Chapter 2: Concrete-Producing
Materials
CE360
Reinforced Concrete Design
Dr. Chun K. Seong
School of Engineering
Saint Martin’s University
The course material is prepared, based on the textbook “Design of Concrete Structures” written by
Arthur H. Nilson, David Darwin, Charles W. Dolan, published by McGraw Hill
Objectives
• To learn about components of concrete members:
Cement, Aggregates, Admixtures, Water
• To learn about Proportioning and Mixing Concrete
• To learn about concrete conveying, compacting, and curing
• To learn about concrete properties in compression and tension
• To learn about material behavior of concrete: shrinkage and temperature effects of concrete
• To learn about reinforcing steels and their properties. 2.1 Introduction of Materials for Concrete
Concrete structures are composed of
Concrete reinforced with
Steels bars,
Pre-stressed with steel wire,
Strand, or
Alloy bars.
Understanding the performance of structural concrete, and to safe, economical, and serviceable design of concrete structure.
2.1 Introduction
Mixture of
Cement
Fine aggregate
Coarse aggregate
Water
Admixtures(frequently)
Chemical hydration reaction of cement-water mix results hardened concrete.
2.2 Cement
Cementitious material – adhesive and cohesive material to bond inert aggregates into solid mass of adequate strength and durability
Structural Concrete
• Hydraulic Cements – calcium silicates & aluminates of lime, are hydrated (hydration) with water to set and harden into solid mass. Lime stones CaO, SiO2, Al2O3 are grinded and fused to clinkers in kiln. Gypsum is added and the mixture is ground and shipped in a bag or in bulk.
• Portland Cement – one of the common hydraulic cements was patented by Joseph Aspidin of
Leeds, England in 1824.
2.2 Cement – Types of Portland Cement
Five standard types of cement exist.
– Type I – normal Portland cement: 90% in US
1~2 week to sufficient strength, 28 days full
– Type III – high early strength cements
2.2 Cement
Water added to the mixture for concrete setting and Hardening
• Dissolves materials at surfaces of cement grains and form a gel that increase volume and stiffness
• Hydration continues to proceed deeper, continuing stiffening and hardening of the mass
• Principal product of hydration
– Calcium silicate hydrate-insoluble
– Calcium hydrate-soluble
Concrete setting, hardening and curing
• For complete hydration – 0.25 water-cement ratio required (by weight).
More water needed for mobility and workability.
• For normal concrete, 0.4 ~ 0.6 w/c ratio was common, for high-strength,
0.21 w/c ratio have been used.
• Any amount of water in excess of chemical reaction produces pores in the cement paste.
• The strength of hardened paste decreases inversely with the fraction of total volume occupied by pores. Voids cannot resist stress, no strength.
• Heat of hydration – mass concrete, volume expansion.
2.3 Aggregates
Constitute the bulk of concrete (65~80% of Volume) – remainders are hardened cement paste, uncombined water and air voids.
Densely packed aggregates - Source of concrete strength – well graded aggregates are important
• Coarse aggregate: gravel, crushed stone, blast furnace slag
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–
–
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Particle size larger than ¼ in. (6mm or No. 4 sieve), but less than
1/5 of narrowest dimension of the form work and,
1/3 the depth of slabs and,
¾ of min. distance between the rebars.
• Fine aggregate: natural or manufactured sand No. 4 ~
No.100 US standard sieve size should be well graded and free of organic impurities.
Favorable gradation – aggregates separated by sieving into 2 or 3 size groups of sand, and several size groups of coarse aggregate. 2.3 Aggregates
• Stone Concrete: natural stone aggregate – 140 ~152 lb/ft3 • Lightweight concrete – lightweight aggregate: unprocessed aggregate, processed aggregate
– Low-density concrete (cellular concrete): less than 50 lb/ft3, used for insulation
– Moderate strength concrete: 60~85 lb/ft3 and 1000~2500
psi,
