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Batching, Mixing, Transporting, and Handling Concrete. Ordering Ready Mixed Concrete. ASTM C 94. Specify: Coarse aggregate size Slump Air content Basis for proportioning, select Options A ,B, or C. Ordering Ready Mixed Concrete. ASTM C 94. Option A —performance based:
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Ordering Ready Mixed Concrete ASTM C 94 Specify: • Coarse aggregate size • Slump • Air content • Basis for proportioning, select Options A ,B, or C.
Ordering Ready Mixed Concrete ASTM C 94 Option A—performance based: Purchaser specifies: • Compressive strength Concrete producer selects mix proportions.
Ordering Ready Mixed Concrete ASTM C 94 Option B—prescription based: Purchaser specifies mixture proportions including: • Cement content • Water content • Admixture type and content
Ordering Ready Mixed Concrete ASTM C 94 Option C—mixed option: Purchaser specifies: • Compressive strength • Cement content • Admixture type and content Concrete producer selects mix proportions.
Stationary Mixing • Stationary Mixers • Onsite or Central Mix R/M plant • Used for complete or shrink mixing • Mixer Types ― up to 9m3 • Tilting or non-tilting drum • Open top revolving blade or paddle • Typical complete mixing times • Minimum of 1 min. for up to 1 yd3 or less mixer capacity plus 15 sec. for each additional yd3 or fraction thereof
Ready Mixed Concrete • Shrink-mixed concrete • mixed partially in a stationary mixer and completed in a truck mixer • Truck-mixed concrete • mixed completely in a truck mixer
Ready Mixed Concrete • Central-mixed concrete • mixed completely in a stationary mixer • delivered in • a truck agitator • a truck mixer operating at agitating speed • a nonagitating truck
Truck Mixed Concrete ASTM C 94 • 70 to 100 revolutions required for mixing, mixing speed = 6 to 18 rpm • After mixing, drum revolves at agitating speed, 2 to 6 rpm • Discharge before exceeding 300 drum revolutions • Discharge before 1½ hours
Mobile Batcher Mixer • Used for: Intermittent production of concrete at jobsite, or small quantities. • Advantages: Combined materials transporter and batching and mixing system. One-man operation. • Watch for: Good preventive maintenance program. Materials must be identical to those in original mix design.
Nonagitating Truck • Used for: Transport concrete on short hauls over smooth roadways. • Advantages: Cost of nonagitating equipment is lower than that of truck agitators or mixers. • Watch for: Slump should be limited. Possibility of segregation. Height upon discharge is needed.
Agitator Trucks • Used for: Transporting concrete for all uses. Haul distances must allow discharge of concrete within 1½ hours. • Advantages: Operate usually from central mixing plants. • Watch for: Timing of deliveries should suit job organization. Concrete crew and equipment must be ready onsite to handle concrete.
Remixing Concrete (1) ASTM C 94 (AASHTO M 157) Water may be added at jobsite provided: • Spec. w/c-ratio is not exceeded • Measured slump less than specified • Allowable mixing and agitating time (or drum revolutions) are not exceeded • Concrete is remixed • min. 30 rev. at mixing speed • until uniformity is within limits
Transporting and Handling Wheelbarrows and Buggies • Used for: Short flat hauls on all types of onsite concrete construction. • Advantages: Versatile—ideal inside and on jobsites with changing placing conditions. • Watch for: Slow and labor intensive.
Transporting and Handling Belt conveyor • Used for: Conveying concrete horizontally or higher/lower level. • Advantages: Adjustable reach, traveling diverter, variable speed. • Watch for: End-discharge arrangements needed to prevent segregation and mortar on return belt. Belt cover needed in hot and windy weather.
Transporting and Handling Truck mounted conveyors • Used for: Conveying concrete horizontally or higher/lower level. • Advantages: Conveyer arrives with concrete. Adjustable reach and variable speed. • Watch for: End-discharge arrangements needed to prevent segregation and mortar on return belt. Belt cover needed in hot and windy weather.
Transporting and Handling Buckets • Used with: Cranes, cableways, and helicopters. • Advantages: Enables full versatility of cranes, cableways, and helicopters to be exploited. Clean discharge. • Watch for: Select bucket capacity to conform to size of the concrete batch and capacity of placing equipment.
Transporting and Handling Rear Discharge Front Discharge
Transporting and Handling Cranes and Buckets • Used for: Work above ground level. • Advantages: Can handle concrete, reinforcing steel, formwork, and sundry items. • Watch for: Has only one hook. Careful scheduling between trades and operations is needed to keep crane busy
Transporting and Handling Pumps • Used for: Conveying concrete from central discharge point to formwork. • Advantages: Pipelines take up little space and can be readily extended. Delivers concrete in continuous stream. Pump can move. • Watch for: Constant supply of freshly-mixed concrete is needed without any tendency to segregate.
Transporting and Handling Flexible Hose at End of Pump’s Rigid Pipeline
Transporting and Handling Screw Spreaders • Used for: Spreading concrete over large flat areas. • Advantages: Concrete can be quickly spread over a wide area to a uniform depth. • Watch for: They are normally used as part of a paving train. They should be used for spreading before vibration is applied.
Transporting and Handling Work Above Ground Level
Videos 1/3 Batching Stationary Mixers
Videos 2/3 Truck Mixer Types Nonagitating Mixers
Videos 3/3 Agitators