A mechanical, leaching and radiological assessment of fired bricks with a high content of fly ash

doi:10.1016/j.ceramint.2018.04.162

Ceramics International

Volume 44, Issue 11, 1 August 2018, Pages 13313-13319

https://doi.org/10.1016/j.ceramint.2018.04.162 Get rights and content

Abstract

All building materials contain amounts of natural radioactive nuclides and heavy metals, but when waste materials are to be used in building materials, industrial processing can lead to further enhancement of the concentrations of nuclides and heavy metals in the waste. In this paper fly ashes were used as a raw material to replace natural clay to make fired bricks. The effects of a high replacement ratio (from 0% to 100%) of clay with fly ash on the mechanical, radiological and leaching properties of bricks were analyzed. A study of the different sintering temperatures of bricks was carried out at the selected temperatures of 800, 900 and 1000 °C. When the temperature was increased the mechanical strength was also increased. Two leaching tests (one batch and the other monolithic) were carried out and the bricks with a high replacing ratio did not present problems regarding the heavy metal leaching in either test. The contents of three radionuclides (²²⁰Ra, ²³²Th and ⁴⁰K) were analyzed and the Activity Concentration Index of the bricks was calculated and was lower than 1, indicating a radiation exposure lower than 1 mSv y⁻¹.

Introduction

The European Union produced approximately 70 million tons of coal combustion waste in 2015. Fly ash is obtained from the electrostatic or mechanical precipitation of dust such as particles from the flue gas, and it represents 80% wt of the total coal combustion waste produced [1]. Within the EU, the reuse of fly ash in the construction industry is currently around 50%, and is mainly used as concrete addition, cement raw material, concrete blocks and in road construction [2].

A brick plant may consume large quantities of raw materials. A brick plant of medium size consumes approximately 500 t a day of raw materials. The production of conventional bricks may be a promising application for different types of ashes, considering the large quantities of raw materials needed for brick production, and the fly ash ratio incorporated into bricks is low, only about 10–40% by volume [3], [4], [5]. In the present study, the effects of fly ash with a high ratio for replacing natural clay on the properties of the resulting bricks have been studied. In addition, certain advantages to using fly ash as a raw material for brick production, such as a reduction in the firing energy requirement due to the amount of unburned carbon contained in fly ash have been examined [6].

Many waste materials may have enhanced concentrations of radionuclides and heavy metals of natural origin which result from concentration processes. In particular, energy production from fossil fuels such as coal may lead to a concentration in fly ash by volatilization and adsorption processes [7]. For this reason, the successful incorporation of fly ashes and other waste materials with enhanced concentrations of naturally occurring radionuclides and heavy metals into fired bricks is conditioned by the legislation and standards regulating the quality and environmental safety of the finished construction products. The radionuclides and heavy metals in materials which are usable in building materials are regulated explicitly by the standards of only a relatively few countries. Until recently, there had not been a unified recommendation (no regulation) regarding the restriction of radionuclide contents in building materials or the leaching of heavy metals in Europe.

Section snippets

Raw materials

Fly ashes (FA) from the coal combustion in a Spanish Power Plant and natural clay (NC) from Ceramica Saza (Spain) were used in this study. Their chemical compositions are shown in Table 1. They were measured by X-Ray Fluorescence (Panalytical, AXIOS model). A sum of the three major oxides (SiO₂, Al₂O₃, and Fe₂O₃) in an amount > 80% wt met the classification of class F fly ash (> 70% wt). The contents of SiO₂ (45.02% wt) in fly ash are lower than that in clay (75.66% wt), but the content of Al₂O₃

Firing

When NC was heated (Fig. 5) from 20 °C to 200 °C, a mass loss of 5% was observed due the release of moisture and physically adsorbed water. From 200 °C to 400 °C, the weight was almost constant. From 400 °C to 610 °C, a weight loss of 3% could be assigned to the de-hydroxylation of kaolinite at 480 °C and the structural water of montmorillonite between 400 °C and 580 °C [5]. Finally, in the interval from 580 °C to 760 °C a weight loss of 9.6% was due to the decomposition of calcite and dolomite

Conclusions

Fly ash used as raw material for replacing clay to make fired bricks is an effective measure for saving land and decreasing pollution. The results of the present study indicate that a good firing temperature for bricks with high replacing ratio of clay with fly ash was about 1000 °C and the replacement could be up to 80% for normal weathering. The fired bricks with a high volume ratio of fly ash were of high density and high compressive strength.

Regarding the environmental study, no

Acknowledgements

The authors acknowledge Dr. Santiago Hurtado from the Service of Radionuclides of University of Seville for his technical assistance with the radioactivity measurements.

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ECOBA: European Coal Combustion Products Association. Available online: 〈http://www.ecoba.com/ecobaccpprod.html〉...

Council Directive 2013/59/Euratom of 5 Dec. 2013 Laying Down Basic Safety Standards for Protection against the Dangers...

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A mechanical, leaching and radiological assessment of fired bricks with a high content of fly ash

Abstract

Introduction

Section snippets

Raw materials

Firing

Conclusions

Acknowledgements

Earth Sci. Rev.

Appl. Clay Sci.

Appl. Clay Sci.

Appl. Clay Sci.

Constr. Build. Mater.

Constr. Build. Mater.

Ceram. Int.

J. Build. Eng.

Waste Manag.

Waste Manag

J. Environ. Radioact.