Seminario Internacional: Dosificación y especificación de hormigón por desempeño "Buenas Prácticas y Mejoramiento del Desempeño de Hormigones para Pavimentos"

2. Best Practices
• Dr Peter Taylor

3. Overview
• Design
• Foundation system
• Materials
• Construction

4. Proper Design

5. Design methods
• Programs
• AASHTO Design Guide 1993 (WinPass)
• AASHTO M-E PDG
• StreetPave (ACPA)
• TCP Design

6. Foundation System
TR-525, Design Guide for Improved
Quality of Roadway Subgrades
& Subbases
“The performance of a pavement
depends on the quality of its
subgrade and subbase layers; these
foundational layers play a key role in
mitigating the effects of climate and
the stresses generated by traffic.”
• To provide support
• To control movement

7. Goals
• Support should be
• Uniform
• Stiff / strong enough
• Stable

8. Natural
Subgrades
Movement
• Causes of subgrade movement:
• Non-uniform soils
• Compressible soils
• Expansive Soils
• High Moisture Content
• Low Strength
• Poor Consolidation
• Settlement
• Frost susceptible soils

9. Uniformity
• Critical Areas to Control
• Uniform compaction after disturbing soil.
• Moisture in subgrade

10. Moisture
• Moisture content influences compressive strength
• Granular Soils: Stay ~1-3 percent below optimum
• Silt and Clay: Stay ~ 2 percent of optimum
100
102
104
106
108
110
112
114
116
4 6 8 10 12 14 16 18 20 22 24
Percent moisture content (based on dry unit weight)
DryUnitWeight(lb/ft3)
0
50
100
150
200
250
300
Compressivestrength(lb/in2)
Density
90-day Strength

11. Strength
• California Bearing Ratio (CBR)
• Compares the bearing capacity of soil
with that of a well graded crushed stone.
• Intended for cohesive soils

12. Stability
• Effect of moisture on movement and support

13. Materials
• Aggregates
• Cementitious materials
• Admixtures
• Water
• Mixture

14. Aggregates
• Gradation
• Tarantula
• Stability
• Alkali aggregate reactivity
• D-cracking
• Surface popouts
• Abrasion resistance
• Others?

15. Cementitious Materials
• Hydraulic cement – reacts under water (Portland
cement, Slag and Class C fly Ash)
• Pozzolan – reacts with cement and water- Slag,
Class C and F fly Ash, Silica Fume
• Supplementary cementitious materials –
cementitious materials & pozzolans

16. So What Do SCM’s Do?
• Reduce water requirement
• Make air entrainment more difficult
• Retard setting
• Slow bleeding
• Reduce heat
• Slow initial
strength gain
Time
Property

17. What Do SCM’s Do?
0.0
0.1
0.2
0.3
0.4
0 100 200 300
Expansion,%
Time, days
0%
10% C
20% C
20% F
• Reduce permeability
• Reduce chloride penetration
• Reduce ASR expansion
• Improve sulfate resistance
• Reported higher risk of scaling
• Similar mechanical
(creep, shrinkage)

18. Implications of Using SCMs
• SCMs change concrete properties
• Means we have to allow for them
• Cracking risk changes
• Finishing and curing needs change

19. Chemical Admixtures
• Air entraining admixtures (AEA)
• Water reducers
• Set modifying admixtures
• Make good concrete better – not to fix bad concrete

20. Air Entraining Admixtures
• Essential for resistance to freezing and thawing
• Improved workability, reduced water, and reduced segregation
• Reduces strength
• Inexpensive
• ASTM C 260

21. Water Reducers
• Reduce water required about 5% (12%)
• ASTM C 494 Type A (or F)
• May affect air-entrainment
• May retard setting

22. Mixture Design
• Process of determining required and specifiable characteristics of a
concrete mixture:
• i.e. Choosing what you want

23. Mixture Proportioning
• Process of determining the quantities of concrete ingredient
• i.e. choosing what to use to get what
you want

24. Construction
• Batching, mixing and hauling
• Placing, consolidating and finishing
• Sawing and curing

25. Batching
• Control
• Uniformity
• Batching sequence
• Calibrations
• Goal
• Batch-to-batch uniformity
25

26. Manage Stockpile
• Prevent contamination
• Maintain uniform
• Gradation
• Moisture

27. Adjust for Aggregate Moisture

28. Monitoring
• Watch materials uniformity
• Beware of “incompatibility”
• Allow for changes in weather
• Don’t add excess water

29. Excess water
• Adding 1 gal. of water to 1 yd3 of concrete:
• Increases slump 1 in.
• Decreases compressive strength by 200 psi
• Wastes the effect of 1/4 sack (23.5 lb) of cement
• Increases shrinkage by 10%
• Increases permeability by up to 50%
• Increases risk of air void problems

30. Concrete Mixing and Delivery
• The concrete must be thoroughly mixed either at the plant or in the
transit mixer.
• If allowed by specifications, adjustments to the mix are possible if a
transit mixer is used.
• Ideally, the paver controls the production and delivery rate.
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31. Field Adjustments
• Ambient temperatures
• Material variability
• Material supply changes
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32. Control Workability
• Affected by
• Water content
• Aggregates
• Air
• Time
• Temperature
• SCMs
• Admixtures

33. Consolidation
• Ensure adequate consolidation
• Required around dowels and tie bars
• Throughout the slab
• But not too much
• Control amplitude, speed and frequency

34. Curing
• Cement hydration starts fast, slows, and goes a long time
• Has to have water available
• Has to be warm enough
• Cure early cure often

35. Thermal Protection
• Avoid thermal shock
• Protect from cold fronts

36. Sawing Joints
• Concrete expands as temperature rises and as moisture falls

37. Drying or Thermal?
• Thermal
• 140 to 350 millionths (40°F)
• Starts with cooling
• Drying
• 400 to 800 millionths
• Starts with drying, continues for a long time

38. Joints
• Pay attention to
• Locations
• Type
• Timing
• Details
T/3

39. Sawing

40. Late Sawing Poor Detailing
Sawing

41. Closing
• It’s complicated
• Details are important
• Education is critical
• Enjoy!

42. • Questions?