Resea ch A icle
E ec o di e en ashes om biomass oli e pomace on he me-
chanical and i e p ope ies o gypsum-based ma e ials
Begoña Peceño 1, E a M. Pé ez-So iano 2 , *, J.D. Ríos 3, Yolanda Luna 4, Héc o Ci uen es 5, Ca los
Lei a 4
1
Uni e sidad Ca ólica del No e, Coquimbo (Chile); [email protected]
2
Depa men o Ma e ials Science and Enginee ing and T anspo , Escuela Poli écnica Supe io , Uni e sidad de
Se illa, Se ille (Spain)
3
Depa men o Mechanical, Ene gy, and Ma e ials Enginee ing. Escuela de Ingenie ías Indus iales, Uni e sidad
de Ex emadu a, A da. de El as, Badajoz, (Spain); jd [email protected]
4
Depa men o Chemical and En i onmen al Enginee ing, Escuela Supe io de Ingenie os, Uni e sidad de Se illa,
Se ille, (Spain); [email p o ec ed], celiaga ciaa [email protected], clei [email protected]
5
Depa men o Con inuum Mechanics and S uc u al Analysis, Escuela Técnica Supe io de Ingenie ía, Uni e si-
dad de Se illa, Se ille, (Spain); [email p o ec ed]
*Co espondence: e [email protected]
Recei ed: 03.03.22; Accep ed: 30.12.2022; Published: 30.04.2023
Ci a ion: Peceño, B., Pé ez-So iano, E.M., Ríos, J.D., Luna, Y., Ci uen es, H. and Lei a, C. (2023). E ec o di e en ashes
om biomass oli e pomace on he mechanical and i e p ope ies o gypsum-based-gypsum ma e ials. Re is a de la Con-
s ucción. Jou nal o Cons uc ion, 22(1), 122-134. h ps://doi.o g/10.7764/RDLC.22.1.122.
Abs ac : In his s udy, biomass ashes om di e en ene gy alo iza ion p ocesses and s o age condi ions we e used o
make i e- esis an ma e ials. Some o he ashes we e subjec ed o a ca bona ion p ocess. An 80/20 ash/gypsum a io was
used in all composi ions. The densi y and di e en mechanical p ope ies (comp essi e and lexu al s eng h, supe icial
ha dness, and dynamic modulus o elas ici y), as well as i e esis ance p ope ies (insula ing capaci y and hea abso p ion
capaci y), we e e alua ed a 28 days. The ene gy alo iza ion had a g ea in luence on he pa icle size and he Loss On
Igni ion (LOI) o he ly ash. By inc easing bo h, ma e ials wi h lowe mechanical p ope ies (90%) we e p oduced. Fi e
esis ance was simila o he di e en ashes es ed, bu 50% lowe han he gypsum ma e ial. When he ashes o he
ma e ials we e ca bona ed, he ma e ial inc eases comp essi e s eng h by 400% compa ed o ashes wi hou he ca bona-
ion p ocess, and he i e esis ance was simila o hose ma e ials composed exclusi ely o gypsum, bu also a sou ce o
CO2 cap u e is p oduced.
Keywo ds: biomass ashes, oli e pomace, ene gy alo iza ion, i e esis ance, mechanical equi emen s.
1. In oduc ion
Oli e pomace, also called o ujillo, is he biomass ob ained du ing he ex ac ion o oli e oil. Oli e pomace is he main
solid was e esul ing om he p oduc ion o oli e oil. Collec i ely, 60% a e skin and pulp, and 40% a e s ones (oli e husk o
pi s). A ound 0.27 ons o oil and 0.73 ons o oli e pomace a e ob ained pe e e y on o p ocessed oli es, and, he e o e,
abou 3,000,000 ons pe yea o oli e pomace in an a e age campaign a e gene a ed only in Spain, wi h an app oxima e
humidi y be ween 60-65%.
Re is a de la Cons ucción 2023, 22(1) 122-134
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Typically, in Spain, oli e pomace was disposed o in land ills o la ge ac s o land wi h poo soil as bio- e ilize (Val a
e al., 2015), bu i can p oduce a possible oxic e ec . Ne e heless, new al e na i es o disposal a e being s udied. In Anda-
lucía (Sou h o Spain), many ini ia i es on he use o oli e pomace o ene gy pu poses (d y oli e pomace possesses
14,600 kJ/kg as he mean calo i ic alue) a e cu en ly unde going; his biomass is mainly ocused on i s combus ion in boile s
o u naces, in o de o gene a e s eam o elec ic ene gy. Cu en ly, app oxima ely 30% o he oli e pomace gene a ed in
Andalusia goes o he p oduc ion o elec ici y (Conseje ía de Ag icul u a y Pesca – Jun a de Andalucía, 2010).
In an a e age campaign, abou 740,000 ons pe yea o oli e pomace a e consumed in he 18 Andalusian powe plan s
and ano he 200,000 ons o sel -consump ion in he indus y i sel . The e a e di e en sys ems o bu ning pomaces, such
as o a y kilns, sc ew bu ne s, and luidized bed combus ion, bu he mos widely used a e g ill sys ems. These can be ixed
g ills, mobile g ills, ib a ing g ills, and inclined g ills. The la e is he mos used comme cially since hey can be adap ed o
biomass wi h di e en pa icle sizes and wa e con en .
Be ween 4% and 8% o he bu n -oli e pomace is con e ed in o ly and bo om ashes (Conseje ía de Ag icul u a y Pesca
– Jun a de Andalucía, 2010). Due p ima ily o he high po assium con en o he oli e pomace ashes, hey ha e been used
mainly as e ilize s (Nogales e al., 2011). O he s udies show i s use as a soil amendmen (Nogales e al., 2006), as a low-
cos adso ben (Chan e al., 2017), glasses o semi-conduc o applica ions (Sha ma & Singh, 2019), geopolyme -ligh weigh
agg ega es (Río Me ino e al., 2020; Nguyen e al., 2019; Rashad, 2020), and as a b ick componen (Moudache e al., 2021;
Pé ez-Villa ejo e al., 2020; Eliche-Quesada & Lei e-Cos a, 2016; Fe nández-Pe ei a e al., 2011).
Compa ed o coal combus ion ash, biomass shows e y peculia p ope ies, e.g., a high con en o alkaline componen s
and unbu ned ma e . These p ope ies in alida e hei use in ypical ecycling applica ions in la ge quan i ies, such as conc e e
and cemen addi ions (Jid ada e al., 2016), bu hese cha ac e is ics migh be use ul in i e insula ing p oduc s (Beh e al.,
2021). Consequen ly, new lines o esea ch should be pu sued on he ecycling o his ype o ash.
Due o he non-inhe en esis ance o i e o a ious cons uc ion ma e ials, solu ions ega ding hei i e p o ec ion a e
essen ial o be ound (P age e al., 2020; Vilches, Lei a, Oli a es, Vale, & Fe nández, 2005). These measu es can be classi ied
in o wo g oups: i) ac i e (au oma ic de ec ion and ex inc ion sys ems), and ii) passi e (slowing down he sp ead o he i e).
Wi hin his las g oup, he main goal is o keep he empe a u e o he componen below i s c i ical alue, as long as possible
o a oid i s collapse (Wu e al., 2021).
As commen ed p e iously, he ashes o oli e oil pomace con ain ele an pe cen ages o alkaline elemen s (po assium and,
o a lesse ex en , sodium) and alkaline elemen s o he ea h (calcium and magnesium). A e combus ion, hese elemen s
appea in he o m o oxides. Du ing cooling, we ing, and subsequen s o age, oxides a e pa ially ans o med in o hyd ox-
ides, ca bona es, and bica bona es, changing he na u e o ash (López e al., 2018) and ans o ming i in o a p oduc wi h
op ions o become a i e p o ec ion solu ion (Magnano e al., 2021).
In his wo k, he physical, mechanical, and i e esis ance p ope ies o a cons uc ion ma e ial composed by 20% w . o
gypsum and 80% w . o di e en ypes o ashes om a ious combus ion p ocesses using oli e pomace biomass ha e been
s udied. The e ec o a p e ious ca bona ion p ocess o ly ashes on he di e en p ope ies o he cons uc ion ma e ial has
also been analyzed.
This p oduc would allow he end-o -li e cycle o oli e oil p oduc ion o be closed wi h a ma e ial o high alue added.
Fu he mo e, he en i onmen al impac caused by was e disposal in land ills is educed by ecycling his was e in his way.
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2. Ma e ials and me hods
2.1. Ma e ials
2.1.1. Gypsum and oli e pomace ashes
In his s udy, ou di e en oli e pomace ashes and one comme cial gypsum we e p ope ly combined. All o he ashes
came om di e en ene gy gene a ion p ocesses, which only use oli e pomace in an inclined g ill o en. O-LOM and E-LOM
a e ly and bo om ashes om he LA LOMA powe plan (Jaén, Spain) wi h a powe o 16 MW. O-ESP is a ly ash om he
ESPUNY powe plan (Có doba, Spain) wi h a powe o 17 MW. LO ashes we e p oduced on a labo a o y scale (5 hou s a
750ºC) in he Escuela Supe io de Ingenie os (Se ille, Spain) on a ixed g ill. Gypsum, acco ding o he li e a u e (CEN EN
13279-1:2009), was used as a binde . The oxide composi ion o di e en biomass ashes is lis ed in Table 1.
Table 1. Majo componen s o di e en ashes o oli e pomace ly.
Pa ame e s/oli e pomace ly ashes
O-LOM
E-LOM
O-ESP
LO
Gypsum
Humidi y (%)
2.1
1.7
5.3
0.0
6.1
Loss on igni ion (% w .)
9.4
9.3
9.8
0.0
9.1
CaO (% w .)
17.3
16.2
19.7
15.1
43.7
MgO (% w .)
6.3
5.0
3.8
6.8
2.0
Fe2O3 (% w .)
5.5
4.2
1.6
2.1
0.3
Al2O3 (% w .)
7.0
10.3
0.8
2.6
0.7
SiO2 (% w .)
36.8
45.4
29.9
19.7
-
K2O (% w .)
22.5
17.1
22.9
33.1
-
Na2O (% w .)
1.5
1.7
1.8
0.7
-
SO3 (% w .)
-
-
-
-
49.9
D50 (μm)
60
80
180
150
27
Rega ding he chemical composi ion, all oli e oil pomace ashes ha e simila main componen s. These we e silica, po as-
sium, and calcium, and hey a e e y simila in all he di e en ypes o ashes. Fu he mo e, he aluminum con en is lowe
han his Si, K, and Ca (Pé ez-Villa ejo e al., 2020; Eliche-Quesada & Lei e-Cos a, 2016; De la Casa & Cas o, 2014).
As can be seen in Table 1, he main di e ence be ween hese oli e pomaces ly ashes was ela ed o he con en o unbu ned
ma e (LOI), his being a consequence o he di e en ypes o sys ems used o ene gy p oduc ion. The humidi y in he oli e
oil pomace was a iable, unlike he coal ash (Alcaza -Ruiz e al., 2021).
F om he poin o iew o pa icle size, he ashes p oduced in a u nace wi hou mo emen (LO) had a la ge size han
hose p oduced in an indus ial g ill (Table 1), and he bo om ashes had a la ge size han he ashes p oduced in he same
sys em.
2.1.2. Tes ed blends
Wi h he aim o es ablishing a clea compa ison o he e ec o di e en ypes o oli e oil pomace ashes in he pas es
acco ding o Table 2, a composi ion o 80% w . o ly/bo om ash and 20% w . o gypsum was used o all ashes acco ding o
p e ious s udies (Lei a e al., 2005; Lei a e al., 2007). An addi ional composi ion wi h O-LOM ashes was also manu ac u ed
a e 16 weeks subjec ed o a ca bona ion p ocess.
Table 2. Tes ed blends.
Type o ash
Ash (% w .)
Gypsum (% w .)
Wa e /solid a io
B1
O-LOM
80
20
0.4
B1-C
O-LOM ca bona ed
80
20
0.4
B2
E-LOM
80
20
0.4
B3
O-ESP
80
20
0.4
B4
LO
80
20
0.4
100% Gypsum
-
-
100
0.4
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As can be seen in Figu e 1, each pas e was p epa ed by mixing he ash and gypsum o 3 min. The wa e /solids a io o all
mixes was kep cons an wi h a alue o 0.4 and mixed again o ano he 3 min. Subsequen ly, he pas es we e pou ed in o he
mold, unmolded a e 24 hou s, and cu ed a an a e age empe a u e equal o 20ºC and an a e age humidi y o 50% o 27
days mo e.
Figu e 1. Sample p epa a ion and es ing.
2.2. Tes me hods
2.2.1. Densi y and mechanical p ope ies
The densi y o he biomass pas es was de e mined by hei weigh and olume. Fo each composi ion, i e specimens we e
measu ed.
The comp essi e s eng h was de e mined acco ding o he s anda d (CEN EN 12859:2012). Fou p isma ic samples o
16 x 4 x 4 cm o each composi ion we e es ed using a comp ession machine (Suzpeca , MEM-102/500kN).
Su ace ha dness was de e mined acco ding o he s anda d (CEN EN 13279-2:2014). The me hod is based on he esis ance
o pene a ion o a Sho e C du ome e ob ained by a panel. This es was execu ed wice on 2 cm hick panels. The su ace
a ea was 16 cm2.
The ul asonic me hod (CNS Elec onics L d, CNS elec onic po able ul asonic non-des uc i e es e ) was used o es i-
ma e he panels’ dynamic modulus o elas ici y (ED); he eloci y o he ul asonic wa e is p oo o be ela ed o he ED
acco ding o he equa ion:
𝐸𝐷= 𝐾 · 𝑣2·𝜌 (1)
whe e K is a cons an ha is ela ed o he Poisson coe icien o he ma e ial, is he eloci y o he ul asonic pulse
p opaga ion, and ρ is he densi y o he pas e (He nández-Oli a es & Ba luenga, 2004). The es s we e ca ied ou on 33-mm-
diame e and 40-mm-heigh cylinde s.
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2.2.2. The mal p ope ies
The c i e ion used o measu e he mal insula ing capaci y was simila o he ac ual condi ions used o es cons uc ion
ma e ials such as s eel sec ions o passi e p o ec ion (CEN EN 1363-1:2021). Figu e 2 shows a diag am o he es se up o
de e mine he insula ing capaci y o a sample. Cylinde s wi h dimensions o 50 x 200 mm (diame e x heigh ) had o be placed
in an o en and subjec ed o an ex e nal empe a u e acco ding o he exis ing li e a u e (Lei a e al., 2005; CEN EN
1363-1:2021). The empe a u e o i e should ise acco ding o he law:
𝑇𝑓𝑖𝑟𝑒 =20 +345 ·log(𝑡 + 1) (2)
whe e T i e is he i e empe a u e (ºC), and is he ime (minu es). As indica ed in he Eu opean s anda d, he de e mina ion
o he insula ing capaci y is de ined as he necessa y ime o each 600ºC ( 600) in he cen e o he cylinde (Tin). The cylind ical
assemblies we e insula ed on he bo om and op su aces using ce amic ibe s wi h e y low he mal conduc i i y. Subse-
quen ly, only a adial and symme ic hea low is p oduced du ing he es .
Figu e 2. Schedule o he i e insula ing capaci y es .
The Di e en ial Scanning Calo ime y (DSC) es was used, in o de o measu e he ene gy abso bed by he pas es du ing
he hea ing. The samples we e placed in aluminum con aine s and subjec ed o hea ing o 3ºC/min om 30ºC o 300ºC,
ni ogen was used as pu ging gas (Vilches, Lei a, Vale & Fe nández-Pe ei a, 2005). To iden i y he weigh a io o he di -
e en endo he mic peaks in he pas es, a he mog a ime ic s udy (TG-SDTA Me le Toledo 851) was ca ied ou . A hea ing
a e o 10°C/min was chosen, using ai as he pu ging gas.
3. Resul s and discussion
3.1. Ca bona ion p ocess
A ce ain e olu ion in he ashes was obse ed o e ime due o i s ca bona ion es , p oduced by i s high po assium con en ,
which also p oduced high wa e e en ion (Cheng & Chiu, 2003) and en i onmen al condi ions du ing i s 16-week s o age
( empe a u e = 20-25ºC; humidi y = 50-60%, 1-3% CO2) (Vassile & Vassile a, 2020; Ohenoja e al., 2020; Supancic e al.,
2014; Suescum-Mo ales e al., 2021).
The simul aneous ac ion o bo h ci cums ances acili a ed he ca bona ion o o ujillo ashes (O-LOM). This p oduced he
p og essi e o ma ion o pa a-alumohyd ocalci e (CaAl2(CO3)2(OH)4·6H2O and kalinicini e (KHCO3). Figu e 3 shows he
di ac og ams o he ashes a e combus ion (non-ca bona ed) and a e 16 weeks (ca bona ed). Fu he mo e, hese ashes had
a high po assium con en in he o ms o syl i e (KCl) and a cani e (K2SO4).
Tin
Tou
THERMOCOUPLES
INSULATORS
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Figu e 3. X- ay di ac og ams: (a) non-ca bona ed, and (b) ca bona ed ly ashes.
When hese ashes we e subjec ed o he DSC es , he compounds p oduced du ing ca bona ion caused he appea ance o
new endo he mic peaks be ween 100 and 200ºC, due o he elease o he wa e con ained in he pa a-alumohyd ocalci e
(Ji ianu e al., 2000), as shown in Figu e 4, signi ican ly inc easing he ene gy abso bed by he ash du ing he hea ing p ocess.
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Figu e 4. Release o wa e in O-LOM as a esul o he ca bona ion p ocess.
As can be seen in Figu e 4, wo days a e i s p oduc ion, he ashes showed only a small peak a 90ºC in he DSC es . The
amoun o chemically bonded wa e inc eased du ing he ca bona ion p ocess. The i s wa e molecules we e eleased a 90ºC
(S achowicz e al., 2015). When he chemical bonded wa e was inc eased, a new peak appea ed a 128ºC. This displacemen
co esponded o a o “sel -agglome a ion” (Figu e 5). The dehyd a ion p ocess o CaAl2(CO3)2(OH)4·6H2O p ocess o he
las wa e molecules was p oduced a 150ºC, because hey we e bounded in a s onge way (S achowiczn e al., 2015).
Figu e 5. SEM-images om he ashes: (a) non-ca bona ed, and (b) ca bona ed.
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3.2. Physical and mechanical p ope ies
Table 3 shows he densi y (ρ), comp essi e s eng h (RC), dynamic modulus o elas ici y (ED), and supe icial ha dness (H)
o pas es wi h di e en ypes o oli e oil pomace ash.
Table 3. Physical and mechanical p ope ies.
80% w . ash - 20% w . gypsum
100%
Gypsum
Pa ame e
B1
O-LOM
B1-C
O-LOM
(16 weeks)
B2
E-LOM
B3
O-ESP
B4
LO
ρ (g/m3)
1078
1270
1028
894
910
1371
RC (MPa)
0.9
4.2
0.7
0.3
0.5
8.3
H (Sho e C)
44
72
22
30
21
90
ED (GPa)
1.4
2.9
0.9
0.5
0.4
8.1
As can be seen, he densi y o he pas es depended on se e al ac o s. The i s was ha each one had a di e en pa icle
size; he la ge he pa icle size, he highe he po osi y p oduced, and, he e o e, he lowe he densi y. Second, he densi y
also depended on he speci ic g a i y o he pa icles, which depended on he unbu ned con en due o i s e y low speci ic
g a i y compa ed o he ash i sel (Lei a e al., 2008). Rega ding he LOI, i depended la gely on he ype o p ocess o g ill
used. When he LOI was high, in e nal po osi y also inc eased, leading o a educ ion in densi y, and he e o e, lowe me-
chanical p ope ies (Lei a e al., 2008). Finally, i also depended on he deg ee o ca bona ion o he ashes. Ca bona ion
dec eased he olume o po es be ween he pa icles (Figu e 5), hus inc easing he densi y o he ma e ials.
The comp essi e s eng h was in e sely p opo ional o he po osi y o he ma e ial and, hence, i s densi y; he e o e, i
was a ec ed by he same ac o s. Ca bona ion signi ican ly imp o ed all mechanical p ope ies (RC, H, and ED). When com-
pa ing pas es wi h low ca bona ed ashes (O-LOMAS) wi h mo e ca bona ed ones (O-LOMAS a e 16 weeks), an inc ease in
mechanical p ope ies was obse ed.
The dynamic modulus o elas ici y a ied signi ican ly wi h he ype o ash. Those wi h highe densi ies p oduced pas es
wi h highe ED and, p edic ably, had a highe lexu al s eng h (Lei a e al., 2018).
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3.3. Insula ing capaci y
The a e age empe a u es in he cen e o he cylinde s du ing he i e es a e shown in Figu e 6.
Figu e 6. E olu ion o he empe a u e in he cen e o he cylinde e sus he exposu e ime o a s anda d i e.
The po ous ma e ial can con ain ee, adso bed, and/o c ys allized wa e . When his wa e e apo a es as a esul o a
hea ing p ocess, such as a i e, i p oduces an o e p essu e inside he pas e. Due o such an o e p essu e, his s eam is ou ed
o inne zones in he cylinde ; as hese a eas a e colde , he wa e s eam cools down and, subsequen ly, condenses again. As
a esul , a liquid ilm is c ea ed, ha is sligh ly displaced and mo ed o he co e o he cylinde . While his is happening, he
i e ene gy is consumed in his p ocess, main aining he empe a u e a ound 100ºC in he cen e o he ma e ial. This e ec
leads o he appea ance o an e apo a ion pla eau, a pe iod in which he empe a u e in he cen e o he cylinde is cons an ,
as shown in Figu e 6 (Ríos e al., 2020).
Figu e 6 shows ha pas es wi h di e en ly and bo om ashes om o ujillo p esen ed a simila insula ing capaci y ( 600),
bu smalle han ha ob ained by a ma e ial composed solely o comme cial gypsum. Acco ding o Figu e 7, a i s endo he -
mic peak is p oduced be ween 100ºC and 120ºC, due o mois u e e apo a ion and chemically bonded wa e om gypsum.
The gypsum was ans o med in o calcium sulpha e eleasing he wa e (CaSO4·2H2O → CaSO4 + 2H2O) (Lei a e al., 2010).
As all pas es we e placed unde he same mois u e condi ions and con ain he same gypsum con en , his peak is simila o
all composi ions wi h o ujillo. By con aining only 20% gypsum, he pas es wi h he di e en ypes o ly and bo om ashes
educed he du a ion o hei pla eau and, he e o e, he 600 compa ed o 100% gypsum.
