Self-compacting mortars and concretes for horizontal structures are cementitious mixtures that are both fluid and homogeneous, with the particularity of flowing under the effect of their own weight. Thanks to their homogeneous texture they offer the possibility of achieving good quality of finishing and many such advantages become the reason for their applications especially in slabs and floors. However, self-compacting mortars or concretes show considerable shrinkage and cracking problems when used in floors and slabs (Weiss et al., 1998). Because of their large moisture exchange surfaces, the floor screeds are subjected to significant drying effects and in particular plastic shrinkage. If the movements are restrained, the risk of cracking is high. In this respect the use of fibers is a good alternative to using reinforcement bars and welded wire mesh. Indeed on site a clear decrease in cracking caused mainly by the shrinkage can be observed as soon as the fibers are incorporated in the screed. This study is conducted to demonstrate the effectiveness and the effects of glass fibers on the control of cracking phenomena due to shrinkage by determining their mechanisms of action at young age. The study is carried out in two parts: Firstly, free shrinkage behavior is analyzed in the fiber reinforced floor screed. Secondly, the restrained behavior at young ages using recently developed uni-axial tensile testing machine is investigated.

A new partially prefabricated elevated slab has been recently introduced in two different industrial buildings, to propose a viable alternative to the classical double tee deck with the addition of an in-situ RC topping. The solution is characterized by an adjustable spacing in the orthogonal direction, 40 mm thick FRC plates used as predalles and a cast-in-place FRC finishing, designed according to a continuous slab resting on the simply-supported beams. The proposed deck is a structural solution that tries to fit different issues like construction speed, transport and cost reduction, structural optimization, high fire resistance (R120) and quality performance. All elements are made of SFRC, characterized by different mix designs. This paper presents a design investigation on this kind of floor element, aimed at optimizing the global structural solution by minimizing the whole floor weight. Longitudinal and transverse bending, as well as vibration limit state, were considered in the design. The optimization strategy will be here presented, through the discussion of the parameters considered in the design, the variables taken into account and the constraints adopted within the procedure. A Model Code 2010 design approach was followed.

During bridge construction, the concrete finishing machine weight, along with other dead and live loads, affects the stability of the structure during construction and the service life of the bridge. These eccentric unbalanced loads lead to torsional moments in the exterior girders of the bridge, deflection of the overhang, and excessive rotations in the exterior girders. In skewed bridges, the finishing (screed) machine can be oriented parallel to the skew or perpendicular to the girders during construction. This study focused on evaluating different orientations of the machine along the span of skewed bridges. Finite element models of bridges with different skew angles were developed using SAP2000 to simulate construction conditions. These bridge models were then subjected to different machine orientations to form a better understanding of this phenomenon and to find the most effective method to operate the concrete finishing machines. The results showed that moving the screed machine parallel to the skew angle led to rotations that were more balanced between the exterior girders compared to moving it perpendicular to the girders. Therefore, a more leveled concrete surface can be obtained when running the machine parallel to the skew.

During hot weather concreting, contractors have several options for dealing with slump loss and rapid drying of concrete surfaces. Limiting slump loss requires cooperation between the concrete producer and contractor, especially with respect to reducing truck waiting time. Several options for minimizing surface drying are compared, based on effectiveness and cost. Finally, providing for adequate initial curing of concrete test cylinders can reduce the possibility of schedule delays and increased costs related to low strength-test results.

PCA researchers interested in the problem of evaporation of bleed water from concrete surfaces borrowed an equation developed by hydrologists to predict evaporation from Lake Hefner in Oklahoma. PCA’s graphical representation of that equation, subsequently modified to its present form by NRMCA, was later incorporated into multiple ACI documents, and is known by concrete technologists world-wide as the “Evaporation Rate Nomograph.” The most appropriate use of this formulation in concrete construction is to estimate the evaporative potential of atmospheric conditions (known as “evaporativity”). Since the difference between actual and estimated evaporation rate can be in the range of ± 40% of the estimate, best use of the equation as routinely applied is as a semi-quantitative guide to estimate risk of early drying and inform decisions about timing and conduct of concrete placing and finishing operations. Use of the “Nomograph” and related “Apps” in specifications is more problematic, however, given: 1.) the inherent uncertainty in its underlying equation, 2.) the difficulty in obtaining input data that appropriately characterize jobsite microclimate, and 3.) establishing a mixture-specific criterion for tolerable evaporation rate.