Editors: Corina-Maria Aldea and Mahmut Ekenel

Fiber reinforcement is the most effective way of improving the resistance of concrete to cracking, but little is known of the extent of the reduction of crack width with fiber. The papers included in this special publication discuss the role of fiber reinforcement in reduction of crack width and lay the foundation for Life Cycle Engineering Analysis with fiber reinforced concrete.

Recognizing the reduction of crack width with fibers in cement-based materials, ACI Committee 544 Fiber Reinforced Concrete, together with 544F Fiber Reinforced Concrete Durability and Physical Properties sponsored two technical sessions entitled Reduction of crack width with fiber at the Fall 2016 ACI Convention in Philadelphia. Papers were presented by invited international experts from Belgium, France, Germany, Italy, Portugal, United Arab Emirates and the United States of America.

This Symposium Publication (SP) contains eleven papers which provide insight on the state of the art of the topic in the academia, in the industry and in real life applications. The topics of the papers cover the reduction of crack widths in steel reinforced concrete bridge decks with fiber, 15 years of applying SFRC for crack control in design from theory to practice, the effectiveness of macro synthetic fibers to control cracking in composite metal decks, conventional and unconventional approaches for the evaluation of crack width in fiber reinforced concrete (FRC) structures, reduction of water inflow by controlling cracks in tunnel linings using fiber reinforcement, a review of Engineering Cementitious Composites (ECC) for improved crack-width control of FRC beams, tailoring a new restrained shrinkage test for fiber reinforced concrete, a model to predict the crack width of FRC members reinforced with longitudinal bars, a probabilistic explicit cracking model for analyzing the cracking process of FRC structures, toughening of cement composites with wollastonite sub micro-fibers and self healing of FRC: a new value of “crack width” based design.

The papers included in this publication have been peer reviewed by international experts in the field according to the guidelines established by the American Concrete Institute.

Note: The individual papers are also available. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP-319

Bridge deck cracking is a common problem in the United States, and affects the durability and service life of reinforced concrete bridges. Physical inspections of three-span structural slab bridges in Ohio revealed cracks wider than ⅛ inch (3.2 mm). ACI 224R-01 recommends a maximum crack width of 0.007 inch (0.18 mm) for members exposed to de-icing chemicals. The primary objective of this study was to investigate the effects of fiber addition on crack resistance. In an attempt to minimize deck cracking, slab specimens with basalt MiniBar or polypropylene fiber were also investigated in the test program. Slab tests revealed that the specimens with longitudinal epoxy-coated bars developed first crack at smaller loads, exhibited wider cracks and a larger number of cracks, and failed at smaller ultimate loads compared to the corresponding test specimens with uncoated (black) bars. Test specimens with fiber exhibited higher cracking loads, smaller crack widths, smaller mid-span deflections and higher ultimate failure loads compared to identical specimens without fiber. Addition of fiber to concrete with no changes to internal steel reinforcement details is expected to reduce the severity and extent of cracking in reinforced concrete bridge decks demonstrating that fiber addition improves crack resistance of bridge decks.

The progress of concrete research during the last three decades has highlighted the possibility of enhancing the properties of cement-based materials, such as compressive strength or workability of the fresh mixes, as well as for other important properties like toughness, durability or volumetric stability. Among these, the resistance to shrinkage cracking is gaining an increasing attention, due to its strict relation to durability. In fact, shrinkage cracking occurs in all concrete structures when the free deformation of concrete is restrained. The higher the shrinkage deformation and the degree of restraint, the higher the risk of cracking, for the same concrete strength. Fiber Reinforced Concrete (FRC), now widely available into the market, allows for a better crack control due to the higher post-cracking strength; the latter is related to the links provided by fibers between the crack faces. However, shrinkage-cracking resistance should be determined with tailored methodologies measuring the crack development under restrained shrinkage conditions. The aim of this paper is a critical discussion on the current standard test procedures and, eventually, a proposal for a novel and enhanced testing set-up for measuring the shrinkage-cracking resistance of FRC. The effects of polymer fibers and Shrinkage Reducing Admixture (SRA) are discussed with reference to the time-to-cracking and the crack width development. Keywords:

A hybrid analytical/numerical approach for the evaluation of the moment-rotation behavior of a cross section of fiber reinforced concrete (FRC) elements flexurally reinforced with longitudinal bars is briefly described. This model is applied to FRC elements failing in bending, and considers the constitutive laws of the constituent materials, where a special focus on the simulation of the post-cracking tensile behavior of FRC was given, as well as the bond behavior between flexural reinforcement and surrounding FRC. The predictive performance of the proposed model is assessed by simulating experimentally tested FRC beams of different geometry, fiber content, and longitudinal reinforcement ratio. Furthermore, the predictive performance of RILEM TC 162 TDF and fib Model Code 2010 design guidelines for the prediction of the crack width in FRC elements failing in bending is also discussed in the present work. The potentiality of the developed model is then explored for the assessment of the influence of toughness classes of FRC and the bond stiffness between flexural reinforcement and surrounding FRC on the moment-crack opening response of FRC flexural members.

Combined reinforcement, a combination of traditional reinforcement and steel fiber reinforcement, has become an established construction method for joint free industrial floors and heavy raft foundations. Besides the positive contribution to the flexural, the shear and punching capacity, combined reinforcement has a big impact on the limitation of crack widths. The post crack tensile strength of steel fiber reinforced concrete can be taken into account for serviceability as well as for ultimate limit state. Structures which were built with combined reinforcement can be found all over the world. Some of them will be presented in this paper, giving insight information why combined reinforcement was chosen.