International Concrete Abstracts Portal

The paper presents aspects of an investigation made upon the cracking states induced by early age restrained shrinkage of concrete, at the piers and abutments of the bridges from the new Transylvania Motorway, Romania. The National Building Research Institute [INCERC] Cluj-Napoca Branch and Technical University of Cluj-Napoca performed the investigation at the request of the general contractor Bechtel International Inc. Ltd. At approximately one month age of concrete, cracks width range between 0.05-0.5 mm (0.002-0.02 in) were observed. The paper emphasizes the analyses, interpretations and analytical predictions for the future progress of the cracking states, based on the data acquired from the technical documentation supplied by general contractor, and monitoring of the crack widths. The good match of theoretical results with the real registered data led to the conclusion that cracking states are caused mainly by restrained volume contraction within the first week. Thus, repair measures could be done in time and the normal progress of the works continued.

This paper shows the importance of autogenous shrinkage on serviceability performance of reinforced high-strength concrete (HSC) flexural beams, and also the effectiveness of low-shrinkage HSCs (LS-HSC) that is made by using an expansive additive and/or shrinkage-reducing chemical agent and/or Belite-rich low heat Portland cement with regards to the improvement of flexural serviceability performances of the beams. In addition, this paper, from a simple design equation point of view, proposes a new concept for evaluating flexural crack widths and deformation of RC beams, considering the early age deformation of concrete before loading. The experimental results show that autogenous shrinkage of HSC increase crack width and deformation of the RC beams significantly, while LS-HSCs markedly improve its serviceability performances. The present concept, taking into account strain change in tension reinforcement and curvature change at cracked section before and after loading, is effective in explaining the effects of shrinkage and expansion of concrete before loading on maximum crack width and flexural deformation. JSCE (Japan Society of Civil Engineers) code equations for predicting maximum crack width and flexural deformation into which the present concept is incorporated improve the prediction accuracy compared with conventional ones and show fairly good agreement with experimental results.

The effect of shrinkage on short-term and long-term flexural deformation and crack width of structural concrete members is investigated numerically and experimentally. The numerical analysis was performed by solving simultaneous differential equations relating to bond slip based on bond stress-slip relationship. The equations were formulated for an element between adjacent two cracks, taking shrinkage, creep, time dependent of bond and tension softening based on fictitious crack model into consideration. To verify the present method, load tests were carried out on structural concrete members with 200mm wide x 250mm high section made of conventional high shrinkage concrete and expansive high strength concrete, in which curvature and crack width were measured in a constant bending moment zone with 800mm length. In addition to this, creep and shrinkage tests were also performed. The following conclusions are drawn from the present study; (1) Tension in concrete at a cracked section contributes dominantly to decreasing the stress in a tension reinforcing bar resulting in enhancing the flexural stiffness and in decreasing the flexural crack width, when the stress in the tension reinforcing bar is below 150 N/mm2 and the tension reinforcing bar ratio is below 1.5%. (2) Flexural crack widths increase with time after the application of sustained loading mainly due to loss of tension stiffening at cracked section, which is caused by shrinkage. (3) The above conclusions are explained by the present method.

The Burj Dubai tower, which is currently under construction, will be the world’s tallest structure. This paper addresses the structural system utilized for the Burj Dubai tower and the structural design implications of creep and shrinkage of the high performance reinforced concrete vertical load carrying elements.

This paper describes laboratory tests on nine simply supported one-way reinforced concrete members subjected to immediate live load and sustained load. The specimens are 12 ft (3.66 m) long supported on an 11 ft. (3.35 m) span, 12 in. (304.8 mm) wide, and 5 in. (127 mm) deep with two #3 bars at an effective depth of 4 in. (101.6 mm) providing a reinforcement ratio of 0.0046. The specimens were moist cured for up to seven days. Three specimens each were removed from the forms and subjected to immediate live load at three days, seven days, and twenty eight days followed by sustained load due to self weight. Each specimen was subjected to immediate full live load again after six months. Applied load and mid-span deflections were recorded under immediate live load and sustained load. The test results demonstrate the effect of shrinkage restraint provided by embedded bars on the flexural cracking of the specimens under applied load, as well as effects of early age loading on time-dependent response. Calculated deflections based on effective moment of inertia for immediate deflection and long time multipliers for time-dependent deflection are compared with measured deflections.