The paper investigates the shear strength and the failure modes of high strength concrete beams with and without steel fibers ( fC = 110 MPa). Sixteen reinforced high strength concrete beams (3600x350~200 mm) were tested under different combinations of shear force and bending moment. The beams were singly reinforced and without shear (web) reinforcement. The test results indicated that the addition of steel fibers to high strength concrete increases the ultimate shear strength, improves the brittle characteristic and transforms the failure mode into a more ductile one. The average gain of the ultimate shear strength due to the addition of steel fibers varied from about 14% to 14 1% depending on the shear span to depth ratio and the longitudinal steel ratio. Four modes of failure of reinforced high strength concrete are clearly distinguished as; diagonal tension, shear compression, shear flexure, and flexural failure. In general, cracks in fiber reinforced concrete beams are closer, narrower, and more than those in beams without fibers. This reflects the effect of steel fibers in redistributing the stresses beyond cracking.

Durability limitations of steel reinforced concrete are well documented. Corrosive environments (e.g. the presence of chlorides), carbonation of concrete structures, poor workmanship and other factors can cause corrosion of the reinforcing steel. Normally, reinforcing steel embedded in concrete is protected because the concrete cover acts as a barrier and the high pH value of the pore fluid assures a passive state. Both the presence of chloride ions at concentrations above a given threshold level and carbonation can put reinforcing steel into an active state and result in corrosion rates that markedly decrease the expected service live of reinforced concrete structures. Aqueous surface-applied corrosion-inhibiting impregnations are featuring the ability to reduce the corrosion rate of corroded steel reinforcement embedded in hardened concrete due to their corrosion-inhibiting action and in the case of a carbonated concrete structures by realkalization. Additionally the corrosion rate is further reduced due to the water repellent action of organosilicone compounds. The careful selection of hydroxyalkylamino compounds as well as of inorganic-or organic acid compounds allows the formulation of corrosion-inhibiting impregnations with high buffer capacity. When applied on the surface of a concrete structure, said corrosion-inhibiting compositions are capable of penetrating into the concrete, and raising the pH value of the pore fluid in the vicinity of the reinforcing steel to a level, where the corrosion rate is markedly reduced. Laboratory tests and results from field applications are reported.

Inhomogeneous stress situations are prevailing in some engineering problems, such as around corroding steel bars or around aggregate particles expanding due to alkali-silica reaction. Micro-mechanics and macromechanics will significantly differ in those cases. The present article focuses on experiments simulating the effect of steel bar corrosion on four cementitious composites. For that purpose, prismatic specimens containing an excentrically located slightly tapered cylindrical hole, where subjected to controlled push-through of a metal cone of similar shape. Behaviour in the pre-peak range was reflected by strain gauges, and in the post-peak region by clip gauges. Simulateneously, acoustic emission measurements were performed. Various aspects of the tests have been highlighted before in publication to which is referred when relevant. This paper merely presents illustrative data, evidencing typical micro- and macro-mechanical processes taking place under the given conditions. Successively, on macro-level, the elastic range terminates at Discontinuity Point (DP), at ultimate (BOP) a stage of quasi-plastic yielding is obtained, and a mechanism is formed at Crack Opening Point (COP), after which energy due to bar expansion is stored in opening up of only the leading crack. On micro-level, dispersed crack initiation and coalescence in radial direction starts at the interface. this process gradually concentrates in one of the two ‘weakest’ sections of the covercrete. This process slows down, whereupon cracks are initiated at the exterior of the second weakest section. Here they propagate to coalesce with the interor microcracks to form the major crack.

A laboratory test and a case history of deteriorated reinforced concrete slab repair are presented. Since several structural problems have been reported for reinforced concrete slabs, it is necessary to establish repair techniques for such slabs. Many structural problems of reinforced concrete slabs derive from a decline in rigidity with age. Although several techniques have been developed, their effectiveness has not been ascertained, especially over the long term. A laboratory test was conducted to ascertain the effectiveness of repair techniques. Based on the test results, the overlay repair technique was applied to actual slabs. In the case history, short and long-term performances of the repaired slabs were measured for more than 2000 days. Changes in the rigidity and natural frequency of the slabs were examined. The material properties and adhesive strength of old and new concrete were also examined. Although the static and dynamic performances of the repaired slabs improved remarkably, their performances gradually decreased with age. It is important to allow a reasonable margin of error for repairing deteriorated slabs.

Expansion joints in bridge slabs are designed to absorb horizontal displacement due to the temperature fluctuation and moving vehicular load. The expansion joints, however, are very often damaged due to a repeated loading of the moving vehicles. The joints in the existing simple span structures can be eliminated by converting the structural types into continuous spans. When existing simple span bridges are converted into continuous spans, rigid (pin and roller) support conditions have to be changed to elastic supports in order to absorb and distribute the energy of horizontal motion due to an earthquake loading. However, development of additional reaction forces and stresses on the concrete slab due to the unequal displacement of the elastic supports have been overlooked. In this study, two-span continuous specimen, which is converted from two simple span structures is tested and analyzed to investigate the stress distributions of the concrete slab. Durability of the concrete slab under the service load is also discussed. The results of this study show that the change of strain in the longitudinal direction can be reduced by using the elastic supports and the vertical shear stress increases, directly affecting the fatigue life of the concrete slab.