Giovanni dos Santos Batista

This study investigates the rheological behavior of oil well cement pastes (OWCPs) modified with core/shell TiO₂@SiO₂ (nTS) nanoparticles and polycarboxylate-ether (PCE) superplasticizers at different temperatures (25, 45, and 60 °C). Results show that nTS particles increased static and dynamic yield stresses and the apparent viscosity of the cement slurries due to an increased solid volume fraction and reduced free water availability. The increase in the slurry dispersion by adding PCE superplasticizers enhanced the effect of the nanoparticles on the rheological parameters. Oscillation rheometry demonstrated that nTS nanoparticles enhanced the structural buildup, while PCE retarded hydration. Furthermore, slurries hydrated at 60 °C experienced higher initial values of the elastic modulus and a faster exponential increase in this rheological parameter due to the acceleration of the cement hydration.

Lime stabilization is a sustainable technique due to its use of local materials, increased durability, reduced maintenance, and improved resistance to water action. This paper examines the impact of lime stabilization on the mechanical, microscopic, and mineralogical properties of a tropical soil. Two types of lime, calcitic and dolomitic, were tested at 3% and 5% by weight. Compressive, indirect tensile and flexural test results and statistical analysis revealed that calcitic lime mixtures had higher strength and stiffness, whereas dolomitic lime mixtures exhibited greater deformability with higher tensile strain at break. Scanning electron microscopy indicated that the soil’s porous matrix closed within 7 days for both lime types due to flocculation, with increased matrix interlocking over time. The calcitic lime mixture developed a more closed matrix compared to the dolomitic lime, which showed weaker cementing. X-ray diffraction analysis indicated higher consumption of clay minerals and a notable reduction in calcium hydroxide peaks in the lime-treated soils. The study concludes that calcitic lime provides better pavement performance for stabilizing the soil, enhancing its engineering properties while also being sustainable by reducing the need for raw material extraction and improving resilience to climate-related issues such as floods.

The class G cement behavior after adding n-Al 2 O 3 (0.5 and 1.5 wt.%) was investigated using two dispersive methods, solid/liquid (UPS) and solid/solid (PBM), under CCS conditions at 90 °C and 15 MPa for 21 d. The effects of n-Al 2 O 3 and dispersion were evaluated through gas pycnometry, compressive strength, SEM/EDS, XRD, FTIR, microtomography, and Vickers microhardness. The unreacted specimens with the added n-Al 2 O 3 exhibited a higher density and compressive strength. When the specimens were dispersed using the PBM method, the cement particle size decreased from 7.30 to 4.20 µm. The UPS dispersive method was more efficient than the PBM method. The CH content decreased, and a higher C-S-H polymerization was observed in the specimens with n-Al 2 O 3 . Microtomography results showed that the carbonation mechanism was the same for all specimens, but the UPS method enhanced the matrix densification. The UPS specimens with n-Al 2 O 3 exhibited a smoother and thinner transition zone with a lower Ca/Si ratio. A lower carbonation depth was observed for the UPS specimens with 0.5 wt.% of n-Al 2 O 3 . An increase in hardness and density after CO 2 exposure was observed in the UPS specimens. The best results in terms of chemical and mechanical properties were obtained using the UPS method for 0.5 wt.%.