Acoustic Inspection of Coated Steel Bar in Reinforced Concrete Structure

Bridges with reinforcement corrosion problems are now under careful inspection in Taiwan. Costly maintenance programs are underway and raising serious safety concern. There are various engineering solutions to salt-induced corrosion. Among them epoxy-coated reinforcing bars, commonly referred to as rebar, are frequently used in marine environment and other areas due to its durability, reasonable cost, and convenience. However, coated rebar has lower bond strength and is less ductile than uncoated rebar. Thus it could result in larger crack width during pull-out tests [1,2]. The bond strength between coated steel bars and covered concrete results from the adhesion at the steel-concrete boundary, the factional force, and the interlocking force provided by the raised ribs at the steel bar surface. The interlocking force is much stronger than the other two, while the factional force occurs only if the adhesion vanishes after delamination or disbonding starts

Finite element analysis of cracking and delamination of concrete beam due to steel corrosion

This paper presents the analytical results to investigate cracking and delamination of concrete beam due to steel corrosion. A series of concrete beams were idealised as two dimensional models via their cross section and analysed using the finite element software – LUSAS. The corrosion of steel bars was simulated using a radial expansion. The FE results show that cracking of beam section due to steel corrosion can be clarified into four types, i.e., Internal Cracking, Internal Penetration, External Cracking (HS) and External Cracking (VB). The amount of corrosion in term of radial expansion required to causes Internal Cracking, Internal Penetration, External Cracking (HS) and External Cracking (VB) varies almost linearly with bar diameter d, bar clear distance s and concrete cover c, respectively. If the ratio s/c was less than the critical value of about 2.2, the delamination of concrete cover could occur before the cracks can be visualised on the concrete surface, which does concern engineers

Environmental Remediation and Conversion of Carbon Dioxide (CO2) into Useful Green Products by Accelerated Carbonation Technology

This paper reviews the application of carbonation technology to the environmental industry as a way of reducing carbon dioxide (CO2), a green house gas, including the presentation of related projects of our research group. An alternative technology to very slow natural carbonation is the co-called ‘accelerated carbonation’, which completes its fast reaction within few hours by using pure CO2. Carbonation technology is widely applied to solidify or stabilize solid combustion residues from municipal solid wastes, paper mill wastes, etc. and contaminated soils, and to manufacture precipitated calcium carbonate (PCC). Carbonated products can be utilized as aggregates in the concrete industry and as alkaline fillers in the paper (or recycled paper) making industry. The quantity of captured CO2 in carbonated products can be evaluated by measuring mass loss of heated samples by thermo-gravimetric (TG) analysis. The industrial carbonation technology could contribute to both reduction of CO2 emissions and environmental remediation

Bonding problems with the cathodic protection of steel in reinforced concrete structures. Part 2

The first part of this paper, published on pages 132-133 of our October, 1991, issue, discussed the consequences of overprotection in cathodically-protected reinforced concrete structures, and examined the effects of hydrogen evolution. The second part, published below, analyses in detail the effects of concentration of sodium and potassium cations, and enumerates the authors\u27 conclusions

Cathodic protection current accelerates alkali-silica reaction

Results from a study on the effect of cathodic protection (CP) current on the enhancement of alkali-silica reaction are presented in this paper. Steel embedded in mortar specimens made of high alkali cement and reactive crushed Pyrex glass were subjected to 215 and 1076 ma/m2 (20 and 100 ma/ft2) cathodic protection current at the steel surface. CP current densities of 215 and 1076 ma/m2 (based on the reinforcing steel surface area) advanced the cracking time by 40 and 60 percent, respectively, compared to cracking time in specimens which were not current treated. 34 and 15 percent reductions in compressive strength due to increased alkali-silica reaction occurred when the specimens were exposed to 1076 and 215 ma/m2, respectively, for 80 days. Hardness of mortar adjacent to the steel is reduced with increase in current densities at the steel surface. CP current has no effect on the tensile strength and ductility of low strength reinforcing steel in concrete. Results obtained from a simple staining technique suggested the formation of higher alkali-silica gel contents near the steel at a higher current density

Environmental influence on cathodic protection criteria for reinforced concrete structures. A theoretical approach

A theoretical study has been made showing the reflection of the environmental factors on cathodic protection criteria to be applied to reinforced concrete structures. It is found that lowering of the steel potential to a value less than -0.65 volt with respect to standard hydrogen electrode (SHE) provides adequate protection against corrosion irrespective of the variations in temperature, humidity and chloride content

Polarization period, current density, and the cathodic protection criteria

The -850 mV CSE ``instant off\u27\u27 potential and the 100 mV decay potential cathodic protection (CP) criteria applicable to reinforced concrete structures have been studied with the focus on their dependence on the polarization period and current density. Four constant current densities of 1, 3, 20, and 60 ma/ft2 of the steel surface area were maintained on reinforcing steel embedded in mortar specimens, and the ``instant off\u27\u27 potentials as well as the decay potentials were recorded for different polarization periods and current densities. The ``instant off\u27\u27 potential value was observed to increase with polarization time and current density. The same trend has been noticed in the case of 4-hr decay potential. A current density of 1 ma/ft2 of the steel surface area was found to be inadequate to satisfy either the ``instant off\u27\u27 potential or the decay potential criterion, whereas a current density of 3 ma/ft2 is more than sufficient to satisfy the decay potential criterion, but it is inadequate to satisfy the ``instant off\u27\u27 criterion. Complete depolarization in a 4-hr period is possible with 1, 3, 20, and 60 ma/ft2 CP current densities. The aggregate type has no noticeable effect on the ``instant off\u27\u27 potential and the decay potential values