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Quantitative study of hydration of C3S and C2S by thermal analysis
Evolution and composition of C–S–H gels formed
of C 3 S and C 2 S hydration, C–S–H gel and portlandite (Ca(OH) 2 ), the importance of the C–S–H gel deserves special mention from the points of view of its engineering properties, elasticity and durability [ 11 – 15 ]. Therefore, it is well known
Thermogravimetrical analysis for monitoring carbonation of cementitious materials
Uptake of CO2 and deepening in C–S–H knowledge
Introduction Cement paste carbonation, i.e., the reaction between CO 2 and the hydrated cement phases, mainly calcium hydroxide or portlandite and calcium–silicate–hydrate (C–S–H) gel, can lead to a pH decrease, which in turn
than those of 100% Portland cement [ 3 ]. C. Alonso proved that after calcination at 750 °C, C–S–H gel transforms into a nesosilicate form with a C 2 S stoichiometry close to larnite, but less crystalline, and rehydration of the new generated
CSH reformation from the new nesoxilicate with a CaO/SiO 2 ratio close to the initial C–S–H gel and recovering its initial stoichiometry is not observed. The studies are carried out using a combination of DTA–TG with magnetic nuclear resonance (MNR
Summary
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.
–gel process is a low-temperature process from which hydrated calcium silicates (mainly type C–S–H gel and/or hyllebrandite) with high-surface areas are obtained as precursors to belite cement. The precursors are then dehydrated by heating without grinding at
diffraction peaks corresponding to C–S–H gel and AFt crystals in SSBC paste are relatively low, and a much higher diffraction peak of C 2 S is observed, indicating large amount of C 2 S in steel slag remains un-hydrated after 28 days curing. In contrast, the
Use of decomposition of portlandite in concrete fire as indicator of temperature progression into the material
Application to fire-affected builds
hydrated products of the bulk, like C–S–H gel or portlandite. Other transformations are related with the carbonates that can be formed due to the natural carbonation or by recarbonation processes associated with the CO 2 or CO formation during the fire
.35, 0.30, and 0.25 w/b ratios as compared to the normal mix. This is because of the pozzolanic reaction amongst metakaolin and portlandite, which results in the development of a C–S–H gel. It refines the microstructure of concrete as well as the bonding
Fig. 2a . The micrographs indicate stable and dense structures, even at 28 days of curing, and so there are no empty spaces for the growth of new minerals. The C–S–H gel forms fine-grained crystal aggregate, probably with structural parameters under