Cement Paste Mixture Proportioning with Particle Packing Theory: An Ambiguous Effect of Microsilica

Abstract

Recently, the research of innovative building materials is focused on applying supplementary materials in the form of micro- and nanopowders in cementitious composites due to the growing insistence on sustainable development. Considering above, in paper, a research on the effect of microsilica and SiO2 nanoparticles addition to cement paste, designed with Andreasen and Andersen (AA) packing density model (PDM), in terms of its physical and mechanical properties was conducted. Density, porosity, compressive strength, hardness, and modulus of indentation were investigated and compared regarding different amount of additives used in cement paste mixes. Microstructure of the obtained pastes was analyzed. The possibility of negative influence of alkali-silica reaction (ASR) on the mechanical properties of the obtained composites was analyzed. The results of the conducted investigations were discussed, and conclusions, also practical, were presented. The obtained results confirmed that the applied PDM may be an effective tool in cement paste design, when low porosity of prepared composite is required. On the other hand, the application of AA model did not bring satisfactory results of mechanical performance as expected, what was related, as shown by SEM imaging, with inhomogeneous dispersion of microsilica, and creation of agglomerates acting as reactive aggregates, what as a consequence caused ASR reaction, crack occurrence and lowered mechanical properties. Finally, the study found that the use of about 7.5% wt. of microsilica is the optimum in regards to obtain low porosity, while, to achieve improved mechanical properties, the use of 4 wt. % of microsilica seems to be optimal, in the case of tested cement pastes.

A Study on the Cement Gel Formation Process during the Creation of Nanomodified High-Performance Concrete Based on Nanosilica

“…Modification with microsilica is currently very popular due to its effectiveness in improving the properties of concrete both separately and in combination with other additives [ 15 , 19 , 26 , 27 , 28 , 39 , 40 , 41 , 42 , 43 ]. The most effective dosages of microsilica vary from 5 to 20%, depending on the raw materials used and the types of concrete.…”

“…At the same time, the increase in strength characteristics varies from insignificant, when only microsilica is added, to quite impressive (30–80%), when other additives are used along with microsilica, in particular, flask and diatomite [ 27 ], fly ash [ 19 ], carbon nanotubes [ 26 ], nanosilica, and nanosilica sol [ 19 , 41 , 43 , 44 ]. Microsilica densifies and strengthens the structure, increasing its uniformity and stabilizing the cement hydration process [ 19 , 27 , 40 , 41 , 42 , 43 , 44 ].…”