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Carbonation in concrete pores happens only at a relative humidity (RH) of 40-90%—when RH is higher than 90%, carbon dioxide cannot enter the concrete pores, and when RH is lower than 40%, CO 2 cannot be dissolved in water. [28] Pore structures in fresh concrete and air entrained in concrete
The carbon dioxide in the air reacts with the alkali in the cement and makes the pore water more acidic, thus lowering the pH. Carbon dioxide will start to carbonatate the cement in the concrete from the moment the object is made. This carbonatation process will start at the surface, then slowly moves deeper and deeper into the concrete.
Earth's natural greenhouse effect makes life as we know it possible, and carbon dioxide in the atmosphere plays a significant role in providing for the relatively high temperature on Earth. The greenhouse effect is a process by which thermal radiation from a planetary atmosphere warms the planet's surface beyond the temperature it would have in ...
When atmospheric carbon dioxide (CO 2), or carbonate ions (HCO − 3, CO 2− 3 dissolved in water) diffuse into concrete from its external surface, they react with calcium hydroxide (portlandite, Ca(OH) 2) and the pH of the concrete pore water progressively decreases from 13.5 – 12.5 to 8.5 (pH of water in equilibrium with calcite).
This reaction is slow, because the partial pressure of carbon dioxide in the air is low (~ 0.4 millibar). The carbonation reaction requires that the dry cement be exposed to air, so the slaked lime is a non-hydraulic cement and cannot be used under water. This process is called the lime cycle.
The air sample is dried by passing it through multiple dry ice traps and then collecting it in a five-liter vessel. The temperature is taken via a thermometer and pressure is calculated using manometry. Then, liquid nitrogen is added, causing the carbon dioxide to condense and become measurable by volume. [1]
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This is an accepted version of this page This is the latest accepted revision, reviewed on 24 January 2025. Gas in an atmosphere with certain absorption characteristics This article is about the physical properties of greenhouse gases. For how human activities are adding to greenhouse gases, see Greenhouse gas emissions. Greenhouse gases trap some of the heat that results when sunlight heats ...