Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: A construction method that proves to be the best today will not necessarily be the best method for application in 20 years. Therefore, with changing circumstances, engineers have to consider all the options before selecting a specific method. Options that are weighed in this study are in-situ concrete construction and hybrid concrete construction. Hybrid concrete construction is the combination of in-situ and precast concrete in structures, with the purpose to exploit the advantages of each to its full potential. This construction method gained popularity in the United States and in Europe due to its distinctive benefits. However, the increase of its application in some countries (including South Africa) has been slow and possible reasons for this are investigated in this study. With the intention of improving the South African construction industry, a model is developed for decision making between hybrid concrete construction and insitu concrete construction. The main purpose of a larger research project is to assist project teams in the decision making between precast concrete and in-situ concrete in building construction projects. This decision making is not based on decision making models with mathematical output, since the decision of a construction method is influenced by many variables that may not all be quantifiable. Consequently, instead of prescribing a decision making method, the relevant information is to be provided for the decision maker. The aim of this study is to identify the relevant parameters and to set a framework for further in depth investigation by subsequent theses. A decision making process in any field normally involves having a list of advantages and disadvantages of the different options. Therefore this study includes the following managerial discussion topics: factors that influence hybrid concrete construction, as well as benefits, barriers and other aspects to consider, structural systems and elements, decision making methods and important factors that will be the basis of the decision making process. Traditionally the most important factors for decision making between construction methods were construction cost and duration, but more recently sustainability is becoming increasingly important. It is the civil duty of all parties involved in a project to foresee that most of the criteria of sustainability are met. Sustainability covers all the aspects of economic, social and environmental impacts. Furthermore quality is identified as an important aspect in the decision making process for a construction method. The comparison of precast and in-situ concrete construction is therefore discussed, considering all the abovementioned criteria and investigating possible quantification methods. This information, together with information from future studies, would then allow the project team to consider each aspect involved in the decision making process. / AFRIKAANSE OPSOMMING: Die beste konstruksiemetode vandag sal nie noodwendig die beste metode oor 20 jaar wees nie. Met veranderende omstandighede, moet ingenieurs altyd al die moontlike opsies oorweeg voordat ‘n spesifieke konstruksiemetode gekies word. Opsies wat in hierdie studie bestudeer word, is in-situ betonkonstruksie en hibriede betonkonstruksie. Hibriede betonkonstruksie is die kombinasie van in-situ en voorafvervaardigde beton elmente in strukture, ten einde die voordele van elke metode ten volle te benut. As gevolg van sy voordele, het hierdie konstruksiemetode al hoe meer gewild geraak in Amerika en Europa. Nietemin is die toename in die gebruik van hierdie metode in sommige lande (insluitend Suid-Afrika) traag en moontlike redes hiervoor word in hierdie studie ondersoek. Met die voorneme om die Suid- Afrikaanse konstruksie-industrie te bevorder, is ‘n model vir besluitneming tussen hibriede betonkonstruksie en in-situ betonkonstruksie ontwikkel. Die hoofdoel van ‘n groter navorsingsprojek is om projekspanne te help met die besluitneming tussen voorafvervaardigde en in-situ beton in konstruksieprojekte vir geboue. Hierdie besluitneming is nie gebaseer op besluitnemingsmodelle wat wiskundige resultate lewer nie, want die keuse van ‘n konstruksiemetode word deur te veel veranderlikes, wat nie altyd kwantifiseerbaar is nie, beïnvloed. Gevolglik word relevante inligting aan die besluitnemer verskaf, eerder as om ‘n gekwantifiseerde besluitnemingsmetode voor te skryf. Die doel van hierdie studie is om relevante aspekte te identifiseer en om ‘n raamwerk te skep vir verdere, in diepte studies van volgende tesisse. ‘n Besluitnemingsproses in enige veld word gewoonlik gebaseer op ‘n lys van voordele en nadele van die verskillende opsies. Daarom sluit hierdie studie die volgende bestuursaspekte in: faktore wat hibriede betonkonstruksie beïnvloed, asook voordele, beperkings en ander aspekte om te oorweeg, strukturele sisteme en –elemente, besluitnemingsmetodes en belangrike faktore wat die basis van die besluitnemingsproses sal wees. Tradisioneel was die belangrikste faktore vir besluitneming tussen konstruksiemetodes die koste en tydsduur daaraan verbonde, maar deesdae word volhoubaarheid al hoe meer belangrik geag. Dit is die plig van alle persone betrokke by ‘n projek om te sorg dat die projek aan so veel as moontlik van die kriteria van volhoubaarheid voldoen. Volhoubaarheid sluit al die aspekte van ekonomiese-, sosiale- en omgewingsimpakte in. Verder is kwaliteit ook geϊdentifiseer as ‘n belangrike aspek in die besluitnemingsproses van ‘n konstruksiemetode. Die vergelyking van voorafvervaardigde- en in-situ betonkonstruksie word dus bespreek met die oog op al die bogenoemde kriteria en, sover moonlik, word die kwantifisering van hierdie aspekte ondersoek. Met hierdie inligting en die inligting van toekomstige studies, kan die projekspan dan elke aspek in die besluitnemingsproses oorweeg.

Thesis (MEng) -- Stellenbosch University, 2014. / ENGLISH ABSTRACT: Geopolymer concrete is an alternative construction material that has comparable mechanical properties to that of ordinary Portland cement concrete, consisting of an aluminosilicate and an alkali solution. Fly ash based geopolymer concrete hardens through a process called geopolymerisation. This hardening process requires heat activation of temperatures above ambient. Thus, fly ash based geopolymer concrete will be an inadequate construction material for in-situ casting, as heat curing will be uneconomical. The study investigated fly ash/slag based geopolymer concrete. When slag is added to the matrix, curing at ambient temperatures is possible due to calcium silicate hydrates that form in conjunction with the geopolymeric gel. The main goal of the study is to obtain a better understanding of the mechanical properties of geopolymer concrete, cured at ambient temperatures. A significant number of mix variations were carried out to investigate the influence that the various parameters, present in the matrix, have on the compressive strength of fly ash/slag based geopolymer concrete. Promising results were found, as strengths as high as 72 MPa were obtained. The sodium hydroxide solution, the slag content and the amount of additional water in the matrix had the biggest influence on the compressive strength of the fly ash/slag based geopolymer concrete. The modulus of the elasticity of fly ash/slag based geopolymer concrete did not yield promising results as the majority of the specimens, regardless of the compressive strength, yielded a stiffness of less than 20 GPa. This is problematic from a structural point of view as this will result in large deflections of elements. The sodium hydroxide solution had the most significant influence on the elastic modulus of the geopolymer concrete. Steel and polypropylene fibres were added to a high- and low strength geopolymer concrete matrix to investigate the ductility improvement. The limit of proportionality mainly depended on the compressive strength of the geopolymer concrete, while the amount of fibres increased the energy absorption of the concrete. A similar strength OPC concrete mix was compared to the low strength geopolymer concrete and it was found that the OPC concrete specimen yielded slightly better flexural behaviour. Fibre pull-out tests were also conducted to investigate the fibre-matrix interface. From the knowledge gained during this study, it can be concluded that the use of fly ash/slag based geopolymer concrete, as an alternative binder material, is still some time away as there are many complications that need to be dealt with, especially the low modulus of elasticity. However, fly ash/slag based geopolymer concrete does have potential if these complications can be addressed. / AFRIKAANSE OPSOMMING: Geopolimeerbeton is ‘n alternatiewe konstruksiemateriaal wat vergelykbare meganiese eienskappe met beton waar OPC die binder is, en wat bestaan uit ‘n aluminosilikaat en ‘n alkaliese oplossing. Vliegas-gebaseerde geopolimeerbeton verhard tydens ‘n proses wat geopolimerisasie genoem word. Hierdie verhardingsproses benodig hitte-aktivering van temperature hoër as dié van die onmiddellike omgewing. Gevolglik sal vliegas-gebaseerde geopolimeerbeton ‘n ontoereikende konstruksiemateriaal vir in situ gietvorming wees, aangesien hitte-nabehandeling onekonomies sal wees. Die studie het vliegas/slagmentgebaseerde geopolimeerbeton ondersoek. Wanneer slagment by die bindmiddel gevoeg word, is nabehandeling by omliggende temperature moontlik as gevolg van kalsiumsilikaathidroksiede wat in verbinding met die geopolimeriese jel vorm. Die hoofdoel van die studie was om ‘n beter begrip te kry van die meganiese eienskappe van geopolimeerbeton, wat nabehandeling by omliggende temperature ontvang het. ‘n Aansienlike aantal meng variasies is uitgevoer om die invloed te ondersoek wat die verskeie parameters, aanwesig in die bindmiddel, op die druksterkte van die vliegas/slagmentgebaseerde geopolimeerbeton het. Belowende resultate is verkry en sterktes van tot so hoog as 72 MPa is opgelewer. Daar is gevind dat die sodiumhidroksiedoplossing, die slagmentinhoud en die hoeveelheid water in die bindmiddel die grootste invloed op die druksterkte van die vliegas/slagmentgebaseerde geopolimeerbeton gehad het. Die styfheid van die vliegas/slagmentgebaseerde geopolimeerbeton het nie belowende resultate opgelewer nie. Die meeste van die monsters, ongeag die druksterkte, het ‘n styfheid van minder as 20 GPa opgelewer. Vanuit ‘n strukturele oogpunt is dit problematies, omdat groot defleksies in elemente sal voorkom. Die sodiumhidroksiedoplossing het die grootste invloed op die styfheid van die vliegas/slagmentgebaseerde geopolimeerbeton gehad. Staal en polipropileenvesels is by ‘n hoë en lae sterke geopolimeer beton gevoeg om die buigbaarheid te ondersoek. Die die maksimum buigbaarheid het hoofsaaklik afgehang van die beton se druksterkte terwyl die hoeveelheid vesels die beton se energie-opname verhoog het. ‘n OPC beton mengsel van soortgelyke sterkte is vergelyk met die lae sterkte geopolimeerbeton en daar is gevind dat die OPC beton ietwat beter buigbaarheid opgelewer het. Veseluittrektoetse is uitgevoer om die veselbindmiddel se skeidingsvlak te ondersoek. Daar kan tot die gevolgtrekking gekom word dat, alhoewel belowende resultate verkry is, daar steeds sommige aspekte is wat ondersoek en verbeter moet word, in besonder die styfheid, voordat geopolimeerbeton as ‘n alternatiewe bindmiddel kan optree. Volgens die kennis opgedoen tydens hierdie studie, kan dit afgelei word dat die gebruik van vliegas/slagmentgebaseerde geopolimeerbeton, as 'n alternatiewe bindmiddel, nog 'n geruime tyd weg is, as gevolg van baie komplikasies wat gehandel moet word, veral die lae elastisiteitsmodulus. Tog het vliegas/slagmentgebaseerde geopolimeerbeton potensiaal as hierdie komplikasies verbeter kan word.

published_or_final_version / Civil Engineering / Master / Master of Science in Engineering

published_or_final_version / Civil Engineering / Master / Master of Science in Engineering

No description available.

No description available.

No description available.

No description available.

No description available.

No description available.