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Many Corps of Engineers rubble-mound breakwaters and jetties have become permeable to sand transport and wave transmission, resulting in increased dredging costs, risks and delays to navigation, and damage to moored vessels by excessive wave activity. Some Corps coastal districts have applied grouting techniques for sealing these structures by using cementitious and chemical grouts for creating a vertical barrier through a series of vertical holes drilled along the centerline of the structure. To ascertain the effective useful life of such grouts, durability time-dependent tests were conducted by U. S. Army Engineer Waterways Experiment Station (WES) to determine how the materials would endure under near-actual field conditions. A cementitious mixture previously used at Buhne Point, California (Buhne Point Mixture), and a new mixture design (WES Mixture) developed by the WES Structures Laboratory (SL) were evaluated. Specimens were exposed at three weathering stations (including Treat Island, Maine) for the eight-year period 1987 to 1995. Nondestructive tests (ultrasonic pulse velocity and transverse flexural frequency) were conducted periodically during the eight-year evaluation period. Long-term durability exposure field tests revealed spalling of the Buhne Point Mixture due to freezing and thawing. However, nondestructive tests indicated the integrity of all specimens was maintained, as there appeared to be minimal changes in the properties of these cementitious grouts. Grout laced within the core of rock structures may not actually be exposed to the extreme conditions on the weathering platform at Treat Island. Either the WES Mixture or the Buhne Point Mixture may be used as grouting materials to rehabilitate existing Corps rubble-mound breakwaters and jetties by filling voids to prevent passage of excessive wave energy and sediment through such structures.

The use of dry-mix shotcrete for the repair of structures in a marine environment was the subject of an investigation carried out for the Canadian Coast Guard. In addition to the control mixture, four different mixtures using two aluminate-based accelerating admixtures at two different dosages were prepared. All mixtures contained steel fibers and silica fume and were air- entrained. For each mixture, a panel of approximately 1.0 m x 1.0 m was shot on a wharf (in the St. Lawrence River north of Quebec City) to study the influence of freezing and thawing cycles in the presence of salt water, the influence of wetting and drying cycles, and the abrasion due to ice packs. Three panels were also shot with each mixture for laboratory testing purposes (mechanical strength, durability, and microstructure). The accelerating admixtures that were used were not found to have any adverse effects on any of the properties of the hardened shotcretes. The initial setting time was reduced to values below six minutes. For all five mixtures, the resistance to scaling due to freezing in the presence of deicer salts (ASTM C672) was found to be not very good. This confirms the results of previous tests which have also shown a negative influence of silica fume on the scaling resistance of dry-mix shotcrete measured in the laboratory.

To determine the most effective end-anchorage protection for post- tensioned beams, 20 air-entrained post-tensioned concrete beams were fabricated and placed at the Treat Island severe exposure station in 1961. The beams were fabricated using four types of post-tensioning systems with 12 different types of end-anchorage protection over external and recessed anchorages. End- anchorage protection was applied to the beams using six different types of joint preparation: bush-hammering, epoxy adhesive on sandblasted concrete surface, retarding agent, sandblasted, sandblasted with primer, and no preparation. The end protections were made from three different mixtures: portland cement concrete, epoxy concrete, and sand-cement mortar. The 20 post-tensioned test beams have been inspected annually by the Corps and biennially by other interests. Eleven of the beams were autopsied at the Waterways Experiment Station (WES) in 1973-74 and 1983. This paper assembles the data obtained, evaluates the data, and summarizes the important findings related to durability. The main findings are that the flush (recessed) anchorage protection using portland cement concrete is the superior detail. The external portland cement concrete anchorage protection, properly anchored with reinforcing steel across the join with adequate concrete cover, also provides an effective protection.

Long-term research studies on the effectiveness of corrosion protection systems for reinforced concrete exposed to aggressive environmental conditions of the United Arab Emirates have been in progress at the exposure site adjacent to Dubai Creek since December 1991. These studies cover reinforcing bar coating systems and different products comprising pore blocking admixtures and a penetrating surface sealer. The parameters included in the studies are two water-cement ratios of 0.44 and 0.6, two types of curing regimes (laboratory conditions and actual construction practices), two concrete reinforcing bar covers (10 mm and 30 mm), and three site exposure conditions above ground, below ground, and in the tidal zone). The effectiveness is assessed through accelerated laboratory tests and site exposure tests. The tests performed at different ages include compressive strength, water absorption, water penetration, capillary rise and chloride ingress, crack appling, and measurements. Also conducted were electrochemical testing comprising half-cell potential, resistivity, linear polarization, corrosion current, and AC impedance. One-year and two-year results have been previously published; the present paper updates the findings, emphasizing the electrochemical testing results. The results to date show that the performance of the epoxy coated reinforcing bar is encouraging, while the performance of the most of the products studied is not satisfactory.

The marine environment provides a severe durability test for reinforced concrete structures with premature deterioration often being associated with steel corrosion. The rate of chloride ingress from the sea through the concrete cover is of primary importance since the depassivation of steel and subsequent corrosion are largely controlled by the chloride concentration at the reinforcement. Accurate service-life predictions are made by defining the material, assessing the severity of exposure, and monitoring the durability performance in that environment. Concrete, therefore, needs to be characterized in terms of early age properties that control the diffusion of chlorides through the cover concrete. These characterized values may then be related to long-term characteristics which determine durability for different environmental conditions. Early age tests should only be used as indicators of potential durability once suitable relationships have been established with the durability performance of concrete under marine conditions. Results from a research program are presented, in which concrete specimens were initially characterized at 28 days before being exposed to four marine environments in South Africa. The concrete was tested using a newly developed chloride conductivity test which determined the chloride resistance of concrete using an accelerated technique. Chloride contents were measured after 24 months of exposure and the diffusion coefficients were related to the initial characterization values. Results indicated that the severity of exposure has a major influence on the relative rate of chloride ingress into the concrete. The chloride conductivity test was found to be a useful indicator of chloride resistance, but the results are specific to the type of concrete being tested. Comparisons of potential durability of concretes based solely on the results of rapid chloride tests at early ages may be misleading and should be used with caution.