The Effect of Rice Husk on the Variability of Physical and Mechanical Properties of Composites

Rice husk (RH) is one of the most commonly grown and consumed cereals in the world. Because of its low nutritional value, it is not commonly used as a food or fertilizer. Instead, it is often burned or landfilled. To develop RH-based composites for thermal and acoustic nonstructural applications, a balance between achieving satisfactory performance in physical and mechanical properties is essential as well as ensuring reliability and predictability in the behavior of the composites. The inclusion of RH in composites can result in increased variability in their performance because of the husk's elastic behavior during compaction and its hydrophilic properties. The RH used in the study was collected from Baixo Mondego, Portugal, and approximately 90 % of the particles had sizes ranging from 1 to 4 mm. To reduce cement usage, different mixtures were produced and categorized based on the use of two types of cement, varying percentages of limestone filler, and different quantities of RH. Robust descriptive and inferential statistics (Student's t-test and Mann-Whitney U test) were employed to analyze the variability of physical and mechanical properties in 10 different RH-based composites. A study was conducted to assess whether a specific mixture formula within a given group exhibited consistent behavior across different batches or yielded intrinsically different results. This helps to identify the key adaptations required in the industrial process of incorporating this biomaterial into composites. The results have shown that it is possible to produce RH-based composites with less variability of performance and potential for nonstructural applications. In this case, cement CEMI/A-L 42.5 R type with limestone filler addition and paste-to-RH ratio by volume between 1.54 and 2.22 was the most sustainable mix design because it had a small variability of results and reduced the cement content.