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Waste from the olive oil indus­try like olive stone ash, ground olive stones, and sludge from pomace oil extrac­tion can be used as effec­tive sec­ondary raw mate­ri­als in the mak­ing of clay bricks and cement paste.

The extrac­tion of pomace oil and the process of oil refin­ing cre­ate waste water in the form of sludge. This is some­times used as a fer­til­izer in agri­cul­ture but most often it’s dumped in land­fills or water bod­ies, or incin­er­ated — cre­at­ing a neg­a­tive envi­ron­men­tal impact.

A 2015 study titled Reusing of Oil Industry Waste as Secondary Material in Clay Bricks by the Department of Chemical, Environmental, and Materials Engineering at the University of Jaén, Spain, found that the use of sludge left­over from pomace oil extrac­tion in the mak­ing of clay bricks had a sim­i­lar com­pres­sive strength as con­ven­tional bricks, but they had bet­ter ther­mal con­duc­tiv­ity.

The study also revealed that indus­trial oil waste prod­ucts like sludge, as well as spent fil­tra­tion and bleach­ing earth (both are used for refin­ing oils) can be used effec­tively as sub­sti­tutes to brick clay because their chem­i­cal com­po­si­tion closely resem­bles it.

The same research team released an arti­cle in 2016 that eval­u­ated the use of olive stone ash as a sec­ondary raw mate­r­ial for fired clay bricks. It found that adding 10 to 30 wt% (weight per­cent) of olive stone ash to clay had a ​“pro­nounced effect on the evo­lu­tion of phys­i­cal and mechan­i­cal prop­er­ties of the resul­tant bricks fired at 900°C.” However, adding higher pro­por­tions ​“decreased the com­pres­sive strength and bulk den­sity of bricks” while increas­ing their poros­ity and rate of water absorp­tion.

Another 2016 study looked at the effects of the addi­tion of ground olive stones on the phys­i­cal and mechan­i­cal prop­er­ties of clay bricks.

It ana­lyzed the prop­er­ties of bricks made with clay and ground olive stones and found that the addi­tion of the lat­ter reduced water absorp­tion which can have a pos­i­tive effect because it decreases the chance of crum­bling while cre­at­ing a good bond­ing effect.

The study also revealed that the addi­tion of ground olive stones improves the ther­mal con­duc­tiv­ity of the bricks but decrease their mechan­i­cal prop­er­ties com­pared to pure clay bricks. Tests also showed that that over­all com­pres­sive strength val­ues sur­passed the min­i­mum require­ments set by exist­ing reg­u­la­tions.

The study con­cluded that clay bricks man­u­fac­tured with ground olive stones ​“offer excel­lent returns on the energy used in fir­ing”, and ​“are rec­om­mended as one of the most cost-effec­tive alter­na­tive addi­tions that can be used in fired clay brick man­u­fac­tur­ing.”

The reuse of these olive waste prod­ucts as alter­na­tive raw mate­ri­als in the con­struc­tion indus­try not only reduces indus­trial waste but can also off­set the cost of raw mate­ri­als. At the same time, this is an eco-friendly and sus­tain­able way of recy­cling waste that also saves nat­ural resources.

• Journal of Mineral Metal and Material Engineering


• Materiales de Construccion