TM 5-822-10/AFM 88-6, Chap. 6
(4) Old concrete structural elements broken down into manageable pieces by a combination of jackhammers
and demolition balls.
b. Transport equipment. Cranes and front-end loaders are then used to load the rubble concrete into dump trucks
for hauling to the crushing plant.
c. Crushing equipment. The crushing plants are either a portable type and located on the job site or a stationary
plant situated at an existing pit or quarry.
5-6.
Crushing process.
The crushing process consists of breaking the fractured concrete pieces to the required sizes and then stockpiling.
a. Crushing and screening. The salvaged concrete is brought to the crushing plant where it is reduced to the
maximum size called for in the specifications. The equipment used to crush and size the existing concrete is also a
common type used in the construction industry. The crushing equipment should include jaw or cone crushers. The
preferred sequence of equipment utilization consists of a primary jaw crusher which breaks the material down to a
maximum size of about 3 inches. The secondary cone crusher then breaks the particles down to the maximum size required
which, depending upon specification, may vary between and 2 inches. A hammermill secondary crusher should not be
used because of the excess amount of fines such a unit produces. After crushing, the material is separated over appropriate
screens and stockpiled separately. A 3/8-inch screen is normally used to separate the coarse from the fine aggregates. The
coarse aggregates may be split between fractions under and over inch. Another screen should be used to scalp off
particles above the maximum size specified.
b. Stockpiling. The stockpiling should be accomplished in a manner that will prevent segregation and contamination
by foreign materials. Each size of aggregate should be stored separately in free-draining stockpiles. Vehicles for
stockpiling or moving aggregates should be kept clean of foreign materials. Processing equipment shall include a means
by which excessive fines can be controlled so that no more than 5 percent of the fine aggregate passes the No.200 sieve.
c. Aggregate preparation. Usually it is not necessary to wash the crushed recycled aggregates unless they are
contaminated with base or subbase material. State laws governing pollution control must be observed in the crushing
operation.
d. Reinforcing steel. Any reinforcing steel not removed previously must be separated from the recycled concrete
after it is processed through the primary crusher. The pieces of reinforcing steel should be removed either by
electromagnet, suspended above the conveyor belt leading from the primary crusher, or removed manually. The steel will
be the property of the contractor and must be removed from the project.
5-7.
Evaluation and testing.
These aggregates must meet the requirements for normal aggregates. The recycled portland cement concrete
aggregates will be subjected to all tests used to evaluate new aggregates as specified.
5-8.
D-crack concrete pavement recycling.
The deterioration of concrete pavement through D-cracking is a fairly widespread phenomenon. D-cracking occurs
adjacent to joints and is caused by alkali aggregate reaction and freeze-thaw problems. In order to alleviate the problem,
all recycled aggregates from an existing pavement that has experienced this type of deterioration must pass the -inch
sieve if they are to be used as aggregates for a new portland cement concrete pavement. Experience has shown that
crushing the reclaimed portland cement concrete to pass through the 3/4 inch sieve prevents D-cracks from reoccurring
in the recycled pavement.
5-9.
Fine aggregates.
To improve workability of a new portland cement concrete pavement using recycled concrete, natural sand can be
added to the fine aggregates. But when two or more types of fine aggregates are used, each must be stockpiled separately.
5-10. Utilization of recycled aggregates.
Once the old portland cement concrete has been crushed and stockpiled, and the quality has been found to be
satisfactory for its intended use, the material will then be treated as any other aggregate. An applicable document to use
as a guide from that point is TM 5-822-7/AFM 88-6, chap 8.
5-3
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