International Concrete Abstracts Portal

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.

Rheology has the purpose to study the flux and deformation of materials when submitted to some tension or outer mechanical solicitation. In practice, the effective scientifi c fi eld broached by rheology is restricted only to the study of homogeneous fluids behavior, in which are included eminent liquids, particles suspensions, and emulsions. The viscosity (?) and the yield stress (t0) are the two basic values that defi ne the fl uids’ behavior. The fi rst one is the proportionality constant that relates the shear rate (?) with the shear stress (t) applied, while the second indicates the minimal tension for the fl owage beginning. The fluids that obey the Newton’s relation - Newtonians fluids - display the constant viscosity and the null yield stress. It’s the case of diluted suspensions and grate amount of the pure liquids (water, acetone, alcohol, etc.) in which the viscosity is an intrinsic characteristic that depends on temperature and, in a less signifi cant way, pressure. The suspension, titled "Cement Paste," is defined as being a mixture of water and cement with, or without, a superplasticizer additive. The cement paste has a non-Newtonian fl uid behavior (pseudoplastic), showing a viscosity that varies in accord to the applied shear stress and signifi cant deformations are obtained from a delimited yield stress. In some cases, systems can also manifest the infl uence of chemical additives used to modify the interactions fluid/particles, besides the introduced modifi cations by the presence of incorporated air. To the cement paste the rheometric rehearsals were made using the rheometer R/S Brookfi eld that controls shear stress and shear rate in accord to the rheological model of Herschel-Bulkley that seems to better adapt to this kind of suspension’s behavior. This paper shows the results of rheometrical rehearsals on the cement paste that were produced with cements HOLCIM MC-20 RS and CPV- ARI RS with the addition of superplasticizer additives based of napthaline and polycarboxilate, with and without a constant agitation of the mixture. The obtainment of dosages of superplasticizer additives, as well as the water/cement ratio, at the cement at the fl uidity rate determination, was done in a total of 12 different mixtures. It’s observed that the rheological parameters seem to vary according to the cement type, the superplasticizer type, and the methodology applied at the fl uidity rate determination.

The flexural behavior of precast concrete beams is strongly infl uenced by their end connections. Connections can be considered as zones of discontinuity within the precast structure, wherein stress concentrations occur. Depending on the connection effi ciency in terms of mobilizing displacements and transferring forces, there will be a correlative redistribution of the internal forces throughout the precast structure. This paper deals with the study of the behavior of precast prestressed beams with semi-rigid connections, wherein analytical procedures considering the interaction between moment-curvature relation of the precast beam and the moment-rotation relation of its beam-column connections have been proposed and experimentally validated. By using these procedures, equations based on the fixity factor of the connections were combined with experimental results, allowing the integration between the stiffness of the beam and the rotational stiffness of the beam-column connections. Within the experimental methodology, fl exural tests of prestressed beams were conducted, considering both pinned and semi-rigid connections. Therefore, it has been possible to evaluate the effect of semi-rigid connections on the fl exural behavior of the precast beam, in which defl ections, rotations, and curvature of the semi-rigidly connected beam were compared with equivalent parameters from the fl exural test of the simply supported beam, in order to estimate the partially restrained moment at the beam ends. This approach provided accurate results for the partially restrained moments at the beam ends, indicating that the beam supports were semi-rigid. Based in the experimental results of the studied model, the effective partially restrained end moment considering ULS has been estimated between 60% and 70% of the full restrained moment.

In 1988, self-compacting concrete (SCC) - a high-fl uidity concrete that maintains its stability - was developed in Japan. However, even nowadays, there is still a lack of knowledge about SCC, especially regarding the few practical mix design methods available. Without a standardized mixture proportioning method, researchers have to use the trial-and-error method, spending time and resources without being certain about the concrete quality. In this paper, a new mix design method for SCC is introduced that allows the production of concrete from local materials, in an attempt to reach the desired mechanical and durability properties at the lowest cost. This method is explained in detail elsewhere. To explain how to use such a method, a family of SCC was carried out, presented at the end of the paper. Moreover, this methodology has been applied successfully in Brazil, obtaining SCC with costs very close to those of normal vibrated concrete (NVC) for the same strengths or durability measures.