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No. 100

Design Mix for Pumped Concrete for Underwater Use [Quantities indicated are per cubic yard of concrete.]

Table 2-25

Design Mix for Pumped Concrete for Underwater Use [Quantities indicated are per cubic yard of concrete.]

Item

Quantity

Cement (Type II)

640 pounds (8 sacks)

Fly Ash

112 pounds

Sand

2,100 pounds

Gravel (3/8-inch maximum)

800 pounds

Water

40 gallons

Admixture - Water Reducer

In accordance with manufactuer's recommendations

Slump

6 inches

Strength

4,000 psi

When placing pumped concrete, surfaces J that might trap air are trimmed, or vent pipes are provided in the form work. (A rough profile on the concrete substrate resulting from surface preparation of existing concrete prior to a repair will not entrap air.) The formwork is designed to accommodate the weight and pressure of the concrete. The minimum design pressure is 14 psi. The maximum pressure occurs when the formwork cavity is full and pressurized. The pump hose is attached to the formwork with flanged plumbing fittings and ball valves, or the pump line is attached using hand-held friction fit insertion followed by wooden plugs.

The pumping sequence is from bottom 1 to top. Large repairs may require bulkheads to separate placements into manageable areas. Pumping continues until the concrete flows out of die top of the form or through a vent. Once the form is full, pump pressure is exerted on the concrete, causing it to consolidate and make intimate contact with the form, or existing substrate in the case of a repair.

Before concrete is discharged into the hopper, 3 to 4 gallons of water should be sprayed into the hopper followed by about 5 gallons of a creamy cement and water slurry (1/2 bag of cement to 5 gallons of water). This procedure lubricates the hose and prevents separation and blockages. Delays as long as 1-1/2 hours can generally 1 be tolerated if the mixture is moved several feet at least every 5 minutes (while in the hose or pipeline) until continuous pumping j is resumed. If the concrete becomes exces sively stiff because of a long delay, the concrete should not be retempered by adding , water but should be discarded and a fresh . batch mixed. If the concrete contains a high j ' range water reducer (superplasticizer), the slump can decrease substantially after 3/4 to 1 hour. Concrete in the mixer can have

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