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2.5 CONCRETE MIX DESIGN AND REDESIGN

2.5 CONCRETE MIX DESIGN AND REDESIGN . 2.5.1 Mix design 2.5.2 Mix re-design 2.5.3 Self-Compacting Concrete. Concrete Batching Plants. Moisture control in aggregates. Normal Distribution. mean = failure level + z  standard deviation. Percentage failure permitted. z value. 16. 1.00.

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2.5 CONCRETE MIX DESIGN AND REDESIGN

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  1. 2.5 CONCRETE MIX DESIGN AND REDESIGN • 2.5.1 Mix design • 2.5.2 Mix re-design • 2.5.3 Self-Compacting Concrete

  2. Concrete Batching Plants

  3. Moisture control in aggregates

  4. Normal Distribution mean = failure level + z  standard deviation.

  5. Percentage failure permitted z value 16 1.00 10 1.28 5 1.64 2.5 1.96 2 2.05 1 2.33 A table of z (or n) values for various values of percentage failures (table 1.10.1 in section 1.10 of the notes)

  6. Figure 3

  7. Table 2 Approximate compressive strengths (Mpa) of concrete mixes made with a free w/c ratio of 0.5 Age (days) Type of Cement Type of Coarse Aggregate 3 7 28 90 Ordinary Portland (OPC) or Sulphate Resisting (SRPC) EN Class 42.5 Uncrushed 22 30 42 49 Crushed 27 36 49 56 Rapid Hardening (RHPC) EN Class 52.5 Uncrushed 29 37 48 54 Crushed 34 43 55 61 Table 2

  8. Figure 4

  9. Table 3 Approx water contents (kg/m3) required to give workability Slump (mm) 0-10 10-30 30-60 60-180 Vebe time (s) more than 12 6-12 3-6 0-3 Maximum aggregate size (mm) Type of aggregate 10 Uncrushed 150 180 205 225 Crushed 180 205 230 250 20 Uncrushed 135 160 180 195 Crushed 170 190 210 225 40 Uncrushed 115 140 160 175 Crushed 155 175 190 205 Table 3

  10. Figure 5

  11. Figure 6 (10mm)

  12. Figure 6 (20mm)

  13. 2.5 CONCRETE MIX DESIGN AND REDESIGN • 2.5.1 Mix design • 2.5.2 Mix re-design • 2.5.3 Self-Compacting Concrete

  14. Self Compacting Concrete Why change to SCC? Mix Design Testing

  15. Why change to SCC? • Lower labour cost (no vibration needed) • Better finish • Faster placing • No risk of white-finger • Less noise • Can be placed with congested reinforcement.

  16. Self Compacting Concrete Why change to SCC? Mix Design Testing

  17. Principles of mix design for SCC • Design the concrete mix to achieve the required strength and a slump of 100mm. • If the cement content is less than 500kg/m3, add PFA so that: • The total cementitious (cement + PFA) is 500kg/m3 • The equivalent cement content (= Cement + 0.3  PFA) is the same as the cement content from the original mix design. • Check that the PFA is less than 40% of the total cementitious content. If it is more than 40% some of it will not react, so it will not contribute to the strength. • Add superplasticiser and VMA in the amounts specified by the manufacturers.

  18. Proportioning the admixtures • Add a superplasticiser to get the flow • Add a VMA to prevent segregation • Use the manufacturers’ data on W drive • Note that some VMAs are used in very small quantities.

  19. Self Compacting Concrete Why change to SCC? Mix Design Testing

  20. Test Methods • Slump Flow • V Funnel • L box Slump Flow Test The standards are on W drive

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