by clicking the arrows at the side of the page, or by using the toolbar.
by clicking anywhere on the page.
by dragging the page around when zoomed in.
by clicking anywhere on the page when zoomed in.
web sites or send emails by clicking on hyperlinks.
Email this page to a friend
Search this issue
Index - jump to page or section
Archive - view past issues
Concrete In Australia : March 2013
52 Concrete in Australia Vol 39 No 1 a Nobel Prize in 1977 (Glansdorff & Prigogin, 1971; Prigogin, 1947; Prigogin & Nicolis, 1977; Prigogin & Stengers, 1980). According to Prigogin, systems "far from equilibrium" may still evolve to a steady state when the thermodynamic forces acting on a system create a condition such that the linear region is exceeded. e evaluation of a steady state condition also requires the assessment of how the steady state may react to the different types of fluctuations within a system or in its environment. e mathematical foundations of this theory were adopted by Samarin in order to provide the theoretical base of the structural formation of exceptionally durable concretes (Samarin, 1992; 1993; 1995a; 1995b; 1997; Sychev, 1990). In addition to the mathematical groundwork, physical and chemical concepts of the surface phenomena in dispersing systems, kinetics of the alkaline aluminate-silicate formation, the effects of secondary compaction of concrete as well as the employment of special surface-active admixtures and pozzolanic materials were used by Samarin in developing new types of durable concretes capable of safe, long term encapsulation of hazardous wastes (Rhebinder, 1979; Glukhovsky & Petrenko, 1992; Glukhovsky, Bozhenov & Runova, 1992; Mchedlov- Petrossyan, 1963, 1984; Samarin, 1987; 1989; 1992; 1996; Glasser, 1996). 2.2 Classification of radioactive wastes Hazardous wastes which contain radioactive materials are generally classified into three categories. Low-level radioactive wastes (LLW) are usually those which are generated by industry and hospitals. ey may include such materials as paper, rags, tools, clothing, filters, etc, and as a rule contain a relatively small amount and also short half-life radioactive material. Intermediate-level radioactive wastes (ILW) contain higher quantity, and what is most important, longer half-life radioactive material that the LLW. ese may include resins, chemical sludge and metal nuclear reactor claddings, as well as various types of contaminated materials from reactor decommissioning. High-level radioactive wastes (HLW) are the by-products of nuclear reactors. ey are highly reactive and usually have very long radioactive half-life. High level radioactive wastes require special methods of treatment, disposal, destruction or storage, and are well outside the scope of the waste disposal method proposed in this paper. e proposed methodology of waste disposal covers the intermediate level radioactive waste as well as the low-level radioactive wastes, should these be considered unsafe if they are disposed as a non-radioactive, low-risk hazardous waste. e amount of radioactivity of waste materials is measured in the terms of transformation rate -- the number of decays which occur in the unit time. e unit of radioactive activity is Becquerel (Bq), and one Bq represents one transformation per second. us Giga Becquerel (GBq) denotes 109 transformations per second. e activity per unit volume of radioactive material is measured in Bq per litre. e absorbed dose is the energy deposited per unit mass of a material by the ionising radiation. e unit of absorbed dose is the Gray (Gy) defined as one joule per kilogram. Absorbed dose is calculated as a dose rate per unit activity, times the integral activity, ie: D=(Δ×ϕ×A)÷ mv (1) Where D = absorber dose (in Grays), Δ = mean energy of radiation emitted per nuclear transformation (in joules) ϕ = the fraction of the energy emitted and then absorbed by the target organ (no units, of course!) A = the time integral activity (Becquerels × seconds) mv = mass (in the kilograms) of the organ, whose absorbed dose is being evaluated. e harmful effects of ionising radiation depend on the radiation dose (Gy), on the proximity of a person to the source of radiation and on the time of exposure. Even at a very high radiation dose of between 4 Gy and 6 Gy, the direct exposure of a person for the duration of up to 48 h usually results in the nausea, vomiting, fatigue and lethargy, with the rapid recovery from these symptoms (Samarin, 2001). ere are inevitably many natural sources of radiation, which are usually expressed in the units of "dose equivalent", or in Sieverts (Sv), such that 1Sv = 1 Jkg -1. Typical values of the natural sources of radiation are shown in Table 1. Table 1. Cosmic radiation 300μSv Terrestrial gamma rays 380μSv Radon decay products 800μSv e radiation emitted from the low-level and even intermediate level radioactive wastes, encapsulated in the proposed special highly durable concrete should not exceed, if properly implemented, the intensity of the natural sources of radiation. Obviously, each specific type of radioactive waste, and also the variability of properties of raw materials (cements, admixtures, additives, coarse and fine aggregates) will produce slightly different results in different applications. I shall address this problem in some detail later in the text. 2.3 Laboratory evaluation of the effectiveness of encapsulation One cubic metre of concrete, on average, has a mass of some 2400 kg. In the proposed method of encapsulation, 20 kg of concrete is replaced with a particular hazardous waste. e amount of waste can vary slightly, depending on its type and toxicity. e composition of concrete, that is the ratio of hydraulic cement to fine and coarse aggregates, the amount and the type of additives (such as fly ash or granulated slag) and also specific types of surface-active admixtures can also vary, depending on the nature of hazardous waste and on the availability of local materials for the production of concrete. In order to evaluate the effectiveness of waste encapsulation,