Factors Affecting Segregation and Cohesiveness Maximum size of coarse aggregate Combine grading of fine and coarse aggregate Amount of clay-size fines High cement factor fines provide cohesion Low cement factor requires presence of fines in aggregates Air entrainment
Factors Affecting Bleeding of Concrete Mixture Proportions Air Content Slump Chemical Admixtures Cementitious Materials Angularity and grading of fine aggregate
Bleeding and Settlement Bleed water on the surface of a freshly placed concrete slab. Bleeding is the development of a layer of water at the top or surface of freshly placed concrete. It is caused by sedimentation (settlement) of solid particles (cement and aggregate) and the simultaneous upward migration of water.
Factors Affecting WorkabilityAggregate grading, Shape & Surface Texture Quantity and characteristics of cementing materials Concrete consistency (slump) % entrained air Water content Admixtures
Aggregate Properties Influencing Fresh Concrete Proportions Aggregate Grading Particle Shape Maximum Size Texture Bulk Unit Weight Absorption Specific Density Amount of fines
Aggregate Grading Influence the proportions Economy of mix Amount of mixing water Maximum size of coarse aggregate Particle size range Aggregate Fines Coarse aggregate limit 3/8” sieve Fine aggregate limit #50 mesh sieve
Aggregate Particles Angularity and roughness Increased Water Demand Higher Mortar Content Flat and Elongated pieces Harshness for placement Voids and honeycombing Pump blockages
Aggregate Particle Degradation Increased water demand Slump Loss Decreased air content Absorption of mix water by porous aggregate Extended mixing time
Relationship Between Aggregate Size - Cement Content - Air Content Relationship between aggregate size, cement content, and air content of concrete. The air-entraining admixture dosage per unit of cement was constant for air- entrained concrete.
Relationship Between Aggregate Size - Cement Content - Air Content Relationship between percentage of fine aggregate and air content of concrete.
Relationship Between Freeze-Thaw Resistance, W/C-Ratio, and Different Concretes and Curing Conditions (1) Relationship between freeze-thaw resistance, water-cement ratio, and drying for air-entrained and non-air-entrained concretes made with Type I cement. High resistance to freezing and thawing is associated with entrained air, low Type I cement water-cement ratio, and a drying period prior to freeze-thaw exposure.
Relationship Between Freeze-Thaw Resistance, W/C-Ratio, and Different Concretes and Curing Conditions (2) Relationship between freeze-thaw resistance, water-cement ratio, and drying for air-entrained and non-air-entrained concretes made with Type I cement. High resistance to freezing and thawing is associated Type I cement with entrained air, low water-cement ratio, and a drying period prior to freeze-thaw exposure.
Effect of weathering on boxes and slabs on ground at the Long- Time Study outdoor test plot, Project 10, PCA, Skokie, Illinois. Specimens at right are air-entrained, specimens. 21
At right exhibiting severe crumbling and scaling are non- air-entrained. All concretes were made with 335 kg (564 lb) of Type I portland cement per cubic meter (cubic yard). Periodically, calcium chloride deicer was applied to the slabs. Specimens were 40 years old when photographed (see Klieger 1963 for concrete mixture information). (69977, 69853, 69978, 69854)
Factors Affecting Compressive Strength of Structural Lightweight Concrete Cement Content Slump Air Content Typical ranges: 20 to 35 MPa (3000 to 5000 psi)
Structural Lightweight Concrete Strength vs. Cement Content Relationship between compressive strength and cement content of field structural lightweight concrete using lightweight fine aggregate and coarse aggregate.
Structural Lightweight Concrete Air Entrainment Resistance to Freezing and thawing Resistance to Deicer Applications Improves workability, reduces bleeding, and segregation Compensates for minor grading deficiencies Air Contents range 5% to 8% depending on max size of aggregate Tested by Volumetric method (ASTM C 173)
Lightweight Concrete Considerations Bleeding Workability Pumpability (slump loss/absorption) Segregation Vibration Minimum amount of floating and troweling
Lightweight AggregatePlease return to Blackboard and watch thefollowing videos: Video 1: Particle Shape & Surface Texture Video 2: Gap Graded Aggregate Video 3: Max Size Video 4: Nominal Size