The dehydration of Portland cement paste plays an important role in the concrete structure explosive spalling at fire. Calcium silicate hydrate (CSH) and calcium hydroxide (CH) are the main hydration phases which
Authors:Esperanza Menéndez, Carmen Andrade, and Luis Vega
temperature on the hydration products of the cement gives rise to alterations in it. Thus, it is possible to identify the temperature intervals in which the decomposition of certain compounds present in the cement paste takes place. Thus, the portlandite
Authors:M. S. Amin, S. A. Abo-El-Enein, A. Abdel Rahman, and Khaled A. Alfalous
revealed that silica fume accelerated both the C 3 S and C 3 A hydration in the first few hours [ 2 ]. In addition, the compressive strengths of silica fume cement paste and mortar were evaluated at various water–cementitious ratios; the results showed that
Authors:S. M. A. El-Gamal, F. S. Hashem, and M. S. Amin
Thermal dehydration, which occurs by exposure of hardened cement pastes or concrete to high temperature, was become of important interest due to economic and safety sides. This effect may decrease the expected
strength and durability benefits for use as a construction material [ 11 – 13 ]. However, the hydration study of this mix in the paste system is limited [ 14 , 15 ]. For the first 24 h the hydration of Portland cement-Fly ash silica fume paste has been
This work focuses on the thermal and mineralogical transformations of red wall tile pastes. The pastes contain different amounts of calcareous and are prepared with Brazilian raw materials. Thermal transformations are evaluated by TG, DTG and DTA, dilatometric analysis, and X-ray diffraction. Four endothermic transformations were identified and interpreted as the release of physically adsorbed water, dehydration of hydroxides, dehydroxylation of kaolinite, and decomposition of carbonate. An exothermic transformation within the 925–950°C range is associated to crystallization of new phases such as calcium aluminosilicates and mullite. TG measurements indicate that the total mass loss of the pastes is dependent on the amount of calcareous addition. Dilatometric analysis indicates the onset of sintering at around 900°C, leading to shrinkage of the pellets. The thermal analysis results agree well with the X-ray diffraction.
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:S. Christopher Gnanaraj, Ramesh Babu Chokkalingam, G. Lizia Thankam, and S.K.M. Pothinathan
rheological properties of cement paste or mortar. The rheological property of concrete or mortar or cement paste is mainly affected by its yield stress and plastic viscosity. At yield stress, the cementitious material will initiate, restrict the flow. Concrete