Olive Pomace Ash Shows Promise as Eco-Friendly Cement Substitute

Summary

A study in the jour­nal Materials explored the use of olive pomace ash as a sus­tain­able alter­na­tive to ordi­nary Portland cement in mor­tar to reduce envi­ron­men­tal impacts of cement pro­duc­tion. The research found that up to 20 per­cent pomace ash could be used in mor­tar mixes to decrease car­bon diox­ide emis­sions with­out sig­nif­i­cant loss in mechan­i­cal per­for­mance, although fur­ther study is needed to assess long-term dura­bil­ity and real-world per­for­mance.

A new study has exam­ined the use of olive pomace ash as a sus­tain­able par­tial replace­ment for ordi­nary Portland cement in mor­tar. 

With cement pro­duc­tion being a major con­trib­u­tor to global car­bon diox­ide emis­sions, the research aims to reduce the envi­ron­men­tal impacts of the indus­try.

Published in a spe­cial issue of the jour­nal Materials, the study assesses how com­bin­ing pomace ash affects the phys­i­cal, mechan­i­cal and dura­bil­ity prop­er­ties of mor­tar to deter­mine its suit­abil­ity for large-scale use.

Olive pomace ash is derived from incin­er­ated olive pomace (resid­ual olive skins, pulp and pits). When ground, the result­ing pow­der con­tains sig­nif­i­cant amounts of car­bon diox­ide, sil­ica and lime. 

Compared to ordi­nary Portland cement, its lighter weight and finer par­ti­cle size influ­ence mor­tar char­ac­ter­is­tics such as den­sity and work­a­bil­ity (the ease with which mor­tar can be mixed, placed and com­pacted).

Mortar sam­ples were cre­ated by sub­sti­tut­ing Portland cement with pomace ash in ten per­cent incre­ments up to 50 per­cent. 

Each mix under­went tests for flowa­bil­ity (the abil­ity of the mix to flow and spread into place when poured), strength, water absorp­tion, and resis­tance to freeze – thaw cycles over peri­ods of seven, 28, and 90 days.

The researchers found that the work­a­bil­ity and flowa­bil­ity of the mor­tar decreased as pomace ash lev­els increased. 

At lev­els of up to ten per­cent, mor­tar sam­ples exhib­ited min­i­mal changes in both wet bulk den­sity and flow time, indi­cat­ing their suit­abil­ity for prac­ti­cal appli­ca­tions.

Between ten and 20 per­cent, the mix­tures became harder to work with, but main­tained accept­able flow. Beyond 20 per­cent, flow rates were dras­ti­cally affected.

Both com­pres­sive and flex­ural strength tests yielded sim­i­lar results, with pomace lev­els of up to 20 per­cent exhibit­ing reduced strength, but remain­ing within the accept­able range for struc­tural mor­tars. 

The researchers noted that strength con­tin­ued to increase over 90 days, con­sis­tent with the activ­ity of poz­zolanic reac­tions — the chem­i­cal processes by which cer­tain mate­ri­als, such as ashes, react with water and cement to form bind­ing com­pounds that enhance the strength and dura­bil­ity of con­crete over time.

Freeze-thaw resis­tance tests fur­ther con­firmed the 20 per­cent limit for pomace ash lev­els. Beyond this thresh­old, mix­tures exhib­ited sub­stan­tial vul­ner­a­bil­ity.

Water absorp­tion, which can lead to dura­bil­ity-related dam­age and per­for­mance degra­da­tion, increased in sam­ples with pomace ash lev­els above ten per­cent. 

All sam­ples exhib­ited a max­i­mum absorp­tion of 6.92 per­cent, which is well within the ten to 15 per­cent range deemed accept­able for ade­quate long-term per­for­mance.

Interestingly, the ten per­cent mix­ture showed slightly lower absorp­tion than the ordi­nary Portland cement con­trol mix­ture. This was attrib­uted to the fine ash par­ti­cles fill­ing voids and oth­er­wise refin­ing the mixture’s pore struc­ture.

An envi­ron­men­tal analy­sis com­pared the energy usage and car­bon diox­ide emis­sions of pomace ash mor­tar pro­duc­tion to those of the con­trol mix, which is made entirely of ordi­nary Portland cement. 

Carbon diox­ide emis­sions were cal­cu­lated based on elec­tric­ity gen­er­a­tion in Algeria, where the study was con­ducted.

Production of the con­trol mix con­sumed 1,000 kilo­watt-hours per ton (kWh/t) and emit­ted 500 kilo­grams of car­bon diox­ide per ton (kg CO2/ton). 

In con­trast, pro­duc­tion of the ten per­cent pomace ash mix con­sumed 953.5 kWh/t and pro­duced 476.75 kg CO2/t, while that of the 20 per­cent mix con­sumed 907 kWh/t and pro­duced 453.5 kg CO2/t.

The authors con­clude that the ten and 20 per­cent mix­tures are asso­ci­ated with a mean­ing­ful decrease in envi­ron­men­tal impact while main­tain­ing accept­able mechan­i­cal per­for­mance, sup­port­ing their can­di­dacy as envi­ron­men­tally friendly con­struc­tion mate­ri­als. 

They believe, how­ever, that fur­ther study is needed to exam­ine the long-term dura­bil­ity, microstruc­tural behav­ior and per­for­mance in real-world set­tings. 

They also note that broader adop­tion would require such mate­ri­als to be incor­po­rated into updated build­ing codes and spec­i­fi­ca­tions.