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Over the past decades, numerous laboratory studies have clearly indicated that the use of supplementary cementing materials, and particularly fly ash, can significantly reduce the scaling durability of properly air-entrained concrete. Despite the great deal of research done on the topic, the reasons behind the detrimental influence of fly ash remain unclear. In order to bring more information on the subject, an investigation of the influence of fly ahs on the deicer salt scaling resistance of concrete has been recently carried out. Test variables include water/binder ratio (.40, .50 and .66), class of fly ash (two class C and a class CF), and the percentage of replacement of the cement by the fly ash (, 20 and 40%). An additional series of mixtures was prepared with 25% slag as cement replacement. All deicer salt scaling tests were performed according to a modified version of ASTM C 672 on both troweled and sawed surfaces. The air-void characteristics of all mixtures were determined according to ASTM C 457, and the microstructure of selected mixtures was studied by mans of SEM observations. All test results confirmed that the use of fly ash and slag can reduce the salt scaling durability of concrete as determined in the laboratory. The influence of fly ash and slag does not appear to be linked to their effect on the material pore structure. An explanation linked to its influence on the characteristics of the air-void network is suggested.

Solidification/stabilization (S/S) is an effective management of toxic wastes, consisting in mixing a waste product with a binder and other ingredients, if any, to reduce the mobility or solubility of contaminants. In the present work, a contaminated marine sediment of the Venice lagoon was treated with cement, aggregates and different amounts of an acrylic superplasticizer to produce cement mortars with different W/C. The characteristics of the resulting mortars were evaluated by compressive strength, water permeability, observation of microstructure of the comment past, and leaching of contaminants. The durability in aggressive environments of the best performing mortar, corresponding to the mixture with W/C=.38, was evaluated in comparison to a reference mortar. The results of the test indicated that W/C affects no only the strength of the mortars but also improves the leaching characteristics of the stabilized waste. This could be ascribed mainly to the reduction of the micro porosity of the mortars with lower W/C. The durability test indicated that the mortar containing the sediment is less sensitive to the attack of CaCl2 in comparison to the reference mortar, as confirmed by the higher strength after different periods of immersion in a 30% aqueous solution of CaCl2 at 5 degrees C. Furthermore, the linear expansion in sulphate solution seems not to be substantially influenced by the presence of the sediment. Thermal and XRD analyses suggested that these results could be ascribed to a pozzolanic effect of the sediment. The results of the present work confirmed the possibility of producing high performance concrete by using the contaminated sediments of the Venice lagoon.

Hysteresis effects are very frequent in experimental studies of porous building material. In the case of frost deicing salt resistance, hysteresis effects between freezing and thawing were reported in calorimetric and expansion experiments. They often were explained by a difference in the active pore diameter. However, our calorimetric and ultrasonic pulse velocity measurement show much smaller hysteresis effects which support another explanation: supercooling. A model based on non-connected pore water which may supercooling. A model based on non-connected pore water which may supercool was developed to explain the experimental differences. This model allows a reinterpretation of experimental expansion data. The moment of damage formation in frost deicing salt resistance tests can be studied. The analysis of the causes of hysteresis effects therefore leads to improved models of frost deicing salt damage mechanisms.

The results tests on rock aggregate and manufactured sand from Paleozoic carbonate rocks from quarries in SW Ontario were compared those of mortars containing the manufactured sand. The aggregate tests included petrographic analysis, water absorption and adsorption, linear expansion under various conditions, analysis, water absorption and adsorption, linear expansion under various conditions, thermal expansion, insoluble residue content, micro-Deval abrasion loss, freeze-thaw loss, and rate of settlement of -.075 mm. (-#200) fraction. The mortar tests consisted of drying shrinkage, water absorption and adsorption, linear expansion under various conditions, thermal expansion, and scaling and freeze-thaw loss. Multivariate statistical techniques (factor, D-cluster, tree, and stepwise regression analysis) were used to compare and group the properties of aggregates and mortars. Factor analysis showed that the results could be grouped into four factors: (1) Durability factor, (2) Porosity factor, (3) Thermal and (4) Isothermal Expansion Factors. The first two factors were found to be the most encompassing, and grouped the most significant test for aggregate and mortar frost resistance. Stepwise regression predictive models of mortar resistance to salt scaling were developed, based on results of simpler tests on aggregates. K-cluster analysis successfully classifies the aggregates and mortars made from them into good and poor categories. The tree analysis provides the passing limits that can be applied to aggregate tests of any defined group of aggregates.

The acid resistance of six different sets of concrete materials was measured using hydrochloric acid in a test method developed at the University of Cape Town. The concrete mixtures included a standard mix used for the preparation of sewer pipes by the roller suspension method, and five modifications of the standard mix. Four of the test mixtures were modified by partial replacement of normal portland cement with a mineral admixture, namely slag, fly ash, condensed silica fume or meta-kaolin. In the fifth test mixture, normal portland cement was replaced with a calcium aluminate cement. Silica fume concrete showed better acid resistance compared to the standard concrete. In general, at 28 days the physical properties of concrete with fine mineral admixtures (condensed silica fume, meta-kaolin) were superior to the other concretes. However, the acid resistance of the meta-kaolin concrete was not improved despite its superior quality. Improvement in the acid resistance of the concrete with condensed silica fume indicates that the concrete is improved both chemically and physically by the addition of silica fume.