advances in natural and applied sciences
issn: 1995-0772 published by aensi publication
eissn: 1998-1090 http://www.aensiweb.com/anas
2016 september 10(13): pages 112-124 open access journal
to cite this article: sihama i. salih, fadhel a. hashem, auda j. braihi., preparation and characterization of concrete
reinforced by the super-absorbent hydrogel nano composites (sahncs) used for construction applications. advances in
natural and applied sciences. 10(13) pages: 112-124
preparation and characterization of
concrete reinforced by the super-
absorbent hydrogel nano composites
(sahncs) used for construction
applications
1sihama i. salih, 1fadhel a. hashem, 2auda j. braihi
1materials engineering department, university of technology, baghdad, iraq.
2babylon university-college of materials engineering, babylon, iraq.
received 7 june 2016 accepted 12 september 2016 available 20 september 2016
address for correspondence:
sihama i. salih, materials engineering department, university of technology, baghdad, iraq.
e-mail: sihama_salih@yahoo.com
copyright © 2016 by authors and american-eurasian network for scientific information (aensi publication).
this work is licensed under the creative commons attribution international license (cc by).
http://creativecommons.org/licenses/by/4.0/
abstract
in this research cementinoushybrid composites werepreparedby addition of super-absorbent hydrogelnano composites (sahncs)
tothe concrete and mortar pastes.the sahncs iscomposed of carboxymethyle cellulose / starch blend loaded with 0.3 wt % of
nano graphite oxide and its absorbency reaches to 69 g/g. concert cubes have dimensions of 15x15x15 cm with a fixed cement:
sand: gravel ratios (1:1.18:1.86) and the ratio of water to cement is 0.4.the sahncs was added to concrete cubes with 0.2, 0.4,
0.6, 0.8 and 1wt%.mortar cubeshave dimensionsof 70.7×70.7×70.7 mm with 1:3 ratio of cement:sand and 0.40 ratio of
water:cement.the sahncs loading in mortar are 0.1, 0.2, 0.4and 0.6 wt%. compression and ultrasonic pulse velocity(upv) tests
were used to evaluate the compressive strength for these hybrid cementinouscomposites.upv was also used to evaluate
theirelastic constantsandqualities. consistency and setting times of mortar paste were measured by vicat apparatus. acoustic
impedance, portions of the energy reflected and the energy transmitted were calculated using the steel as the second medium.
results showed that compressive strength for bothconcrete and mortar decreased firstly and then exceeds their initial valueswhen
the addition ratio of sahncs exceeds 0.6 wt% in concrete , and exceeds 0.3wt % in mortar. the additional amount of water to get
the standard consistency seems to be reasonable. initial and final setting times of mortar increased with sahncscontent except at
0.2 wt%.elastic modulusexceeds its initial value at 0.6 wt% for concrete and at 0.5wt% for mortar.shearmodulusfor concrete
increased at higher ratios and there is some fluctuations in mortar shear modulus. most values of poisons ratios are within the
typical range for standard concrete.concrete quality for all samplesisexcellentaccording to the bs, 1881, 1983 code because all the
longitudinal velocities are more than 4500 m/sec.the acoustic impedance increased, whilethe energy reflected reaches to its
minimum value at higher sahncs ratios and the energy transmitted reaches to its maximum value.
keywords: superabsorbent hydrogel nanocomposites,concrete,compressive strength, ultrasonic pulse velocity,acoustic
impedance.
introduction
superabsorbent polymers (saps)are hydropinghilic networks that can absorb and retain huge amounts of water
or aqueous solutionsand the absorbed water is hardly removed under some pressure[1].superabsorbent hydrogel
nano composites (sahncs) are formed from incorporation of clays and oregano-modified clays into
superabsorbent polymers formulations [2]. these materials consist of a network of polymer chains that are
113 sihama i. salih et al., 2016/ advances in natural and applied sciences. 10(13) september 2016, pages: 112-124
cross-linked to avoid dissolution. usually there are ionic functional groups along the polymer chains to
encourage diffusion of water within the network[3].
the hydropinghilic groups are hydrated in an aqueous environment, thereby creating a hydrogel structure[4].
due to theirswelling properties,so,these hydrogelscan be utilized in many applications, such asin drug delivery
systems[5], agriculture [3], separation processes [6] and others.in cementinous hybrid composites (concrete and
mortar), sahncs used as additives to:
1- improve concrete performance by acting as a water-reducing agent.
2- eliminate the negative effect of water on the hardening of cement.
3- act as an air-entraining agent by virtue of its polar nature which may reduce surface tension and hence
stabilize the fine foam of bubbles originating from the mixing process[7].
4- prevent or reduce self-desiccation(orautogenous shrinkage) during hydration [8]. they rapidly absorb
water(forming water-filled cavities), then release it when cement paste self-desiccates or is exposed to drying
[9].
5- promote internal curing of concrete to mitigate its autogenous shrinkage [10]. the water gel created in
the fresh concrete by the use of sap provides cushioning and lubrication in the concrete mass, which in turn
improves the concrete workability as well as concrete stability[11].
consistencyof standard paste for any given cement determines the water content of the paste which will
produce the desired consistency.
setting process involves losing of plasticity with time and becoming dense and stiff. it refers to a change
from a fluid to a rigid state and happened in two stages initial setting and final setting [8]. initial setting time
refers to the beginning of solidification, while final setting time refers to the beginning of hardening process.
setting is important in concrete work to keep fresh concrete plastic for enough time which helps the
processes of transporting, casting, and compaction. setting times influences by many factors, such as: fineness
types of cement, age, water content, temperature, and humidity.
ultrasonic pulse velocity(upv)method used toevaluate the quality of concrete and mortar as well as to
calculate the elastic constants.the idea is to project the sound inside a material and measure the time necessary
for thewave to propagate through it [12]. the ultrasonic pulses depend on the density and elastic properties ofthe
material.
upv method was used to measure times required to transport the ultrasonic pulse wave in the longitudinal
and transverse paths tl and tt. then, these two times were substituted in equations1 to 6 to calculate the
longitudinal and transverse ultrasonic velocities (vl and vt respectively) as well as the elastic constants such as,
elastic modulus (e), shear modulus (g) and poison s ratio (?) for both the concrete and mortar cubes [13].
vl = (l/tl) x10 (1)
vt = (d/tt) x10 (2)
? = w / v (3)
e = ? x vl
2 (4)
g = ? x vt
2 (5)
? = (e/2g) -1 (6)
where
tl: time for longitudinal pulse (?s), tt: time for transverse pulse (?s)
l : length of cube (15 cm for concrete and 7.07cm for mortar)
d : width of cube (10.6 cm for concrete and 5cm for mortar)
? : density (g/cm3) , w: weight (g)
v: cube volume (3375 cm3 for concrete and 353.4cm3 for mortar)
as well as, upv measurements can be used to:
1. determine the uniformity of concrete in and between members.
2. measures of changes occurring with time in the properties of concrete [14].
3. evaluate concrete quality [12].
4. using both the longitudinal velocity (vl) and the density (?), the acoustic impedance (z) was
calculated by equation7 [15].
z = ?v (7)
the aim:
this research aims to preparecementinoushybrid composites reinforced by the super-absorbent hydrogel
nano composites (sahncs) and their characterization study.
114 sihama i. salih et al., 2016/ advances in natural and applied sciences. 10(13) september 2016, pages: 112-124
experimental part:
materials:
super-absorbent hydrogel nano composites (shncs):
this material is prepared fromcomposed of carboxymethyle cellulose (cmc) / starch blend cross-linked by
alum and loaded with 0.3 wt% nano graphite oxide (go). free water absorbency of this material reaches to 69
g/g and reaches to 29 g/g under 2.068 kpa load.this polymeric blend contains 1.5 wt% alum cross-linker.
ordinary portland cement (opc):
used in this research, have the chemical composition shown in table 1.
sand: the properties, grading and chemical composition of the used sand are shown in table 2.
gravel: the grading and properties of the used gravel showed in table 3.
preparations and testing:
1-preparation and testing of concrete cubes:
concrete cubic sampleshave dimensions(15x15x15 cm) were prepared with a fixed cement: sand: gravel
ratio of 1:l.18:1.86 according to astm c 192-90a with water/cement ratio equal to 0.4. the weight percent of
sahnc used are 0.2%, 0.4%, 0.6% 0.8and 1 wt%.
cubic samples were subjected to humid environment for 24 hr, immersed in the water for another 27day,
then tested (compressive strength) according to astm c579-01 method b using impact machine of 2000 kn
maximum capacity, resolution 1 kn, and loading rate 3kn/sec.
table 1: chemical composition of the used opc
oxide sio2 al2o3 fe2o3 cao mgo so3 loss on ignition
(l.o.1)
% 22.01 5.26 3.3 62.13 2.7 2.4 1.45
table 2: properties and grading of the used sand
property value
fineness modulus 2.51
so3% 4.45
sieve openings size (mm) passing%
10.0 100
4.75 94.76
2.36 88.38
1.18 79
0.6 65.55
0.3 17.17
0.15 3.79
table 3: grading and properties of the used gravel
property value
so3% 0.095
sieve openings size (mm) passing%
3.75 100
20 70
14 40
10 10
5 0
2-preparation and testing of mortar cubes:
mortar cubic samples have dimensions(70.7×70.7×70.7 mm) were prepared according tobs 4550-
3.4:1978with 1:3 ratio of cement:sand, 0.40 ratio of water:cement and the mass of water in the mix is 10 percent
of the mass of the dry materials. the sahnc loading ratios are 0.1, 0.2, 0.4and 0.6wt%, as shown in table 4.
these ratios were calculated as a percent to the cement weight.
table 4: ingredient of mortar samples
water sahnc
(ml)
sand
(g)
cement
(g) % (g)
200 600 80 0 0
199.8 600 80 0.1 0.2
199.6 600 80 0.2 0.4
199.2 600 80 0.4 0.8
198.8 600 80 0.6 1.2
then, these ingredients were mixed for four minutes using a spark mixer and the resultant mixture was
further mixed by a vibrating machine with a frequency of 200 hz for another four minutes.cubic samples were
115 sihama i. salih et al., 2016/ advances in natural and applied sciences. 10(13) september 2016, pages: 112-124
subjected to humid environment for 24 hr and immersed in the water for another 27 daybefore
testingusingeitherimpact machine or upv methods.
3-preparation and testing for consistency and setting timespurposes:
in order to measure the consistency and the setting times by vicatapparatus, neat cement pastes were
prepared. these pastes include fixed weight of cement (400g) and variable amounts of water.these two
components were mixedcarefully for four minutes and then moulded in the cylindricalmould before testing.
the consistency is measured using a 10 mm diameter plunger(bs en 196-3: 2005). the plunger is brought
into contact with the top surface of the paste and released. paste is considered to be standardwhen the plunger
penetrates the paste to a point 6 ± 1 mm from the bottom of the mould. the water content of the standard paste
is expressed as a percentage by mass of the dry cement, the usual range of values being between 26 and 33 per
cent[9].
the setting times of cement are measured using different penetrating attachments (bs en 196-3 : 2005)[9].
for the initial set, a round needle with a diameter 1.13 ± 0.05 mm is used. when the paste stiffens sufficiently
for the needle to penetrate no deeper than to a point 5 ± 1 mm from the bottom, initial set is said to have taken
place. final set is determined by a similar needle fitted with a metal attachment hollowed out so as to leave a
circular cutting edge 5 mm in diameter and set 0.5 mm behind the tip of the needle. final set is said to have
taken place,when the needle, gently lowered to the surface of the paste, penetrates it to a depth of 0.5 mm but
the circular cutting edge fails to make an impression on the surface of the paste.
ultrasonic pulse velocity (upv) test:
in order to measure the elastic constants forhybrid cementinous composites, the non-destructive upv test
was adopted. this test uses the csi type cc-4 testerwith 26000 hz with aluminum reference bar which possess
a 32.5 ?s transition time. test equipment generates a pulse which transmits through the concrete mass, then
receiving the pulse to measure the elapsed time.upv outputs was also utilized to evaluate the quality of concrete
and mortar according to the is code (bs, 1881, 1983) as well as to calculate the elastic constants[14].in thistest,
two transducers arrangements were used opposite faces (direct transmission) to measure vland adjacent faces
(semi- direct transmission) to measure vt.
results and discussions
1- compressive strength (cs):
the effect of additionshncs toconcrete and mortaron the behavior ofcompressive strength (cs)are shown
in figures1 and 2 respectively. it is clearfrom figure 1 that csof concrete was decreased from 40.2 mpafor pure
concreteto 35.9 mpa when the addition of (sahnc) in concrete reach to ratio of 0.4% wt.
this behavior is due to the competition between the cement paste and sahnc particles to absorb the
available water. this competition leads to reduce the hydration reaction between cement and water (decreasing
in h-bonds formed between cement paste and water), therefore cs will decrease. the reduction in the hydration
reaction results also in the formation of entraining pores. these pores were initially filled with the curing water
and then dried out therefore, these voids affect the cs negatively.
beyond the 0.4wt% sahncs, the cs increased up from 35.9 mpa to 45.8 mpa when the (sahnc) content
in the concrete reach to ratio of 1 wt % which means there are 14% increasing compared with the pure concrete.
this new manner is due to the fact that the negative influence of additional voids induced by the addition of
sahnc particles was compensated by the improved degree of hydration and the self-curing effect in the matrix
containing 0.4wt%sahnc. also, loading levels from 0.4 to 1wt% lowering the internal stresses due to the
hindrance of shrinkage deformations by stiff aggregates[8].
results of these two behaviors are in a good agreement with dudziak and mechtcherine conclusions which
were reported in [10].also, this overall enhancement in the compressive strength property results coincides with
results of both gao et al (12.3% increasing) and hareendran et al(10.6% increasing) [10].
116 sihama i. salih et al., 2016/ advances in natural and applied sciences. 10(13) september 2016, pages: 112-124
fig. 1: compressive strength of concretehybrid composites as a function of shncs content
effects of sahncs addition on the mortar cs are shown in figure 2. through this figure, a decrease is
noted at the first in cs, especially at 0.1wt% of sahncsfrom 41.5 mpa (for pure sample) to 40.1 mpa with the
addition of 0.1wt% sahncs. after that, the cs increased with any increasing in the sahnc contents. highest
cs value was obtained at the 0.5wt% ratio of sahncs (42 mpa), then it became stable.
fig. 2: compressive strength ofmortarhybrid composites as a function of shncs content
by comparing the two previous curves in figures 1 and 2, asimilarity is observed in the concrete and mortar
behaviors of the curves, except there is stability in the mortar compressive strength at higher sahnc levels.
2. consistency of standard mortar paste test:
consistency ofcementinous paste is considered a critical property because of its strong relation with water
amount in the paste. certain quantity of water is required for hydration process and to obtain the desired
rheological properties for proper mixing, compacting and transporting. increasing water content causes
segregation, bleeding, increased porosity of the hardened concrete, reduction in the mechanical performance,
reduction in durability, increased shrinkage and increased creep deformations. therefore, there is a real need to
control the water content in the paste.
figure 3 shows the effect of sahnc ratios on the amount of additional water required to obtain the
standard consistency of the mortar paste. from this figure, it was found that these additional amounts increased
with the increasing sahnc content, and reached to maximum level with 0.6 wt % sahnc ratio. so, these
amounts of the required water increased from 110 ml for the reference mortar paste (without sahncs) to 150
ml for the paste with 0.6wt% sahnc.
117 sihama i. salih et al., 2016/ advances in natural and applied sciences. 10(13) september 2016, pages: 112-124
fig. 3: the amount of additional water required to obtain the standard consistency of the mortar paste as a
function of sahnc content
this amount of additional water 40 ml, seems to be reasonable, since the excessive amount (more than 160
ml) added to the fresh concrete alters its properties (reduces both its strength and workability, increases its
shrinkage). also, it seems to be reasonable from economical viewpoint.
3.setting timesresults:
setting time is an important factor in concrete work to keep fresh concrete plastic for enough time, which
helps the processes of transporting, casting, and compaction. initial setting time refers to the beginning of
solidification, while final setting time refers to the beginning of hardening process. the initial and final setting
times of the pure sample, and the effect of the addition of sahnc with ratios of 0.2, 0.4, 0.6, and 0.8wt%are
shown in table 5. it is clear that these two times have the same behavior they increased linearly with the
sahnc ratios except at 0.2 wt% sahnc. this indicates that sahnc materials act as retarder at high
concentrations.
table 5: sahnc effects on the setting times of mortar paste
the hydration of tricalcium aluminate (3cao.al2o3) is responsible for the setting of cement[8]. therefore,
small internal water sources (corresponded to low sahnc ratio 0.2 wt%) cannot complete the hydration
reaction. during hydration process, insolublecalcium or aluminum compounds are formed and interspersed
through the crystalline mass. these compounds are not removable from the stiffened mass, thus retard the rate
of absorption of h3o+ ions on cement surface and slow down the setting reaction[11].
4. ultrasonic pulse velocity (upv) results:
the longitudinal and transverse ultrasonic velocities (vl and vt)were calculated according to equations 1
and 2 respectively,as well as the elastic constants, such as elastic modulus(e) eq. 4, shear modulus(g) eq. 5 and
poison s ratio(?) eq. 6 for both the concrete and mortar cubes, as shown in tables 6 and 7 and figures from 4 to
9.
118 sihama i. salih et al., 2016/ advances in natural and applied sciences. 10(13) september 2016, pages: 112-124
table 6: ultrasonic velocities and elastic constants for concrete cubes
sahnc
%
?
g/cm3
tl
?s
vl
km/s
tt
?s
vt
km/s
e
mpa
g
mpa
?
0 2.318 30.60 4.90 33.65 3.15 55.655 23.000 0.209
0.2 2.316 31.25 4.80 34.19 3.10 53.360 22.256 0.198
0.4 2.315 31.50 4.76 34.52 3.07 52.452 21.818 0.202
0.6 2.320 30.30 4.95 34.08 3.11 56.845 22.439 0.266
0.8 2.331 30.00 5.00 33.54 3.16 58.275 23.276 0.251
1 2.364 29.82 5.03 33.12 3.20 59.811 25.743 0.161
it is clear from table 6 that for concrete hybrid composites with low sahnc contents (up to 0.4 wt. %),
the ultrasonic waves elapsed increasing times when transported through concrete cubes in both longitudinal and
transverse directions.
in contrast, for hybrid composites with high sahnc contents (0.6-1wt %), the ultrasonic waves elapsed
decreasing times. so, vl decreased from 4.9 km/s for pure sample to 4.76 km/s for hybrid composite with 0.4
wt% sahnc, and then increased up to 5.03 when the sahnc content increased up to 1 wt%. in similar
manner, vt decreased from 3.15 km/s to 3.07 km/s then increased up to 3.2 km/s in the same ratio.
these opposite two behaviors are due to heterogeneity and voids in hybrid composites with low sahnc
contents (up to 0.4 wt%). this heterogeneity arises from the presence of both hydrated and anhydrated portions
in the cementinouspastes therefore the sound energy will dissipate and attenuate at the interfacial boundaries
between these phases.
it was observed from figure 4 that elastic modulusof concrete firstly
fig. 4: elastic modulusof concrete hybrid composites as a function of sahnc content
decreased from 55.655mpa for pure sample to 52.6 mpa for hybrid composite with 0.25 wt% sahnc, and then
increased up to 59.811 mpa for hybrid composite with 1 wt% sahnc. these behaviors are due to insufficient
amount of stored water to complete the hydration process with sahnc ratios up to 0.4 wt%, and then water
amounts be enough to complete the setting reaction. therefore, concrete became stiffer.
figure 5 shows the shear modulus as a function of sahnc contents in hybrid concrete. it is clear that the
shear modulus decreased from 23 mpa for pure sample to 21.8 mpa for hybrid composite having 0.4 wt%
sahnc, then increased up to 25.743 mpa when sahnc content increased up to 1wt%.
declined values at low sahnc contents are due the attenuation counter waves in voids which are
available in the un-reacted zones.in contrast, when sahnc contents areincreased(more than 0.4 wt %),
chemical reaction occurs through chemical bonds. this bonding increases the homogeneity between the
composite ingredients and reduces the phase separation. thus, waves elapsed short time, wave velocity becomes
high and the shear modulus increased.
119 sihama i. salih et al., 2016/ advances in natural and applied sciences. 10(13) september 2016, pages: 112-124
fig. 5: shear modulus of concrete hybrid composites as a function of sahnc content
the effects of addition of sahncs on the poisson s ratio of concretes hybrid composite was shown in
figure 6.it is clear from this figure that the variations inpoisson s ratio were limited to small range (0.161-
0.252), which indicates that the longitudinal extension and the transverse contraction are equal.
fig. 6: poison s ratioof concrete hybrid composites as a function of sahnc content
furthermore, since the poisson s ratio values, for concrete are within the range of 0.2- 0.35, and the typical
value reaches to 0.24 [8], therefore the obtained poisson’s ratios considered as acceptable values except that for
1 wt% sahnc.
table 7 shows the values of ?,vl,vt, e, g and ? for the mortar hybrid composites with
differentcontentratios of sahnc.
table 7: ultrasonic velocities and elastic constants for mortar cubes
sahncs
%
?
g/cm3
tl
?s
vl
km/s
tt
?s
vt
km/s
e
mpa
g
mpa
?
0 2.223 14.34 4.93 16.0 3.125 54.03 21.71 0.244
0.1 2.153 14.40 4.91 15.8 3.164 51.90 21. 56 0.203
0.2 2.130 14.45 4.90 15.5 3.225 51.14 22.15 0.154
0.3 2.100 14.36 4.92 15.7 3.185 50.83 21.3 0.193
0.4 2.124 14.25 4.96 15.9 3.145 52.25 21.0 0.244
0.5 2.128 14.14 5.00 16.1 3.105 53.20 20.52 0.296
0.6 2.280 14.00 5.05 16.3 3.067 58.15 21.44 0.356
120 sihama i. salih et al., 2016/ advances in natural and applied sciences. 10(13) september 2016, pages: 112-124
from table 7, it is clear that the ultrasonic pulses elapsed times (tland tt) in mortar cubes are less than
times elapsed in concrete cubes mentioned earlier in table 6. and, this is related to the dimensions of mortar
cube that are less than the dimensions of concrete cube.
also, it is clear that vl decreased firstly from 4.93 km/s for the pure sample to 4.9 km/s for hybrid
composite with0.2 wt% of sahnc,then increasedup to 5.05 km/s for sample with 0.6 wt% of sahnc. such
trend (increasing vlwith sahnc content) is in a accordance with the works published bywinker and nur,1982
ohdaira andmasuzawa,2000 as well as by veraara et al., 2001[10].
the behavior of mortar elastic modulus shown in figure 7, this modulus continues its deceasing from its
initial value 54.03 mpa (for pure sample) to reach its minimum value 50.7 mpa at 0.3 wt% of sahnc, then
increases gradually to reach 58.15 mpa at 0.6 wt% of sahnc.the elastic modulus exceeds its initial value only
with the later ratio 0.6wt%sahnc,which indicates that the hydration process completes only with this ratio.
fig. 7: elastic modulusof hybrid mortarcomposite as a function of sahnc content
shear modulus values for mortar composite are shown in figure 8.this figure shows the fluctuating
behavior in shear modulus values with the increase sahnc contents. shear modulus reaches its maximum
value at 0.2 wt% sahnc, then reach its minimum value at 0.5 wt% sahnc and then increased at 0.6 wt%
sahnc to reach21.44 mpa which is lower than its initial value. this means that the optimum sahnc ratio in
mortar paste is the 0.2 wt% from the shear modulus viewpoint.
fig. 8: shear modulusbehaviorof mortarhybrid composite as a function of sahnc content
effects of sahncsaddition on the values ofpoisson s ratio for mortar hybridcomposites are shown in
figure 9.firstly, there is a decrease from 0.224value (for pure sample) to 0.193value at 0.3wt% of
121 sihama i. salih et al., 2016/ advances in natural and applied sciences. 10(13) september 2016, pages: 112-124
sahnc.then, the poisson s ratio increased with the increasing of sahnc ratios reaching to 0.356 at 0.6wt% of
sahnc.
fig. 9: poisson s ratioof mortar hybridcomposites as a function of sahnc content
so the poisons ratios, seems to be more affected than those for concrete its range extended from 0.154 to
0.356. the value corresponded to the 0.4wt% sahnc 0.244 seems to be a typical value.
5. quality evaluation:
all longitudinal velocities (vl) for concrete and mortar hybrid compositesare more than 4.5 km/s more
than 4500 m/sec as shown in tables 6 and 7.therefore the quality for all samples seems to be excellent
according to the bs, 1881, 1983 code (table 8)[13].
table 8: concrete quality as a function of upv (bs, 1881, 1983)[13]
upv(m/s) concrete quality
above 4500 excellent
3500 to 4500 good
3000 to 3500 medium
below 3000 doubtful
these high velocitiesalso indicate the high homogeneity and uniformity levels of pastes, which in turn
meanthe good dispersion of the sahncs in the hybrid cementinous composites.
6. acoustic impedance results:
using both the longitudinal wave velocity (vl) and the density (?), the acoustic impedance (z) for concrete
and mortar was calculated according to equation 8[14].
z = ?v (8)
so, the acoustic impedance (z) for concrete and mortar are shown in figures 10 and 11respectively.
fig. 10: acoustic impedance for concrete as a function of sahnc
122 sihama i. salih et al., 2016/ advances in natural and applied sciences. 10(13) september 2016, pages: 112-124
the acoustic impedance of concrete samples (figure 10) decreased from (11.35× 106 kg/m2. s) for pure
sample to reach (11.02× 106 kg/m2. s) for sample with 0.4wt% ratio of sahnc, and then increased to its
maximum value (11.89× 106 kg/m2. s) at 1wt% of sahnc. theseopposite two behaviors give evidence about
the completing of hydration process at high sahnc ratios.
whereas, the acoustic impedance of mortar samples (figure11) decreased from (10.95× 106 kg/m2. s)for
pure sample to reach (10.33× 106 kg/m2. s) for sample with 0.3wt % of sahnc, andthen increased to (11.5×
106 kg/m2. s) at 0.6wt% sahnc ratio.
fig. 11: acoustic impedance for mortar as a function of sahnc content
to determine the percentages of both the energy reflected (er) and the energy transmitted (et) when the
wave projected on a plane between two media, steel (z = 45.41) was used in this study as the second medium.
er and et were calculated according to equations 9 and 10respectively [15].
er= [(z1-z2) / (z1+z2)]2 x 100 (9)
et= (4z1z2) / (z1+z2)2 x100 (10)
the percentages of both the energy reflected (er) and the energy transmitted (et) are shown in figures 12
and 13 for each of the concrete hybrid composite and mortar hybrid composite respectively. in both two figures,
er reaches to their minimum values at higher sahncs ratios while et reaches to their maximum values at
higher ratio of sahncs. this means that at higher sahncs ratios content, the energy will dissipate due to
high porosity levels. also, both figures contain a maximum point in both er and et which support that the
maximum hydration levels occur at these points.
fig. 12: percentages of reflected (a) and transmitted (b) energies between steel and concretehybridcomposites
123 sihama i. salih et al., 2016/ advances in natural and applied sciences. 10(13) september 2016, pages: 112-124
fig. 13: percentages of reflected (a) and transmitted (b) energies between steel and mortarhybrid composites
conclusions:
in this research an attempt was down to improve the concrete and mortar properties by adding
sahncs.based on this, it was concluded the following:-
1- compressive strength for concrete and mortar hybrid composites exceeds their initial values at higher
sahncs ratios.
2- the additional amounts of water which is required to get the standard consistency in mortar seem to be
reasonable.
3- elastic modulus for these hybrid composites increased at higher ratios.
4- shear modulus increased at higher ratios and there is some fluctuations in mortar shear modulus.
5- most values of poisons ratio within the typical range for concrete.
6- initial and final setting times of mortar increased with sahncs loadings.
7- concrete quality are excellent according to the bs, 1881, 1983 code.
8- the acoustic impedance increased, while the energy reflected reaches to its minimum value at higher
sahncs ratios and the energy transmitted reaches to its maximum valueat this ratio.
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