# The maximum specified strength of concrete is defined

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The maximum specified strength of concrete is defined as the 28-day compressive strength determine from a uniaxial compression test using cylinders 6” in diameter by 12’’ in height. It is denoted by f’ c . 9. Is the water/cement ratio a ratio of volumes or weights? The water/cement (w/c) ratio is a ratio of weights. 10. A reinforced concrete beam spans 100 ft. What is the overall dimensional change in its length from a low atmospheric temperature of (-10 ° F) to a high atmospheric temperature of (+100 ° F)? Span (L) = 100 ft = 1200 in Change in Temperature Δ T ° = 100- (-10) = 110 ° F Thermal expansion coefficient for concrete ( α ) = 0.0000055 in/in ° F ≤ α 0.0000075 in/in ° F Change in length due to temperature change L = α( T ° )L 0.73 in Δ L 0.99 in 11. List three advantages and three disadvantages of the use of fly ash in concrete. Advantages of fly ash: Improves workability Decreases permeability Improves sulfate resistance Increases cohesiveness Reduces water content Improves alkali-aggregate reaction (ASR) resistance Disadvantages of fly ash: Slows gain of strength at early age (7 days) Reduces freeze-thaw resistance Increases concrete setting time (an advantage in hot weather)

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12. The harmful effects of hot weather on freshly poured concrete may be minimized by a number of practical procedures in the construction operation. List three of those specific procedures.
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• Spring '09
• bin-shafique
• ACI, sulfate resistance, strength reduction factors, massive concrete structures, early concrete strength

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