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  1. 1. Prestress Concrete Design Sessional CE-416 Presented by Md Mashqur Ul Alam Student ID: Department of Civil Engineering Ahsanullah University of Science and Technology
  2. 2. Content Definition Classification of Concrete States of Concrete Material Properties of Concrete Workability Uniformity Non-segregation Strength Durability Watertightness Admixtures
  3. 3. Definition: Concrete is a mixture of aggregate and often controlled amounts of entrained air held together by a hardened paste made from cement and water. Although there are other kinds of cement, the word cement, in common usage, refers to portland cement.
  4. 4. Classification of Concrete Based on unit weight     Ultra light concrete <1,200 kg/m3 Lightweight concrete 1200- 1,800 kg/m3 Normal-weight concrete ~ 2,400 kg/m3 Heavyweight concrete > 3,200 kg/m3 Based on strength (of cylindrical sample)     Low-strength concrete < 20 MPa compressive strength Moderate-strength concrete 20 -50 MPa compressive strength High-strength concrete 50 - 200 MPa compressive strength Ultra high-strength concrete > 200 MPa compressive strength Based on additives:     Normal concrete Fiber reinforced concrete Shrinkage-compensating concrete Polymer concrete
  5. 5. States of concrete Concrete has three different states:  PLASTIC : Plastic concrete in a relatively fluid state can be readily molded by hand like a clump of modeling clay.  SETTING: The stiffening of concrete, when it is no longer soft  HARDENING: This is the end product of any concrete design.
  6. 6. Material Properties of Concrete The Properties of Concrete are its characteristics or basic qualities :  Workability  Uniformity  Non-segregation  Strength  Durability  Watertightness Plastic concrete Hardened concrete
  7. 7. Workability Workability means how it is easy to place, handle, compact and finish a concrete mix. Facts needed to be considered for good workability:  Proportions of fine and coarse aggregate  Consistency  Amount of slump
  8. 8. Slump Test
  9. 9. Penetration Test  It is a measure of consistency  The ratio of slump to penetration is usually between 1.3 and 2.0 Fig: Kelly Ball Penetration
  10. 10. Nonsegregation Plastic concrete must be homogeneous and carefully handled to keep segregation to a minimum. For example, plastic concrete should not drop (free-fall) more than 3 to 5 feet nor be transported over long distances without proper agitation.
  11. 11. Uniformity The uniformity of plastic concrete affects both its economy and strength. Uniformity is determined by how accurately the ingredients are proportioned and mixed according to specifications. Each separate batch of concrete must be proportioned and mixed exactly the same to ensure that the total structural mass has uniform structural properties.
  12. 12. Strength The ability of concrete to resist a load in compression, flexure, or shear is a measure of its strength. This is the most important property of concrete for engineers. Concrete strength is largely determined by w/c ratio in the mixture.  Time  Curing
  13. 13. Curing
  14. 14. Durability Concrete's ability to resist the effects of wind, frost, snow, ice, abrasion, and the chemical reaction of soils or salts is a measure of its durability. Climate and weather exposure affect durability.  As the w/c ratio increases, durability decreases correspondingly.  Air-entrained concrete has improved freeze-thaw durability.  Durability should be a strong consideration for concrete structures expected to last longer than five years. 
  15. 15. Watertightness The watertightness of concrete is judged by the depth of penetration of water forced in under pressure with the mechanism of flow of seepage water examined theoretically and experimentally. depends on the w/c ratio and the extent of the chemical reaction progress between the cement and water. W/C ratio should be 0.48 for concrete exposed to fresh water and 0.44 for concrete exposed to salt water. The watertightness of airentrained concrete is superior to that of non-air-entrained concrete.
  16. 16. Admixtures Admixtures are mixed into the concrete to change or alter its properties. Chemical Admixture: Retarders: sugar, sucrose, sodium gluconate, glucose, citric acid, and tartaric acid Air entrainment agent: Lime Plasticizers: Lignosulfonate Accelerator: CaCl2, Ca(NO3)2 and NaNO3 Mineral Admixture: Fly ash Ground granulated blast furnace slag Silica fume High reactivity Metakaolin(HRM)
  17. 17. Thank You