Geochemical Modeling

 
EES-1 researchers are active in the use of geochemical modeling to interpret the environments of formation and alteration of natural, low-temperature mineral deposits, including zeolite and clay assemblages. Geochemical modeling has recently been applied to understand the geochemical factors responsible for the formation of the carcinogenic zeolite erionite in volcanic tuffs. The results of modeling are being used to predict the distribution of erionite at Yucca Mountain, Nevada. Another signficant concern at Yucca Mountain is the stability of the zeolite clinoptilolite (up to 80% of some rock units) under the elevated temperature and modified fluid environment of a high-level radioactive waste repository. The modeling represents a unique integration of field observations of the distribution of clinoptilolite and silica polymorphs etc.; a 3-D computational grid describing permeability and other rock properties; thermodynamic models for zeolite chemistry; and kinetic models for the rates of dissolution and precipitation of clinoptilolite, cristobalite, opal, and other minerals.

In another geochemical modeling effort, EES-1 is developing a program in the development of high performance concrete. The approach is to treat the reactions occuring in concrete (cement, water, and rock materials) as a geochemical system, and apply geochemical principles and theories to the evolution of the concrete mineralogy. The modeling encompasses hydration reactions of the cement phases, the properties of the cementing (CSH) gel, dissolution reactions of the aggregate, and the hydrologic conditions of the concrete. A primary focus is understanding the origin of deleterious reactions (e.g., the alkali-silica reaction or sulfate attack), finding an explanation for the efficacy of certain treatments in preventing the deleterious reactions (e.g., the addition of flyash), and developing a geochemical basis for modifying cement chemistry to yield super-durable concrete.

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