Politécnica de Madrid

Olive stones can be used to make more sustainable building materials

UPM researchers have developed a method to lighten and improve the isolated and absorption properties of building materials by reusing olive stones.

A team led by the full professor Mercedes del Río, from the School of Building Engineering (ETSEM), and the full professor Francisco Fernández, from the School of Industrial Design and Engineering at Universidad Politécnica de Madrid, have shown that calcined olive stones can replace the lightweight aggregates currently used in building construction and civil works.

This new usage of the waste produced by olive oil reduces the density of building materials and improves their thermal and acoustic properties. Besides, the energy demand is lower during its production cycle. All this makes the olive stones a sustainable alternative to produce lightweight aggregates in construction mortars.

Spain is the world's largest producer of olive oil and olives. This industry produces 37,500 tons of olive-stone waste every year. This waste is currently used as biomass, but its calorific value is seven times lower than heating oil. Therefore, the aim of the Building Technology and Environment group at UPM is to find out a new more profitable use of this waste.

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They studied its usage as substitutes of the lightweight aggregates most used in construction of buildings and civil works: perlite, vermiculite and expanded clay which are added to mortars and concretes to reduce density and improve their thermal and acoustic properties.

These lightweight aggregates require a great amount of energy for their manufacturing.  However, the olive-stone waste has a low energy demand during its production cycle. Francisco Fernández said, “If its effectiveness were proved as lightweight aggregate in construction mortars, we would obtain more sustainable building materials”.

To verify the viability of this new use of the stone olive, the researchers, in collaboration with the student Javier Guijarro, carried out trials with different types of waste: whole, crushed and calcined stones.

The trials included the physical characterization of the olive stones, the preparation of mortar specimens and testing, and the sand replacement of this mortar with three types of stone olives and with expanded clay in order to compare the results with the different aggregates.

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The conclusion, after the analysis of the three different olive stones wastes, was that it is only viable to substitute expanded clay by calcined olive stones to manufacture lightweight mortars. This is due to their great porosity, uniform granulometry, low real and bulk density and its degree of adhesion with concrete. They definitely proved to work as lightweight aggregates.

Besides, all lightweight aggregates in mortars using calcined olive stones had a bulk density below the reference (1500Kg/m³).  In particular, the sample containing the plasticizer achieved the lowest values of density 30% lower than the reference, increases the strength in about 20%.

The only particularity of these new lightweight mortars with olive stones is that they need a higher water/concrete ratio than other lightweight mortars with other type of lightweight aggregates, but this does not affect their mechanical resistances.

Mercedes del Rio, a female researcher of the group, says, “the excellent quality of these aggregates can be used in building or civil works to make not only lightweight mortars for coating but also structural or isolated lightweight concretes “.


Viability of using olive stones as lightweight aggregate in construction mortars. del Rio Merino, Mercedes; Guijarro Rodriguez, Javier; Fernandez Martinez, Francisco; Cruz Astorqui, Jaime Santa. REVISTA DE LA CONSTRUCCION, 16 (3):431-438; DEC 2017