The civil engineering community is acquainted with the fact that existing reinforced concrete structures require constant maintenance in order to increase their service life. Nevertheless, maintenance might be not sufficient when a change of use, which entails for an increase of the service loads, damage due to aggressive environment, or the need of withstanding natural and man-made hazards were not taken into account when the structure was designed. Fiber-reinforced composites are a suitable tool to strengthen and thus increase the capacity of the structural element without changing the original configuration and adding mass. Steel reinforced grout (SRG) is a relatively new tool in the realm of fiber-reinforced composites that consists of steel fibers embedded in a cementitious mortar. This paper presents a state-of-the art on SRG that includes a literature review and points out the effectiveness of SRG for flexural strengthening and confinement of concrete members. It also proposes a design approach to strengthen reinforced concrete beams based on the available data on flexural tests on beams, bond tests on SRG-concrete joints, and tensile tests on SRG coupons.

U.S. and Japan have had a history of collaboration to mitigate the effects of earthquakes. In 1977, a cooperative agreement set forward a plan to improve the safety of building structures. This plan led to collaborative research over the next several decades that included studies of reinforced concrete, masonry, steel, and precast structural systems. This paper summaries some of the research on structural subassemblages at the University of Minnesota that stemmed from that collaboration. The intent of this paper is to also recognize the contributions provided by Prof. James K. Wight who played a key role in the U.S. Japan collaboration and in the dissemination of the outcomes of research through his leadership at the American Concrete Institute (ACI) including his roles with technical committees including ACI Committees 318 – Structural Concrete Building Code and 352 – Joints and Connections in Monolithic Concrete Structures.

Most maintenance problems associated with industrial concrete floors result from the joints. This paper emphasizes a method to eliminate saw-cut joints in slabs-on-grade by the use of steel fiber reinforced concrete (SFRC) only. The performance of the composite material is directly linked with the choice of a specific concrete mix design and an improved technique to uniformly mix a high dosage of steel fibers. Tests and experience have shown that high level post-cracking ductility of the SFRC can control micro-cracking caused by flexural and shear stresses combined with restrained shrinkage. The proposed design approach, based on the yield-line theory, gives an objective view of the safety factor in relation to the ultimate state. Case studies demonstrate that typical areas of 25,000 ft² (2322 m²), without saw-cut joints, are regularly achieved by experienced contractors with relevant site quality control. Practical site aspects such as armored contraction joints, slab details, aspect ratio, installation techniques etc., are an integral part of the case study as well. The second part of this paper details the use of this technique for structural applications such as suspended slabs on piles and mat foundations. To demonstrate the structural capacity of concrete solely reinforced with a high dosage of steel fibers, real scale tests and practical case studies are presented.

The modeling and analysis of un-reinforced masonry walls strengthenedwith externally bonded unidirectional composite laminates and subjected to out-of-plane loading is investigated. The model is based on variational principles, staticequilibrium, and compatibility between the structural components, which include themasonry units (blocks), the mortar joints, the FRP strips, and the adhesive layers. Themodeling of the masonry block and the mortar joints follows the small displacementsand the Bernoulli-Euler beam theories. The strengthening FRP strips are modeledfollowing the lamination theory and the adhesive layers are modeled as twodimensional linear elastic continuum. The effects of cracking of the mortar joints andthe debonding of the composite laminates near the mortar joints are also considered. Anumerical example is presented. The numerical results quantitatively describe some ofthe phenomena that govern the behavior of the strengthened wall and may lead to itsfailure. A summary and conclusions close the paper.

The shrinkage of concrete originates stresses on restrained structural elements, which can cause cracks. In some cases, for instance to reduce the number of structural joints, it is important to decrease drying shrinkage by the use of a shrinkage reduction admixture (SRA). The effectiveness of a SRA depends on porosity and stiffness of concrete. In order to evaluate the performance of two SRA products, shrinkage tests have been done on concretes with and without SRA. Two different concrete mixtures were evaluated: a low strength concrete mixture (for housing purposes) and a medium strength concrete mixture (use in bridges). Results show the effectiveness of the SRA on the two reference concrete mixtures, with different W/C and different cement contents.