An in situ air permeability test method that does not require assumptions for the often-difficult unidirectional flow has been developed to calculate the air permeability coefficient of the near surface concrete. The proposed method involves applying a constant pressure head to a surface mounted ring and measuring the steady state air flow rates. The analysis is based on modification of the flownet theory, which needs a calibration factor accounting for the influence of specimen and ring geometries. Effects of test area, width of seal, depth and width of test specimen were investigated using numerical simulation of the air flow. The repeatability of the proposed test method was assessed by the signal noise ratio (SNR) and discrimination ratio (DR). A new formula is offered and it only requires the steady state air flow rate to calculate the coefficient of air permeability, thus assisting engineers and researchers to quickly determine this property of structural concretes.

Determining the water permeability of concrete in structures remains a challenge because of difficulties in removing the influence of its moisture content. Saturating concrete with water could be one option, but this is not easy to achieve on site. This paper reports a testing programme carried out to assess the reliability and effectiveness of two field saturation methods, viz. vacuum saturation and ponding. The water permeability test results after applying the vacuum saturation and ponding were compared with that obtained after incremental immersion. It was found that ponding was unable to remove the influence of moisture, whilst vacuum saturation was effective for wet concretes. The results obtained from the electrical resistance measurements after incremental immersion suggested that the water permeability of concretes can be accurately determined by carrying out in situ permeability tests if the near surface region up to a depth of 25 mm is fully saturated.

Saturating high performance concrete (HPC) on site for assessing water permeability is a challenge. This paper reports a testing programme established to assess the reliability and efficiency of two field saturation approaches, viz. vacuum saturation and ponding. The water permeability test results after applying the vacuum saturation and ponding were compared with that after incremental immersion. It is found that ponding was unable to remove the influence of moisture, while vacuum saturation can achieve this for wet concretes. Although the influence of moisture can be removed for different HPCs with high initial moisture contents by using the vacuum saturation method, it is not effective when the initial moisture content is low. The results obtained from numerical simulation model and the electrical resistance measurements after incremental immersion suggested that the water permeability of HPCs can be accurately determined if the surface region (140 mm width and 25 mm depth) is fully saturated.

The 1840's Teewell Hill arch bridge, in the suburbs of Bristol, UK, was no longer adequate for increasing local traffic levels and needed to be widened. Several widening options were considered and it was concluded that the innovative ‘FlexiArch’ would best accommodate the complex geometry of the existing structure while minimising social and economic impacts. In order to elegantly accommodate the raked spandrel walls of the existing bridge Macrete and WSP|Parsons Brinckerhoff worked collaboratively to produce a custom-designed, high-quality, precast concrete FlexiArch, which matched the contours of the existing bridge. As the FlexiArch system has no corrodible reinforcement, it is highly sustainable and will result in reduced maintenance, as for the existing bridge. The elimination of centring and speed of construction (hours not months) minimised disruption to road traffic and to cyclists on the cycle network below the bridge – a key project criterion required by the client. Thus, in addition to addressing an accident black spot, the FlexiArch solution provided South Gloucestershire Council (the client) with an aesthetically pleasing and fully functional solution at a competitive cost.

Determining the water permeability of concrete in structures remains a conundrum because of difficulties in removing the influences of moisture. This study describes the extended flow-net theory developed on the basis of the two-pressure-head concept, which provides a means of measuring permeability under the partially saturated condition. Surface-mounted tests and standard laboratory water penetration tests were carried out to verify this approach. Before determining the water permeability, steady-state flow rates at two different pressure levels were evaluated and the effects of initial moisture conditions on flow behavior were investigated. The results indicate that the proposed approach does offer a useful means of determining the water permeability of structural concrete, although it cannot be claimed to be universally applicable for all moisture conditions likely to be encountered in practice.

In this paper, a review of techniques is given so that both, the challenges and opportunities for assessing transport properties of high-performance concrete, are highlighted. A knowledge of performance of structural concrete is required for design and compliance purposes. One driving force for the use of high performance concretes (HPC) is enhanced durability yet it would be wrong to assume that all HPCs can deliver the desired performance level. In situ characterisation of the permeation properties of concrete is the most viable means for assessing durability and has become increasingly important over the past 20 years. A variety of methods exist that provide a range of parameters, e.g. air permeability, water absorption rate, sorptivity and chloride migration coefficient.

Arch bridges are strong, durable, aesthetically pleasing and require little maintenance but very few have been built since the early 1900s. However, this trend has changed as more than 60 FlexiArch bridges have been installed since the system was launched in 2007. The FlexiArch uses precast concrete voussoirs, requires neither corrodible reinforcement, nor centring, can be installed in hours and is contractor friendly. Details of this innovative method of construction and installation of arch bridges are given and the enormous potential of the system for multi-span viaducts is also highlighted.

Chloride-induced corrosion of steel in reinforced concrete structures is one of the main problems affecting their durability, but most previous research projects and case studies have focused on concretes without cracks or not subjected to any structural load. Although it has been recognised that structural cracks do influence the chloride transport and chloride induced corrosion in reinforced concrete structures, there is little published work on the influence of micro-cracks due to service loads on these properties. Therefore the effect of micro-cracks caused by loading on chloride transport into concrete was studied. Four different stress levels (0%, 25%, 50% and 75% of the stress at ultimate load – fu) were applied to 100mm diameter concrete discs and chloride migration was measured using a bespoke test setup based on the NT BUILD 492 test. The effects of replacing Portland cement CEMI by ground granulated blast-furnace slag (GGBS), pulverised fuel ash (PFA) and silica fume (SF) on chloride transport in concrete under sustained loading were studied. The results have indicated that chloride migration coefficients changed little when the stress level was below 50% of the fu; however, it is desirable to keep concrete stress less than 25% fu if this is practical. The effect of removing the load on the change of chloride migration coefficient was also studied. A recovery of around 50% of the increased chloride migration coefficient was found in the case of concretes subjected to 75% of the fu when the load was removed.

Arch bridges are strong, durable, aesthetically pleasing and require little maintenance but very few have been built since the early 1900's. However, there has been a mini renaissance of this proven form of construction since the FlexiArch was launched in 2007 as it uses precast concrete voussoirs, has no corrodible reinforcement, does not need centring, can be installed in hours and is contractor friendly. After installation the FlexiArch system acts like a traditional arch and not surprisingly, has been found to be exceptionally strong and stiff. To date over fifty FlexiArch bridges ranging in span from 4-16 metres have been installed in the UK/Ireland and in this paper exemplars will be given. As it is very sustainable and has very low full life cycle costs, the need for longer spans (30 metres plus), and multi-span viaducts has been recognized and solutions under development will be described.

Adrian Long finds this to be a well-written and useful book, which will be of value to structural engineers involved in reinforced concrete design and, particularly, to lecturers thanks to its extensive list of references to research papers.

This paper investigates the use of solid and hollow core voussoir blocks in an innovative FlexiArch bridge system. The system is formed from precast concrete voussoirs connected by a polymeric reinforcement, enabling the arch to be built and transported as a flat pack and lifted into shape after delivery to site, thus avoiding the use of centring for construction. This research is novel in that it trials and compares the use of hollow core and solid FlexiArch rings in third-scale models with granular backfill. The use of hollow core voussoirs reduces the loading on the polymeric reinforcement during construction and should allow for increased spans. This paper presents the test results of two similar third-scale 5 m × 2 m (span × rise) arch systems, using both solid and hollow construction. The use of hollow core voussoir blocks reduces the weight of the system. Non-linear finite-element analysis (NLFEA) has been used to further compare arch behaviour and the thrustline position.

The design, development and evaluation of an optical fibre pH sensor for monitoring pH in the alkaline region are discussed in detail in this paper. The design of this specific pH sensor is based on the pH induced change in fluorescence intensity of a coumarin imidazole dye which is covalently attached to a polymer network and then fixed to the distal end of an optical fibre. The sensor provides a response over a pH range of 10.0–13.2 with an acceptable response rate of around 50min, having shown a very good stability over a period of longer than 20 months thus far. The sensor has also demonstrated little cross-sensitivity to ionic strength (IS) and also excellent photostability through a series of laboratory tests. These features make this type of sensor potentially well suited for in situ long term monitoring of pH in concrete structures, to enhance structural monitoring in the civil engineering sector.

Authors from Queen's University Belfast and Macrete Ireland Ltd cite four recent bridge projects that have benefitted from an innovative system, providing a cost-effective alternative to the standard masonry arch.

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The presence of chloride ions is one of the primary factors causing the degradation of reinforced concrete structures. An investigation to monitor ingress of chlorides during a 24-week wetting and drying exposure regime to simulate conditions in which multiple-mode transport mechanisms are active was conducted on a variety of binders. Penetration was evaluated using free and total chloride profiles. Acid extraction of chlorides is quantitatively reliable and practical for assessing penetration. X-ray diffraction was used to determine the presence of bound chlorides and carbonation. The ability of the cement blends to resist chloride penetration was, from best to worst, ground granulated blast-furnace slag, microsilica, pulverised-fuel ash, Portland cement. The effect of carbonation on binding capability was observed and the relative quantity of chlorides also showed a correlation with the amount of chlorides bound in the form of Friedel's salt.

Masonry arches are strong, durable, aesthetically pleasing and largely maintenance free, yet since 1900 there has been a dramatic decline in their use. However, designers, contractors and clients now have access to a new method of constructing arches incorporating precast concrete voussoirs interconnected via polymeric reinforcement and a concrete screed. No centring is necessary, as the FlexiArch, when it is lifted, transforms under the forces of gravity into the desired arch shape. After discussing general aspects of innovation, the basic concept of the arch bridge system is presented along with technological advances since it was patented. Experiences gained from building over 40 FlexiArch bridges in the UK and Ireland and from model and full-scale tests carried out to validate the system during installation and in service are described. Thus under load the system behaves like a traditional masonry arch and existing analysis methods can be used for design and assessment.