Technical data
GRC technical data sheet
Typical formulation and mechanical properties of glass fibre reinforced concrete made by the spray-up and premix methods, with a summary of how each is produced and cured. Use these values for early design; project values are confirmed by testing.
Table 1
Typical GRC formulation (per batch)
| Component | Spray GRC | Premix GRC |
|---|---|---|
| Cement (OPC 53) | 50 kg | 50 kg |
| Fine silica sand | 50 kg | 50 kg |
| AR glass fibre | 4.5–5% by weight | 2–3.5% by weight |
| Superplasticiser | 0.5 kg | 0.5 kg |
| Acrylic polymer | 5 kg | 5 kg |
| Water | 13.5 litres | 14.5 litres |
Fibre content is by weight of the total mix. Polymer is an acrylic curing polymer; plasticiser is a water-reducing admixture.
Table 2
Typical strength properties at 28 days
| Property | Unit | Spray GRC | Premix GRC |
|---|---|---|---|
| Flexural strength (MOR) | MPa | 20–30 | 10–14 |
| Limit of proportionality (LOP) | MPa | 7–11 | 5–8 |
| Compressive strength | MPa | 50–80 | 40–60 |
| Interlaminar shear | MPa | 3–5 | — |
| In-plane shear | MPa | 8–11 | 4–7 |
| Impact strength | kJ/m² | 10–25 | 10–15 |
| Elastic modulus | GPa | 10–20 | 10–20 |
| Strain to failure | % | 0.6–1.2 | 0.1–0.2 |
| Dry density | t/m³ | 1.9–2.1 | 1.8–2.0 |
Reading the table: MOR (modulus of rupture) is the ultimate flexural strength; LOP (limit of proportionality) is the stress at which the first micro-cracking begins, and is the value used for design. GRC is graded by MOR, e.g. Grade 8, 10 and 18.
Process A
Spray-up GRC
- Water, admixture and polymer go into a high-shear mixer; cement and sand are added until a smooth, creamy slurry forms (about 1–2 minutes). Consistency is checked with a slump test.
- A pump feeds the slurry to the spray gun, where glass fibre roving is chopped to about 32 mm and sprayed with it onto the mould.
- Material is built up in thin layers to the required thickness, normally 10–15 mm, and compacted with hand rollers between layers.
- The unit stays in the mould under polythene overnight, then is demoulded.
- Units are cured under polythene for about 7 days, or a polymer curing system is used and units are protected from direct sun for a day or two.
Process B
Premix GRC
- Sand and cement are dry-mixed, then water, admixture and polymer are added in a two-speed mixer; high speed makes a smooth slurry in 1–2 minutes.
- At low speed, chopped strand fibre (about 13 mm) is blended in for about 1 minute.
- The mix is poured or pumped into moulds on a vibrating table.
- The unit stays covered in the mould overnight, then is demoulded.
- Curing as for spray-up: about 7 days moist, or a polymer curing system.
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