Abstract
Magnesium potassium phosphate cements (MKPCs) are currently considered as the matrix materials for immobilization of radioactive waste of low and medium activity, as an alternative to Portland cements. At the same time, MKPC compound has the following advantages: fast hardening, high early strength, low shrinkage and high chemical resistance. Magnesium potassium phosphate cement is prepared at room temperature by an acid-base reaction between calcined magnesium oxide (MgO), potassium dihydrogen phosphate (KH2PO4) and water to form magnesium potassium phosphate hexahydrate MgKPO4 ∙ 6H2O known as K-struvite. To obtain MKPC, starting components of high purity and, accordingly, high cost are required. From an industrial point of view, this leads to an excessive price of the final product, and therefore, the use of inexpensive industrial waste as cement fillers is economically cost effective.
 In the present paper, the effect of fly ash and blast-furnace slag additives on the microstructure, compressive strength, and chemical resistance of MKPC samples was studied. The results indicate that particles of both ash and blast-furnace slag are involved in the reaction of MKPC obtaining with the formation of predominantly crystalline K-struvite. According to X-ray diffraction analysis, the content of K-struvite in samples with additives of both fly ash and blast-furnace slag is almost the same and amounts to 58–60 %. With the same addition of filler, samples with the addition of blast-furnace slag have a denser structure, which is formed due to the increased reactivity of blast-furnace slag particles. Moreover, MKPC samples with the addition of blast-furnace slag exhibit higher strength and better chemical resistance to leaching compared to MKPC samples with fly ash additions. The obtained results demonstrate the prospects of using industrial waste additives in the production of MKPC compounds characterized by high mechanical strength and chemical resistance.
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