Structural System. Design Considerations Concrete Structures. Materials Formwork Labor Time

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1 Structural System Understand Behavior of Elements in System & Load Transfer through Structure Joists and Beams Columns (and Walls) Beam-Column Joints One- or Two-way slabs Foundation (Footings, Mats) Design Considerations Concrete Structures Materials Formwork Labor Time 1

2 What do we want from our structure? Strength Stiffness Ductility Durability Economy What do we want from our concrete? Strength Stiffness Workability Durability Economy Properties of Fresh Concrete Result of Poor Concrete Placement due to Inadequate Workability of the Mix Workability ease of placement; resistance to segregation; wellmixed Consistency ability to flow Hardened Concrete Properties Strength and Stiffness Compressive strength, f c, 2,000-12,000 psi Tensile strength, f t, 200-1,200 psi Modulus of Elasticity 57,000*sqrt(f c ) Durability Resistance to freezing and thawing; Cracking; Corrosion Cement Content $/ton (8/1/11) Aggregates 6-8 $/ton (6/1/11) Steel 810 $/ton Economy Minimum cement required at the minimum water cement ratio, with the maximum strength and durability Economy is not just materials also consider formwork, labor, & time (concrete 20%; rebar 30%; formwork 50%) 2

3 Portland Cement 2/3 lime (CaO) from limestone 1/3 silica (SiO 2 ) and aluminum (Al 2 O 3 ) and iron from sand and clay and iron ore Dry powder of very fine particles Forms a paste when mixed with water that surrounds the individual pieces of aggregate to make a plastic mixture Chemical reaction (Hydration) takes place between cement and water that is exothermic (it gets hot). Hydration forms a crystalline paste that fills in the voids between the aggregate particles Hardens and forms a solid mass PCA Table 2-1. Sources of Raw Materials Used in Manufacture of Portland Cement Calcium Iron Silica Alumina Sulfate Alkali waste Blast-furnace flue dust Calcium silicate Aluminum-ore refuse* Anhydrite Aragonite* Clay* Cement rock Bauxite Calcium sulfate Calcite* Iron ore* Clay* Cement rock Gypsum* Cement-kiln dust Mill scale* Fly ash Clay* Cement rock Ore washings Fuller s earth Copper slag Chalk Pyrite cinders Limestone Fly ash* Clay Shale Loess Fuller s earth Fuller s earth Marl* Granodiorite Limestone* Ore washings Limestone Marble Quartzite Loess Marl* Rice-hull ash Ore washings Seashells Sand* Shale* Shale* Sandstone Slag Slag Shale* Staurolite Slag Trap rock (just don t take from Giant s Causeway, Ireland) Note: Many industrial byproducts have potential as raw materials for the manufacture of portland cement. Cement Production Facility Cement production is responsible for 7% of the man-made CO 2 production in the world 1/2 from chemical process & ½ from burning fossil fuels Promote use of Fly Ash & Silica Fume w/ cement 410 kg/m3 reduced to 290 kg/m3 with 30% fly ash Aggregates Cheap fillers Hard material Provide for volume stability Reduce volume changes Provide abrasion resistance Water/Cement Ratio The most important indicator of strength is the ratio of the water used compared to the amount of cement Advantages of a low w/c ratio Increased strength Lower permeability Increased resistance to weathering Better bond between concrete and reinforcement Reduced drying shrinkage and cracking Less volume change from wetting and drying 3

4 Internal voids Strength and Curing Strength 100% moist cured entire time in air after 7 days in air after 3 days in air entire time 28 time Stiff 0-2 massive sections, little reinforcement Medium 2-5 columns, beams, retaining walls Fluid 5-7 (sometimes even 10 ) heavily reinforced section, flowable concrete Factors affecting slump-paste content Low paste content Harsh mix High paste content Rich mix angular and rough aggregate smooth aggregate river gravel 4

5 Larger particles, less surface area, thicker coating, easy sliding of particles Smaller particles, more surface area, thinner coating, interlocking of particles Taipei 101 STRUCTURAL PLAN OF HIGHER STORIES Pumping Test of HPC 5

6 Slump Achieved w/ Superplasticizers 6