The role of metakaolin in pore structure evolution of Portland cement pastes revealed by an impedance approach

Cai, Rongjin; Tian, Zushi; Ye, Hailong; He, Zhen; Tang, Shengwen

doi:10.1016/j.cemconcomp.2021.103999

Cited by 36 publications

(6 citation statements)

References 37 publications

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“…The MIP pore size distributions of reference OPC and LC 3 pastes without and with natural carbonation are compared in Figure 12. The comparison of pore structures of non-carbonated OPC and LC 3 pastes with the same w/p ratio has been reported in the literature, suggesting that LC 3 generally has a refined pore structure than OPC-counterparts at late ages, owing to the physiochemical roles of MK [3,45,46]. In non-carbonated states, the incorporation of sulfate salts noticeably enlarges the porosity and coarsens the pore structure of LC 3 , particularly for the Na 2 SO 4 and K 2 SO 4 salts.…”

Section: Pore Structure Alterationssupporting

confidence: 55%

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

Li¹,

Ye²

2021

Sustainability

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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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Section: Pore Structure Alterationssupporting

confidence: 55%

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

Li¹,

Ye²

2021

Sustainability

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“…Due to the filling effect contributed by the small MK particle size, the cracks that typically form in cement specimens are largely filled, which improves the density and compressive strength of the workpiece. Moreover, the high pozzolanic activity enables the large number of Al 2 O 3 and SiO 2 within MK to react with Ca(OH) 2 to generate a fibrous calcium silicate hydrate (C–S–H) gel, which further improves the compressive strength of the specimen [ 28 , 29 ]. However, if metakaolin exceeds 10% substitution, the compressive strength of the specimen instead declines substantially.…”

Section: Resultsmentioning

confidence: 99%

Investigating the Mechanical Properties and Durability of Metakaolin-Incorporated Mortar by Different Curing Methods

Dong

Pei

et al. 2022

Materials

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In this paper, the traditional, silicate-based Portland cement (PC) was employed as the control to explore the impact of adding varying amounts of metakaolin (MK) on the mechanical properties of cement mortar. In fact, as a mineral admixture, metakaolin (MK) has the ability to significantly improve the early strength and sulfate resistance of cement mortar in traditional, silicate-based Portland cement (PC). In addition to this, the performance of Portland cement mortar is greatly affected by the curing mode. The previous research mainly stays in the intermittent curing and alkaline excitation mode, and there are few studies on the influence of relatively humidity on it. Moreover, the paper investigated the impact of four different curing methods about humidity on the mechanical properties and sulfate resistance. The results show that the best content of metakaolin in Portland cement is 10% (M10), and the best curing method is 95% humidity in the first three days followed by 60% humidity in the later period (3#). Based on previous literature that suggests that adding MK thickens water film layer on the surface of mortar, the mechanism of MK increasing the early strength of cement was analyzed. The compressive strength of the Portland cement containing 10% MK (M10) after 1 day curing is 3.18 times that of pristine PC mortar, and is comparable if PC is cured for three days under the same curing conditions. The traditional PC mortar is highly dependent on the wet curing time, and normally requires a curing time of at least seven days. However, the incorporation of MK can greatly reduce the sensitivity of Portland cement to water; MK cement mortar with only three days wet curing (3#M10) can reach 49.12 MPa after 28 days, which can greatly shorten the otherwise lengthy wet curing time. Lastly, the cement specimens with MK also demonstrated excellent resistance against sulfate corrosion. The work will provide a strong theoretical basis for the early demolding of cement products in construction projects. At the same time, this study can also provide a theoretical reference for the construction of climate drought and saline land areas, which has great reference value.

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“…Due to the serious environmental problems posed by the production of cement, a series of green supplementary cementitious materials (SCMs) are being studied and developed to partially replace cement and thus decrease environmental pollution [ 5 ]. SCMs can be mainly classified into two categories: natural pozzolanic minerals (such as pozzolana, kaolin or metakaolin, and calcined clay) [ 6 , 7 , 8 ] and industrial by-products [ 9 , 10 , 11 ]. Considering their relatively low cost and the benefits to environmental protection, industrial by-products with high pozzolanic activity and/or hydration capacity, such as steel slag [ 12 ], slag [ 13 , 14 ], fly ash [ 15 , 16 ], and silica fume [ 17 ], are very suitable to be used in the development of cementitious composites as a substitute for cement.…”

Section: Introductionmentioning

confidence: 99%

Effect of Particle Size and Morphology of Siliceous Supplementary Cementitious Material on the Hydration and Autogenous Shrinkage of Blended Cement

Zhao

et al. 2023

Materials

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Supplementary cementitious material (SCM) plays an important role in blended cement, and the effect of the particle size and morphology of siliceous supplementary cementitious material on hydration should not be ignored. In this study, 0.5 h and 1 h of wet grinding was applied to pretreat iron ore tailing powder (TP), and the divergence in pozzolanic behavior and morphology were investigated. Then, the treated TPs were used to replace the 30% cement contents in preparing blended cementitious paste, and the impact mechanism of morphology on performance was studied emphatically. M, the autogenous shrinkages of pastes were tested. Finally, hydration reaction kinetics was carried out to explore the hydration behavior, while X-ray diffraction (XRD) and thermogravimetric analysis (TGA) were used to characterize the hydration product properties, respectively. Meanwhile, microscopy intrusion porosimetry (MIP) was also carried out to characterize the pore structures of hardened specimens. Results indicated that wet grinding has a dramatic effect on particle size and morphology, but hardly affects the phase assemblages and pozzolanic reactivity of TP, while the particle shape of TP changes from sub-circular to clavate and, finally, back to sub-circular. The results of hydration reaction kinetics, representing the morphology of particles, had a significant effect on hydration rate and total heat, and compared with the sub-circle one, the clavated particle could inhibit the hydration procedure. With the increasing grinding time, the compressive strength of cementitious paste was increased from 17.37% to 55.73%, and the micro-pore structure became denser; however, the autogenous shrinkage increased.

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The role of metakaolin in pore structure evolution of Portland cement pastes revealed by an impedance approach

Cited by 36 publications

References 37 publications

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

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

Investigating the Mechanical Properties and Durability of Metakaolin-Incorporated Mortar by Different Curing Methods

Effect of Particle Size and Morphology of Siliceous Supplementary Cementitious Material on the Hydration and Autogenous Shrinkage of Blended Cement

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