cause an abrupt change in thickness without suitable reinforcement. Edges
shall be tapered to leave no square shoulders at the perimeter of a cavity.
The surface shall be dampened but without visible free water.
3.2.3
Rock
Rock surfaces shall be cleaned to remove loose or drummy material, mud,
running water, and other foreign matter that will prevent bond of the
shotcrete. The rock surface shall be dampened prior to placement of
shotcrete.
3.2.4
Shotcrete
When a layer of shotcrete is to be covered by a succeeding layer at a later
time, it shall first be allowed to develop its initial set. Then all
laitance, loose material, and rebound shall be removed by brooming or
scraping. Hardened laitance set shall be removed by sandblasting and the
surface thoroughly cleaned.
3.2.5
Construction Joints
Unless otherwise specified, construction joints shall be tapered to a
shallow edge form, about 25 mm 1 inch thick. If nontapered joints are
specified, special care shall be taken to avoid or remove trapped rebound
at the joint. The entire joint shall be thoroughly cleaned and wetted
prior to the application of additional shotcrete.
3.3
PLACEMENT OF SHOTCRETE
3.3.1
General
Shotcrete shall be placed using suitable delivery equipment and procedures.
The area to which shotcrete is to be applied shall be clean and free of
rebound or overspray.
3.3.2
Placement Techniques
3.3.2.1
Placement Control
Thickness, method of support, air pressure, and water content of shotcrete
shall be controlled to preclude sagging or sloughing off. Shotcreting
shall be discontinued or suitable means shall be provided to screen the
nozzle stream if wind or air currents cause separation of the nozzle stream
during placement.
3.3.2.2
Corners
Horizontal and vertical corners and any area where rebound cannot escape or
be blown free shall be filled first.
3.3.3
Placement Around Reinforcement
The nozzle shall be held at such distance and angle to place material
behind reinforcement before any material is allowed to accumulate on the
face of the reinforcement. In the dry-mix process, additional water may be
added to the mixture when encasing reinforcement to facilitate a smooth
flow of material behind the bars. Shotcrete shall not be placed through
more than one layer of reinforcing steel rods or mesh in one application
unless demonstrated by preconstruction tests that steel is properly encased.
SECTION 03371
Page 14
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