Abstract: Ordinary Portland cement (OPC) is known for its significant contribution to carbon dioxide emissions. Geopolymer has a lower footprint in terms of CO2 emissions and has been considered as an alternative for OPC. A well-developed understanding of the use of fly-ash-based and slag-based geopolymers as separate systems has been reached in the literature, specifically regarding their mechanical properties. However, the microstructural and durability of the combined system after slag addition introduces more interactive gels and complex microstructural formations. The microstructural changes of complex blended systems contribute to significant advances in the durability of fly ash/slag geopolymers. In the present review, the setting time, microstructural properties (gel phase development, permeability properties, shrinkage behavior), and durability (chloride resistance, sulfate attack, and carbonatation), as discussed literature, are studied and summarized to simplify and draw conclusions.

Abstract: Variations in the nature and extent of southern Africa’s winter rainfall zone (WRZ) have the potential to provide important information concerning the nature of long-term climate change at both regional and hemispheric scales. Positioned at the interface between tropical and temperate systems, southern Africa’s climate is influenced by shifts in the Intertropical Convergence Zone, the westerlies, and the development and position of continental and oceanic anticyclones. Over the last glacial–interglacial cycle substantial changes in the amount and seasonality of precipitation across the subcontinent have been linked to the relative dominance of these systems. Central to this discussion has been the extent to which the region’s glacial climates would have been affected by expansions of Antarctic sea-ice, equatorward migrations of the westerlies, more frequent/intense winter storms and an expanded WRZ. This paper reviews the developing body of evidence pertaining to shifts in the WRZ, and the evolution of ideas that have been presented to explain the patterns observed. Dividing the region into three separate axes, along the western and southern margins of the continent and across the interior into the Karoo and the Kalahari, a range of evidence from both terrestrial sites and marine cores is considered, and potential expansions of the WRZ expansions are explored. Despite the limitations of many of the region’s proxy records, a coherent pattern has begun to develop of a significantly expanded WRZ during phases of the last glacial period, with the best-documented being between 32–17 ka. While more detailed inferences will require the recovery and analysis of longer and better-dated records, this synthesis provides a new baseline for further research in this key region.

Abstract: High concentrations of uranium (mean=620μg/L) were detected in water samples collected from private wells in a residential community. Based on isotopic analyses, the source of the uranium contamination appeared to be from naturally occurring geological deposits. In homes where well water concentrations of uranium exceeded the drinking water standard, the residents were advised to use an alternate water source for potable purposes. Several months after the residents had stopped drinking the water, urine samples were collected and tested for uranium. Elevated concentrations of uranium (mean=0.40μg/g creatinine) were detected in urine samples, and 85 percent of the urine uranium concentrations exceeded the 95th percentile concentration of a national reference population. Urine uranium concentrations were positively correlated with water uranium concentrations, but not with the participants’ ages or how long they had been drinking the water. Six months later, a second urine sample was collected and tested for uranium. Urine uranium concentrations decreased in most (63 percent) of the people. In those people with the highest initial urine uranium concentrations, the urine levels decreased an average of 78 percent. However, urine uranium concentrations remained elevated (mean=0.27μg/g), and 87 percent of the urine uranium concentrations exceeded the 95th percentile concentration of the reference population. The results of this investigation demonstrated that after long-term ingestion of uranium in drinking water, elevated concentrations of uranium in urine could be detected up to 10 months after exposure had stopped.

Abstract: Rainwater harvesting (RWH) systems have been developed to compensate for shortage in the water supply worldwide. Such systems are not very common in arid areas, particularly in the Gulf Region, due to the scarcity of rainfall and their reduced efficiency in covering water demand and reducing water consumption rates. In spite of this, RWH systems have the potential to reduce urban flood risks, particularly in densely populated areas. This study aimed to assess the potential use of RWH systems as urban flood mitigation measures in arid areas. Their utility in the retention of stormwater runoff and the reduction of water depth and extent were evaluated. The study was conducted in a residential area in Bahrain that experienced waterlogging after heavy rainfall events. The water demand patterns of housing units were analyzed, and the daily water balance for RWH tanks was evaluated. The effect of the implementation of RWH systems on the flood volume was evaluated with a two-dimensional hydrodynamic model. Flood simulations were conducted in several rainfall scenarios with different probabilities of occurrence. The results showed significant reductions in the flood depth and flood extent, but these effects were highly dependent on the rainfall intensity of the event. RWH systems are effective flood mitigation measures, particularly in urban arid regions short of proper stormwater control infrastructure, and they enhance the resilience of the built environment to urban floods.

Abstract: Settlement in Israel’s Negev desert historically has been dependent on water conservation techniques. Fieldwork carried out on settlement sites constructed during the Byzantine period, when agriculture and trade flourished, revealed a variety of water installations some of which are in use today. Perennial springs in the Negev are generally small and difficult of access. Cisterns were the most common conservation devices and came in both large, enclosed and single, open forms. Cisterns were common particularly in the towns, where they were usually built as part of house foundations. Dams were discovered at several sites but proved to be inefficient and easily abandoned because of evaporation and siltation problems. Public reservoirs were part of the structure of the largest towns and were open and among the larges structures uncovered at settlement sites. Wells were distributed widely throughout the desert and were part of the only conservation system that did not depend directly on surface rainfall. A qanat system was located in the eastern Negev dating from the late settlement period before the area was abandoned at the turn of the eighth century. These various water systems raise questions about their builders and their origins, and suggests that builders originating in more humid Mediterranean environments tended to produce less adaptable installations than builders derived from the south or the east.