Sediments as renewable raw earth for producing unfired bricks and mortars

The texture of fine sediments, whether from rivers, harbours, waterways or dam reservoirs, contains clays in varying quantities depending on the source from which they are extracted. These clays confer certain properties to sediments, such as plasticity and cohesion. Additionally, the clay minerals present and associated oxides can contribute to reactive or binding properties. This research focuses on the oxides present in fine sediments, with a view to proposing low-CO2 blended cement formulations incorporating calcined sediments and other industrial by-products such as slags or ashes. Although the flash-calcination technique for dredged sediments is promising as it reduces the temperature required for calcination, it is still an energy-consuming process [1]. Consequently, cements mixed with flash-calcined dredged sediments cannot be fully considered as eco-friendly cements. The presence of clays in sediments gives them plasticity and even cohesion, depending on their water content. This plasticity allows for a certain workability, enabling them to be shaped. Sediment-based unfired earth bricks are therefore conceivable, as their suitability has been demonstrated in recent projects using dredged river sediments. Whether or not these sediments are suitable for the manufacturing of unfired earth bricks needs to be verified by means of reference charts covering plasticity and particle size distribution. Corrections can be achieved by incorporating additions of clay particles (lack of plasticity) or coarse elements (granular correction). These additives are mainly sourced from waste soils excavated from temporary deposits. Once shaped, these sediment-based bricks are air-dried, making them eco-friendly. These sediment-based bricks are designed to meet specific strength requirements, depending on the application: filling material, earthen bricks, earth walls. During the shaping process, green bricks can be pressed, compacted or kneaded, all of which densify them. However, the introduction of natural fibers provides shaped bricks with mechanical reinforcement, giving them a ductile behavior whose toughness indexes can be used to assess their improvement. Bricks reinforced with waste plant fibers are still eco-friendly, while increasing their mechanical strength and conferring hygroscopic and thermal properties. Raw sediments can also be used to produce sediment-based mortars. Depending on their composition, sediment-based mortars can partially replace the sand or hydraulic binder used in traditional mortars. According to the quality and quantity of clays contained, sediments can be reused directly as unbaked bricks or mortar reinforced with plant fibers. This is a renewable resource, considered as a waste product, which can be combined with other waste products, such as plant fibers, to produce an eco-friendly material. First, a methodology is presented for the production of unfired sediment-based bricks reinforced with waste fibers. Two case studies are reported using local materials: river sediments and short oil palm fibers (case 1, [2]) or flax tow fibers (case 2). The methodology includes material characterization (sediments and fibers), sediment suitability, definition of optimum moisture content, compaction of the sediment mixture, control of fiber distribution and orientation using digital imaging, and strength-optimized testing. Once brick production protocols have been defined, strength properties (flexural and compressive) are evaluated in order to optimize fiber content and length according to the standards. In both case studies, the strengths obtained are discussed regarding the different influences. A case study (case 3, [3]) on the production of a sediment-based mortar without fibers is also presented. The methodology followed is similar: sediment characterization, suitability tests, strength optimization according to sand and/or cement substitution.