• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 31
  • 26
  • 24
  • 23
  • 12
  • 3
  • 2
  • 2
  • 1
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 137
  • 137
  • 59
  • 56
  • 50
  • 50
  • 50
  • 50
  • 50
  • 50
  • 50
  • 48
  • 34
  • 32
  • 32
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
51

Transfer and development length of 06-inch diameter prestressing strand in high strength lightweight concrete

Meyer, Karl F. 05 1900 (has links)
No description available.
52

The structural, serviceability and durability performance of variable density concrete panels

Saevarsdottir, Thorbjoerg January 2008 (has links)
Conventional concrete is a poor insulating material but has good thermal mass, while lightweight concrete provides good insulation at the price of thermal mass. Precast concrete wall systems have not been widely used in residential homes due to poor thermal and acoustic performance, despite being high quality products that are easy to construct. The variable density concrete panel was designed to combine good thermal storage, insulation and high quality precast concrete. It is produced from a single concrete mix which is vibrated to get a lightweight top layer and a normal/heavyweight bottom layer. The lightweight layer is the wall exterior, having low thermal conductivity providing good thermal insulation while the normal/heavyweight layer is the dense wall interior, having high specific heat to provide good thermal mass and sufficient strength for construction handling and to withstand service loads. The intention of this research was to estimate the hardened performance; that is the structural, serviceability and durability performance of the variable density concrete panel. Further developments to the mix design were made where the fresh properties were measured and thermal performance estimated on hardened specimens. Most of the major technical concerns were proved not being as severe as first thought, making the production of variable density concrete panels promising. To ensure that the variable density concrete would stratify, the concrete mix had to have defined fresh properties. Defined rheological ranges gave a good indication of the stratification potential, but the degree of stratification was also found to be dependent on the intensity and time of vibration. Slump flow had to be within a certain range to achieve good stratification but this alone did not guarantee stratification. Variable density concrete was found to have adequate strength capacity both in axial compression and in tension for likely service loads but the strength required to withstand handling loads at early ages was not assessed. The strength of the variable density concrete was found to be affected by several factors such as; degree of stratification, relative strength and thickness of the layers, curing environment and amount of defects. As the stratification of the concrete increased the thermal insulation improved whereas the strength decreased. Warping was found not to significantly affect the serviceability of panels despite differential shrinkage within the element. The amount of warping was mainly related to the degree of stratification. Warping decreased with better stratification as more stress and strain was relieved in the lightweight layer. The lightweight concrete was significantly weaker as well as being less stiff than the structural concrete and therefore creeps to follow the structural concrete. The thermal properties aimed for were generally not reached, but these mixes were not designed to optimise the thermal performance and were tested before the concrete was fully dried. This increased thermal conductivity and therefore reduced the measured R-values. Stratified concrete had good absorption resistance, poor permeability properties and was highly porous. If the concrete was over-vibrated it tended to have a rough surface finish that would require a coating. Delamination of the panels was not assessed in this research but is a likely mode of failure.
53

Evaluation of high strength lightweight concrete precast, prestressed bridge girders

Dunbeck, Jennifer 08 April 2009 (has links)
This thesis evaluates the use of High Strength Lightweight Concrete (HSLW) in bridge girders for the I-85 Ramp "B" Bridge crossing SR-34 in Cowetta County, Georgia. This bridge consisted of four spans; all girders were constructed using lightweight expanded slate aggregate. Spans 2 and 3 had a design strength of 10,000 psi, and span 2 was chosen for this research. The BT-54 girders were 107 ft 11½ inches in length. The prestressing strands used in these girders were 0.6 in diameter, grade 270, low relaxation strands. Material properties and member properties were tested. All 5 girders of span 2 were instrumented with vibrating wire strain gages at midspan, as well as with DEMEC inserts for transfer length measurements and with a deflection measurement system. Transfer length measurements found the transfer length of the girders to be 23% less than the values suggested by AASHTO and ACI equations. The deflection measurements showed 4.26 inches of camber at 56-days while the girders were stored at Standard Concrete Products. The camber measurements matched theoretical predictions within 5%. Mechanical property tests found the concrete to be within all design requirements. A stiffness, load test was performed on each of the 5 girders at Standard Concrete Products. The average stiffness value of 8.428 x 106 kip ft2 is recommend for use by GDOT engineers in designing the deck and road profile. This thesis discusses all short term findings from construction to the end of storage. A later report will address long term issues such as creep and shrinkage, as well as the performance of the girders as part of the bridge.
54

Dimensionamento de elementos estruturais em concreto leve

Ferreira, Cláudia Nunes Gomes 22 April 2015 (has links)
Submitted by Izabel Franco (izabel-franco@ufscar.br) on 2016-09-21T20:16:49Z No. of bitstreams: 1 DissCNGF.pdf: 3859904 bytes, checksum: 2fa6f704c030b58e303d83e761c6a771 (MD5) / Approved for entry into archive by Ronildo Prado (ronisp@ufscar.br) on 2016-09-28T19:06:41Z (GMT) No. of bitstreams: 1 DissCNGF.pdf: 3859904 bytes, checksum: 2fa6f704c030b58e303d83e761c6a771 (MD5) / Approved for entry into archive by Ronildo Prado (ronisp@ufscar.br) on 2016-09-28T19:06:50Z (GMT) No. of bitstreams: 1 DissCNGF.pdf: 3859904 bytes, checksum: 2fa6f704c030b58e303d83e761c6a771 (MD5) / Made available in DSpace on 2016-09-28T19:14:29Z (GMT). No. of bitstreams: 1 DissCNGF.pdf: 3859904 bytes, checksum: 2fa6f704c030b58e303d83e761c6a771 (MD5) Previous issue date: 2015-04-22 / Não recebi financiamento / The lightweight concrete for structural purposes is a material that has great potential for application in various construction areas. Its main feature is the reduced density compared to conventional concrete. This characteristic is a great advantage, since one of the main shortcomings of conventional concrete is its heavy weight. Thus there is a reduction in foundation loads, reduction in moving cost due to smaller weight, low consumption cost of cement and, in some cases, improved thermal and acoustic performance. However, despite the great potential application of lightweight concrete, there is a lack of studies regarding the design criteria of elements made of this material type. The lightweight concretes have different strength properties when compared to conventional concrete, thus require special design criteria. As there is no specific Brazilian standard, the design is taken to be similar to the design principles of conventional concrete. In this context, the present study aims to evaluate design criteria for lightweight concrete elements in compression, shear and bending available in national and international standardization and specific technical literature. The study includes both the analysis of the design criteria for the Ultimate Limit State (ULS) and for checking the Limit State Service (LLS). Finally, cases are compared assessing beams, slabs and walls on four different types of lightweight concrete, taking into account factors such as material consumption, cost, weight and cement consumption. / O concreto leve com finalidade estrutural é um material que apresenta grande potencial de aplicação nas mais diversas áreas da construção civil. Sua principal característica é a reduzida massa específica em comparação ao concreto convencional. Tal característica torna-se uma grande vantagem, uma vez que uma das principais deficiências do concreto convencional é seu elevado peso próprio. Com isso há redução nas cargas na fundação e no peso de transporte, menor consumo de cimento e custo em algumas situações, melhoria do desempenho térmico e acústico. Entretanto, apesar do grande potencial de aplicação dos concretos leves, observa-se uma carência de estudos no que tange a critérios de dimensionamento de elementos feitos com esse material. Os concretos leves apresentam diferentes propriedades físicas e mecânicas quando comparados aos concretos convencionais, diante disso, exigem critérios especiais de dimensionamento. Como não existe norma brasileira específica para este fim, o dimensionamento segue princípios similares ao dimensionamento de concreto convencional. Nesse contexto, a presente pesquisa tem como objetivo fazer um levantamento sobre a utilização de concreto leves, suas propriedades e critérios para dimensionamento à compressão, cisalhamento e flexão disponíveis em normalização nacional e internacional e em literatura técnica específica. O estudo inclui tanto a análise dos critérios para dimensionamento no Estado Limite Último (ELU) quanto para verificação no Estado Limite de Serviço (ELS). Por fim, são comparados casos de dimensionamento de vigas, lajes e paredes em quatro diferentes tipos de concreto leve, levando em conta fatores como consumo de materiais, custo, peso e consumo de cimento.
55

Emprego de EPS reciclado em blocos vazados de concreto para otimização do conforto térmico das edificações

Gonçalves, Paulo José Simão, 9299344-3501 06 February 2018 (has links)
Submitted by Divisão de Documentação/BC Biblioteca Central (ddbc@ufam.edu.br) on 2018-04-11T15:10:22Z No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Dissertação_Paulo J. S. Gonçalves.pdf: 7857623 bytes, checksum: 3677132bdb6d0d4f5c32c230cf3e630a (MD5) / Approved for entry into archive by Divisão de Documentação/BC Biblioteca Central (ddbc@ufam.edu.br) on 2018-04-11T15:10:45Z (GMT) No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Dissertação_Paulo J. S. Gonçalves.pdf: 7857623 bytes, checksum: 3677132bdb6d0d4f5c32c230cf3e630a (MD5) / Made available in DSpace on 2018-04-11T15:10:45Z (GMT). No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Dissertação_Paulo J. S. Gonçalves.pdf: 7857623 bytes, checksum: 3677132bdb6d0d4f5c32c230cf3e630a (MD5) Previous issue date: 2018-02-06 / FAPEAM - Fundação de Amparo à Pesquisa do Estado do Amazonas / The natural resources preservation and implementation of sustainable factor in projects are two of main concerns obeserved currently by researchers and engineers resident around world. The developed research seeked to make feasiable new concretes that incorporate these guidelines inserting expanded polystyrene, from mechanical recycling, in partial replacement of traditional coarse aggregate used in Amazonas. Firstly was carried out a physicochemical characterization in involved components to verify their uses on production of hollow concrete blocks. After that, the experimental dosage was obtained in association of Compressible Packaging Model with Tango´s adapted methodology for four concretes produced (with content ratios of 0, 5, 10 and 15% as partial volumetric replacement of coarse aggregate by recycled EPS) and w/c ratio of 0,5 was found for all concretes. The tests performed procedures to check physical and mechanical properties followed the NBR 12118:2013, and resulted in two classifications in terms of compressive strenght: referencial (0%) and 5% gravel’s parcial replacement by recycled EPS (defined as limit for employing this exchange according to NBR 6136:2014) attested their uses for structural applications, while 10 and 15% EPS’ partial replacement couldn´t be used because their compressive strenght were lower than minimum acceptance strenght. Regarding thermal analysis, it was verified that all blocks partially attented NBR 15575-4:2013, necessitating adjustments to ensure the minimum perfomance level required for that standard. The thermal comfort provided by referential blocks and blocks with 15% of recycled EPS presented similar results as a function of thermal transmittance and different radiant temperatures, became similar average heat flows in both specimens. However, at times when environment peak temperature were recorded, it was verified greater delay and thermal inertia in the masonry with recycled EPS, reducing heat transmition through the walls. / A preservação dos recursos naturais e a implantação do fator sustentável na concepção de projetos são duas das principais preocupações observadas atualmente por pesquisadores e engenheiros em todo mundo. A pesquisa desenvolvida buscou viabilizar uma nova elaboração de concretos que incorporassem estas diretrizes ao inserir o poliestireno expandido, oriundo da reciclagem mecânica, em substituição parcial ao agregado graúdo tradicional empregado no estado do Amazonas. Inicialmente, realizou-se a caracterização físico-química dos componentes envolvidos com o intuito de verificar o emprego destes na produção de blocos vazados. Após esta fase, obteve-se a dosagem experimental por meio da associação do Modelo de Empacotamento Compressível com a metodologia adaptada de Tango para os quatro tipos de concretos produzidos (com teores de substituição volumétrica de 0, 5, 10 e 15% do agregado graúdo por EPS reciclado), definindo um fator a/c igual a 0,5 para todos eles. Os ensaios executados para verificação das propriedades físicas e mecânicas seguiram as diretrizes da NBR 12118:2013, e resultaram em duas classificações quanto à resistência à compressão encontrada: os blocos referenciais (0%) e com 5% de substituição da brita pelo EPS reciclado (definido como o limite para empregar esta troca segundo a NBR 6136:2014) poderiam ser direcionados para fins estruturais, enquanto que os com 10 e 15% de substituição não atenderam a resistência mínima de aceitação. A respeito da análise térmica, verificou-se que os blocos atenderam parcialmente a NBR 15575-4:2013, necessitando de adequações para garantir o nível de desempenho mínimo exigido por esta norma. Os confortos térmicos proporcionado pelos blocos referenciais e com 15% de EPS apresentaram resultados semelhantes em função da transmitância térmica que, juntamente com as distintas temperaturas radiantes, equipararam os fluxos médios de calor em ambos exemplares. Contudo, no horário de pico da temperatura ambiente, verificou-se o maior atraso e inércia térmica na alvenaria com EPS reciclado, reduzindo da transmissão de calor entre as faces das paredes.
56

Agregado leve de argila calcinada para uso em concreto estrutural: viabilidade de cerâmica vermelha do Estado de São Paulo / Calcined clay lightweight aggregate for use in structural concrete: viability of the red ceramic from the state of São Paulo

Bruno Carlos de Santis 26 November 2012 (has links)
Este trabalho tem por objetivo o estudo da viabilidade da utilização de cerâmica vermelha para a confecção de agregados leves de argila calcinada para utilização em concretos estruturais. Inicialmente, foram coletadas amostras de solo de cinco diferentes empresas produtoras de cerâmica vermelha do estado de São Paulo. As massas cerâmicas foram caracterizadas por meio das técnicas de limites de liquidez (LL) e plasticidade (LP), análise granulométrica, análise química e difração de raios X (DRX). Os corpos de prova confeccionados com essas massas cerâmicas, queimados à temperatura de 900ºC, foram caracterizados por meio da avaliação da retração linear, absorção de água, porosidade aparente, massa específica aparente, expansão por umidade e resistência à compressão. Após a caracterização dos corpos de prova de cerâmica vermelha, foram escolhidas duas amostras para a confecção dos agregados leves de argila calcinada. Em seguida, foram confeccionados corpos de prova de concreto com agregados leves de argila calcinada, argila expandida e brita. Os corpos de prova de concreto leve foram caracterizados pelos ensaios de slump, massa específica fresca, teor de ar incorporado, resistência à compressão, resistência à tração, módulo de deformação, retração por secagem, absorção de água, índice de vazios e massa específica aparente. Os resultados desta pesquisa indicaram a viabilidade da produção de agregados leves de argila calcinada para utilização em concretos e os valores da massa específica (1.555 a 1.785 kg/m³) e da resistência à compressão (18,0 a 55,8 MPa) apresentaram-se em um patamar intermediário entre os valores observados para concretos com argila expandida e com basalto. / This paper aims the study the viability of using red ceramic to make calcined clay lightweight aggregates in order to use in structural concrete. At first, soil sample were collected from five different red ceramic producing companies from São Paulo State. Liquid and plastic techniques, particle size analysis, chemical analysis and X-ray diffraction (XRD) were used to characterize ceramic masses. The specimens made from these ceramic masses, burned at the temperature of 900ºC, were characterized by evaluating of linear shrinkage, water absorption, apparent porosity, specific mass, moisture expansion and compressive strength. After the red ceramic specimens characterization, two samples were chosen for the manufacture of calcined clay lightweight aggregates. After that, concrete specimens with calcined clay lightweight aggregate, expanded clay and basalt were made. These concrete specimens were characterized by slump test, fresh specific mass, incorporated air content, compressive strength, tensile strength, modulus of elasticity, water absorption, voids and bulk density. Results of this research indicated the viability of production of calcined clay lightweight aggregate for concrete utilization and the specific mass values (1.555 and 1.785 Kg/m³) and the compressive strength values (18,0 to 55,8 MPa) presented at a intermediated level between those observed for the expanded clay and basalt.
57

Bond behavior of lightweight steel fibre-reinforced concrete

Ali, Ahsan 09 November 2017 (has links) (PDF)
This research was undertaken for studying the bond behaviour of Lightweight Fibre-reinforced Concrete (LWFC). Lightweight concrete is inherently weak in tension and has higher brittleness than the conventional concrete. To improve these and other properties, it is generally reinforced with deformed bars and fibres. There are number of studies that favour the use of Steel fibres, however such studies are mainly focused either on normal weight concrete or on the mechanical properties of different concretes. There are also different committee reports and in some cases specific sections of codes that specifically deal with the normal weight fibre-reinforced concrete. However, such is not the case with lightweight fibre-reinforced concrete; there is limited literature available especially on the Bond of lightweight fibre-reinforced concrete. In current research work effect of fibres is studied on the bond behaviour of the lightweight reinforced concrete. Since most of code provisions for bond are based on experimental work originally carried out on conventional concrete, effect of fibres on bond of conventional concrete was therefore also included in present research domain. Main bond tests were carried out using Pull-out test methodology. Test results indicate that the ultimate bond strength of conventional concrete when reinforced with steel fibres increased by 29%. However due to very low density and high porosity of lightweight aggregates, no significant improvement on bond strength of LWFC, as a result of fibres’ addition could be observed. Nevertheless, there is noteworthy improvement in the post-cracking bond strength of LWFC. Besides this, current bond-stress slip law as defined by Model Code 2010 does not reflect the positive effect of fibres, hence some modifications are suggested. It is also found that among the existing code expressions for estimation of bond strength, expression proposed by Model Code 2010 presents better results and its effectiveness can be further increased if fibre factor and factor for lightweight concrete are considered.
58

Sambandet mellan radarsignaler och fukthalt i en lättbetongkonstruktion

Gellerstedt, Jennifer, Westman, Simon January 2017 (has links)
Fukt i byggnader är vanligt och kan leda till skador. Fukten kan ge upphov till mögel och röta, vilket inte är bra för människors hälsa. Fukten kan också påverka olika egenskaper hos byggnadsmaterialen såsom hållfasthet, värmeisoleringsförmåga och ge dimensionsförändringar. Eftersom höga fukthalter kan ha en stor påverkan på materialen är det viktigt att upptäcka och fastställa problemet i ett tidigt skede. Syfte och mål med den här rapporten är att se om det finns ett samband mellan radarsignaler och fukthalt och avgöra om radarteknik är en användbar metod för att mäta fukthalt i ett byggnadselement. I det här arbetet har litteraturstudier, mätningar och analyser gjorts. Materialet som använts är lättbetong som byggts upp till fyra väggar i två olika tjocklekar, två stora och två små väggar. De stora testväggarna användes för radarmätningar och de små som provväggar till den gravimetriska metoden. Väggarna byggdes upp i ett tält där relativa luftfuktigheten (RF) och temperatur kunde styras. I början av experimentet var RF i tältet inställt på 98-99 % och temperaturen på 22 °C som därefter reglerats för att torka ut väggarna. Mätningar har utförts med radar och den gravimetriska metoden parallellt, där den sistnämnda gjorts genom att väga provväggarnas lättbetongblock vid samma tillfällen som radarmätningarna. Provväggarnas lättbetongblock torkades därefter i torkningsugn i 105 °C för att fastställa dess torrdensitet. Insamlade data från radarmätningarna har bearbetats av Radarbolagets personal. Resultaten för de olika metoderna har därefter analyserats och jämförts för att se om det finns ett samband. Resultaten från studien visar att det finns ett samband mellan fukthalt och signalerna från radarmätningarna. Fukthalten kan bestämmas på en lättbetongvägg med en felmarginal på ± 4 kgH20/m3 material, vilket motsvarar cirka 4 %. Det går att få ett bra resultat med radarmätning, metoden är däremot komplicerad men det kan finnas värde för fortsatta studier på flerskiktade konstruktioner för att avgöra om tekniken kan vara användbar för befintliga byggnadskonstruktioner. / Moisture in buildings is common and can lead to damage. The moisture can cause moldand rot, which is not good for human health. The moisture can also affect different properties of the building materials such as strength, thermal insulation and dimensional changes. Because high moisture levels can have a major impact on the materials, it is important to detect and fix the problem at an early stage. The purpose and aim of this report is to see if there is a correlation between radar and moisture content and determine whether radar technology is a useful method of measuring moisture contentin a building element. In this work, literature studies, measurements and analyzes have been made. The material used is lightweight concrete that is built up to four walls in two different thicknesses, two large and two small walls. The large test-walls were used for radar measurements and the small ones as sample-walls for the gravimetric method. The walls were built in a tent where relative humidity (RF) and temperature could be controlled. At the beginning of the experiment, the RF in the tent was set to 98-99 % and the temperature of 22 °C, which was then regulated to dry out the walls. Measurements have been made with radar and the gravimetric method in parallel, where the latter was made by weighing the sample-walls light concrete blocks at the same time as the radar measurements. The blocks of the sample walls were then dried in an oven at 105 °C to determine drydensity. The collected data from the radar measurements have been processed by the Radarbolaget’s personnel. The results for the different methods have then been analyzed and compared to see if there is a relationship. The results from the study show that there is a connection between moisture content and the signals from the radar measurements. The moisture content can be determined on a light concrete wall with a margin of error of ± 4 kgH20/m3material, which corresponds to about 4 %. It is possible to get a good result with radar measurement. However, the method is complicated, but there may be value for further studies on multilayered structures to determine whether the technology can be useful for existing building constructions.
59

Thermo-mechanical behaviour of a novel lightweight concrete and its application in masonry walls

Al-Sibahy, Adnan Flayih Hassan January 2012 (has links)
The development of lightweight concretes has made a contribution to advances in structural design. It would be useful to further improve the mechanical properties of lightweight concrete formulations whilst enhancing their resistance to fire degradation and reduced thermal conductivity. Improving the sustainability of any new proposed lightweight concrete formulation is desirable, for example by the inclusion of waste stream components into the formulation.This thesis describes an investigation of the mechanical, thermal and fire resistance properties of a new type of expanded clay lightweight concrete formulation in which varying quantities of sand are replaced by crushed glass aggregate, in conjunction with the addition of metakaolin (which may be available as a waste component from the manufacture of paper) as a partial replacement for the cement. The investigation involved short and long-term laboratory testing of a range of mechanical and thermal properties of individual concrete formulations and small scale structural elements consisting of masonry blocks made from these formulations (so called wallettes). An extensive programme of Finite Element Analysis using Abaqus was also performed.The results obtained show that it is possible to produce a structural expanded clay lightweight concrete that possesses good thermal properties by incorporating of ground glass and metakaolin. Compressive and splitting tensile strengths, as well as the modulus of elasticity, increased with an increase in the metakaolin content, while concrete density decreased. Reductions in thermal conductivity and improvements in fire resistance criteria were also observed in comparison with conventional lightweight concrete mixtures. For example, measured thermal conductivity values ranged from 0.092 W/m.K to 0.177 W/m.K, and the insulation criterion (an indicator of resistance to fire) reached up to 110 minutes for a concrete member with a thickness of 29 mm. The highest resistance to the effects of high temperatures was observed for concrete mixes containing either 15% or 30% recycled glass with 10% metakaolin.The maximum axial loads at failure were 474 kN and 558 kN for reference and modified wallettes respectively, implying corresponding bearing capacities of 7.1 MPa and 8.3 MPa. The critical path of the failure mode was similar for all of the wallettes tested and normally began underneath the load point, then passed through the concrete blocks and head joint to reach the toe of the wallette. The masonry wallettes formulated using reference lightweight concrete blocks exhibited failure due to explosive spalling at 400 oC with no applied mechanical load, whereas the second type of masonry wallettes (the modified wallettes) did not show such behaviour.The results of Finite Element Analysis showed that the coefficient of thermal convection had the most influence upon the insulation criterion. From a structural perspective, the key parameters were the value of penalty stiffness and imperfections in wallette construction. In general, a close agreement between the measured and simulated results was observed for both the thermal and structural finite element models at ambient and high temperatures.
60

Manufacturing and Performance of Fly Ash Based Synthetic Lightweight Aggregate

Hofmeyr, Stuart Grant January 2020 (has links)
In South Africa, as much as 33 million tons of ash, a waste product of burning coal, are produced per year. Of the total ash produced, just over 8% is sold for utilisation, the remainder of which is disposed of in landfills or ash lagoons. Countries like the UK, USA, Germany, Poland and Russia are producing Lightweight Aggregates (LWAs) commercially by using fly ash and clay, however, this technology is not available in many developing countries. The opportunity to utilise the fly ash produced in South Africa for the production of coarse LWA for use in structural concrete has therefore been identified and investigated in this dissertation. This dissertation consists of two phases, firstly to determine a suitable method for the manufacture of a high quality LWA, and secondly to determine the manufactured aggregate’s performance and potential for use in structural concrete. In the first phase, different LWA batches were produced using fly ash as the main constituent and kaolin clay, in contents of 0%, 10%, 20% and 30% by mass, as a binder. Green aggregate particles were produced in a disc granulator and then hardened using sintering at 1200°C for one hour. It was found that the LWA batch containing 20% kaolin produced LWA with the most suitable mechanical properties for use in concrete, and was therefore mass produced for further aggregate testing and for the production of concrete specimens for concrete testing. The final LWA produced was found to have an apparent density of 1600 kg/m3 and 24 hour water absorption of 12% by mass. The produced LWA was also found to have an Aggregate Crushing Value (ACV) and 10% FACT of 24.4% and 185 kN, respectively, which indicated that it would be suitable for use in High Strength Concrete (HSC). The sintering process was found to induce liquid phase sintering and the formation of new phases, mainly mullite, which contributed to the relatively high strengths of the aggregates. In the second phase of this dissertation, the manufactured LWA was then used to produce HSC and Normal Strength Concrete (NSC) specimens for concrete testing, which were compared to control mixes made with normal weight dolomite aggregate. In the HSC testing, concrete with a density of 2300 kg/m3 and compressive strength of 90 MPa was produced with the LWA. In HSC, it was found that internal curing was improved when up to 50% of the normal weight coarse aggregate was replaced by saturated LWA for this specific concrete mix. By using different stiffness relationship models between the concrete constituents, it was found that the manufactured LWA modulus of elasticity was between 8-23 GPa, and had a compressive strength of between 49-60 MPa. The Interface Transition Zone (ITZ) in concrete produced with the LWA was found to be stronger than the LWA as a result of the impregnation of the cement paste within the aggregate, and that the LWA was reactive in an alkaline environment. This resulted in an improved early age strength development, as well as caused the concrete failure surface to occur through the LWA particles rather than at the ITZ. Finally, Lightweight Concrete (LWC), having a dry density below 2000 kg/m3, was produced with the manufactured LWA. The LWC, produced with a water-to-cement ratio of 0.75, 28 day compressive strength of 24 MPa, modulus of elasticity of 21 GPa and dry density of 1800 kg/m3, was found to be suitable for use as structural concrete when assessed in terms of EN 1992-1-1 (2004). / Dissertation (MEng (Structural Engineering))--University of Pretoria, 2020. / Civil Engineering / MEng (Structural Engineering) / Restricted

Page generated in 0.0727 seconds