An official website of the United States government
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
Influence of size‐classified and slightly soluble mineral additives on hydration of tricalcium silicate
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
- PAR ID:
- 10457801
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Journal of the American Ceramic Society
- Volume:
- 103
- Issue:
- 4
- ISSN:
- 0002-7820
- Format(s):
- Medium: X Size: p. 2764-2779
- Size(s):
- p. 2764-2779
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
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
-
Amziane, S; Merta, I; Page, J. (Ed.)Portland cement is one of the most used materials on earth. Its annual production is responsible for approximately 7% of global carbon dioxide (CO2) emissions. These emissions are primarily associated with (1) the burning of fossil fuels to heat cement kilns and (2) the release of CO2 during limestone calcination. One proposed strategy for CO2 reduction includes the use of functional limestone fillers, which reduce the amount of portland cement in concrete without compromising strength. This study investigated the effect of using renewable, CO2-storing, biogenic CaCO3 produced by E. huxleyi as limestone filler in portland limestone cements (PLCs). Biogenic CaCO3 was used to synthesize PLCs with 0, 5, 15, and 35% limestone replacement of portland cement. The results substantiate that the particle sizes of the biogenic CaCO3 were significantly smaller and the surface areas significantly larger than that of reagent grade CaCO3. X-ray diffraction indicated no differences in mineralogy between reagent-grade and biogenic CaCO3. The use of biogenic CaCO3 as a limestone filler led to (i) increased water demand at the higher replacements, which was countered by using a superplasticizer, and (ii) enhanced nucleation during cement hydration, as measured by isothermal conduction calorimetry. The 7-day compressive strengths of the PLC pastes were measured using mechanical testing. Enhanced nucleation effects were observed for PLC samples containing biogenic CaCO3. 7-day compressive strength of the PLCs produced using biogenic CaCO3 were also enhanced compared to PLCs produced using reagent-grade CaCO3 due to the nucleation effect. This study illustrates an opportunity for using CO2-storing, biogenic CaCO3 to enhance mechanical properties and CO2 storage in PLCs containing biologically architected CaCO3.more » « less
-
Abstract Magnesium silicate hydrate (M‐S‐H) represents a promising alternative to traditional cement, particularly for low‐pH construction applications such as nuclear waste encapsulation and carbon dioxide injection. The durability of construction materials, a critical aspect of their suitability for various purposes, is primarily governed by the kinetics of dissolution of the binder phase under service conditions. In this study, we employed in situ atomic force microscopy to assess the dissolution rates of M‐S‐H in water equilibrated with air. Quantitative analysis based on changes in volume and height revealed dissolution rates ranging from 0.18 to 3.09 × 10−12 mol/cm2/s depending on the precipitate Mg/Si ratio and morphology. This rate surpasses its crystalline analogs, talc (Mg3Si4O10(OH)2) and serpentine (Mg3(Si2O5)(OH)4), by about three to five orders of magnitude. Interestingly, oriented M‐S‐H dissolved faster than non‐oriented M‐S‐H. Spatially resolved assessments of dissolution rates facilitated a direct correlation between rates and morphology, showing that edges and smaller crystallites dissolve at a faster pace compared to facets and larger crystallites. The outcomes of this study provide insights into the mechanisms governing the dissolution of M‐S‐H and the factors dictating its durability. These findings hold implications for the strategic design and optimization of M‐S‐H for various applications.more » « less
-
Abstract Optoelectronics are crucial for developing energy‐efficient chip technology, with phase‐change materials (PCMs) emerging as promising candidates for reconfigurable components in photonic integrated circuits, such as nonvolatile phase shifters. Antimony sulfide (Sb2S3) stands out due to its low optical loss and considerable phase‐shifting properties, along with the non‐volatility of both phases. This study demonstrates that the crystallization kinetics of Sb2S3can be switched from growth‐driven to nucleation‐driven by altering the sample dimension from bulk to film. This tuning of the crystallization process is critical for optical switching applications requiring control over partial crystallization. Calorimetric measurements with heating rates spanning over six orders of magnitude, reveal that, unlike conventional PCMs that crystallize below the glass transition, Sb2S3exhibits a measurable glass transition prior to crystallization from the undercooled liquid (UCL) phase. The investigation of isothermal crystallization kinetics provides insights into nucleation rates and crystal growth velocities while confirming the shift to nucleation‐driven behavior at reduced film thicknesses—an essential aspect for effective device engineering. A fundamental difference in chemical bonding mechanisms was identified between Sb2S3, which exhibits covalent bonding in both material phases, and other PCMs, such as GeTe and Ge2Sb2Te5, which demonstrate pronounced bonding alterations upon crystallization.more » « less
