Submitted in fulfillment for the Master of Engineering, Department of Civil Engineering and Surveying, Durban University of Technology. Durban. South Africa, 2015. / Beam and block slab systems have become a preferred suspended flooring technology in South Africa. Their structural efficiency and relatively low cost makes them suitable for low to medium cost developments. Like all other structural components, they are required to demonstrate sound structural integrity. Concerns were raised by some manufacturers and users in Durban (South Africa) about (a) the lack of basic technical information which makes it difficult to identify methods of improving efficiency and effectiveness of these flooring systems in general, (b) the efficiency and effectiveness of concrete masonry rebated filler blocks - with respect to the load carrying capacity and protecting the structural topping from fire, (c) what constitutes acceptable quality of a deliberately roughened precast concrete surface, (d) interfacial tensile bond strength of special connections and (e) an alternative rib that can span 5 metres without temporary props. These issues were investigated by the student. Thus, this project aimed at improving the structural efficiency and effectiveness in designing, manufacturing and constructing beam and block slab systems was undertaken in Durban, South Africa, between 2012 and 2013. Pilot studies (involving questionnaires), interviews with manufacturers, site visits, and testing of non-structural and structural components were also undertaken. The first aim (in order to address concern (a)) was to provide users of beam and block slab systems with basic technical information about the possible ways to improve efficiency and effectiveness in the design, manufacturing and construction of beam and block slab systems by undertaking an exploratory (pilot) study to better understand users of these systems concerns. The second aim (to address concern (b)) was to investigate, by conducting a series of strength to weight ratio tests, how efficient or inefficient these filler blocks are, examine the structural integrity with respect to the integrity of the manufacturing methodologies and the product thereof, and formulate a method to quantify the fire-resistivity of concrete masonry rebated filler blocks to the structural topping with respect to confining fire. The third aim (to address concern (c)) was to determine what constituted acceptable quality of a deliberately roughened precast concrete surface through a literature review and by conducting a survey to learn about the construction methodologies used by manufacturers. Site visits were undertaken to validate information given by the contractors. The fourth aim (to address concern (d)) was to determine interfacial tensile bond strength through physical testing of deliberately roughened concrete ribs which are sometimes used in special connections. The fifth aim (to address the last concern (e)) was to make an assessment by undertaking a basic comparison study between one local beam and block slab system that uses a shallow rectangular precast pretensioned rib to beam and block slab systems used in the United Kingdom and propose an ideal section (precast pretensioned rib) that spans up to 5 metres without temporary props. With respect to the first aim, it was found that the lack of technical knowledge, including access to critical information about the design philosophy, manufacturing and construction standards of these flooring systems leads to reluctance in selecting them. The outcome of the second aim is that all concrete masonry rebated filler blocks tested were found to be effective because they supported more than the required construction load but some were shown to be inefficient as more materials, such as binders, are wasted in producing over-strength filler blocks and also, undertaking trial mix designs and the testing of samples prior to batch production will reduce costs. A method is formulated in the thesis that could also show that concrete masonry rebated filler blocks provide significant protection to the structural topping thereby preventing fire progression. With respect to the third aim, although a broom or brush is effective in providing a surface roughness (Rz) of 3 mm, it is not always efficient when considering factors like the variation in uniformity, appearance of laitance and roughening frequency, which are not addressed by the South African codes. The outcome of the fourth aim is that connections should be designed such that they do not rely purely on the tensile bond strength but through reinforcing bars (or ties) taking the full tension load causing delamination. With respect to the fifth aim, a basic comparison study indicates that T-section beams are more efficient than common rectangular ribs (±150 mm wide x ±60 mm deep) since they can eliminate completely the use of temporary props for spans of up to 4.51 m. Consequently, further research is underway to design an inverted T-section rib by using high strength precast pretensioned concrete that can span up to 5 m without using temporary props.

Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: A major challenge for our society is the protection of the environment. Some of the important issues are the reduction in the consumption of energy and natural raw materials, as well as the increase in consumption of waste materials. At present these topics are getting considerable attention as part of sustainable development programs. The use of recycled concrete aggregates (RCA) from construction and demolition waste (C&DW) in construction, as alternative to virgin (natural) aggregates, has strong potential. The use of RCA preserves natural resources and reduces the space required for the disposal of RCA in landfill. It is estimated that 16 thousand million (billion) tons of concrete (and 25 billion tons of aggregate) were used in 2010. Of the 2-3 billion tons of C&DW which are produced worldwide every year, South Africa contributes 5-8 million tons. This amount is increasing rapidly every year. Significant amounts of demolished concrete find their way to landfill sites. A solution for excess waste production would be the utilization of RCA together with an improvement in the final quality of RCA. It might be an important breakthrough for our society in our attempt towards sustainable development. Worldwide, infrastructure has developed a great deal since the beginning of the twentieth century. Much of the core infrastructure, including roads, bridges, water systems, and sewers, was put in place during the first half of that century. Aggregates used as construction materials, as for instance in road pavements, or as an ingredient of concrete, are important components of infrastructure. Urbanization involves reduction of natural aggregate (NA) resources, but environmental concern and the rising cost of NA is the reason that recycled materials from different sources (like roads, buildings) are being used more and more with NA in new construction work. Environmental awareness is increasing in every country for many reasons and sustainable development is demanded of all industries, including the building and construction industries. By nature, construction is not environmentally friendly, and sometimes it also changes the behavior of nature in many ways. Recycling is one of the most important ways to minimize the waste that comes from different sources, thereby avoiding repetition of, and additional environmentally hazardous practices. It may create new wealth by diminished transport and production costs and sparing of landfill site space and cost. It has the potential to extend the life of natural resources by adding a source of material, thereby reducing environmental interference and impacting on nearby construction sites, all of which improve sustainability of our natural resources. Much research on the uses of RCA has been performed during the last few decades. In fact, most of them showed that the strength class of recycled aggregate concrete (RAC) is adequate for use as structural concrete although volume changes in and durability performance of RAC in comparison with natural aggregate concrete (NAC) are still being debated and researched. Some researchers found that the durability of concrete produced with RCA is inferior, but others have found it to be sufficient for use in structural concrete. The fact that an insufficient number of studies have been carried out on the durability aspects, has limited the use of RCA as material for road construction. The aim of this study is to determine the suitability of using the RCA in structural concrete based on its strength, stiffness, dimensional stability and durability. Three types of RCA designated RCA1, RCA2 and RCA3 in this study, were taken from three different sources. These materials were tested to establish their mechanical characteristics for use as aggregates in concrete. In the experimental program RCA was used at replacement percentages of 0%, 30% and 100% to (partially) replace NA in order to study its suitability as aggregate in concrete, and to what level of NA replacement its behavior is satisfactory for structural application. A single compressive strength class was studied, due to the limited time. By performing tests of compressive strength, Young’s modulus, creep, shrinkage, and durability performance, it has been found that selected types of RCA show a real possibility for use as aggregate in concrete. When concrete with a RCA replacement of 100% was compared with NAC100% there was a small decline in strength, but when concrete with a RCA replacement of 30% was compared with NAC100% the results showed almost equal strength. A slight reduction in durability performance was found for RAC30% compared with NAC100%, but similar dimensional stability performance in terms of specific creep and drying shrinkage was measured for RAC30% and NAC100%. Based on detailed experimental results obtained from this thesis project, a number of recommendations have therefore been made for RCA characteristics that will be used in concrete mixes also taking into account the quality of RCA. Some suggestions are proposed based on the mechanical properties and durability of the concrete. In the final conclusions, future studies on RCA properties are suggested, which would help us in increasing our knowledge in the application of RCA, and which may lead to the optimal production of structural concrete in a sustainable way. In general the use of RCA in concrete is feasible and good quality RCA at 30% replacement of NA may be suitable for any kind of structural concrete. / AFRIKAANSE OPSOMMING: ‘n Groot uitdaging vir ons samelewing is die beskerming van die omgewing. Van die belangrike sake is die vermindering in die verbruik van energie en van natuurlike, onverwerkte materiale asook die groter verbruik van afvalmateriaal. Hierdie onderwerpe kry tans aanienlike aandag as deel van volhoubare ontwikkelingsprogramme. Die gebruik van betonaggregate, herwin vanaf konstruksie-en slopingsafval, en gebruik in konstruksie as alternatief vir ongebruikte natuurlike aggregate, het goeie potensiaal. Die gebruik van herwonne aggregaat beskerm natuurlike hulpbronne en verminder die oppervlakte en volume wat nodig is vir die weggooi daarvan op stortingsterreine. Dit is beraam dat 16 duisend miljoen (biljoen) ton beton (en ongeveer 25 biljoen ton aggregaat) gedurende 2010 gebruik is. Van die 2-3 biljoen ton konstruksie-en slopingsafval wat jaarliks wêreldwyd gegenereer word, dra Suid Afrika 5-8 miljoen ton by. Hierdie hoeveelheid word elke jaar vinnig meer. Beduidende hoeveelhede gesloopte beton beland elke jaar op stortingsterreine. ‘n Oplossing vir die probleem van te veel atval generering sou wees die gebruik daarvan as herwonne beton-aggregaat, sou saamval met ‘n verbetering in die uiteindelike kwaliteit van herwonne aggregaat beton. Dit kan dalk ‘n belangrike deurbraak wees vir ons samelewing in ons strewe na volhoubare ontwikkeling. Infrastruktuur het wêreldwyd baie ontwikkel sedert die begin van die twintigste eeu. Baie van die kerninfrastruktuur insluitende paaie, brue, waterstelsels en riole is gebou tydens die eerste helfte van daardie eeu. Aggregaat gebruik as konstruksiemateriaal, byvoorbeeld in padplaveisels of as’n bestanddeel van beton, is ‘n belangrike deel van infrastruktuur. Verstedeliking veroorsaak vermindering van natuurlike aggregaat hulpbronne maar besorgdheid oor die omgewing en die stygende koste van nataurlike aggregaat veroorsaak dat herwonne materiale vanaf verskillende bronne (soos paaie en geboue) meer en meer aanvullend tot natuurlike aggregaat in nuwe konstruksiewerke gebruik word. Omgewingsbewustheid is om baie redes aan die toeneem in elke land en volhoubare ontwikkeling word vereis van alle industrieë. Herwinning is een van die hoofmaniere om afval vanaf verskillende bronne tot ‘n minimum te beperk. Dit skep nuwe rykdom, verminder vervoeren vervaardigingskoste en benut afval wat anders op stortingsterreine verlore sou gegaan het. Dit het die potensiaal om die lewensduur van natuurlike hulpbronne te verleng deur ‘n materiaalbron by te voeg, deur inmenging in die omgewing te verminder, wat almal bevorderlik is om volhoubare benutting van ons hulpbronne te verbeter. Baie navorsing is gedurende die laaste paar dekades gedoen aangaande die gebruik van herwonne aggregaat. Die meeste van die navorsing het inderdaad getoon dat die sterkte van beton met herwonne aggregaat genoegsaam is vir gebruik as struktuurbeton alhoewel daar wel debatte gevoer word oor die volumeveranderings en duursaamheid prestasie van herwonne aggregaat beton vergeleke met dié van natuurlike aggregaat beton. Sommige navorsers het bevind dat die duursaamheid van beton wat met herwonne aggregaat gemaak is, minderwaardig is maar andere het bevind dat dit voldoen aan die vereistes van struktuurbeton. Slegs die feit dat daar onvoldoende toetse rakende duursaamheid gedoen is, het die gebruik van herwonne beton aggregaat beperk tot padboumateriaal. Die doel van hierdie navorsing is om te bepaal wat die geskiktheid van herwonne betonaggregaat is vir gebruik in struktuurbeton, gegrond op sterkte en duursaamheid. Drie soorte herwonne betonaggregaat wat in hierdie studie as RCA1, RCA2 and RCA3 aangedui word, is elk vanaf ‘n ander bron geneem. Hierdie materiale is getoets om hulle meganiese kenmerke vas te stel vir gebruik as aggregaat in beton. In die eksperimentele program is 0%, 30% en 100% herwonne betonaggregaat gebruik om natuurlike aggregaat gedeeltelik be vervang om sodoende die geskiktheid as betonaggregaat te bestudeer. Deur toetse uit te voer op ‘n beperkte sterkte-klas beton, soos toetse vir die bepaling van druksterkte, Young’s modulus, kruip, krimp en duursaamheid, is daar bevind dat sekere soorte herwonne betonaggregaat heel moontlik gebruik kan word in struktuurbeton. Toe beton met 100% herwonne betonaggregaat vergelyk is met beton met 100% natuurlike aggregaat, is bevind dat daar ‘n klein vermindering in sterkte was, maar waar beton met 30% herwonne betonaggregaat vergelyk is met beton met 100% natuurlike aggregaat, het die resultate byna dieselfde sterkte getoon. Dus op grond van gedetaileerde eksperimentele resultate is ‘n aantal aanbevelings gemaak vir kenmerke van herwonne betonaggregaat wat in betonmengsels gebruik sal word met inagneming van die gehalte van herwonne betonaggregaat. Die resultate vir beton met 30% en 100% herwonne betonaggregaat word vergelyk met beton wat slegs natuurlike aggregaat bevat. Sekere voorstelle gegrond op meganiese eienskappe en duursaamheid van die beton word gemaak, asook aanbevelings vir toekomstige studies van herwonne betonaggregaat wat ons sal help om ons kennis vir die toepassing van herwonne betonaggregaat uit te brei.

Time dependent deformations in concrete, both creep and shrinkage, play a critical role in prestressed concrete structures, such as bridge girders, nuclear containment vessels, etc. These strains result in lossess, through release of prestress, and thereby influence the safety of these structures. The present study comprises of an experimental and analytical program to assess the levels of creep and shrinkage in normal and heavy density concrete. The experimental program includes tests on creep using standard cylinder specimen, while shrinkage studies have been conducted using prism specimen, both under controlled environmental conditions. The experimental results suggest that creep and shrinkage strains are higher in heavy density concrete than in normal concrete. This may be attributed to the relatively smaller pore structure of heavy density concrete, that results in larger availability of free water and a relatively slower hydration process in comparison to normal concrete. While there is some scatter in the results, creep strains decrease with age of loading and both creep and shrinkage strains are smaller when the relative humidity is higher. Statistical model reported in the literature for normal concrete is able to predict the test results for both normal and heavy density concrete quite well. Long term predictions of creep and shrinkage using this model, accounting for uncertainties, is also projected and shown to predict some long term measured results not used in the model calibration. The long term predictions are sensitive to the initial data used in model calibration.

This research focuses on the characterization of damage accumulation in concrete specimens. Specifically, a nonlinear vibration technique is used to characterize the damage introduced by ongoing alkali-silica reactions (ASR). The nonlinear resonance testing consists of an analysis of the frequency response of concrete specimens subjected to impact loading. ASR introduces a third gel like phase, which can be expansive in the presence of moisture. The result of ASR is the formation of microcracks and debonding between aggregate and cement phases. Collectively, these changes act to increase the specimens' nonlinearity. As a result, it is found that the concrete samples exhibit nonlinear behavior; mainly a decrease in resonance frequency with an increasing level of excitation strain. The relationship between the amplitude of the response and the amount of frequency shift is used as a parameter to describe the nonlinearity of the specimen. The specimens used in this research are of varying reactivity with respect to ASR, which is induced in accordance with ASTM C 1293. The level of nonlinearity is used as a measure of damage caused by the progress of ASR throughout the one year test duration. These nonlinear resonance results are compared to the traditional measures of expansion described in the standard. The robustness and repeatability of the proposed technique is also investigated by repeated testing of samples assumed to be at a specific damage state. Finally, a petrographic staining technique is used to complement nonlinearity measurements and to further gain understanding of ASR. The results of this study show that the proposed nonlinear resonance methods are very sensitive to microstructural changes and have great potential for quantitative damage assessment in concrete.

This dissertation investigates the level of acid‐resistance of concrete degradation. Concrete specimens obtained from four mixtures (M1, M2, M3 and M4) were prepared with calcareous, siliceous and a blend of calcareous and silica sand; and then, tested in low (30 g/l) and highly (200 g/l) concentrated sulphuric acid solutions. To this end, an architecture of artificial neural networks (ANNs) was implemented to predict the performance of concrete specimens due to sulphuric acid solutions. Neural networks were composed with one hidden layer for one input and output layer. Nine input parameters were: cement composition, proportions of coarse and fine aggregates, water content, and compressive strength, weight loss of concrete, time impacting corrosion, acid concentration and sulphur concentration. Thickness expansion and concrete conductivity are used as output targets to evaluate the degree of deterioration. In this study, the learning through ANNs from training data sets have been proved to be better than measured data. Excellent results were found with a coefficient of determination (R2 ) of 0.9989, 0.9999, 0.9989 and 0.9998, respectively for the four mixtures M1, M2, M3 and M4 using siliceous aggregate. Also, the results show that two ANN models performed with both the thickness (expansion) and the electrical conductivity can successfully learn the prediction of concrete corrosion. In both low and highly concentrated sulphuric acid condition, the model thickness was more accurate in predicting concrete corrosion compared to the model conductivity. The lowest error in neural networks was provided by the mixture (M2) for the concrete using siliceous aggregate. For this purpose, the root mean squared error (RMSE) and the average absolute error (AAE) were of 0.0049 and 0.0048 % respectively. / College of Engineering, Science and Technology / M. Tech. (Chemical Engineering)

No description available.

Ultra-high performance concrete (UHPC) is relatively a new generation of concretes optimized at the nano and micro-scales to provide superior mechanical and durability properties compared to conventional and high performance concretes. Improvements in UHPC are achieved through: limiting the water-to-cementitious materials ratio (i.e., w/cm < 0.20), optimizing particle packing, eliminating coarse aggregate, using specialized materials, and implementing high temperature and high pressure curing regimes. In addition, and randomly dispersed and short fibers are typically added to enhance the material¡¦s tensile and flexural strength, ductility, and toughness. There is a specific interest in using UHPC for precast prestressed bridge girders because it has the potential to reduce maintenance costs associated with steel and conventional concrete girders, replace functionally obsolete or structurally deficient steel girders without increasing the weight or the depth of the girder, and increase bridge durability to between 75 and 100 years. UHPC girder construction differs from that of conventional reinforced concrete in that UHPC may not need transverse reinforcement due to the high tensile and shear strengths of the material. Before bridge designers specify such girders without using shear reinforcement, the long-term tensile performance of the material must be characterized. This multi-scale study provided new data and understanding of the long-term tensile performance of UHPC by assessing the effect of thermal treatment, fiber content, and stress level on the tensile creep in a large-scale study, and by characterizing the fiber-cementitious matrix interface at different curing regimes through nanoindentation and scanning electron microscopy (SEM) in a nano/micro-scale study. Tensile creep of UHPC was more sensitive to investigated parameters than tensile strength. Thermal treatment decreased tensile creep by about 60% after 1 year. Results suggested the possibility of achieving satisfactory microstructural refinement at the same temperature input despite the maximum temperature applied. For the first time, the presence of a 10 Ým (394 micro inch) wide porous fiber-cementitious matrix interface was demonstrated by nanoindentation and SEM for non-thermally treated UHPC only. Tensile creep at 90 days increased by 64% and 46% upon eliminating fibers for thermally and non-thermally treated UHPC, respectively. Increases in creep upon reducing the fiber content suggested that fibers carry part of the sustained load and thus reduce creep. Tensile creep strain was proportional to the stress applied up to 60% of the ultimate strength. No tensile creep failure occurred for a period of 1 year for pre-cracked UHPC under stress level of 40%. Also, no tensile creep failure occurred for a period of 90 days under stress level of 60%. Tensile creep failure occurred at stress levels of 70% and 80%. This study showed that fibers cannot be accounted for as shear reinforcement in lieu of stirrups unless micro-defect-free fiber-matrix interface is achieved.

Thesis (Ph. D.)--University of Alabama at Birmingham, 2007. / Title from PDF title page (viewed Feb. 4, 2010). Additional advisors: James S. Davidson, Robert J. Dinan, Alan E. Eberhardt, Jason T. Kirby, Talat Salama, Houssam A. Toutanji. Includes bibliographical references (p. 139-146).

Title page, abstract and table of contents only. The complete thesis in print form is available from the University of Adelaide Library. / The major contribution of this thesis is towards the shear capacity and shear failure mechanism of reinforced concrete beams with adhesively bonded transverse near surface mounted fiber reinforced plastic plates. In shear strengthening, there are two forms of plate debonding that interact with each other consisting of intermediate crack debonding that is governed by the axial forces in the plate are induced by shear deformations. This research considers both forms of debonding and in particularl their interaction. -- From abstract. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1283733 / Thesis (Ph.D.) -- University of Adelaide, School of Civil and Environmental Engineering, 2007

Title page, abstract and table of contents only. The complete thesis in print form is available from the University of Adelaide Library. / The major contribution of this thesis is towards the shear capacity and shear failure mechanism of reinforced concrete beams with adhesively bonded transverse near surface mounted fiber reinforced plastic plates. In shear strengthening, there are two forms of plate debonding that interact with each other consisting of intermediate crack debonding that is governed by the axial forces in the plate are induced by shear deformations. This research considers both forms of debonding and in particularl their interaction. -- From abstract. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1283733 / Thesis (Ph.D.) -- University of Adelaide, School of Civil and Environmental Engineering, 2007