Understanding hydration heat of mortars containing supplementary cementitious materials with potential to immobilize heavy metal containing waste

Phung, Quoc Tri; Ferreira, Eduardo Gurzoni Alvares; Seetharam, S. C.; Nguyen, Van Tuan; Govaerts, Joan; Valcke, Elie

doi:10.1016/j.cemconcomp.2020.103859

Cited by 29 publications

(12 citation statements)

References 52 publications

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“…The granulated blast furnace slag was supplied by Ecocem Benelux with a chemical composition determined by X-ray fluorescence (XRF) 39 listed in Table 1 . Solid NaOH pellets (99% purity, VWR Chemicals) were dissolved in deionized water to obtain a solution of 5 mol/l, which was then mixed with a commercial sodium silicate solution from VWR Chemicals (consisting of 8.97% Na 2 O, 26.78% SiO 2 , and 64.25% H 2 O) to form the alkali activating solution.…”

Section: Methodsmentioning

confidence: 99%

Alteration in molecular structure of alkali activated slag with various water to binder ratios under accelerated carbonation

Nguyễn

Phung

et al. 2022

Sci Rep

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Carbonation of alkali activated materials is one of the main deteriorations affecting their durability. However, current understanding of the structural alteration of these materials exposed to an environment inducing carbonation at the nano/micro scale remains limited. This study examined the evolution of phase assemblages of alkali activated slag mortars subjected to accelerated carbonation (1% CO2, 60% relative humidity, up to 28 day carbonation) using XRD, FTIR and 29Si, 27Al, and 23Na MAS NMR. Samples with three water to binder (w/b) ratios (0.35, 0.45, and 0.55) were investigated. The results show that the phase assemblages mainly consisted of C-A-S-H, a disordered remnant aluminosilicate binder, and a minor hydrotalcite as a secondary product. Upon carbonation, calcium carbonate is mainly formed as the vaterite polymorph, while no sodium carbonate is found after carbonation as commonly reported. Sodium acts primarily as a charge balancing ion without producing sodium carbonate as a final carbonation product in the 28-day carbonated materials. The C-A-S-H structure becomes more cross-linked due to the decalcification of this phase as evidenced by the appearance of Q4 groups, which replace the Q1 and Q2 groups as observed in the 29Si MAS NMR spectra, and the dominance of Al(IV) in 27Al MAS NMR. Especially, unlike cementitious materials, the influence of w/b ratio on the crystalline phase formation and structure of C-A-S-H in the alkali activated mortars before and after carbonation is limited.

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Section: Methodsmentioning

confidence: 99%

Alteration in molecular structure of alkali activated slag with various water to binder ratios under accelerated carbonation

Nguyễn

Phung

et al. 2022

Sci Rep

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“…Three different w/c ratios (0.4, 0.5, 0.6) were used to obtain different microstructures to study their effects on the carbonation process. The cement paste was prepared using a 5 L laboratory mixer in order to obtain a homogeneous mixture [31]. Then it was vibrated to remove entrapped air and was cast in sealed cylindrical PVC molds with an inner diameter of 9.75 cm and height of 40 cm that prevented carbonation during curing for 28 days [17].…”

Section: Cement Paste Mixing Casting and Curingmentioning

confidence: 99%

Synergistic Effects between Carbonation and Cracks in the Hardened Cement Paste

et al. 2022

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This paper investigates the synergistic interaction between carbonation and microcracks in hardened cement pastes. Ordinary Portland cement pastes with three different water/cement ratios of 0.4, 0.5 and 0.6, hydrated for 28 days with crack apertures ranging from 10 to 150 μm were subjected to accelerated carbonation in a climate chamber that controls the targeted relative humidity (65 and 75%), CO2 concentration (0.3 vol.% and 1 vol.%) and temperature (20 ℃). Mercury intrusion porosimetry, N2-adsorption and thermogravimetry analysis were used to quantify the carbonation-induced changes in pore size distribution, porosity and phase assemblages. Additionally, the changes in crack apertures were followed during carbonation. The results indicated that cracks within the investigated range facilitate the carbonation along the crack surface due to a faster gas diffusion process. The cracks with apertures below 50 μm increase the carbonation depth at least by a factor of two for all studied w/c and environmental conditions. We observed a constant increase in crack openings during carbonation and its linear relationship with the amount of precipitated calcium carbonate. Due to depletion of CH and decalcification of C-S-H close to the sample surface, the crack aperture increase becomes limited. Therefore, the crack apertures do not increase further after the material around the crack is carbonated. It was also found that the densification of the carbonated cement matrix coexists with large capillary pores (>50 nm) or cracks, especially for the low w/c samples. The shift in pore size distribution from about 100 nm towards smaller pores (4.5–50 nm) and a decrease in gel pore fractions after 28 days of carbonation also indicate a simultaneous calcium carbonate precipitation in meso/capillary pores and decalcification of C-S-H at the nanoscale.

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“…The high heat of cement hydration can be encountered in mass concrete with a high cement content where the temperature can exceed 65 • C, which can lead to DEF [18,19]. As it has been shown in previous studies [20][21][22], partial replacements of supplementary cementitious materials (SCM) such as silica fume, blast furnace slag, limestone, fly ash, and metakaolin can significantly reduce the heat generated during hydration while resulting in equal or even better mechanical properties. In particular, Kolani et al [23] show the extent of hydration heat reduction with the use of slag-based blended cement.…”

Section: Introductionmentioning

confidence: 99%

Numerical Study of Potential Delayed Ettringite Formation in Cemented Nuclear Wasteforms

Danfour,

Perko,

Seetharam

et al. 2023

Sustainability

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This paper presents a numerical study to investigate delayed ettringite formation (DEF) that may pose a long-term durability risk by altering the microstructure with consequent swelling leading to cracking. A chemo–thermal model is used to predict the evolution and distribution of temperature and hydration phases in a wide range of blended cements. In particular, the influence of nuclear waste loading, waste package size, and the addition of supplementary cementitious materials (SCMs) on DEF is systematically and numerically investigated. The analyses show that higher amounts of ordinary Portland cement (OPC) and waste loadings result in higher hydration temperatures and consequently increased DEF potential by enhancing sulfoaluminate dissolution and hydrogarnet precipitation. Partial replacement of OPC with SCMs reduced hydration heat and mitigated DEF risks. The analysis indicated that the DEF evolution may be different for waste packages of different sizes due to a shift from sulfate-controlling to aluminate-controlling reactions at high temperatures. Interestingly, higher temperatures did not necessarily induce higher DEF potential due to the excessive precipitation of aluminates in the form of hydrogarnet. This research enriches our understanding of DEF’s complex behavior, providing valuable insights for engineering applications beyond civil engineering, such as nuclear waste conditioning.

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Understanding hydration heat of mortars containing supplementary cementitious materials with potential to immobilize heavy metal containing waste

Cited by 29 publications

References 52 publications

Alteration in molecular structure of alkali activated slag with various water to binder ratios under accelerated carbonation

Alteration in molecular structure of alkali activated slag with various water to binder ratios under accelerated carbonation

Synergistic Effects between Carbonation and Cracks in the Hardened Cement Paste

Numerical Study of Potential Delayed Ettringite Formation in Cemented Nuclear Wasteforms

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