Authors:E.T. Stepkowska, J. Perez-Rodriguez, M. Aviles, M. Jimenez de Haro and M. Sayagues
Specific surface, S, of CSH-gel particles of disordered layered structure, was studied by water sorption/retention in two cement pastes differing
in strength, i.e. C-33 (weaker) and C-43 (stronger), w/c=0.4. Hydration time in liquid phase was th=1 and 6 months, followed by hydration in water vapour either on increasing stepwise the relative humidity, RH=0.5→0.95→1.0 (WS) or on its lowering in an inverse order (WR). Specific surface was estimated from evaporable (sorbed) water
content, EV (110C), assuming a bi- and three-molecular sorbed water layer at RH=0.5 or 0.95, respectively (WS). On WR it was three- and three- to four-molecular (50 to 75%), respectively, causing a hysteresis
of sorption isotherm. At RH=0.5 the S increased with cement strength from 146 m2 g-1 (C-33, 1 m) to 166 m2 g-1 (C-43, 1 m) and with hydration time to 163 (C-33, 6 m) and to 204 m2 g-1 (C-43, 6 m). At RH=1.0 (and 0.95), higher S-value were measured but these differences were smaller: S amounted to 190-200 m2 g-1 in C-33 (1 and 6 m) and 198-210 m2 g-1 in C-43 (1 and 6 m). Thus no collapse occurred on air drying of paste C-43 (6 m).
Authors:E. Stepkowska, J. Perez-Rodriguez, M. Jimenez de Haro and M. Sayagues
Main hydration products of two cement pastes, i.e. CSH-gel, portlandite (P) (and specific surface S) were studied by static heating, and by SEM, TEM and XRD, as a function of cement strength (C-33 and C-43) hydration time (th) and subsequent hydration in water vapour.Total change in mass on hydration and air drying, Mo, increased with strength of cement paste and with hydration time. Content of water escaping at 110 to 220°C, defined as water bound with low energy, mainly interlayer and hydrate water, was independent on cement strength but its content increased with (th). Content of chemically bound (zeolitic) water in CSH-gel, escaping at 220-400°C, was slightly dependent on strength and increased with (th). It was possibly derived from the dehydroxylation of CSH-gel and AFm phase. Portlandite water, escaping at 400-500°C, was independent on cement strength and was higher on longer hydration. Large P crystals were formed in the weaker cement paste C-33. Smaller crystals were formed in C-43 but they increased with (th). Carbonate formated on contact with air (calcite, vaterite and aragonite), decomposed in cement at 600-700oC. It was high in pastes C-33(1 month) and C-43(1 month), i.e. 5.7 and 3.3%, respectively; it was less than 1% after 6 hydration months (low sensitivity to carbonation) in agreement with the XRD study showing carbonates in the air dry paste (1month), and its absence on prolonged hydration (6 months) and on acetone treatment. Water vapour treatment of (6 months) pastes or wetting-drying increased this sensitivity.Nanosized P-crystals, detected by TEM, could contribute to the cement strength; carbonate was observed on the rims of gel clusters.
Authors:E. T. Stepkowska, J. M. Blanes, C. Real and J. L. Perez-Rodriguez
The hydration products in two aged cement pastes (DTA/DTG/TG) were compared with those in fresh ones (static heating, SH)
and were also studied by mass spectrometry (MS), IR and thermo XRD-analysis. The products considered here were: the sorbed
water, the CSH gel including hydrates, portlandite, calcite, aragonite and vaterite. Except carbonates their content was higher
in the stronger paste C-43, than in C-33, but lowered with ageing (only the CSH gel water remained approximately unchanged).
The sorbed water content became with time lower and similar in both pastes (it evaporated up to 155-185C in TG); the escape
of the rest moved to higher temperatures (500-700C). The three DTG peaks at 200-400C indicated jennite-like phase in the
CSH gel; the mass loss (155-460C) was higher on ageing due to development of organic matter, especially in C-43 (DTA, TG,
IR). Portlandite content changed little and carbonate content increased considerably. They decomposed in air at 470 and 720-740C,
in argon at 450 and 680-710C and in vacuum at 400 and 630C, respectively (DTG peak, XRD). Between 500 and 700C the simultaneous
evolution of H2O and CO2was observed by MS, which is attributed to dehydroxylation of jennite-like phase and/or to decomposition of some carbonate
hydrate and/or hydrocarbonate (three peaks on CO2evolution curve, MS). The d(001) peak of portlandite exceeded the nominal value and will be analyzed separately.
Authors:E. T. Stepkowska, J. M. Blanes, A. Justo, M. A. Aviles and J. L. Perez-Rodriguez
Summary Two hydrated and aged cement pastes from India (NCB), w/c=0.4, of a similar chemical composition but of a different specific surface and different strength (OPC, C-33 and C-43), hydrated at w/c=0.4 for 1 month, were studied by XRD after 1 year and 5-6 year ageing on contact with air. They were tested by static heating (SH) in fresh state, and by DTA/DTG/TG, IR and mass spectrometry (MS), after ageing, presented elsewhere. The main XRD peaks of (i) portlandite were decreasing with T and disappearing about 450°C, (ii) calcite peak at room T was small and broad, it increased gradually, especially after portlandite disappearance; above 600°C it was lowered and it was lost above 700°C. Important variation in the d(001) of portlandite with ageing was observed, exceeding the standard value of d(001)=4.895 Å (72-0156). It was higher in the paste C-33 (4.925-4.936 Å), containing more carbonates, than in the paste C-43 (4.916-4.927 Å). Small variations only were found in the value of d(101), i.e. 2.627-2.635 Å (nominally 2.622 Å), whereas the d(104) of calcite could be used as internal standard and other calcium carbonates (vaterite and aragonite) showed a small variation only. The increase ind(hkl) with temperature was straight linear (in portlandite ?d(001)=0.095 Å, at 30-400°C) and the thermal expansion coefficient estimated thereform was high (4.75-4.95·10-5 K-1). Close to the T of decomposition the ?d/?T became steeper. The thermal variation of d(104)=3.035 Å of calcite (?d=0.015 Å at 30-400°C) was smaller than that ofd(101) of portlandite (?d=0.025 Å at 30-400°C) and was similar in C-33 and C-43. The thermal expansion coefficient was 1.54 10-5 K-1, thus higher than the reported aa=0.65·10-5 K-1.
Authors:Xin Jin, Zhen Wang, San-Ping Chen, Zhu-Jun Wang and Sheng-Li Gao
compounds were identified by elemental analysis as the formula C 9 H 8 O 5 Na 2 (Calculated: C, 44.64%; H, 3.33%; O, 33.04%. Found: C, 44.26%; H, 3.61%; O, 33.28%) and C 8 H 5 O 4.5 Na 2 (Calculated: C, 43.85%; H, 2.30%; O, 32.86%. Found: C, 43.29%; H, 2
Authors:Tea Mihelj, Zoran Štefanić and Vlasta Tomašić
) found: C, 62.90; H, 9.56; N, 9.16%; requires C, 62.92; H, 9.57; N, 9.17%; for C43 H 80 N 4 O 7 ( 3 ) found: C, 67.48; H, 10.56; N, 7.33%; requires C, 67.50; H, 10.54; N, 7.32%.
The scheme of the