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.
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 and
- PAR ID:
- 10457801
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Journal of the American Ceramic Society
- Volume:
- 103
- Issue:
- 4
- ISSN:
- 0002-7820
- Page Range / eLocation ID:
- p. 2764-2779
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract -
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
-
more » « less
Abstract The hydration of tricalcium silicate (C3S)—the major phase in cement—is effectively arrested when the activity of water (
a H) decreases below the critical value of 0.70. While it is implicitly understood that the reduction ina Hsuppresses the hydration of tricalcium aluminate (C3A: the most reactive phase in cement), the dependence of kinetics of C3A hydration ona Hand the criticala Hat which hydration of C3A is arrested are not known. This study employs isothermal microcalorimetry and complementary material characterization techniques to elucidate the influence ofa Hon the hydration of C3A in [C3A + calcium sulfate (C$) + water] pastes. Reductions in water activity are achieved by partially replacing the water in the pastes with isopropanol. The results show that with decreasinga H, the kinetics of all reactions associated with C3A (eg, with C$, resulting in ettringite formation; and with ettringite, resulting in monosulfoaluminate formation) are proportionately suppressed. Whena H ≤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 whena H ≤0.45. On the basis of this criticala H, the solubility product of C3A (K C3A) 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, criticala HandK C3A) that are prerequisites for numerical modeling of C3A hydration. -
more » « less
Abstract It is demonstrated that the addition of nanoparticles can decrease the viscosity of an entangled polymer matrix (plasticization). While there has been considerable effort in understanding the role of bare nanoparticles on viscosity, the corresponding study on grafted particles is nascent. Two nanometer radius zirconia fillers with a bimodal population of grafted PDMS is used. Two fillers are considered: one has grafted chains with a molecular weight, Mg, less than the entanglement M, Mg < Me(ZrO21k 10k), and the other filler has grafted chains M > Mc(the critical Me) (ZrO21k 36k). The ZrO21k 10k composites exhibit plasticization for large matrix molecular weight Mm. The ZrO21k 36k composites, in contrast, have Einstein‐like behavior. The plasticization effects are either due to: the small filler size relative to the tube diameter or an increase in chain mobility at the interface due to autophobic dewetting.
-
more » « less
Abstract For the fiberglass industry making E‐Glass fiber products predominantly, reduction in glass batch melting energy can be achieved by using alternative raw materials that improve the kinetics of the batch‐to‐melt (B
t M) conversion process. The present study evaluates the effects of the following five types of natural silicate minerals: kaolin (comprising low [<5 wt%] and high [>50 wt%] “free” quartz), pyrophyllite, anorthosite, and wollastonite, on the Bt M conversion process using a reference commercial E‐Glass composition. The study used isothermal heat treatment of individual silicate minerals and batch samples containing them, infrared spectroscopy, powder x‐ray diffraction, and differential scanning calorimetry (DSC) to characterize the stages of the BtM conversion process in detail. Based on the results of this study, a simplified reaction scheme or mechanism is proposed to account for the effect of batch chemistry on the Bt M kinetics, namely, “free SiO2” + “free CaO” → CaSiO3controls the kinetics of the batch melting. Relative to the E‐Glass control batch made using kaolin, sand, and limestone, the DSC tests showed the benefits of using pyrophyllite (replacing kaolin and sand), anorthosite (replacing kaolin and some limestone), and wollastonite (replacing limestone) in lowering the Bt M conversion energy (from room temperature [RT] to 1200°C) between 20% and 50%.
