A condition assessment performed on a substructure of a balance bridge revealed that reinforcement corrosion had been initiated by chloride penetration and carbonation. For the eastward wall, cathodic protection with impressed current was proposed to protect the reinforcing steel. In view of the average thickness of the concrete cover of 60 mm together with the extensive delamination covering approximately 50% of the surface area, a cathodic protection system was designed based on discrete titanium anode strips, inserted perpendicular to the concrete surface. In order to achieve a uniform distribution of protective current to the steel, an average of 10 strips per square meter of concrete surface was placed in holes drilled to a depth of 35cm. The substructure was subdivided into two independently controlled anode zones. During the installation several problems were encountered regarding electrical continuity within the reinforcement network and electrical contact between the reinforcing steel and the anode system. In view of the innovative nature of the design and the increased risk of non-uniform current distribution provisions were made for additional monitoring of the performance of the cathodic protection system. Measurements included concrete resistance, current distribution over the concrete surface and frequent depolarization. The results revealed a pronounced non-uniform current distribution over the concrete surface and a high current demand in one of the zones. Eventually, this resulted in an anodic current density exceeding the FHWA limit. Frequent monitoring is performed to verify if this high current output will decrease with time. There is a strong need for quantitative information regarding anodic and cathodic current distribution as affective by local condition of the embedded steel, concrete resistivity and cover thickness. This information will be of benefit for the design of cathodic protection installations.

Based on the recently developed DuraCrete Report, that is a manual for designing and rehabilitating concrete structures by a probability-based approach, four examples dealing with corrosion of steel reinforcement in concrete due to chloride ingress are given in the present paper using the above approach. The first example illustrates the difference in the required concrete cover for different environments (I.e. different temperature). The second example concerns the update of the service lifetime of the Great Belt Link in Denmark on the basis of the measurements made five years after construction. The third example deals with the design of the Western Scheldt Tunnel in the Netherlands, and finally, an example is given concerning a column being designed with regard to initiation of corrosion both by the means of a partial safety factor method and by a probabilistic analysis. When designing a new structure, most often the concrete cover and the diffusion coefficient of the concrete are to be determined while the service life of the structure is given by the owner or the investigator together with the acceptable reliability level. On the other hand, when rehabilitating an existing structure, geometrical and material quantities are known, and an analysis may give the answer to an estimate of the remaining lifetime or the reliability level. The above examples are discussed in order to show, in a practical way, the methods of the probabilistic approach and the type of input used in the DuraCrete design approach.

The objective of this paper is to characterize sulfate resistance of the mortars (cement to sand =1;3 by weight, W/C =.6) made from blended portland pozzolan cement with 15wt.% of zeolite, and to compare it to that of mortars made from normal portland cement an sulfate resistant portland cement. The improved sulfate resistance of mortars with portland pozzolan cement is caused by : 1-decreased C3A in the blended cement in comparison with that in normal portland cement; 2-decreased content of Ca(OH)2 capable of reacting with a sulfate solution due to pozzolanic reaction of zeolite with the cement relative to that in normal portland cement; 3-ion-exchange capacity of zeolite to Ca2+ ions (1.82 mmol Ca2+.g-1 = .073 g Ca2+.g-1); 4-negligible change in pore structure of portland pozzolan cement mortars compared to portland cement mortar which is characterized by significant conversion of capillary pores to gel pores, as a result of formation of voluminous reaction products of the sulfate attack. The results show that sulfate resistance of portland pozzolan cement was similar to that of the sulfate resistant portland cement.

Solidification/stabilization (S/S) is an effective management of toxic wastes, consisting in mixing a waste product with a binder and other ingredients, if any, to reduce the mobility or solubility of contaminants. In the present work, a contaminated marine sediment of the Venice lagoon was treated with cement, aggregates and different amounts of an acrylic superplasticizer to produce cement mortars with different W/C. The characteristics of the resulting mortars were evaluated by compressive strength, water permeability, observation of microstructure of the comment past, and leaching of contaminants. The durability in aggressive environments of the best performing mortar, corresponding to the mixture with W/C=.38, was evaluated in comparison to a reference mortar. The results of the test indicated that W/C affects no only the strength of the mortars but also improves the leaching characteristics of the stabilized waste. This could be ascribed mainly to the reduction of the micro porosity of the mortars with lower W/C. The durability test indicated that the mortar containing the sediment is less sensitive to the attack of CaCl2 in comparison to the reference mortar, as confirmed by the higher strength after different periods of immersion in a 30% aqueous solution of CaCl2 at 5 degrees C. Furthermore, the linear expansion in sulphate solution seems not to be substantially influenced by the presence of the sediment. Thermal and XRD analyses suggested that these results could be ascribed to a pozzolanic effect of the sediment. The results of the present work confirmed the possibility of producing high performance concrete by using the contaminated sediments of the Venice lagoon.

Erosion damage has been reported for approximately one-half of the more than 600 hydraulic structures owned and operated by the U.S. Army Corps of Engineers. The causes of this erosion are about equally divided between cavitation and abrasion. In some cases this damage has been severe, requiring extensive repairs. Many different materials have been used in these repairs with varying degrees of success. Consequently, a study was initiated as part of the Repair, Evaluation, Maintenance, and Rehabilitation (REMR) Research Program, to evaluate the caviation resistance of a wide range of repair materials and protective coatings. A venturi-type apparatus which produces moderate to severe caviation was used to evaluate the caviation resistance of approximately 80 materials. A ceramic-filled epoxy; a metal-filled, fiber-reinforced epoxy; and a polyurethane exhibited the best caviation resistance. Cementitious-based materials generally performed rather poorly. Results of the laboratory tests are summarized herein.