Pre-saturación de los áridos reciclados procedentes de residuos de construcción y demolición para la fabricación de hormigones eco-eficientes

Resum

As established in Article 15 of the Code on Structural Concrete EHE-08, recycled aggregates used in the manufacture of new concrete mixes have to present values of water absorption below 7%. However, this limitation is frequently breached in the case of mixed or ceramic recycled aggregates, which are the main product in Spanish construction and demolition waste management plants. Recycled concrete aggregates have higher absorption rates than natural aggregates due to the existence of mortars or other pastes adhered to their surface. But, in the case of ceramic recycled aggregates this problem is exacerbated due to the natural characteristics of the material. The ability of these aggregates to absorb more water directly affects the amount of available water during the mixing, which alters the cement hydration and the concrete mix workability in the short term, and influences the mechanical properties as well as the durability of the hardened concrete in the long term. An employed technique to solve the aforementioned problem of water absorption is the saturation of the aggregates prior to their use. This method allows the recycled aggregate to achieve a moisture state in which its natural tendency to absorb more water disappears, a problem occurring in the initial moisture state of the aggregate without treatment. In the present research work, the presaturation technique previously mentioned was performed. To that end, a preliminary study was conducted to determine an immersion time that allows the recycled aggregates reach a moisture state which does not present any effect on the available mixing water. Defined a suitable presaturation method, concrete mixes were elaborated in order to comparatively assess the resulting consistence improvement with the treated and the untreated aggregates. Finally, compressive strength test were carry out on the concrete specimens in order to demonstrate that the proposed solution allows to achieve the desired compression strength, even if the presaturation procedure increases the total water proportion on the concrete mix. This aspect poses a great importance, since a higher water demand in the concrete dosage generally decreases the compressive strength. In summary, it is possible to conclude that a simple, quick and inexpensive technique as the presaturation solves the water absorption problem of the recycled aggregates.