The study of autoclaved cellulose fiber-reinforced cement composites: Fid-Bau Portal

The study of autoclaved cellulose fiber-reinforced cement composites

Bakula, F. / Kaucic, V.

The effect of addition of either 26 wt.% of sodium water glass (SWG) and 10 wt.% of calcite or 5 wt.% of CaCl2 on the starting mixture comprising 92 wt.% of Portland cement with sand (60:40) and 8 wt.% of cellulose fibers was studied on autoclaved products, treated for 6 hours at 180 deg C under saturated steam conditions and dried for 6 hours at 105 deg C. Bending strength, bending toughness and module of elasticity were determined. Autoclaved products were also investigated by X-ray diffraction (XRD), mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM). All results were compared to the product obtained without additions. The optimal addition of 26 wt.% of SWG and 10 wt.% of calcite resulted in increased degrees of conversion of SiO2, (3CaO)(SiO2) and (2CaO)(SiO2) and in larger amount of 1.1 nm tobermorite. Total porosity of products increased; the fraction of pores with the diameter of less than 30 nm increased also. The above addition resulted in higher bending strength and bending toughness, 20.0 MPa and 2.9 kJ/m³, respectively, than in the product obtained without additions for which the corresponding values are 16.3 MPa and 1.6 kJ/m³, respectively. There was a decrease in the fraction of larger pores and the elastic modulus decreased from 11.2x10⁴ MPa for the product without additives to 4.7x10⁴ MPa for the product containing SWG and calcite. The addition of 26 wt.% of SWG and 5 wt.% of CaCl2 resulted in changes that were largely similiar to corresponding changes in the products with added SWG and calcite. Significant differences were, however, observed in the increased fraction of crack-like pores with the diameter of less than 10 nm and in a large increase of bending toughness to 8.9 kJ/m³ as compared to 2.9 and 1.6 kJ/m³ for samples containing either SWG and calcite or no additives, respectively.