International Concrete Abstracts Portal

In hot climate countries drying shrinkage of concrete is one of the major characteristics influencing its durability. In Australia, the majority of project specifications for concrete with requirements on durability set up criteria for drying shrinkage. Incorrect specification of this characteristic affects concrete durability and/or increases costs of construction. The paper analyses different sources of drying shrinkage variability, namely, metrological, within-sample, batch-to-batch, day-to-day, etc. The variabiiity of drying shrinkage resuits is compared with that of compressive strength data. Project specification requirements in terms of frequency of testing and acceptance criteria of drying shrinkage are discussed. The authors provide recommendations on drying shrinkage for project specification requirements which (a) decrease the consumer’s risk from the stand point of guarantee of getting the specified drying shrinkage and (b) decrease the concrete producer’s risk in the case of non-compliance of concrete in terms of drying shrinkage.

By now the theoretical foundations of the rational use of the SO called protective properties of concrete as a physico-chemical system have been laid. They are: the capacity to maintain stability and a non-equilibrium state in a changing environment. It should be kept in mind that concrete is practically the only material with such sensitivity to the environment components as clinkers, slags, ashes, and other relicts which can be considered reserve sources of creative processes in the building of structure by hydration and pozzolanic reaction. The technical state of knowledge of hydraulic cement concrete includes a wide range of characteristics defining its functioning and reaction to various factors of environment. During the service life of constructions it is possible to rely on the natural process of partial rehabilitation or of maintaining the reacted state of the concrete at a certain level of physico-chemical adaptation resulting from continuing hydration of reaction of clinker, slag, ashes, and other relicts. Moisture, electrolites, and elevated temperatures especially contribute to it. Here it should be ne marked as important for providing stable polymorphism in the form of stable hydrate phases, the appearance in their structure of ion-modifiers, specific for environment. to ensure correctness of the practical result it is necessary to observe the multitude of parameters of hydraulic cement concretes because real exploitation of the environment determines rather complicated responses of the object. It is especially important during comparative tests of durability of concretes intended for use in media with many kinds of impact. The modern theory of such tests is characterized by mathematical models elaborated by it that do not basically take into account the evolution of internal state in the cement paste caused by creative (hydration) and destructive (corrosion) processes. The determination of concrete adaptability by means of imitation modelling, while taking into consideration genetic and technological factors, should be perspective. All mentioned above is to provide optimal regimes for exploitation of concrete and reinforced concrete constructions.

Reinforced concrete is one of the most durable building materials in use today. However, it is often used in applications in which it is subjected to chloride ingress. When the chloride reaches the reinforcing steel corrosion initiates and the subsequent expansive corrosion products cause the concrete to crack or spall. This results in an acceleration of the corrosion and the need for repair. Numerous approaches have been utilized to prevent corrosion of embedded steel in concrete. Data from long-term laboratory tests over periods exceeding 3 years are presented for several commonly used methods to extend durability against corrosion of the reinforcing steel. The data show that reducing concrete permeability to chloride ingress by lowering the water-to-cement ratio or adding pozzolans are not sufficient for long-term performance in severe chloride environments. Furthermore, some of these mixture designs can result in increased shrinkage and thermal cracking compromising long-term performance. The conclusions from the studies performed in our laboratory are that a systems approach is needed for long-term durability for steel reinforced concrete in severe chloride exposures. It starts with low permeability concrete mixture designs that have reduced drying and thermal shrinkage. Corrosion inhibitors are added to protect the reinforcing steel which may or may not be coated. This is known as a ‘belt and suspenders approach, and has the added advantage of being amenable to modeling.

The non-linear diffusion equation has been successfully applied to water movement but only during the drying process. As a model which can be applied to both drying and wetting processes, capillary flow is considered to be worth examining as one possibility in order to establish a universal model. In the first step, one-dimensional water movement within mortar was studied both analytically and experimentally. A model consisting of capillaries with various sizes was adopted and water movement was analyzed by assuming that it was caused by capillary action. A good correlation w a s obtained between numerical results and experimental data. Useful information was also obtained from the analysis concerning the behavior of moving water within mortar.

In this study, the macro-cell induced corrosion behavior of steel bars embeded in concrete members was experimentally investigated specially for the influence of the permeation of oxygen and chloride ions throught joints. Steel bars composed of 7 elements were embedded in mortar or concrete, and repair materials such as polymer cement mortar. The electric current flowing in the steel bars, the polarization resistances, and the potentials of the steel bars, as well as the macro-cell and micro-cell current densities of the steel bars were measured. The differences between the type of joints and the permeation of oxygen and chloride were then studied. The influence of the quality of repair materials on the macro-cell corrosion was also investigated. Results showed that the permeation of oxygen and chloride ions through the joint and the qualities of the repaired concrete members played important roles in macro-cell corrosion behavior. Results showed that the permeation of oxygen and chloride ions through the joint and the qualities of the repaired concrete members played important roles in macro-cell corrosion behavior.Results showed that the permeation of oxygen and chloride ions through the joint and the qualities of the repaired concrete members played important roles in macro-cell corrosion behavior.