This paper reviews investigations into a novel composite of concrete and steel, particularly as relating to seismic resistant structures. The primary novelty is that all the steel reinforcement, whether required for tensile or shear resistance, is provided as sheet rather than bar. This sheet steel is fabricated into closed box sections insi de which the concrete is cast insitu and hence fully contained. The sheet is not profil ed or specially prepared. The composi material made in this manner has been termed 1s t e Externally Reinforced Concrete, and abbreviated to ERC. The material is very strong and ductile and offers scope for simplification and cost savings in construction.

Bamboo fiber-reinforced polymer-modified pastes using the bamboo fibers treated with humic acid solutions with different humic acid concentrations and a styrene-butadiene rubber latex are prepared with various fiber contents and polymer-cement ratios, and tested for flexural behavior and compressive strength. The flexural deformation, flexural strength, flexural toughness and compressive strength of the humic acid-treated bamboo fiber-reinforced polymer-modified pastes are discussed. The results show that the humic acid treatments of the bamboo fibers cause marked improvements in the flexur al behavior after a maximum load, flexural strength- and toughness of the bamboo fiber-reinforced polymer-modified pastes. Flexural

Severe deterioration caused by corroding reinforcing steel in concrete structures is a major concern in the maintenance of safe and reliable infrastructure. The corrosion behavior of steel fibers and steel bars under two different aggressive conditions of modified ferroxyl gel reagent and wet-dry salt spray are described. In general, the results in the aggressive gel environment indicate that when steel fibers and steel bars were contacting each other, the initiation of corrosion in the steel fibers became considerable. When the steel fibers were electrically connected to the steel bars, the steel fibers tend to become the anode while the steel bars tend to become the cathode. The corrosion initiation, its propagation and the growth of the corrosion zones occurred in the steel fibers. The steel bars, set in the cathode zone, were protected by the surrounding steel fibers which formed a corrosion protective shield. This galvanic protection behavior by steel fibers was clearly observed in ferroxyl transparent gel. To generalize the galvanic protection behavior of steel fibers in the gel environment, the behavior of reinforced concrete specimens under an accelerated aggressive environment with both a no-fiber and fibrous concrete matrix were investigated. For this purpose, galvanized steel fibers were used. Corrosion phenomenon in the galvanized steel fibers contacting steel bars showed a sacrificial role of fibers in protecting the steel bars. No corrosion of the embedded steel bars occurred in the steel fiber-reinforced concrete matrix, while corroded steel bars occurred in the no-fiber reinforced concrete beam, thus confirming the merit of galvanized steel fibrous matrix as a protection shield to inhibit corrosion of reinforced concrete members.

This paper describes the results of an ongoing test program to evaluate the performance of polymer-modified cement-based mortars for repairing surfaces up to a depth of 75 mm (3 inches) of concrete structures damaged due to exposure to cold climates. Twenty-five selected commercially available polymer-modified products, seven containing styrene butadiene rubber (SBR) and 18 containing acrylics were evaluated. They were compared with a pure cement-based mortar containing 8% silica fume with a water/(cement + silica fume) (W/C) ratio of 0.3 1. All of the mortars were subjected to physical and mechanical tests such as thermal compatibility with base concrete, drying shrinkage, permeability, abrasion-erosion resistance, bond strength, compresive strength and freezing and thawing. The thermal compatibility with the base concrete test at temperatures from -50°C to +5O°C was used as a preselection test. The test data indicated that the polymer-modified mortars, even from the same family, i.e. SBR or acrylics, showed mixed results, with their performance varying from one manufacturer’s product to another. This paper also presents the performance of the three best polymer-modified cement-based mortars (included in the 25 mortars), installed in 1992 on two spillways of a dam in a very severe environment. These mortars were exposed to the abrasive action of water-borne sediments as well as the stresses related to hydraulic pressure and rigorous freezing and thawing and drying/wetting cycles. The six inspections so far have found that these three products are still performing well after an exposure to very low temperatures for a period of four years.

The transition zone which is formed at the interface between cement paste and aggregate affects decisively the properties of hardened concrete. The transition zone in ordinary concrete consists mainly of a highly porous three dimensional network structure of calcium hydroxide crystals with pores from 50 nm to 2pm in diameter. Its thickness is usually 30 to 4Opm. The structure of the transition zone is closely related to the conditions of concrete manufacturing, including composition and structure of materials, proportions and curing conditions. The effects on concrete properties by the formation of the transition zone and the measure to reduce the formation of the transition zone, which causes the deterioration of concrete quality, are also described.