Natural Fiber Reinforcement of Ceramic Slurry Compacts

Background: ceramic tile wastewater slurry contains a large amount of fine kaolinite particles acting as a matrix for mineral filler particles of quartz and mullite. Reinforcing it with natural fibers increases its compression strength. A novel approach is using Stipa pennata fibers because of their local availability, good mechanical properties, and feathery aspect, making them able to reinforce ceramic slurry compacts. Preparation and investigation methods: Slurry conditioned at 33% humidity and milled at 6000 rpm for 5 min contains 39% quartz, 37% kaolinite, 16% mullite and 8% lepidocrocite (observed via XRD correlated with mineralogical microscopy). Kaolinite particles ensure optimal binding of the mineral filler and the Stipa pennata fibers into a dense composite structure, as observed via SEM. EDS maps reveal a local increase in C content, along with the natural fibers being associated with significant levels of Al and Si, indicating the microstructural compactness of the reinforcement layer. An additional compaction load enhances microstructural cohesion. Results: The sample without reinforcement has a compressive strength of 1.29 MPa. This increases to 2.89 MPa by adding a median reinforcing layer and reaches 3.13 MPa by adding a compaction load of 20 N. A median crossed fiber-reinforcing layer combined with the compaction load of 20 N ensures a compressive strength of 4.78 MPa. Introducing two reinforcing layers oriented perpendicular to one another ensures a compressive strength of 2.48 MPa. Lateral placement of the two reinforcing layers regarding the sample median plan causes a slight decrease in the compressive strength. SEM fractography reveals that the feather-like structure of Stipa pennata fiber acts as an anchor for the median site of the samples, slowing crack initiation under compressive efforts, creating a novel approach compared to natural fiber without lateral flakes. Conclusions: The optimal place for the reinforcement layer is the median site of the sample, and interlaced reinforcement ensures the best compressive resistance. Ceramic slurry reinforced with Stipa pennata is useful as an intermediary layer on the modular walls of ecologic buildings.