Batching, Mixing, Transporting, and Handling Concrete

1. Batching, Mixing, Transporting, and Handling Concrete

2. Ordering Ready Mixed Concrete ASTM C 94 Specify: • Coarse aggregate size • Slump • Air content • Basis for proportioning, select Options A ,B, or C.

3. Ordering Ready Mixed Concrete ASTM C 94 Option A—performance based: Purchaser specifies: • Compressive strength Concrete producer selects mix proportions.

4. Ordering Ready Mixed Concrete ASTM C 94 Option B—prescription based: Purchaser specifies mixture proportions including: • Cement content • Water content • Admixture type and content

5. 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.

6. Batching

7. 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

8. 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

9. 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

10. Ready Mix Plant

11. 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

12. 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.

13. 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.

14. 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.

15. 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

16. 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.

17. 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.

18. 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.

19. 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.

20. Transporting and Handling Rear Discharge Front Discharge

21. 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

22. 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.

23. Transporting and Handling Flexible Hose at End of Pump’s Rigid Pipeline

24. 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.

25. Transporting and Handling Work Above Ground Level

26. Videos 1/3 Batching Stationary Mixers

27. Videos 2/3 Truck Mixer Types Nonagitating Mixers

28. Videos 3/3 Agitators