Influence of Fly Ash Denitrification on Properties of Hybrid Alkali-Activated Composites

Abstract

This article deals with the possibility of partial replacement of blast furnace slag (GGBFS) with fly ash after denitrification (FAD) in alkali-activated materials. Physical-mechanical and durability properties were tested, hydration reaction was monitored, and infrared spectroscopy was performed. Results were compared between mixtures prepared with fly ash without denitrification (FA), and also with a mixture based only on GGBFS. The basic result is that hybrid alkali-systems with FAD show similar trends to FA. The significant effect of fly ash is manifested in terms of its resistance to freeze-thaw processes. Reactions in a calorimeter show a slower development of reactions with increasing replacement of GGBFS due to the lower reactivity of the fly ash. Through testing the leaching resistance, a decrease in flexural strength was found. This may be due to the descaling of the main hydration product, C–(A)–S–H gel. After 28 days of maturation, compressive strengths of all monitored mixtures ranged from 96 to 102 MPa. The flexural strengths ranged from 6.8 to 8.0 MPa. After 28 days of maturation, the higher strengths reached mixtures without replacing GGBFS. In terms of resistance to freeze-thaw processes, the largest decrease (almost 20%) of flexural strength was achieved by a mixture with 30% of GGBFS replacement by FA. No fundamental differences were found for the mixtures in the FTIR analysis.

Possibilities of using fly ash after denitrification to various types of building materials

“…Compared to the reference sample the flexural strength decreased by 7 to 41%, with fly ash content 20-60%. The results are in agreement with results of similar experiments [16,17]. An assessment of flexural strength was carried out and a frost resistance coefficient was calculated.…”

“…Using Czech fly ashes after denitrification was tested in alkali-activated materials. Procházka [16,17] carried out an experimental study with fly ash from the power plant Ostrava-Třebovice. After denitrification an amount of ammonia was determined as 22.8 mg•kg -1 .…”

A Comprehensive Review on Fly Ash-Based Geopolymer

“…Research has shown that fly ash from flue gas denitrification is characterized by a higher value of losses on ignition and ammonia content in comparison to ashes without denitrification; it has also been shown that the ammonia content in the analyzed range does not limit the use of fly ash as an additive to cement and concrete. Procházka et al [159] explained the influence of fly ash denitrification on the properties of hybrid alkali-activated composites. The purpose of this study was to evaluate the effect of SNCR denitrification on fly ash for usage in hybrid alkali-activated materials that were based on blast furnace granulated slag.…”