Influence of Alkalis on Natural Carbonation of Limestone Calcined Clay Cement Pastes

Vulnerability to atmospheric carbonation is one of the major durability concerns for limestone calcined clay cement (LC3) concrete due to its relatively low overall alkalinity. In this study, the natural carbonation behaviors of ternary ordinary Portland cement-metakaolin-limestone (OPC-MK-LS) blends containing various sulfate salts (i.e., anhydrous CaSO4, Na2SO4, and K2SO4) are studied, with the aim of revealing the influence of alkali cations (Na+, K+). Detailed analyses on the hydrated phase assemblage, composition, microstructure, and pore structure of LC3 pastes prior to and post indoor carbonation are conducted. The results show that the incorporation of sulfate salts accelerates the setting and strength gain of LC3 pastes, likely through enhancement of ettringite formation, but undermines its later age strength achievement due to the deleterious effect of alkali cations (Na+, K+) on late age OPC hydration. The carbonation resistance of LC3 systems is considerably undermined, particularly with the incorporation of Na2SO4 or K2SO4 salts, due to the simultaneous pore coarsening effect and reduced CO2-binding capacity. The carbonation-induced phase and microstructural alterations of LC3 pastes are discussed and compared with those of reference OPC pastes.

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Durability of clinker reduced shotcrete: Ca2+ leaching, sintering, carbonation and chloride penetration

Materials and Structures ◽

10.1617/s11527-021-01644-7 ◽

2021 ◽

Vol 54 (2) ◽

Author(s):

Marlene Sakoparnig ◽

Isabel Galan ◽

Florian R. Steindl ◽

Wolfgang Kusterle ◽

Joachim Juhart ◽

...

Keyword(s):

Binding Capacity ◽

Cementitious Materials ◽

Chloride Penetration ◽

Supplementary Cementitious Materials ◽

Conventional Concrete ◽

Sprayed Concrete ◽

Carbonation Resistance ◽

Negative Environmental Impact ◽

The Impact ◽

Positive Effect

AbstractThe reduction of clinker use is mandatory to lower the negative environmental impact of concrete. In shotcrete mixes, similarly to the case of conventional concrete, the use of supplementary cementitious materials (SCMs) and proper mix design allow for the substitution of clinker without compromising the mechanical properties. However, the impact of the substitution on the durability of shotcrete needs to be further assessed and understood. The results from the present study, obtained from real-scale sprayed concrete applications, show a reduction of the Ca2+ leaching and sintering potential of clinker-reduced shotcrete mixes due to the presence of SCMs. This positive effect, crucial for low maintenance costs of tunnels, is mainly related to a reduced portlandite content, which on the other hand negatively affects the carbonation resistance of shotcrete. Additionally, the hydration of SCMs positively influences the chloride penetration resistance presumably due to a combination of microstructural changes and changes in the chloride binding capacity. Differences found in the pore size distribution of the various mixes have low impact on the determined durability parameters, in particular compared to the effect of inhomogeneities produced during shotcrete application.

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Influence of pH on the chloride binding capacity of Limestone Calcined Clay Cements (LC3)

Cement and Concrete Research ◽

10.1016/j.cemconres.2020.106031 ◽

2020 ◽

Vol 131 ◽

pp. 106031 ◽

Cited By ~ 4

Author(s):

François Avet ◽

Karen Scrivener

Keyword(s):

Binding Capacity ◽

Chloride Binding ◽

Calcined Clay ◽

Influence Of Ph

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Slag Blended Cement Paste Carbonation under Different CO2 Concentrations: Controls on Mineralogy and Morphology of Products

Materials ◽

10.3390/ma13153404 ◽

2020 ◽

Vol 13 (15) ◽

pp. 3404

Author(s):

Wei Liu ◽

Shifa Lin ◽

Yongqiang Li ◽

Wujian Long ◽

Zhijun Dong ◽

...

Keyword(s):

Blended Cement ◽

Co2 Concentration ◽

Magic Angle Spinning ◽

Magic Angle ◽

Accelerated Carbonation ◽

X Ray Diffraction ◽

Cement Pastes ◽

Co2 Concentrations ◽

Angle Spinning ◽

Natural Carbonation

To investigate the effect of different CO2 concentrations on the carbonation results of slag blended cement pastes, carbonation experiments under natural (0.03% CO2) and accelerated conditions (3, 20, and 100% CO2) were investigated with various microscopic testing methods, including X-ray diffraction (XRD), 29Si magic angle spinning nuclear magnetic resonance (29Si MAS NMR) and scanning electron microscopy (SEM). The XRD results indicated that the major polymorphs of CaCO3 after carbonation were calcite and vaterite. The values of the calcite/(aragonite + vaterite) (c/(a + v)) ratios were almost the same in all carbonation conditions. Additionally, NMR results showed that the decalcification degree of C-S-H gel exposed to 0.03% CO2 was less than that exposed to accelerated carbonation; under accelerated conditions, it increased from 83.1 to 84.2% when the CO2 concentration improved from 3% to 100%. In SEM observations, the microstructures after accelerated carbonation were denser than those under natural carbonation but showed minor differences between different CO2 concentrations. In conclusion, for cement pastes blended with 20% slag, a higher CO2 concentration (above 3%) led to products different from those produced under natural carbonation. A further increase in CO2 concentration showed limited variation in generated carbonation products.

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Recycling of Reverse Osmosis (RO) Reject Water as a Mixing Water of Calcium Sulfoaluminate (CSA) Cement for Brick Production

Applied Sciences ◽

10.3390/app9235044 ◽

2019 ◽

Vol 9 (23) ◽

pp. 5044

Author(s):

Hwan Lee ◽

Dongho Jeon ◽

Haemin Song ◽

Sung Won Sim ◽

Dohoon Kim ◽

...

Keyword(s):

Reverse Osmosis ◽

Toxicity Characteristic Leaching Procedure ◽

Cement Pastes ◽

Calcium Sulfoaluminate ◽

Reject Water ◽

Ettringite Formation ◽

Friedel’S Salt ◽

Mixing Water ◽

Strength Improvement ◽

Leaching Procedure

This study explored the possibility of using reverse osmosis (RO) reject water as a mixing water for producing cementitious bricks using calcium sulfoaluminate (CSA) cement along with gypsum, and it investigated the changes in the properties of CSA cement pastes when RO reject water was used. The results were compared with those obtained using purified water and seawater. Overall, the use of RO reject water improved the cement paste’s strength. Given that the use of RO reject water very slightly affected ettringite formation but more significantly influenced the Al2O3-Fe2O3-mono (AFm) phases (i.e., monosulfate, kuzelite, and Friedel’s salt) and amorphous aluminum hydroxide (AH3), the strength improvement was likely mainly due to the formation of Friedel’s salt rather than ettringite formation. This study also demonstrated that the use of RO reject water for brick production satisfied the Korean Standards (KS) F 4004 and toxicity characteristic leaching procedure (TCLP); thus, it is recommended to use RO reject water as a mixing water to produce CSA cement bricks for use in construction.

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Delayed ettringite formation in 4-year old cement pastes

Cement and Concrete Research ◽

10.1016/s0008-8846(96)00161-5 ◽

1996 ◽

Vol 26 (11) ◽

pp. 1649-1659 ◽

Cited By ~ 31

Author(s):

R. Yang ◽

C.D. Lawrence ◽

J.H. Sharp

Keyword(s):

Delayed Ettringite Formation ◽

Cement Pastes ◽

Ettringite Formation

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Effect of Limestone Fillers on Ca-Leaching and Carbonation of Cement Pastes

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.711.269 ◽

2016 ◽

Vol 711 ◽

pp. 269-276 ◽

Cited By ~ 3

Author(s):

Quoc Tri Phung ◽

Norbert Maes ◽

Diederik Jacques ◽

Geert de Schutter ◽

Guang Ye

Keyword(s):

Nitrate Solution ◽

Elevated Pressure ◽

Economic Benefits ◽

Chemical Degradation ◽

Leaching Rate ◽

Carbonation Depth ◽

Cement Pastes ◽

Microstructural Alterations ◽

Ammonium Nitrate Solution ◽

Degradation Rates

Because of its environmental and economic benefits, part of cement is replaced by limestone fillers (LS). However, the effect of LS on the chemical degradation of cement-based materials is still unclear. In this study, accelerated leaching and carbonation were applied on cement pastes to study the effects of LS replacement on the degradation rates and microstructural alterations of degraded materials. Ammonium nitrate solution was used to accelerate the leaching process, while carbonation was speeded up by applying an elevated pressure gradient of pure CO2 on samples with 65% relative humidity. The carbonation rate was characterized by phenolphthalein carbonation depth and CO2 uptake, while leaching rate was quantified by phenolphthalein leaching depth and Ca-leached amount. Leached/carbonated samples were analyzed by a series of post-analysis techniques to characterize the microstructural and mineralogical changes. Results showed that, for a similar w/c ratio, a higher LS replacement resulted in lower leaching rate. For carbonation, LS replacement promoted the CO2 uptake despite similar carbonation depth. Furthermore, LS replacement led to less C-S-H carbonation compared to samples without LS.

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