Manufacture of Bamboo-Cement Composites III. Effects of sodium carbonates on cement curing by steam injection pressing

This study dealt with the effects of the additions of sodium carbonates (NaHCO3, Na2CO3) Or their combinations with MgCl2 on the degree of curing and on the properties of cement-bonded bamboo composites (CBC) manufactured by steam injection pressing. Their hydration degrees were examined by X-ray diffraction (XRD), scanning electron microscope (SEM), and thermogravimetric differential thermal analysis (TG-DTA). The results are as follows: 1) The initial setting of cement is accelerated by the addition of sodium carbonates. Although there was not much difference between the effects of the addition of NaHCO3 and Na2CO3, there was some improvement in the hydration rate and the board properties with increases in additive content; however, these are not significant enough, 2) Cement hydration was not improved during water soaking because the Ca (OH)(2) and CO2 generated from the cement clinker and the sodium carbonates, respectively may have reacted to form CaCO3 which covered the cement clinker, 3) The hydration of cement under water-soaked condition was also accelerated by the addition of sodium carbonates in combination with MgCl2, and the modulus of rupture (MOR) of CBC exceeded 100 kgf/cm(2) with the addition of 10% carbonates of sodium and 5% MgCl2, 4) CBC manufactured at 2.6 cement/bamboo ratio have better mechanical properties than those at a 2.2 ratio, and 5) There were high correlations between the mechanical properties of CBC and the XRD intensity of the cement clinker and C3S, the weight losses at 200 degrees C and at 900 degrees C under TG-DTA, and the estimated yield of Ca(OH)(2). From these relationships, the mechanical properties of bamboo CBC using carbonates as additives might be predicted.