Mechanical and Microstructural Investigation of Geopolymer Concrete Incorporating Recycled Waste Plastic Aggregate.

The effective use of waste materials is one of the key drivers in ensuring sustainability within the construction industry. This paper investigates the viability and efficacy of sustainably incorporating a polylactic acid-type plastic (WP) as a 10 mm natural coarse aggregate (NA) replacement in geopolymer concrete. Two types of concrete (ordinary Portland cement-OPC and geopolymer) were produced for completeness using a concrete formulation ratio of 1:2:3. The ordinary concrete binder control was prepared using 100% OPC at a water/binder ratio of 0.55, while the geopolymer concrete control used an optimum alkaline activator/precursor-A/P ratio (0.5) and sodium silicate to sodium hydroxide-SS/SH volume ratio (1.2/0.8). Using the same binder quantity as the control, four concrete batches were developed by replacing 10 mm NA with WP at 30 and 70 wt% for ordinary and geopolymer concrete. The mechanical performance of the developed concrete was assessed according to their appropriate standards, while a microstructural investigation was employed after 28 days of curing to identify any morphological changes and hydrated phases. The results illustrate the viability of incorporating WP in geopolymer concrete production at up to 70 wt% replacement despite some negative impacts on concrete performance. From a mechanical perspective, geopolymer concrete indicated a 46.7-58.3% strength development superiority over ordinary concrete with or without WP. The sample composition and texture quantified using automated scanning electron microscopy indicated that adding WP reduced the presence of pores within the microstructure of both concrete types. However, this was detrimental to the ordinary concrete due to the low interfacial zone (ITZ) between calcium silicate hydrate (CSH) gel and WP, resulting in the formation of cracks.

Petrological and geochemical characterisation of the sarsen stones at Stonehenge.

Little is known of the properties of the sarsen stones (or silcretes) that comprise the main architecture of Stonehenge. The only studies of rock struck from the monument date from the 19th century, while 20th century investigations have focussed on excavated debris without demonstrating a link to specific megaliths. Here, we present the first comprehensive analysis of sarsen samples taken directly from a Stonehenge megalith (Stone 58, in the centrally placed trilithon horseshoe). We apply state-of-the-art petrographic, mineralogical and geochemical techniques to two cores drilled from the stone during conservation work in 1958. Petrographic analyses demonstrate that Stone 58 is a highly indurated, grain-supported, structureless and texturally mature groundwater silcrete, comprising fine-to-medium grained quartz sand cemented by optically-continuous syntaxial quartz overgrowths. In addition to detrital quartz, trace quantities of silica-rich rock fragments, Fe-oxides/hydroxides and other minerals are present. Cathodoluminescence analyses show that the quartz cement developed as an initial <10 µm thick zone of non-luminescing quartz followed by ~16 separate quartz cement growth zones. Late-stage Fe-oxides/hydroxides and Ti-oxides line and/or infill some pores. Automated mineralogical analyses indicate that the sarsen preserves 7.2 to 9.2 area % porosity as a moderately-connected intergranular network. Geochemical data show that the sarsen is chemically pure, comprising 99.7 wt. % SiO2. The major and trace element chemistry is highly consistent within the stone, with the only magnitude variations being observed in Fe content. Non-quartz accessory minerals within the silcrete host sediments impart a trace element signature distinct from standard sedimentary and other crustal materials. 143Nd/144Nd isotope analyses suggest that these host sediments were likely derived from eroded Mesozoic rocks, and that these Mesozoic rocks incorporated much older Mesoproterozoic material. The chemistry of Stone 58 has been identified recently as representative of 50 of the 52 remaining sarsens at Stonehenge. These results are therefore representative of the main stone type used to build what is arguably the most important Late Neolithic monument in Europe.

Identification and analysis of man-made geological product particles to aid forensic investigation of provenance in the built environment.

Small (sub-mm) fragments of construction materials derived from geological products are common components of soil and dust samples from urban and industrial environments. These particles increase the complexity of a soil through the admixture of man-made materials with natural minerals within the soil matrix. One application of such indicators is in nuclear security investigations, where there is a requirement to determine the origin and process history of a nuclear material discovered outside of regulatory control. In such cases, analysis of trace environmental materials accumulated from locations where the material was produced, transported and stored may help to establish material provenance. Given a suitable sample, the recognition of particles derived from construction materials can aid such investigations by helping to determine potentially distinctive properties of the originating environment, such as types and potential sources of building materials. Correct identification of man-made particles is also necessary to prevent misidentification of soil mineral particle profiles, and therefore enable determination of the natural mineralogy of associated soil material. In this paper the application of automated mineralogy (based on scanning electron microscopy) analysis for the characterisation of sub-mm particles of man-made construction materials is tested. Thirty-three examples of concrete, construction blocks, cement, brick, plaster and render were analysed. Based on both the particle texture and the minerals/chemical phases present, it is shown that the different construction materials can be readily recognised and characterised. Comparison of natural and artificial cemented particles derived from sedimentary rocks and concrete, and of natural and artificial fine-grained particles derived from mudstone and brick fragments highlights how salient features can be recognised from automated mineralogy data to distinguish man-made geological products from soil mineral assemblages.

The Search for "Fred": An Unusual Vertical Burial Case.

Police witness intelligence stated a murdered adult male "Fred" had been vertically buried in wooded hilly terrain 30 years ago in the Midlands, U.K. Conventional search methods were unsuccessful; therefore, the police requested a geophysical investigation to be undertaken to determine whether "Fred" could be detected. A multiphased geophysical approach was conducted, using bulk ground conductivity and metal detectors, then follow-up magnetics and ground penetrating radar (GPR) survey profiles on electromagnetic (EM) anomalous areas. A tight grid pattern was used to account for the reduced target size. Relatively high-resolution EM and GPR techniques were determined optimal for this terrain and sandy soil. Geophysical anomalies were identified and the most promising intrusively investigated, and this was found to be a large boulder and tree roots. Study implications suggest careful multiphase geophysical surveys are best practice and give confidence in cold case searches. This study yielded a no-body result, effectively saving police time and costs from further investigations.

Testing the efficiency of soil recovery from clothing for analysis by SEM-EDS.

Soil forensics is widely used to test associations between questioned samples and known locations. Improvements in analytical techniques mean that increasingly small amounts of soil can be analysed. This is particularly important as individual traces of soil relate to individual geographical locations and need to be analysed separately. However, improved analytical capability means that methods of soil recovery also need to improve. Three different methods of recovering soil from clothing for subsequent analysis by scanning electron microscopy with linked energy dispersive spectrometers (SEM-EDS) were tested. Three fabric types were analysed with duplicate samples being recovered by (a) dry brushing, (b) direct sticky tag lifting and (c) washing. The resultant soil samples were analysed using automated scanning electron microscopy with linked energy dispersive spectrometers. All three methods recovered a population of particles, the mineralogy of which corresponded with the control soil sample. However, the sticky tags recovered between 6 and 8× more particles than either the dry brushings or the washing samples. The direct lifting of trace soil evidence using sticky tags also has the advantage that the context of the analysed soil sample can be clearly imaged prior to recovery. Any soil evidence can be observed in context with the surface it is to be removed from, and as such, sampling can be targeted to specific areas or specific phases of soil deposition on a surface.

Composition and abundance of particles present on "powder-free" examination gloves.

Seven widely available brands of powder free nitrile gloves, commonly used in forensic laboratories during the handling of exhibits were examined. Samples were collected from the outer surfaces of the gloves and the particle types present were characterised using automated mineral analysis. Particles less than 10µm in diameter are abundant on the surface of all of the gloves examined. Although the particles are dominated by common compounds/minerals (e.g. calcite, gypsum, NaCl, Fe oxides/carbonates, Al oxides, quartz, plagioclase, kaolinite) each glove brand analysed has a distinct population of particles present which allows the samples to be differentiated from each other. These particle types may be transferred from the gloves to exhibits during handling. In addition, these distinct populations of particles may be transferred to anyone wearing powder free nitrile gloves.

Automated mineralogical analysis of PM10: new parameters for assessing PM toxicity.

This work provides the first automated mineralogical/phase assessment of urban airborne PM10 and a new method for determining particle surface mineralogy (PSM), which is a major control on PM toxicity in the lung. PM10 was analyzed on a TEOM filter (Aug.-Sept. 2006 collection) from the London Air Quality Network Bexley, East London, U.K. A cross-section of the filter was analyzed using a QEMSCAN automated mineralogical analysis system which provided 381,981 points of analysis for 14,525 particles over a period of 9 h 54 min. The method had a detection limit for individual mineral components of 0.05 ppm (by area). Particle shape and mineralogical characteristics were determined for particles in the size ranges PM(10-4), PM(4-2.5), and PM(2.5-0.8). The PM(2.5-0.8) fraction contained 2 orders of magnitude more mineral particles than the PM(10-4) and PM(4-2.5) fractions, however the PM(10-4) fraction forms 94% and 79% of the mineral mass and surface area, respectively. PSM of the PM10 was dominated by gypsum (36%), plagioclase (16%), Na sulphates (8%), and Fe-S-O phases (8%) in the PM(10-2.5), which may be important in explaining the toxicity of the coarse fraction. The wider implications of the study are discussed.