International Concrete Abstracts Portal

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

This paper presents results of an ongoing experimental program to study the effectiveness of macro synthetic fibers to control cracking in composite metal slabs. Both short- and long-term performance is being investigated in this experimental program. Two types of experiments for composite slabs on corrugated steel deck are conducted: restrained shrinkage tests and large-scale loaded composite continuous slabs. The restrained shrinkage test provides data on crack width caused by shrinkage, while the large- scale continuous slab was intended to monitor the crack width development across the middle support caused by the load, shrinkage and creep. The crack width measurements of both experiments indicate that the investigated fiber can provide comparable performance in terms of long-term crack control to conventional steel mesh reinforced concrete specified by the standards. Crack width measurements in the restrained shrinkage test over a period of 250 days of drying suggest that macro synthetic fibers at the minimum dosage specified by the ANSI/SDI can provide similar crack control as the minimum steel mesh. Long-term monitoring of load-induced cracking in the slab at the middle support over a period of up to 5 years indicate that the crack width for both reinforcing systems (fibers and steel mesh) increased asymptotically with loading time and stabilized thereafter. The results indicated that creep across the crack occurred for both reinforcing systems suggesting that the creep deformation across the crack is not only related to the type of reinforcing materials and the creep of the fiber/cement paste interface but also by creep of concrete section in compression.

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.

This paper analyzes the repeatability of autogenous and engineered self-healing in fiber reinforced concrete (FRC) with and without crystalline admixtures. To this purpose, the tensile behavior of two different mixes, differing by pindirect testing methodology has been employed to the aforementioned purpose, i.e. Double Edge Wedge Splitting (DEWS) test. Three different exposure conditions were considered: open air exposure, water immersion and wet/dry cycles. Specimens were pre-cracked up to a crack width of 0.25mm (0.01 in.) (precrack cycle). Then, specimens were healed for one month and tested again up to a crack width of 0.25mm (0.01 in.) (cycle after 1st healing). After that, specimens were healed for two months further (2nd healing) and finally, they were cracked once again up to 0.25mm (0.01 in.). The highest healing rate was reached for specimens immersed in water; moreover, as expectable, the larger the initial crack width, the lower is the percentage of crack closure. Regarding the repeatability, a general better trend was found for the mix with crystalline admixtures, in which, in addition, the maximum load regain was measured after the 2nd healing cycle rather than after the 1st healing Keywords:

SFRC (Steel Fibre Reinforced Concrete) is increasingly used for structural applications. Existing national and international recommendations are efficient for designing simple statically determinate structures (beams and slabs) loaded in bending. However, they do not possess a sufficient physical base to propose relevant solutions for more complex structures such as statically indeterminate structures. Moreover, the control of cracking in the serviceability limit state is one of the main interests of using SFRC (for durability aspects) compared with using traditional reinforcement bars. Nowadays, existing design recommendations are not able to provide sufficient relevant information regarding cracking in the serviceability limit state. In this way, the best approach for designing structures with respect to both safety and sustainable development is the use of finite element analysis. The present paper is devoted to a probabilistic explicit cracking model developed since 1985. It is used to analyze the cracking behaviour of different SFRC beams submitted to different loading conditions: bending, shear, statically indeterminate situation. It is demonstrated that this numerical model is fully capable to provide precise information about the cracking process related to this types of structural behaviour, especially concerning the cracks opening evolution.