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Properties of Fresh Concrete. State: Prior to setting Fluid like material – plastic concrete Properties: Adequate flow for several hours – Workability.

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Presentation on theme: "Properties of Fresh Concrete. State: Prior to setting Fluid like material – plastic concrete Properties: Adequate flow for several hours – Workability."— Presentation transcript:

1 Properties of Fresh Concrete

2 State: Prior to setting Fluid like material – plastic concrete Properties: Adequate flow for several hours – Workability No segregation and separation – Uniform  Bleeding

3 Properties of Fresh Concrete Workability – ease with which a fresh concrete mix can be handled – mixing, transporting, compacting, finishing

4 Properties of Fresh Concrete Factors influence Workability Fine materials - Adequate quantity  Deficiency – harsh mixture ( segregation and mixing difficulty) Coarse aggregate – Low water content – High Addition of fine rounded materials – e.g., fly ash, silica fume Air-entraining admixtures Ambient temperature

5 Water and Aggregate Effects

6 Rounded particles – better workability Angular particles – poor workability

7 Properties of Fresh Concrete Factors influence workability 1. Increase of Max. size of the CA 2. Rounded Decrease of Surface area Workability improves Increase in ambient temp. 1. Increase in hydration rate 2. Increase in rate of evaporation Delay in placing or consolidation reduces workability

8 Properties of Fresh Concrete Workability Consistency – Wetness or fluidity  Measured by slump test Mobility Compactibility

9 The Slump Test - ASTM C 143 Zero-slump – dry mix with low W/C Normal slump – 2-4 inch Shear slump – non-cohesive / lacks of plasticity, collapse slump – extremely wet, harsh concrete

10 Properties of Fresh Concrete Shear slump or collapse slump segregate and bleed Causes: Lack of sufficient content of fines – non-cohesive High W/C

11 Amount of Mixing Water Relatioship between slump and water content is non- linear

12 % Loss of Slump Slump decreases with time Hydration Evaporation Rate increases with increase in ambient Temp.

13 Properties of Fresh Concrete Changes in slump due to variation in water content Grading and proportioning of aggregates Amount, fineness and brand of cement ambient Temp.

14 Workability test

15 T = g + h N T is the torque N is the impeller rotational speed g - flow resistance h - torque viscosity

16 Properties of Fresh Concrete Mixing Machine mixing - Ready mix plant Pumping and Placing Finishing

17 Placing

18 Properties of Fresh Concrete Segregation and bleeding Segregation separation between large and fine particles Very wet or deficient in finer particles mixtures High slump concrete e.g., Honeycombing, crazing, surface scaling Air-entrainement or adding finer particles (e.g., fly ash) decreases segregation

19 Honeycombing

20 Bleeding

21 Mixture Design  For a paving project with a 9 inch slab and a minimum strength of 3000 psi, determine using ACI 211:  1) the w/cm  2) the slump  3) # of sacks of cement  4) the CAF  Assume: FM = 2.9 Agg Size = 1.0 in

22 Concrete Setting Behavior ASTM C-403 Initial set – beginning to stiffen (loses fluidity) Final set – beginning to harden

23 Chemical Admixtures

24 Water Reduction

25 AEA

26 Testing for Air Content

27 Type B Pressure Meter

28 Roll-a-Meter

29 Chace Air Indicator

30 Fly Ash and Air Content Effects

31 Unit weight (W), Air content T = W1/V, Air content = ((T-W) / T) X100

32 Strength Specimen Preparation

33

34 Slump, Air, and Cylinder Casting

35 Curing Maintains favorable condition of Temp. and moisture


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