Simone Hempel

Mineral-Based Coating of Plasma-Treated Carbon Fibre Rovings for Carbon Concrete Composites with Enhanced Mechanical Performance

Surfaces of carbon fibre roving were modified by means of a low temperature plasma treatment to improve their bonding with mineral fines; the latter serving as an inorganic fibre coating for the improved mechanical performance of carbon reinforcement in concrete matrices. Variation of the plasma conditions, such as gas composition and treatment time, was accomplished to establish polar groups on the carbon fibres prior to contact with the suspension of mineral particles in water. Subsequently, the rovings were implemented in a fine concrete matrix and their pull-out performance was assessed. Every plasma treatment resulted in increased pull-out forces in comparison to the reference samples without plasma treatment, indicating a better bonding between the mineral coating material and the carbon fibres. Significant differences were found, depending on gas composition and treatment time. Microscopic investigations showed that the samples with the highest pull-out force exhibited carbon fibre surfaces with the largest areas of hydration products grown on them. Additionally, the coating material ingresses into the multifilament roving in these specimens, leading to better force transfer between individual carbon filaments and between the entire roving and surrounding matrix, thus explaining the superior mechanical performance of the specimens containing appropriately plasma-treated carbon roving.

Performance of Lightweight Concrete based on Granulated Foamglass

The paper presents an investigation of lightweight concretes properties, based on granulated foamglass (GFG-LWC) aggregates. The application of granulated foamglass (GFG) in concrete might significantly reduce the volume of waste glass and enhance the recycling industry in order to improve environmental performance. The conducted experiments showed high strength and thermal properties for GFG-LWC. However, the use of GFG in concrete is associated with the risk of harmful alkali-silica reactions (ASR). Thus, one of the main aims was to study ASR manifestation in GFG-LWC. It was found that the lightweight concrete based on porous aggregates, and ordinary concrete, have different a mechanism of ASR. In GFG-LWC, microstructural changes, partial destruction of granules, and accumulation of silica hydro-gel in pores were observed. According to the existing methods of analysis of ASR manifestation in concrete, sample expansion was measured, however, this method was found to be not appropriate to indicate ASR in concrete with porous aggregates. Microstructural analysis and testing of the concrete strength are needed to evaluate the damage degree due to ASR. Low-alkali cement and various pozzolanic additives as preventive measures against ASR were chosen. The final composition of the GFG-LWC provides very good characteristics with respect to compressive strength, thermal conductivity and durability. On the whole, the potential for GFG-LWC has been identified.

Improved Bonding of Carbon Fiber Reinforced Cement Composites by Mineral Particle Coating

The low penetrability of cement product into the interior of multifilament yarns hinders the utilization of textile reinforced concrete (TRC). This inferior fiber-matrix bond often leads to premature failure. Therefore, improved bonding of such textile reinforced composite is much needed. This study focuses on the improvement of multifilament carbon yarns’ bond to cement matrix by mineral particle coatings. A carbon multi-filament was impregnated by micro-sized alumosilicate, nano- and micro-sized silica. The penetrability of the particles into the multifilament was characterized and the effects of the coatings on the fiber/matrix bond were compared to an epoxy-polymer coated-carbon multifilament. The micro-sized silica and alumosilicate coatings coated the yarn efficiently and enhanced both pull-out strength and toughness as compared to both nano-silica and epoxy coatings. This was mainly attributed to superior bonding due to a postulated pozzolanic effect. Contrarily, the nano-silica failed to show the same beneficial effects due to extensive agglomeration. It is concluded that coating of carbon multifilament with mineral fillers should be highly considered for TRC. However, the filler has to be thoroughly deagglomerated prior to the coating step.