3501-11 - Progress in Concrete Technology Challenge...

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Progress in Concrete Technology Challenge: Compared to steel, normal concrete has a low strength/weight ratio. Concrete with a higher strength/weight ratio is needed for tall buildings and long- span bridges. Solution: To increase the strength/weight ratio, reduce the weight by using ___________________ or increase the strength by using ____________________ . Challenge: Normal concrete has low toughness and low resistance to impact. Solution: Use _________________________ . Challenge: Low permeability and high chemical resistance are needed for durability of concrete. Solution: Use _______________ . Challenge: Control of temperature rise in mass concrete use for dams and other large structures is needed to reduce the chance of cracking of the concrete. Solution: Use techniques for ____________________ ________ or _________________________ . Challenge: High density material is needed for use as radiation shielding in nuclear power plants. Solution: Use _____________________ . Structural Lightweight Concrete Definition : Concrete having a 28-day compressive strength greater than 2500 psi (17 Mpa) and an air-dried unit weight ______________________ (1850 kg/m 3 ). Composition : Similar to normal concrete except that it is made with lightweight aggregates or combination of lightweight and normal-weight aggregates. ______ ___________ concretes use both lightweight coarse and lightweight fine aggregates. ___________________ concretes used natural sand and lightweight coarse aggregates. Lightweight aggregates used : expanded clays, shales, slates and slags.
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Strength Requirements for Structural Lightweight Concrete as specified in ASTM C 330 Structural Lightweight Concrete (continued) Problem with high slump : For fresh concrete with high consistency, the lightweight aggregate tends to segregate and float to the surface. It is often necessary _________ ________________ and ____________ to lower the mixing water requirement. ACI 213 recommends a maximum slump of 100 mm (4 in.). Air entrainment is generally between 4.5 and 9%.
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