Abstract
Pozzolanic activity of materials can initially be assumed from the quantity of the pozzolanic oxides SiO2, Al2O3 and Fe2O3. Some of the methods for assessing pozzolanic reactivity of materials include measurement of CaO consumption (Frattini test), decrease in electrical conductivity and pH of a solution containing pozzolanic material, or measurement of an increase in strength of mortar with replacement of cement by pozzolanic material (strength activity index, SAI). The above-mentioned pozzolanicity tests are used in this study to evaluate reactivity of wood biomass fly ashes (WBA-F). The results presented in the paper show that only the SAI method can fully reveal the hydraulic and pozzolanic activity of WBA-F.
Highlights
The use of wood biomass as a renewable energy source (RES) results in generation of wood biomass ash (WBA) as waste in power plants
Tested WBA fly ash (WBA-F) show a lower amount of pozzolanic oxides compared to the criteria for the assessment of the pozzolanicity of fly ash from coal combustion plants specified in standard EN 450-1 [20]
When the Frattini test was performed with pure WBA-F, a rapid decrease in the available amount of CaO was observed after 7 and 15 days, due to the hydraulic activity at an early age, and pozzolanic activity at later age
Summary
The use of wood biomass as a renewable energy source (RES) results in generation of wood biomass ash (WBA) as waste in power plants. Pozzolanic activity of bottom WBAs and three fly WBAs tested with the Frattini method according to EN 196-5 [8] was evaluated negatively [9], regardless of a significant amount of pozzolanic oxides in one of the ashes (56.01 %) [10]. Testing the pozzolanic reactivity with indirect methods (Strength Activity Index) showed a positive [11] and negative result [12], depending on characteristics of WBA used in the test. Pozzolanic material is characterized by its ability to react with portlandite and form additional C-S-H gel, which fills cavities between cement particles and aggregate, and contributes positively to the mechanical and durability properties of cement composites. The aim of this study was to evaluate feasibility of these common pozzolanic tests to indicate the reactivity of wood biomass fly ashes (WBA-Fs)
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