STUDY ON WATER VAPOR ADSORPTION ISOTHERMS OF HYDRATION PRODUCTS IN HARDENED CEMENT PASTE

Cement hydration products carbonation is not only blamed for the carbonation-induced hardened cement paste or concrete cracking, also attributed to the pore water PH-value decrease, which causes the reinforcement corrosion under the existence of water and oxygen due to removal of oxide film passivating rebar surface, in hardened cement paste and concrete. Based on chemical thermodynamics, this paper presents the susceptibility of different cement hydration products to carbonation through calculating their Standard Gibbs Free Energy respectively, Gibbs free energy under temperature variation and the minimum equilibrium pressure of carbon dioxide triggering the carbonation process. The calculated results show that, under standard state (25°C, 100kpa), the minimum equilibrium pressure of carbon dioxide triggering carbonation process is significantly variable for different types of cement hydration products. For example, mono-sulfate sulfoferrite hydrates (3CaOFe2O3CaSO412H2O) is the most susceptible to carbonation, followed by mono-sulfate aluminate hydrates (3CaOAl2O3CaSO412H2O), while multi-sulfate sulfoaluminate hydrates (3CaOAl2O33CaSO432H2O) is the least vulnerable to carbonation, followed by silicate hydrates (5CaO6SiO25.5H2O). The findings in this paper are significant in understanding thermodynamic mechanism of cement hydrates carbonation and seeking the solution to prevent cement hydrates from carbonation-induced deterioration.

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Difference between Internal and External Hydration of Hardened Cement Paste under Microwave Curing

Advances in Materials Science and Engineering ◽

10.1155/2021/3307325 ◽

2021 ◽

Vol 2021 ◽

pp. 1-9

Author(s):

Guoshun Yan ◽

Jiazheng Li ◽

Yuqiang Lin ◽

Xia Chen

Keyword(s):

Cement Paste ◽

Outer Part ◽

Total Porosity ◽

Fracture Morphology ◽

Hardened Cement ◽

Hydration Products ◽

Hardened Cement Paste ◽

Hydration Degree ◽

Microwave Curing ◽

The Difference

In order to investigate the difference between internal and external hydration of hardened cement paste under microwave curing, a comparative study on the hydration products, hydration degree, fracture morphology, and pore structure between the inner part and outer part of hardened cement paste (Φ120 mm × 120 mm) under microwave curing was carried out by XRD-Rietveld refinement, TG-DSC, SEM, and MIP methods. The results show that the total hydration degree of the inner part is lower at early ages, but with the hydration, there is little difference in the hydration degree between inner and outer parts at later ages. Apart from granular AFt crystal formed in the inner part of hardened cement paste, there is little difference in the fracture morphology between internal and external hydration. The total porosity of the outer part is lower than that of the inner part.

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Effect of Ultrafine Additives on the Morphology of Cement Hydration Products

Crystals ◽

10.3390/cryst11081002 ◽

2021 ◽

Vol 11 (8) ◽

pp. 1002

Author(s):

Grigory Yakovlev ◽

Rostislav Drochytka ◽

Gintautas Skripkiunas ◽

Larisa Urkhanova ◽

Irina Polyanskikh ◽

...

Keyword(s):

Silica Fume ◽

Cement Paste ◽

Cement Hydration ◽

Chemical Reactivity ◽

Xrd Analysis ◽

Hardened Cement ◽

Hydration Products ◽

Hardened Cement Paste ◽

X Ray ◽

Strong Adhesion

The present research is focused on the investigation of the influence of ultrafine additives on the structure formation of hardened cement paste and the establishment of the mechanisms of the morphological transformations, which determine the properties of hydrated products. In the course of the research, the modification of ordinary Portland cement was performed by the suspension of multi-walled carbon nanotubes (MWCNTs), carbon black (CB) paste, and silica fume (SF). Scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) microanalysis, X-ray diffraction (XRD) analysis, thermal analysis, and Fourier-transform infrared (FTIR) spectroscopy were used to study cement hydration products. The morphology of hardened cement paste depends on the chemical reactivity of additives, their geometry, and their genesis. The action mechanism of the inert carbon-based additives and pozzolanic silica fume were considered. The cement hydration products formed in the process of modification by both types of ultrafine additives are described. In the case of the modification of cement paste by inert MWCNTs and CB paste, the formation of cement hydration products on their surface without strong adhesion was observed, whereas in the case of the addition of SF separately and together with MWCNTs, the strong adhesion of additives and cement hydration products was noted.

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