Long-Term Hindrance Effects of Algal Biomatter on the Hydration Reactions of Ordinary Portland Cement

The incorporation of carbon-fixing materials such as photosynthetic algae in concrete formulations offers a promising strategy toward mitigating the concerningly high carbon footprint of cement. Prior literature suggests that the introduction of up to 0.5 wt % chlorella biological matter (biomatter) in ordinary Portland cement induces a retardation of the composite cement’s strength evolution while enabling a long-term compressive strength comparable to pure cement at a lower carbon footprint. In this work, we provide insights into the fundamental mechanisms governing this retardation effect and reveal a concentration threshold above which the presence of biomatter completely hinders the hydration reactions. We incorporate Chlorella or Spirulina, two algal species with different morphology and composition, in ordinary Portland cement at concentrations ranging between 0.5 and 15 wt % and study the evolution of mechanical properties of the resulting biocomposites over a period of 91 days. The compressive strength in both sets of biocomposites exhibits a concentration-dependent long-term drastic reduction, which plateaus at 5 wt % biomatter content. At and above 5 wt %, all biocomposites show a strength reduction of more than 80% after 91 days of curing compared to pure cement, indicating a permanent hindrance effect on hardening. Characterization of the hydration kinetics and the cured materials shows that both algal biomatters hinder the hydration reactions of calcium silicates, preventing the formation of calcium hydroxide and calcium silicate hydrate, while the secondary reactions of tricalcium aluminate that form ettringite are not affected. We propose that the alkaline conditions during cement hydration lead to the formation of charged glucose-based carbohydrates, which subsequently create a hydrogen bonding network that ultimately encapsulates calcium silicates. This encapsulation prevents the formation of primary hydrate products and thus blocks the hardening of cement. Furthermore, we observe new hydration products with composition and micromorphology deviating from the expected hardened cement compounds. Our analysis provides fundamental insights into the mechanisms that govern the introduction of two carbon-negative algal species as fillers in cement, which are crucial for enabling strategies to overcome the detrimental effects that those fillers have on the mechanical properties of cement

Factors Controlling the Enhanced Mechanical and Thermal Properties of Nanodiamond-Reinforced Cross-Linked High Density Polyethylene

A systematic investigation of the factors influencing the notable enhancement of the mechanical and thermal properties of nanodiamonds (NDs)-reinforced cross-linked high density polyethylene (PEX) is presented in this work. The effects of crystal structure and molecular conformation as well as filler dispersion and adhesion with the matrix were found to govern the mechanical properties of the final composites. A considerable increase in the strength, toughness, and elastic modulus of the materials was found for the composites with filler content below 1 wt %. For higher NDs concentrations, the properties degraded. When filler concentration does not exceed 1 wt %, enhanced adhesion with the matrix is achieved, allowing a more successful load transfer between the filler and the matrix, thus enabling an effective reinforcement of the composites. The higher degree of crystallinity along with larger crystal size are also positively influencing the mechanical properties of PEX. Higher filler concentrations, on the other hand, lead to the formation of larger aggregates, which lead to lower adhesion with the matrix, while they also constitute stress concentrators and therefore reduce the positive reinforcement of the matrix. The thermal conductivity of the composites was also found to be significantly increased for low-filler concentrations. This enhancement was less significant for higher NDs concentrations. It is concluded that this reinforcement is due to the heat capacity increase that NDs incorporation causes in PEX. Additionally, a thermal stability enhancement was found for the composite with minimum filler content

Amino-Functionalized Multiwalled Carbon Nanotubes Lead to Successful Ring-Opening Polymerization of Poly(ε-caprolactone): Enhanced Interfacial Bonding and Optimized Mechanical Properties

In this work, the synthesis, structural characteristics, interfacial bonding, and mechanical properties of poly­(ε-caprolactone) (PCL) nanocomposites with small amounts (0.5, 1.0, and 2.5 wt %) of amino-functionalized multiwalled carbon nanotubes (<i>f</i>-MWCNTs) prepared by ring-opening polymerization (ROP) are reported. This method allows the creation of a covalent-bonding zone on the surface of nanotubes, which leads to efficient debundling and therefore satisfactory dispersion and effective load transfer in the nanocomposites. The high covalent grafting extent combined with the higher crystallinity provide the basis for a significant enhancement of the mechanical properties, which was detected in the composites with up to 1 wt % <i>f</i>-MWCNTs. Increasing filler concentration encourages intrinsic aggregation forces, which allow only minor grafting efficiency and poorer dispersion and hence inferior mechanical performance. <i>f</i>-MWCNTs also cause a significant improvement on the polymerization reaction of PCL. Indeed, the in situ polymerization kinetics studies reveal a significant decrease in the reaction temperature, by a factor of 30–40 °C, combined with accelerated the reaction kinetics during initiation and propagation and a drastically reduced effective activation energy