Physicochemical change of cement pastes at elevated temperatures

AbstractPermeabilities to water and diffusion of ionic species in cementitious grouts, pastes and mortars are important keys to concrete durability. Investigations have been made of numerous materials containing portland and blended cements, and those with fine-grained filler, at room temperature and after prolonged curing at several elevated temperatures up to 90°C. These constitute part of studies of fundamental material relationships performed in order to address the question of long-term durability. In general, the permeabilities of the materials have been found to be low [many <10−8 Darcy (10−13 m·s−1)] after curing for 28 days or longer at temperatures up to 60°C. The results obtained at 90°C are somewhat more complex. In some sets of studies of blended cement pastes with w/c varying from 0.30 to 0.60 and cured at temperatures up to 90°C the more open-pore structure (at the elevated temperature and higher w/c) as evident from SEM microstructural studies as well as mercury porosimetry are generally correlated also with a higher permeability to liquid. The degree of bonding and permeability evident in paste or mortar/rock interfacial studies present somewhat more conflicting results. The bond strength (tensile mode) has been shown to be improved in some materials with increased temperature. The results of permeability studies of paste/rock couples show examples with similar low permeabilities, and some with increased permeability with temperature.Ionic diffusion studies also bring important bearing to understanding the effect of pore structure. The best interrelationships between chloride diffusion and pore structure appear to relate diffusion rate to median pore size. Similar results were found with “chloride permeability” test.

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Modeling the instantaneous phase composition of cement pastes under elevated temperatures

Cement and Concrete Research ◽

10.1016/j.cemconres.2020.105987 ◽

2020 ◽

Vol 130 ◽

pp. 105987 ◽

Cited By ~ 1

Author(s):

Chao Jiang ◽

Jing Fang ◽

Jun-Yu Chen ◽

Xiang-Lin Gu

Keyword(s):

Phase Composition ◽

Elevated Temperatures ◽

Cement Pastes ◽

Instantaneous Phase

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Dewatering Kinetics from Fresh Cement Pastes Enriched with Superabsorbent Polymer (SAP) Samples at Ambient and Elevated Temperatures Visualised and Quantified by Neutron Radiography Imaging

3rd International Conference on the Application of Superabsorbent Polymers (SAP) and Other New Admixtures Towards Smart Concrete - RILEM Bookseries ◽

10.1007/978-3-030-33342-3_14 ◽

2019 ◽

pp. 123-131 ◽

Cited By ~ 1

Author(s):

Christof Schröfl ◽

Viktor Mechtcherine ◽

David Mannes

Keyword(s):

Elevated Temperatures ◽

Neutron Radiography ◽

Superabsorbent Polymer ◽

Cement Pastes

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Behavior of blended cement pastes at elevated temperature

Chemical Industry and Chemical Engineering Quarterly ◽

10.2298/ciceq0602133k ◽

2006 ◽

Vol 12 (2) ◽

pp. 133-136

Author(s):

G. Kakali ◽

R. Leventi ◽

V. Benekis ◽

S. Tsivilis

Keyword(s):

Portland Cement ◽

Fire Resistance ◽

Elevated Temperatures ◽

Blended Cement ◽

Ultrasonic Pulse Velocity ◽

Ultrasonic Pulse ◽

Pulse Velocity ◽

Building Structures ◽

Cement Pastes ◽

Blended Cements

Fire can cause severe damage to building structures. This fact has increased the importance of the fire resistance of concrete. The consideration of the fire resistance of concrete requires the complete knowledge of the behaviour of each concrete component under elevated temperatures. The resistance of blended cement pastes upon heating was studied in the present paper. Natural pozzolana, fly ash, ground granulated blast-furnace slag, metakaolin and limestone were used as the main cement constituents. Blended cements were prepared by replacing a part of Portland Cement (PC) with the minerals mentioned above (10% w/w in the case of metakaolin, 20% w/w in the case of the rest materials). The specimens were water-cured for 3 months and then they were thermally treated at 200, 400, 600 800 and 1000?C for 1h. Visual inspection, mass measurements and ultrasonic pulse velocity measurements were carried out after each thermal treatment. It was concluded that the cohesion of the pastes was strongly affected by the kind of the main constituent, added to the Portland cement. The use of pozzolanic materials and especially metakaolin improved the fire resistance of the pastes, while the samples with limestone show the worst behavior.

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Evaluation of Properties and Microstructure of Cement Paste Blended with Metakaolin Subjected to High Temperatures

Materials ◽

10.3390/ma12060941 ◽

2019 ◽

Vol 12 (6) ◽

pp. 941 ◽

Cited By ~ 6

Author(s):

Wenqiang Wang ◽

Xinhao Liu ◽

Liang Guo ◽

Ping Duan

Keyword(s):

Compressive Strength ◽

Cement Paste ◽

Elevated Temperatures ◽

Blended Cement ◽

Thermal Exposure ◽

Polynomial Equation ◽

Cement Pastes ◽

Maximum Value ◽

Before And After ◽

Blended Cement Paste

The effects of 10% metakaolin addition on compressive strength, water absorption, shrinkage and microstructure evolution of cement paste after elevated temperatures exposure from room temperature to 800 °C were evaluated. The experimental results show that compressive strength increases at 200 °C and 400 °C compared with that obtained at ambient temperature. Up to 800 °C, compressive strength decreases rapidly. The addition of 10% metakaolin leads to the enhancement of compressive strength regardless of exposure temperatures. After thermal exposure at 400 °C, compressive strength reaches the maximum value. Thermal exposure degrades pore structure. A polynomial equation was used to indicate the shrinkage of cement paste or metakaolin-blended cement paste with testing days. Mechanical properties, permeability resistance, and shrinkage in cement pastes are closely related to the microstructure development. 10% metakaolin addition presents better thermal resistance, lower shrinkage and denser microstructure compared with pure cement paste before and after thermal exposure.

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