International Concrete Abstracts Portal

Editors: Corina-Maria Aldea and Mahmut Ekenel

This CD contains 8 papers from sessions sponsored by ACI technical committees 544, 549, and 130 at the Fall 2012 ACI Convention in Toronto and two technical sessions at the Fall 2013 ACI Convention in Phoenix. The topics of the papers cover sustainability aspects of using fiber reinforced concrete ranging from durability and interface mechanisms of natural fiber reinforced concrete (FRC), evaluation of eco-mechanical performance of FRC, reducing carbon dioxide emissions of concrete, as well as applications of fiber reinforcement for self-consolidating concrete, bridge link slabs, extruded prefabricated elements, slab systems and fabric-reinforced cementitious matrix systems for strengthening unreinforced masonry walls.

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-299

The durability performance and interface transition zone of natural fiber reinforced concrete has always been a major concern. Natural fibers due to its hydrophilic nature present a high volume variation which may cause degradation in the fiber-matrix interface. Furthermore, natural FRC may undergo an enhanced aging process, while submitted to a humid environment during which they may suffer a reduction in ultimate strength and toughness. This paper presents how the use of a matrix with low content of calcium hydroxide can mitigate the embrittlement process of natural fibers. The durability performance of the composite systems is examined and the mechanisms for the significant delay in the fiber degradation when the total amount of calcium hydroxide is reduced from the matrix discussed. Furthermore, it is shown how the repeated wetting and drying cycles affects the fiber-matrix interface. Pull-out tests were performed in sisal fiber cement composite systems to study the mechanisms that influence the fiber-matrix bond. The results showed that the use of a matrix with low amount of calcium hydroxide improved the composite durability and that the wetting and drying process reduced the water absorption capacity of the fiber and increased the fiber-matrix bond.

A major limitation of the durability of bridge decks is the area around an expansion joint which allows drainage of de-icing salts to the underlying substructure. Fiber-reinforced concrete link slabs are proposed as a more durable alternative to traditional expansion joints. This study was developed to evaluate the possibility of using more common fiber-reinforced concrete (FRC) mixtures rather than the highly designed ultra-high performance fiber-reinforced concrete (HPFRC) with fibers that has often been recommended for link slabs. In this study, the matrix proportioning and the type and volume of polymeric and steel fibers have been investigated to determine their effects on compressive, tensile and flexural strength, fracture behavior and residual strength. A standard mixture design was first optimized for workability with one steel fiber type and one polymeric fiber type. With the optimal mixture design, a selection of six fiber types were then tested for the selected mechanical properties. Although the FRCs tested did not reach the performance of the HPFRC, significant increases in performance were observed with the common fibers that could be useful in the design of a FRC link slab with the most promising results obtained with hooked-end steel macro-fibers.

A comparison among different structural concretes is herein performed in order to select, or tailor, new eco-friendly and high performance cement-based composites. The ecological impact and the mechanical behavior of reinforced concrete (RC) ties and beams are both assessed by of means the so-called eco-mechanical index (EMI). The crack width of RC structures, the embodied energy and the carbon dioxide released by the production of concretes, are the main parameters of EMI. As a result, the best eco-mechanical performances can be easily achieved by using a normal strength cementitiuos concrete having high fracture toughness (i.e., by adding steel fibers to normal strength concrete). Moreover, in an eco-mechanical analysis, the work of fracture, either in tension or in bending, is sufficient to define the mechanical performances and durability of normal and high-strength of RC structures, without measuring crack width.

Un-reinforced masonry (URM) walls have proven to have low shear strength to withstand in-plane loads caused by earthquakes. Retrofitting masonry walls with novel materials such as fiber-reinforced composites has shown to increase the in-plane shear capacity of the walls and minimize damage by enhancing pseudo-ductility. In this study, a new fabric-reinforced cementitious matrix (FRCM) composite system is applied to URM walls to determine its feasibility as an externally-bonded retrofitting technique. The experimental program consists of testing under diagonal compression a total of 18 wall specimens, made from clay bricks and concrete blocks with two FRCM strengthening reinforcement schemes (one and four plies fabric). The experimental results demonstrate the effectiveness of FRCM strengthening on improving the shear capacity of masonry walls. Experimental data from other research programs using fiber reinforced polymer (FRP) composites are presented to demonstrate that when the normalized shear capacity is related to a calibrated reinforcement ratio, the two technologies show similar enhancements.