PROPERTIES:PHYSICO-CHEMICAL 323A Weibull's statistical theory of the strength of materials. The body of heterogeneous concrete material is simulated as a continuum comprising a large population of microscopic 'weakest-link' isoenergy elements, each of which contains a unit-volume of representative micro-structural material which is linearly elastic, homogeneous and isotropic. The statistical modelling is derived from the stochastic evaluation of the tensile micro-fracture probabilities of these isoencrgy ele- ments at increasing global uniaxial compressive strains. (from Authors) 957146 Modemng the fracture of concrete: the cohesive crack G. V. Guinea, Materials & Structures, 28(178), 1995, pp 187- 194. This paper shows the ability of the cohesive crack model to predict reasonably well the bchaviour of concrete specimens. To demonstrate this two very different examples are con- sidered. The fn'st is an engineering problem related to the breakage of precase concrete piles; it is shown that the cohesive crack model points to the relevant parameters and suggests ways to improve the behaviour of the concrete. The second example analyses the well known effect of size on the modulus of rupture when measured during the three point bending of beams. This work shows how this model not only predicts accurately the maximum loads for different geome- tries and sizes but also is able to make reasonably good predictions of load and displacement at any instant throughout the test. (Author) Time dependent behaviour 957147 The role of clay minerals in durability of rocks: observa- tions on basaltic rocks R. A. Kuhnel, S. J. Van der Gaast, J. Brych, G. J. Laan & H. Kulnig, Applied Clay Science, 9(4), 1994, pp 225-237. Knowledge of the durability of rocks, is essential for determining the safety and lifetime of structures and monu- ments. Hydraulic structures in particular require a high probability of survival of at least 100 years and monuments closer to a millennium. The degradation of a rock is often caused by clay minerals present from its origin and/or formed during geological history. In their fresh state during quarrying and mining it is difficult to recognise tendencies toward degradation and decay in rocks with time. For the selection of high quality construction materials (basaltic rocks) a series of new testing techniques has been developed in which the focus is on the role of clay minerals. This paper deals with occurrences, neoformation and behaviour of clay minerals which contribute to an early recognition of tendencies of rock decay. (from Authors) 957148 Controversy: mechanical fatigue or hardening of rocks after their excavation W. C. Kowalski, Bulletin - International Association of Engineering Geology, 50, 1994, pp 51-57. It is pointed out that strength value of rock samples changes with time after sample excavation from a quarry. Three main stages of strength variability with time are distinguished: 1) the stage of hardening connected with increase in the compression strength; 2) stage of equilibrium of the antag- onistic processes: hardening and mechanical fatigue; 3) stage of manifestation of mechanical fatigue. Mechanical fatigue is favorable to the manifestation latent weakness surface to new crack formation and at last to total disintegration in rock samples. (Author) Physico-chemical properties 957149 Modeling minerni/mlutiea interactions: the thermody- namk and kinetic code KINDISP B. Made, A. Clement & B. Fritz, Computers & Geosciences, 20(9), 1994, pp 1347-1363. The kinetic and thermodynamic geochemical model KIN- DISP (KINetics of DISsolution and Precipitation) describes the interactions between minerals and aqueous solutions, taking into account the irreversible dissolution of the reactants and the reversible precipitation of secondary products. The model has been used to simulate natural or induced water/rock interactions, at low temperatures, to study the effects of acid rain on surface weathering of a granite formation, estimate the formation time of a laterite layer, and the effects of pollution on the environment, and also at higher temperatures, to describe and account for diagenetic reactions in sedimentary b~qins for the purpose of reservoir exploitation as well as to study a system of hydrothermai reactions mused by heat storage or disposal of nuclear waste packages. (from Authors) 957150 The pH influence on the index proporties of clays U. Gori, Bulletin - International Association of Engineering Geology, 50, 1994, pp 37-42. Three clay sediments, Pliocenic clay, Chaotic Complex clay and commercial kaolinic clay, have been studied in order to verify the pH influence on the index properties. The index properties differ between the three clays. The kaolin is not much affected, only a limited WL% increase is recotmizable when the pH decreases. The Chaotic complex clay shows a considerable rise of the WL with pH increase. In the Pliocenic clay the WL value increased with the pH. The described process can be related to the natural environment, connected also with various pollution phenomena. (from Author) 957151 Sorption of cesium on bentonite S. A. Khan, Riaz-ur-Rehman & M. A. Khan, Waste Management, 14(7), 1994, pp 629-642. In view of the nuclear waste management, the sorption studies of radionucfides on various materials is of great importance and significance in predicting the migration of these nuclides in geological formations near waste storage sites and also for evaluating the feasibility of a particular natural material for the disposal of low level radioactive waste into the ground. In this paper the sorption of Cs on bentonite has been studied by using hatch technique. Distribution coefficients 0(d) were determined for bentonite-cesium solution system as a func- tion of contact time, pH, sorbent and sorbate concentration and temperature. The desorption studies with 0.01 M CaCI2 and ground water at low cesium loading on bentonite show that about 95% of the element is irreversibly sorbed probably due to the fLxation of the cesium by isomorphous replacement in the crystal lattice of the sorbent. (from Authors) 957152 Modelling of potassium exchange in a natural, polyionic montmorillonite under hydrothermal conditions F. J. Huertas, J. Cuadros & J. Linares, Applied Geochem- istry, 10(3), 1995, pp 347-355. One type of High-Level Nuclear Waste Repository includes bentonite as a barrivr. Bentonite with high smectite content combines a number of desirable properties for such reposi- tories. Nevertheless, smectite is transformed into illite under the temperature conditions of the repository if K is available. The first step of this transformation is the exchange of K + ions for the initial cations present in the smectite interlayer.