1 / 40

MIX PROPORTIONING

MIX PROPORTIONING. Prepared by Marcia C. Belcher Construction Engineering Technology. Design Consideration: Obtaining Good Workability. Design Consideration: Obtaining Good Workability. Obtaining Good Workability. Obtaining Good Workability.

Audrey
Download Presentation

MIX PROPORTIONING

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. MIX PROPORTIONING Prepared by Marcia C. Belcher Construction Engineering Technology

  2. Design Consideration: Obtaining Good Workability

  3. Design Consideration: Obtaining Good Workability

  4. Obtaining Good Workability

  5. Obtaining Good Workability

  6. Design Consideration: Prevent Segregation & Bleeding

  7. Well Graded Aggregates Will Reduce Segregation & Bleeding Well Graded Poorly Graded

  8. Measuring Workability: Slump

  9. The Slump Cone

  10. Approximate Required Slump Values (PCA)

  11. Goals: Maximize strength = minimize water = control bleeding & segregation Reduce Cost = use largest gravel possible for the job = minimize paste requirement Provide good durability = use well graded aggregates = maximize void packing = reduced segregation Economics of Mix Design

  12. Cost Comparison of Constituents

  13. Guidelines We Use For Mix Design • PCA Manual • Tables for w/c ratio based on compressive strength requirement & slump (workability) • Volume of stone required based on max. agg. size and sand fineness. • Water required based on max. agg. size, slump & w/c ratio (compressive strength)

  14. Design Method We Will Use:Absolute Volume Method • Assumes no air voids in concrete • Amount of concrete is sum of solid volumes: 1 CUBIC YARD • Cement • Sand • Coarse aggregate • Water • Air

  15. WATER CORRECTION • Any water content in aggregates above SSD water content must be subtracted from the water requirements • Any water requirement of aggregates (below the SSD water content) must be added to the water requirements

  16. Material Values & Constants Needed For Design: • SSD (Absorption) of Sand • Unit Weight & SG of Sand • SSD (Absorption) of Stone • Unit Weight & SG of Stone • Density of Cement = 195 pcf • SG Cement = 3.15 • Density of Water = 62.4 pcf • 1 Cubic Foot Water = 7.48 gal • 1 Gal. Water = 8.34 lbs

  17. ACI Standard Mix Design Method • The standard ACI mix design procedure can be divided up into 8 basic steps: • Choice of slump • Maximum aggregate size selection • Mixing water and air content selection • Water-cement ratio • Cement content • Coarse aggregate content • Fine aggregate content • Adjustments for aggregate moisture

  18. Step #1: Select Slump Table 9.6

  19. Step #2: Determine Mixing Water and Air Content Table 9.5

  20. Step #3: Max. Agg. Size Check • DEFINITION: Nominal maximum aggregate size is the largest sieve that retains some of the aggregate particles. • ACI Limits: • 1/3 of the slab depth • 3/4 of the minimum clear space between bars/form • 1/5 minimum dimension of non-reinforced member • Aggregate larger than these dimensions may be difficult to consolidate and compact resulting in a honeycombed structure or large air pockets.

  21. Step #4: Select W/C Ratio Table 9.3

  22. Step #5: Cement Content • The calculated cement amount is based on the selected mixing water content and water-cement ratio. • W/C= Wt. of Water Wt. of Cement

  23. Step #6: Coarse Agg. Content Table 9.4

  24. Step #7: Fine Agg. Content

  25. Step #8: Batch Weight & Water Adjustment • Aggregate weights.  • Aggregate volumes are calculated based on oven dry unit weights, but aggregate is batched in the field by actual weight.  • Any moisture in the stockpiled aggregate will increase its weight. • Without correcting for this, the batched aggregate volumes will be incorrect. • Amount of mixing water.  • If the batched aggregate is anything but saturated surface dry it will absorb water (if dry) or give up water (if wet) to the cement paste.  • This causes a net change in the amount of water available in the mix and must be compensated for by adjusting the amount of mixing water added.

  26. Mix Design Example: 10” Thick Unreinforced Pavement Slab

  27. Properties of Concrete Specified By Engineer: Slump =1.0 inch 28-day strength of 5000 psi Air content: 4.5 - 6.5 percent

  28. Information About Materials: • Coarse aggregate we are using (ODOT #467): • nominal maximum size = 1.5 inch (see Agg. Size Table) • dry-rodded weight = 100 lb/ft3 • specific gravity = 2.68 • moisture content = 1.0 percent • absorption = 0.5 percent • Fine aggregate: • fineness modulus = 2.80 • specific gravity = 2.64 • moisture content = 5 percent • absorption = 0.7 percent

  29. WE ARE DESIGNING BATCH WEIGHTS FOR ONE CUBIC YARD • Step #1: Select Slump • Engineer Specified 1” (correlates w/table) Table 9.6

  30. Step #2: Determine Mixing Water and Air Content 1.5” Stone Table 9.5 1” Slump

  31. Step #2: Determine Mixing Water and Air Content • Weight of Water = 250 lbs/yd3 • Volume of Water = 250 lbs/yd3= 4 ft3 62.4 lbs/ft3 Volume of Water = 4 ft3 per cubic yard of concrete

  32. Step #3: Max. Agg. Size Check • ACI Limits: • 1/3 of the slab depth • 10”/3 = 3.33 inches > 1.5” OK

  33. Step #4: Select W/C Ratio Table 9.3

  34. SG Cement Step #5: Cement Content • W/C= Wt. of Water Wt. of Cement • Wt. of Cement = 250 lbs/yd3 .40 =625 lbs/yd3 • Volume of Cement = 625 lbs/yd3 (Concrete) 3.15 x 62.4 lbs/ft3 Volume of Cement = 3.18 ft3 per cubic yard of concrete

  35. Step #6: Coarse Agg. Content Table 9.4

  36. Step #6: Coarse Agg. Content Weight(Dry) =.71 x 27 ft3/yd3 x 100 lb/ft3 = 1,917 lbs Volume = 1,917 lbs = 11.46 ft3 2.68 x 62.4 lbs/ft3 Dry Rodded Unit Wt of Stone SG Stone

  37. Step #7: Fine Agg. Content Wt of Sand(Dry) = 6.87 ft3 x 2.64 x 62.4 lbs/ft3 = 1,131.7 lbs. SG Sand

  38. Step #8: Aggregate Batch Weights & Water Adjustment Since there is moisture in both coarse & fine aggregate, their batch weights must be adjusted 1% Moisture 5% Moisture • Wt of Stone(Wet) = 1,917 lbs x 1.01= 1,936.2 lbs • Wt of Sand(Wet) =1,131.7 lbs x 1.05= 1,188.3 lbs

  39. Step #8: Aggregate Batch Weights & Water Adjustment Mixing water needs to be adjusted. Both the coarse and fine aggregate are wet of SSD and will contribute water to the cement paste. Water from Stone = 1,917 lbs. x (.01-.005) = 9.59 lbs Water from Sand= 1,131.7 lbs x (.05-.007) = 48.66 lbs Water = 250 lbs – 9.59 lbs – 48.66 lbs = 191.75 lbs Dry Wt. Moisture Absorption Dry Wt. Moisture Absorption

  40. Final Batch Wts. (1 Cubic Yard)

More Related