Scholarly record

IMPROVEMENT OF CONSISTENCY AND SETTING TIME OF MAGNESIUM POTASSIUM PHOSPHATE CEMENT PASTES AND MORTARS

Zbyšek Pavlík, Simon Marusiak, Adam Pivák, Milena Pavlíková

Abstract

Magnesia based cement is known for over 150 years. Compared to Portland cement (PC), magnesium potassium cement (MPC) is more environmentally friendly material, because of its high carbonation capability and a lower environmental impact on the overall ecosystem quality and resources than PC. Fast setting connected with high early strength leads to the satisfying parameters achieved after a few hours. Therefore, MPC finds use as the concrete repair material for buildings, roads or concreting runways, etc. In the presented study, magnesium potassium phosphate-based pastes and mortars were designed and tested. The examined samples were composed of the commercially delivered dead burned magnesia, phosphate binder in a molar ratio M/P 8/1, various dosing of the setting retarder (borax), and batch water. In MPC-based mortar, standardized silica sand was used as only filler. First, the fresh paste mixtures were researched. Form the initial fresh state of the particular pastes, temperature and dynamic elastic modulus were continuously recorded. Consistency of the analysed pastes was characterized by the spreading diameter. The setting time was measured by a Vicat apparatus. In the next step, the hardened mortar samples blended with silica sand filler were investigated. For the basic characterization of studied materials, bulk density, specific density, and total open porosity were measured. Mechanical resistance was described by flexural and compressive strength tests conducted after 2, 5, and 14 days of hardening. Obtained results pointed to the prolongation of the setting time with the increasing dosage of borax in mixtures, up to 15 min. at 5 wt. % of the retarder content, lower production of exothermic heat during the hydration reaction, and better workability of fresh mixtures, whereas the basic structural properties remained nearly unchanged and good mechanical resistance was also retained. Generally, the application of borax retarder led to the improvement of fresh mixtures performance and made material more usable in practice.

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DOI resolver: doi.org/10.5593/sgem2021/6.1/s26.47

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