ABSTRACT
Abstract A i r p e r m e a b i l i t y and p o r o s i t y of p o r t l a n d and p o z z o l a n i c cement pastes, prepared w i t h w/c r a t i o s of 0.32 and 0.40 and w i t h or without s u p e r p l a s t i c i z e r , were determined. P e r m e a b i l i t y measurements have a l s o been taken i n p a r a l l e l on d i s k s c o n s i s t i n g of a r i n g made up of the same paste and c a s t around a limestone core. The comparison between the p e r m e a b i l i t y of pastes as r e c e i v e d and the p e r m e a b i l i t y of composites emphasized the i n t e r f a c e area's c o n t r i b u t i o n t o t h i s c h a r a c t e r i s t i c . The i n t e r f a c e p e r m e a b i l i t y i s reduced as the w/c r a t i o decreases. The r e s u l t s have shown t h a t , the w/c r a t i o being equal, the p e r m e a b i l i t y of the i n t e r f a c e i s markedly higher than t h a t of the pure paste i n the f i r s t 7 days of c u r i n g but then the d i f f e r e n c e s d i m i n i s h . The a d d i t i o n o f s u p e r p l a s t i c i z e r , the w/c r a t i o being equal, has l i t t l e e f f e c t on the p e r m e a b i l i t y of the p o r t l a n d and p o z z o l a n i c cement pastes even though i t s l i g h t l y i n c r e a s e s p o r o s i t y . However, the s u p e r p l a s t i c i z e r h i g h l y reduces the i n t e r f a c e p e r m e a b i l i t y not only when i t i s used as water reducer but a l s o as f l u i d i f i e r owing t o the i n c r e a s e d w o r k a b i l i t y of the cement paste, which favours i t s adhesiveness t o the aggregate s u r f a c e s .
