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Intentional contamination of drinking water with anthrax spores is a concern to water utilities. The spores may become embedded in the distribution pipe corrosion and biofilm, where they will be protected from residual disinfectants. This paper compares the disinfection effectiveness of chlorine and chlorine dioxide on Bacillus globigii , a surrogate for B. anthracis . Batch experiments were performed using both disinfectants. Data was analyzed using the delayed Chick-Watson model to determine the corresponding CTlag (CT = concentration × time) values and Watson plots, which indicate the dominant factors affecting disinfection kinetics. Chlorine dioxide had CTlag values almost one tenth of those observed for chlorine. However, Watson plots showed that exposure time and disinfectant concentrations have equal weights on the inactivation rate of both disinfectants.

This work investigated the longevity of inhibitors and the performance of corrosion-inhibited deicer products under two storage conditions. Three liquid deicers (MgCl2-based FreezGard, CaCl2-based CCB, and NaCl+GLT) were selected for the field storage monitoring and the key properties tested included the chloride and inhibitor concentrations, corrosion parameters (Ecorr and PCR), pH, electrical conductivity, and performance parameters (Tc and IMC30°F). The three liquid deicers investigated did not lose their quality over the 14 months of field storage, regardless of the storage condition (mixed or non-mixed). As such, it is not necessary to implement any mixing for the liquid deicer tanks during storage. It is however essential to mix the tanks immediately prior to the use of the liquid deicers, to ensure uniform composition. This study also revealed that the investigated corrosion inhibitors did not show side benefits in suppressing effective temperature or in providing ice melting capacity of their corr...

In this paper, the cracking of concrete cover caused by steel bar corrosion was discussed and studied based on the three-period model of steel bar corrosion in concrete. In the analysis, the contour of the corrosion layer was simplified into a semi-ellipse according to the non-uniformity of steel bars in reinforced concrete under a natural environment. The steel bar corrosion was divided into three different periods by two corrosion points, namely, the void to be filled was exactly filled and the concrete cover was exactly cracked. Different assumptions are made for each corrosion period. Before the concrete cover cracks, it is developed into an elastic plate. Based on the theory of elastic mechanics, the maximum corrosion depth of steel bar when concrete cover cracks is predicted. After the concrete cover cracks, a model of the relationship between the crack width of the concrete cover and the maximum corrosion depth of steel bar was established by considering the filling of cracks by corrosion products. The rationality of the model was tested by employing experimental data from the literature, and it was found that the calculated value of the model was in good agreement with the experimental data in the literature.

This paper outlines the static and fatigue behavior of cast-in-place, second-generation steel-free bridge decks. Although cast monolithically, the first bridge deck was divided into three segments. The first segment was reinforced with steel, according to conventional design. The other two segments were steel-free designs with internal crack-control grids, one consisting of carbon-fibre-reinforced polymer (CFRP) and the other consisting of glass-fibre-reinforced polymer (GFRP). This hybrid CFRP or GFRP and steel strap design is called the second generation of the steel-free concrete bridge deck. The hybrid system limits the width of any longitudinal cracks that develop and eliminates corrosion from within the deck slab. All three segments were tested under cyclic loads of 222 and 588 kN to investigate fatigue behavior. The second bridge deck comprises an internal panel and two cantilevers and also incorporates a complete civionics system. The static tests outlined in this paper are useful in the development of the fatigue theory, which was derived from the fatigue testing of the first bridge deck.Key words: steel-free, cantilever, fatigue testing, static testing, glass-fibre-reinforced polymer, carbon-fibre-reinforced polymer, civionics.

The paper is concerned with the assessment of ship plates in which corrosion has reduced their overall thickness making them vulnerable to buckling-related failures. The uniaxial buckling of simply supported square plates is studied for several corrosion patterns, which are allowed to progressively engulf the entire plate. The finite element method is employed for computing buckling loads of corroded plates with different boundary conditions. Numerical results are presented in the form of generic plots of buckling load versus volumetric metal loss for several corrosion patterns considered in the paper. The mechanics of buckling load variations by corrosion is discussed in detail. The spatial location of the corrosion patch appears to have a significant effect on the buckling strength. It is noted that the case of uniform corrosion is not the most detrimental case, rather corrosion confined in a corner or central area appears to be more critical.Key words: ship structures, square plate, buckling load, corrosion, uniaxial compression, finite element method.

The use of post-tensioned masonry can lead to economic and elegant structures. A major problem associated with post-tensioning is the corrosion of the steel tendons, especially for unbonded tendons. If carbon fibre reinforced polymer (CFRP) tendons could be used to replace the traditional steel tendons, the corrosion problem would be overcome. However, a number of issues need to be resolved before CFRP tendons can be used comfortably in post-tensioning applications. The first part of this paper deals with a diaphragm wall post-tensioned using CFRP tendons. The post-tensioning procedures are described and the prestress losses occurring in the past 12 months are presented. Results from thermal, flexure, and racking shear tests performed on the wall are reported. The second part of the paper deals with the development of design procedures and equations based on both the test results and the database currently available. The equations presented are specifically for CFRP unbonded post-tensioned masonry diaphragm walls but with appropriate modification could be applied to the design of any CFRP post-tensioned masonry wall. A design example is included.Key words: anchorage system, carbon fibre reinforced polymers, diaphragm walls, flexural strength, masonry walls, prestress losses, prestressed masonry, post-tensioning, shear strength, thermal loads.

The issue regarding the corrosion of steel ties connecting brick veneer to a structural backing is well documented. In this paper, the predicted corrosion rate and resulting service life estimates, produced by a time-stepped service life model developed in Visual Basic for EXCEL, for metal ties embedded in mortar, are compared with the empirically determined corrosion rates and service lives of 16 zinc galvanized tie specimens taken from 13 buildings located in 6 different Canadian cities. This tie service life model, coined the “Tie Service Life Predictor”, correlates the external environment of the building to the tie life. As with most corrosion models for steel embedded in concrete (or mortar), the model is broken into two distinct phases: corrosion initiation using Fick’s law of diffusion and corrosion propagation. By considering the mortar surrounding the tie as the tie’s atmosphere, the Tie Service Life Predictor characterizes the microenvironment (atmospheric conditions) surrounding the tie from the macroenvironment conditions. Once the atmospheric conditions were established, the ISOCORRAG atmospheric corrosion model could be used to predict the corrosion rate of zinc galvanized steel ties embedded in the mortar joints of the exterior wythe of brick veneer wall systems. The methods used to create the Tie Service Life Predictor could also be applied to service life estimation of reinforcing steel in concrete structures such as bridge decks and parking structures.

This paper reports a study carried out to evaluate the effects of corrosion inhibiting admixtures, calcium nitrite and disodium tetrapropenyl succinate, in combination with supplementary cementitious materials, fly ash and silica fume Portland cement, on the compressive strength and certain durability properties of high performance concrete. Mixture formulations, including binary and ternary combinations of these admixtures were evaluated. Chloride profiles after 91 and 365 days of exposure and the compressive strength and electrical resistivity at 1, 7, 14, 28, 180, and 365 days of age were estimated. Also, results of corrosion evaluation after five-year exposure to a natural marine environment at Treat Island Maine, USA are presented and discussed. Results indicate that the use of corrosion inhibitors in combination with supplementary cementitious materials was beneficial, albeit to various degrees, in enhancing the strength and durability properties of high performance concrete with no noticeable adverse effects.

The strength of pipeline with multiple corrosion patches depends on the number of corrosion patches within an area on the pipe surface, the locations of corrosion patches along the longitudinal and circumferential directions of the pipe. In this paper, the strength and deformation characteristics of corroded pipeline are investigated using finite element analysis. Pipes with different diameters and different depths of corrosion patches are considered. The spacing of the corrosion patches is varied along longitudinal, diagonal, and circumferential directions of the pipes. The study shows that the limiting spacing for interaction of corrosion patches depends predominantly on pipe wall thickness, corrosion depth, and the location of the defects. The diameter of the pipe has some influence on the interaction for large diameter pipes. A new interaction rule for the limiting spacing for interaction is developed for longitudinally spaced corrosion patches. For circumferentially spaced corrosion patches, the ASME recommendation for the limiting spacing is found to be reasonable.

A number of burst pressure models were developed to determine the remaining strength of corroded pipelines. However, no single model has been found to be acceptable for predicting the burst pressure correctly. In this paper, the burst pressure models for corroded pipelines are revisited based on the structures of three existing models. The model parameters are re-evaluated using an optimization (differential evolution) algorithm with a database developed based on finite element (FE) analysis. A series of FE analysis are performed to determine the burst pressures of corroded pipelines with varying pipe diameters, wall thicknesses, corrosion dimensions and material strength grades. The models with new sets of model parameters provide the burst pressure reduction factors that match with the FE results and experimental data better than the existing models. The study reveals that FE analysis along with an optimization algorithm can effectively be used to develop improved models for better fitness-for-service a...

Corrosion of steel bars is a serious issue compromising the reliability of reinforced concrete structures. Previous research has proven that confined concrete has increased confined strength, ductility, energy dissipation capacity, etc. However, existing confined concrete models cannot accurately predict the strength and stress–strain relationship of concrete confined with corroded stirrups. This paper presents an experimental study on the behavior of eight square columns confined with stirrups damaged by accelerated chloride corrosion. The weight loss of the stirrup ranges from 5% to 31.7%. The stress–strain curves of confined concrete are obtained from the concentric compression loading tests. Based on the well-established Mander model, modification factors are introduced to account for the effect of corrosion on the confined strength, confined strain, and descending branch of the curves. These modification factors predict the constitutive relationship of concrete confined with square stirrups as a function of the weight loss and localization levels of corrosion.

Corrosion of the reinforcing steel is a primary deterioration mechanism for reinforced concrete bridges. The spatial distribution of such spalling, relative to bar splices and laps, has not been considered in previous studies and may have a significant influence on structural capacity. In this paper, a modified area concept for considering this spalling is proposed. A methodology has been developed that employs this concept for the practical evaluation of existing bridges. It uses graphical spalling surveys, reinforcement layout information, and existing information regarding material and geometric properties as inputs for the flexural and shear analysis of deteriorated bridge girders. This methodology is easily adapted for full bridge analysis and to consider the effects of bar section loss and bond deterioration. A case study bridge is evaluated to show that this methodology offers a viable tool for the rapid assessment of spalled bridge girders to facilitate the prioritization of rehabilitation projects.

This paper reports experimental data on the structural performance of disturbed regions in reinforced concrete beams with corrosion damage to the embedded steel stirrups. A total of 15 reinforced concrete beams were constructed and tested. The test beams were 350 mm deep, 125 mm wide, and 1850 mm long. The beams were tested in three-point bending under a simply supported span of 1500 mm. Nine beams had the embedded stirrups subjected to accelerated corrosion. The test variables were the corrosion damage level and the shear span-to-depth ratio. The test results indicated that the corroded beams exhibited reduced shear strength in comparison to the uncorroded control specimens. The shear strength reduction was up to 53%. Furthermore, the reduction in shear strength due to the corrosion was found to be greater at smaller shear span-to-depth ratios.

This paper discusses the relationship between crack widths, chloride diffusivity, and corrosion rate of cracked mortar beams. Flexural loads are introduced to generate crack widths ranging from 29 to 390 µm. The specimens were subjected to accelerated corrosion by immersion in a 5% NaCl solution and a constant voltage of 12 V. In addition, salt ponding tests were conducted to determine the chloride ion transport properties. The results showed that as the crack width increased, the effective diffusion coefficient (corrosion initiation) and mass loss of steel reinforcing bars due to the accelerated corrosion (corrosion propagation) also increased. For crack widths less than about 135 µm, the effect of crack width on the effective diffusion coefficient and mass loss of steel reinforcing bars embedded in mortar specimens was found to be marginal when compared with the virgin specimens. Therefore, it was concluded that the effect of crack width on the corrosion initiation and propagation period was more pronounced when the crack width is greater than about 135 µm. Moreover, a significant amount of self-healing was observed for the cracks that have widths below 50 µm when subjected to the NaCl solution exposure.

Infrastructure corrosion is an expensive problem worldwide. In the case of reinforced concrete (RC) structures, corrosion reduces the steel cross sectional area and thus decreases the capacity of the corroded RC members. The expansion of the corroded steel also induces tensile stresses in the concrete causing the concrete cover to crack and spall, thus reducing the bond capacity between concrete and steel. This paper reports on a research program conducted at the University of Waterloo that studied the effect of corrosion on flexural and bond fatigue strength. The effect of the addition of fibre-reinforced-polymer (FRP) sheets on the fatigue life of corroded RC beams was also assessed. Eighteen beams (152 mm × 254 mm × 2000 mm) were tested in two groups, with each group consisting of three sets of tests. Group F was designed to study the fatigue flexural behaviour; the repaired beams in this group were strengthened with a flexural FRP sheet along their tension side and confined by intermittent U-shaped FRP sheets along their length. Group B was designed to study the fatigue bond behaviour; hence, the repaired beams in this group were confined with U-shaped FRP sheets in the anchorage zone. The variables in each group were the percentage of corrosion (0% and 5% theoretical mass loss), the load range, and the use or omission of a FRP repair method. Results showed that a mild level of corrosion (5% theoretical mass loss) caused on average 10% and 20% reductions in flexural and bond fatigue strength, respectively. Strengthening the corroded beams with FRP sheets enhanced the fatigue behaviour of the beams. In both groups, the fatigue strength was on average 15% higher than that of the corroded unrepaired beams.Key words:corrosion, fibre-reinforced-polymer (FRP) sheets, fatigue strength, steel–concrete bond, flexural performance, durability.

This paper examines the basic influence of corrosion on bond strength at the steel–concrete interface and the associated slip and cracking. A nonlinear finite-element model is developed to account for the effect of corrosion on deterioration of the bond. Deterioration of the mechanical interaction between the corroding reinforcing steel and the concrete is modeled with the nonlinear finite-element program ABAQUS. The contact pressure normal to the steel–concrete interface is reduced when the concrete cracks, which occurs along with a decrease in the cross-sectional area of the steel bar and the decrease of the friction coefficient between the steel and the concrete. The loss of contact pressure and the decrease in the friction coefficient with the mass loss of steel bars are evaluated using pullout test specimens with different levels of rebar corrosion. Finally, the relationship between the loss of bond strength and the mass loss of the steel rebar is established. The model gives reasonably accurate predictions of bond strength for three independent experimental studies. Key words: bond, concrete, corrosion, mechanical interaction, reinforcing steels, slip, steel-concrete interface.

Corrosion resistance, high strength, and advantageous strength-to-weight ratio enable fiber reinforced polymers (FRPs) to have substantial potential to replace steel tendons in prestressed applications. One of the main technical obstacles to wide use of FRPs in the construction industry is the methodology to anchor FRP tendons to achieve their full strength. High tensile to compression and shear strength ratios make it necessary to develop a new anchorage design concept for FRP tendons. This paper gives a literature review of bond-type anchorage systems and the mechanics of stress transfer by bond from FRP tendons to grout and reports an experimental study on a newly developed bond-type anchorage system with carbon fiber reinforced polymer (CFRP) Leadline 8-mm-diameter rods. The test program consisted of nine monotonic tensile tests, two pullout tests, and two proving tests on the anchorage system with Leadline single- or 9-rod tendons. The test results showed that the developed anchorage system with 250-mm bond length ensures full development of the tensile strength of Leadline mono-rod tendons. The bond strength of Leadline 9-rod tendons is 14 MPa for a bond length of 95 mm, 62% of that of mono-rod ones with a bond length of 80 mm. The anchorage system with a 400-mm bond length gives at least 90% of the tensile strength of Leadline 9-rod tendons and also demonstrates an acceptable sustained loading behaviour in accordance with existing codes.Key words: anchorage, bond stress, creep, grout, polymers, rod, slip, tendon.

This paper presents the results and the applicability of an electrochemical technique, the Tafel plot method, for determining the corrosion rate of reinforcing steel embedded in laboratory ordinary portland concrete (OPC) and high-performance concrete (HPC) specimens. Fifty-two OPC and 52 HPC concrete cylinders, each with a single embedded reinforcing steel rod, have been subjected to various laboratory conditions, and the corrosion rate of each specimen has been monitored. Results indicate that HPC specimens performed much better than OPC specimens in terms of resisting corrosion, as the corrosion rates were far lower for the HPC specimens than for the OPC specimens. Sodium chloride concentration played an important role in the propagation of corrosion: the higher the NaCl concentration, the higher the corrosion rate. In addition, different cycles of wetting and drying of concrete specimens had different impacts on corrosion rates. Results for the chloride concentration based on the American Society for Testing and Materials (ASTM) destructive testing method C1218 were in agreement with the corrosion rate results from the Tafel plot method used in the study.Key words: corrosion, electrochemical, reinforced concrete, Tafel method, high-performance concrete.

The viability of carbon fibre reinforced polymer (CFRP) laminates for the strengthening of corrosion damaged reinforced concrete bridge girders is addressed in this paper. Ten reinforced concrete beams (100 × 150 × 1200 mm) with variable chloride levels (0-3%) were constructed. Six beams were strengthened by externally epoxy bonding CFRP laminates to the concrete surface. The tensile reinforcements of three unstrengthened and four strengthened specimens were subjected to accelerated corrosion by means of impressed current to 5, 10, and 15% mass loss. Strain gauges were placed on the CFRP laminates to monitor and quantify tensile strains induced by the corrosion process. Following the corrosion phase, the specimens were tested in flexure in a four-point bending regime. Test results revealed that CFRP laminates successfully confined the corrosion cracking, and the total expansion of the laminate exhibited an exponential increase throughout the corrosion process. All the strengthened beams exhibited increased stiffness over the unstrengthened specimens and marked increases in the yield and ultimate strength. The CFRP strengthening scheme was able to restore the capacity of corrosion damaged concrete beams up to 15% mass loss.Key words: CFRP laminates, corrosion, confinement, expansion, load tests, strengthening, bond strength, reinforced concrete.

The use of corrosion free fibre reinforced polymer (FRP) composites as reinforcement to concrete is currently being seen as a promising option to generate durable concrete structures. However, there exists very little credible information about its field application and performance. This paper describes the Joffre Bridge project, in Sherbrooke (Québec, Canada), over the St-François River, where Carbon Fibre Reinforced Polymer (CFRP) was used as reinforcement for a portion of the concrete deck slab. The bridge consists of five longitudinal spans with lengths varying from 26 to 37 m. Each span has a concrete deck supported by five steel girders at 3.7 m. A part of the concrete deck slab (7.3 × 11.5 m) and a portion of the traffic barrier and the sidewalk were reinforced with Carbon (CFRP) and Glass Fibre Reinforced Polymer (GFRP) reinforcement. The bridge was extensively instrumented with many different types of gauges, including integrated fibre optic sensors (FOS) into FRP reinforcement. The performance of the bridge had been assessed under static and dynamic loading using calibrated heavy trucks. Moreover, structural design and construction details of the bridge and instrumentation were performed. The results from calibrated field tests on the bridge are presented in this paper.Key words: concrete bridge deck, FRP reinforcement, fibre optic sensors (FOS), field calibrated tests, performance monitoring.

Corrosion on prestress strands affects their mechanical properties as well as the coefficient of friction in the surface strand/duct. In previous research on prestress beams, the authors have observed different coefficients of friction depending on the surface condition of the strands and wires used in investigation. Some of the strands used for the experiments were stored for some months in the laboratory and gained some rust on the surface. This was enough to influence the coefficient of friction in a noticeable manner. To study the influence of corrosion on the mechanical properties of prestress strands several samples were stored under different environmental conditions to produce various levels of corrosion. These samples were tested afterwards to determine the influence of corrosion on fatigue properties and the coefficient of friction. Apart from the coefficient of friction, light rust decreases none of the other studied mechanical properties of the strands and may even increase the bond characteristics. The presence of rust does not necessarily mean that the strands should be rejected. The work described in this paper was conducted to investigate the level of rust that could be considered acceptable and how corrosion influences some mechanical properties of prestressing strands.Key words: reinforced concrete, prestressed concrete, prestressed beams and girders, structural design, structural members, corrosion, fatigue, losses.

The overall aim of this paper is to establish the process and amount of chlorides penetrating reinforced concrete elements when exposed to a salt-laden environment. For this purpose, a number of slabs were subjected to 70 cycles of wetting-drying regime with a 4% sodium chloride solution over a period of 2-3 years. To examine the direction of transportation of the chlorides, some of the slabs were partially coated with a surface coating system known to be highly resistant to chloride penetration. The amount and depth of penetration of chlorides in the coated and uncoated parts of the slab were then determined. The results show conclusively that, in large exposed areas of concrete, chlorides diffuse both in the direction of depth and in a direction lateral to the depth of the element. The amount of chlorides and the distance of their lateral diffusion depend on the water-to-cement (w/c) ratio of the concrete and the duration of exposure. Concrete mixes with a high w/c ratio (0.75) are highly conducive to this lateral diffusion of chlorides. Although concrete mixes of lower w/c ratios (0.45 and 0.60) are less conducive to lateral diffusion of chlorides, in practice, all concretes should be considered to be prone to chloride diffusion in both the direction of gravity and the lateral direction because of the effects of cracking. In unprotected concrete, reducing the w/c ratio from 0.60 to 0.45 is far more effective in decreasing chloride penetration than that achieved by reducing the w/c ratio from 0.75 to 0.60. The acrylic-based surface coating system is totally resistant to chloride penetration.Key words: chloride diffusion, concrete slabs, durability, water-to-cement ratio, surface coating, lateral diffusion.

With high corrosion resistance, high tensile strength, electromagnetic neutrality, and lightweight, the newly emerged aramid and carbon fibre-reinforced plastic (FRP) tendons are being used for prestressed ground anchors. FRP ground anchors can be used when the corrosion protection of steel tendons becomes expensive or difficult to achieve, or where electromagnetic insulation is required. Although FRP tendons are more expensive than steel tendons, the total cost on transportation, handling, fabrication, drilling, installation, and maintenance can be significantly reduced due to lightweight and no requirement for corrosion protection. In addition, optical fibre sensors can be integrated into FRP tendons for permanent monitoring of ground anchors. This paper gives an introduction of the currently available aramid and carbon FRP tendons and an overview of the important properties of FRP tendons and their constituent materials. The design, fabrication, installation, and field applications of aramid and carbon FRP ground anchors are described. (A)

The corrosion of steel prestressing tendons exposed to deicing salts is increasingly becoming a significant problem in Canada. New fibre reinforced plastic (FRP) materials with high strength-to-weight ratios and noncorrosive characteristics are strong alternatives to solve this problem. Carbon fibre reinforced plastic (CFRP) is one of the most promising among available FRPs. Nevertheless, for CFRP rods to gain acceptance in Canada and other cold regions, their behaviour at low temperatures must be investigated. This paper describes an investigation of the feasibility of using CFRP LEADLINE rods to prestress concrete beams. The results of an experimental program on the short-term behaviour of CFRP prestressed concrete beams at low temperature (−27 °C) are discussed. A simple analytical model is used to predict the flexural response of CFRP beams at low temperature. The experimental results agree well with the analytical predictions. The behaviour of the CFRP tendons is shown to be unaffected by short-term exposure to this low temperature. Key words: carbon fibre, fibre reinforced plastic (FRP), advanced composite materials, prestressed concrete, low temperature, cold regions.

In unbonded, post-tensioned prestressed concrete slabs and beams, corrosion of prestressed tendons due to moisture ingress and their subsequent breakage has been identified as a major problem raising serious concern over the safety of aged structures. The paper presents a practical Bayesian approach to reliability assessment of such structures based on the inspection of a randomly selected sample of prestressing tendons. To minimize inspection costs, clear guidelines are presented for selecting the minimum sample size necessary to demonstrate that the annual probability of failure of an existing structure is below the target value of 10−5, implied in the Canadian Standards Association concrete design code CAN3-A23.3-M84. A systematic and cost-effective incremental strategy is developed for inspection of existing prestressed concrete structures. Key words: reliability, Bayes theorem, prestressed concrete, unbonded post-tensioned system, inspection, corrosion, probability distribution, CSA Standard CAN3-A23.3-M84, slab.

Sealers are used to enhance concrete durability through their ability to prevent moisture penetration and chloride intrusion, and, consequently, improve the freeze–thaw performance of the concrete and prevent corrosion of the steel reinforcement, respectively. This paper summarizes the results of three years of comprehensive field and laboratory investigations, undertaken at The University of Manitoba, to study the effectiveness of boiled linseed oil and mineral spirits in comparison to a silane and a siloxane sealer. The field investigation examined the performance of the sealers applied to the concrete pavements of a city street, a provincial highway, and an airport apron in Winnipeg, Manitoba. The laboratory investigation included sealer penetration, salt-water absorption and vapour transmission, abrasion, chloride ion intrusion, surface scaling resistance, and rapid freeze–thaw cycling. Test results of the field and laboratory investigation indicated that boiled linseed oil and mineral spirits was the most effective sealer at reducing chloride ion intrusion. It was found that boiled linseed oil and mineral spirits was comparable to siloxane and much more effective than the silane at reducing salt-water absorption. The results also indicated that boiled linseed oil and mineral spirits was most effective at reducing surface scaling and remained effective when subjected to salt-water absorption after abrasion. Key words: concrete sealers, linseed oil, silane, siloxane, absorption, scaling, chloride intrusion.

It is now well established that concrete deck slabs of slab-on-girder bridges subjected to concentrated loads develop an internal arching system provided that certain conditions of confinement of the concrete are met. Because of this arching system, the deck slab, being predominantly in compression, fails in punching shear rather than in flexure. This aspect of deck slab behaviour, coupled with the corrosion problems associated with steel reinforcement in concrete, has prompted the authors to investigate the feasibility of fibre-reinforced concrete decks that are entirely devoid of steel. Through tests on a small number of half-scale models, it has been established that fibre-reinforced concrete slab with inexpensive non-ferrous fibres is indeed feasible, provided that the top flanges of the steel girders are connected just below the deck by transverse steel straps and the concrete deck is joined to the girders and diaphragms by shear connectors. The straps and shear connectors together provide the restraint necessary for development of the internal arching system in the slab, whilst the fibres control cracking due to the effects of shrinkage and temperature in the concrete. This paper describes the exploratory model tests and presents their results. Key words: deck slab, fibre-reinforced concrete, internal arching, punching shear, slab-on-girder bridge.

Many aspects of the action of calcium chloride in concrete are ambiguous, controversial, or incompletely understood. Examples include: (a) the restrictive definition of calcium chloride as an accelerator; (b) the lack of clarity in prescribing the dosage for practical applications; (c) the classification of calcium chloride as an antifreezing agent; (d) the misconception regarding corrosion of reinforcement in the presence of CaCl2; (e) the divergence of opinion on the mechanism of action; and (f) incomplete understanding of the changes in the intrinsic properties of cement containing calcium chloride. This paper attempts to deal with these aspects citing typical examples.