Pore structures of hydrated calcium silicates and portland cements by nitrogen adsorption

Abstract

The pore structures of sixteen hardened pastes of hydrated calcium silicates and portland cements were analyzed by nitrogen adsorption-desorption isotherms. Analysis by means of water vapor adsorption, which will be reported later, indicates that only a part of the pore system of the pastes was accessible to nitrogen. The micropores of the pastes were inaccessible to nitrogen; consequently the “corrected modelless” method of Brunauer and coworkers was used for the complete analysis. The shapes and sizes of the hysteresis loops, as well as the pore data, indicated that the majority of the pastes contained mostly ink-bottle pores with large bodies and narrow necks; for these pastes the adsorption branch gave acceptable pore structure results. Other pastes contained only a small fraction of ink-bottle pores or none; for these the desorption branch gave good results. The number of pores accessible to nitrogen is estimated to be of the order of 10 15 per gram of paste with an uncertainty of about one order of magnitude.