Radiological and material characterization of high volume fly ash concrete

Abstract

The main goal of research presented in this paper was the material and radiological characterization of high volume fly ash concrete (HVFAC) in terms of determination of natural radionuclide content and radon emanation and exhalation coefficients. All concrete samples were made with a fly ash content between 50% and 70% of the total amount of cementitious materials from one coal burning power plant in Serbia. Physical (fresh and hardened concrete density) and mechanical properties (compressive strength, splitting tensile strength and modulus of elasticity) of concrete were tested. The radionuclide content ( 226 Ra, 232 Th and 40 K) and radon massic exhalation of HVFAC samples were determined using gamma spectrometry.Determination of massic exhalation rates of HVFAC and its components using radon accumulation chamber techniques combined with a radon monitor was performed. The results show a beneficial effect of pozzolanic activity since the increase in fly ash content resulted in an increase in compressive strength of HVFAC by approximately 20% for the same mass of cement used in the mixtures. On the basis of the obtained radionuclide content of concrete components the I-indexes of different HVFAC samples were calculated and compared with measured values (0.27 -0.32), which were significantly below the recommended 1.0 index value. The prediction was relatively close to the measured values as the ratio between the calculated and measured I-index ranged between 0.89 and 1.14. Collected results of mechanical and radiological properties and performed calculations clearly prove that all 10 designed concretes with a certain type of fly ash are suitable for structural and non-structural applications both from a material and radiological point of view. KeywordsFly ash, Concrete, NORM, I-index, Radon exhalation 1. Introduction BackgroundThe building industry has one of the largest environmental impacts among all human activities:an annual consumption of 10 -11 billion tons of aggregate (Meyer, 2002) and 4.18 billion tons of cement (USGS, 2015). Apart from extremely high resource and energy consumption, cement production is a significant source of CO2 emissions, accounting for approximately 4.4% of global CO2 emissions from industry in 2007(Boden et al., 2010.There are many ideas that have been proposed to make concrete "greener" and more sustainable but they are all based on two principles: reuse and reduce. Concepts based on the "reduce" principle are oriented towards decreasing cement production based on natural materials and result in a reduction in CO2 emissions. With respect to the requirements for concrete as the world's most used man-made material, a lower production of Ordinary Portland cement must be compensated with alternative sources of binders in concrete production. There are several industrial sectors which produce significant amounts of residues such as fly ash (FA), bottom ash, red mud, steel slag, nonferrous slag, etc. which can be used for that purpose (Shi et al., 2006).Millions of tons of FA,...

A Review on Early Age and Long-term Compressive Strength of High-volume Fly Ash Concrete

“…The compressive strength of HVFA concrete with 50% Class C FA replacement was 22.6%, 21.7% and 18.3% less than that of ordinary concrete, respectively, for 3, 14 and 28 days curing [15]. When the curing period is 28 days, compressive strength of HVFA concrete increased by nearly 20% as the FA content increased from 50% to 70% by mass of total cementitious materials [16]. Michelle R. Nokken et al [17] found nearly 47.6% and 85.7% reduction of compressive strength, respectively, for 60% and 80% FA replacement level by mass at the curing age of 28 days.…”

Radiological evaluation of by-products used in construction and alternative applications; Part I. Preparation of a natural radioactivity database

“…The calculation of I-index of any raw (sand, aggregate), construction materials (cement, lime) or by-products would imply that 100% of these materials are used as building materials. Of course, this not realistic for most construction materials where only a fraction of certain by-products can be included, but it provides an opportunity for their screening or prediction [6] of the I-index of the final product. If needed, a dilution factor could be used for a given application to achieve more realistic screening (Fig.…”

“…The radionuclide content of recycled by-products cannot be ignored since they can cause increased radiological risk. According to EU-BSS [27], the dilution factor has to be determined as the function of the activity concentration of the components [6,104]. The screening of by-products and construction materials can be a practical tool to identify and manage potential material resources which can pose an elevated risk.…”

“…rocks, granite, gypsum, clay, etc. or by means of reuse of industrial by-products such as fly ash [6,7], bottom ash [8], phosphogypsum [9], steel slag [10], red mud [11], etc. The minerals contain terrestrial radionuclides from natural origin (U-238 and Th-232 series, furthermore K-40 and their progenies) which do not cause significantly higher radiation exposure than normal background levels.…”

Shrinkage Effects of Using Fly Ash instead of Fine Aggregate in Concrete Mixtures

“…Historically, fly ash has been substituted for up to 30-40% of the cementitious materials in concrete mixtures [6][7][8][9]. However, when fly ash is used as an alternative to cement, the concrete's early strength is slow to develop, limiting the viability of this type of utilization [10]. Some studies have indicated that a more viable utilization of fly ash is as a substitute for the fine aggregate in concrete mixtures [4,11].…”