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

Wollastonite, a calcium meta-silicate mineral with acicular microstructure can be used in cementbased materials for micro-reinforcing the brittle matrix. Contribution of wollastonite particles in toughening and crack mitigation of cement mortar systems in its early age and hardened state, were studied. Elaborate testing was conducted to quantify the ability of wollastonite to restrain early age plastic shrinkage cracking, and fracture toughness of hardened cement mortar materials. Microstructural investigations on these blended systems validated the contribution of these wollastonite particles in the enhancement of mechanical properties through classical toughening mechanisms such as crack bridging, fiber pullout and rupture. Keywords:

Although, concrete has proven its performance in resisting compressive loads as a construction material, its increased brittleness and tendency to crack under small tensile forces and the lack of ductility of un-reinforced concrete elements has led to the development of new cementitious materials that address these limitations. Even though the introduction of short fibers in concrete (leading to Fiber Reinforced Concrete, FRC) has somewhat addressed the performance deficiency of this material under tensile forces, the FRC material itself was shown to soften in tension, leading to the continuous opening of cracks once formed. In response, high performance fiber reinforced cementitious composites such as Engineered Cementitious Composites (ECCs) have been introduced in recent years as an alternative to ordinary concrete and FRC in applications requiring crack width control, high ductility, high energy absorption, and damage tolerance. The use of ECC (instead of FRC) in these applications leads to the development of cracks that tend to spread all over the loaded element due to its strain-hardening property under sustained tensile stresses, a feature that is seen mostly in ductile metals. This paper presents a review of the effectiveness of ECC in controlling the crack width and crack growth in various reinforced concrete elements.

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.

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.