This research work focuses on the recycling of gypsum, a key component of drywall panels commonly used in construction. It proposes this practice as a technically and economically viable strategy that also aligns with the circular economy model. In this context, waste loses its status as refuse and is transformed back into raw material. A technical feasibility analysis was conducted based on a sample extracted from a specific project, which was subjected to characterization tests and mechanical behavior assessments in both laboratory and real construction conditions. Additionally, an economic feasibility analysis was performed by comparing the budgets of the same project in two scenarios: the traditional plastering process and the use of recycled gypsum. This analysis highlighted the fiscal and legal benefits that adopting the circular model could offer to stakeholders in the construction industry. This study began with a market analysis to determine the availability of recyclable material and to assess the multiple benefits that its reuse can provide. Based on the characterization of the material obtained from the construction site and the mechanical tests conducted, the economic advantages were evaluated for contractors as well as for the potential establishment of companies focused on gypsum recycling. All of this analysis was framed within the context of sustainability, emphasizing the positive environmental impacts of this practice, as well as the development of a strategy that serves as a valuable proposal for the construction sector. This work concludes that recycling gypsum in construction projects represents a technically, environmentally, and economically sustainable alternative that can positively transform the industry.

This study assesses the effect of both silica nanoparticles of different sizes and different types of superplasticizers on rheological properties and 28-day compressive strength of Portland cement pastes. The experimental program comprised the utilization of 36 and 264 nm sizes nanoparticles and the superplasticizers used were polyhydroxyl and polycarboxylate-based high-range water reducers. Subsequently, the nanoparticles and superplasticizers were added to cementing pastes on which rheology tests were performed under a controlled rate (CR) mode, in order to quantify the yield stress and the plastic viscosity according to the Binghamian rheological model. As a result, it was found a saturation range between 0.8 wt % and 1.2 wt % of the used polyhydroxyl and polycarboxylate-based superplasticizers, from which the reduction of the rheological properties of the pastes was not further modified. Also, pastes using a simultaneous addition of 0.5 wt % of 36 nm-size nanosilica and 0.6 wt % of polyhydroxyl superplasticizer further optimize both the rheological and mechanical properties of the control mixture, and the compressive strength of the pastes increased up to 9% for using this nanoparticle dosage. It was found that the coarser nanoparticles (264 nm) provide pastes with enhanced mechanical properties and better workability compared to the ones provided by the finer nanoparticles (36 nm). Finally, several practical equations were proposed for the prediction of the rheological properties of yield stress and plastic viscosity of Portland cement pastes based on the nanosilica and superplasticizer additions.

Nanosilica is a new material that has been recently used in the construction industry on a mass scale, featuring several advantages and limitations. Despite the extensive research about the nanosilica effect on cement-based materials, so far there is no consensus regarding the optimal nanosilica dosage that further enhances the mechanical performance and durability of mortar and concrete. With the aim of solving this issue, this paper reports on the optimal nanosilica dosage in normal-strength mortar and concrete regarding their mechanical and durability properties. Experiments on fresh (setting time and flow) and hardened state (compressive strength, tensile strength and chloride migration tests) were carried out on mortar and concrete using two silica nanoparticles of 264 nm and 36 nm average size. As a result, it was found that mortar and concrete using 1.5 wt.% to 2.0 wt.% doses of nanosilica showed the best performance for the mechanical and durability properties. Coarser nanoparticles (264 nm) provide mortar and concrete with enhanced mechanical and durability properties compared to the finer nanoparticles (36 nm). Finally it was found that nanoparticle size had no effect on the optimal nanosilica dosages identified in this study.

This paper assesses the influence of nanosilica particles (in low dosages) under limited dispersal conditions on some properties of pastes and mortars made out of conventional cement (without the use of plasticizers). For this, characterisation of mixtures in fresh and hardened states were carried out through setting times, fluidity, early compressive strength and scanning electron microscopy tests. As results, flowability of the analysed mortars was higher when the silica nanoparticles were larger in size, and consequently lower flowability values were obtained for the smaller nanoparticles. It was not possible to determine an optimum content of nanoparticles since no significant increases in the early compressive strength of mortars were achieved. The obtained results in this research show that for mortars with water/cement ratio of .55 a minimum nanosize and a high amorphous content of silica particles are not sufficient to enhance mechanical strengths, but mainly a better dispersion in the cementitious matrices should be guaranteed using plasticizing admixtures in order to optimise workability and mechanical performance.

The effect of nanosilica under the influence of dispersing agents on the fresh empirical and fundamental rheological properties of self-compacting concrete (SCC) is a complex phenomenon which has been investigated in this paper. Models to predict the rheological properties of nanosilica blended SCC are also lacking to avoiding/saving comprehensive and costly rheology laboratory trials mainly when these tests are unavailable or limited. To these ends, 315 laboratory tests were performed on 15 blended SCC mixtures, manufactured using five nanosilica dosages, 0%, 0.5%, 1%, 1.5%, 2%, and three dispersing superplasticizer dosages, 0.62%, 0.66%, 0.70%, by weight of cement. Fundamental rheological properties of the SCC mixes were assessed by using a rotational concrete rheometer based on the nonlinear modified Binghamian model. Results showed that SCC mixes are sensitive to nanosilica and superplasticizer admixtures producing a complex non-linear effect on their empirical and rheological properties. Based on these trends, eleven empirical models were proposed to predict the fresh empirical and rheological properties of the SCC mixes. A statistical analysis demonstrated the good fitting of the proposed models with the measured properties of SCC mixes during the laboratory trials. These models could serve for design and production of nanosilica blended SCC as alternative approach.

La presente investigación está orientada a la implementación de ceniza volante activada alcalinamente como sustitución total del cemento Portland en la elaboración de tabletas prefabricadas. El programa experimental comprendió la caracterización fisicoquímica de materias primas, hallazgo de la relación óptima activador alcalino/ceniza volante y ensayos mecánicos de resistencia a la compresión y módulo de rotura. Adicionalmente se incluyó un comparativo de la huella de carbono de un lote de tabletas prefabricadas de mortero de cemento Portland y ceniza volante. La activación de ceniza volante se realizó por medio de la combinación de activadores alcalinos compuestos por NaOH y Na₂SiO₃. Los resultados demostraron que los morteros de ceniza volante presentan buenas propiedades mecánicas y viabilidad ambiental en términos de huella de carbono. La ceniza volante puede ser acogida en la industria de tabletas prefabricadas como opción de menor impacto ambiental con óptimas resistencias a la compresión y módulo de rotura.