Effect of particle size of aluminosilicate microspheres on the change of hydration heat of cement mortars and selected physical, chemical, and mechanical properties.

This subject of the work is the study of selected properties of cement mortars containing two fractions of aluminosilicate microspheres with grain size in the range of 125 to 250 μm and from 250 to 500 μm. Mortar mixtures with ordinary Portland cement (OPC 42.5R) and three substitution rates of cement by microspheres, 1.5%, 3.5%, and 5.0%, were investigated. For all cement mixes, the constant water–binder ratio (w/b) equal to 0.50 was used. The research program included the determination of chemical and phase composition, as well as select physical properties of the tested material. The heat of hydration was determined for the initial time (7 days) of samples curing at 23oC. The analysis showed that the micro-spheres consist of three main elements: silicon, aluminum, and iron, whose oxides constitute about 89% of the material. The compressive strength showed that the addition of aluminosilicate microspheres with a grain size below 250 μm increases cement mortars’ strength compared to the control mortar and cement mortars with a grain size above 250 mm. The total cumulative heat, measured in cement mortars at 7 days, ranges from 280.1 to 249.2 J/g for the grain sizes below 250 μm and from 298.5% to 266.4 % for the grain sizes above 500 μm and is higher for the control mortar. The aluminosilicate microspheres with a particle diameter of < 250 μm have a relatively high level of activity pozzolanic at 28 days compared to particles with a diameter of > 250 mm. The SEM analysis proved that the use of microspheres of grain size below 250 mm increases the CSH phase in the structure of cement mortars at 7 days. This is not only due to the much smaller particle size of FAM but also because of its higher calcium oxide (CaO) content compared with FAM of grain size up to 500 μm