Arch bridges – unlocking their potential

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. </jats:p

Performance of Anaerobic Digestion Systems: A Review

Anaerobic digesters contain extreme environments that change drastically during the production cycle. Organic material is broken down first into amino and fatty acids, then into volatile fatty acids, ammonia, CO2, H2S and other by-products. These acids and alcohols are converted to acetic acid as well as CO2 and H2, which is then used to create methane. All these biological processes mean that the pH, temperature and type of bacteria vary, creating conditions outside the scope of current standards, such as a concentration of ammonium ions 8 times greater than the upper limit of the XA3 class of highly aggressive chemical attack for concrete in BS EN 206-1:2000. Depending on the source, the concrete may be exposed to heavy metals, antibiotics or surfactants, which are not even considered by current standards. Anaerobic digestion is a growing industry, with 576 plants currently in the UK using organic wastes for biogas generation and reduction in the volume of waste going to landfill. £160m was invested in the UK sector between 2013 and the start of 2015, $2 billion was invested across Europe in 2015, with an estimated$8 billion European investment by 2024. This means that anaerobic digestion has sizable economic value as well as positive environmental effects. However, as part of maximising these benefits, it is necessary to better understand the chemical and biological attack the concrete that is used to build these digesters undergoes, so that steps can be taken towards limiting premature deterioration. This article will show the current gaps in both knowledge and legislation, with the aim of promoting further research into the aforementioned areas

Efficient mix design of alkali activated slag concretes based on packing fraction of ingredients and paste thickness

Many studies have been dedicated to the properties of alkali-activated slag concretes as a form of low-carbon high performance concrete, but less work has been focused on the application of mix design procedures to have a dense, durable and cost-efficient alkali-activated concrete. This study proposes a method for selecting the mix proportions of alkali-activated concretes based on the packing fraction of materials. The design method is based on the selection of the volumetric proportions of sand and coarse aggregate according to an ideal particle gradation curve. To validate this method, trial castings were carried out for concrete mixes containing alkali activated slag (AAS) with different paste contents to suggest the most cost-efficient concrete for different classes of workability and applications. Compaction and pore structure of these mixes studied by optical microscopy have shown that the design of AAS concretes based on the proposed method resulted in a dense and workable mix

Influence of chloride ions on progress of carbonation in concretes

Our infrastructure and environment face unprecedented challenges in addressing a low carbon future with limited natural resources, expanding population, increased pollution and climatic uncertainties. Adaptation and innovations must therefore play a vital role in addressing the anticipated wide ranging complex scenarios ahead. The environment in which construction materials will need to function will become far more complex and aggressive and hence a fundamental revaluation of the most appropriate materials for future infrastructure and environment will be required in order to tackle those challenges. This paper focuses on a class of construction materials, both old and new, based on magnesia (MgO). They include a wide range of materials from those that contain MgO as a small additive to those which solely consist of MgO. They include concrete with MgO as an expansive additive, pervious concrete, alkali-activated cements, magnesium phosphate cements, carbonated products, stabilising additives for ground improvement, self-healing additives, carbon capture and storage materials and binders for waste 105 and contaminated land remediation. Those materials and products offer a range of technical and sustainability benefits for a range of structural, geotechnical and environmental applications. The paper highlights the applications and benefits that would be achieved with magnesia-bearing construction materials

Monitoring the hygrothermal and ventilation performance of retrofitted clay brick solid wall houses with internal insulation: Two UK case studies

This work assesses the hygrothermal and ventilation performance of two ‘hard-to-treat’ historic, clay brick, solid wall houses that are internally insulated. Retrofit A is a two bedroom bungalow with the addition of internal plasterboard and air cavity and Retrofit B is a 5 bedroom house with sheep wool, phenolic and plasterboard insulation. To evaluate the long term performance of the retrofit measures, the testing is carried out 7 and 8 years respectively after completion. The first part of the work investigates whole building hygrothermal performance, ventilation and internal conditions. It was found that both retrofits are operating below specification in regards to their ventilation performance. An in-situ performance based specification for mechanical ventilation via CO2 monitoring is proposed. The second part focuses on the hygrothermal behaviour of the clay brick wall assembly. Both presented high relative humidity within critical layers of the wall make up. In Retrofit A the wall thermal transmittance was found to be much higher than designed due to inappropriate construction detailing while Retrofit B showed excellent thermal performance and minimal effects of thermal bridging