Production of Waste Fiber-Reinforced Raw Earth Specimens by Controlled Compaction

The shaping of raw earth reinforced with natural fiber waste poses problems in the distribution of fibers and the homogeneity of the composite material. These same problems are encountered when making laboratory specimens and the scale effect. These specimens must be as homogeneous and reproducible as possible. As part of a specific study on the reinforcement of mud bricks with natural fiber waste, prismatic test specimens were prepared. The dimensions used are those of standard mortar specimens, i.e., 4 × 4 × 16 cm3. These specimens can also be subjected to indirect bending tensile tests like mortars. The data resulting from the test allow the influence of the incorporation of fibers into the raw earth to be analyzed. The shaping of the specimens requires, first of all, the development of a rigorous and repetitive mixing procedure. Then follow the filling of molds and compacting of the volume of reinforced raw earth within the mold. To make the compaction procedure repetitive, a compaction system adapted to the selected mold (4 × 4 × 16 cm3) was used to compact the reinforced raw earth specimen at controlled energy. This procedure is indeed repetitive. The choice of this dynamic compaction method was preferred to impact or tamping compaction or static compaction. The level of energy applied is adjustable and can be equivalent to that required for a normal or modified Proctor test in the case of stabilized soils. The control of the fiber distribution within the specimen makes it possible to judge the specimen’s homogeneity and the fibers’ good distribution. A procedure for counting the fibers in a cross-section of the specimen is proposed. All these procedures (mixing, filling, compacting, and fiber distribution) are presented and discussed when making prismatic sediment (raw earth) specimens reinforced with natural fibers (hemp). The method of compaction is also detailed.