Resea ch o Mechanical and The mal P ope ies o Composi e Ma e ial Based on
Gypsum and S aw
Nikola Va říno á
*
, Ka eřina S ejskalo á, Jiří Teslík, Ka eřina Kubenko á and JiříMaje
Facul y o Ci il Enginee ing, VSB–Technical Uni e si y o Os a a, Os a a, 70800, Czech Republic
*Co esponding Au ho : Nikola Va říno á. Email: [email p o ec ed]
Recei ed: 24 Augus 2021 Accep ed: 10 Decembe 2021
ABSTRACT
This a icle is ocused on he in es iga ion o he mechanical and he mal p ope ies o composi e ma e ial ha
could be used o he p oduc ion o plas e o plas e boa ds. This composi e ma e ial is made o gypsum and
ein o cing na u al fibe s. The a icle e ifies whe he his na u al ein o cemen can imp o e he in es iga ed
p ope ies compa ed o con en ional plas e s and gypsum plas e boa ds made o pu e gypsum. F om his com-
posi e ma e ial, high-s eng h plas e boa ds could hen be p oduced, which mee he highe demands o use s
han con en ional gypsum plas e boa ds. Fo hei p oduc ion, na u al was e ma e ials would be used e ficien ly.
As pa o he de elopmen o new building ma e ials, i is necessa y o speci y essen ial cha ac e is ics o hei
la e use in ci il enginee ing. C ushed whea s aw and h ee gypsum classes wi h s eng hs G2 (2 MPa)—gypsum
Class I., G5 (5 MPa)—gypsum Class II. and G16 (16 MPa)—gypsum Class III. we e used o c ea e he es sam-
ples. Samples we e made wi h di e en a ios o he wo ing edien s, wi h he pe cen ages o s aw being 0%, 2.5%,
and 5% o each gypsum g ade. The fi s pa o he a icle desc ibes how he inc easing p opo ion o s aw
a ec s he composi e’s mechanical p ope ies (flexu al s eng h and comp essi e s eng h). The second pa o
he a icle ocuses on he change o he mal p ope ies ( he mal conduc i i y and specific hea capaci y). The las
pa o he a icle men ions he e ifica ion o he fi e p ope ies (single-flame sou ce fi e es and g oss hea o
combus ion) o his composi e ma e ial. The esea ch has shown ha he inc easing p opo ion o s aw ein o -
cemen caused a de e io a ion in he flexu al s eng h (up o 56.49% in he 3. se ies o gypsum Class II.) and com-
p essi e s eng h (up o 80.27% in he 3. se ies o gypsum Class III.) and an imp o emen in he specifichea
capaci y and he mal conduc i i y (up o 31.40% in he 3. se ies). This composi e ma e ial is hus no sui able
o he p oduc ion o high-s eng h plas e boa ds, bu i s educed mechanical p ope ies do no p e en i s use
o in e io plas e s. Based on he pe o med fi e es s, i can be said ha his composi e ma e ial can be classified
as a non-flammable ma e ial o eac ion o fi e Classes A1 o A2. F om an ecological poin o iew, i is ad an a-
geous o use a composi e ma e ial wi h a highe s aw con en .
KEYWORDS
Composi e ma e ial; gypsum; plas e boa d; c ushed s aw; flexu al s eng h; comp essi e s eng h; he mal
conduc i i y; specific hea capaci y; igni abili y; g oss hea o combus ion
This wo k is licensed unde a C ea i e Commons A ibu ion 4.0 In e na ional License, which
pe mi s un es ic ed use, dis ibu ion, and ep oduc ion in any medium, p o ided he o iginal
wo k is p ope ly ci ed.
DOI: 10.32604/j m.2022.018908
ARTICLE
ech
T
P essScience
1 In oduc ion
Gypsum and p oduc s made om gypsum a e s anda d building ma e ials and he e a e many ways o
using hem in ci il enginee ing [1]. Gypsum is he base aw ma e ial o he p oduc ion o many ypes o
building ma e ials. Typical examples a e in e io plas e s and gypsum plas e boa ds. Gypsum
plas e boa ds a e o en used o c ea e in e io pa i ions, ceiling so fi s, o pi ched oo s. Gypsum has
good p ope ies in esponse o fi e, so gypsum p oduc s a e well sui ed as p o ec i e cladding s uc u es
o o he flammable ma e ials. Thei use slows he sp ead o fi e and inc eases he fi e esis ance o he
s uc u e. One o he ypical examples is oo s, whose bea ing s uc u e consis s o wooden beams. The
gypsum cladding plas e boa ds he e a e no only a isual cladding, bu also empo a y fi e p o ec ion o
he oo agains collapse, a leas du ing e acua ion o people. Ano he sui able use o gypsum
plas e boa ds is as cladding, o example, o a ceiling wi h wooden beams o a ceiling wi h he mal
insula ion made o polys y ene, which mel s and d ips quickly in he e en o a fi e. This p ope y o
gypsum plas e boa ds is undoub edly impo an and desi ed, so i should also be me in he case o he
composi e ma e ial discussed in his esea ch. In con as , he disad an ages o gypsum plas e boa ds a e
hei s eng h and wa e abso p ion [2]. The p oblem is hei use in en i onmen s wi h highe mechanical
demands. A possible solu ion o his p oblem is o imp o e he s eng h o gypsum plas e boa ds by
adding ein o cing fibe s o he gypsum binde . The mos commonly used a e cellulosic fibe s o
syn he ic fibe s. Wi h ega d o he economic and especially ecological bu den in he p oduc ion o
syn he ic fibe s, i is possible o use na u al ma e ials, which would o he wise be disposed o wi hou use
as na u al was e. Rice [3,4], whea [5–9], ba ley [10,11], wood fibe [11], flax, ju e, hemp [12,13], co n
fibe s [14], e c., [15–17] can be used. In his o y, he use o na u al ma e ials was due o hei a ailabili y,
knowledge, and low economic di ficul y.
Na u al c ushed whea s aw, wi hou chemical addi i es, was chosen o his esea ch. One o he
ad an ages o using s aw as a building ma e ial is he educ ion o ene gy consump ion om he
en i onmen al poin o iew. These fibe s a e usually ag icul u al was e, so hey consume less ene gy in
p oduc ion. They also o e good he mal p ope ies due o hei po ous na u e, which leads o educed
ene gy consump ion in he ope a ion o buildings [18]. Acco ding o [19], he addi ion o s aw o he
gypsum-based composi e educes he he mal conduc i i y o he samples. Ismail e al. [7] success ully
ied o u he imp o e he he mal p ope ies o a biocomposi e based on ce eal s aw and mine al
binde s using hemoglobin, casein and gela in. The ea ed composi e is e en sui able o use in building
insula ion. Thus, s aw as a na u e ma e ial can compe e wi h syn he ic fibe s in a a ie y o enginee ing
applica ions.
The ques ion is how adding na u al fibe s o he composi e will a ec i s mechanical p ope ies. Yang
e al. [19] p esen ed he e ifica ion o he p ope ies o gypsum-based composi e wall ma e ials. They
in es iga ed he e ec o cemen , ino ganic was es, and s aw fibe on he mechanical and wa e
esis ance p ope ies o flue gas desul u iza ion (FGD) gypsum. The esul s indica e ha he p ope ies o
he gypsum-based composi es imp o ed wi h he addi ion o cemen and was e due o he syne gis ic
e ec be ween hem and he addi ion o 3 w % o so ghum s aw fibe (SSF) significan ly imp o ed he
flexu al s eng h and dec eased he appa en densi y o he samples. In con as , An unes e al. [3] ound
in he s udy o ice husk-ea h-based composi es ha inc easing he ice husk con en dec eases he
flexu al s eng h. Ashou e al. [11] e en added whea and ba ley s aw o he composi ion o unfi ed
ea h b icks. In con as o he esea ch men ioned abo e, his pape examines he p ope ies o a
composi e ma e ial made o gypsum and s aw using di e en classes o gypsum s eng h. This will be
used o de e mine he applicabili y o he composi e ma e ial in he case o equi emen s o i s highe
s eng h.
1860 JRM, 2022, ol.10, no.7
The disad an age o s aw ein o cemen may be i s smoo h su ace, which educes he cohesion wi h
he binde . This was he subjec o esea ch in which s aw fibe s we e modified by ea men wi h ac ylic acid
coa ing and he mechanical p ope ies o s aw fibe - ein o ced gypsum composi e we e in es iga ed. The
esul s o his esea ch showed ha by he ea men wi h ac ylic acid coa ing, he oughness o he s aw
fibe s inc eased ma kedly, and he d y flexu al s eng h and he d y comp essi e s eng h o he gypsum
composi e inc eased espec i ely by 71.3% and 52.4% [20]. The disad an age o his ea men is he
wo k wi h acid, which in oduces a sa e y isk in o he p oduc ion p ocess. Acid is a flammable caus ic
ha is dange ous o he en i onmen . Ano he disad an age o using s aw could be a de e io a ion in he
fi e esis ance o he composi e because gypsum is a non-flammable ma e ial, bu s aw is e y flammable
[5]. Acco ding o [21], samples wi h un ea ed s aw fibe s also me he igni abili y equi emen .
Howe e , composi es wi h ea ed s aw fibe s ha e be e fi e esis ance.
The aim o his esea ch is o e i y whe he hese na u al fibe s can inc ease he s eng h o he
plas e boa ds as well as syn he ic fibe s. These would be used indoo s jus like common gypsum
plas e boa ds, bu would also mee highe mechanical use equi emen s. Due o he ein o cing fibe s,
hey could be s onge and ha e a highe load-bea ing capaci y. These composi e plas e boa ds di e
om commonly a ailable high-s eng h plas e boa ds p ecisely in ha hey a e no ein o ced wi h
syn he ic fibe s bu e ec i ely use na u al fib ous ma e ials. The s aw was mixed wi h gypsum in a ious
p opo ions. The pe cen age amoun o s aw and he class o gypsum ha influence he mechanical and
he mal p ope ies in es iga ed can also a ec he igni abili y o composi e ma e ials. This esea ch
ocuses on in es iga ing he basic p ope ies o a new composi e ma e ial made o gypsum and s aw,
which can be u he used o he p oduc ion o in e io plas e s and gypsum plas e boa ds.
This pape fi s desc ibes he p oduc ion o composi e ma e ial and me hods o es he indi idual
p ope ies o his composi e. Specifically, his esea ch is ocused on he de e mina ion o he ollowing
cha ac e is ics: flexu al s eng h P
(N·mm
−2
), he comp essi e s eng h R
c
(N·mm
−2
), he he mal
conduc i i y λ(W·m
−1
·K
−1
), he specific hea capaci y c(J·kg
−1
·K
−1
), he igni abili y, and he g oss hea
o combus ion Q
PCS
(MJ·kg
−1
) o he composi e ma e ial c ea ed. Finally, all esul s a e p esen ed and
compa ed wi h each o he , and he causes o he ob ained alues o hese p ope ies a e discussed.
2 P epa a ion o Tes Samples
2.1 Used Ma e ials
2.1.1 Gypsum
Fo he p oduc ion o he es samples, gypsum was selec ed as he binde . I is a powde mix u e o
hemihyd a e o calcium sul a e (CaSO
4
·1/2 H
2
O). Fo esea ch, h ee ypes o gypsum wi h s eng hs G2
(2 MPa)—gypsum Class I., G5 (5 MPa)—gypsum Class II. and G16 (16 MPa)—gypsum Class III. we e
es ed [22].
2.1.2 S aw
The a ian o c ushed whea s aw as ein o cing fibe was chosen due o i s ela i ely high ensile
s eng h [23]. C ushed s aw is p oduced by cu ing and g inding s aw s alks in o small pieces. The
c ushed s aw is p oduced using a s aw choppe . I is easily a ailable, inexpensi e, and ully ecyclable.
Fo esea ch, c ushed s aw s alks in he leng h o 0.5–1.5 cm we e used. The c ushed s aw used in he
esea ch is shown in Fig. 1. The s aw used in his esea ch was pu chased as bedding o ho ses. The
name o he s aw p oduce is MIKÓ STROH (Hunga y).
JRM, 2022, ol.10, no.7 1861
2.2 P oduc ion P ocess
Fo expe imen al es ing, h ee se ies o samples we e p epa ed. The se ies and numbe s o es samples
p oduced a e desc ibed in Table 1. To es mechanical and he mal p ope ies, es samples measu ing
40 mm × 40 mm × 160 mm [24] we e made in s eel moulds o es he mechanical p ope ies o mo a
and cemen ma e ials. Fo he single-flame sou ce fi e es , es samples (gypsum-s aw pla es) wi h
dimensions 250 mm × 90 mm × 15 mm we e made. Fi s , plywood o ms we e made. These o ms we e
filled wi h he esh gypsum-s aw mix u e (Fig. 2). The pe cen age con en o s aw in he es samples
was 0%, 2.5% and 5.0%. A e filling, he su ace o he es samples was smoo hed wi h a s eel owel.
A e cu ing, he es samples we e emo ed om he o ms. Since he ma e ial o he es samples was
no deg aded in any way du ing he fi e es , i could be used o de e mine he g oss hea o combus ion
(calo ific alue). The ma e ial o his fi e es was c ushed wi h a hand c ushe .
The samples we e c ea ed in a echnical labo a o y adap ed o his. The ing edien s o each se ies we e
weighed in p opo ion and amoun and he es samples we e made in he numbe acco ding o Table 1.
A e weighing and mixing he d y ing edien s, a powde y mix u e was o med and mixed wi h wa e o
1 min [24]. Fig. 2 shows he mix u e o gypsum wi h c ushed s aw s alks.
Figu e 1: C ushed s aw used in he esea ch
Table 1: Pe cen ages and weigh s o es samples
Gypsum
class
Se ies Pe cen age
p opo ions o
gypsum (%)
Weigh o
gypsum (kg)
Pe cen age
p opo ions o
c ushed s aw (%)
Weigh o
c ushed
s aw (kg)
Tes ing
samples (pcs)
I. 1. 100.0 1.00 0.0 0.000 4
2. 97.5 0.975 2.5 0.025 3
3. 95.0 0.950 5.0 0.050 3
II. 1. 100.0 1.00 0.0 0.000 4
2. 97.5 0.975 2.5 0.025 6
3. 95.0 0.950 5.0 0.050 6
III. 1. 100.0 1.00 0.0 0.000 4
2. 97.5 0.975 2.5 0.025 6
3. 95.0 0.950 5.0 0.050 6
1862 JRM, 2022, ol.10, no.7
The esul ing mix u e filled he p epa ed s eel moulds, which we e ib a ed on he ib a ing able o
one min. o achie e comple e filling o he mould. A e 24 h, he samples we e emo ed om he
moulds, d ied a 40°C o s eady weigh , and hen s o ed o se en days in he es en i onmen
( empe a u e (23 ± 2)°C and ela i e ai humidi y (50 ± 5)%) [24]. Fig. 3 shows he es samples in he
es mould.
3 Tes Me hods
Samples wen y-eigh days old we e weighed and he dimensions o each sample we e measu ed. The
bulk densi y o he measu ed composi e ma e ial was de e mined as he a i hme ic mean o he weigh o he
es samples o each se ies di ided by he olume o he es samples. Samples o he I. gypsum class we e
es ed in he mal conduc i i y and specific hea capaci y es s. A e hese es s, he flexu al s eng h
measu emen was pe o med on each sample. The comp essi e s eng h alues we e hen measu ed in he
indi idual hal es o he samples. The indoo ai empe a u e and ela i e humidi y du ing he sample
es ing we e 21.9°C and 55.0%. Igni abili y and g oss hea o combus ion we e de e mined in he samples
o fi e p ope ies es s.
3.1 Flexu al S eng h
The main pu pose o his es was o measu e he o ce needed o b eak he es samples.
The samples we e placed in he Fo mTes p ess and o ien ed so ha hei ho izon al axis was
pe pendicula o he suppo s o he es p ess machine. The e o e, he load was pe pendicula o he
Figu e 2: Mix u e o gypsum wi h s aw s alks
Figu e 3: Tes samples in he es mould (Gypsum Class II.; Pe cen age p opo ion o 100% gypsum, 0% s aw)
JRM, 2022, ol.10, no.7 1863

di ec ion o filling he es moulds. The load olle ans e ed he load pe pendicula o he opposi e su ace
o he es sample. The load eloci y was se o 10 N/s o all samples. The load was e enly inc eased un il he
sample b oke [24], see Fig. 4.
The measu ed alues o he maximum applied load Po he indi idual es samples we e eco ded.
Acco ding o Eq. (1), he alues o he flexu al s eng h P
we e calcula ed. Then, he a e age alues o
he flexu al s eng h P
o each se ies we e calcula ed.
Calcula ion o flexu al s eng h [24]:
P ¼0:00234 P(1)
whe e: P
Flexu al s eng h (N·mm
−2
)
PMaximum applied load (N).
3.2 Comp essi e S eng h
Hal o he samples we e c ea ed by he flexu al s eng h es o each o iginal sample and we e ma ked by
he p opo ion o s aw con en . Immedia ely a e his es , hese new samples we e es ed o comp ession
s eng h. The samples we e placed in he Fo mTes p ess so ha he load was pe pendicula o he di ec ion o
filling; he samples we e cen e ed in ela ion o he load boa ds. The a ea o he load boa ds is 40 mm ×
40 mm, so he en i e a ea o he load boa d was in con ac wi h he sample. The load eloci y was se o
50 N/s o all samples. The load was e enly inc eased un il he damage o he sample [24](Fig. 5).
Figu e 4: B oken es sample a e he flexu al s eng h es
Figu e 5: Damage o he es sample a e he comp essi e s eng h es
1864 JRM, 2022, ol.10, no.7
The measu ed alues o he maximum applied load F
c
o he indi idual es samples we e eco ded.
Acco ding o Eq. (2), he alues o he comp essi e s eng h R
c
we e calcula ed. Then he a e age alues
o comp essi e s eng h R
c
o each se ies we e calcula ed.
Calcula ion o comp essi e s eng h [24]:
Rc¼Fc
1600 (2)
whe e: R
c
Comp essi e s eng h (N·mm
−2
)
F
c
Maximum applied load (N)
1600 40 mm × 40 mm is he a ea o load boa ds (mm
2
).
3.3 The mal P ope ies
The measu emen was pe o med on only one se o samples. Samples con aining gypsum class G2 (I.)
we e selec ed o measu e he mal p ope ies using he ISOMET 2114 de ice. This de ice can de e mine he
alue o he mal conduc i i y λ(W·m
−1
·K
−1
) and olume ic hea capaci y C
ρ
(J·m
−3
·K
−1
)[25]. The ISOMET
de ice was equipped wi h a needle senso [25], which was inse ed in o a p ed illed hole in he es sample
filled wi h he mal conduc i e silicone gel (Fig. 6). This senso uses a non-s a iona y ho wi e me hod o
measu emen . The p inciple o he ho wi e me hod is based on he measu emen o empe a u e ise a a
defined dis ance om a linea hea sou ce, which is a ho wi e. Inc easing he empe a u e o he ho wi e
is p o ided by elec ical ene gy. I hea s a hin wi e ha is placed in he es sample and is a sou ce o
hea . The de ice eco ds he ise and all o empe a u es and calcula es he he mal conduc i i y
acco ding o Eq. (3) [26]:
¼Q
4pT2T1
ðÞ
ln 2
1
 (3)
whe e: λThe mal conduc i i y (W·m
−1
·K
−1
)
QPowe pe uni leng h (W·m
−1
)
T
1
,T
2
Tempe a u es (K)
1
,
2
Times (s).
Figu e 6: ISOMET de ice wi h needle senso inse ed in o he es sample
Ano he quan i y ha he ISOMET de ice can measu e is he olume ic hea capaci y C
ρ
(J·m
−3
·K
−1
).
The ISOMET de ice measu es how much hea is needed o hea one m
3
o he es ed ma e ial. Then i is
necessa y o calcula e he specific hea capaci y c(J·kg
−1
·K
−1
) om he measu ed alues o he
olume ic hea capaci y C
ρ
. To calcula e he specific hea capaci y, i is necessa y o de e mine he bulk
densi y o he measu ed ma e ial. F om he measu ed olume ic hea capaci y and bulk densi y, he
specific hea capaci y o each se ies o he es samples was calcula ed acco ding o Eqs. (4) and (5) [26]:
JRM, 2022, ol.10, no.7 1865
Cq¼Q
DT(4)
c¼Q
DTq¼Cq
q
(5)
whe e: C
ρ
Volume ic hea capaci y (J·m
−3
·K
−1
)
cSpecific hea capaci y (J·kg
−1
·K
−1
)
QAmoun o hea pe uni olume (J·m
−3
)
TTempe a u e (K)
ρBulk densi y (kg·m
−3
).
Fo measu emen s, he es samples we e placed in a es chambe whe e he empe a u e (23°C) and ai
humidi y (50%) we e cons an . The esul s o each measu emen we e eco ded.
3.4 Fi e P ope ies–Reac ion o Fi e
In his esea ch amewo k, he igni abili y and g oss hea o combus ion we e measu ed. The single-
flame sou ce fi e es o composi e ma e ial made o gypsum and ein o ced wi h na u al fibe s has been
pe o med [27]. These es s we e ca ied ou o e i y whe he he s aw added o he gypsum would
significan ly impai he fi e esis ance o he esul ing composi e ma e ials. These es s we e based on
p e iously implemen ed esea ch, ocusing on he fi e p ope ies o c ushed s aw [28].
The single-flame sou ce fi e es was ca ied ou on h ee es samples o es fi e p ope ies. On he
exposed su ace o he samples, wo ho izon al axes we e ma ked. The fi s was 40 mm abo e he bo om
edge o he es ing sample, and he second was 150 mm abo e he fi s axis, as shown in Fig. 7. The fi s
axis shows he ouchpoin whe e he gas bu ne wi h a small no ma i e flame [29] ouches he su ace o
he es ed ma e ial. The bu ne ’s angle is 45°, and he leng h o he flame mus be measu ed by a special
me e . The ime a which he flame is allowed o ac on he es ma e ial began o be measu ed. The ime
o he fi e es (flame e ec ) was 30 s. Du ing he fi e es , wo c i e ia a e checked: i he flame igni es
he sample’s su ace and i he flame sp eads om he fi s ho izon al ax ( ouchdown poin ) o he second
ho izon al ax 150 mm abo e he ouchdown poin . I he flame sp eads o he second ho izon al ax, he
es ed ma e ial does no mee he fi e es equi emen s. The ime be o e he flame ouches he second
ho izon al ax (Bu ning ime ack 150 mm c i e ia) is measu ed.
Figu e 7: Desc ip ion o he sample su ace exposed o he flame, ma ked by wo ho izon al axes
1866 JRM, 2022, ol.10, no.7
The es o de e mine he g oss hea o combus ion (calo ific alue) Q
PCS
(MJ·kg
−1
) was pe o med in an
oxygen bomb calo ime e IKA C 200 unde s anda dized condi ions, a cons an olume and in an
a mosphe e o oxygen. The g oss hea o combus ion is calcula ed on he basis o he obse ed
empe a u e ise, aking accoun o hea loss and he la en hea o apo iza ion o wa e . The c ucible
me hod was used wi h 0.5 g o c ushed s aw (Fig. 8) acco ding o [30]. The de ice measu ed he g oss
hea o combus ion o he c ushed s aw i sel . Since gypsum is a non-flammable ma e ial, he g oss hea
o combus ion o he composi e ma e ial was calcula ed om he measu ed alue based on he pe cen age
o s aw in he composi e.
4 Resul s and Discussion
4.1 Bulk Densi y, Flexu al S eng h, Comp essi e S eng h
Table 2 shows he a e age alues o he measu ed bulk densi y, flexu al s eng h, and comp essi e
s eng h o he es samples. S anda d de ia ions we e also calcula ed and eco ded.
Figu e 8: Measu ed sample in he c ucible o he bomb calo ime e
Table 2: Bulk densi y, flexu al, and comp essi e s eng h o he es samples
Gypsum
class
Se ies Bulk
densi y
(kg·m
−3
)
A e age alue o
flexu al s eng h
P
(N·mm
−2
)
S anda d de ia ion
o flexu al s eng h
P
(N·mm
−2
)
A e age alue o
comp essi e s eng h
R
c
(N·mm
−2
)
S anda d de ia ion o
comp essi e s eng h
R
c
(N·mm
−2
)
I. 1. 1434 3.55 0.39 9.23 1.78
2. 1142 2.61 0.20 5.87 0.32
3. 1111 2.09 0.10 3.09 0.30
II. 1. 1314 5.74 0.93 22.52 1.70
2. 1165 4.15 0.34 9.25 1.06
3. 971 2.50 0.23 4.77 0.24
III. 1. 1674 7.38 0.27 39.73 1.18
2. 1388 5.51 0.24 14.93 0.87
3. 1235 3.93 0.20 7.84 0.81
JRM, 2022, ol.10, no.7 1867