International Concrete Abstracts Portal

The Hibernia offshore concrete platform is being constructed in Newfoundland, Canada, and will be used in hydrocarbon production on the Grand Banks off the east coast of Canada. The 111-m tall concrete structure will contain approximately 165,000 m 3 of high-strength concrete. Construction of the concrete platform through 1993 consisted of a 108-m-diameter base slab that rested on a series of precast and cast-in-place concrete skirts. Specified 28-day compressive strengths (cylinder) for the skirts and base slab were 49 and 69 MPa, respectively. Actual average compressive strengths achieved were73.8 and 81.7 MPa, respectively. The remaining construction will be completed by 1996. The use of two different concrete production systems and their results are described.

When a damaged concrete slab is repaired, new concrete will generally be placed in a downward direction. Form panels must be set up first under the damaged concrete slab, and then concrete must be placed between the form panels and the damaged slab. However, compaction by vibrator is needed in most concrete (slump: 8 to 21 cm), and therefore concrete placement under a damaged slab that needs repair is impossible realistically. A repair method using high-performance concrete without vibration or compaction was developed. The method was applied to the repair of concrete slabs that had been damaged by heat. It was confirmed that this repair method was easier and that repair was possible while the slab was in use. In addition, the costs and construction period were reduced greatly by this repair method.

The twin 450-m Petronas Towers under construction in Kuala Lumpur City Centre, Malaysia, are discussed. These world's tallest buildings use concrete columns, ring beams and a core of 40- to 80-MPa cube strength concrete, and steel long-span floor beams. Benefits of high-strength concrete are discussed, including occupant comfort achieved using mass-to-length building period and high inherent damping to reduce building response, high lateral stiffness, simple monolithic cast in situ connections, reasonable member sizes, local labor use, and light erection equipment. Special design features include deep barrette foundations acting in friction, temperature control measures for a massive mat pour, treatments at stepped and sloping columns, and use of haunched beams to accommodate mechanical ducts. The construction approach to creep and shrinkage is also discussed.

Mixing torque is highly related to the consistency of concrete. A high-performance concrete with a unit amount of water as low as 165 kg/m 3 is viscous and exhibits higher torque at mixing, and the decrease in torque with the mixing time is not so great. Flowing concrete, a high-performance concrete with high flowa bility, with a unit amount of water of 180 kg/m 3 shows characteristic low viscosity on the contrary, which may require more practical consistency control. Paper proposes a new method of controlling the consistency of high-performance concrete by means of load current at the ready-mixed concrete plant.

Recently, there has been a great demand for high-quality concrete and concrete structures with high performance. In this context, silica fume is one of the most remarkable mineral admixtures that can give concrete high performance, such as high workability, strength, and durability. However, it is unclear as to the types of form silica fume takes in concrete, mortar, and cement paste. Some researchers point out that silica fume may be in high agglomeration. Therefore, it is very important to disperse silica fume in concrete effectively to get high-performance concrete. Consequently, this paper deals with the effect of physical treatment (ultrasonic homogenizer) and chemical treatment (superplasticizer) of silica fume on the properties of mortar. In this study, different silica fumes were used, one Japanese and five imported. The investigated properties of mortar were workability (flow values), compressive strength, and total pore volume. The study resulted in the following conclusions: 1) Silica fumes in the Japanese market were highly agglomerated in the natural state. This agglomeration of silica fume can be broken up by using some treatment methods, such as ultrasonic homogenizer and superplasticizer. 2) Physical treatment (ultrasonic homogenizer) before mixing mortar was useful to improve compressive strength and to decrease total pore volume of mortar containing silica fume. The use of superplasticizer could result in highly workable mortar. 3) The effectiveness of ultrasonic homogenizer treatment and that of superplasticizer treatment are different.