International Concrete Abstracts Portal

During 1994, a new 50,000 m 2 warehouse and similar area of external pavement was constructed at Ingleburn near Sydney, Australia. The client required that the warehouse meet very onerous performance criteria that required the construction of a very flat, prestressed concrete floor that would be crack free, with excellent abrasion resistance, and having a minimal number of joints. The design required that the concrete base provide the wearing surface for the floor without application of a surface topping. A second industrial project which required the construction of high performance concrete floors is a new integrated printing facility for a major newspaper, commenced at Chullora near Sydney in late 1994. The plant is highly automated; sections of the floor are designed to be frequently loaded with turning transporters carrying full rolls of newsprint. Such floors require exceptional abrasion resistance. The designers decided to seek a level of abrasion resistance even higher than that provided at Ingleburn. To minimize joints and cracking, the concretes were designed to have 56- day drying shrinkage of less than 450 microstrain and to exhibit an abrasion resistance, when tested in situ using the Chaplin abrasion machine, of less than 0.10-mm depth of wear. This marks the first time such a direct measurement of abrasion resistance has been specified and assessed in Australia. Key elements of both projects were the high performance concrete floors, which were required to meet tolerances on surface flatness ¦ 2 mm on 3-m straight-edge and ¦ 4 mm overall. These and other strict performance criteria were met consistently during construction providing clients with world class low maintenance warehouses.

A superworkable concrete, which has excellent deformability and resistance to segregation and can be placed in heavily reinforced formwork without vibrators, was developed and employed in the construction of a 70-story building. The height of the building is 296 m, and the height of the superworkable concrete in the tubular columns is about 40 m. Some of the columns have two diaphragms with opening ratio of seven percent at each joint of column and beams. Before actual construction, the placing of the concrete into three model columns was conducted. From the tests, it was confirmed that the superworkable concrete had excellent filling ability and left no voids under the diaphragms. A 6-m high removable column was set on top of the 40-m high column of the building to check the quality of filled concrete. The superworkable concrete was placed successfully into 66 columns of the tallest building in Japan.

Presents an overview of the technical aspects of concrete for a major bridge project in Eastern Canada. The bridge is unique in that it is being designed, finances, and constructed by the private sector; it will also be subsequently operated by the private sector. Private sector partnering with government is a relatively new concept in Canada. This project is an example of the merits of such agreements. The design life of this structure being constructed in a marine environment is 100 years. The length of the bridge will be 12.9 km, constructed in upwards of 35 meters of water. Ice floes throughout the winter and early spring have a major influence on the design and resultant configuration of the structure. Durability of the concrete with respect to chloride ingress, sulfate attack, freezing and thawing, abrasion resistance, and alkali-aggregate reactivity are addressed in the proportioning of concrete mixtures and in the structural design. Extensive use is made of silica fume and fly ash as a measure to reduce chloride diffusivity and heat rise in the more massive sections.

The intrinsic nature of lightweight concrete is to produce a material which, in addition to having high strength, can also have high performance in severe service conditions. The reason for high performance is examined in light of physical, chemical, and mechanical properties of the vesicular aggregate used to produce lightweight concrete. The manufacturing process usually involves heating the aggregate to 1200 C which, in addition to rendering it more stable than conventional aggregates when concretes made from it are exposed to fire, also results in a less stiff aggregate inclusion that more closely matches the stiffness of the cement paste matrix. The use of less stiff aggregates results in a reduction in internal stress concentrations in the concrete which, in turn, leads to reduced microcracking. The role that this plays in enhancing the performance of this type of concrete is discussed in the paper. The special nature of lightweight concrete provides opportunities for design professionals. Recommendations on how best to achieve high performance concrete using lightweight aggregate are provided.

This paper covers analytical and experimental investigation of high- strength concrete beams reinforced with high-strength prestressed concrete prisms as main reinforcement. Fiber optics technology has been developed and used in this investigation to measure the flexural crack widths developed throughout the full loading history of the specimens. Thirteen beams, 8 in. x 12 in. (200 x 300 mm) is cross section and having a 9.0 ft (2.74 m) span were tested to failure. The embedded prestressed prisms had a length of 9 ft, 6 in. (2.90 m) and cross-sectional dimensions ranging between 1.5 in. x 3.0 in. (38 mm x 76 mm) and 4.5 in. x 3.0 in. (114 mm x 76 mm). The prisms were prestressed with 7-wire, 3/8 in. (10 mm) diameter, 270 ksi (1860 MPa) tendons. Concrete strength in both the prisms and the beams was in excess of 14,000 psi (100 MPa) using silica fume as a partial cementitious replacement, as well as a high-range water reducer (superplasticizer) to attain the desired workability and compressive strength. A study of the extensive data accumulated in this research program, supported by the National Science Foundation, resulted in expressions for the evaluation of flexural crack widths in ultra-high-strength concrete composite beams. Test results also showed that the embedded prisms delayed the development of cracks, while the additional use of non-prestressing steel significantly reduced the crack spacing in the beams and limited the crack width at the onset of prism cracking.