Effect of the densification of C–S–H on hydration kinetics of tricalcium silicate

Abstract

Effect of water to cement (w/c) ratio and temperature profiles on the densification of C–S–H (calcium silicate hydrate gel) and hydration kinetics of triclinic tricalcium silicate (C3S) is studied beyond the first day of hydration. Calorimetry and quantitative X‐ray diffraction/Rietveld analysis show that degree of hydration is unaffected by w/c up to 7 days and marginally thereafter. Coupling the degree of hydration with the portlandite content measured from thermal analysis indicate that C/S ratio of C–S–H decreases with increasing w/c. There is a clear increase in the portlandite content with increasing w/c, even though the degree of hydration is unchanged, due to the variations in C/S ratio of C–S–H. On the other hand, when C3S is initially cured at a lower temperature (20°C) and then at a higher temperature (40°C), there is a significant increase in the reactivity even until 28 days and vice versa. These experimental results were explained using the densified volumetric growth hypothesis, which assumes that hydration kinetics are dependent on the internal surface area of C–S–H.

Engineering hydration model for ordinary Portland cement based on heat flow calorimetry data

“…with parameters k, n and Q 1 determined by the Levenberg-Marquardt algorithm [22,30] and depicted in an Arrhenius diagram in Fig. 3, where the reduction of the overall heat release Q 1 with increasing curing temperature is consistent with the previous results in the literature [14,16]. Let us try to assess whether the separation in Eq.…”

Hydration of polyphase Ca3SiO5‐Ca3Al2O6 in the presence of gypsum and Na2SO4

“…Since EDS measurements carried out at high voltages (15kV) 23 are subjected to high interaction volumes, and hence, could lead to significant errors, the results are not always conclusive. 76 The coagulation of AFm phases on the C-S-H would further increase the Al/Si ratio measured by EDS. On the contrary, the Al IV / Si ratios from 29 Si NMR do not account for five-and sixfold coordinated Al in the C-(A)-S-H phase.…”

“…However, the Al IV /Si ratios determined in the present study from 29 Si MAS NMR (Table 3, Figure ) clearly show that there is a significant amount of Al incorporated in the C‐(A)‐S‐H phase but no clear variations in the incorporated amount of Al with different gypsum contents. Since EDS measurements carried out at high voltages (15kV) 23 are subjected to high interaction volumes, and hence, could lead to significant errors, the results are not always conclusive 76 . The coagulation of AFm phases on the C‐S‐H would further increase the Al/Si ratio measured by EDS.…”

Influence of water activity on hydration of tricalcium aluminate‐calcium sulfate systems

“…In an isothermal calorimetry profile (ie, heat evolution profile), this is observed as rapid increase in heat flow rate up to an intense exothermic peak, followed by a sharp decline, and then an exponentially decaying shoulder that lasts for several hours . Depending on the C 3 A and C$ particulate sizes, and their contents, characteristics of this peak (ie, approach to, departure from, and intensity of the peak) are subject to change . During this stage (ie, stage II), ettringite reacts with C 3 A and water to form monosulfoaluminate [C 4 A$H 12 ; an alumina‐ferric oxide‐monosulfate (AFm) hydrate phase as described in Equation ]; Δ H of the reaction is −237.64 kJ per mole C 3 A …”

“…12,34,36,42 Depending on the C 3 A and C$ particulate sizes, and their contents, characteristics of this peak (ie, approach to, departure from, and intensity of the peak) are subject to change. 12,33,43 During this stage (ie, stage II), ettringite reacts with C 3 A and water to form monosulfoaluminate [C 4 A$H 12 ; an alumina-ferric oxide-monosulfate (AFm) hydrate phase as described in Equation 3]; ΔH of the reaction is −237.64 kJ per mole C 3 A. 4,[33][34][35] The kinetics of C 3 A hydration during stage II-albeit, not fully understood-is assumed to be dictated by the nucleation-and-growth of monosulfoaluminate.…”