Effect Of Organic Matter On The Carbonation Process And The Performance Of Calcium Oxide

The archaeological evidences suggest that the firmness and integrality ofthe ancient city wall of Xi’an, Nanjing and Jingzhou，as the representative ofancient Chinese architectures, are attributed to its lime mortar system containingsticky rice paste and other natural organic matter. This traditional stickyrice-lime mortar is strong bond, environmentally friendly and compatible withthe ancient buildings. The glutinous rice composition which is similar to theorganic template in biomineralization process has influence on themicrostructure of lime mortar and the production calcium carbonate whichdetermine the good performance of mortar.Inspired by ancient sticky rice-lime mortar, this dissertation carried outwith some organic additives, such as egg white, starch, etc, in the carbonation oflime in order to further explore the impact of glutinous rice paste and the naturalorganic matter on the carbonation process of lime and discussed theperformance of lime/organic composite cementitious materials. The aim of thisresearch is providing useful evidence to use calcium hydroxide with organicadditives as the environmentally friendly historic preservation materials.Calcite which displayed different morphology was synthesized by bubblingCO₂gas through calcium hydroxide slurry with adding egg white proteinsolution. Effects of egg white on the carbonation of Ca（OH）₂have beeninvestigated by conductivity test, XRD （X-Ray diffraction）, SEM （Scanningelectron microscopy） and FT-IR spectroscopy. It is found that XRD peaks ofcalcite become to broaden and the diffracted intensity drop with increasingconcentration of egg white protein. This indicates that egg white protein leads toa decrease in particle size and crystallinity. Compared with CaCO₃which wasproduced without egg white protein, the CaCO₃prepared in the presence of eggwhite protein occurs about30cm^-1red shift in FT-IR spectra. The resultssuggest that some polar groups of egg white protein, such as–OH and–NH, could cause hydrogen bonding interaction with CO₃^2-.Calcium carbonate was synthesized by blowing CO₂gas through calciumhydroxide slurry with adding sticky rice paste, potato starch paste, corn starchpaste and dextrin solution, respectively. The results show that the production iscalcite. The reaction system of starch/Ca（OH）₂appears gelation and theviscosity first increases and then decreases when the conductivity is a trend ofdecline-recover-decline. Thereby, the productions display different morphologydue to the effect of gelation caused by starch macromolecules on grain growth.But dextrin has no significant role on the morphology of calcium carbonate.FT-IR results show that the O–C–O asymmetric stretching vibration absorptionpeaks occur about24cm^-1blue shift. It is because that the macromolecules ofsticky rice paste, gelatinized potato or corn starch change the O–C–O chemicalenvironment of the production calcium carbonate. However, dextrin is a smallmolecule sugar so it has no effect.The natural carbonation process of calcium oxide in the air with thepresence of egg white, sticky rice, potato starch paste, corn starch and dextrinwere investigated. Both the microstructure changes of calcium hydroxide andthe crystal growth characteristics of calcium carbonate were observed bypolarizing microscope and SEM. The phase composition was tested by XRD.The interaction between functional groups of starch, dextrin, egg white proteinand Ca²⁺was analyzed. The results show that sticky amylopectin wrapping inthe surface of calcium hydroxide particles limit the carbonation reaction ofcalcium hydroxide. As a result, the grain is irregular, small size and compactstructure. While amylose, dextrin and egg white protein may promote thecarbonation reaction.According to different recipe, cylindrical lime/organic compositecementitious materials were prepared by lime slurry and additives, such as eggwhite, sticky rice, potato starch, corn starch. The compressive strength, watertolerance, weather resistance and environmental corrosion resistance of thesespecimens are tested after hardening. The results show that compared with purelime, the compressive strength of the specimens containing3%egg white and5%sticky rice increased by17%and22%, water tolerance, weather resistanceincreased and corrosion resistance significantly improved, respectively. Lime samples with3%potato starch paste have a13%increase in compressivestrength while its water tolerance and weathering resistance are very poor. Inaddition, adding corn starch could weaken the performance of the lime.