a b s t r a c tA numerical methodology is proposed in this paper to simulate the degradation of cementitious materials under external sulfate attack. The methodology includes diffusion of ions in and out of the structure, chemical reactions which lead to dissolution and precipitation of solids, and mechanical damage accumulation using a continuum damage mechanics approach. Diffusion of ions is assumed to occur under a concentration gradient as well as under a chemical activity gradient. Chemical reactions are assumed to occur under a local equilibrium condition which is considered to be valid for diffusion controlled reaction mechanisms. A macro-scale representation of mechanical damage is used in this model which reflects the cracking state of the structure. The mechanical and diffusion properties are modified at each time step based on the accumulated damage. The model is calibrated and validated using experimental results obtained from the literature. The usefulness of the model in evaluating the mineralogical evolution and mechanical deterioration of the structure is demonstrated.

This paper provides an improved understanding of the leaching behavior of waste incineration air-pollution-control (APC) residues in a long-term perspective. Leaching was investigated by a series of batch experiments reflecting leaching conditions after initial washout of highly soluble salts from residues. Leaching experiments were performed at a range of pH-values using carbonated and noncarbonated versions of two APC residues. The leaching data were evaluated by geochemical speciation modeling and discussed with respect to possible solubility control. The leaching of major elements as well as trace elements was generally found to be strongly dependent on pH. As leaching characterization was performed in the absence of high salt levels, the presented results represent long-term leaching after initial washout from a disposal site, that is, liquid-to-solid ratios above 1-2 L/kg. The leaching of Al, Ba, Ca, Cr, Pb, S, Si, V, and Zn was found influenced by solubility control from A12O3, Al(OH)3, Ba(S,Cr)04 solid solutions, BaSO4, Ca6Al2(SO4)3(OH)12 x 26H2O, CaAl2Si4O12 x 2H2O, Ca(OH)2, CaSiO3, CaSO4 x 2H2O, CaZn2(OH)6 x 2H2O, KAlSi2O6, PbCO3, PbCrO4, Pb2O3, Pb2V2O7, Pb3(VO4)2, ZnO, Zn2SiO4, and ZnSiO3. The presented dataset and modeling results form a thorough contribution to the assessment of long-term leaching behavior of APC residues under a wide range of conditions.

Quantifying the environmental impact of potentially hazardous materials in a wide variety of applications and disposal scenarios is essential to proper management of these materials. In an environmental assessment, the release of contaminants from the waste body with time has to be determined rather than aiming at concentration limits as currently used. In this approach, test results should yield information on leach rates. This implies the use of test methods other than those currently applied in the regulatory framework (EP, TCLP, DIN 38414-S4). The tank leaching procedure proved to be a proper method for characterizing the leaching behavior of trace contaminants from construction materials and stabilized waste products. Distinction between different leaching mechanisms is possible: dissolution, surface washoff, and matrix diffusion. Leach parameters, which allow estimating release at much longer time scales than the duration of the actual experiment, can be obtained from the tank leaching test. These parameters [availability for leaching, physical retardation (tortuosity), and chemical retention] offer control over the environmental quality of materials. A calculation method, different from the methods that have been published so far in the literature, is proposed for determinating the leaching mechanism in the material. The paper shows that the traditionally used one-dimensional model cannot predict long-term release with sufficient accuracy in actual applications because it does not take into account the limited leachable amount and the dimensions of the material. Since a one-dimensional model cannot describe the release with time as a function of different material shapes, even when depletion of the source is accounted for, at Netherlands Energy Research Foundation (ECN) a three-dimensional model is currently being developed that does offer these capabilities. Some preliminary results are presented. The variation found in the test results within one category of materials is relatively small and indicates that possibilities for developing short tests exist. For certification activities and quality control, this would be useful in creating a framework for environmental control parallel to technical product quality. At ECN a database for leach data has been developed. Storing detailed leach data on different construction materials and stabilized waste products in a database offers opportunities for a more efficient use of costly leaching studies. The knowledge gained by gathering information on a wide variety of materials may prove particularly useful in establishing systematic trends in leaching and selecting new directions for reusing waste materials. Also, a database will be a very useful tool in the environmental certification process for construction materials containing waste materials. It can be concluded that test methods tailored to a utilization option offer better possibilities than a single shake test for making proper choices in the wide variety of materials in an even wider range of possible applications.

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