When nanoparticles hurt: A critical assessment of SiO2 and Al2O3 in cement mortar

The combined interactive effect of SiO2 and Al2O3 nanoparticles is illustrated in this paper on the mechanical and microstructural properties of cement mortar in hot climatic conditions similar to that in Baghdad/Basra city. The aim was to investigate the effect of various doses (0–2.0 wt %) of nanoparticles with emphasis on workability, compressive and flexural strength, drying shrinkage, and thermal conductivity. In an attempt to simulate more practical results that are similar to the location characteristics, the tested specimens are further submitted to 45 °C with 40 km/h wind speeds and 30–35 % relative humidity after testing. The microstructural properties and analysis are further carried out by SEM techniques, mercury intrusion porosimetry analysis (MIP), and helium pycnometry analysis. The result shows that the lower dosages (≤1.0 wt %) of nanoparticles led to more desirable packing density and strength with lower shrinkage. At higher dosages, there is more agglomeration with higher open porosity as well as poor mechanical properties. The study determines that there exists a dosage beyond which the use of nanoparticles is more hazardous than beneficial and thus draws attention to the need to optimize such dosages with hot and windy conditions.