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.

Many prediction criteria for evaluating the ultimate strength of high strength concrete deep beams are compared in this research. Added to the theoretical values obtained by the equations, a strut and tie model was developed, using the load path obtained by the Finite Element Method. The values found are also compared with test results in three high strength concrete deep beams with web openings. The test specimens consist of simply supported deep beams with openings located next to one of the supports. It is shown that there is great difference in the values encountered by theoretical analysis, and only ACI's prediction gets close to the test results, in spit of not considering the opening.

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.

The scope of this work is to quantify the synergic action of fly ash when mixed with other pozzolans, through the performance of microstructural and durability parameters of HPC. Eleven mixture proportions were tested with fly ash, rice husk ash and silica fume in binary and ternary mixtures, with cement substitution, in mass, from 10 to 50%. The following tests related to HPC durability were made: axial compression strength, elasticity modulus, shrinkage, total chloride content, Cl/OH ionic relationship, water penetration and accelerated carbonation. Some micro structural parameters were determined such as bound water, amount of C-S-H, remaining (C3S+C2S) and C-H. The results were calculated related tot the unitary mass of cement, compared to each other in compressive strength equality of 70 Mpa. Practically all the variables linked to the durability presented better performance in the ternary mixtures, than the arithmetic sums of the respective binary mixtures and this behavior is validated with micro structural evidence. It is suggested that the fly ash have a synergic action in ternary mixtures probably due to the higher dispersion of the cement grains, similar of plasticizing mixture action, resoling in additional nucleation sites and larger amounts of hydration products. A synergic action model of fly ash in ternary mixtures is provided.

The objective of this paper is to report test results of gas-permeability of high-performance concretes, measured on laboratory specimens and directly on site. The test refer to three concretes used in two projects: a tunnel (50MPa concrete) and a cable-stayed bridge deck (50 Mpa concrete) and pylon (75 MPa concrete). In particular, the investigation was focused on comparing the permeability of the "covercrete", measured on laboratory specimens, with that measured directly on the site concretes, I.e. subjected to strongly different placing, compaction and curing conditions. The air-permeability of the cover of the three concretes was measured with a non-destructive technique, which takes into account the effect of moisture. Cores were drilled from the same elements and the oxygen permeability measured on them. When core-drilling was not allowed, parallel tests were conducted on large cubes, site cured, cast with the same concrete mixture used for the actual construction. For the three structures investigated, the air-permeability of the site concrete was higher that that measured on the companion laboratory specimens. The largest difference was found for the 75 Mpa-strength concrete; this difference is attributed to thermal cracking in the pylon, the center of which exhibited 55 degrees C temperature rise. This indicates the risk of impairing the potential durability of HPC through inappropriate practices. The results presented show the importance of checking the quality of the concrete, not only on laboratory-prepared specimens, but also directly on site.