Plant fibre reinforced cement components for roofing

Composites of blast furnace slag (BFS) based cement mortar reinforced with vegetable fibres are presented. Roofing components are produced with these composites through a simple and low-energy consuming method, including ordinary vibration and curing in a wet chamber. Composites reinforced with eucalyptus pulp, coir fibres and with a mixture of sisal fibre and eucalyptus pulp gave a suitable performance, with compressive strength higher than 20 MPa and modulus of rupture (MOR) higher than 3 MPa. The performance of tiles made with these composites is in accordance with international requirements, with maximum load higher than 450 N, in wet conditions.     

Concrete protection using acrylic latex paints: Effect of the pigment volume content on water permeability

Concrete can be protected by coatings, which may reduce the ingress of aggressive agents coming from external sources. Paints have a great importance on concrete durability due to the advantage of being applied to both newly built and old structures, the latter being for maintenance and repair purposes. Five acrylic latex paint formulations were prepared in laboratory. Their relative performance in inhibiting the ingress of water and their drying behavior were evaluated on concrete substrates. The relative absorption and loss of water over a length of time were determined on medium and high porosity concretes. The results showed a correlation between the paint pigment volume content and water permeability. The viability of using acrylic resin in architectural paint formulations for concrete protection against water penetration was confirmed.     

Squeeze flow as a tool for developing optimized gypsum plasters

This paper presents a rheological investigation of pure gypsum (PG) and a commercial gypsum–lime–filler plaster (CP) using the modified Vicat apparatus and squeeze flow method. The samples were tested at several different intervals after manual or mechanical mixing. The results confirmed squeeze flow to be more sensitive in determining fresh paste behavior than the modified Vicat apparatus. PG set faster when prepared in mechanical mixer than when manually mixed. Conversely, the CP composition presented longer setting when mixed mechanically. The study also included the analysis of two ready-to-use polymer-based products for leveling and rendering (drywall joint compound – DJC; acrylic putty – AP) measured by squeeze flow and compared to the commercial composition.     

On the Fixed-Parameter Tractability of the Maximum Connectivity Improvement Problem

Theory of Computing Systems - In the Maximum Connectivity Improvement (MCI) problem, we are given a directed graph G = (V,E) and an integer B and we are asked to find B new edges to be added to G...     

Effects of power reserve control on wind turbine structural loading

As the penetration of wind energy in worldwide electrical utility grids increases, there is a growing interest in the provision of active power control (APC) services from wind turbines and power plants to aid in maintaining grid stability. Recent research has focused on the design of active power controllers for wind turbines that can provide a range of APC services including inertial, primary frequency and secondary frequency control. An important consideration for implementing these controllers in practice is assessing their impact on the lifetime of wind turbine components. In this paper, the impact on the structural loads of a wind turbine providing a power reserve is explored by performing a load suite analysis for several torque‐based control strategies. Power reserve is required for providing those APC services that require the ability of the wind turbine to supply an increase in power. To study this, we performed a load suite on a simulated model of a research turbine located at the National Wind Technology Center at the National Renewable Energy Laboratory. Analysis of the results explores the effect of the different reserve strategies on turbine loading. In addition, field‐test data from the turbine itself are presented to augment and support the findings from the simulation study results. Results indicate that all power‐reserve strategies tend to decrease extreme loads and increase pitch actuation. Fatigue loads tend to be reduced in faster winds and increased in slower winds, but are dependent on reserve‐controller design. Copyright © 2015 John Wiley & Sons, Ltd.     

Weathering of vegetable fibre-clinker free cement composites

Ground iron blast-furnace slag (BFS) activated by a mixture of gypsum and hydrated lime was examined as an alternative binder for fibre-cement mortars produced by a low energy consumption method. Brazilian fibrous wastes from sisal and banana crops and also from a eucalyptus pulp mill were chosen for reinforcement. The composite preparation followed conventional mixing, ordinary vibration and wet chamber curing for the seven initial days. The composites achieved a modulus of rupture of up to 3.92 MPa at an age of 28 days. Flexural toughness was at least 40% superior to that of the non-reinforced matrix. Microstructure analyses presented additional information on the understanding of fibre-matrix interaction and its correlation with composites macrostructural behaviour. The effects of natural weathering on the performance of fibre-cement composites were investigated in comparison with accelerated ageing tests. Sixteen months of exposure in tropical climate conditions caused the severest decay in the loading capacity and composite embrittlement, in spite of the absence of superficial darkening or visible cracks. The reduction of the mechanical properties was attributed to a combination of different processes, such as matrix carbonation, fibre mineralization and transition zone degeneration.

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Résumé Les laitiers de haut foumeau broyés et activés par un mélange de phosphogypse et de chaux hydratée ont été examinés comme un liant alternatif pour des mortiers en fibre-ciment produits par une méthode de basse consommation d'énergie. Des déchets, tels que les fibres de récoltes du sisal et de la banane et aussi ceux de la pate à papier d'eucalyptus, ont été choisis comme renforcement. Le mélange du composite a suivi le processus conventionnel de malaxage, vibration et cure en chambre humide pendant sept jours. Les composites ont présenté des modules de rupture jusqu'à 3,92 MPa après 28 jours. La tenacité en flexion a été au moins 40% supérieure à celle de la matrice non renforcée. Une analyse de la microstructure a exposé des informations supplémentaires sur la compréhension du mécanisme d'interaction de la fibre-matrice et sa corrélation avec le comportement macrostructural des composites. Les performances des composites fibres/ciment ont été étudiées sous des conditions climatiques naturelles et par des essais de vieillissement accéléré. Le stockage du matériau sous des conditions tropicales, pendant seize mois, a provoqué les pertes les plus sévères concernant la capacité de résistance et la fragilisation du composite, malgré l'absence de noircissement superficiel ou de fissures visibles. La réduction des performances mécaniques a été attribuée à une combinaison de différents processus, comme la carbonatation de la matrice, la pétrification de la fibre et la dégénérescence de la zone de transition.

     

Integrated high-concentration PV near-term alternative for low-cost large-scale solar electric power

Large-scale photovoltaic electric power generation deployment and utilization is no longer dictated by limitations in technology, but rather by the economics of PV systems vs. other renewable or traditional options. This paper describes a near-term alternative option for cost-effective solar electric power generation based on a novel sunlight concentrating technology: integrated high-concentration PV(IHCPV). The advantages of high-concentration systems have been well analyzed, but development was constrained by the lack of solar cell capable of withstanding the rigors of concentrated sunlight. The development of a stable, high-concentration back-junction, point-contact cell, by Amonix, paved the way for high-concentration system development. System designers had to insure that the cost savings inherent in concentration systems through the reduction of costly solar cell content were not over-shadowed by the ancillary costs of structure and tracking elements used in concentrating arrays. The IHCPV system has met these goals. Economic factors specific to the IHCPV system are presented including (1) low cost of entry, (2) enhanced energy production, (3) reduced and utilization, and (4) accelerated benefits of volume production.