SUMMARY


The agricultural activity, of the most of the South American countries, generates in many cases abundant wastes, what bears a great environmental impact and a concern on the appropriate handling of the same ones. The possibility of its use in the building industry would diminish those impacts, it would produce value added to the farmers and it would offer alternative to construction materials manufacturers.  
   
Aware of the importance on the use of the industrial and agriculture-industrial residues, for contributing to a sustainable world, different residual materials from agricultural origin have been studied, looking for their possible applications in mortars and concretes.  
  
One of the most important technological advances in construction materials, in the last years, becomes the incorporation of additives for improving the properties of the concrete, in fresh or in hardened state. One of them is the air-entraining agent which incorporates, during the mixing, a quantity of small air bubbles, uniformly distributed. These air bubbles remain after the hardening of concrete. Some of these additives are organic and they can be obtained from vegetable matter. Chemically, the air-entraining agent works as a surfactant that reduces the surface tension of the water in the mixture, allowing the incorporation of air when stirred. The electrical charge of the bubbles allows the mutual repulsion, avoiding the coalescence in form of bigger bubbles.  
  
In this study, the behaviour of two organic extracts from vegetable origin has been studied. These extracts were prepared from the Agave americana and the Furcraea cabuya (fique cenizo) species, and were added to binding materials like Portland cement and gypsum (plaster). These plants are part of the Agavaceae family, some of whose genera are exploited in a commercial way in countries of America and whose residuals, the fiber and the liquor, could be use as additives in building materials. These plants are characterized by their thick leaves, lanceolated, green or blued coloured and some of them with maginal teeth. Leaves could be more than 1,75 m long and 30 cm wide; in Europe, this family of plants, can be find in wild way and it is not known its industrial production at the moment.  
  
Therefore, the objective of this study is to verify the air entraining effect of the extracts from Agave americana and Furcraea cabuya plants, in mortars and Portland cement concretes and plasters, and their effect on the rest of properties of the binders.  Physical and chemical characterization of  both extracts were carried out: determination of the dry extract content, loss on calcination to 1050°C, halide content and chemical reducers (sugars), conductivity, determination of the pH and thermogravimetric analysis.   
  
For cement pastes the viscosity was determined, for different  water/cement ratios and different percentages of additives; by means of thermogravimetric analysis, the production of  calcium hydroxide from the cement hydration has been determined at different curing ages; it was also studied the influence of these additives in the setting times. Some of these tests were also applied on plaster pastes.  
  
For cement mortars the consistency was determined, the content of occluded air and the capillary absorption to 7 and 90 days curing times and the flexural and compressive mechanical strengths were evaluated. In concretes the effect of the extracts on the consistency and the bleeding were studied in fresh mixtures. In hardened concretes, the characteristics of the pores and the compressive mechanical strength were studied. Lastly, selected studies on durability were carried out: the sulphate attack and icing-thawing cycles.
  
In this research, it has been demonstrated that the tested extracts are characterized by their high content of water, low halide content and high content of reducers; they are acids (pH 4,5) and their density is 1,06 g/ml. It was also demonstrated that these additives reduce the content of water of the mixture, guaranteeing the same workability than the control mix, and they diminish the bleeding in the fresh concrete, but in contrast, they increase the setting times due to its organic compounds content. For  mortars and for hardened concretes, the capillary absorption and the density are diminished; the mechanical strengths are also diminished by effect of the occluded air bubbles, but hardly ever below 75% of the strength of control mix. The additives improve considerably the resistance to the shrinkage-swelling due to the action of sulphates or icing-thawing cycles.