Controlling and mitigating cracks in concrete is one of the most serious and inherent problems. In this research, improvement of crack resistance against thermal stress and shrinkage of the mass concrete at an early age were investigated using the hybrid fiber reinforced concrete. The fibers used were steel and polypropylene fibers with the lengths of 6,12, and 30mm. The physical properties as well as crack resistance capabilities of the hybrid fiber-reinforced concrete were evaluated. As for the evaluation of crack resistant property, strain energy release rate, calculated by the fracture mechanics, has been proposed as a result of this research.

This investigation was conducted to evaluate the effect of sulfate concentration and associated caution type on chloride-induced reinforcement corrosion. Reinforced concrete specimens were exposed to chloride-sulfate environments for a period of 600 days and reinforcement corrosion was evaluated by measuring corrosion potentials and corrosion current density. The corrosion current density increased with increasing sulfate concentration and the action type associated with the sulfate ions significantly influenced chloride-induced reinforcement corrosion. Reinforcement corrosion in the concrete specimens exposed to sodium chloride plus magnesium sulfate solution was more than that in the concrete specimens exposed to sodium chloride plus sodium sulfate solution.

This work estimated experimentally the critical amount of steel corrosion (Xcrit) needed for concrete cover cracking of a reinforced concrete element where only a fraction of the steel bar length is corroding. The amount of corrosion needed to crack the concrete cover (Xcrit) was ~49 um to ~137 um in specimens with localized corrosion, in comparison to ~15 um to 75 um for uniform corrosion reported for other investigations in comparable systems. An empirical equation is proposed for Xcrit as a function of specimen dimensions (concrete clear cover, C; rebar diameter, ; and anodic length, L). In this equation Xcrit is proportional to the first power of C/ and to the higher power of [C/L+1]. Quantitative determinations of the development and magnitude of stresses produced by corroding steel in concrete have been obtained. Estimated pressures at the steel/concrete interface for C/ > 3 reached values comparable to the concrete compressive strength. The potential use of a fracture-energy-based model to predict Xcrit was supported by indications of approximate agreement between estimates of the work of corrosion expansion and the energy required to crack the concrete.

The Faroe Bridges are two bridges connecting the Danish islands of Zealand and Falster crossing the island of Faroe. The bridges carry the southern motorway which connects Copenhagen with Germany and the rest of Europe. The total length of the bridges is 3.3 km. The bridges were constructed in the period from 1980 to 1997 several investigations were carried out on the columns. The objective was to evaluate the risk of initiation of reinforcement corrosion as a result of chloride penetration. The investigations included, inter alia, measurements of chloride content (in dust samples and on dust ground from drilled cores), measurements of reinforcement corrosion, concrete condition, etc. The future chloride penetration has been modeled using a probabilistic approach. It can be concluded that the decrease in chloride penetration ratio that might have taken place in the time span from 1988 to 1997 was insignificant in comparison with the random variation caused by the concrete characteristics. It has been calculated that corrosion initiates after 15-40 years in the tidal zone (level .5 m above water) and after 25-40 years in the splash zone (level 1.5m above water) given a critical chloride content of .5-.10% CI by mass of concrete and the specified cover of 50mm. As a pilot project cathodic protection was installed on one column using magnetite anodes in the sea. It was found that the conditions believed necessary to prevent corrosion were established below water level and in the tidal zone.

Hysteresis effects are very frequent in experimental studies of porous building material. In the case of frost deicing salt resistance, hysteresis effects between freezing and thawing were reported in calorimetric and expansion experiments. They often were explained by a difference in the active pore diameter. However, our calorimetric and ultrasonic pulse velocity measurement show much smaller hysteresis effects which support another explanation: supercooling. A model based on non-connected pore water which may supercooling. A model based on non-connected pore water which may supercool was developed to explain the experimental differences. This model allows a reinterpretation of experimental expansion data. The moment of damage formation in frost deicing salt resistance tests can be studied. The analysis of the causes of hysteresis effects therefore leads to improved models of frost deicing salt damage mechanisms.