Self-Consolidating Concrete (SCC) is recognized by those in the industry as a mixture that can flow into place and completely fill formwork with little or no vibration. This concept immediately brings to mind an image of a highly fluid concrete mixture that flows like water. It is the level of fluidity that provides the self-consolidation and ease of placement characteristics that both precast concrete producers and concrete con-tractors are anticipating when they use SCC. The characteristic of fresh concrete stability, however, is also important although it may sometimes be overlooked. Stability is critical both during the placement operations (dynamic stability) as well as once placement is complete (static stability). Because the stability of the SCC mixture has significant impact on the final hardened properties of the concrete, it should be considered during the mixture development and quality control process. This paper outlines some of the variables that influence SCC static stability and provides insight on how to control them.

A comprehensive research program was undertaken to determine the influence of coarse aggregate concentration, binder type and content, and the use of set-modifying admixtures on lateral pressure exerted by self-consolidating concrete (SCC). Experimental columns measuring 200 mm in diameter and either 2100 or 2800 mm in height were used to determine the distribution of lateral pressure during the plastic stage of cement hydration. The effect of thixotropy of the concrete on pressure variations was investigated. Test results show that lateral pressure exerted by SCC is significantly affected by the development of shear strength properties of the plastic concrete, namely internal friction and cohesion. Mixtures incorporating greater coarse aggregate volumes and/or lower binder contents were found to exhibit higher degree of internal friction. This can reduce the mobility of the concrete and result in lower initial pressure. However, given that internal friction is an inherent property of the material which remains constant with time, the rate of drop in pressure was shown to depend mainly on the increase in cohesion. Therefore, mixtures containing higher binder contents and/or a set-accelerating admixture can exhibit sharper rate of pressure drop with time. Concrete with higher degree of thixotropy was found to develop lower initial lateral pressure and higher rate of pressure drop with time. This is attributed to the stiffening effect which enables the material to re-gain its shear strength when left at rest with-out any shearing action.

The Citadel in Charleston, South Carolina is steeped in tradition down to the buildings at the campus. Currently under construction is a replacement for the Padgett-Thomas Barracks, which was demolished in 2001. The new structure will be identical to the original barracks. It will showcase a classic fortress design that requires intricate forming and careful planning in the proportioning and placement of the concrete mixtures, in order to minimize/eliminate cost over-runs that have been experienced in previous construction projects at the campus. Through a cooperative effort involving all parties in the construction of the new barracks, self-consolidating concrete (SCC) is now being used in lieu of the originally specified regular slump concrete. The use of SCC in the construction of the narrow 150mm (6 in.) thick walls have significantly increased placement/construction efficiency. It has also resulted in a greatly enhanced surface finish and sharper edges. This paper chronicles the project from the pre-construction meetings and trial placements to the placement efficiencies that have been realized due to the use of SCC. About 7646 cubic meters (10,000 cubic yards) of SCC are going to be used for this project, which is scheduled for completion in 2004. Data on the properties of the SCC mixture from the field and companion laboratory studies are presented and discussed.

Autogenous healing of cracks; and ingress of chloride and sulfate through the cracks in concrete were investigated utilizing 15 years old precracked prism specimens. The size of the specimens was100x 100x600 mm. The specimens were made with ordinary portland, slag (Types A, B and C), and fly ash (Type B) cements. A round steel bar of diameter 9 mm was embedded in each specimen. W/C were 0.45 and 0.55. Crack widths were varied from 0.1 to 5 mm. The specimens were exposed to the tidal and sub-merged zones. Deposits along the path of the healed cracks as well. as the de-bonded areas over the steel bars located at the root of the crack were investigated by scanning electron microscope (SEM) and X-ray diffraction (XRD). Mappings for chloride, sulfate, and magnesium oxide through the cracks in concrete were carried out by electron probe micro analyzer (EPMA). Autogenous healing is observed for narrower cracks (5 0.5 mm) irrespective of the cement types and exposure zones. Healing continues along the crack path. It extends to the debonded area over the steel bars at the cracked region. The deposits are con-firmed as calcium carbonate, ettringite, magnesium hydroxide, and rust. Accumulation of more chloride is found in the vicinity of the unhealed wider cracks (> 0.5 mm), especially for slag cements with a high amount of slag content. Sulfate ingress was limited over a very thin region from the crack plane. Interestingly, chloride concentration at the sulfate rich region is remarkably low. It indicates dissolution of chemically ad-sorbed chloride as well as the loss of ability of adsorption of chloride in the pore structures with the presence of sulfate.

During the last decades new cementitious materials were available. These represent a technical revolution with respect to the traditional concretes. The most important innovative "High Tech" materials are Self-Compacting Concretes (SCCs). In the present paper the compositions, the performances and some practical applications of high-performance SCCs are shown. In particular, some performance improvements carried out in our laboratories are shown for these specific uses: a) SCC for a Building Engineering application (S. Peter Apostle Church in Pescara, Italy) with white concrete characterized by a marble-like skin; b) SCC in the form of high-strength concrete with compressive strength over 90 MPa devoted to a work in the field of Civil Engineering (World Trade Cen ter in San Marino); c) SCC in the form of mass concrete structure with a reduced risk of cracking in duced by thermal difference between the nucleus and the skin of the elements; d) SCC in the form of lightweight precast concrete with a density of 1750 kg/m3, 28-day compressive strength of 35 MPa, and 28-day flexural strength of 5 MPa; e) SCC in the form of a shrinkage-compensating concrete for reinforced concrete walls 8 m high and 55 m long.