MODIFIED POLYAMINIC ADDITIVES AGAINST THE CARBONATION OF PORTLAND CONCRETE AND CORROSION OF REINFORCING STEEL BARS

In the absence of aggressive environmental media, such as carbon dioxide, a good quality Portland concrete may be realized without chemical admixtures in the mixes; however in severe environmental conditions, even a good quality concrete cannot provide the protection against the carbonation of the cured cement and consequently the corrosion of the steel bars, above all in the presence of chloride ions. In this paper the effect of some organic additives intended for the control and prevention of the carbonation of cement mortars, together with chloride corrosion of steel reinforcement is experimentally investigated. Some polyaminoalkylolic and polyaminophenolic additives, respectively obtained by reacting tetraethylenepentamine (TEPA) with formaldehyde and with formaldehyde and phenol are experimented: their resistance against carbonation was tested on cylindrical specimens of mortars, containing different type and percentage of abovementioned chemical admixtures. The carbonation depth was measured after six weeks in a carbonation room. Weight loss and electrochemical measurements were also carried out on steel specimens submerged in a simulated pore solution containing chloride ions in presence of the additive to be tested. The best results were obtained by using the chemical admixtures which definitely absorb the carbon dioxide from the surrounding environment; at a ‘critical’ percentage the best additives determine also the protection of the steel bars against the chloride-corrosion.