This journal, which has become well established as a reputable and reliable guide for busy practising engineers during its relatively short life, seeks to provide balanced coverage for a full range of construction materials; for example, ranging from timber to metals, from asphalts to fired clay products, from plastics to plaster and many, many more, all variously historic, modern or innovative. Nevertheless, the submitted papers continue to be dominated by concrete and the multifarious constituents and prospective constituents of concrete, as amply demonstrated by three of the five excellent papers in this issue.
Perhaps this concrete dominance is not surprising, nor necessarily unacceptable, given the persistent and unchallenged position of concrete as by far the most widely used construction material worldwide, which has powerful influences on both civil and structural engineers and, indeed, on all the world's inhabitants. Many have a love–hate relationship with concrete, relying on it for highways and other transport infrastructure, major civil engineering structures (such as dams, docks, power stations and flood defences) and a wide range of building works, yet frequently also regarding it disparagingly (as used in the deprecating term ‘concrete jungle’ for bleak urban developments) and today definitely with added environmental suspicion.
In continuous use since at least the time of the Ancient Greeks, the modern manifestations of concrete remain a fabulously versatile material in construction, maturing into a hardened product exhibiting a range of desirable qualities. The present product is relatively complicated compared to its simple yet revolutionary beginnings, yielding a range of improved properties, as variously required by engineers, architects and all those charged with turning concepts and designs into functioning structures. At the same time, the growing historic stock of concrete facilities and edifices continue to give rise to concern, especially regarding longevity and appearance, so that topics of threats to durability and the means of either prevention or remedy, continue to attract researchers. Moving forward, the demands of ever more challenging structures have led to the desire for concretes that need minimal human activity in their placement and/or which deliver ever higher strengths in their hardened form; moreover, after a disappointing start in the final decades of the 20th century, there is now a return to the search for fair-faced direct concrete finishes for architectural applications.
All this and more gives rise to the rich variety of concrete-related topics that are reported in this journal, alongside a host of helpful papers and briefings on other types of construction materials. This particular issue (detailed in the following paragraphs) starts with a fascinating briefing on the ballistic resistance of ‘insulated concrete formwork’ (ICF), about the robustness of the building system, rather than the concrete infilling material. Afterwards, there is an insightful and practically helpful paper on the improved interpretation of standard tests for gypsiferous roadbed soils in Iraq and other parts of the Middle East. The last three papers are about concrete. The first of these is a thought-provoking work, which suggests that concrete structures, which ‘form an essential part of the world’, might be at an enhanced risk of deterioration as a result of climate change. Two further papers consider a new approach to the alkali-reactivity assessment of aggregates and the mechanical effect of the environmentally beneficial process of replacing some of the cement with limestone fines.
Barnes and Hanrahan (2014) address ICF structures, which are new to the UK, but have been used in North America since the 1960s and become mainstream in some parts of Europe. They have been found to display good blast resistance and are accordingly used in war zones. This briefing concerns ICF structures, using a variety of materials to fill the space between the permanent insulation formwork (unbound materials as well as the usual concrete) and their resistance to repeated small arms fire (using an AK 47 assault rifle!). The authors found that ICF filled with concrete provided enduring ballistic protection, whilst ICF filled with coarse aggregate (rock type not stated) or glass cullet also had potential as a ballistic barrier and could be constructed quickly.
Razouki et al. (2014) focus on an improved interpretation of the California bearing ratio (CBR) for various types of gypsiferous subgrade and embankment soils used for road construction in Iraq and neighbouring regions. During soaking, such materials typically become inhomogeneous, leading to separate load-penetration tests being recommended for the top (CBRT) and bottom (CBRB) of the specimen. Razouki and his colleagues carried out a systematic test programme on gypsiferous (25 to 30% gypsum) sand and clay soils from around Baghdad, seeking a correlation between CBRT and CBRB. They found that the CBR was always greater for CBRB than for CBRT with these materials, but that the rate of decrease in CBR on soaking gradually slowed, such that the ratio of soaked to unsoaked conditions could be established after 120 days of soaking. A strong correlation was found between CBRT and CBRB, enabling the latter to be estimated from the former, variously for sandy gypsiferous and clayey gypsiferous soils.
Whatever its causes, there is growing international acceptance of global climate change. Talukdar et al. (2014) consider that the risk of such changes will accelerate and that their potential impact on concrete infrastructure has been overlooked. They have focused on the influence of the likely climate changes on the familiar process of concrete carbonation, which progressively endangers the protection that concrete usually provides to its embedded steel reinforcement. Their study of climate change and carbonation models has confirmed that carbonation rates and depths might ultimately be greater than presently anticipated, with resultant earlier initiation of reinforcement corrosion. New reinforced concrete construction could improve the thickness and/or quality of the cover in compensation.
Ghanem et al. (2014) have contributed to the continuing debate about alkali-silica reactivity in concrete, by considering a new kinetic approach to the accelerated testing of aggregates. Three aggregates (two gravels and a rhyolite), all found to be expansive in the accelerated mortar-bar test, were subjected to testing in a dilatometer, while variously being soaked in three concentrations of alkaline solution (sodium hydroxide, with or without calcium hydroxide) and stored at three temperatures. The authors show that such results can potentially help to characterise and predict reactivity of an aggregate, using its ‘activation energy’ (Ea). Doubtless further work with a wider range of reactive and non-reactive aggregate combinations will determine the usefulness of the proposed method compared with the established procedures.
Use of limestone fines to replace proportions of the cement or sand in concrete is seen as a contribution to sustainable development world-wide, and Menadi et al. (2014) have investigated the effect of some cement replacement by limestone fines on the fracture behaviour of mortar and concrete beams. Their work confirmed that both strength and fracture parameters were reduced with increasing proportions of limestone fines, especially with cement replacements exceeding 5%.
I trust that you will enjoy reading the papers in this issue as much as I have appreciated reviewing them for this editorial.
