Influence of perlite addition on the strength development and thermal stability of calcium aluminate cement mortars

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2018
Şengül, Kemal
Calcium aluminate cement is a special cement that reaches high strength in a short time but suffers a considerable loss of strength due to moisture and temperature-related conversion of metastable calcium aluminum hydrates. The study aimed to produce stratlingite as a stable hydration product to completely stop or reduce this chemical conversion using an inexpensive and abundant silica source. Ground perlite was chosen as the source of silica. Perlite was mixed with calcium aluminate cement in different proportions and two different water-to-binder ratios. The paste and mortar samples obtained were cured under different temperature and humidity conditions. Na2SO4 and Ca(OH)2 were also added in small quantities to these mixtures to investigate their influence on strength development and hydrated phases at early ages. A strength loss is observed in the pure cement samples due to conversion, after 20-30d for the dry-cured samples but after only 2-3d for the wet-cured samples. The loss is small and slow (<10-20 %) for the dry-cured samples, but quite significant (up to ~ 80 %) and rapid in wet-cured cases. As the amount of ground perlite that replaces the cement increases strength decreases. However, the early strength gained is maintained more for the perlite-incorporated mixtures. Stratlingite formation is confirmed by X-ray diffraction analysis in several of the perlite-containing mixtures. Loss of strength was completely prevented by the addition of 1-2 % Na2SO4 to mixtures containing more than 50 % perlite. Addition of Ca(OH)2 was not very effective against conversion, however, it greatly reduced setting time. Addition of perlite also decreased setting time. In contrast, Na2SO4 addition delayed setting. The heat of hydration decreased with increasing perlite content. Although the addition of perlite or chemicals proved beneficial, none of the mixtures were able to maintain a significant portion of their original strengths or masses after exposure to 600 ℃ or 1100 ℃.

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Citation Formats
K. Şengül, “Influence of perlite addition on the strength development and thermal stability of calcium aluminate cement mortars,” M.S. - Master of Science, Middle East Technical University, 2018.