| Modern concrete is one of the building materials today, but the cement used inmodern concrete is a kind of building materials with high pollution and large energyconsumption. In comparison, ancient Chinese organic Sanhetu concrete (COSC) is akind of environment-friendly building materials with low pollution and low energyconsumption. It has been found that calcium carbonate (CaCO3) was the primarilyinorganic component and sticky rice (SR) was the organic component in COSC. Theproperties (such as strength, water resistance, toughness and durability) of COSCwere improved by adding organic materials such as SR and brown sugar (BS), but theinfluence of SR or other organic materials on the formation of CaCO3in COSC arestill unclear. It is difficult to observe the effect of SR on the formation and growth ofCaCO3, but it is more easily in solution. In order to investigate the mechanism oforganic materials in COSC, different concentration of SR, BS and anionicpolyacrylamide (APAM) were added to the calcium chloride-urea (CaCl2-CO(NH2)2)reaction system. The influence of additive concentration, reactant concentration andreaction time on the morphology, size, polymorph and crystallization ratio of CaCO3crystals was studied. And then the mechanism of the influence of organic materials onCaCO3crystallization and COSC property were analysed, which may help us to betterreproduce the COSC.CaCl2and CO(NH2)2were chosen as the reactant to form CaCO3crystals. Theexperimental results showed that the morphology and size of CaCO3crystals could beaffected by the concentration of additives and reaction time, while only the size ofCaCO3crystals could be affected by the concentration of reactant.As a whole, the crystals became larger and more regular when the concentrationof additives was low. And then the crystals became irregular when the concentrationexceeded a certain value, even the agglomeration of crystals occurred at highconcentrations. The crystal size generally increased with time extending, but morphology became more irregular. The morphology of CaCO3crystals almost hadno variation, but the crystal size gradually decreased with the increasing of reactantconcentration. However, the polymorph of CaCO3crystals was always calcite,according to analysis of XRD and FTIR. While the crystallization ratios of CaCO3crystals remained at61.5%-65%, suggesting that there was little effect of organicmaterials on the crystallization ratio.However, the effects of SR, BS and APAM on the CaCO3crystals were different.The critical values when crystals became irregular respectively were800mg/L(SR),200mg/L(BS) and200mg/L(APAM). But when the reaction time was increased to120h, the values were reduced to200mg/L(SR),20mg/L(BS) and20mg/L(APAM).When the concentration of organic materials was800mg/L, the morphology ofcrystals with SR was agglomerated and became the X-like shape; Rhombus crystalswith BS were formed; Large crystals with APAM became spherical particles andsmall particles were formed around large crystals. These results indicated there waslittle effect of low concentration of organic materials on the morphology of CaCO3crystals. Therefore, additive concentration should be enough in the process ofreproducing the COSC.The morphology and size of CaCO3crystals could be affected by SR, BS andAPAM. These results show that SR and BS can be considered as templates to inducethe crystallization of CaCO3and control the morphology and size of crystals.However, APAM also have the same roles. Namely, the APAM can be used in theprocess of reproducing the COSC just like SR and BS and even the amount of APAMin COSC will be less. Even through the variation of morphology and size of crystalscan be observed in solution, it is difficult in soil because of complex environmentsand many interference factors. The reproduction of COSC based on this experimentalresults and mechanism analysis of organic materials in COSC are the problems whichstill needs to be researched in future. |
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