International Concrete Abstracts Portal

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.

High-fluidity concretes have been developed recently and are being more widely accepted in order to realize highly durable and easier-to-build concrete structures. However, very little research has been made so far on the permeability and pore structure of high-fluidity concretes. This paper discusses the influences of water-binder ratio, type of admixture and amount of fly ash upon the permeability and pore structure of high-fluidity concretes. Permeability of high-fluidity concrete decreased with a decrease in water-binder ratio regardless of the type of chemical admixture and addition of fly ash used. It also decreased with additions of fly ash and this tendency was noticeable at lower water-binder ratio and was affected by factors such as the applied pressure, type of concrete and water-binder ratio. Air permeability of all types of concrete decreased with an increase in applied pressure. Total pore volume (pore radius from 3.75 to 7500 nm) of high-fluidity concrete decreased with a decrease in water-binder ratio and the number of fine pores increased. This tendency was noticeable when fly ash was added to the mixtures.

Porous concrete is used as top layer on highway roads and is characterized by a very open structure due to the use of gap-graded aggregates. This provides good drainage capabilities and noise reducing properties. In a preliminary test program, the durability of concrete, a polymer emulsion was added to the concrete mixture. Three different types of polymer emulsions were used. The resistance against freezing and thawing cycles, deicing salts, temperature variation and wetting and drying cycles were investigated on samples with a polymer-cement ratio of .10. Minimum film forming temp4erature, strength and elasticity of the polymer emulsion and of the hardened polymer film were determine as well. This paper deals with the results of the durability tests and investigates the relation between the properties of the polymer emulsion and the behavior of the polymer modified porous concrete. The role of the polymer film concerning structure formation as well as durability behavior in the hardened concrete is discussed.