Portland carbonation

Mixed with sand it hardens as mortar and plaster by taking up carbon dioxide from the air. Calcium from limestone is an important element in Portland cement. 

Portland cement is susceptible to corrosion by CO2 and H2S. The chemical attack by CO2 is called carbonation. A microsample technique has been developed to study the CO2 corrosion in cements, because the corrosion is difficult to monitor with common test procedures [264]. This technique is also advantageous as an accelerated testing method. A polymer-modified cement has been tested in field studies [694]. The addition of silica also improves chemical resistance [146], in particular brine corrosion. 

O. K. Angelopulo, A. Kh. Ali, K. A. Dzhabarov, A. A. Rusaev, E. A. Konovalov, and I. V. Bojko. Plugging solution contains plugging Portland cement, waste from semiconductors production containing dispersed silica, chloride(s), carbonate(s), phosphate(s) and water. Patent SU 1700202-A, 1991. 

Corrosion-resistant cements have been developed for use in wells used to inject supercritical carbon dioxide for enhanced oil recovery (32). These are based on Portland cement and high levels (as much as 40% wt.) of additives such as fly ash. Epoxy resins have been successfully used as cements in corrosive environments... 

Thus, consistent results are obtained about one-fourth of the fine particle mass, or 80 percent of the carbon is accounted for by vegetative-(slash) burn carbon. (The corresponding mass density of fine particles in downtown Portland from slash burning is 21 pg/m3 [33].) The only other major source of carbon is seen to be auto exhaust. 

Roche Research Center, Hoffmann-La Roche Inc., Nutley, NJ 07110. The authors would like to thank Mr. Ted Carbone and Mr. Louis Portland for their technical assistance in the high-pressure hydrogenation. 

Data on urban soil from the Portland Aerosol Study (21) were used to obtain an order of magnitude comparison of source ratios to the coefficients of MN(C) in the models. If volatile carbon (21) is assumed to be approximately equal to extractable organic matter (this study) and using a 1 1 ratio for coarse to fine particle mass in New York City (based on our unpublished data), then a ratio of extractable organic matter to MN(C) of 118 can be estimated for urban soil. The coefficients for MN(C) in the models were 46 11 [equation (16)] and 70 26 [equation (19)] for CYC and ACE, respectively. This is quite reasonable agreement in view of the approximations made to obtain a ratio for the soil source. 

A.D. 79 and calcium carbonate, the stuff of seashells, chalk, and limestone. Adding water to these sets off a complex set of chemical reactions that convert the gritty pasty stuff into what is essentially artificial stone. The nineteenth-century rediscovery of Roman cement, the aforementioned Portland cement, is made from a combination of burned limestone, clay, and water. It is the single most heavily used human-made material on earth. 

Enhancing the Properties of Portland Cements Using Supercritical Carbon Dioxide... 

Supercritical C02 (sc C02) is being used to accelerate the natural aging reactions (i.e., carbonation) of Portland cement. This treatment method alters the bulk properties of cement, producing profound changes in both structure and chemical composition. As a result of these changes, the mechanical and transport properties of these cements are also dramatically affected, and they display reduced porosity, permeability and pH, as well as increased density and compressive strength. 

The natural curing reactions that occur in a standard Portland cement involve the formation of calcium hydroxide (portlandite) and Ca(OH)2, as well as calcium silicate hydrate (CSH). Over time, the cement will absorb C02 from the air, converting the Ca(OH)2 and some of the CSH, to calcium carbonate, CaC03, through reactions such as those shown in Figure 15.1 (Siegers and Rouxhet, 1976 Suzuki et al., 1985 Taylor, 1990). Supercritical C02 processing carbonates the calcium hydroxide, removes water from the... 

Figure 15.1. Supercritical fluid carbonation of cast cement. (Top) Idealized chemical reactions occurring during the manufacture of a cast Portland cement. (Bottom) Idealized chemical reactions occurring during the accelerated carbonation using supercritical C02.

Figure 15.4. Micrograph of unmodified Portland cement (a) before supercritical C02 carbonation, (b) after supercritical C02 carbonation. 

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