Repair Evaluation Maintenance And Rehabilitation Research Program Review Of The State Of The Art For Underwater Repair Using Abrasion Resistant Concrete

Concrete hydraulic structures that are subjected to severe abrasion require periodic inspection, evaluation, and repair. Not only are these procedures costly and sometimes disruptive, but repeated repairs also make guaranteeing the integrity of the underlying layers difficult. This review was conducted, on an international level, to identify new techniques and potential areas of research that might lead to more abrasion-resistant materials and more effective repair methods and that would avoid the high cost and disruptions associated with dewatering. Topics of study in the review include: (a) underwater inspection, (b) concrete mixtures, (c) underwater placement of concrete, (d) underwater compaction of concrete, (e) polymer concretes and coatings, (f) surface preparation, and (h) support vehicles. Keywords: Concrete admixtures, Hydro-valve, Pneumatic valves, Polymer concrete, Robotics, Support vessels.(jes).

Concrete mixtures were evaluated to determine which were most suited for placement underwater in thin lifts. The concretes were proportioned to have good workability, good abrasion erosion resistance, and good resistance to washing out of the cement paste. High-range water reducers (HRWR) were used to increase the workability and permit the use of low water cement ratios (W/C) to increase the resistance to abrasion erosion. Low W/C, silica fume, and antiwashout admixtures (AWA) were used to increase the resistance to washout. A washout test was used to determine the relative amount of cement paste lost when the concrete is exposed to a large volume of water. The two-point workability test was used to evaluate the relative workability properties of each mixture. The slump and air content were also measured for most of the mixtures. The test method for abrasion erosion resistance of concrete (underwater method) was used to determine the abrasion erosion resistance of each mixture. The results of these tests were used to determine the combination of materials necessary to produce concrete with the desired properties. Significant correlations that exist between the two-point measurements and washout measurements were examined. The effects that W/C, HRWR's, AWA's, fly ash, and silica fume have upon washout resistance and abrasion-erosion resistance were examined.

Concrete mixtures were placed underwater using six placement techniques to (a) examine the cohesive and flow parameters of selected concrete mixtures under different placement situations, (b) estimate those parameters necessary for successful underwater placement, (c) examine the quality of bonding of the repair concrete to the existing concrete, and (d) examine the effect of underwater placement upon the abrasion resistance of the concrete. A washout test was used to determine the relative amount of cement paste lost when the concrete is exposed to a large volume of water. The two-point workability test was used to evaluate the relative workability properties of the concrete. The slump, tremie flow, and air content were also measured. The test method for abrasion-erosion resistance of concrete (underwater method) was used to determine the abrasion-erosion resistance of each concrete. A point-load test for tensile strength was used to determine the bond strength of the repair concrete to the existing concrete.

This synthesis on underwater bridge maintenance and repair will be of special interest to bridge maintenance engineers and others involved with repair of bridge elements located below the waterline and in the splash zone. Procedures for correctly assessing the problem and engineering the repair within the constraints of individual situations, including bridge scour considerations, are described. Protection, maintenance, and repair of concrete, masonry, steel, and timber bridge foundation elements are also addressed. This synthesis updates the maintenance and repair portion of NCHRP Synthesis 88: Underwater Inspection and Repair of Bridge Substructures. This report of the Transportation Research Board identifies and describes current practices and innovative repair techniques for problems associated with settlement, scour, and deterioration of underwater bridge elements. The synthesis considers various types of protection, maintenance, and repair work on bridge substructures, both underwater and in the splash zone, and includes techniques, and their effectiveness. Current research in the topic area and critical research needs are also identified. A limited bibliography is also provided.

The grinding action of waterborne debris circulating in concrete stilling basins, open channels, navigation locks, and other hydraulic structures can lead to abrasion damage several feet in depth. Damaged areas need to be periodically repaired to ensure the functionality and safety of the hydraulic facility. Traditionally, these repairs have been carried out after dewatering the damaged area; however, such practice can interfere with the operations of the facility and can prove to be very costly. Therefore, it is desirable to carry out the repairs while the damaged portion of the structure is submerged. The objective of this research was to develop concrete mixtures and placement methods to repair typical scour holes underwater. Approximately 70 concretes were evaluated to optimize mixture proportions. The four most promising fluid concretes and one control concrete were selected to fill small and relatively shallow depressions underwater using the conventional tremie and the proposed inclined tremie methods. Concrete was placed in the laboratory in a test box with the bottom especially shaped to simulate a small scour hole. Surface profiles and in-place mechanical properties of eight underwater-cast slabs and one slab that was cast above water were evaluated to compare concrete mixtures and placement techniques.