Evaluation of CNTs and SiC Whiskers Effect on the Rheology and Mechanical Performance of Metakaolin-Based Geopolymers

Abstract

Despite geopolymers having emerged as a more sustainable alternative to Portland cement, their rheological properties still need to be thoroughly investigated, aiming at the material’s applicability. Additionally, studies that evaluated the fresh state of geopolymer composites with nanomaterials are scarce. Thus, two metakaolin-based geopolymer systems were reinforced with nanomaterials with a similar geometry: carbon nanotubes (CNT) and silicon carbide whiskers (SCW). The nanomaterials incorporation was assessed by rotational rheometry (conducted up to 110 min), isothermal calorimetry, compressive strength after 7 and 28 days, and the microstructure was investigated using X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR). CNT and SCW incorporation (0.20 wt.%) did not significantly affect the yield stress and viscosity of the R2-group (based on metakaolin type 2), while increasing the rheological parameters up to 56.0% for the R1-group (based on metakaolin type 1). Both additions modified the reaction kinetics. Increments of up to 40.7% were observed in the compressive strength of geopolymer pastes with the incorporation of a SCW content of 0.2 wt.%. XRD and FTIR results suggest similar structural modifications between precursors. Nevertheless, R2 showed substantial transformations while the R1 group exhibited anhydrous material that can react over time. Overall, incorporating CNT and SCW contributed to higher mechanical increments on systems with average mechanical strength (R1) compared to systems with higher potential mechanical performance (R2).

Propriedades Físico-Mecânicas De Argamassas Geopoliméricas Reforçadas Com Fibras Poliméricas Naturais E Sintéticas

“…As relações molares do sistema foram especificadas na tabela 2 e sua molaridade foi de 6,16 M de NaOH. Esta foi escolhida como uma adaptação de trabalho realizado por [16]. As aparências das fibras estão registradas na Figura 2 e na Tabela 3 são indicadas as medidas de comprimento médio das fibras incorporadas.…”

Temperature-Dependent Pullout Behavior of Geopolymer Concrete Reinforced with Polymer- or Mineral-Impregnated Carbon Fiber Composites: An Experimental and Numerical Study

“…The good mechanical response of continuous-fiber GP composites under temperatures ranging above 200 °C has been demonstrated in several earlier investigations, − targeting solely high-tech automotive or aerospace applications. The replacement of cement with more environmentally friendly GP in construction can deliver comparable mechanical strength, excellent heat/fire resistance, high durability, low shrinkage, reduced carbon footprint, zero degradation under UV light, and high corrosion resistance to all organic solvents and acids. , GPs are commonly synthesized by an activated polycondensation reaction in a highly alkaline or an acid medium from a variety of naturally occurring minerals, e.g., metakaolin (MK), or industrial byproducts, e.g., fly ash and rice husk ash. − In earlier studies, , a GP-impregnation matrix implied some chemical incompatibility with fresh cement concrete substrates and required further treatment by washing with water to reduce the presence of excess alkali and ensure adequate bond properties. Hence, GP concrete is expected to provide high compatibility with fiber-reinforced GP composites.…”

Editorial: New Advances in Nanomaterials

“…However, the dispersibility of nanomaterials significantly impacts the performance of composite materials. A series of tests were conducted on the rheological properties of geopolymers by Madeleing Taborda Barraza's group [11]. In this study, the influence of carbon nanotubes (CNT) and silicon carbide whiskers (SCW) with similar geometric shapes on the rheological properties of metakaolin-based geopolymers was evaluated.…”