Material cost of viable materials

In this section, the cost of the structural face panels, core panel materials and adhesives are compared.

6.6.1. Materials for structural face panels

The costs of FFC, WPC and GFRP are compared in terms of cost per square meter and are shown in Table 6.7. This table is based on a thickness of 11mm. Note the WPC and FFC prices were supplied by manufactures, which includes finishing (to ensure a smooth surface), lubricant, and coupling agent costs. The GFRP does not include finishing cost (to ensure a smooth surface), lubricant, and coupling agent cost. This can result in a higher actual cost. The cost of unreinforced plastic used for GFRP can also differ.

For Table 6.7, it is clear that FFC is the least expensive and GFRP is the most expensive. The cost estimation of WPC depends on the manufacturer, where EverJade is a company based in China. This implies that transport cost needs to be added to the cost estimate.

Table 6.7: Cost estimation of viable materials for face panel for the walling system (Friul Filiere Spa, [S.a]; Fisher, 2013; Fisher, 2013; Eva-Last, [S.a]; Murphy, 1998; Harper, 1975)

Material Description Price (R/m²)

FFC PVC, vegetal fibres and other additives 128.63

WPC

Everjade (WPC) 137.03

ECOWOOD (50%PVC, 50% Wood flour) 244.22

4EVERDECK (PE,PP, Wood flour) 278.52

EVA-LAST (40%recycled HDPE, 60%wood flour) 279.15

GFRP

Acrylonitrile butadiene styrene (ABS) 20% GF 2952.52 Polyester (unsaturated) (UP) 30% GF 4069.85

Polypropylene (PP) 40% GF 4094.80

Polycarbonates (PC) 10% GF 4911.88

Nylon 6.6 30%GF 5581.08

Nylon 6 30%GF 5606.96

Polyester (PET) 30%GF 5941.71

Epoxy (EP) 80%GF 7481.50

Note:

GF = Glass fibre R9.88/ USD R 12.85/EURO

GFRP is known to be stronger than the rest of the materials in Table 6.7. Thus, as an extreme example, if the GFRP walling system is assumed to have a thickness of 1mm (which will create an extremely slender member) and the rest of the materials have a thickness of 11mm, the cost comparison results are as shown in Table 6.8. The cost of the FFC and WPC products includes surface finishes, whereas the cost of the GFRP products does not include surface finishes. Thus, in all instances except one, the FFC and WPC products are cheaper than the GFRP, however additional cost for surface finishes should be added to the cost of the GFRP products. The cost estimation calculations are shown in Appendix B.

Table 6.8: Cost comparison of a 1mm thick GFRP structural face to an 11mm thick FFC and WPC structural face (Friul Filiere Spa, [S.a]; Fisher, 2013; Fisher, 2013; Eva-Last, [S.a]; Murphy, 1998;

Harper, 1975)

Material Description Price

(R/m²)

FFC PVC, vegetal fibres and other additives 128.63

WPC

Everjade (WPC) 137.03

ECOWOOD (50%PVC, 50% Wood flour) 244.22

4EVERDECK (PE,PP, Wood flour) 278.52

EVA-LAST (40%recycled HDPE, 60%wood flour) 279.15

Glass fibre agents used in XPS include pentane and hydrochlorofluoro-carbon. When EPS is burnt, the fumes have the same or lesser toxic risk as natural materials, such as wood or wool (Lee, et al., 2006). Gasses produced by burning EPS are carbon monoxide (CO), which is, to some extent, always emitted by fires (Baker, 2002).

The odor when EPS burns can be detected at a concentration of 25 parts per million (ppm), whereas a fatal intake is approximately 10000ppm of CO. The amount of CO released when EPS burns, increases with an increase in temperature. For example, when EPS burns at 30°C a CO concentration of 50ppm is released and at 600°C a CO concentration of 1000ppm is released (Baker, 2002), which is lower than the fatal intake threshold. However, the plastic foam (EPS or XPS) is enclosed in structural face panels (Figure 6.4), which reduce the risk of the emissions of CO in the housing unit (Baker, 2002).

EPS is produced by moulding polystyrene beads saturated with the blowing agent (Agarwal & Gupta, 2011).

These polystyrene beads are heated and the expansion of the blowing agent results in a foam-like structure (Lee, et al., 2006). The blowing agent of XPS, hydrochlorofluoro-carbon, is considered a harmful product,

especially when burnt and is thus banned from use in Europe (Chau, et al., 2011). Other blowing agents are currently investigated for XPS, which is produced by a complex extrusion process.

EPS is considered the least expensive core panel material, when EPS and XPS are considered, since EPS is produced by a simpler and less expensive process. According to Stec & Hall (2011), EPS is also considered as the plastic foam material that emits the least toxic fumes when burnt.

6.6.3. Adhesive

Some adhesives were considered for the structural application. The adhesives are limited due to the compatibility of the adhesive with the plastic foams. The costs per square metre as well as cost per litre of the compatible adhesives are shown in Table 6.9. It is clear that epoxy adhesives are the most expensive adhesives. Thus, the least expensive adhesives, The Pekadur A663 polyurethane adhesive and the GB685 spray grade rubber adhesive were selected as the viable adhesives.

Table 6.9: Costs of the adhesives

Adhesive (manufacturer) Cost Amount (ml) Rand/litre Rand/m²

Pekadur A663 Polyurethane Adhesive (Pekay) 136.45 5000 27.29 5.46

GB685 Spray grade synthetic rubber adhesive (Pekay) 183.39 5000 36.68 12.23

Stixall (EverBuild) 114 300 380.00 20.73

Polystyrene foam adhesive (Genkem) 105 500 210.00 35.00

Geocell : Flexible Acrylic Fillers (Abe) 40 310 129.03 64.52

MaxTrack (Sika) 70 300 233.33 77.78

Sick2 Rapid Epoxy Syringe Adhesive (EverBuild) 62 24 2583.33 80.73

Rapid Epoxy (Alcolin) 82 24 3416.67 106.77

Spabond 340LV (Amt) 497.21 1000 497.21 248.61

6.7. Summary

As this design is for a low-income house, the cost needs to be as low as possible, but the mechanical properties required for structural use, need to be met. Therefore, the roof trusses as well as the rafters are made from grade 5 Pinewood.

FFC has properties that are relatable to the properties of WPC. However, GFRP exhibits much higher and thus better mechanical properties compared to the WPC and FFC. FFC is the cheapest material of the viable structural materials considered, especially when compared to GFRP. For the roof sheeting, the structural face panels of the walling system and the flooring system, FFC is considered the most viable, with WPC as an alternative material. However, due to logistical problems, FFC was not available. Therefore, WPC was used as the viable material.

EPS and XPS, which were both considered for the core material, exhibit nearly the same mechanical and thermal properties, with insignificant differences. However, the process to produce EPS is less expensive than the process used to produce XPS. Therefore, EPS is considered the least expensive material of the viable core material considered. XPS also uses a blowing agent that is harmful. Therefore, EPS with a density of 15kg/m³ is considered the most viable core material. This was supplied by Isolite Cape.

The Pekadur A663 polyurethane adhesive and the GB685 spray grade rubber adhesive manufactured by Pekay were considered the two most viable adhesives. The Pekadur A663 polyurethane adhesive is used mainly in the cooling industry, where an adhesive is used to attach steel plates to polystyrene foam. The steel undergoes contraction and expansion, which results in large residual stresses. These stresses are absorbed by the adhesive to ensure no failure in the polystyrene foam. The GB685 spray grade rubber adhesive is mainly used for the bonding of polystyrene foam when used as a contact adhesive. This adhesive creates a soft glue line. The relative bond strength of these two adhesives is compared in Chapter 7.