The effect of 5- to 70-nm SiO₂ nanoparticles on the mechanical properties of nanocement materials was examined. The strength development of portland cement with nano-SiO₂ and superplasticizing admixture was investigated. Experimental results demonstrate an increase in the compressive and flexural strengths of mortars with SiO₂ nanoparticles. Because the distribution of nano-SiO₂ particles within the cement paste plays an essential role and governs the overall performance of these products, the addition of a superplasticizer was proposed to facilitate the distribution of nano-SiO₂ particles. The application of superplasticizer and high-speed dispergation were found to be effective disagglomeration techniques to improve the strength of superplasticized portland cement mortars, which reached up to 63.9 and 95.9 MPa (Sample 4B3, synthesized by using the sol–gel method in a base reaction medium at ethanol-to-tetraethoxysilane and water-to-tetraethoxysilane molar ratios of 24) at the ages of 1 day and 28 days, respectively. At corresponding ages, the compressive strength of reference portland cement mortars was 53.3 and 86.1 MPa. It is concluded that the effective dispersion of nanoparticles is essential to obtain composite materials with improved performance.

This research evaluates four sustainable cementitious composites with sustainable plant fibers and bio-aggregates: (1) cementitious matrix composite with lechuguilla fibers (LFC) and (2) with flax fibers (FFC); and (3) cementitious matrix composite with wood shavings (WSC) and (4) with hemp shavings (HSC). The fibers are for reinforcement and the shavings act as bio-aggregates as a total replacement for limestone aggregates. The lechuguilla (LF) and flax (FF) fibers were treated; wood (WS) and hemp (HS) bio-aggregates were also processed. Nineteen mixtures were manufactured, and five were used as controls, and the hygrothermal, mechanical, and durability properties were evaluated. The results for LFC and FFC showed that fiber treatment negatively affected flexural–compressive strength; untreated LFC with accelerated deterioration had better mechanical behavior, higher density, and lower porosity than FFC. Strength and density decreased, but porosity increased with increasing fiber volume (Vf). Regarding WSC and HSC, the microstructure of WS and HS had a significant effect on the physical and mechanical properties. The high porosity influenced the results obtained, since it decreased compressive strength and bulk density; however, thermal conductivity, hygroscopicity, and vapor resistance showed better behavior in most cases than the control specimens, i.e., without bio-aggregates.

The corrosion risk in reinforced mortar slabs containing untreated sugarcane bagasse ash (UtSCBA) (0%, 10%, and 20% replacement of cement) was analyzed for 75 months. The mortars were prepared with a constant 0.63 water/cementitious-materials ratio. Cylinders and reinforced slabs were cast with the mortars. Two galvanized wire meshes were used as reinforcement for the slabs. Curing regimes of 0, 7, and 28 days were applied to the samples. The cylinders were used to obtain the compressive strength (CS) and the chloride diffusion coefficient ($D_{eff}$ ) of the mortars. To evaluate the corrosion risk, the slabs were exposed to wet-dry cycles of 12 h each in a 3% NaCl solution. Corrosion potential measurements and linear polarization resistance tests were taken every 28 days for that purpose. It was found that the addition of 10% and 20% UtSCBA reduces the workability of the mortar binders and leads to a slight decrease in the CS of hardened mortars. However, it significantly reduced the $D_{eff}$ of the mortars by 50% and 65% ($p\ll 0.05$ ), respectively, and also decreased the corrosion risk of mortar slabs over time.