1. Concrete Prepaid by: 130670106098 130670106099

2. One Definition of Portland Cement Concrete…  Portland cement concrete (PCC) is a heterogeneous system of solid, discrete, gradiently sized, inorganic mineral aggregates, usually plutonic or sedimentary-calcareous in origin, embedded in a matrix compounded of synthesized polybasic alkaline and alkaloidal silicates held in aqueous solution and co-precipitate dispersion with other amphoteric oxides, this matrix being originally capable of progressive dissolution, hydration, re- precipitation, gelation and solidification through a continuous and co-existent series of crystalline, amorphous, colloidal and cryptocrystalline states and ultimately subject to thermo- allotriomorphic alteration, the system when first conjoined being plastic during which stage it is impressed to a predetermined form into which it finally consolidates, thus providing a structure relatively impermeable and with useful capacity to transmit tensile, compressive, and shear stresses.  (source unknown)

3. A Real Definition of PCC…  A mixture of:  Portland Cement  Fine Aggregate  Coarse Aggregate  Water  Air  Cement and water combine, changing from a moist, plastic consistency to a strong, durable rock- like construction material by means of a chemical reaction called “hydration”

4. Further Defined…  Concrete exists in three states  Plastic  Curing  Hardened

5. Mix Design  Combination of materials to provide the most economical mixture to meet the performance characteristics suitable for the application  Developed in laboratory - produced in a batch plant  Mix proportions will typically vary over a range for a given job  Required strength and exposure conditions  Mix consistency must be ensured to guarantee concrete performance

6. Mixture Design Concepts  Cement content  Sacks/yd 3 or lbs/yd 3  To a point, increasing cement content increases strength and durability  Too much cement is uneconomical and potentially detrimental  Amount of water  Proper selection of aggregate and grading  Admixtures?

8. Water-to-Cement Ratio  The ratio of water-to-cement, or w/c, is the single most important parameter with regards to concrete quality  Theoretically, about 0.22 to 0.25 is required for complete hydration  Practically, the useful limit is around 0.33  Reducing the water for a given amount of cement will move the cement particles closer together, which in turn densifies the hydrated cement paste  This increases strength and reduces permeability  It also makes the concrete more difficult to work  In combination, the w/c and degree of hydration control many of the properties of the hardened concrete

10. Voids in Hydrated Cement  Concrete strength, durability, and volume stability is greatly influenced by voids in the hydrated cement paste  Two types of voids are formed in hydrated cement paste  Gel pores  Capillary pores  Concrete also commonly contains entrained air and entrapped air

11. Voids in Hydrated Cement Paste  Gel Pores  Space between layers in C-S-H with thickness between 0.5 and 2.5 nm  Includes interlayer spaces, micropores, and small isolated capillary pores  Can contribute 28% of paste porosity  Little impact on strength and permeability  Can influence shrinkage and creep

12. Voids in Hydrated Cement Paste  Capillary Voids  Depend on initial separation of cement particles, which is controlled by the w/c  It is estimated that 1 cm 3 of anhydrous portland cement requires 2 cm 3 of space to accommodate the hydration products  Space not taken up by cement or hydration products is capillary porosity  On the order of 10 to 50 nm, although larger for higher w/c (3 to 5 mm)  Larger voids affect strength and permeability, whereas smaller voids impact shrinkage

13. Source: Mindess, Young, and Darwin, 2004 w/c = 0.5

14. Source: Mindess, Young, and Darwin, 2004

17. Capillary Pores C-S-H Framework Neville High Permeability (Capillary Pores Interconnected)

18. Capillary Pores C-S-H Framework Low-Permeability Capillary Pores Segmented and Only Partially Connected

21. Dimensional Range of Solids and Voids in Hydrated Cement Paste Source: Mehta and Monteiro, 1993

22. Source: Mindess, Young, and Darwin, 2004

25. Interfacial Transition Zone  Zone between the aggregate and bulk paste  Has a major impact on the strength and permeability of the concrete  The interfacial zone is 10 to 50 mm in thickness  Generally weaker than either the paste or aggregate due to locally high w/c and the “wall effect” (packing problems) – in some cases predominately large crystals of calcium hydroxide and ettringite are oriented perpendicular to aggregate surface  Greater porosity and few unhydrated cement grains  Microcracking commonly exists in transition zone  Results in shear-bond failure and interconnected macroporosity, which influences permeability  Modification of transition zone is key to improving concrete

28. Entrained Air  Provides the path for water to migrate from larger voids to smaller voids  Water in smallest capillary/gel pores won’t freeze  For adequate protection  6-8% air by volume  Entrained air spacing factor = 0.2mm

29. Entrained Air Measurement  Proper air entrainment is one of the most critical aspects of producing durable concrete  Air entrainment affects  Strength  Freeze-Thaw durability  Permeability  Scaling Resistance  Workability  Air content must be measured accurately at the job site

30. Air-Void System Stereo Microscope ASTM C 457 ASTM C 231 and C 173