No abstract

Implementation of construction works on weak (e.g., compressible, collapsible, expansive) soils such as peatlands often is limited by logistics of equipment and shortage of available and applicable materials. If preloading or floating roads on geogrid reinforcement or piled embankments cannot be implemented, then soil stabilization is needed. Sustainable soil stabilization in an environmentally friendly way is recommended instead of applying known conventional methods such as pure cementing or excavation and a single replacement of soils. Substitution of conventional material (cement) and primary raw material (lime) with secondary raw material (waste and byproducts from industries) corresponds to the Sustainable Development Goals set by the United Nations, preserves resources, saves energy, and reduces greenhouse gas emissions. Besides traditional material usage, soil stabilization is achievable through various secondary raw materials (listed according to their groups and subgroups): 1. thermally treated waste products: 1.1. ashes from agriculture production; 1.2. ashes from energy production; 1.3. ashes from various manufacturing; 1.4. ashes from waste processing; 1.5. high carbon content pyrolysis products; 2. untreated waste and new products made from secondary raw materials: 2.1. waste from municipal waste biological treatment and landfills; 2.2. waste from industries; 3. new products made from secondary raw materials: 3.1. composite materials. Efficient solutions in environmental engineering may eliminate excessive amounts of waste and support innovation in the circular economy for sustainable future.

Construction of road embankments in peatlands commonly involves replacement of the peat with a fill-up soil of an adequate load-bearing capacity. This usually requires a lowering of the water level, turning a peatland from a carbon sink to a source of greenhouse gases. Thus, alternatives are sought that are less costly in both economic and ecological terms. Mass-stabilization technology can provide a cheap substitute for Portland cement. Calcareous ashes (waste materials), supplemented with pozzolanic and alkali additives to facilitate and accelerate the setting and hardening processes, are attractive alternatives to soil excavation or replacement techniques. Silica fume and waterglass were used as pozzolanic agents and KOH as a soil-alkalizing agent. X-ray fluorescence (XRF), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) analyses and stress–strain tests were performed for the hardened samples. Crystallization of alkali feldspars was observed in all test samples. Comparable hardening of peat soil was achieved for both ashes. It was shown that the ashes of Estonian kukersite (oil shale) from both pulverized firing and a circulating fluidized bed incineration process (produced in energy sector as quantitatively major solid waste in Estonia) can be used as binding agents for peat stabilization, even without the addition of Portland cement. Hardened peat soil samples behaved as a ductile material, and the cellulose fibers naturally present in peat gave the peat–ash composite plasticity, acting mechanically in the same way as the steel or glass fiber in ordinary reinforced concrete. The effect of peat fiber reinforcement was higher in cases of higher load and displacement of the composite, making the material usable in ecological constructions.

No abstract

CAD/FEM/CAM software is used to design the 3D model of grid shell. The longitudinal length of the laths is measured along the curved side. The position of the crossing nodes (x, y, z; different on each lath) is used to produce the half lap joints at exact places by CNC-workstations on straight laths. The laths will be connected by half lap joints with half-dovetailed joints (without metallic fasteners) to bear internal forces from the top of the shell to the edges. There is no more need for excessively long laths. The length is limited only by the cross-sectional measure of the lath capable to carry the dead weight of the cantilever laths themselves while supported only from the first and second crossing node. The laths will be connected longitudinally with a gradual tenon on one end and mortise at the other end. The laths are produced as glue-laminated wood, but in this case of lamellae, they are installed together as multiple hollow square-tubes, one in another. Different species of timber with various physical properties can be used. By gradually displacing the square-tubes of lamellae upwards, starting from the inside layer, the tenon and mortise will be generated during the gluing process. After fixing the first row of laths (inclined with respect to the foundation plane) to the external beam or foundation, the shell structure starts "rising" upwards by connecting the laths longitudinally. Every subsequent layer of laths has mirrored inclination, adding thickness and strength to the grid shell. Laths will be bent and twisted during the assembly process, until the half-dovetailed and half lap joints of two crossing laths lock. The internal forces generated by the bending and torsion of the laths keep the designed shape of the grid shell without any need for additional supports.