S0883-2927(99)00109-210.1016/S0883-2927(99)00109-2
Perkins RB Palmer CD Solubility of chromate hydrocalumite (3CaO·Al2O3·CaCrO4·nH2O) 5–75°C Cem Concr Res 2001 31 983 992 10.1016/S0008-8846(01)00507-5
Perkins RB, Palmer CD (2001) Solubility of chromate hydrocalumite (3CaO·Al2O3·CaCrO4·nH2O) 5–75°C. Cem Concr Res 31:983–992. 10.1016/S0008-8846(01)00507-510.1016/S0008-8846(01)00507-5
Pöllmann H Auer S Cr6+-containing phases in the system CaO−Al2O3−CrO42−−H2O at 23°C J Solid State Chem 2012 185 82 88 10.1016/j.jssc.2011.10.022
Pöllmann H, Auer S (2012) Cr6+-containing phases in the system CaO−Al2O3−CrO42−−H2O at 23°C. J Solid State Chem 185:82–88. 10.1016/j.jssc.2011.10.02210.1016/j.jssc.2011.10.022
Rae R Graham MC Kirk CA Investigating the hydration of C3A in the presence of the potentially toxic element chromium-a route to remediation? RSC Adv 2022 12 29329 29337 10.1039/d2ra04497h 36320754
Rae R, Graham MC, Kirk CA (2022) Investigating the hydration of C3A in the presence of the potentially toxic element chromium-a route to remediation? RSC Adv 12:29329–29337. 10.1039/d2ra04497h36320754 10.1039/d2ra04497h
Rengaraj S Yeon K-H Moon S-H Removal of chromium from water and wastewater by ion exchange resins J Hazard Mater 2001 87 273 287 10.1016/S0304-3894(01)00291-6 11566415
Rengaraj S, Yeon K-H, Moon S-H (2001) Removal of chromium from water and wastewater by ion exchange resins. J Hazard Mater 87:273–287. 10.1016/S0304-3894(01)00291-611566415 10.1016/S0304-3894(01)00291-6
Saha B, Amine A, Verpoort F (2022) Special Issue: Hexavalent Chromium: Sources, Toxicity, and Remediation. Chem Africa 5: 1779–1780. 10.1007/s42250-022-00443-z
Saha B Orvig C Biosorbents for hexavalent chromium elimination from industrial and municipal effluents Coord Chem Rev 2010 254 2959 2972 10.1016/j.ccr.2010.06.005
Saha B, Orvig C (2010) Biosorbents for hexavalent chromium elimination from industrial and municipal effluents. Coord Chem Rev 254:2959–2972. 10.1016/j.ccr.2010.06.00510.1016/j.ccr.2010.06.005
Saha R Nandi R Saha B Sources and toxicity of hexavalent chromium J Coord Chem 2011 64 1782 1806 10.1080/00958972.2011.583646
Saha R, Nandi R, Saha B (2011) Sources and toxicity of hexavalent chromium. J Coord Chem 64:1782–1806. 10.1080/00958972.2011.58364610.1080/00958972.2011.583646
Saha R Saha B Removal of hexavalent chromium from contaminated water by adsorption using mango leaves (Mangifera indica) Desalin Water Treat 2014 52 1928 1936 10.1080/19443994.2013.804458
Saha R, Saha B (2014) Removal of hexavalent chromium from contaminated water by adsorption using mango leaves (Mangifera indica). Desalin Water Treat 52:1928–1936. 10.1080/19443994.2013.80445810.1080/19443994.2013.804458
Sanna A Uibu M Caramanna G Kuusik R Maroto-Valer MM A review of mineral carbonation technologies to sequester CO2 Chem Soc Rev 2014 43 8049 8080 10.1039/c4cs00035h 24983767
Sanna A, Uibu M, Caramanna G, Kuusik R, Maroto-Valer MM (2014) A review of mineral carbonation technologies to sequester CO2. Chem Soc Rev 43:8049–8080. 10.1039/c4cs00035h24983767 10.1039/c4cs00035h
Scrivener K Snellings R Lothenbach B A practical guide to microstructural analysis of cementitious materials 2016 Boca Raton Boca Raton CRC Press
Scrivener K, Snellings R, Lothenbach B (2016) A practical guide to microstructural analysis of cementitious materials. Boca Raton CRC Press, Boca Raton
Snellings R, Chwast J, Cizer O, De Belie N, Dhandapani Y, Durdzinski P, Elsen J, Haufe J, Hooton D, Patapy C, Santhanam M, Scrivener K, Snoeck D, Steger L, Tongbo S, Vollpracht A, Winnefeld F, Lothenbach B (2018) RILEM TC-238 SCM recommendation on hydration stoppage by solvent exchange for the study of hydrate assemblages. Mater Struct 51. 10.1617/s11527-018-1298-5
Takahashi S, Daimon M, Sakai E (2003) Sorption of CrO42− for cement hydrates and the leaching from cement hydrates after sorption. In: Proceedings of the 11th International Congress on the Chemistry of Cement Cement’s Contribution on the Development in the 21st Century, Durban, South Africa, pp 2166–2172
United Nations Environment Programme (2020) 2020 Global status report for buildings and construction: towards a zero-emission. In: Efficient and resilient buildings and construction sector. UNEP, Nairobi
Wang S Vipulanandan C Solidification/stabilization of Cr(VI) with cement Cem Concr Res 2000 30 385 389 10.1016/S0008-8846(99)00265-3
Wang S, Vipulanandan C (2000) Solidification/stabilization of Cr(VI) with cement. Cem Concr Res 30:385–389. 10.1016/S0008-8846(99)00265-310.1016/S0008-8846(99)00265-3
Wu Y Song S Xv Y Xue Z The formation mechanism and thermal stability of CaCrO4 IOP Conf Ser Earth Environ Sci 2020 514 052024 10.1088/1755-1315/514/5/052024
Wu Y, Song S, Xv Y, Xue Z (2020a) The formation mechanism and thermal stability of CaCrO4. IOP Conf Ser Earth Environ Sci 514:052024. 10.1088/1755-1315/514/5/05202410.1088/1755-1315/514/5/052024
Wu YH Lin JC Wang TY Lin TJ Yen MC Liu YH Wu PL Chen FW Shih YL Yeh IJ Hexavalent chromium intoxication induces intrinsic and extrinsic apoptosis in human renal cells Mol Med Rep 2020 21 851 857 10.3892/mmr.2019.10885 31974625
Wu YH, Lin JC, Wang TY, Lin TJ, Yen MC, Liu YH, Wu PL, Chen FW, Shih YL, Yeh IJ (2020b) Hexavalent chromium intoxication induces intrinsic and extrinsic apoptosis in human renal cells. Mol Med Rep 21:851–857. 10.3892/mmr.2019.1088531974625 10.3892/mmr.2019.10885
Zhang J Scherer GW Comparison of methods for arresting hydration of cement Cem Concr Res 2011 41 1024 1036 10.1016/j.cemconres.2011.06.003
Zhang J, Scherer GW (2011) Comparison of methods for arresting hydration of cement. Cem Concr Res 41:1024–1036. 10.1016/j.cemconres.2011.06.00310.1016/j.cemconres.2011.06.003
