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The temperature when the concrete is placed can be somewhat controlled by using cold water for the mix, cooling down aggregates using ice, or pouring at night when temperatures are naturally lower.
To prevent thermal cracking of mass concrete, the hydration heat of concrete can be controlled by using a low-heat concrete mixture, the pre-cooling method, the pipe cooling method, etc.
How Much Heat is Generated? As a general rule, the Portland Cement Association estimates that for every 100 pounds of cement, the concrete gains anywhere from 10 to 15 degrees Fahrenheit in temperature.
The heat of hydration is the heat generated when water and portland cement react. Heat of hydration is most influenced by the proportion of C3S and C3A in the cement, but is also influenced by water-cement ratio, fineness and curing temperature. As each one of these factors is increased, heat of hydration increases.
compound tricalcium aluminate
A. False set is a form of premature stiffening of the paste or concrete, which occurs within 1 to 5 min after mixing. False set can be eliminated by continuous mixing or by reworking and may not be noticed on jobs supplied by truck mixers or with central-mixed concrete that is agitated during delivery to the site.
What is the most dominant constituent of cement? Explanation: Cement contains about 60-65% of lime. Silica constitutes 17-25%, alumina 3-8% and magnesia 1-3%. Explanation: Presence of lime in sufficient quantity is necessary to form silicates and aluminates of calcium.
Portland cement particles are generally in the range of 1–50 micrometre (μm) while fly ash particles are usually much finer with the average size in bituminous fly ashes being in the range of 7–12 μm.
about 30 min
In conclusion, mixing and curing concrete in seawater increases the early compressive strength, but the seawater has a negative effect on the compressive strength of concrete at ages over 28 days.
Underwater concrete was specially designed to enhance constructability and performance in water environments. … It can be characterized by the concrete resistance to washout, segregation and bleeding and is affected by the mix proportioning, aggregate shape and gradation, admixtures, vibration and placement conditions.