skip to main content

This content will become publicly available on November 1, 2024

Title: Hydration and phase evolution of blended cement composites containing lithium and saturated metakaolin
Although the high efficiency of coupled lithium and saturated metakaolin in alkali-silica reaction mitigation has been documented, its influence on cement hydration remains uninvestigated. In this study, saturated metakaolin with varying degrees of saturation and its combined influence with lithium on the hydration kinetics, phase evolution, and development of microstructure and molecular structures of hydration products in the blended cement composite was investigated. The experimental and thermodynamic modeling results indicate the synergistic effect between saturated metakaolin and lithium in enhancing the hydration of cement, interaction between metakaolin and cement, incorporation of Al in the silicate chains, and precipitations of Al-rich phases. In the blended cement matrix, the dissolution of metakaolin, formation of calcium silicate hydrates with incorporated aluminum (C-(A)-S-H), and precipitation of strätlingite are improved by 19.6%, 17.6%, and 20.0%, respectively, and the formation of cubic siliceous hydrogarnet was triggered.  more » « less
Award ID(s):
Author(s) / Creator(s):
Publisher / Repository:
Date Published:
Journal Name:
Cement and Concrete Composites
Edition / Version:
Page Range / eLocation ID:
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract

    The hydration of tricalcium silicate (C3S)—the major phase in cement—is effectively arrested when the activity of water (aH) decreases below the critical value of 0.70. While it is implicitly understood that the reduction inaHsuppresses the hydration of tricalcium aluminate (C3A: the most reactive phase in cement), the dependence of kinetics of C3A hydration onaHand the criticalaHat which hydration of C3A is arrested are not known. This study employs isothermal microcalorimetry and complementary material characterization techniques to elucidate the influence ofaHon the hydration of C3A in [C3A + calcium sulfate (C$) + water] pastes. Reductions in water activity are achieved by partially replacing the water in the pastes with isopropanol. The results show that with decreasingaH, the kinetics of all reactions associated with C3A (eg, with C$, resulting in ettringite formation; and with ettringite, resulting in monosulfoaluminate formation) are proportionately suppressed. WhenaH ≤0.45, the hydration of C3A and the precipitation of all resultant hydrates are arrested; even in liquid saturated systems. In addition to—and separate from—the experiments, a thermodynamic analysis also indicates that the hydration of C3A does not commence or advance whenaH ≤0.45. On the basis of this criticalaH, the solubility product of C3A (KC3A) was estimated as 10−20.65. The outcomes of this work articulate the dependency of C3A hydration and its kinetics on water activity, and establish—for the first time—significant thermodynamic parameters (ie, criticalaHandKC3A) that are prerequisites for numerical modeling of C3A hydration.

    more » « less
  2. Abstract

    Early‐age hydration of cement is enhanced by slightly soluble mineral additives (ie, fillers, such as quartz and limestone). However, few studies have attempted to systematically compare the effects of different fillers on cementitious hydration rates, and none have quantified such effects using fillers with comparable, size‐classified particle size distributions (PSDs). This study examines the influence of size‐classified fillers [ie, limestone (CaCO3), quartz (SiO2), corundum (Al2O3), and rutile (TiO2)] on early‐age hydration kinetics of tricalcium silicate (C3S) using a combination of experimental methods, while also employing a modified phase boundary and nucleation and growth model. In prior studies, wherein fillers with broad PSDs were used, it has been reported that between quartz and limestone, the latter is a superior filler due to its ability to partake in anion‐exchange reactions with C‐S‐H. Contrary to prior investigations, this study shows that when size‐classified andarea matchedfillers are used—which, essentially, eliminate degrees of freedom associated with surface area and agglomeration of filler particulates—the filler effect of quartz is broadly similar to that of limestone as well as rutile. Results also show that unlike quartz, limestone, and rutile—which enhance C3S hydration kinetics—corundum suppresses hydration of C3S during the first several hours after mixing. Such deceleration in C3S hydration kinetics is attributed to the adsorption of aluminate anions—released from corundum's dissolution—onto anhydrous particulates’ surfaces, which impedes both the dissolution of C3S and heterogeneous nucleation of C‐S‐H.

    more » « less
  3. A novel internal conditioning (InCon) technique based on saturated sodium montmorillonite (sMT) functionalized with two non-ionic surfactants, polyoxyethylene (9) nonylphenylether and t-octyl phenoxy poly ethoxyethanol, is investigated in this study. With the integration of water for internal curing and pozzolanic reactivity in a single system, the role of InCon in modifying cement hydration kinetics is comprehensively elucidated. The results indicate that, in the presence of InCon, both silicate reaction and secondary aluminate reaction rates are enhanced, and the apparent activation energy (Ea) of cement hydration was decreased from 34.3 KJ/mol to 28.7 KJ/mol indicating a lower temperature sensitivity and threshold of the cement hydration reactions. In addition, decreased CH contents, improved degree of hydration, increased chemical shrinkage, and the formation of additional Csingle bondSsingle bondH and aluminum-containing phases were obtained from the cement with InCon. The autogenous shrinkage of cement and the negative impact of dry sMT on the early age strength of cement can be offset by InCon paving a new path to improve the overall properties of concrete. 
    more » « less
  4. Abstract

    The focus of this study is to elucidate the role of particle size distribution (PSD) of metakaolin (MK) on hydration kinetics of tricalcium silicate (C3S–T1) pastes. Investigations were carried out utilizing both physical experiments and phase boundary nucleation and growth (pBNG) simulations. [C3S + MK] pastes, prepared using 8%massor 30%massMK, were investigated. Three different PSDs of MK were used: fine MK, with particulate sizes <20 µm; intermediate MK, with particulate sizes between 20 and 32 µm; and coarse MK, with particulate sizes >32 µm. Results show that the correlation between specific surface area (SSA) of MK's particulates and the consequent alteration in hydration behavior of C3S in first 72 hours is nonlinear and nonmonotonic. At low replacement of C3S (ie, at 8%mass), fine MK, and, to some extent, coarse MK act as fillers, and facilitate additional nucleation and growth of calcium silicate hydrate (C–S–H). When C3S replacement increases to 30%mass, the filler effects of both fine and coarse MK are reversed, leading to suppression of C–S–H nucleation and growth. Such reversal of filler effect is also observed in the case of intermediate MK; but unlike the other PSDs, the intermediate MK shows reversal at both low and high replacement levels. This is due to the ability of intermediate MK to dissolve rapidly—with faster kinetics compared to both coarse and fine MK—which results in faster release of aluminate [Al(OH)4] ions in the solution. The aluminate ions adsorb onto C3S and MK particulates and suppress C3S hydration by blocking C3S dissolution sites and C–S–H nucleation sites on the substrates’ surfaces and suppressing the post‐nucleation growth of C–S–H. Overall, the results suggest that grinding‐based enhancement in SSA of MK particulates does not necessarily enhance early‐age hydration of C3S.

    more » « less
  5. Metakaolin (MK) has been widely used in modifying cement and designing high-performance concrete, while the role of this alumino-silicate mineral has not been fully exploited due to its low reaction degree, especially at high-volume incorporations. To enhance the pozzolanic reactivity, functionalization of MK particles with two non-ionic surfactants, namely polyoxyethylene (9) nonylphenylether (PONPE9) and t-octyl phenoxy poly ethoxyethanol (TX100), are investigated in this study under a hypothesis that the intercalations of the surfactants into MK’s interlayer space can trigger changes in structure and properties. The dry MK particles were mixed with aqueous solutions with two surfactant concentrations to reach two surfactant loadings in MK at its 1.0 and 6.0 cation exchange capacity (CEC). The surfactant uptake behavior of MK and its influence on the hygroscopic swelling, pozzolanic reactivity, and dissolution behavior in simulated cement pore solution were characterized. The results indicate that, compared with TX100, PONPE9 can be absorbed by MK more easily. After functionalization at 1.0 and 6.0 CEC, MK exhibited surfactant mass fractions of 1.85% and 3.81% for TX100, and 1.95% and 5.39% for PONPE9, respectively. The intercalation of surfactants resulted in an up to 28.6% increase in the swell index of MK when absorbing water. A more robust aluminum and silicon dissolution behavior in the simulated cement pore solution was observed from the functionalized MK. Increases in reaction heat and lime consumption capacity were obtained in the MK-lime blends indicating the enhanced pozzolanic reactivity of MK after functionalization and paving a path to enhance the role of MK in future sustainable concrete design. 
    more » « less