Reinforced concrete--Cracking

Steel reinforced concrete specimens of loaded and unloaded
configuration were placed in contact with seawater in a state of
accelerated corrosion. They were simultaneously monitored for acoustic
emission and the results were analyzed in an evaluation of the use of
acoustic emission as a nondestructive monitor of corrosion induced
cracking. It was shown that, in a laboratory environment, counts and
amplitude information are sensitive indicators of the levels of
cracking within the concrete specimen; and thereby the degree of
corrosion damage may be inferred. Analytical models applicable to the
representation of acoustic emission amplitude distribution are
discussed also.

This report presents the experimental and theoretical studies on the feasibility of using CFRP laminates for strengthening damaged reinforced concrete beams in cold environment. Experimental work includes investigation on fatigue strength, ultimate capacity and failure modes of repaired reinforced concrete beams in cold environment and room temperature. The repaired concrete beams subjected to fatigue in cold environment exhibit fewer number of cracks than those observed in beams at room temperature. The crack propagation and resulting damage were faster in beams tested in room temperature than those at cold temperatures. The study also includes investigation of thermal response of repaired plain concrete beams with CFRP laminates subjected to thermal cycles. Analytical studies on the distributed shear forces and peeling forces of repaired reinforced concrete beams were carried out to analyze the interaction between the laminate and the concrete interface. The temperature distribution and strains developed by the temperature differential are determined in the repaired plain concrete beams subjected to thermal cycles and the analytical results compared with the measured values.

Dimensional changes of thin cement paste specimens were monitored during exposure to distilled water, hydrochloric acid, alkaline and FeCl$\sb2$ solutions; and comparison was made with the experimental results obtained by other authors. Post experimental examination of reaction products formed on the specimen surface exposed to FeCl$\sb2$ was conducted using X-Ray diffraction. The data resulting from the measured dimensional changes were input to a finite element model to project the stresses that should occur in association with localized corrosion of embedded steel and wetting of adjacent cement by aqueous FeCl$\sb2$. Implications of the findings with regard to cement and concrete cracking in association with embedded metal corrosion are discussed.

Corrosion-induced spalling of reinforced concrete and prestressed concrete is a major problem in coastal structures. Statistics on the rehabilitation and replacement of damaged concrete in the U.S.A. indicates substantial expenditure. This study is an investigation of the use of electro-deposited minerals for in-situ concrete repair in a cost-effective manner to extend the service life for marine reinforced concrete structures. During the first phase of this investigation, the reinforcing steel in specimens was corroded by an impressed voltage technique to a point where concrete cracking occurred. The second phase addressed the rehabilitation in which the calcareous deposits were precipitated in the cracks by an impressed cathodic current. This investigation included both laboratory testing with once-through circulating seawater and field testing in the ocean environment. The findings indicate that the structural strength of the concrete specimens decreased as a result of the impressed voltage.

The objective of this investigati.on was to contribute to
the determination of a suitable metallic coating for steel
reinforcement in concrete exposed to a marine environment
and possibly to stray current. Concrete specimens embedded
with steel, aluminum, cadmium, copper, molybdenum, nickel,
and galvanized steel were exposed to sea water. Direct
current was impressed on these to accelerate corrosion of
the reinforcement so that cracking of the concrete could be
observed within the time limit of the investigation. Aluminum,
cadmium, copper, and nickel were found to have no beneficial
effect on concrete cracking as compared to steel. In
addition, no correlation between oxide-metal volume ratio
and concrete time-to-cracking could be observed. It was
found that corrosion of molybdenum has little or no tendency
to crack concrete and its corrosion potential and active
behavior approximates that of steel, indicating it may be
an excellent coating.