International Concrete Abstracts Portal

Many recent innovations in advanced concrete materials technology have made it possible to produce concrete with exceptional performance characteristics. High Performance Concrete (HPC) is defined as concrete which meets special performance and uniformity requirements that cannot always be achieved by using only the conventional materials and normal mixing, placing and curing practices. The performance requirements may involve enhancements of: placement and compaction without segregation, long-term mechanical properties, early-age strength, toughness, volume stability, or service life in servere environments. International Workshop on High Performance Concrete addresses technical papers presented during the workshop. A total of 32 papers are included and cover subjects including: * Self-compactable high-performance concrete in Japan * Durability of DSP mortars exposed to conditions of wetting and drying * Ferrocement: Applications for urban environment * Studies of high-performance concrete structural members * High performance and durability through design * United States government's role in high-performance materials for infrastructure * Tensile properties of high-performance concrete * High-performance concretes for highway applications * Bending properties of high early strength fiber reinforced concrete * High-strength concrete research for buildings and bridges Note: The individual papers are also available as .pdf downloads.. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP159

This paper discusses recent research on high performance concrete with a focus on cemenentitious materials designed for durability. A major key to suchp erformance originates with the concrete microstructure. Recent advances in optimizing cement and concrete materials by using calculated packing diagrams offer the promise of superior products achieved by increased packing efficiency. A high packing density coupled with adequate processing and cement binder characteristics makes possible the formation of a fine microstructure. In turn, this fine microstructure results in a low permeability and therefore provides a resistance to aggressive forces from the environment, which together enhance its long term durability. The favorable interaction among physical and chemical phenomena gives rise to better long term performance, whether the application is structural, or chemical, such as in waste management.

Although the cement-paste matrix is intrinsically protective to steel, it also permits the ingress of deleterious agents that leads to its own progressive deterioration and consequent destabilisation of steel. Further, the development of a highly impermeable cement matrix, per se, may not ensure a high- performance concrete structure in practice, since the development of strength and pore structure are both time-dependent phenomena and aggressive elements somehow find a means of penetrating concrete and initiate a cumulative process of structural damage. This paper advocates an integrated design philosophy from concept to completion and during service life of a concrete structure. It is shown that by selecting concrete constituents that encourage synergic interactions, it is possible to develop a concrete matrix of high strength and excellent durability. However, concrete also needs to be protected from aggressive agents to enable it to attain its full potential and examples are given to show how such techniques can be adopted to ensure durable service life even in the most unfriendly environment. The application of this integrated design strategy is further illustrated with the design of columns exposed to alkali-silica reactivity and the production of cost-effective, fiber-reinforced thin sheets.

Properties of high strength concrete under uniaxial states of stress were studied. Main emphasis was given to tensile, compressive, and fracture properties of concrete with compressive strengths ranging from 6000 to 12000 PSI. Complete stress-deformation curves under uniaxial tension were obtained using a closed-loop servo-hydraulic testing system. Important mechanical and fracture properties such as moduli of elasticity, fracture energy, and the critical crack tip opening displacements, were evaluated from the experimental results. Fracture energies were evaluated from the descending branch of stress-crack separation curves using the direct tension test results. For the range of high-strength concretes studied, experimental results indicate that the relationship between tensile and compressive strengths are different from those of normal strength concretes. Comparison of stress-deformation curves in tension reveals a significant decrease in post peak compliance of the higher strength concretes.

This paper provides a summary of part of the results of SHRP project C-205 on the Fresh and Hardened Properties of High Early Strength Fiber Reinforced Concrete (HESFRC). HESFRC was defined as achieving a minimum target compressive strength of 5 ksi (35 MPa) in 24 hours. Fresh HESFRC properties included air content, inverted slump test, temperature, and plastic unit weight. Tests on the mechanical properties included compressive strength, elastic modulus, flexural strength, splitting tensile strength, and fatigue life. Seventeen different combinations of parameters were investigated for each type of test. The main parameters included: (1) three different matrix mixtures (one control, one with silica fume, and one with latex), (2) two different volume fractions of fibers (1 percent) and (2 percent), (3) two fiber materials (steel and polypropylene), (4) two steel fiber lengths corresponding to aspect ratios of 60 and 100 respectively, and (5) hybrid mixes containing either an equal amount of steel and polypropylene fibers, or an equal amount of steel fibers of different lengths. The compression and the bending tests also included a time variable; the compressive properties were measured at ages 1, 3, 7, and 28 days, and the bending properties at ages 1, 7, and 28 days respectively. Information from the compression tests comprised the compressive strength, the elastic modulus, and the strain capacity. Information from the bending tests included the modulus of rupture and the toughness indices as per ASTM standards. Optimum mixtures that satisfied the minimum compressive strength criterion, and showed excellent values of modulus of rupture, toughness indices in bending, and fatigue life in the cracked state are identified. Potential applications in repair, rehabilitation, or construction of transportation structures are suggested. In this paper a description is given of key results of the bending tests only.