International Concrete Abstracts Portal

Corrosion of steel reinforcement is now universally recognized as the major factor affecting the material stability and structural integrity of concrete structures. In very aggressive environments, the material degradation and structural distress arising from steel corrosion can reduce dramatically and useful service life of structures, affect their strength, stability and safety, and indeed, even lead to premature failure. The aim of this paper is to offer an integrated, holistic approach-a global design/management strategy-which will enable us to design new structures with a specified durable service life, and which will also enable us to enhance the durable service life of existing deteriorating structures. The paper identifies the design parameters that need to be satisfied and the strategy that needs to be adopted to ensure long-term corrosion-free service life of concrete structures, whether they are to be newly built or are existing but deteriorating due to environmental attack or otherwise damaged. The paper is accompanied by relevant and appropriate test data.

High Performance High Strength Concrete (HPHSC) has been utilized in columns and in other compression members. The author and his research team at Curtin University have conducted significant research into the behaviour and strength of HPHSC columns for the last eight years. The research comprised extensive experimental work and analytical calculations. Numerous column specimens have been tested in combined axial compression and uniaxial (single and double curvature) bending or biaxial bending. Analytical methods have been developed to predict the response and strength of test columns. Based on the research various proposals for design have been formulated. The paper describes the salient features of this research.

Employment of High Performance Concrete (HPC) for thin overlays construction for aged flexible pavements has become a reality during the 90's, specially in USA and some northwest European countries. While whitetopping old pavements was a technique employed from earlier decades of the twenty century, the construction of ultra-thin concrete overlays (by 100 mm) for rehabilitation of pavements has been enhanced by the availability of technology for manufacturing HPC and the possibility of fast tracking. Ultra-thin whitetopping is a technique requiring several field conditions to be met concerning the old asphalt pavement in order to perform well as an overlay. They are full bond condition at the interface of HPC and asphalt concrete (generally provided by milling), asphalt concrete without fatigue cracking and rational joint spacing. All these factors, by the other hand, must be taken into account on the basis of the peculiar resistance of the HPC are going to be used. Within this context, in this paper is presented a study with regard to the HPC strength to be achieved for UTW purposes, supported by a numerical analysis based on a finite element solution for slabs-on-grade and taking into account the elastic properties position. An international review of HPC applied on whitetoppings around the world is also presented that includes recent works in this field.

The use of high reactivity pozzolanas, such as silica fume in portland cement concrete, has increased significantly in the last two decades owing to improved resistance and durability of the concrete incorporating these materials. These properties were achieved through increased density of the cement paste generated by the micro-filler effect and pozzolanic relations with calcium hydroxide liberated in hydration reactions of cement compounds. However, this beneficial effect on concrete properties involves a considerable cost increase due to the large use of superplasticizers necessary to confer the desired workability to concrete mixtures. A recently studied alternative pozzolana is rice-hush ash, which has been shown to present a performance compatible to that of silica fume, once is produced under controlled conditions. Nevertheless, recent research in Brazil have shown that even residual rice-husk ash (a by-product of the cereal husk burning for energy production) presents excellent performances as a pozzolana. As part of that research, this work has been carried out in order to compare silica fume performance with that of residual rice husk-ash in high-performance concrete. Both the demand of a superplasticizer admixture and strength development were investigated against a control concrete (without pozzolana). Three water/cementations materials (keeping constant the absolute volume of cementations materials) were studied. Residual rice-husk ash has been demonstrated to be a highly reactive pozzolana, superplasticizer admixture that the concrete with silica fume. As to performance evaluation, concrete mixtures with silica fume showed greater strengths than other concretes. However, the results have shown an increase in residual rice-husk ash concrete strength from the 28th day on, reaching strength values close to those of silica fume at 90 days, an indication that the performance of both pozzolans may be the same at later ages.

Results from tests on eight high strength concrete external beam-column connection specimens are presented an compared with results from a similar set of normal strength concrete specimens. The number of connection zone column ties was varied from zero up to a total of seven. The technique of internally strain gauging the reinforcement was used to measure strains in the main beam and column reinforcement. Additionally, connection zone column ties were also strain gauged in the eight specimens which had one or three such ties in the connection zone. Results are presented to illustrate the performance several are present. Twelve other specimens were tested. Nine sued normal strength concrete augmented with steel fibres whilst the other three used non-standard reinforcement details involving steel plates. Results are presented to compare the performance of these specimens with those using high strength concrete.