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Table 2-23: Vehicle fuel consumptions
Vehicle Fuel Consumption Source Fixed Hire
cost
Source
Isuzu KB 250 (4 x2) 9.9 litres /100 km (Isuzu, 2014) R150/hour Kempston Hire Qixing 10 ton dump
truck
24 litres / 100 km (Qixing Auto, 2014)
R254/hour Contractor
Table 2-24: Distance to waste sources from Pinetown
Destination Distance from Pinetown station (one-way)
Re-SA Prospecton 26.5 km (N2 via M7)
Sezela sugar mill 86.3 km
The QTO method (Dalton, et al., 2011) combined with costing methods for materials (Popescu, et al., 2005) and transport (Carter & Troyano-Cuturi, 2009) provided a sound costing methodology to develop the costing models required for this study.
It must also be considered that projects may not always be solely profit-centred. Considering that the construction industry contributes largely to natural resource depletion and pollution there is a need to integrate environmental requirements into the decision making process (Addis & Talbot, 2001) (Carroll, 1999). This study relates to both reductions in natural resource depletion as well as pollution by utilizing the waste materials (HDPE, SCBF, BA) mentioned.
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The review investigated HDPE pellets, SCBF and bottom ash, as well as the material properties (relative density, workability, compression elastic modulus etc.) to be tested and analyses to be carried out in the study. The intended outcome of the literature review was to provide a thorough theoretical background for this study and identify potential knowledge gaps in past research which could be addressed in this study.
Materials
The HDPE selected for this study was readily available from recycling plants located in major CBD’s (Durban, Johannesburg and Cape Town), however the SCBF and BA obtained from the sugar mill were limited by the locations of sugar mills. The implications in terms of transportation associated costs were subsequently evaluated in the costing scenario analysis (see section 4.12 of this study).
The volumetric substitutions of the wastes used in this study were shown in past research to have a significant impact on concrete properties depending on whether a low <5% or high volume >10% substitution was used (Magistri, et al., 2011). High volume substitutions generally yielding worse results in strength and durability than conventional concrete. It also was noticed that past research was mainly focused on a particular type of substitution (low or high) and research into the critical volume at which performance peaked between low and high volume substitutions was limited. In the case of BA and HDPE, low-volume substitution research was also limited and hence investigation into low to high volume substitutions formed a significant component of this study to fill the knowledge gaps.
With regard to SCBF, the strength and durability of SCBF mixes were of concern due to the tendency of SCBF to degrade in alkaline environments such as concrete and thereby introduce voids to the concrete mix, increasing permeability. This was confirmed in findings by Racines & Pama (1978) who showed at high volume substitutions (>10%) compressive and flexural strength decreased. Findings by Omoniyi & Akinyemi (2013) also showed that for substitutions above 3%, permeability increased. This warranted a further study into the strength and durability of SCBF in concrete which was carried out in sections 4.6 .and 4.9 respectively, as these properties have a large bearing on the viability of the concrete mixes.
The use of HDPE was limited to non-load bearing applications based on research by Rahman, et al. (2012), due to reductions in strength. However, these findings were based on high volume substitutions and hence low-volume substitutions were also investigated in
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this study to evaluate if findings by Rahman, et al. (2012) applied to both low and high volume substitutions. HDPE was also shown to improve thermal performance by Elzafraney, et al. (2005). This was assessed in section 4.7 of this study.
BA was shown to be sensitive to changes in particle size. BA samples were therefore sieved before use in this study. BA was also shown in past research to reduce 7 to 28 day strength of concrete relative to a conventional mix. This was due to the pozzolanic reaction being a slow reaction and the hydrates in the mix being reduced because of cement substitution.
The decreased rate of strength development was investigated in his study by comparing the 7 to 28 day compressive strength of the BA mixes with a conventional mix (see section 4.6.1). The use of BA was shown by Cheriaf, et al. (1999) to reduce the deterioration of natural fibres by lowering alkalinity in the mix. The effect of BA when mixed with SCBF was therefore investigated in this study in terms of compressive strength performance and rate of strength gain compared to a conventional mix (see section 4.6.1).
Tested properties
Strength, workability and durability are key aspects of concrete. This study investigated these main aspects as well as tested further properties such as specific heat and SEM analysis to further enrich the study. The following properties and analyses were discussed and carried out in this study.
Material properties (waste absorption, R.D, F.M, shape observations)
Workability
Saturated hardened density
Strength (compression, flexure, splitting)
Durability (OPI, CC, WS)
Elastic modulus
Specific heat
SEM analysis
Moisture effects
An economic scenario analysis
Testing procedures were mostly standard. Specific heat and the waste material absorption tests used however were non-standard due to the lack of specialist equipment and recognised testing procedure respectively.
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The different material properties of each waste constituent such as: absorption, shape and texture, were shown in past research to have varying influences on the end properties of the concrete mix. For example, the absorption and long fibre lengths of SCBF may cause reductions in workability, in contrast to HDPE, which can potentially increase workability due to its smooth surface and cylindrical particle shape. It was for this reason that factors such absorption were investigated in this study in order to comment on such variations to concrete properties (see sections 4.2.4 and 4.11).
In terms of concrete properties to be tested, it was noticed from literature on the use of waste materials in concrete, that strength, elastic modulus, durability and workability were common concrete assessment criteria.
Compressive strength is a critical factor in concrete specification. If the compressive strength does meet the required target strength, the mix is not fit for purpose. The critical volumetric substitution was therefore based on the best performing volumetric substitution from 2.5%-40% in terms of compressive strength. This critical volume was used for further material property research into elastic modulus, oxygen permeability index, water sorptivity, chloride conductivity, moisture effects and cost analysis.
Direct measurements of the effect on cracking behaviour are relevant to the fibres, however this testing was beyond the scope of this study, due to the diverse nature of crack behaviour in concrete that would serve as a separate research topic. Testing on elastic moduli and tensile strength properties from this study could however give an indication of the mixes resistance to deformation under load and the load at which possible cracks could occur.
The economic analysis was based on costing methodologies by Sabol (2008), Dalton, et al., (2011), Popescu, et al. (2005), Carter & Troyano-Cuturi (2009) and Ingram (2014). It was carried out to evaluate the monetary significance of using the waste mixes, in terms of the difference in material cost, from conventional concrete. It also gave an indication of the percentage of the total project cost attributed to concrete cost. Materials such as BA and SCBF may be cheaper to purchase (see section 2.4) but the cost to transport the materials may potentially render them unfeasible (See section 4.12 for the economic analysis).
The next chapter will explain the methodology used for this study to achieve research objectives and aims.
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