Self-compacting concrete versus normal compacting concrete : a techno-economic analysis

Malherbe, Jan Stephanus (2015-12)

Thesis (MSc)--Stellenbosch University, 2015.

Thesis

ENGLISH ABSTRACT: Self-compacting concrete (SCC) also referred to, as self-consolidating concrete, is a relatively new concrete technology used in the construction industry. It is able to flow under its own weight and compact into every corner of the formwork, purely by means of its own weight. According to the University of Johannesburg, engineers can expect a strong demand for their services over the next four years and construction projects might start experiencing even higher pressure on their schedules. This will force the industry to look at possible time saving technologies. It is therefore useful to investigate possible construction methods that might accelerate project schedules and to understand their financial impact. It is also important to see if it will be worthwhile for the South African construction industry to follow the international trend for SCC application. The primary objective of this study was to construct an accurate cost implication model to quantify the impact of the decision to implement self-compacting concrete on a South African construction project. This was done by constructing a static costing model and by performing a sensitivity analysis and a Monte Carlo analysis on the static results of the relevant Key Performance Indicators (KPI’s). As a secondary aim, the study examined the labour requirements at a typical South African construction project. This was done to enable a project leader to easily implement self-compacting concrete technology without facing the perceived challenges concerning job creation policies in South Africa. The technical information regarding the material properties of SCC is well researched and guidelines for implementing the material in a project already exist. The knowledge gap about the detailed cost impact of using SCC on a South African construction project still exists. Interviews with industry representatives showed a good, but fragmented, knowledge of SCC in the South African industry. The factors that influence the cost of using SCC and how these factors influence the construction cost are known, but the size of the influence on the different cost constituents are still uncertain. The labour requirements set out by the National Development Plan (NDP) and the Expanded Public Works Programme (EPWP) for labour-intensive construction was also identified as a perceived obstacle for SCC implementation. A modelling and calculation methodology was proposed in this research to quantify the financial impact of using SCC on a South African construction project. This methodology was tested and found to be useful when applied to a case study. The case study was a six span bridge constructed near George in the Western Cape. The results obtained are of particular value to the client and contractor in a project team. The cost quantification results are presented in terms of cost KPI’s that can be used for interpreting the influence of SCC on the construction cost. For this case study it was found that the construction cost would increase by 17.4% if SCC had been used. This is mainly due to the increased material and formwork cost. The higher cement content of SCC raises the material unit price and the increased formwork strength requirements, needed to accommodate hydrostatic pressures, manifests as an increased expense. A Monte Carlo analysis yielded a 90% confidence that the total cost difference would be between 14.0% and 20.9% (R294 800 and R438 200) on a total amount of R2 098 700. The labour requirements set by the EPWP and the NDP for labour-intensive infrastructure projects was shown to have a limited influence on the decision to implement SCC. The labour reduction resulting from the use of SCC implementation is small. The labour reduction should not prevent the implementation of a new technology. The main risks applicable to this case study are the lack of SCC expertise and the possibility of formwork failure or leakage that can result in total concrete material loss during concrete placement. The cost comparison should be done prior to the construction phase in order to manage and lower the cost difference by identifying the most efficient way to focus cost reduction strategies. A project dashboard with all the graphical results and the KPI summary, can be used to summarise the effect of implementing SCC at a South African construction project if the proposed calculation method is used. The information contained on the dashboard can then be altered to suit the needs of a specific decision maker. The heuristic modelling, especially the Monte Carlo analysis, should be tailored to cover only the information that has inherent uncertainty for a specific project. To minimise the cost increase, the incorporation of cement extenders should be considered. SCC expertise and a formwork specialist should be included in the project team during the project inception phase. Further research should be done to enhance the knowledge about the SCC cost implication, opportunities of SCC in the South African market as well as the implementation intensity and success of SCC in South Africa.

AFRIKAANSE OPSOMMING: Self-kompakterende beton (SKB), ook bekend as self-konsoliderende beton, is ‘n relatief nuwe betontegnologie wat in die konstruksie industrie gebruik word. Dit het die vermoë om onder die las van eie gewig te vloei en te kompakteer tot in elke hoek van die bekisting. Volgens die Universiteit van Johannesburg kan ingenieurs ‘n sterk aanvraag na hul dienste verwag in die volgende vier jaar en konstruksie projekte kan hoër druk ervaar op skedules. Dit sal die industrie dwing om tydsbeparende tegnologieë te oorweeg. Dit is dus van waarde om konstruksiemetodes te ondersoek wat projekskedules kan versnel en om die finansiële impak van die metodes te verstaan. Dit is ook belangrik om te ondersoek of dit die moeite werd is om die internasionale tendens van SKB toepassing te volg vir die Suid-Afrikaanse konstruksie industrie. Die primêre doelwit van hierdie studie was om ‘n akkurate koste-implikasiemodel op te stel wat die impak kwantifiseer van die besluit om SKB tegnologie te implementer op ‘n Suid-Afrikaanse konstruksieprojek. Dit is gedoen deur ‘n statiese kostemodel op te stel en ‘n sensitiwiteits analise, sowel as ‘n Monte Carlo analise, op die statiese model se relevante Sleutel Prestasie Aanwysers(SPA) uit te voer. As ‘n sekondêre doelwit het die studie die arbeidsvereistes bestudeer by ‘n tipiese Suid-Afrikaanse konstruksieprojek. Dit was gedoen om ‘n projekleier te bemagtig om SKB tegnologie maklik te implementeer, sonder om gekniehalter te word deur die verwagte uitdagings aangaande werkskeppingsbeleid in Suid-Afrika. Die tegniese inligting aangaande die materiaaleienskappe van SKB is reeds deeglik nagevors en riglyne is reeds daargestel oor die implementering van die materiaal op ‘n projek. Daar is egter steeds ‘n gebrek aan kennis aangaande die werklike koste-invloed van SKB implementering. Onderhoude is gevoer met verteenwoordigers van die industrie en goeie, maar gefragmenteerde, kennis is waargeneem oor SKB in die Suid-Afrikaanse industrie. Die faktore wat die koste van SKB beïnvloed, sowel as hoe die faktore die koste beïnvloed is bekend. Die relatiewe bydraes van die onderliggende koste komponente is egter steeds onbekend. Die arbeidsvereistes wat daargestel is deur die Nationale Ontwikkelingsplan en die ‘Expanded Public Works Programme’ (EPWP) vir arbeidsintensiewe konstruksie was ook geïdentifiseer as ‘n verwagte uitdaging vir die implementering van SKB. ‘n Modelering en berekeningsmetodologie is voorgestel in die navorsing om die finansiële impak van SKB implementering op ‘n Suid-Afrikaanse projek te kwantifiseer. Die metodologie is getoets op ‘n gevallestudie en het tot insiggewende gevolgtrekkings gelei. Die gevallestudie was ‘n ses-span brug wat naby George, in die Wes-Kaap, gebou is. Die resultate is die nuttigste vir die besluitnemende partye van kliënte en kontrakteurs in die projekspan. Die resultate wat afkomstig is van die koste kwantifisering word voorgestel deur middel van die onderskeie SPA’s wat gebruik kan word om die koste-invloed te interpreteer. Vir hierdie spesifieke gevallestudie is ‘n kosteverhoging van 17.4% op die konstruksiekoste bereken indien SKB benut sou word. Die verhoging is hoofsaaklik as gevolg van die verhoogde materiaal en bekistingkoste. Die verhoogde sementinhoud van SKB verhoog die eenheidsprys van die beton en die hoër sterktevereistes vir bekisting, om hidrostatiese drukke te weerstaan, manifesteer as ‘n prysverhoging. ‘n Monte Carlo analise het ‘n 90% vlak van betroubaarheid opgelewer dat die totale kosteverskil as gevolg van SKB tussen 14.0% en 20.9% (R294 800 en R438 200) sal wees, op die basiskoste van R2 098 700. Die vereistes vir arbeidsintesiewe infrastruktuurprojekte, wat daargestel is deur die EPWP en die NDP, het beperkte invloed getoon op die besluit om SKB te implementeer. Die arbeidsmag vermindering as gevolg van die gebruik van SKB is ook klein en behoort nie ‘n hindernis te wees vir die implementering van die nuwe tegnologie nie. Die grootste risiko’s vir die gevallestudie is die tekort aan SKB kundigheid (kennis en vaardigheid) en die moontlikheid van bekistingfaling of –lekkasies wat tot totale materiaalverlies kan lei tydens die plasing van die vars beton. Die kostevergelyking moet uitgevoer word voor die konstruksiefase geskied. Dit sal ‘n beter begrip tot gevolg hê oor hoe om die kosteverskil te bestuur en te verminder deur kosteverlagingsstrategieë meer doeltreffend aan te wend. Indien die voorgestelde berekeningsmetodiek gebruik word, kan ‘n projek paneelbord opgestel word wat al die grafiese resultate en die Sleutel Prestasie Aanwyser (SPA) opsomming bevat. Hierdie paneelbord kan dien as ‘n opsomming van die effek van SKB implementering by ‘n Suid-Afrikaanse konstruksieprojek. Die inligting wat hierdie paneelbord bevat kan aangepas word om te voldoen aan die behoeftes van ‘n spesifieke besluitnemer. Die heuristiese modelering, veral die Monte Carlo analise, moet aangepas word om slegs die inligting te dek wat inherent onseker is vir ‘n spesifieke projek. Om die kosteverhoging te minimaliseer kan die insluiting van sementvervangers oorweeg word. Die SKB kundigheid en die bekisting spesialis moet ook vanaf die beginfase van die projek ingesluit word in die projekspan om SKB verwante risikos te minimaliseer. Verdere studie kan gedoen word om die kennis te verbeter oor die koste implikasie, die geleenthede van SKB in die Suid-Afrikaanse mark en die implementeringsintensiteit sowel as die sukses van SKB in Suid-Afrika.

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