Concrete (1)

1. Portland cement, water, stone and sand

• 2. SCMS (supplementary Cementitous Materials      
•     e.g fly ash, silica fume and natural pozzolans

• 3. Other non-portland cements -
•       Calcium aluminate, magnesium phosphate, and many others
•     
•  4. Chemical admixtures
•     Air entrainment, water reducers, viscosity modifying, set modifiers and many others

• 5. Fiber Reinforcement
•    Organic, natural and metallic : macro and micro
• 6. Conventional Reinforcement
•    Plain, coated, stainless, non ferrous and others(mainly steel)

• <2 MPa controlled low-strength materia
• 15-20 MPa Residential concrete
• 20-25 MPa Commercial buildings
• 25-35 MPa Pavements
• 45-60 MPa bridges
• >70 High Rise buildings
• >100 Special applications

• Normal concrete
• Slip formed
• Self compacting
• Shot crete
• Light weigh concrete
• High density concrete

• Improper Reinforcement placement
• Wet burlap and plastic
• Curing Membrane
• Re bar located to low to carry tensile loads in negative moment area
• Salt corrosion

• Reduce cost
• Stability
• Thermal capability between concrete and steel
• Technical reasons (abrasion and chemical resistance)
• Aesthetics

• Improves workability 
• Sand must be well graded from fine to coarse sizes

Use to provide dimensional stability and reduce cost

• Grading (important for sand)
• Relative density and volume
• Particle shape and texture (interface)
• Aggregate strength
• Geological source (durability)
• Shrinkage
• Moisture content

• FM <2.0 fine sand (too sticky)
• FM >3.0 coarse sand (too boney)

Saturated Surface Dry (SSD) is the ideal moisture condition for aggregates since no extra water is added r removed from concrete during mixing and fresh concrete state

Mass

High surface area may retain excess water when damp

Lower surface area and larger size makes material free draining

Important to allow for moisture in damp aggregate when doing mix design

• Aggregate contains no moisture
• pores are empty

Agg contains some moisture but is not saturated, pores partially filled

Aggregate is saturated pores are filled but there is no free water on surface

Aggregate is saturated pores are filled and there is excess water on the surface

More water is required to lubricate agg with angular shapes than well rounded and smooth particles

Kaitaia 190L/m^3

Auckland - 175 L/m^3

Christchurch - 165 L/m^3

150 L/m^3

• Shape and texture of aggregates
• Grading of aggregates (esp sand) 
• Amount of fine material (high surface area)
• Temperature of concrete

• Make concrete sufficient workable
• React with cement to give strength

• Potable (drinking or town) water is preferable where possible
• 1. Chlorides = corrosion of steel
• 2. Sulphates = setting and strength
• 3. Carbonates = accelerate setting
• 4. Organic matter i.e = prevents setting
• 5. Silts in clays = setting and strength
• 6. Organic acids =delay setting 

pH, softness, Cl- , So4 , Co3 and organics