C Arya

Effect of cement type on chloride binding and corrosion of steel in concrete

Abstract Chloride binding and its influence on the rate of reinforcement corrosion has been investigated in a range of mixes by, respectively, pore solution analysis and measuring the galvanic current in macro corrosion cells formed by embedding mild steel bars in two layers of concrete. For chloride derived from NaCl and introduced at the time of mixing, chloride binding occurred in the order of: GGBS > PFA > OPC > SF and the amount of unbound (ie free) chloride increased with increasing chloride content. However the corrosion rates occurred in the order of PFA > SF > GGBS > OPC at 1 % Cl− and PFA > OPC > GGBS > SF at 3 % Cl−. The corrosion rates increased with increasing chloride content for all mixes due to an increase in the amount of free chloride. The higher rates of corrosion for PFA (and GGBS at 1 % Cl−) compared with OPC was attributable to a reduction in the OH concentration as a result of the pozzolanic reaction. The relatively low rate of corrosion for SF at 3 % Cl− is thought to largely depend upon the physical characteristics of the matrix rather than the pore solution chemistry.

Influence of crack frequency on reinforcement corrosion in concrete

Abstract The relationship between crack frequency and reinforcement corrosion was investigated using two models: (a) reinforced concrete beams, 1.36 m long, containing 0, 1, 4, 8, 12, 16 or 20 parallel sided cracks of equal width giving in each case a sum total width of 2.4 mm and (b) a 4 m long beam containing a 20 mm diameter bar in nineteen segments, ten 352 mm long stainless steel segments and nine 10 mm long mild steel segments which simulated the position of cracks. Corrosion was initiated in (a) by spraying the beams with a 3% chloride solution and in (b) by using concrete dosed with 5% Cl (by weight of cement). The weight loss due to corrosion of the reinforcement was estimated via linear polarisation resistance and/or galvanic current measurements using a zero resistance ammeter. The results obtained from both models suggest that decreasing the frequency of cracking leads to a decrease in corrosion. Possible implications of this finding on the design of concrete structures are discussed.

FACTORS INFLUENCING ELECTROCHEMICAL REMOVAL OF CHLORIDE FROM CONCRETE

Electrochemical chloride removal was studied using prisms made from concrete containing various levels of chlorides derived from sodium chloride added during mixing. The amount of chloride removed during the treatment was assessed by analysing the anolyte. Chloride removal increased with increasing applied potential, number of reinforcing bars at a particular depth and initial chloride content of the concrete. A greater percentage of chloride was removed from prisms where the thickness of the chloride bearing layer of concrete was less than the depth of cover to the reinforcement. Where the thickness of the chloride bearing layer exceeded the cover to the reinforcement, the use of an external cathode significantly increased the total amount of chloride removed. Chloride removal from a face remote from the source of the chloride contamination (soffit desalination) was shown to be feasible.

INFLUENCE OF CATHODE-TO-ANODE AREA RATIO AND SEPARATION DISTANCE ON GALVANIC CORROSION CURRENTS OF STEEL IN CONCRETE CONTAINING CHLORIDES

Abstract Corrosion of steel embedded in concrete was modelled using a 4m long beam containing a bar in seven segments, one mild steel and six stainless steel, which could be electrically connected or isolated by external switches. The concrete mix was dosed with 3% Cl to initiate corrosion. The current flowing between the mild steel and the stainless steel was monitored using a zero resistance ammeter for a range of connections to investigate the influence of the ratio of cathode anode area and cathode-anode separation. It was found that the current increased with increasing cathode anode area ratio but the rate of increase decreased with increasing cathode anode ratio. The current decreased with increasing separation between the anode and cathode although the cathode elements most distant from the anode contributed a significant current.

Design of structural elements : concrete, steelwork, masonry and timber design to British Standards and Eurocodes

Part One: Introduction to Structural Design Philosophy of Design Basic Structural Concepts and Material Properties Part Two: Structural Design to British Standards Design in Reinforced Concrete to BS8110/BS8500 Design in Structural Steelwork to BS5950 Design in Unreinforced Masonry to BS5628, BS EN771, BS EN845 and BS EN998 Design in Timber to BS5268 Part Three: Structural Design to the Eurocodes The Structural Eurocodes: An Introduction Eurocode 2: Design of Concrete Structures Eurocode 3: Design of Steel Structures Eurocode 6: Masonry Design Eurocode 5: Timber Design

Numerical Modeling of Electrochemical Chloride Removal from Concrete

A numerical model of electrochemical chloride removal from concrete (desalination) based on the Nernst-Planck and the Laplace equations is proposed. The model relies on experimentally derived chloride transport number profiles. It is shown that the model can make realistic predictions of both the chloride removed and the chloride remaining in concrete made with admixed sodium chloride.

TR 55: Design Guidance for Strengthening Concrete Structures Using Fibre Composite Materials — A Review

Publisher Summary This chapter reviews the contents of a recent Concrete Society publication on the use of externally bonded fiber reinforced plastic materials for strengthening concrete structures. The chapter describes the background, nature, and mechanics of producing the report. Set in the context of limit state philosophy, the report provides design guidance on: flexural strengthening of beams and slabs, shear strengthening of beams and columns, flexural, and compressive strengthening of columns. Other aspects of the report, which deal with material properties and manufacture, field applications, workmanship and installation, and long-term monitoring, are summarized in the chapter as well. The chapter also outlines areas of needed research.

Assessing the sustainability of methods of repairing concrete bridges subjected to reinforcement corrosion

Sustainability should be at the heart of all decision making, according to the UK government. The construction industry has a key role in delivering this objective because its products impinge on many facets of human activity and the environment, and also because it consumes vast amounts of resources each year. The repair and maintenance of concrete bridges suffering from reinforcement corrosion remains a significant problem in the UK. Many methods of treatment are available but the challenge facing engineers is how to select options that are demonstrably sustainable. Because sustainability is a relatively new Subject and the information required to Study it quantitatively is not currently available, either because the measurements have not been made or because the data has not been compiled into an accessible form, a pseudoquantitative method has been developed which can be used to appraise sustainability. The paper describes the background to the method and discusses its application to three commonly used bridge maintenance strategies: silane application, concrete repair and cathodic protection.