Ct-18 Special Construction Methods

Concrete Technology Special Construction Methods

Harza Engineering Company

Special construction methods and materials Tunnel lining ■ ■ ■ ■ ■ ■

■

Horizontal slipform paving Canal lining Vertical slipform construction Roller-compacted concrete Controlled Low Strength Material (CLSM) Pervious concrete

Concrete tunnel lining ■

Types Circular tunnels  Horseshoe Shaped 

■

Lining types Full-circle (Smaller diameters)  Multiple placements (Large diameter) 

Invert  Sidewalls  Crown 

Placement methods ■

Invert and sidewalls Conveyors  Pumping  Invert slipform 

■

Arch or crown section 

Pumping

Types of placement ■

■

Bulkhead sections dependent on length of form Continuous placement 

Telescoping forms

Important items ■ ■ ■

■

■

■

Rock cleanup and control of water Cleaning of construction joints Equipment capable of placing the required concrete mixture Segregation during handling and placement Proper consolidation (limited access) - form and immersion vibrators Filling upper most reaches of the crown

Horizontal slipform paving ■

Paving machines Slabs  Curbs  Barriers 

■

■

All horizontal paving requires low slump concrete and good vibration Consistent concrete is essential

Slope paving ■ ■

Canal lining machine Slipform screed 

Alternating panels

Vertical slipform construction ■ ■

Jacking system on vertical rods Suitable for silos and shafts

Pervious concrete

Controlled Low Strength Material (CLSM) ■

■

CLSM is a self-compacted, cementitious material used primarily as a backfill in lieu of compacted fill. (ACI 229R) Most current CLSM applications require unconfined compressive strengths of 300 psi or less. This strength requirement is necessary to allow for future excavation of CLSM.

Applications ■ ■ ■ ■ ■ ■ ■

Backfill Structural fills Insulating fills Pavement bases Conduit bedding Erosion control Void filling

Materials ■ ■

Cement Fly ash Class C  Class F 

■

Fine aggregate ASTM C 33  Silty sand (up to 20% minus #200) 

■ ■

Coarse aggregate (occasionally) Air-entraining admixture

Mixture proportions ■ ■ ■ ■

■ ■

Slump range - 6 to 8 inches Cement content - 50 to 200 pcy Fly ash content - none to 2000 pcy Water contents - typically 325 to 580 pcy Air content as high as 20% Balance of mixture is aggregate