Ingredients
Generic UHPC is made of the following ingredients:
Ordinary Portland Type I cement
Ground Granulated Blast Furnace Slag (GGBS) cement (slag cement)
Silica fume
Graded silica sand
Steel fibers
High Range Water Reducer (HRWR)
Water
Defoaming agent
The mix proportions of a generic UHPC mix per cubic yard are shown in the table. Four mixes are listed with different amounts of High Range Water Reducers (HRWR).
How to use the Table below: The ability to successfully mix UHPC depends on the type of HRWR you are using and the carbon content of the silica fume. Carbon particles are extremely fine and can increase the water demand, causing mixing problems. The figures below shows three different types of silica fume with different carbon contents (you can tell by the color, the darker it is the greater the carbon content). The best way to find the optimal HRWR dosage is by conducting trial batches. Start with Mix A then work your way up until you achieve the recommended spread. The spread should be between 175 mm (7 in) and 300 mm (12 in). Spread values outside this range indicate that the mix should be rejected. See tab below labeled ‘Spread Test‘.
Table: Mix proportions by weight of cement (OPC+GGBS = 1.0). Weights listed in pounds.
1Mixes A, B, C and D have HRWR dosages of 1.5%, 2%, 2.5% and 3%, respectively
2Grain sizes: 80-200 microns
3Grain sizes 400-800 microns
4Polycarboxylate ether-based high range water reducer
5High range water reducer dosage rates can be adjusted to meet the paste flowability requirements, Dosages range vary with the type of silica fume and range from 1.5% to 3.0% by weight of the cement.
6The steel fibers are 2% by volume.
NOTE: If needed, use a defoaming agent at the rate of 0.5 lb per cubic yard. This will reduce the bubbles that form during vigorous mixing. Typically you would need that in truck mixing. See next section on ‘Truck Mixing‘.
Figure above: Color of silica fume with different carbon content.
Figure above: Silica sands used for the preparation of UHPC.
