Recycled concrete aggregates (RCAs) have been demonstrated as an alternative source to exhaustible natural aggregates. In this paper, we focus on the enhancement treatments for coarse and fine RCAs and the effect of these treatments on the durability of recycled concrete (RC) made from treated RCAs by the weakening and strengthening of the cement paste adhered to their surface. We conducted comparative analyses on the improvement of durability and mechanical properties. The results showed that the reduction of water absorption in RCAs increases the compressive strength of RC and that there is a strong linear trend of improvement in the carbonation depth, chloride ion penetration, and compressive strength of RC. For fine and coarse RCAs, the treatment mechanism and particle size are determinants in efficiently improving RC durability.

This study evaluates a binary mixture of fly ash and lime as a stabilizer for natural soils. A comparative analysis was performed on the effect on the bearing capacity of silty, sandy and clayey soils after the addition of lime and ordinary Portland cement as conventional stabilizers, and a non-conventional product of a binary mixture of fly ash and Ca(OH)₂ called FLM. Laboratory tests were carried out to evaluate the effect of additions on the bearing capacity of stabilized soils by unconfined compressive strength (UCS). In addition, a mineralogical analysis to validate the presence of cementitious phases due to chemical reactions with FLM was performed. The highest UCS values were found in the soils that required the highest water demand for compaction. Thus, the silty soil added with FLM reached 10 MPa after 28 days of curing, which was in agreement with the analysis of the FLM pastes, where soil moistures higher than 20% showed the best mechanical characteristics. Furthermore, a 120 m long track was built with stabilized soil to evaluate its structural behavior for 10 months. An increase of 200% in the resilient modulus of the FLM-stabilized soils was identified, and a decrease of up to 50% in the roughness index of the FLM, lime (L) and Ordinary Portland Cement (OPC)-stabilized soils compared to the soil without addition, resulting in more functional surfaces.

Carbon nanotubes as additions in Portland cement based matrices have a great potential to improve the mechanical properties of mortars and concretes; however, little work has been done regarding the effect that they have on the chemical durability of the cement matrix and reinforcing steel. In this work, carbon nanotubes are dispersed in water solution with Triton X 100 surfactant and blended in Portland cement mortars. A sharp decrease in compression resistance was observed at all curing ages (7, 14, 21 and 28 days) while a depth increase in the carbonation profile was found, which is associated with a decrease in the matrix durability.

This work studies the hydration kinetics of portland cement pastes blended with multiwalled carbon nanotubes (MWCNTs) aqueous dispersions. Anionic, cationic, and nonionic surfactants—i.e., surfactants that have different charged functional groups in their structure—were used as dispersing agents. MWCNTs in powder form were dispersed in deionized water with sodium dodecyl sulfate, cetylpyridinium chloride, and triton TX-100. Three concentrations of each surfactant (1, 10, and 100 mM) were tested, and all samples were sonicated until an adequate dispersion degree was obtained. Cement pastes blended with carbon nanotubes were prepared, and their hydration kinetics were studied using the Vicat needle and isothermal calorimetry tests. It was concluded that the effect of MWCNTs on the hydration kinetics of portland cement can be masked by the effect of surfactants used as dispersing agents for the nanotubes in the mixing water.