Reports on high-strength lightweight and normal weight concretes. Sintered fly ash lightweight aggregates, crushed limestones, and two types of cement with different contents were investigated. All the concretes contained silica fume and a high-range water-reducing admixture. To obtain high specific strengths (i.e., ratio of strength to relative density), lightweight concretes were prepared with only lightweight particles (coarse and fine), reaching strengths higher than 60 MPa with density of about 1700 kg/m3. The results of physical (permeability, thermal conductivity, thermal diffusivity, and thermal expansion coefficient) and mechanical (compression, direct tension, direct shear, modulus of elasticity, bond strength, fracture energy, and compression softening behavior) tests, carried out on specimens cured for different ages at two curing conditions (20 C and 95 and 50 percent relative humidity, respectively), are reported and discussed.

Two bridges, the Joigny and Pertuiset, have recently been built in France using high-strength concrete. It was necessary to measure the shrinkage and creep deformation of the concretes for their design. Two series of samples were taken, corresponding to the two kinds of concretes (one with and one without silica fume). The specimens were loaded at different levels and ages (including early ages). Some cylinders were carefully sealed to avoid any drying. Besides the mathematical equations deduced from these trials and detailed in the paper, the following results were discovered: the nonsilica fume high-strength concrete (HSC) is quite comparable to the normal strength concrete (NSC); during the setting, the silica fume HSC exhibits a certain autogenous shrinkage which is higher than that of the NSC concrete; for the silica fume HSC, the magnitude of the creep deformation is highly dependent on the age of concrete at loading, compared with elastic strains, so that the creep is much lower than for NSC (except when loading occurs at a very early age); regarding NSC, the theory of superposition applies fairly to the creep of high-strength concrete for nondecreasing loadings; and, finally, the desiccation creep is reduced for nonsilica fume HSC and entirely cancelled for silica fume HSC, meaning that creep does not depend on size for these materials. Some physical models are proposed at the paper's conclusion to explain these phenomena.

Presents a summary of the results from a systematic in situ testing program on the concrete compressive strength in three Norwegian offshore platforms representing 460,000 m3 of high-strength concrete. The goal of the testing program was to document that the in-situ strength in these platforms is higher than assumed in relevant design codes and thus substantiates a higher utilization of the compressive design strength. The specified concrete quality for these projects has been in the range of C55 to C70. In a systematic manner, approximately one thousand 75 mm concrete cores have been tested and evaluated. Comparison has been made to the results of 100 mm cube specimens as reference. The main factor influencing the in situ strength proved to be the effective compaction applied to the fresh concrete. Thus, slipformed concrete shows systematically higher strength than conventionally placed concrete in stationary formwork. The in situ strength was significantly higher than presumed in relevant design codes. The results further indicate that the increase with time of the in situ strength was slightly higher than for the laboratory-cured reference specimens. For concrete platforms that are subjected to rigorous quality control programs and stringent working procedures, like the Condeep platforms, it is suggested that an increase in the compressive design strength should be allowed with 5 to 10 percent for slipformed concrete compared to the actual values given in the recently revised Norwegian design code.

Fatigue properties of high-strength concrete in compression were studied. Two types of normal-density concrete and one type of lightweight aggregate concrete have been tested. The numbers indicate the planned mean strength in MPa of 100 x 100 x 100 mm cubes. The influence of different moisture conditions was studied in an introductory investigation. Three different sizes of cylinder were tested for each of the three curing and testing conditions: in air, sealed, and in water. The tests showed that the fatigue properties of both the air and water conditions were scale-dependent, while the sealed condition was hardly influenced by the sizes of the specimens. The main investigation dealt with the influence of the variation in stress levels on the fatigue life. Test conditions with constant maximum stress levels showed significantly longer lives when the stress range was reduced. If the load levels were defined relative to the static strength, there was no obvious difference between the fatigue properties of the concrete qualities included in these tests. An additional investigation was performed on ND95 cylinders exposed to different combinations of cyclic load levels. It was found that initial cycling at lower load levels was beneficial for the fatigue life at the higher load levels. Based on the results of the experimental work, a design proposal for fatigue of concrete in compression was established.

Three earthquake-type loading tests of reinforced concrete (RC) columns, short beams, and beam-column joints using high-strength concrete were carried out. The main objectives of this program were to investigate the seismic behavior of RC members using high-strength concrete, and to obtain guidelines for their design in high-rise buildings. Concretes having three levels of compressive strength, 400, 600, and 800 kg/cmý (39, 59, and 78 MPa), were used. High-strength reinforcing bars with nominal yield strengths of 8500 and 14,000 kg/cmý (834 and 1370 MPa) were provided for lateral reinforcement. Longitudinal reinforcement with a yield strength of 6000 kg/cmý (588 MPa) was also used for beam-column joint test. Emphasis was put on the combination of high-strength concrete and high-strength reinforcing bars. The seismic behavior of columns, short beams, and beam-column joints under high axial load, high beam shear, and high joint shear, respectively, were observed. The relationship between ductility and amount of lateral reinforcement were particularly discussed in the column and short beam tests. In the beam-column joint test, several joint details were considered, and their behavior was investigated. The design guidelines for these high-strength concrete members were also presented in this paper. The results of this experimental program show that the combination of high-strength concrete and high-strength steel bars can be quite effective in improving strength and ductility of RC members of high-rise buildings.