ABSTRACT
A b s t r a c t Concrete carbonation induces a pH drop of the pore s o l u t i o n down to values around the n e u t r a l i t y . When the carbonation f r o n t reaches the rebar, the s t e e l i s depassivated and i t s c o r r o s i o n s t a r t s at a r a t e which depends on the humidity i n s i d e the concrete pores. In order to prevent or avoid t h i s c o r r o s i o n , s e v e r a l methods have been developed which, i n ge n e r a l , need to be foreseen d u r i n g the design or the c o n s t r u c t i o n . In the present paper, r e s u l t s on the i n h i b i t i n g e f f e c t of n i t r i t e s , added as admixtures d u r i n g the mix, on the rebar c o r r o s i o n i n carbonated concrete, are presented. N i t r i t e s have been t e s t e d i n concrete as i n h i b i t o r s of the c h l o r i d e a t t a c k , but t h e i r e f f e c t a g a i n s t carbonation i s p o o r l y known. The t e s t s have been c a r r i e d out i n mortar. The r e s u l t s show t h a t n i t r i t e s p a s s i v a t e the s t e e l i n carbonated media, r e g a r d l e s s the s o l u t i o n pH value or the cement type. When the i n h i b i t i n g a c t i o n i s not complete, at l e a s t the r e d u c t i o n o f the corroding area i s very h i g h . The i n h i b i t i n g e f f e c t was not detected when c h l o r i d e s were added to the mixing before carbonation. Key Words: Concrete, carbonation, rebars c o r r o s i o n , N i t r i t e s .
