Structural performance of fibrous plaster. Part 1:Physical and mechanical properties of hessian and glass fibre reinforced gypsum composites

Hessian fibre-reinforced gypsum, known as fibrous plaster, is a common material used for the manufacture of decorative features, including ceilings and walls in historic buildings, such as theatres and ballrooms, since the mid 19th century. It is still fabricated with modern materials for the decoration of new buildings in the UK, the Middle East and elsewhere. Following several recent failures of historic fibrous plaster ceilings in England, there is an urgent need to understand how these materials perform. There is no previous scientific investigation into the physical and mechanical properties of this material.As an initial experimental study, the microstructure of low and high density gypsum plaster were evaluated together with traditional hessian fabrics and modern glass fabrics, which are supplementing or replacing hessian fabrics. The chemical and physical characteristics were evaluated by X-ray diffraction,mercury intrusion porosimetry and dynamic vapour sorption. For the hessian, fibre density was measured and single filament strength measured to ascertain the effect of long-term ageing in new and historic material. Flexural tests were performed on gypsum plaster reinforced with different configurations of hessian and glass fabric reinforcements. Single filaments from historic hessian were weaker than filaments from new hessian and the larger scatter in strength was demonstrated using a Weibull distribution function. High density gypsum absorbed less moisture (0.2%) than low density gypsum (1%), as expected, but the jute fibres in the hessian absorbed more than 20% of the moisture. High density gypsum was considerably stronger than low density material, and random glass mats as reinforcement resulted in the highest flexural strengths and ability to yield to higher strains, due to enhanced interfacial bonding. This work will have high impact by providing a much needed basis for understanding the long-term degradation of fibrous plaster systems

Interfacial bond strength and failure modes of traditional and modern repair materials for historic fibrous plaster

Many culturally important historic buildings contain fibrous plaster ceilings. The collapse at London’s Apollo Theatre in 2013, which injured 88 people, highlighted the importance of inspecting and restoring ceilings effectively. This study focuses on traditional and modern materials which are applied to the topsides of existing historic fibrous plaster ceiling elements during repair and maintenance. Fibrous plaster ceilings are commonly suspended from primary or secondary structural roof members using fibrous plaster wadding ties or ‘wads’. The application of additional repair material requires the formation of an interface, defining the strength of the repair. Properties of this interface were evaluated through a novel methodology employing pull-off tests’ of approximately 200 specimens consisting of Alpha plaster, Beta plaster, Jesmonite and Aramid gel. Notably, the effect of fibrous reinforcement, and compatibility with historic and degraded material was also investigated. This study has enabled quantification of interfacial properties and evaluated cohesive and adhesive failure modes. Importantly, the extent of redundancy within historic plaster ceiling practice has been demonstrated, with pull-off occurring from 0.5 kN to 2 kN loading, and the ductile behaviour of repair materials evaluated. Results highlight the importance of surface condition, with clean surfaces exhibiting double the tensile loading capacity compared to soiled (dirty) surfaces representative of those encountered on-site. The significance of this study lies in the quantification of repair material performances and consideration of variations in performance, methodology and in-situ environmental factors. Impact stems from the ability of practitioners to make informed decisions relating to adhesion performance when carrying out repairs. A key outcome is more effective preservation of historic elements in heritage buildings, higher levels of safety and serviceability.</p

Optimal discrete stopping times for reliability growth tests

Often, the duration of a reliability growth development test is specified in advance and the decision to terminate or continue testing is conducted at discrete time intervals. These features are normally not captured by reliability growth models. This paper adapts a standard reliability growth model to determine the optimal time for which to plan to terminate testing. The underlying stochastic process is developed from an Order Statistic argument with Bayesian inference used to estimate the number of faults within the design and classical inference procedures used to assess the rate of fault detection. Inference procedures within this framework are explored where it is shown the Maximum Likelihood Estimators possess a small bias and converges to the Minimum Variance Unbiased Estimator after few tests for designs with moderate number of faults. It is shown that the Likelihood function can be bimodal when there is conflict between the observed rate of fault detection and the prior distribution describing the number of faults in the design. An illustrative example is provided

OPTIMIZATION OF CLOUD PLATFORMS

Embodiments presented herein provide a mechanism for optimizing the cost of a cloud platform. A cognitive cloud platform is trained using performance counters to process unstructured data in order to identify underutilized cloud resources. The platform may also generate policies to shut down during idle times. Present embodiments may utilize techniques such as robotic process automation (RPA), straight through processing (STP), and/or natural language processing (NLP)

Moisture and fungal degradation in fibrous plaster

Fibrous plaster degradation has been a key concern over recent years, with ceiling failures occurring suddenly in historic buildings, including the Apollo theatre in 2013. This rigorous investigation explores fibrous plaster degradation through subjecting 290 specimens to a range of moisture and fungal-related treatment conditions over periods of up to two years and analysis using mechanical flexural tests, Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM) and Deoxyribonucleic Acid (DNA) sequencing. Using FTIR peak ratios from spectra of hessian fibres and mechanical tests in conjunction, an original methodology for identifying mechanisms and severity of fibrous plaster degradation through moisture and fungal exposure was developed. Results showed defined clusters for differing moisture and fungal treatments when two peak ratios are plotted together and compared with mechanical data. Fungal exposure over two years, water submersion and wetting and drying were particularly detrimental conditions for fibrous plaster. Fungal exposure resulted in degradation of cellulose bonds in hessian fibres, with defined clusters on the extreme left of peak ratio plots correlating with a pronounced reduction in fibrous plaster mean flexural strength of 51%. Fungal species Penicillium and Chaetomium were identified on test samples. Moisture affected plaster matrices significantly with wetting/drying and water submersion treatments resulting in a 71% reduction in mean flexural strength for unreinforced plaster, reducing to 26% with hessian-reinforced fibrous plaster. Many buildings containing fibrous plaster are listed and removal of material is often minimised - the high impact of this research stems from the ability to rapidly assess the mechanical integrity of a very small quantity of harvested historic hessian fibres using FTIR. Identifying the location of weakened fibres in a ceiling is highly important for effective restoration and conservation

Electrophoretic field gradient focusing with on-column detection by fluorescence quenching

Native, uncoloured, proteins can be focused in a column containing a fluorescent packing material, using hydrodynamic flow and a counteracting non-linear electric field, and imaged along the length of the channel by fluorescence quenching