CHAPTER 14 MISCELLANEOUS EQUIPMENT

Mixing equipment, drilling equipment, compressed air equipment, and miscellaneous construction and maintenance equipment are procured for the Naval Construction Force (NCF) to support specific construction and maintenance operations.

This chapter covers the characteristics and basic principles of operations of mixing equipment, drilling equipment, compressed air equipment, and miscellaneous construction and maintenance equipment. These types of equipment play a vital part in NCF operations; therefore, as an equipment operator, you should become familiar with the capabilities of the equipment and how it can be used to serve the purpose for which it was designed.

CONCRETE TRANSIT MIXER

A concrete transit mix truck, sometimes called a TM, is a traveling concrete mixer (fig. 14-1). The truck carries a mixer and a water tank from which the operator can, at the proper time, introduce the required amount of water into the mix. The operator picks up the dry ingredients at the batch plant along with a chit that tells how much water is to be introduced to the mix. The mixer drum is kept revolving en route and at the jobsite, so the dry ingredients do not segregate.

When a TM is used for mixing concrete, 70 to 100 revolutions of the drum at the rate of rotation, designated by the manufacturer as mixing speed, are usually required to produce the specified uniformity. No more than 100 revolutions at mixing speed should be used. All revolutions after 100 should be at the rate of rotation designated by the manufacturer as agitating speed. Agitating speed is usually about 2 to 6 revolutions per minute, and mixing speed is generally about 6 to 18 revolutions per minute. Mixing for long periods of time at high speeds, about 1 or more hours, can result in concrete strength loss, temperature rise, excessive loss of entrained air, and accelerated slump loss.

Concrete, mixed in a transit mixer, should be delivered within 1 1/2 hours or before the drum has revolved 300 times after the introduction of water to cement and aggregates or the cement to the aggregates. Mixers and agitators should always be operated within the limits of the volume and speed of rotation designated by the manufacturer.

DISCHARGE CHUTES

The operator must have the proper chutes at the delivery site or on the truck before delivering concrete. Open-trough chutes should be of metal or metal-lined,

Figure 14-1.-Concrete transit mixer.

preferably round-bottomed, and large enough to guard against overflow (fig. 14-2).

The maximum or minimum slope should be determined by the condition of the concrete as discharged from the chute. Quality control personnel on the jobsite should provide guidance in this area. When possible, you should install a downpipe on the end of the chute to help keep the concrete from segregating when coming off the end of the chute.

OPERATION

Be sure to read the operator's manual for the type of concrete mixer you are operating. Give special attention to the following:

1. Ensure the chain drip oiler is filled and turned on at the beginning of operation.

2. Check the oil level in the hydrostatic drive unit at the sight glass.

3. Check the water tank and meter valves of the on-board water system for the following: operating condition, clean tank, and all valves are clear.

Cleaning

Give special care to cleaning the transit mixer. At the beginning of each workday, the mixer should be coated with form oil to prevent cement and concrete from sticking to the paint or bare metal. After the load of concrete is discharged from the mixer, the operator should wash off all excess concrete in the mixer drum and blades, the discharge chute opening, and the discharge chute before it has a chance to harden.

Spraying 15 to 25 gallons of water into the drum while it is rotating will clean the inside of the drum as well as remove all grout which may have collected in the water nozzle during discharge. A washdown hose is provided on the mixer to clean areas accessible from the outside.

CAUTION

Consult your supervisor about any environmental regulations that require

Figure 14-2.-Chutes used for discharging concrete.

collection or diversion of wash water from mixer equipment.

At the plant, flush a minimum of 150 to 250 gallons of water, depending on the size of the mixer, into the drum. With the flushed water in the drum, rotate the drum in the mixing direction for a few minutes, then discharge the flushed water at the maximum drum rpm. Complete the cleaning of the mixer, particularly around the discharge end.

Never pound the bottom of the drum to loosen materials, since this procedure may cause dents and bumps in which concrete and cement can stick. During cold weather, the water tank, pump, and lines must be drained to prevent possible damage from freezing.

The mixing blades inside the drum must be kept clean and free of built-up concrete. If not cleaned properly, the blades in the drum will wear down and this can result in improper mixing. If this occurs, the blades should be either changed or built up by using hardfacing procedures.

If a minor repair is required on a loaded transit mixer, take the TM to the shop for a quick fix. If the downtime is going to be for more than an hour, mix in 5 pounds of sugar or concrete retarder to keep the concrete from setting up inside the truck.

NOTE: A small amount of sugar (5 pounds) acts as a retarder; however, a large amount will act as an accelerator.

If a quick fix is not possible, the concrete must be removed as quickly as possible. Either check for a hydraulic adapter, which can be hooked up to another TM to operate the drum to discharge the concrete, or remove the access hatch from the drum, roll the drum until the access hatch is facing down, and washout the concrete mix, if possible.