Construction waste accounts for more than 75% of all solid waste in Qatar and the majority is landfilled in the desert outside the capital, Doha, contaminating an increasingly large area of land. Significant improvements in the management of this waste are required if the target in the National Development Strategy of recycling 38% of solid waste by 2016 is to be met. A collaborative approach is being taken to address construction waste, involving government departments, research organisations and industry. Codes of practice for construction and demolition are being developed to improve the quality of waste on site. Much of the construction and demolition waste can potentially be recycled as aggregate, and construction trials have been carried out to demonstrate use in high-value applications such as concrete. However, to effectively implement the use of recycled aggregates, a range of further measures are required, including amending the Qatar Construction Specifications, addressing concerns about quality and durability, and raising awareness of the economic and environmental benefits. The collaborative approach is enabling real progress to be made. The issues facing Qatar are applicable to other Middle East and North Africa countries undergoing similar rapid expansion.

Assigned to their outstanding physicochemical properties, TiO2-based materials have been studied in various applications. Herein, TiO2 doped with different Mo contents (Mo-TiO2) was synthesized via a microwave-assisted solvothermal approach. This was achieved using titanium (IV) butoxide and molybdenum (III) chloride as a precursor and dodecylamine as a surface directing agent. The uniform effective heating delivered by microwave heating reduced the reaction time to less than 30 min, representing several orders of magnitude lower than conventional heating methods. The average particle size ranged between 9.7 and 27.5 nm and it decreased with increasing the Mo content. Furthermore, Mo-TiO2 revealed mesoporous architectures with a high surface area ranging between 170 and 260 m2 g−1, which is superior compared to previously reported Mo-doped TiO2. The performance of Mo-TiO2 was evaluated towards the adsorption of Rhodamine B (RhB). In contrast to TiO2, which revealed negligible adsorption for RhB, Mo-doped samples depicted rapid adsorption for RhB, with a rate that increased with the increase in Mo content. Additionally, Mo-TiO2 expressed enhanced adsorption kinetics for RhB compared to state-of-the-art adsorbents. The introduced synthesis procedure holds a grand promise for the versatile synthesis of metal-doped TiO2 nanostructures with outstanding physicochemical properties.

Autism spectrum disorder (ASD) is an umbrella term that includes many different disorders that affect the development, communication, and behavior of an individual. Prevalence of ASD has risen exponentially in the past couple of decades. ASD has a complex etiology and traditionally recognized risk factors only account for a small percentage of incidence of the disorder. Recent studies have examined factors beyond the conventional risk factors (e.g., environmental pollution). There has been an increase in air pollution since the beginning of industrialization. Most environmental pollutants cause toxicities through activation of several cellular receptors, such as the aryl hydrocarbon receptor (AhR)/cytochrome P450 (CYPs) pathway. There is little research on the involvement of AhR in contributing to ASD. Although a few reviews have discussed and addressed the link between increased prevalence of ASD and exposure to environmental pollutants, the mechanism governing this effect, specifically the role of AhR in ASD development and the molecular mechanisms involved, have not been discussed or reviewed before. This article reviews the state of knowledge regarding the impact of the AhR/CYP pathway modulation upon exposure to environmental pollutants on ASD risk, incidence, and development. It also explores the molecular mechanisms involved, such as epigenesis and polymorphism. In addition, the review explores possible new AhR-mediated mechanisms of several drugs used for treatment of ASD, such as sulforaphane, resveratrol, haloperidol, and metformin.

In hot desert regions, attention is turning to local sources of aggregate that were previously regarded as ‘too difficult' to exploit. This paper describes an investigation of such a deposit in Qatar. The material, known as Wadi gravel, is a gravelly sand of Tertiary age cemented by gypsum. A field survey found the gravel content to be in the range of 10 to 20%. As-dug samples had excessively high sulfate content, which could not be removed with conventional aggregate operations. However, intensive treatment in a local sand-processing plant using multi-stage crushing, screening and washing reduced the sulfate to acceptable levels. Petrographic analysis was carried out to identify rock types potentially susceptible to Alkali Silica Reaction (ASR). Trial concrete mixes using the processed Wadi gravel were found to produce satisfactory C40 and C60 concrete. Full-scale building trials were constructed to demonstrate the practicality of using the gravel and assess in-service performance. The smooth surface and rounded particles of Wadi gravel improved the concrete workability and strength, and durability-related properties were similar to concrete made with imported gabbro. Strata similar to Wadi gravel occur widely in hot desert regions and could be useful sources of coarse and fine aggregate for concrete.

Deposits of Wadi gravel are available in many parts of the Gulf region, but not widely utilized as aggregate for concrete, mainly due to the possibility of internal sulfate attack, plus the perceived risk of alkali aggregate reactivity (AAR). This paper describes the investigations for AAR of the Wadi gravel in this case, as part of the wider study described in Part 1 of this paper.Wadi gravel from the Mekaines site in Qatar was subjected to petrographic analysis, plus the gel-pat and accelerated mortar-bar test methods. The AAR potential was found to be low to normal. The accelerated mortar-bar test exhibited ‘innocuous’ behaviour after 14 days of immersion in alkali solution. When separately testing the constituent rock types of the Wadi gravel, limestone and quartz returned innocuous results, while rhyolite, granite and quartzite returned potentially alkali silica reactive (ASR) results and some reaction was confirmed using post-expansion petrographic examination.Wadi gravel was classified as potentially reactive in the RILEM AAR-4.1 accelerated concrete prism test, but of ‘low reactivity’ in the BS 812-123 test over the longer period of 12 months. Overcoming the potential problems of gypsum content and AAR successfully provides a valuable local resource of Wadi gravel aggregate for concrete.