International Concrete Abstracts Portal

For the calculation of civil engineering structures, designers employ the mechanical aspect underestimating the physicochemical phenomena in connection with the hydration of cement paste. Although the mechanical approach is widely sufficient for classical structures, this is not the case for large structures like dams, where thermophysical phenomena play a leading part. After a short analysis of the degradation observed on a roller compacted concrete dam, showing the importance of the control of hydration effects on mass concrete, the authors present a thermomechanical model able to describe the main evolutions of concrete properties with aging. Application to the Riou dam shows the ability of the approach to simulate temperature, strains, and stresses and, as a consequence, the risk of damage for the structure. Cracks in the middle of the dam are properly represented. This approach permits determination of the position and number of construction joints and setting the schedule of construction as thickness of concrete layers or maximum delay between two layers.

Reinforcement corrosion due to chloride ingress is the most common cause of concrete deterioration in Norway. A wharf with dimensions of 270 x 25 m was built in 1965 to 1966 and required partial repairs in 1980, 1986, and 1989 to 1990. The repair work included some research and development. The conclusion of the 1989 inspection was that no corrosion activity was evident in the earlier repaired areas. Repair mortar with silica fume had somewhat lower chloride ingress and significantly higher electrical resistivity than mortar without silica fume. Latex addition to the repair mortar showed the same effect, as well as a reduced water content. The main conclusion is that materials and working procedures used for the 1980 repair have resulted in a satisfactory service life of at least 10 years.

Under the Strategic Highway Research Program (SHRP), Contract C-206, "Optimization of Highway Concrete Technology," constructibility and performance of concrete for early opening of highway repairs were evaluated. A variety of concretes mixed using different types of rapid strength cements and admixtures were used for full-depth repair (slab replacement) of concrete pavements and for bridge deck overlays in the states of Ohio, Kentucky, and Georgia. For pavement applications, eight mixtures with different strength-gain capacities allowing for a variety of traffic opening times ranging from 2 to 24 hr were evaluated. Latex-modified concrete with Type III cement and silica fume mixes were used for bridge deck overlays. Durability evaluation of these mixtures included freeze-thaw resistance, characterization of the air-void system and deicer scaling tests, and measurement of chloride permeability. Specimens for these tests were prepared in the field and were subject to standard field curing. Tests were also conducted on cores taken from pavements and overlays at opening time. Freeze-thaw tests on beams were conducted following a modified procedure of ASTM Method C 666B, using specimens wrapped in towels during the air freeze to reduce drying from the surface during the freeze cycle. Follow-up surveys were conducted to examine the performance of these concretes under the effects of environmental exposure and traffic loading. Test results showed that overlay mixes have excellent freeze-thaw resistance. Latex-modified concrete mixes showed moderate scaling using the deicer scaling test. Chloride permeability of cores taken from silica fume overlays were lower than those of latex-modified concrete overlays. Poor freeze-thaw performance of many of the pavement repair mixes indicates that many questions still remain regarding durability of concretes designed for early opening applications. Proper air content and adequate air-void systems are necessary, but not sufficient, conditions for obtaining the desired freeze-thaw durability. Microcracking in the concretes may account for some of the poor performance in freeze-thaw testing. The use of calcium chloride should be avoided, as it contributes to reduced freeze-thaw resistance.

First results of the investigation of the corrosion behavior of steel in concrete after local repair measures are described. The examinations in this research project refer to construction practice where local damage due to reinforcement corrosion, e.g., spalls and cracks, is repaired in the area of visible surface damage only. When dealing with damage in this way, the carbonated or chloride contaminated concrete is often not removed completely, thus avoiding stability problems with the structure. Following such a repair measure, reinforcement areas consequently remain, in which there is no guarantee of sufficient corrosion protection and which, therefore, are subject to a higher corrosion risk. With the help of macrocell current measurements between different steel electrodes embedded in concrete, the study investigated circumstances and extent of corrosion problems before and after local repair measures. Further investigation dealt with the measures that have to be taken to guarantee corrosion protection after local repairs.

It is important to have an accurate understanding of the chloride permeability of concrete, especially in the case of RC structures that are susceptible to reinforcement corrosion. The Rapid Chloride Permeability Test (RCPT, AASHTO T-277 831) has often been used during the past several years for a quick evaluation of the chloride permeability of concrete and for comparing the performance of different concrete mixtures. Presents a summary of some of the valuable experimental results published and also briefly discusses the authors' own experience with this method, gathered during a research program presently underway to monitor the chloride permeability of various concretes at different levels of hydration under varying conditions. A study of the literature reveals that AASHTO T-277 has been used for a large variety of concrete mixtures, including those using supplementary cementitious materials, curing conditions, etc., and several attempts have been made to relate the coulombs (obtained using AASHTO T-277) to other parameters and characteristics of concrete, such as resistivity, pore structure, etc. Some of the results from the authors' study included in the paper also show that it may be better at times to work with other voltages than 60 V, and an appropriate conversion factor can be determined to compare the results at different voltages. Further, it was found that, in general, the coulombs decrease as the compressive strength increases, and concrete containing supplementary cementitious material gives lower coulombs at a given strength, which reduce further as the replacement level increases. Paper also discusses some of the possible applications of AASHTO T-277 as a tool for quality control, inspection, and design in concrete engineering.