Thesis (MScFor)--Stellenbosch University, 2004. / ENGLISH ABSTRACT: This research focuses on the utilisation of de-inking sludge from a tissue mill to produce a wood-fibre inorganic composite called the Deviro panel. The study is based on the SA provisional patent 95/9594 by Ysbrandy and Gerischer' and the further research conducted by Crafford'. The patented Deviro panel contains up to 70% de-inking sludge. Cement and a cement extender serve to fortify the composite. The panel's fibre content of 25-30% is significantly greater than encountered in commercial fibre inorganic composites which contain 8-12% fibre by weight. The physico-mechanical characteristics of the Deviro panel compare favourably with resin bonded wood-fibre composites, but less favourably compared to conventional wood and wood-fibre inorganic composites. These properties are strongly dependent on panel density. For instance flexural strength being directly proportional while dimensional stability and hygroscopicity being inversely proportional to density. After confirming the results from the preceding work by Crafford, further improvements were investigated through chemical and curing enhancements. For instance, an autoclaving treatment during the curing period showed an increase in flexural strength. Addition of water glass could be associated with bulking of the panel, which resulted in increased flexural strength and a slight reduction of density. Panel density could be significantly reduced by the addition of Perlite, while inhibiting the concomitant reduction in strength. In addition a pilot production process was developed to produce 1m2 panels, which exhibited similar curing characteristics as the smaller panel units. / AFRIKAANSE OPSOMMING: Hierdie navorsing handeloor die gebruik van ontinkingsslyk van 'n sneespapier meule om die Deviro paneel, 'n houtvesel anorganiese saamgestelde produk, te produseer. Die studie volg uit die SA voorlopige patent 95/9594 deur Ysbrandy en Gerischer en verdere narvorsing deur Crafford'. Die gepatenteerde Deviro paneel bevat tot 70% ontinkingsslyk. Sement en sement-byvoegmiddels dien om die saamgestelde produk te versterk. Die paneel bevat 25-30% vesel wat aansienlik meer is as ander kommersiële anorganiese saamgestelde produkte wat 'n vesel inhoud van 8-12% het. Die megamese eienskappe van die Deviro paneel is vergelykbaar met houtvesel saamgestelde produkte waar hars as kleefiniddel dien, maar vergelyk minder gunstig teenoor konvensionele hout en houtvesel anorganiese saamgestelde produkte. Die paneel se eienskappe is afhanklik van sy digtheid Buig sterkte is eweredig terwyl dimensionele stabiliteit en hygroskopisiteit omgekeerd eweredig aan die digtheid van die paneel is. Die voorafgaande werk van Crafford is eers gestaaf voordat veranderinge aan die chemiese samestelling en drogingsmetodes van die paneel nagevors is. Daar is byvoorbeeld bevind dat, deur die paneel te outoklaveer gedurende die set periode, dit lei tot 'n toename in buig sterkte. Die byvoeging van water glas kan swelling laat plaasvind wat 'n afname in buig sterkte en 'n afname in digtheid tot gevolg het. Digtheid kan ook aansienlik verlaag word deur die byvoeging van Perlite terwyl 'n dienooreenkomstige verlaging in buig sterkte tot 'n mate voorkom word. 'n Loods produksie proses is ook ontwikkel om 'n 1m2 paneel te vervaardig wat dieselfde eienskappe toon as die kleiner paneel.

In this dissertation the effects of different types of Pulverized Fuel Ash (PF A)-types on the workability of cementitious pastes containing relative large amounts of PF A were investigated. The different types of PF A were produced at the same source thus they were chemically similar but differed in terms of average particle size and size distribution (grading). By using a two-point measurement technique based on flow through a J-shaped tube it was possible to detect relative small differences in workability between pastes. It was found and concluded that the different types of PFA had a significant effect on the workability of pastes containing cement and PFA as well as PF A alone. The physical differences between the PF A-types were quantified and their effects on workability investigated. It was concluded that PF A with a broader particle size distribution range produced pastes with higher workability at constant water content. It was found that compressive strength as measured after 28 days were solely a function of the water/cementitious ratio for the curing regime employed. It was concluded that for curing conditions used the type of PF A used could have a significant effect on compressive strength when constant workability is required. / Dissertation (MSc (Transportation))--University of Pretoria, 2006. / Civil Engineering / unrestricted

No description available.

No description available.

Thesis (PhD (Civil Engineering))--University of Stellenbosch, 2007. / ECC (Engineered Cement-based Composites) is a type of HPC (High Performance Concrete) that was engineered to overcome the weaknesses of ordinary concrete. It shows high ductility as it can resist the full tensile load at a strain of more than 3 %. This superior response is achieved with multiple cracking under tensile loading which has a pseudo strain hardening phenomenon as result. The purpose of the research project reported in this dissertation is to investigate and characterise the time-dependant behaviour of ECC and create a constitutive model to numerically simulate the static and time-dependant behaviour of ECC. To investigate the time-dependant behaviour experimentally, rate and creep tests were done on the meso- and macro-level while rate tests were done on the structurallevel. The meso-level was represented by the pull-out testing of fibres embedded in the cement-based matrix and direct tensile tests were done for the macro-level. Flexural tests on thin beams were done to simulate the structural-level. Strong time-dependant behaviour was found on all three these levels. On the meso-level, the most prominent finding is that the failure mechanism can change with a change of strain rate, i.e. fibre pull-out at a low pull-out rate, while with a high pullout rate, fibre rupture can occur. Even though the strength of a tensile specimen on the macro-level showed a dependence on the strain rate, the ductility remained constant over four orders of magnitude of the strain rate. On the structural-level, however, a reduction of the flexural ductility was found with an increase of the ...

Thesis (MScEng (Civil Engineering)--University of Stellenbosch, 2006. / Some experiments utilizing the shear capacity of Engineered Cement-based Composites (ECC) have suggested that elimination of shear reinforcement is feasible when the concrete matrix is replaced by ECC. However, actual application and more rigorous cost analysis are prevented by the fact that the shear stress and strain properties of ECC have not yet been characterized as accurately as the tensile properties. This study focuses on the investigation of the shear property of ECC. The study starts with a survey and comparison of existing shear tests for composite materials. The Iosipescu shear test concept is chosen as the most objective method for ECC, and subsequently, modified for specific application on ECC by simple analytical design and finite element refinement. The modified Iosipescu shear test method is applied on, four types of ECC specimens with different fibre content (0%, 1%, 2%, 2.5% by volume), which have been cast in specially designed moulds and cured in laboratory conditions. Three phases of shear measurements are used to check the shear test appropriateness and study the shear mechanical properties of ECC. The failure mode is verified in the first phase, detailed measurement of the shear strain and shear stress is performed and recorded in the second phase, and in the third phase more information about the ductility of diagonal cracking is obtained by measurement of the tensile principal deformation. By also conducting direct tensile tests on specimens of the exact same mix, information of both uniaxial tension and shear behaviour is available, from which elastic and shear moduli, as well as Poisson’s ratio of ECC are computed. A first step toward application of this knowledge of the shear behaviour of ECC is taken by studying the response of shear-dominated beams and beam-columns of reinforced concrete and reinforced concrete combined with ECC as the outer crusts. These beams were prepared and tested by other members of the research group of the Division for Structural Engineering of the University of Stellenbosch. It is shown that ECC can indeed successfully replace shear reinforcing steel, due to its shear capacity.

Thesis (MScEng (Civil Engineering))--University of Stellenbosch, 2007. / Bonded overlays are increasingly used in concrete and reinforced concrete repair and rehabilitation applications, despite the high probability of interfacial debonding. Reasons for such failures include inefficient substrate surface preparations, inappropriate overlay materials, poor curing conditions and time dependent influences. The introduction of engineered cement-based composite (ECC) as an overlay or repair material, does not only address durability aspects but also structural performance. The associated ductility of the material induces a high performance aspect where applied. It is crucial to execute reliable design methods, especially at interfacial level, in order to harness the ductility at hand. The fact of the matter is that through identifying the required performance, one can engineer an optimal bond through implementation of reliable substrate surface preparation techniques (SSPT’s). ECC is a material which exhibits ductile mechanical behaviour. The material matrix is reinforced with synthetic fibres, in the case of this study, poly vinyl alcohol (PVA) fibres were used. The introduction of fibres induces strain-hardening behaviour when in tension. Strain-hardening occurs from the first crack onwards and is accompanied by ductile behaviour, due to a multiple cracking phenomenon. Multiple cracking continues until the increased tensile load incurs localising of an existing crack. The literature study investigates bond properties and bond model parameter test methods. A review of composite design, mainly concrete to concrete, in local and international codes discloses design specifications towards calculating interfacial shear bonds. The interfacial transition zone (ITZ) between the aggregate and cement matrix of concrete is used to define the interfacial bond characteristics and processes. The next step is to investigate a variety of interfacial shear and tensile test methods, in order to implement the most suitable tests.

This study is to compare the performance of recycled aggregate concrete and the impact of up to 50% cement replacement with fly ash on durability. Water content, sieve analysis, standard and modified compaction tests were performed to assess the physical properties of the recycled aggregate concrete. Accelerated aging tests were performed to predict the long term durability of the recycled aggregate concrete. Following Arrhenius modeling and TTS and SIM accelerated aging protocols, a time versus stiffness master curve was created. This allowed the prediction of equivalent age using experimental data and theoretical analysis. To account for environmental exposure, the specimens underwent 24 and 48 hours of wet-dry cycling and subjected. Overall there was an increase in stiffness and strength from the specimens containing fly ash. All tests performed predicted equivalent age beyond the testing period of 144 hrs. and up to 7 years. Specimens containing fly maintained a constant and higher density to environmental exposure. / by Lillian Gonzalez. / Thesis (M.S.C.S.)--Florida Atlantic University, 2010. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2010. Mode of access: World Wide Web.

Insitu cementitious stabilisation is an economical, environmentally sustainable and socially advantageous means of rehabilitating pavements. With the recent availability of a wide range of binders and advanced construction equipment, the characterisation of cementitiously stabilised pavement materials has become the focus of further advancement of this technology. Australian practice has moved towards the use of Indirect Diametric Tensile (IDT) methods for the characterisation of these materials. A draft protocol for the IDT test has been prepared and specifies samples to be compacted by gyratory compactor. This procedure provides for both monotonic and repeated load testing, which aims to measure the material???s strength, modulus and fatigue life. A range of host materials, including a new crushed rock and a reclaimed existing pavement base course, were assessed when stabilised with a General Purpose cement binder as well as with a slag-lime blended binder. Materials were assess for their inherent material properties, Unconfined Compression Strength (UCS), Unconfined Compression modulus, IDT strength and modulus under both monotonic and repeated load. A number of amendments and refinements to the testing protocol were recommended. These included the use of minimum binder contents to ensure the binder was uniformly distributed and to promote heavy binding of the materials to ensure they behaved elastically. It was also recommended that samples be gyratory compacted to a pre-determined sample height to allow a constant density to be achieved. The variability of the test results was examined. UCS results were found to be comparatively as variable as other researchers had reported. IDT strength results contained a similar level of variability, which was considered to be acceptable. Modulus results, both monotonic and repeated load, were found to be five to ten times more variable than strength results, which is a generally accepted trend for modulus testing. Under repeated loading, some challenges with the test protocol were encountered. The primary challenge was obtaining reliable and repeatable diametrical displacement data for modulus calculation. This was partially overcome by the insertion of smooth spacers to prevent the Linear Voltage Displacement Transformer (LVDTs) becoming caught on the sample sides. The achievement of reliable and repeatable IDT modulus results through improved displacement measurements should be the focus of future research efforts in this area.

Analysis of calcium and oxygen atom arrays of known cement minerals and the structures of cellulose polymorphs were performed to see if it was possible to arrange a cellulose fibre on a cement mineral face such that the fibre is bonded by a repeating array of hydrogen or hydroxide coordination bonds for the full length of the attachment. Of the sixteen important cement minerals modelled, xonotlite, foshagite, tricalcium aluminate hydrate, chondronite and rosenhahnite could form such bonds to modified cellulose fibre. However, this was not the case for other cement minerals, especially tobermorite. Alumium hydroxide, when added to cement-quartz pastes and autoclaved at 180 degrees C, was found to improve the cement's ability to resist carbonation. / Doctor of Philosophy (PhD)