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 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.

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.