International Concrete Abstracts Portal

The trend in offshore and marine concrete is to use higher strength concretes (HSC) than have been used in the past. These concretes provide both additional strength and improved durability due to their improved microstructure. This is achieved by using greater cement content, supplementary cementing materials, and a low water-cementitious material ratio. HSC is more brittle than normal strength concrete and requires additional confining reinforcement to insure ductile behavior of the structural members. Higher strength steels and special methods of confinement, such as the use of T-headed bars, can contribute to the ductility of the concrete. The use of HSC creates some constructability problems such as high concrete temperatures due to a large amount of cement present and significant thermal gradients. Reinforcing bar congestion in HSC requires concrete with smaller coarse aggregate sizes and very high slumps to satisfactorily place the concrete. Lap splicing in HSC can produce problems of concrete splitting unless the splices are properly confined. The use of mechanical couplers for splicing has some advantages in HSC. Proper curing with HSC is essential.

Roller compacted concrete (RCC) can possess hardened material properties similar to conventional concrete, but it can also have properties that are well beyond the range that would normally be attributed to conventionally placed concrete. For example, RCC has been used with a modulus of elasticity about 20 times less than normal. Creep rates can be considerably greater than normal. Compressive and tensile strengths can cover a broad range, starting essentially with zero strength and going to high strength levels. The properties that tend to cover a broad range are generally those that are essentially time-dependent. The ability of RCC to have this broad range of properties means that it can also have substantially different toughness and fracture behavior. Lower strength mixtures tend to be much more elastic and have substantial strain capacity after leaving the elastic range. High-strength RCC tends to behave more like conventional concrete with sudden and rapid failure after reaching its elastic limit. Understanding the potential material properties of RCC and utilizing appropriate values in design is crucial to achieving economical and efficient structures. Obtaining the best overall concrete mixture and structural design for applications ranging from dams on variable foundations to pavements is dependent on these properties.

The use of ultra-high-strength concrete for the construction of some types of structural members can be considered if nonbrittle behavior is achieved. Paper introduces reactive powder concretes (RPC) that exhibit ultra-high strength and high ductility at the same time. Compared to conventional concretes, the ductility estimated in terms of fracture energy is increased by one to two orders of magnitude, while the compressive strength values are in the range of 200 to 800 MPa..

To insure adequate durability and long-term performance of reinforced concrete structures exposed to aggressive environments, relevant quality parameters are needed that can provide a better basis for job specification and control of in situ quality. The

In current construction practice, discontinuous fibers are added to cementitious matrices at relatively low volume fractions (usually < 1 .O%), mostly in order to improve the toughness, or the post-cracking ductility, of the composite. At these addition rates, there is relatively little improvement in strength. Moreover, there are no generally accepted methods of characterizing the improvements in other mechanical properties which the fibers may impart to the concrete. As a result, the various national structural design codes do not recognize fiber reinforced concrete (FRC) as a distinct material, and this inhibits its use in structural applications. However, there is continued research on the use of fibers in conjunction with conventional continuous steel reinforcement to improve the structural behaviour of concrete. In addition, a new generation of micro-fibers is being developed, which can be used at higher addition rates to bring about major improvements in the mechanical properties of FRC. In this review, current FRC technology is described. Likely future developments of FRC are also considered, such as applications in the design of concrete structures subjected to dynamic (blast, impact or earthquake) loading. The next generation of FRC materials will have the capacity of being tailored for a wide range of specific applications, and should be able to compete with other structural materials in a variety of applications.