Coatings for concrete and reinforced concrete protection

The rapid change in the environment in recent decades, caused by several human activities, has produced conditions causing f requent and unexpect ed si t uat i ons of seri ous decay i n t he gene - r a l p r o p e r t i e s o f r e i n f o rc e d c o n c r e t e s t r u c t u r e s ( c i v i l c o n s t r u c - t i ons , gi r de r s , br i dge s , pi l i ngs , pi pe s , e t c . ) . Ac t ual l y t he s t r e n g h t o f c o n c r e t e a n d o f r e i n f o r c e d c o n c r e t e d e c r e a s e s o v e r t i me d u e to the deterioration of their costituents which are exposed to the o u t s i d e e n v i r o n me n t . Besides the nature of aggressive atmospheric agents, other fac - tors depending on the intrinsic quality of concrete are to be con - s i d e re d f o r a c o m p l e t e a n a l y s i s o f t h e m a t t e r o f r e i n f o r c e d c o n - c re t e d u r a b i l i t y : - t h e c h a r a c t e r i s t i c s o f c o n c r e t e c o n s t i t u e n t s ( c e me n t , a g g r e g a t e , w a t e r, a d d i t i v e s ) , - t h e p r o p e r t i e s o f t h e mi x ( w/ c r a t i o , g r a n u l o me t r i c c u r v e o f t h e aggregate), - the construction techniques used, - the curing conditions When speaking about the possible alterations that can affect re i n f o rc e d c o n c r e t e i t i s i mp o r t a n t t o p o i n t o u t t h a t t h e s e a r e a l wa y s a s s o c i a t e d wi t h wa t e r p e n e t r a t i o n o f t h e s t r u c t u re wa t e r plays a leading role in the degradation phenomena since it is the main vehicle for the penetration of aggressive agents such as c hl or i de and s ul phat e i nt o t he c onc r e t e . The penetration of the concrete by atmospheric carbon dioxide i s t h e o t h e r ma i n f a c t o r l e a d i n g t o r e i n f o r c e d c o n c r e t e d e c a y . Some fundamental parameters that have to be considered to a v o i d t h e p r e m a t u r e c o r r o s i o n o f t h e r e i n f o r c e me n t s a r e t h e q u a - l i t y o f t h e c o n c r e t e c o v e r , a n e c e s s a r y c o n d i t i o n f o r t h e p r oduc - tion of durable concrete, a minimum acceptable thickness of the c o n c r e t e c o v e r ( b e t w e e n 2 5 a n d 4 0 mm d e p e n d i n g o n t h e e n v i - ronmental conditions), a necessary condition to assure a dura - ble passivation of the steel embedded in the concrete [1]; an adequate w/c ratio (0,4) to minimise the permeability of the con - crete cover. The most durable concrete is that with the highest impermeabi - lity, able to resist external aggression and protect the r einforce - ments from corrosion, but it is difficult to produce this on site, because of the high number of process variables, a possible s o l u t i o n t o t h e d e g r a d a t i o n o f r e i n f o rc e d c o n c r e t e s t r u c t u re s i s the application of protective coatings to the concrete surface. T h i s c o a t i n g s , i f a p p l i e d o n n e w s t r u c t u re s a s s o o n a s t h e h a r d e - n i n g i s f i n i s h e d , h a v e t h e ma i n f u n c t i o n o f p r e s e r v i n g t h e p r o t e c - tive alkaline environment of the concrete so corrosion of the embedded steel cannot occur.