Calcium carbide residue as auxiliary activator for one-part sodium carbonate-activated slag cements: compressive strength, phase assemblage and environmental benefits

Gao, Xuesong; Xiao, Yao; Yang, Tao; Zhou, Shiming; Wei, Haoguang; Zhang, Zuhua

doi:10.1016/j.conbuildmat.2021.125015

Cited by 75 publications

(23 citation statements)

References 46 publications

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“…The compressive strengths at the specific curing ages increased almost linearly with the increasing Ca(OH) 2 /Mg(OH) 2 ratios. Such an observation is consistent with the current state of knowledge that the addition of a Ca-rich auxiliary activator is beneficial for the formation of the main binding gel phase of C-A-S-H in the binders [ 31 , 32 ]. Additionally, the initial reaction between Na 2 CO 3 and Ca(OH) 2 results in the CaCO 3 precipitation in the aqueous phase, and thus, the presence of additional surfaces probably improves the nucleation and growth of the C-A-S-H gel phase [ 36 ].…”

Section: Resultssupporting

confidence: 91%

“…The dosage of Na 2 CO 3 was fixed as 10 wt% of slag [ 19 , 25 , 33 ]. The blended Ca(OH) 2 and Mg(OH) 2 were used as the auxiliary activators with the purpose of expediting the kinetics of alkali activation [ 32 ]. The total amount of the blended Ca(OH) 2 and Mg(OH) 2 was fixed as 5 wt% of slag, which was chosen according to other studies of Na 2 CO 3 -activated slag binders to achieve reliable early-age strength development during ambient curing [ 23 , 24 , 33 ].…”

Section: Experimental Methodsmentioning

confidence: 99%

“…Kovtun et al [ 29 ] enhanced the 1 day compressive strength of Na 2 CO 3 -activated slag concretes cured at ambient temperature up to 25 MPa via the additions of slaked lime (Ca(OH) 2 ) and silica fume. Akturk et al [ 30 ] observed that only the 3% Ca(OH) 2 addition promoted the hardening of the pastes within 6.5 h. Wang et al [ 31 ] revealed that the CaO addition was beneficial for the formation of C-A-S-H. Gao et al [ 32 ] suggested that the initial reaction between Ca(OH) 2 and Na 2 CO 3 was effective in removing the CO 3 2− ions in the aqueous phase to enhance the alkalinity. Besides CaO and Ca(OH) 2 , some Mg-rich auxiliary activators have also been reported to be effective in expediting the reaction kinetics.…”

Section: Introductionmentioning

confidence: 99%

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Properties and Microstructure of Na2CO3-Activated Binders Modified with Ca(OH)2 and Mg(OH)2

Xie

Liu

2022

Materials

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Delayed strength development and long setting times are the main disadvantageous properties of Na2CO3-activated slag cements. In this work, combined auxiliary activators of Ca(OH)2 and Mg(OH)2 were incorporated in one-part Na2CO3-activated slag binders to accelerate the kinetics of alkali activation. The properties and microstructure evolution were investigated to clarify the reaction mechanism. The results showed that the additions of auxiliary activators promoted the hardening of the pastes within 2 h. The 28 days compressive strengths were in the range of 39.5–45.5 MPa, rendering the binders practical cementitious materials in general construction applications. Ca(OH)2 was more effective than Mg(OH)2 in accelerating the kinetics of alkali activation. The dissolution of Ca(OH)2 released more OH− and Ca2+ ions in the aqueous phase to increase alkalinity in the aqueous phase and promote the formation of the main binding gel phase of calcium-aluminosilicate hydrate (C-A-S-H). An increase in the Ca(OH)2/Mg(OH)2 ratios increased autogenous shrinkage and decreased drying shrinkage of the binders. The formation of a compact pore structure restricted the water evaporation from the binders during the drying procedure.

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Section: Resultssupporting

confidence: 91%

Section: Experimental Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Properties and Microstructure of Na2CO3-Activated Binders Modified with Ca(OH)2 and Mg(OH)2

Xie

Liu

2022

Materials

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“…However, no second exothermic peak was observed in paste CR0S5 during the first 120 h. This indicated that a slow reaction occurred in the one-part Na 2 CO 3 -activated GBFS system. A similar result was reported by Gao et al [ 12 ], who observed an induction period over 72 h of Na 2 CO 3 -activated GBFS with 8 wt.% of Na 2 CO 3 by mass of GBFS and a water-to-binder ratio of 0.53. When the CRCF was added, the CO 3 2− of the reaction system was consumed by CRCF, which increased the amounts of OH − and accelerated the polymerization of C-(A)-S-H gels.…”

Section: Resultssupporting

confidence: 89%

“…In addition, Na 2 CO 3 , as a near-neutral salt, is less harmful to the handler than strong base activators and releases a lower carbon footprint [ 1 , 11 ]. However, compared to the NaOH and Na 2 O·nSiO 2 , Na 2 CO 3 provides a relatively weak alkaline environment for the dissolution of GBFS, and, therefore, a slow hydration process with a very long induction period and low early-age strength development can be observed in one-part Na 2 CO 3 -activated GBFS binders [ 12 , 13 , 14 ]. They even fail to harden after a curing time of more than 28 days at ambient temperature [ 4 , 15 ].…”

Section: Introductionmentioning

confidence: 99%

Accelerating the Reaction Kinetics of Na2CO3-Activated Slag Mortars by Calcined Recycled Concrete Fines

Wang

et al. 2022

Materials

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Sodium carbonate (Na2CO3), an environmentally friendly activator, has been shown to have vast potential for the development of sustainable alkali-activated slag mortars. However, Na2CO3-activated slag mortars exhibit a delayed reaction process and limited early-age strength development, restricting their wider application. In this work, the recycled concrete fines were calcined at a temperature of 800 °C for 1 h and then used as an auxiliary activator to improve the reaction kinetics of Na2CO3-activated slag mortars. The impact of the calcined recycled concrete fines (CRCF) dosage and Na2CO3 concentration on the compressive strength, hydration kinetics, and phase assemblage of mortars was evaluated. The results show that CRCF can react directly with Na2CO3 in the early stages, swiftly removing the CO32− in aqueous solution and providing an alkaline environment suitable for the dissolution of slag. This promotes the development of C-(A)-S-H, hydrotalcite, hemicarbonate, and monocarbonate. The hydration process and strength-giving phase of mortars can be improved further, as an increase in Na2CO3 concentration increases the initial alkaline content. Additionally, the most remarkable compressive strength value of 39.2 MPa was observed at 28 days in the mortar with 6% sodium oxide equivalent (Na2O-E) of Na2CO3 and 15% CRCF because of the synergistic effect of CRCF and Na2CO3.

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Enhancement of impact resistance of alkali‐activated slag concrete through biochar supplementation

Egodagamage,

Yapa,

Buddika

et al. 2024

Structural Concrete

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Biochar is a well‐known sustainable and effective additive used in mortar/concrete to improve its mechanical properties. However, its potential to improve the impact resistance of concrete is still unexplored. This paper investigates biochar's effectiveness in improving the strength and impact performance of alkali‐activated slag concrete (AASC). Five AASC samples with 0%, 2%, 4%, 6%, and 8% rice husk biochar (RB) were employed in an experimental program. The strength and the impact resistance were tested, and the latter was assessed over a drop‐weight test conforming to the ACI Committee 544 guidelines. The crack propagation of the impact‐tested samples was examined using micro‐CT images. The results showed that adding RB up to 6% improved, notably the 28‐day compressive strength of AASC. At 6% RB, the strength enhancement was 44.6%, whereas no additional gain was observed at the 8% RB blend. More importantly, except for the 8% RB sample, the impact resistance was considerably augmented with the RB level increment. The increment in the impact number at the first crack and the failure in the 6% RB sample were as high as 185% and 180%, respectively. The reduction in the solution/binder ratio of the mix with the addition of biochar and the internal curing effect of biochar were deemed to be responsible for these improvements. However, possibly due to biochar's brittle characteristics, the increase in RB dosage from 6% to 8% reduced the impact resistance drastically.

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Calcium carbide residue as auxiliary activator for one-part sodium carbonate-activated slag cements: compressive strength, phase assemblage and environmental benefits

Cited by 75 publications

References 46 publications

Properties and Microstructure of Na2CO3-Activated Binders Modified with Ca(OH)2 and Mg(OH)2

Properties and Microstructure of Na2CO3-Activated Binders Modified with Ca(OH)2 and Mg(OH)2

Accelerating the Reaction Kinetics of Na2CO3-Activated Slag Mortars by Calcined Recycled Concrete Fines

Enhancement of impact resistance of alkali‐activated slag concrete through biochar supplementation

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