The application of Natural Organic Additives in Concrete: Opuntia ficus-indica

The use of synthetic additives as setting retarders and plasticisers has over the past years become a standard practice in mortar mixtures, despite their potential adverse environmental effects. Since antiquity, man has used organic additives ranging from plant and animal-derived extracts, to improve the setting properties of mortars. These practices are slowly being revived and investigated scientifically to promote the use of materials with lower impacts on the environment. Amongst the many different types of plant-derived extracts that have been used as mortar and concrete additives, the prickly pear (Opuntia ficus-indica) mucilage extract, is popular in Meso- and South-America. The scientific basis of these additives lies in the hydrating properties of the mucilage polysaccharide complex. The purpose of this research was to prepare Opuntia ficus-indica (OFI) extracts in different forms and incorporate them in cement pastes and mortar mixtures by either replacing the water in the mixture with OFI mucilage or by replacing the cement in the mixture with OFI lyophilised powder. The inclusion of Opuntia ficus-indica additives in cement-based mortars increased their performance in terms of strength for both water and powder replacements. Conversely results in cement pastes showed that Opuntia ficus-indica additives weakened the cement paste samples in terms of strength in both water and power replacements. Results for both cement-based mortars and cement pastes showed an increase in setting time for both water and powder replacements, indicating that Opuntia ficus-indica additives could be potentially used as retarding agents. (paper)