International Concrete Abstracts Portal

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.

The following materials were studied in this work: one cement paste mixture, four mortar mixtures with diriment fine aggregate-cement ratio, for concrete mixtures with different water-to-cement ratio, three concrete mixtures with different maximum size of coarse aggregate, four concrete mixtures incorporating 50% blastfurnace slag, and three concrete mixtures incorporating 25% fly ash with different air content. All specimens were mainly used for determination of the coefficient of oxygen diffusion. The characteristic of gas transport through various cementitious materials is investigated by determining the coefficient of oxygen diffusion. The pore size distribution and compressive strength experiment are also measured to explain in more details the gas transport process through the concrete. The test results in this study indicate that the coefficient of oxygen diffusion values based on the theory of gas transport thought straight capillaries tends to overestimate the experimental results by a factor of four. However, the analytical result has the same tendency with the experimental result.

The results presented in this paper form part of an investigation into the optimisation of ternary blend systems based on normal portland cement, fly ash and silica fume, for the development of high performance concrete. Chloride permeability and oxygen permeability values at the age of 7, 28, 90 and 180 days of concrete containing portland cement, fly ash and silica fume are reported. Fly ash, up to 40%, and silica fume, up to 15%, were incorporated as partial cement replacements for the preparation of various combinations of ternary blended systems. A water-binder ratio of .27 was used for the main group of mixtures. Two other water-binder ratios, .40and .50 were used with selected concrete mixtures to show the effect of this parameter. Based on the experimentally obtained results, prediction models were developed. These enabled the establishment of isoresponse contours showing the interaction between the various parameters investigated.