Cementitious materials carbonation

Residua are the dark-colored nearly solid or solid products of petroleum refining that are produced by atmospheric and vacuum distillation (Figure 11.1 Chapter 3). Asphalt is usually produced from a residuum and is a dark brown to black cementitious material obtained from petroleum processing that contains very high-molecular-weight molecular polar species called asphaltenes that are soluble in carbon disulfide, pyridine, aromatic hydrocarbons, and chlorinated hydrocarbons (Chapter 3) (Gruse and Stevens, 1960 Guthrie, 1967 Broome and Wadelin, 1973 Weissermel and Arpe, 1978 Hoffman, 1983 Austin, 1984 Chenier, 1992 Hoffman and McKetta, 1993). 

Carbonation The conversion of calcium hydroxide in hardened cementitious material to calcium carbonate by reaction with atmospheric carbon dioxide. 

Castellote, M., I. lo rente, I., and Andrade, C., Influence of the composition of the binder and the carbonation on the zeta potential values of hardened cementitious materials. Cement Concrete Res., 36, 1915, 2006. 

K. Watanabe, K. Yokozeki, E. Sakai and M. Daimon, Improvement durability of cementitious materials by carbonation curing with CjS, Proc. Jpn. Concrete Inst., 26-1 (2004) 735 (in Japanese). 

Two basic approaches to concrete repair have been followed. The first repair methodology utiUzes concrete or other cementitious materials alone. Essentially, these procedures involve the removal of loose, spalled concrete, followed by further systematic removal of the concrete surrounding the corroded rebar. Finally, the rebar and concrete surfaces are cleaned and primed before the new repair concrete is applied. The repair procedures thus create three different material zones that interact with the reinforcing steel (1) the old chloride-con-taminated/carbonated concrete, (2) the new concrete, and (3) the interface between the old and new concrete. The interface may represent a zone of weakness with respect to further ingress of corrosive species. 

Bassi and Davies [7] have described a method for testing carbon-dioxide permeation through a ceramic tile coated with the material under study. The carbon-dioxide resistance may be expressed in various units, of which the equivalent air thickness is most commonly used. An empirical criterion is that a coating should have the same resistance to COj transport as 50 m of still air. A wide range of organic coatings (plus a silicate and a polymer-modified cementitious coating) was tested. 

Before patching carbonated concrete, the cracked and spalled concrete must be removed from around the rebar or as far as the carbonation front goes which ever is the lesser. The cementitious patch material is chosen to ensure that the steel is back in a high pH, alkaline environment. This will encourage the reformation of the passive layer to stop further corrosion. 

Tonoli, G., Santos, S., Joaquim, A., Savastano, H.,2010. Effect of accelerated carbonation on cementitious roofing tiles reinforced with lignocellulosic fibre. Construction and Building Materials, 24(2), pp. 193-201. 

The main difference between CKD and BPD is related to the temperature at which these materials are produced. CKD is taken out of the kiln during its initial length where the temperature is about 300° C, while BPD is from part of the kiln where the temperature is about 1000° C. As a result, BPD contains more cementitious phases compared with CKD, which contains a higher amount of calcium carbonate (limestone). 

It must be stressed that these specific properties of carbonate sands do not imply that they are not suitable as a fill material (crushing, cementitious bonding). Ample experience, in particular in the Middle East, indicates that carbonate sands perform satisfactorily as a bulk fill provided that during design and construction their typical properties are taken into account. 

A. Katz and V.C. Li, Inclination Angle Effect of Carbon Fibers in Cementitious Composites, UMCEE Report No. 94-27, Advanced Civil Engineering Materials Research Laboratory, Departmentof Civil and Environmental Engineering, University of Michigan, 1994. 

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