International Concrete Abstracts Portal

This ACI Special Publication (ACI SP-253) CD-ROM contains 25 papers from the Fifth ACI/CANMET/IBRACON International Conference on High-Performance Concrete Structures and Materials that was held in Manaus, Amazon State (AM), Brazil, June 18-20, 2008. Topics include Durability, Self-Compactability, Curing, Retarders, and Abrasion Resistance. The Fifth Conference is a result of the collaboration of ACI and CANMET along with Sao Paulo University, Federal University of Goias, Amazon State University, and Brazilian Concrete Institute (IBRACON).

During the last decade, the increase in knowledge about the potential of mixtures containing chemicals and mineral materials leads to the high-performance concretes, including high-strength concrete (HSC). When high strength, durability, and elevated service behavior are necessities high-strength concrete can be an economical solution. In general, it is known that increasing the compressive concrete strength leads to the deformability reduction resulting in a more brittle concrete. On the other hand, the low deformability of HSC doesn’t mean low deformability of the high-strength beams, because their behavior comes from a combined effect of concrete and reinforcement. One of the usual reinforcement elements is the stirrups (transversal reinforcement). By ensuring a suffi cient concrete confi nement in the compressive zone, and by its distribution along the beam length, this reinforcement can improve the plastic rotation capacity on the beam critical sections. This paper presents an experimental study about the infl uence of transversal reinforcement (stirrups) on the fl exure plastic rotation capacity of high-strength beams. Flexural tests on fi ve simply supported beams were carried out using a four-point bending load untill the failure load. The load position was favorable to create a central zone on the beam theoretically of pure fl exure behavior without shear stress influence. The beams failures were governed by the pure fl exure in the middle zone of the beams. In this study, only one solution of stirrups was used, corresponding to a transversal reinforcement ratio of 0.295%. The compressive concrete strength was between 75.0 and 90.6 MPa. The longitudinal reinforcement ratio was between 2.2 to 3.5%. The plastic rotation capacity in fl exure is characterized by the use and definition of a plastic trend parameter. From the results of this study, a well-known positive effect on plastic rotation capacity caused by confi nement with transversal reinforcement was shown. A bilinear law can induce the increment of plastic rotation capacity. This law states that the increment of plastic rotation capacity decreases in a large way as the longitudinal tensile reinforcement ratio increases, and becomes equal to zero from longitudinal reinforcement ratio 3.0 to 3.5%.

This paper reports an experimental study on the mortar phase for selfcompacting concrete. A series of mortars were produced with similar fl ow properties, measured by spread and v-funnel tests, adequate to produce self-compacting concrete. The water content and the modifi ed carboxylic superplasticizer dosage were determined experimentally for each mortar. Different percentages of cement replacement materials were used in binary blends, each one combining one of the two types of cement with one of the three mineral additions selected: limestone powder, granite fi ller, and fl y ash. Each of the binary blends of powders was combined in fi ve different proportions in volume with the fi ne aggregate (Vp/Vs). Mortars were tested for compressive strength at 28 days and this value was related to the water/cement ratio, the percentage of replacement materials, and Vp/Vs parameter. The analysis revealed the possibility of establishing adequate mortar parameters to obtain simultaneously the self-compactability and the required compressive strength of self-compacting concrete.

Static and fatigue fl exural tests were performed on transverse sections of a 33.6 m (110.2 ft) Ductal® ultra-high performance fi ber-reinforced concrete (UHPFRC) girder for a single-span, 53 m (173.9 ft) pedestrian overpass to be built in the City of Calgary, Canada. Load tests were performed on three 1 m long, full-width and full-depth slab sections. In the fi rst and second tests, the concrete was reinforced with, 13 mm (0.51 in.) long steel fi bres (2% by volume). The sections were also reinforced with GFRP bars and tested to failure under monotonic loading. The specimens cracked and failed at similar loads. The third specimen had no reinforcement other than the steel fi bers. Initially, the specimen was loaded until it cracked. Subsequently the specimen was subjected to 1 million cycles between 20 and 80% of the design service load, followed by a second million load cycles over a load range of 20 to 80% of the observed fi rst-crack load. As the specimen did not fail under this loading regimen, nor was there any observed degradation of stiffness, a third million load cycles were applied to 20 to 80% of the failure load of the sections with GFRP reinforcement. Static tests were performed to evaluate the specimen stiffness several times during the fatigue test. The service load range was not observed to cause damage to the specimen. Some stiffness degradation was noted during the beginning of the third million cycles of loading, but stabilized at about two thirds of the original stiffness. Subsequent to fatigue testing, the specimen was loaded to failure, with collapse occurring at a load higher than predicted. The compressive strength of the Ductal® concrete used in these tests was over 200 MPa (29,008 psi) and the tensile strength at fi rst crack was over 8 MPa (1,160 psi).

The weather of the Yucatan Peninsula is classifi ed as hot sub-humid, with minor differences of relative humidity and temperature during the year. Local builders, in their search for process optimization and cost reduction, usually do not cure concrete beyond wetting the concrete surface immediately after removing the formwork. Teaching of concrete technology has been based on classic reports, where it is affi rmed that the strength gain is enhanced when moist curing is applied. Preliminary studies in the Yucatan region have not shown that moist curing helped to improve strength gain. Based on the meteorological conditions of the Yucatan region, it is possible that natural curing occurred with no need for additional curing for most of the cases. The objective of this study was to obtain the strength-gain curves as a function of the moist curing time from 0 to 90 days. Preliminary results confirm the hypothesis about the suffi ciency of the natural curing under the weather conditions of the Yucatan region. The use of porous aggregate may have contributed to curing during storage in air.