Abstract
Waste ashes and radiation are hazardous environmental and health factors; thus, a lot of attention is paid to their reduction. We present eco-geopolymer building materials (GPBMs) based on the class F fly ashes (FFAs) from thermal power plants (TPPs) and their implementation as a barrier against radioactive radiation. Different methods of production, ratios of FFA to alkali activator, and temperatures of curing were tested. Small spherical particles and higher content of SiO2 resulted in developed surface area and higher reactivity of Isken TPP FFA than Catalagzi TPP FFA. Lower activator concentration (10% vs. 20%) and curing temperature (70 vs. 100 °C) caused an increase in GPBM compressive strength; the highest value was measured as 93.3 MPa. The highest RA was measured for GPBMs, provided alkali activator ratio (Na2SiO3/NaOH) was >2 and its concentration was 20%. The mathematical model developed in this study proved FFA quantity, and thus GPBM mechanical properties, as key factors influencing RA. In the light of these results, the lightweight GPBMs can be excellent materials for the construction sector dedicated to immobilization, storage, and disposal for radionuclides or barriers against radiation; however, multiple steps of their production require careful optimization.
Highlights
The demand for building materials is increasing every day; currently, the global consumption of concrete is ranked second after water
The CaO amount was less than 10% in both F fly ashes (FFAs); the amount of CaO together with MgO was higher in the Catalagzi thermal power plants (TPPs) FFA than Isken TPP FFA
The suitable features of geopolymer building materials (GPBMs) produced from the Catalagzi and Isken TPP FFAs consist of (i) use of raw materials (FFAs) and chemical activators (NaOH and/or Na2SiO3) instead of the cement, which accounts for a net reduction in energy use and greenhouse gas during the production; (ii) use of waste FFAs instead of the natural non-renewable sources; (iii) reuse of FFAs to reduce the storage of toxic waste; (iv) and increased life of building structures due to the improved material durability
Summary
The demand for building materials is increasing every day; currently, the global consumption of concrete is ranked second after water. A number of studies investigating geopolymer barriers focus on their behavior in the context of radioactive element leaching (e.g., cesium (Cs), strontium (Sr)) In this case, the selection of a precursor material and appropriate activator has a key impact due to immobilization occurring via ion exchange, physical adsorption, and encapsulation by the gel matrix [11]. Eco-geopolymer building materials (GPBMs) were produced based on FFAs from Catalagzi Thermal Power Plant (TPP) (Zonguldak, Turkey) and Isken Sugozu TPP (Adana, Turkey) as raw materials and NaOH and/or Na2SiO3 as alkali activators. The study intended to reduce the environmental problem, contribute to a circular economy and zero waste principles by means of waste FFA reuse as a raw material, and reduce carbon footprint and global warming by using cementless geopolymer technology and GPBMs with a high capacity of RA (comparing to conventional building materials). With the above in mind, we described developed materials as eco-geopolymer
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