| Abstract [eng] |
Portland cement (PC)-based concrete is widely used as the primary building and construction material. Nonetheless, PC production is responsible for large global anthropogenic emissions of greenhouse gases and industrial energy consumption. Meanwhile, the intensive demand for natural aggregates exerts significant stress on non renewable resource conservation. In this context, developing alkali-activated materials based on industrial and agricultural waste as an alternative to traditional PC-based materials is a sustainable approach. As a clean energy source, biofuel energy derived from wood combustion is increasingly welcomed around the globe, especially in forestry countries like Lithuania, which generates a significant amount of wood biomass waste. According to the reports (Teker Ercan et al., 2023; Zhu et al., 2024), the global yearly generation of wood biomass is approximated to be 4600 million tons, which is predicted to grow threefold by 2035. This exerts great pressure on the land resources and environmental conservation. To investigate a sustainable application of this waste at a large quantity in producing alkali activated materials (AAMs), wood ash (WA) containing wood fly ash (WFA) and wood bottom ash (WBBA) was recycled as precursors, and recycled sand (RS) was valorised as fine aggregates. Sodium hydroxide (SH) at a concentration of 7 mol/L, calcium hydroxide (CH) at 10 % by the total precursor mass, and sodium silicate (SS) at an SS to SH mass ratio of 1 were ternarily used as alkaline activators. One challenge of WA utilisation in building and construction materials is its low chemical reactivity, which limits the development of the mechanical properties (Du et al., 2024). Taking it into account, aluminosilicate-rich materials, including metakaolin (MK), natural zeolite (NZ) and coal fly ash (FA), were introduced as a binary precursor to provide extra aluminosilicates at the content of 10 %, 20 %, 30 % and 40 % by precursor weight. Compressive strength, physical properties, and microstructural analysis (SEM-EDS, XRD FTIR, and TG-DTA) were tested to assess the mechanical properties and reaction kinetics, plus a cradle-to-gate lifecycle assessment (LCA) to evaluate the environmental impacts of the produced AAMs. According to the results, the addition of FA, MK, and NZ effectively improves the strength by 47.18 %, 33.12 %, and 57.62 %, respectively, with the highest value attaining 22.71 MPa, 20.54 MPa, and 24.33 MPa. This indicates that NZ was the most effective in improving the mechanical properties of alkali-activated wood ash (AAWA). From SEM images, the usage of binary precursors densified the microstructure of AAMs by introducing more closed pores and decreasing micro-cracks, and based on the EDS, NASH gels were produced, co-existing with C(A)SH. In the TG-DTG analysis, greater weight loss associated with the activation products was observed for samples with FA, MK, and NZ, which was further confirmed in the XRD patterns, with higher intensity in peaks aligned with C(A)SH were identified. In FTIR spectra, the transition of the Si-O-Si and Si-O-Al bands confirmed the production of the hydrates and geopolymeric gels. This indicates that adding an aluminosilicate-rich precursor accelerates the alkaline activation and enhances its degree, favouring the development of mechanical and microstructural properties. In terms of LCA, binary precursors increased the environmental impacts of the production of AAWA, especially NZ, which accounted for a threefold increment in the greenhouse gas emissions due to its energy-intensive mining and processing procedures. Considering the influences on both the engineering performance and environmental impacts, CFA was the most effective among the three materials when used together with WA. |
