International Concrete Abstracts Portal

A National Project lasting five years has been promoted by the Ministry of Construction of Japan since 1988 to develop super high-rise reinforced concrete buildings in seismic zones. The strength of concrete and reinforcing steel bars ranges from 30 to 120 MPa (4.3 to 17.4 ksi) and from 400 to 1200 MPa (58 to 174 ksi), respectively. The following is investigated in the Project: 1) production, quality control, and placement of high-strength concrete; 2) production of high-strength steel bars; 3) mechanical properties of high-strength concrete and steel bars; 4) behavior of members and subassemblages; and 5) structural design methodology.

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.

Two test methods were used to investigate the frost resistance of high-strength concrete with and without air-entraining agents: a volume deterioration method (ASTM C 666) and a salt-scaling method (SwedishStandard SS137244) similar to ASTM C 672. In addition, low-temperature calorimetry was used to measure ice formation in concretes after a drying/resaturation treatment. For concretes with 0 and 10 percent silica fume contents and water-binder ratios from 0.40 to 0.25, the calorimetry results showed only very minor ice formation down to 20 C. The cement used was a high-strength type (Norwegian P30 4A). This result contrasts an earlier calorimeter result with ordinary portland cement, and indicates that the P30 4A cement produces a more finely divided capillary pore structure. The salt-scaling tests showed that the high-strength concrete with water-to-binder ratios less than about 0.37 exhibits acceptable resistance to salt-scaling, even without air entrainment. The ASTM C 666 test results showed relatively severe damage to concretes with water-to-binder ratios down to 0.28. No air-entrained concrete was tested with ASTM C 666. This result is in apparent conflict with the calorimetry results and suggests that the damage may be related not to ice formation but to thermal fatigue effects caused by differences that are too large between the thermal expansion coefficients of aggregates and binders.

Presents data at ages up to 1 year on the strength development characteristics of high-strength concrete ( > 80 MPa) incorporating blast furnace slag and/or silica fume or high volumes of ASTM Class F fly ash. Six concrete mixtures of various compositions were investigated in this study. Five of these mixtures had the same cementitious materials content of 485 kg/m3 of concrete, and the sixth mixture was typical of high-volume fly ash concrete incorporating a cement content of 150 kg/m3 of concrete and large volumes of fly ash. The concrete was obtained from a commercial ready-mixed concrete plant. For each mixture, three types of structural elements simulating a thick wall, a thin wall, and a thick column were fabricated for testing under field curing conditions. Cores, 100 x 200 mm in size, were drilled at ages up to 1 year for determining the in situ compressive strength of the various concrete elements. In addition, a number of 150 x 300 mm cylinders were cast from each mixture for long-term strength testing. The test results indicate that compressive strengths approaching 100 Mpa at 1 year can be achieved using a superplasticizer, with or without the use of supplementary cementing materials. The moist-cured test cylinders and the drilled cores from the various concrete elements indicate continued gain in strength of concrete at ages at least up to 365 days. The use of silica fume is generally required if high early-age strengths are to be achieved in structural elements. However, if high early-age strength is not a critical factor, then the high-volume fly ash concrete seems to be the most promising system.

Reports results of a study undertaken to develop high-strength lightweight concrete having compressive strength of about 700 MPa and a density of less than 2000 kg/m3. The materials used consisted of an expanded shale lightweight aggregate of Canadian origin, ASTM Type III cement, low-calcium fly ash, and condensed silica fume. A series of 7 concrete mixtures involving 14 concrete batches were made. The cement or cementitious material content of the mixtures ranged from 300 to 600 kg/m3. All mixtures were air entrained and superplasticized. A large number of test cylinders and prisms were cast for the determination of mechanical properties and drying shrinkage of concrete. From the results of this investigation, it is concluded that concrete with a compressive strength of about 70 MPa at 365 days and density of less than 2000 kg/m3 can be made incorporating supplementary cementing materials. The highest compressive strength achieved was 69.3 MPa at 365 days for a mixture with a cementitious material content of 600 kg/m3 of concrete; the highest flexural strength obtained was 8.7 MPa at 28 days.