Radiological characterisation of alkali-activated construction materials containing red mud, fly ash and ground granulated blast-furnace slag

Abstract

This study characterises the Naturally Occurring Radionuclides (NORs) content of a suite of secondary raw materials or industrial residues that are normally disposed of in landfills or lagoons but now are increasingly used in green concretes. This includes ashes from a variety of industrial processes and red mud from aluminium production, as well as air pollution control residue and cement kiln dust. The chemical composition of the samples was determined with X-ray fluorescence spectroscopy (XRF). The Ra-226, Th-232 and K-40 activity concentrations were obtained by gamma spectrometry, and the results were compared with recently published NOR databases. The correlation between the NOR content and the main chemical 2 composition was investigated. The radioactive equilibrium in the U-238 chain was studied based on the determination of progeny isotopes. The most commonly used calculation methods (activity concentration index and radium equivalent concentration) were applied to classify the samples. The radon exhalation rate of the samples was measured, and the radon emanation coefficient was calculated. Significant correlation was found between the NORs and certain chemical components. The massic exhalation demonstrated a broad range, and it was found that the emanation coefficients were significantly lower in the case of the residues generated as a result of high-temperature combustion processes. The results showed that a weak correlation between the Ra-226 concentration and the radon exhalation. This emphasizes that managing the Ra-226 content of recycled material by itself is not sufficient to control the radon exhalation of recycled materials used in building products. The investigated parameters and their correlation behaviour could be used to source apportion materials found during the process of landfill mining and recovery of material for recycling.

Properties of red-mud-based geopolymers in the light of their chemical composition

“…Increasing red mud percentage decreases the compressive strength of geopolymer mortar continuously. The maximum compressive strength achieved was 8.0 MPa with 10% red mud under 70⁰C for 24 hours [13]. This low value of compressive strength can be linked to the absence of the alkali activator.…”

“…Ten different sample compositions are categorized as low calcium RM collected from the literature [7,[10][11][12][13][14][15][16][17][18]. From a statistical point of view, the average can be taken as the mean or median value depending on the existence of outliers [19].…”

“…Therefore, the optimal compressive strength requires a lower concentration of sodium hydroxide in the alkali activator. Low calcium red mud has been utilized to replace metazeolite, fly ash and ground granulated blast furnace slag in geopolymer mortar production [11,13,15,17,18,35]. In the case of ground granulated blast furnace slag, the red mud is added without an alkali activator.…”

The use of finely ground slag in portland cement with mineral additives

“…Scientists have conducted studies to develop ways to improve slag cements, cement and other binding compositions containing slag [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]. One of the ways to increase the activity of the slag is thermal activation, which consists in the combination of abrupt heating of the source material with a relatively short isothermal exposure resulting in rapid cooling of the slag [4][5][6].…”

“…In works [7,11,17,[18][19][20][21][22][23][24], the positive effect of slag fineness on the properties of the studied cements was noted, which allows us to consider it as a reinforcing component of the cement matrix. In this regard, the goals and objectives of the study were formulated, which are: to obtain finely ground slag of different dispersity and to study its effect on the properties of Portland cement with mineral additives.…”