Typical Formulation of GRC
| Component | Spray | Premix |
|---|---|---|
| Cement | 50 kg | 50 kg |
| Fine Aggregate | 50 kg | 50 kg |
| Glass Fibre | 4.5-5% | 2-3.5% |
| Plasticizer | 0.5 kg | 0.5 kg |
| Polymer | 5 kg | 5 kg |
| Water | 13.5 liters | 14.5 liters |
Typical Strength Properties of GRC
| Property | Spray | Premix |
|---|---|---|
| Ultimate Strength (MOR) MPa | 20-30 | 10-14 |
| Elastic Limit (LOR) MPa | 7-11 | 5-8 |
| Interlaminar Strength MPa | 3-5 | NA |
| In-Planar Strength MPa | 8-11 | 4-7 |
| Compressive Strength MPa | 50-80 | 40-60 |
| Impact Strength Kj/m² | 10-25 | 10-15 |
| Elastic Modulus GPa | 10-20 | 10-10 |
| Strain to Failure % | 0.6-1.2 | 0.1-0.2 |
| Dry Density t/m³ | 1.9-2.1 | 1.8-2.0 |
Manufacturing Processes
Sprayed GRC
Step 1: Mixing
The water and admixture (and polymer if used) are placed in a high shear mixer, and the sand/cement are slowly added until a smooth creamy slurry is achieved. Mixing time is about 1–2 minutes.
Step 2: Transferring to Pump/Spray Unit
When ready, the mix is transferred to a pump/spray unit. The pump conveys the slurry at a regulated rate of flow to the spray gun.
Step 3: Spraying
At the spray gun, fiber in the form of a roving is chopped to a length of approximately 32mm and added to the slurry. The two materials are projected onto the mold surface using an air supply from a compressor.
Step 4: Building Up Layers
The GRC material is sprayed and built up in thin layers until the required thickness is achieved—normally 10–15mm. Simple hand rollers are used to compact the material between layers.
Step 5: Curing
The product is left in the mold and covered with polythene to prevent moisture loss until the next day. After demolding, the units are covered with polythene and allowed to cure for approximately 7 days.