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Cracking Control in Mezzanine Floor Slabs using Rice Husk Ash and Polypropylene Fibers

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The continuous population increase in recent years requires a greater number of households to be built quickly, with good materials and produced under quality standards that guarantee their manufacturing process. The prefabricated concrete, produced and supplied by concrete plants, is poured into the different structural elements, the mezzanine slabs being the most careful surfaces in the appearance of fissures; because being horizontal and having larger dimensions, the dimensional changes in the concrete appear more frequently due to the rapid loss of water from the surface of the concrete before setting; which generates superior stresses to the resistant capacity of the concrete at early ages, which affect the durability and reduce the resistance of the structures, causing greater economic expenses in maintenance and repairs. In the present investigation, 5%, 10% and 15% of rice husk ash was used as a replacement for cement and 900g/m ³ of polypropylene fiber; The results indicate that as the percentage of rice husk ash increases, there is a reduction in the slump and the crack fissures, and that the resistance to compression and flexion decreases, with respect to the concrete pattern.
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Cracking Control in Mezzanine Floor Slabs using Rice Husk Ash and
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ICMEMSCE 2019
IOP Conf. Series: Materials Science and Engineering 758 (2020) 012065
IOP Publishing
doi:10.1088/1757-899X/758/1/012065
1
Cracking Control in Mezzanine Floor Slabs using Rice Husk
Ash and Polypropylene Fibers
B Cano1, J Galarza1, J Rodríguez2 and F García2
1 Bachelor, Civil Engineering Program, Universidad Peruana de Ciencias Aplicadas,
Lima, Perú
2 Full Professor, Civil Engineering Program, Universidad Peruana de Ciencias
Aplicadas, Lima, Perú
Email: u201322444@upc.edu.pe
Abstract. The continuous population increase in recent years requires a greater number of
households to be built quickly, with good materials and produced under quality standards that
guarantee their manufacturing process. The prefabricated concrete, produced and supplied by
concrete plants, is poured into the different structural elements, the mezzanine slabs being the
most careful surfaces in the appearance of fissures; because being horizontal and having larger
dimensions, the dimensional changes in the concrete appear more frequently due to the rapid
loss of water from the surface of the concrete before setting; which generates superior stresses
to the resistant capacity of the concrete at early ages, which affect the durability and reduce the
resistance of the structures, causing greater economic expenses in maintenance and repairs. In
the present investigation, 5%, 10% and 15% of rice husk ash was used as a replacement for
cement and 900g/m3 of polypropylene fiber; The results indicate that as the percentage of rice
husk ash increases, there is a reduction in the slump and the crack fissures, and that the
resistance to compression and flexion decreases, with respect to the concrete pattern.
1. Introduction
House constructions are constantly growing and the most used material that provides flexibility in its
design is concrete [1], which after being placed on large surfaces, such as solid slabs, tends to crack
due to plastic shrinkage [2]; the magnitude of the cracks depends on the ambient temperature, relative
humidity and wind speed [3], producing in the structures the reduction of their serviceability and
aesthetics [4]; The appearance of cracks in the concrete reduces its useful life and increases the
permeability and the risk of penetration of environmental agents [5]. Rice husk residues are discarded
in landfills and cause pollution [6], their ashes are used as partial cement replacement because they
improve the quality and durability of concrete [7,8,9]; however, high amounts of replacement can
negatively affect its resistance and permeability [10]. On the other hand, polypropylene fibers are used
in the reduction of early cracking [5]; in the control of cracks, in the increase of durability and
serviceability of the structure [12]. The particle size of rice husk ashes (RHA) is important because the
smaller it is, the plastic shrinkage increases [13]; Compressive and flexural strengths are reduced by
adding RHA, 10% being an optimal percentage [14,15]. On the other hand, synthetic fibers are used
to prevent shrinkage cracking, polypropylene fibers stand out for their efficiency and can be applied in
quantities by volume of 0.10% [16]. Fiber length is important in reducing shrinkage, with 19mm fibers
better than 13mm fibers for volume replacements from 0.05% to 0.20% [17]. With regard to the
compressive and flexural strengths, with the amount of 0.9% of total volume, resistances higher than
conventional concrete are achieved [17]. The purpose of this work is to study the effect of RHA on the
settlement, plastic shrinkage cracking, compressive strength and flexural strength in order to make a
concrete to control the fissures of the mezzanine floor slabs.
2. Materials and Method
2.1 Materials
Andino Ordinary Portland Cement Type I was used; Natural fine aggregate from the “Trapiche”
quarry; 1” natural coarse aggregate from the“ Jicamarca ”quarry; polypropylene (FPP) fibers of L = 12
mm, Ø = 0.012 mm, density 910 kg / m3 and tensile strength of 480 MPa; rice husk ash (RHA)
ICMEMSCE 2019
IOP Conf. Series: Materials Science and Engineering 758 (2020) 012065
IOP Publishing
doi:10.1088/1757-899X/758/1/012065
2
obtained from uncontrolled combustion in the open air (temperature of 500 - 600 oC) from the city of
Chiclayo and sieved by the mesh Nº30 (600 µm). The water was drinkable.
2.2 Method
The mix design was made for a concrete f’c = 210 Kg/cm2 and according to [18]. Table 1 shows the
designs of mixtures made for the mixing of standard concrete without inclusion of RHA or FPP. The
elaborated mixtures are shown in Table 1 and in Table 2 the tests, standards, number of specimens and
curing ages. The test specimens for the compressive strength test were cylindrical of 15 cm x 30 cm,
for the flexural strength test with loads to the thirds of the light of 15 cm x 15 cm x 50 cm, which were
demoulded at 24 hours and then rehearsed.
Table 1. Mix design for concrete f’c = 210 Kg/cm2
Mix
OPC
FA
CA
RHA
FPP
(Kg/m3)
(Kg/m3)
(Kg/m3)
(Kg/m3)
(Kg/m3)
Pattern
366
844
944
0
0
RHA-5_FPP
347.7
844
944
18.3
0.9
RHA-10_FPP
329.4
844
944
36.6
0.9
RHA-15_FPP
311.1
844
944
54.9
0.9
Table 2. Tests Performed
Concrete Tests
Methods
No Specimens
Cure Age (days)
Slump
[19]
8
---
Plastic shrinkage
cracking
[20]
2
1
Compressive strength
[21]
9
7, 14 y 28
Flexural strength
[22]
9
7, 14 y 28
3 Results and Analysis
3.1 Slump
Table 3 shows the effect of the percentage of RHA and fixed amount of FPP in the slump. It can be
seen that as the percentage of RHA replacement increases, the slump decreases, by 0.50”, 0.75” and 1”
in relation to the pattern mixture. [23], for a ratio of w/c = 0.60, the slump decrease values of 0.4” and
0.7” are obtained for 10% and 15% with respect to traditional concrete. Similarly [24], for the same
w/c ratio and a replacement of 10% of RHA, the slump decreases by 0.50”. These trends are similar to
those of the study. [25] explains that this behavior is due to the fact that RHAs have a high specific
surface that attracts more water molecules, requiring increasing the water in the mixture to maintain an
optimum level of workability.
3.2 Plastic Shrinkage
Table 3 shows the effect of the percentages of RHA and fixed amount of FPP on plastic shrinkage. It
is observed that the crack reduction ratio (CRR) increases with the percentage of RHA, reaching the
values of 26.67%, 40% and 78.32% for mixtures RHA-5_FPP, RHA-10_FPP and RHA-15_FPP with
respect to the pattern sample. [26] perform concrete mixtures with 1% FPP in total volume, finding
that after 24 hours the mixtures with FPP increase the CRR by 65% compared to traditional concrete.
[27] performs concrete mixtures with a/c = 0.50 and cement replacements of 15% and 25% of fly ash
with 0.05% of basalt fibers in total volume, obtaining that after 24 hours the CRR increases 50% in
average. These trends are similar to those of the present study. According to [28], this behavior can be
ICMEMSCE 2019
IOP Conf. Series: Materials Science and Engineering 758 (2020) 012065
IOP Publishing
doi:10.1088/1757-899X/758/1/012065
3
attributed to the lower cement content compared to control mix, as well as to the pore size and grain
size refinement processes which strengthen the mechanical interlocking in the transition zone.
3.3 Compressive Strength
Figure 2 shows the effect of cure time on compressive strength for different percentages of RHA and a
fixed amount of FPP. It can be seen that as the curing time increases, the resistance increases for all
the mixtures, the pattern mixture being the one that obtains the greatest resistance; reaching for the 28
days the value of 251.33 Kg / cm2 which represents 9.32%, 18.12% and 28.53% more than the RHA-
5_FPP, RHA-10_FPP and RHA-15_FPP mixtures. Similar results after 28 days of curing. [29], that
partially replacing the cement with 5%, 10% and 15% of RHA obtains lower resistance values with
respect to traditional concrete being these of the order of 25.13%, 30.57% and 31.05%. In the same
way, [30] demonstrates for replacements of 10%, 20% and 30% the resistance with RHA, at the age of
28 days, is lower than traditional concrete in 8.88%, 9.96% and 27.20%. These trends are similar to
those of the study. [23,30] indicates that this behavior is due to the increase in RHA content, the
volume of capillary pores increases and Ca (OH)2 accumulates in the interface, resulting in a less
compact structure that causes the resistance to be less; that is, by adding RHA to the concrete, the
porosity increases and the density decreases causing a lower resistance to compression.
3.4 Flexural Strength
Figure 3 shows the effect of curing time on flexural strength for different percentages of RHA and a
fixed amount of FPP. It is seen that as the curing time increases, the resistance increases for all the
mixtures, the pattern mixture being the one that obtains the greatest resistance; reaching for the 28
days the value of 27.40 Kg / cm2 that represents 17.01%, 18.14% and 28.47% more than the RHA-
5_FPP, RHA-10_FPP and RHA-15_FPP mixtures. These results are consistent with [23], which with
10% and 15% RHA for ages 7, 14 and 28 days finds that the flexural strength decreases with respect to
the standard concrete by 1.85%, 2.96%, 16.57% and 2.78%, 3.94%, 27.68% for replacements of 10%
and 15% respectively. In turn, [31] investigates the addition of RHA in flexural strength using 3
calcination methods (outdoors, in stoves and in ovens) for 5%, 10% and 15% replacement at 28, 90
and 150 days; obtaining that the resistance at 28 days for the 3 calcination methods with replacements
of 5%, 10% and 15% RHA, is lower with respect to the control sample in average values of 35%, 48%
and 52% . These trends are similar to those of the present study. [32,33] indicate that this behavior is
due to the low pozzolanic activity of the RHA.
Figure 1. Effect of cure time on compressive
strength
Figure 2. Effect of cure time on flexural strength
0
50
100
150
200
250
300
0 5 10 15 20 25 30
Compressive Strenght (Kg/cm2)
Curing Time (days)
Pattern
RHA-5_FPP
RHA-10_FPP
RHA-15_FPP
0
5
10
15
20
25
30
0 5 10 15 20 25 30
Flexural Strenght (Kg/cm2)
Curing Time (days)
Pattern
RHA-5_FPP
RHA-10_FPP
RHA-15_FPP
ICMEMSCE 2019
IOP Conf. Series: Materials Science and Engineering 758 (2020) 012065
IOP Publishing
doi:10.1088/1757-899X/758/1/012065
4
4. Conclusions
The partial replacement of cement by 10% of RHA and 900 g/m3 of FPP demonstrates that plastic
shrinkage cracks decrease in size and width, preventing the entry of external agents that can
damage the durability of the structure.
The workability of the mixture decreases with the additions of RHA and FPP, because the
hydrophilic nature of the RHA stimulate the absorption of water from the mixture, and the FPP
produce higher friction in the mixture.
Compressive strength and flexural strength decrease, with RHA particles favorable for fissure
reduction and FPP reinforce concrete elements.
Plastic shrinkage cracking decreases, indicating that the combined incorporation of RHA and FPP
helps in reducing the crack fissures.
Table 3. Effect of the percentage of RHA and FPP on slump and CRR
Code
Slump (in.)
# Cracks
Crack Width (mm)
Average
Crack Width
(mm)
CRR (%)
n.
Max.
Pattern
1,5”
10
0,1
0,6
0,375
---
RHA-5_FPP
1”
10
0,05
0,5
0,275
26,67
RHA-10_FPP
0,8”
10
0,05
0,3
0,225
40,00
RHA-15_FPP
0,5”
10
0,05
0,1
0,0813
78,32
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