1,721,025 research outputs found
High Performance Reinforced Hemp-Lime Nanocomposite Construction Materials
Full text linkThe aim of the project is to develop high performance, lightweight, durable, and environmentally friendly construction materials. Construction materials should have high compressive and flexural strength, low porosity, low thermal conductivity, low shrinkage and high water vapour permeability (breathability). The following materials were selected to achieve this aim; lime was selected as the base matrix material with hemp (fibres and shives) and wood glue (Poly vinyl acetate, PVAc). Specially selected nanomaterials were used as fillers. The properties of the developed material were used to design an eco-friendly wall consisting of a central 'Core' which will be the load bearing element, highly insulative layers with low thermal conductivity 'Insulators' and outer rendering materials for enhanced aesthetics purpose and breathability 'Renders'. The research conducted in this project enabled a number of different construction materials to be developed, each exhibiting their own characteristics to enable the aims and objectives of the project to be achieved.
A summary of the findings is as follows:
A load bearing wall requires relatively high compressive and flexural strengths of about 5 MPa and 4.0 MPa, respectively or higher. The 'Core' material designed consisted of 10 wt. % hemp fibres, 12 % PVAc/L, 4 wt. % nZnO (nanozinc oxide) and lime (NHL5, which its quantity was 1 kg for each batch of 4 samples for the whole project) and prepared using air curing method. The compressive strength was 17.7 MPa and the flexural strength was greater than 7.0 MPa, which were the highest results of strength throughout the project. The same mentioned mixture (10 wt. % hemp fibres, 12 % PVAc/L, 4 wt. % nanozinc oxide of lime) was cured using 'Oven-drying', the strengths in compression and flexure were still considerable, being 10 MPa and 4 MPa respectively which were more than the minimum limit of loadbearing material. This material, therefore, due to its high compressive strength, used as the 'Core' load bearing element of the proposed wall in the absence of a timber framework.
The 'Insulator' was developed using a water removal 'Solvent exchange' technique and the mixture was 20 wt. % hemp shives, 12 % PVAc/L, 4 wt. % nanozinc oxide and lime. The thermal conductivity was 0.06 W/mK, much lower than that of pure lime which was 0.16 W/mK. The 'Insulator' will be applied in two layers, one on either side of the 'Core'.
The 'Render' was developed using lime and 4 wt. % nanozinc oxide by wt. of lime and cured via air curing. It possessed a low porosity (18 %) in comparison to that of pure lime (36.4 %) and low thermal conductivity, (0.13 W/mK) in comparison to pure lime 0.16 W/mK cured by solvent exchange.
Shrinkage was lowest in a Render material containing 4 % wt. nZnO, averaging 750 microstrain (μs) compared to the control sample (lime only) of 2428 μs.
Chopped fibres, PVAc and nanozinc oxide were used for the first time with lime and no other examples of this exist in the literature (in the best knowledge of the researcher). Water vapour permeability (breathability), which is a beneficial property for construction materials was generally enhanced by using nanomaterials and the optimum breathability was achieved by adding 2 wt. % nanoclay to lime.
The results achieved were used to design an eco-friendly wall in accordance with the Building Regulations. The U-value target was 0.18 W/m2K and the results show that a decrease in thickness of 40 mm could be achieved by using optimum materials
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developed in this project in comparison to traditional hemp shives/Lime walls, in addition to eliminating timber studding which is normally required to provide support to non-loadbearing lime based walls
Cathodic Protection of Corroded Pre-stressed Tendons
Full text linkThe corrosion of reinforcement in concrete, whether conventional or pre-stressed, remains a significant cause for the loss of durability of reinforced concrete structures. Corrosion costs the UK economy between 3% to 4% of Gross National Product. This is, in turn, has resulted in the development of greatly enhanced methods of remediation and life extension. One possible approach is to use Cathodic Protection (CP) to control further deterioration. CP of reinforcing steel in concrete structures has proved to be effective for preventing or controlling corrosion and been used successfully for over 25 years. CP is able to stop corrosion in a reliable and economical way where the environment has caused reinforcement corrosion and subsequent concrete damage. However, concerns exist about the ability of CP to avert deterioration in pre-stressed structures due to hydrogen generation and subsequent embrittlement of the tendons. This research investigates the performance of pre-stressed steel tendon exposed to an impressed current cathodic protection (ICCP) at varying potentials on a long-term basis to establish its effect on strength and establish optimised criteria for CP that can be safely applied to deteriorated pre-stressed structures.
Twelve timber moulds were manufactured for applying the pre-stressing technique to test specimens. Tendons measuring 5.4mm diameter were selected in both the galvanised and ungalvanised state. Two levels of pre-stressing have been investigated, namely low level (300-400 MPa) and high level (800-1200 MPa). Three different degrees of corrosion Stage I, II and III with target losses of cross-sectional of 0-1 %, 2-4 % and 4-7 % respectively, were employed to replicate in-situ conditions. The actual degree of corrosion was verified gravimetrically by weighing the tendons both before and after testing. The tendons were pre-stressed in two types of electrolyte, namely a saline solution and a sand/cement mortar representing mortar. Upon completion of the corrosion phase using an anodic impressed current method, Impressed Current Cathodic Protection (ICCP) was applied to the tendons at two levels of polarization, normal protection (ICCP-N) in the range of -650 to -750 mV vs Ag/AgCI/ 0.5M KCI and over protection (ICCP-O) ranging between -850 to -1300 mV vs Ag/AgCI/ 0.5M KCI for an extended period to both ungalvanised
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and galvanised pre-stressed steel tendons, to investigate its effect. The potentials of the pre-stressed steel tendon and potential decay resulting from the application of ICCP were monitored and analysed. The strain in the tendons was also monitored throughout the corrosion and ICCP phases to establish pre-stress losses. Finally, the mechanical properties were investigated and the tendon surfaces and fracture modes inspected using an Infinite Focus Microscope (IFM) and Scanning Electronic Microscope (SEM).
The results confirmed that accelerated corrosion is a reliable technique for generating the corrosion of steel. ICCP can be used in the corroded pre-stressed tendons as the long-term application shows there is no significant effect on the surface or damage of the both types of tendons with low or high levels of pre-stress. There has been a long term loss in service stress which due to corrosion, due to ICCP or a combination of both. From the results, the loss is more likely to be corrosion induced rather than ICCP. A higher degree of corrosion leads to a higher loss in pre-stress in highly pre-stressed tendons, which is an additional loss that should be accounted for at the design stage
Long term performance of concrete repair in highway structures.
Full text linkIn recent years, the number of reinforced concrete structures requiring repair and rehabilitation has increased considerably. This is due mainly to the corrosion of the reinforcing steel within the concrete which has become contaminated with a highly corrosive environment containing chlorides and carbon dioxide. Specification of repair materials at present, in accordance with BD 27/86, is based on an inadequate understanding of the interaction between the substrate concrete and repair material. Cracking may occur in the early ages after application of the repair material due to the restraint to shrinkage provided by the substrate concrete and steel reinforcement. This would have serious durability consequences which would aid the onset of further corrosion. Furthermore, it is not clear at present if an efficient composite interaction is developed between the repair patch and substrate concrete in the long term to enable the repair patch to carry external load, or if the repair patch just acts as a barrier to protect the steel reinforcement from further corrosion.This research relates the basic properties of repair materials (elastic modulus, shrinkage and creep) to the long term performance of repair materials applied to actual concrete highway structures and simulated laboratory repairs. The research forms part of a LINK project sponsored by three companies and the Department of Transport. Three deteriorating highway structures were selected for concrete repairs. The repairs were monitored over the long term to gain an understanding of the interaction between the repair material, substrate concrete and steel reinforcement. These were Gunthorpe Bridge, a three span reinforced concrete arch bridge, crossing the River Trent to the east of Nottingham, Lawns Lane Bridge, carrying part of the Ml near Wakefield in West Yorkshire, and finally, Sutherland Street Bridge, carrying the B6080 in Sheffield, South Yorkshire. In order to gain information on the effectiveness of the repair materials in developing an efficient composite action with the substrate concrete, vibrating wire strain gauges were attached to the substrate concrete and steel reinforcement after the deteriorated concrete was removed. Embedment and surface gauges were installed in the repair patches either during or after repair material was applied. Laboratory investigations consisted of repairs to simply supported reinforced concrete beams. Repair patches were applied centrally at mid-span to beams which were subjected to two point loading at one-third span points. The interaction between the repair materials, steel reinforcement and concrete substrates were monitored by a combination of a demec extensometer and electrical resistance strain gauges.A theory is presented which predicts the long term interaction between the concrete substrate and repair materials to unpropped compression members. The analysis is divided into two stages. The first part deals with the distribution of shrinkage strain within the repair patch; the second part deals with the redistribution of external load from the substrate concrete into the repair patch. The distribution of shrinkage strain in the repair patch is based on the analogy of a bi-metallic strip contracting due to adrop in temperature (similar to a repair material contracting due to shrinkage). It has been observed that a repair material with an elastic modulus greater than the elastic modulus of the substrate concrete is able to transfer some shrinkage strain to the substrate concrete. This analysis, therefore, enables the tensile stress in the repair material, due to the partial restraint to shrinkage provided by the substrate concrete, to be predicted. Similarly, the restrained shrinkage strain that is transferred to the substrate concrete is also predicted as an increase in compressive stress in the substrate concrete. The transfer of external load into the repair patch is based on analysing the distribution of stress in a compound member when subjected to an axial force. The compound member consists of two different materials - the substrate concrete and repair material. The analytical expressions require basic properties of the repair material (elastic modulus, shrinkage and creep) and substrate concrete (elastic modulus) to enable a prediction of the stress across the repair patch in the long term to be made. The validity of the model is verified on the basis of the field data from the spray applied repair materials on two of the highway structures (Lawns Lane Bridge and Gunthorpe Bridge)
Correlation between the inspection manual severity codes and moment coefficient for deteriorated concrete beams
Full text linkBridges form a vital part of any countries transport network. Roads users expect that these structures remain safely in-service day after day to enable travelers to complete their intended road journey without disruption. Concrete bridges in particular suffer deterioration due to the harsh environment that they are subjected to such as chloride attack from de-icing salts or carbonation attack due to the atmosphere. Inspection is, therefore, required to ensure that these structures are fit for purpose and safe to use. The UK Bridges Board has developed a comprehensive Inspection Manual to ensure all structures are uniformly inspected and to a high standard. The inspection process involves completing a proforma where defects are graded between 1 (no defect) to 5 (collapse). The inspector is able to use a table (Table G. 10) within the Inspection manual, which provides guidance on severity descriptions for different construction materials. However, for reinforced concrete beams exhibiting main steel corrosion, the relationship between severity of defect and loss of strength is not quantitatively obvious. The paper gives the bridge inspector an appreciation of the loss of strength as a result of corrosion to reinforced concrete simply supported beams. The analysis is mainly concerned with the predicted loss at severity code 3 from the manual, which assumes moderate defect/damage, with some loss of functionality
Properties of biomass fly ash concrete
Full text linkThe environmental concerns of carbon emissions by the energy industry have led to
a change in the way energy is generated as the UK moves to a low carbon future.
While biomass combustion is gaining attraction as the most available renewable
energy source, the resulting ash is most often landfilled and is still not accepted in
the concrete industry as in the case of coal fly ash. This is mainly because of the
limited knowledge of the in-service life of concrete made with this fly ash. This
research investigates the use of two types of wood biomass fly ash, obtained from
two power plants in the UK, in cement and concrete production to provide a
performance-based database for evaluating its utilization in the concrete industry.
The study comprises of three parts, the first part deals with determining the
chemical, mineralogical and physical properties of these two fly ashes enhanced
biomass ash (EBA) and virgin wood biomass ash (WBA). The results show that
EBA has a chemical composition more similar to coal fly ash (CFA) than WBA and
EBA satisfies the BS EN 450-1 requirements for the main oxides and other chemical
components. The mineralogical structure of both ashes is mainly amorphous; EBA
particles are mainly spherical whereas the morphology of WBA particles is fibrous
irregular in shape and size. WBA has a higher surface area than both EBA and CFA
while its pozzolanic reactivity is less. The mechanical and durability properties
investigated in parts 2 and 3 are related to these characteristics (e.g., chemical
compositions, pozzolanic reactivity and particle size) and also to pore properties
investigated in part 2.
Part 2 of this study is concerned with the effect of both ashes on the fresh and
hardened properties of concrete compared to coal fly ash. Blended fly ash pastes and
mortars substituting the cement at 10, 20 and 30% were produced and numerous
tests were performed. The results show that the incorporation of EBA reduces the
water demand and improves the workability similar to the effect of coal fly ash while
the behavior of WBA is the opposite. The coarse and high surface area of WBA
particles contributes to its higher water demand. The early age hydration behavior of
EBA is quite similar to CFA. The CFA and EBA mixes release considerably higher
heat than WBA mixes, indicating a higher rate of hydration. The compressive and
flexural strength decreases gradually as the percentage of both EBA and WBA in the
mix increases. The compressive strength of CFA mixes is higher than EBA mixes while WBA mixes give the lowest strength. The incorporation of EBA and WBA
increases the total porosity of cement pastes.
Part 3 investigates the durability properties of enhanced biomass fly ash
concrete by exposing it to long-term sulphate, chloride and carbon dioxide
environments which are substances that cause deterioration and damage to concrete
structures. Durability properties were tested under laboratory conditions over a
period of one year and control samples of ordinary OPC concrete and coal fly ash
concrete were produced for comparison. Generally, enhanced biomass fly ash
concrete shows better durability properties than OPC concrete except for the
carbonation resistance. The depth of carbonation of enhanced biomass fly ash
concrete is higher than OPC concrete but less than coal fly ash concrete which shows
the highest carbonation depth. The results also show that the incorporation of
enhanced biomass fly ash improves the sulphate resistance compared to control
OPC, however, it is still less effective than coal fly ash in resisting sulphate attack.
The chemically and physically bound chloride of enhanced biomass fly ash concrete
is lower than OPC concrete but it is higher than coal fly ash concrete. The efficiency
of both enhanced biomass fly ash and virgin wood biomass ash in mitigating alkalisilica
reaction was also examined based on the accelerated mortar bar test. The
results show that enhanced biomass fly ash reduced the expansion caused by ASR to
the low-risk level of deterioration according to ASTM C1260/1576 standards
whereas the reduction of expansion in the case of virgin wood biomass ash was not
sufficient to reduce the risk from potentially deleterious level to low risk
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Development of an expert system for reinforced concrete bridge repair.
Full text linkCurrent techniques for selecting reinforced concrete repair materials are often based on ad-hoc methods for specifying repair material properties. The inherent lack of understanding of material behaviour in this approach can lead to premature failure of repairs.This research has examined state of the art methods for repair material property specification and has developed a technique, specifically for application in a computer program, which recommends optimum repair material properties tailored to given repair situations. The technique developed achieves compatibility between the repair material and the substrate concrete through a sophisticated balancing of those repair material properties identified as important, specifically; elastic modulus, shrinkage, creep and tensile strength. Adopting the developed technique minimises the possibility of failure of the repair material.The developed repair material property selection technique is seamlessly integrated into an expert system for reinforced concrete bridge repair also developed as part of this research. A technique has been produced to quickly elicit the complex decision making process of reinforced concrete experts and represent their information in a computer program.The developed expert system diagnoses the causes of reinforced concrete defects. Importantly, the program utilises its in-built intelligence to determine if the severity and extent of the defects identified warrant genuine concern.In order to facilitate efficient inputting of data into the expert system by prospective users, an elemental graphical interface was developed, allowing users to quickly assemble onscreen three dimensional representations of the affected concrete elements. Thereafter, program users locate areas of defects onto the on-screen concrete elements and the inputted data can be interrogated by the expert system.Adopting the mainly graphical approach of data input, the expert system diagnoses reinforced concrete defects, proffers prognoses for concrete elements themselves (such as piers, columns, abutments), recommends testing regimes to confirm the expert system output, and recommends repair techniques.Should the recommendation of the expert system be to break out and replace defective concrete, the technique to recommend optimum repair material properties, developed in this research, will offer its recommendations.The developed expert system for reinforced concrete repair acts as an expert guide through all aspects of bridge inspection and repair. For the assessment of defects it draws together best practice recommendations from literature and experts. For the recommendation of repair material properties it implements the technique developed in the research.The completed research has been incorporated into a commercially available bridge management system (www.bridgemanagementexpert.com)
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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