Study of Portland Cement Based Materials with Addiction from Cactus Opuntia Ficus-indica

Abstract

Reinforcing Steel bars corrosion is one of the most common causes of reinforced concrete structures deterioration. Steel rebars are protected against corrosion by both chemical and physical mechanisms. The chemical protection is provided by the concrete high pH (12–13), which promotes the formation of a passive film on the steel surface. On the other hand, concrete acts as a physical barrier, hindering the access of aggressive agents. With the main aim of extending useful life of the structures and reducing the corrosive process in concrete, currently many investigations focus on the use of organic materials to analyze the electrochemical and mechanical behavior of concrete. For centuries, the use of cactus (Nopal) and its properties had special relevance in the economic, social and religious life of ancient civilizations. Currently, the mixture of cactus mucilage and lime is used as a layer to protect or repair historic buildings in Mexico.The main aim of this work is to analyze the electrochemical and mechanical behavior of Portland cement mixtures with cactus mucilage as a substitute for water. Three concentrations of cactus mucilage, 1:1, 1:2 and 1:3 ratios in cactus-water by weight were obtained. Concrete mixture was designed with a characteristic strength of f'c = 250 kg/cm2, Portland cement CPC 30R, coarse aggregate with a maximum size of 20 mm and river sand as fine aggregate. The proportions of mixtures were designed for a mucilage/cement ratio of 0.45. Each specimen contained three corrugated steel bars grade 42 of 3/8 inch. Samples were placed in a 3% sodium chloride solution after 28 days simulating an aggressive environment such as seawater and there were evaluated for 245 days through different electrochemical techniques. Half-cell potential is one of the most used techniques to analyze corrosion in concrete. Noble potential values were obtained for all samples with cactus mucilage compared to the control sample; calomel saturated electrode (CSE) was used. The electrochemical noise (EN) technique was performed using three nominally identical steel electrodes; noise resistance values and localization index for each sample were obtained. Linear polarization resistance (LPR) is a non-destructive technique, which provides information about the kinetics of corrosion in concrete. The samples with cactus mucilage after 245 days maintained values of corrosion rate close to 0.1 μA/cm2, remaining in the negligible corrosion rate interval while the control sample reached a value of 0.5 μA/cm2 close to the high corrosion rate interval. The compression strength technique was performed after 28 days of concrete curing. The samples with 1:3 concentration of cactus mucilage reached a resistance of 97.6% with respect to the control sample.