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Effects of rice husk ash and fiber on mechanical properties of pervious

concrete pavement

Saeid Hesami a, Saeed Ahmadi a,, Mahdi Nematzadeh b

a Faculty of Civil Engineering, Babol Noshirvani University of Technology, 47148-71167 Babol, Iranb Department of Civil Engineering, Mazandaran University, 47416-13534 Babolsar, Iran

h i g h l i g h t s

Physical and mechanical properties were tested.

Rice husk ash (RHA) and fibers were used to make pervious concrete (PC).

These RHA could be used as pozzolan to produce PC with acceptable properties.

The contribution of RHA and fiber to the mechanical properties was significant.

Reduction of permeability was occurred in containing RHA and fiber concrete.

a r t i c l e i n f o

Article history:

Received 25 July 2013

Received in revised form 3 November 2013

Accepted 20 November 2013

Available online 17 January 2014

Keywords:Rice husk ash (RHA)

Fibers

Pervious concrete

Physical and mechanical properties

a b s t r a c t

The use of pervious concrete pavement is significantly increasing due to reduction of road runoff and

absorption of noise. However, this type of pavement cannot be used for heavy traffic due to a high

amount of voids and consequently low strength of pervious concrete. In this paper, rice husk ash

(RHA) was used in order to strengthen pozzolanic cement paste and the effect of 0%, 2%, 4%, 6%, 8%,

10% and 12% weight percentages as a cement replacement in concrete mixtures on the mechanical prop-

erties was studied. Moreover, 0.2% Vfof glass (whereVfis the proportion of fiber volume to total volume

of concrete), 0.5%Vfof steel and 0.3%Vfof polyphenylene sulfide (PPS) fibers were used to improve the

mechanical properties of the pervious concrete. Also, several water to cement (w/c) ratios were made and

then, physical and mechanical properties of hardened concrete including porosity, permeability, com-

pressive strength, tensile strength and flexural strength were investigated. The results indicated a signif-

icant increase in compressive, tensile and flexural strengths. Also, in all ofw/cratios, a similar trend was

observed in the compressive, tensile and flexural strengths of concrete containing RHA and fibers but the

optimum percentage of RHA was different so that, it increases rapidly to theoptimization point but grad-

ually decreases after this point. Thew/cratio of 0.33 significantly increased the mechanical properties of

the pervious concrete and reduces the amounts of voids and its permeability.

2013 Elsevier Ltd. All rights reserved.

1. Introduction

Pervious concrete consists of cement, water and coarse aggre-gates (with low or without fine aggregates). Regarding the open

structure of pervious concrete, air and water can penetrate into

the subsoil through voids existing within the concrete. Due to con-

nectivity of pervious concrete voids, flow pipes are generated,

which work as a filter and absorb pollutants (e.g. oil or other pol-

lutions on the ground) [1]. Pervious concrete is usually used in

north of Iran because of heavy rainfalls in these regions and also

its environmental benefits such as controlling runoff, restoring

groundwater supplies and finally reduction of underground waterpollution. Pervious concrete has acoustic properties due to its high

porosity that can reduce noise pollution[2,3]. Although pervious

concrete was available since the middle of 19th century, its first

application in many countries specially USA and Japan was about

1980. Pervious concrete pavement is better than asphalt or ordin-

ary concrete pavement environmentally [3]. High penetration

velocity of water into pervious concrete has led into using this kind

of pavement in other cases such as hydraulic structures, tennis

courts, greenhouses and as a base course of heavy traffic pave-

ments [4]. However, because of lower durability and strength of

pervious concrete, compared to ordinary ones, its application is

only in regions with low traffic congestion such as parking lots,

0950-0618/$ - see front matter 2013 Elsevier Ltd. All rights reserved.http://dx.doi.org/10.1016/j.conbuildmat.2013.11.070

Corresponding author. Address: Faculty of Civil Engineering, BabolNoshirvani

University of Technology, Babol, Postal Box: 484, Babol, Postal Code: 47148-71167,

Iran. Tel.: +98 9151173217; fax: +98 1113231707.

E-mail addresses: [email protected] (S. Hesami), [email protected]

(S. Ahmadi), [email protected](M. Nematzadeh).

Construction and Building Materials 53 (2014) 680691

Contents lists available at ScienceDirect

Construction and Building Materials

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c o n b u i l d m a t
http://dx.doi.org/10.1016/j.conbuildmat.2013.11.070mailto:[email protected]:[email protected]:[email protected]://dx.doi.org/10.1016/j.conbuildmat.2013.11.070http://www.sciencedirect.com/science/journal/09500618http://www.elsevier.com/locate/conbuildmathttp://www.elsevier.com/locate/conbuildmathttp://www.sciencedirect.com/science/journal/09500618http://dx.doi.org/10.1016/j.conbuildmat.2013.11.070mailto:[email protected]:[email protected]:[email protected]://dx.doi.org/10.1016/j.conbuildmat.2013.11.070http://crossmark.crossref.org/dialog/?doi=10.1016/j.conbuildmat.2013.11.070&domain=pdf

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road shoulders, streets and local roads[5,6]. Void content of pervi-

ous concrete is usually 1525%, and it is compressive strength is

about 2.828 MPa [4,7]. Since fine aggregates content is low or

sometimes there are no fine aggregates in pervious concrete, ce-

ment paste covers coarse aggregates and preserves integrity of

voids [8]. On the other hand, compressive, tensile and flexural

strengths of pervious concrete is less than ordinary ones due to

its high porosity and lack of fine aggregates [9]. So, the serviceabil-

ity life of this concrete is less than its design life [1,10]. Several

studies have been carried out on mechanical properties of pervious

concrete by Sonebi and Bassuoni [11], Shu et al. [12], Chen et al.

[13], Lian et al.[14]and Agar-Ozbek et al. [15].

The use of various fibers in concrete and making fibrous con-

crete (FRC) is an effective step in preventing the expansion of mi-

cro-cracks and cracks and compensating tensile strength

weakness of concrete [16]. Important characteristics of fibrous

concrete are energy absorption, flexibility and impact resistance

that considerably reduce the risk of concrete failure, especially in

areas under repeated loading. In general, the fibers in the pervious

concrete significantly increase permeability while slightly increas-

ing air in pervious concrete and improve its tensile strength

[5,17,18].

Contact area, the interfacial zone between cement paste and

aggregates or fiber, plays an important role in permeability, dura-

bility and strength of concrete and is a function of the thickness of

the contact area, type of fiber, type of cement, type of pozzolan, w/c

ratio and concrete age. Also, the micro-structure of the cement

paste in the contact area differs from that within the cement paste

and has more porosity and micro-cracks. In this experimental

investigation, rice husk ash (RHA) as artificial pozzolan, was used

to strengthen the contact area. Recycling the components of waste

materials saves energy in cement production and preserves natural

resources and environment. One of pozzolanic materials applicable

in the constituent components of agricultural waste is rice husk

that contains relatively large amounts of silica. In addition, the

use of materials with pozzolanic reactions can often significantly

improve the properties of concrete[1921]. Due to the large num-ber of rice paddies in the north of Iran and other areas of this coun-

try, a large amount of rice husk is produce annually. At present,

these husks are of no or limited used. In addition getting rid of

them will have some serious environmental issues as they are

burned and a lot of smoke and pollutants are emitted. However,

it should be noted that husk is a precious agricultural product

and a raw industrial substance of various uses.

RHA, as a partial replacement of cement, increase compressive

strength of normal concrete and its optimal value is betwee-

n 10% and 30%[22]. Different studies have suggested optimal val-

ues for RHA. Andres et al. [23] reported 10% of RHA as optimal

for achieving maximum compressive strength. In some studies,

including a study by Ganesan et al. [24] 15% replacement leads

to higher compressive strength in comparison with 10%. However,

these differences depend greatly on how it is burnt which, has a di-

rect impact on pozzolanic properties. Therefore, for a comprehen-

sive case, the optimum range of 1015% replacement is a better

suggestion than precisely 10% replacement. It is necessary to be

noted the rice husk obtained from different areas has differ-

ent effects even with the same replacement percentages. For

example, Gemma [25] used the same amount of RHA from two dif-

ferent regions and provided a good comparison between the ob-

tained compressive strength.

In this paper, the effect of fiber type, including PPS, steel and

glass fibers with different percentages of RHA (0%, 2%, 4%, 6%, 8%,

10% and 12%) on the physical and mechanical properties of pervi-

ous concrete is investigated. In addition, three water to cement (w/

c) ratios of 0.27, 0.33 and 0.4 are evaluated. This study is an at-

tempt to establish a balance between permeability and strength

of pervious concrete. The compressive strength, tensile strength,

flexural strength, porosity and permeability of pervious concrete

are examined. The results of this study show that compressive,

tensile and flexural strengths increase for up to 810% higher

RHA replacement (as an optimized value) and then reduce for

higher amounts of RHA. Also, substituting the RHA for cement is

economically justifiable and also helps protect the environ-

ment. Moreover, PPS fibers have caused better improvement phys-

ical and mechanical properties of pervious concrete.

2. Experimental design

2.1. Materials

2.1.1. Aggregate

Coarse aggregate size used in this study was from 2.36 to 19 mm which is

ranked #67 in the standard ASTM C33 [26]. The sand was selected from sieved

No 4.75 mm equivalent value (SE = 80%). Fine and coarse aggregate curves of the

used materials, according to ASTM C33, are shown in Fig. 1.

2.1.2. Cement

The cement used was of Portland type II. The chemical and physical composi-tion is given inTable 1.

2.1.3. Rice husk ash (RHA)

Firstly, rice husk was burned for 2 h in the furnace outdoors. Black products

from the furnace represent a high percentage of carbon content that reduces its

pozzolanic properties. Then the ashis burned and decarbonized in a special furnace.

Consequently, the ash is let to cool in the ambient temperature. This method leads

to an increase in specific surface area and pozzolanic properties of RHA [27]. Chem-

ical and physical properties of RHA can be seen inTable 2.

ComparingTables 1 and 2,we can conclude that the amount of silica and cal-

cium oxide, are completely different from each other in cement and RHA so that

the amount of cement silica and RHA are 21.9% and 86.02%, respectively and the

Calcium oxide of the cement and RHA are 63.33% and 1.12%, respectively. As it

can be seen from the total chemical properties of rice husk, the total amount of

silica and Al2O3and Fe2O3is 86.5%, which are much more than the amount (min

70%) specified in ASTM-C618 standard [28]. Thus, RHA is known as a pozzolanic

0102030405060708090

100

0.1 1 10 100Percentpassingthesieve

Sieve size (mm)

Regulations limit Regulations limit

Gradation curve of gravel Gradation curve of sand

Fig. 1. Gradation curve of fine and coarse aggregates with ASTM C33 standard limits.

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material. According to ASTM-C618, pozzolan is defined as a silica material which is

not adhesive by itself but shows chemical reaction with calcium hydroxide in the

vicinity of moisture at normal temperature and produce compositions with adhe-

sive and cementitous properties. This reduces the porosity of the cement paste

and subsequently increases its strength. So pozzolan is a natural or artificial mate-

rial containing active silica. Being fine is the most important physical property of

RHA that increase the concrete strength. Compared to cement, RHA is finer than ce-

ment and has better efficiency as cementitious materials. Therefore, it is expected

that these factors may significantly impact the strength properties of concrete.

2.1.4. Superplasticizer

A superplasticizer (SP) of carboxylic ether (Glenium-110P, BASF) with1.1 g/cm3

specific gravity (at 20 C) is used.

2.1.5. Fibers

Fibers including PPS, steel andglass were used. The properties of thefibersused

are shown inTable 3andFig. 2.

2.2. Specimen preparation

All specimens were cast by rodding 25 times in three layers while applying a

vibration for 10 s after rodding each layer. After mixing, the specimens were re-

moved from the molds and kept in 2225 C water until they reach the age of

28 days when they are ready for the experiments. Three 150300 mm cylindrical

specimens were made to determine the compressive and tensile strengths. Also

three 100100500mm prismatic beams were cast to obtain the flexural

strength. Moreover, in order to calculate the permeability coefficient and porosity,

three 100 100 mm cylindrical specimens were cast.

2.2.1. Compressive strength test

Compressive strength test was carried out accordingto ASTM C39 [29] standard

to evaluate the compressive strength of 150 300 mm cylindrical concrete speci-

mens.Equivalentloading speed was equal to 0.30 MPa/swhichaccording to the rel-

evant standard, is in the range of 0.150.35 MPa/s.

2.2.2. Tensile strength test

The tensile strength of concrete was measured using the ASTM C 496[30]stan-

dard tensile test. This test was done in accordance with the compressive strength

tests on cylindrical specimens with a diameter of 150 mm and height of 300 mm.

Equivalent loading speed was equal to 1 MPa/min which, according to the relevant

standard, is in the range of 0.71.4 MPa/min.

2.2.3. Flexural strength test

The flexural strength of concrete was measured according to ASTM C 78[31]standard test on prismatic beams with dimensions of 100 100500 mm. Equiv-

alent loading speed was equal to 0.95MPa/min which, according to the relevant

standard, is in the range of 0.861.12 MPa/min.

2.2.4. Permeability test

The best definition for a pervious and permeable concrete is its permeability

and porosity properties. Permeability is a function how pores are related to each

other. To define the permeability of a material, the permeability coefficient

should be determined that is the amount of fluid flowing through a unit area

per unit time under a unit hydraulic gradient (that is usually expressed in terms

of centimeters per second). Pervious concrete permeability can be determined

using the falling head tests. In these tests, lateral surfaces of the specimens are

covered and pressurized water is applied on the upper surface of the specimens.

When there is a steady stream of water, the amount of water passing from a cer-

tain height within a specified time is measured. Average permeability coefficient

is calculated according to Eq. (1) based on Darcys law and layer flow assumption

[32]. The average results of the tests on three cylindrical specimens with a diam-

eter and height of 100 mm are reported as the permeability coefficient. A picture

of the device used to determine the permeability of pervious concrete is shown in

Fig. 3.

kaL

AtLN

h1

h2

1

Table 1

Chemical and physical composition of the cement.

Chemical analyses of cement Weight of percent (%)

SiO2 21.9

Al2O3 4.86

Fe2O3 3.30

MgO 1.15

CaO 63.33

SO3 2.10

Physical properties

Specific gravity 3.14

Specific surface area (cm2/gr) 3050

Table 2

Chemical and physical properties of RHA.

Chemical analyses of RHA Weight of percent (%)

SiO2 86.02

Al2O3 0.36

Fe2O3 0.16

MgO 0.39

CaO 1.12

Na2O 1.15

Physical properties

Specific gravity 2.1

Specific surface area (cm2/gr) 3500

Table 3

Properties of glass, steel and PPS fibers.

Type Length (mm) Diameter (mm) Thickness (mm) Young modulus (kg/cm2 105) Specific gravity (gr/cm3)

Steel 36 0.7 16 7.8

PPS 5054 0.07 3.5 0.90

Glass 12 0.1 8.7 2.65

Fig. 2. (a) Steel fibers, (b) PPS fibers and (c) glass fibers used in this study.

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where k is the coefficient of permeability, cm/s; a the cross sectional area of the

standpipe, cm2;L the length of sample, cm; A the cross-sectional area of specimen,

cm2;tthe time in seconds from h1toh2;h1the initial water level, cm;h2is the final

water level, cm.

2.2.5. Porosity test

Porosity is the amount of the concrete pores and cavities defined as a percent-

age of total volume of the matter. The porosity of the specimens was measured by

calculating the difference between dry and weight under water according to Eq. (2)

[33]. First, specimens are placed in oven at 105 C for 24 h and then weighing the

specimens the dry weight (W2) is obtained. Then, the dried specimens are weighed

in water and the weight under water (W1) is obtained. Using Eq. (2) the porosity of

the specimens are calculated. The average test results on three cylindrical speci-

mens of 100 mm diameter and height is reported as the porosity percentage.

P 1 W2 W1Vol q

W

100% 2

where P is the total porosity, %; W1 the weight under water, kg; W2 the oven dry

weight, kg;Vol the volume of sample, cm3; qw the density of water @ 21 C, kg/cm3.

2.3. Concrete mix design

In this study four mix designs namely A, B, C and D are made. Mixes A, B and C,

respectively have aw/cratio of 0.27, 0.33 and 0.4 and each contains three types of

fiber, 0.5% Vf steel, 0.2%Vf glass and0.3% Vf PPS. Also in each of these mix designs 0%,

2%, 4%, 6%, 8%, 10%, and 12%RHA cement replacement has been used. Moreover, the

mix design of D series includes mixtures without fiber and 4%, 8% and 12% RHA ce-

ment replacement. The amounts of gravel, sand and water were constant in each of

the four mix designs. So that 7 wt.% natural sand was used as coarse aggregate

replacement. The parameterVfin Tables 47represents the percentage of fiber vol-ume to concrete volume.

Considering the mix designs in the given tables, specific surface area of RHA is

significantly greater than the cement. Therefore the concrete performance is re-

duced drastically and more water is needed to fix it. Because the concrete perfor-

mance should not be changed, the amount of superplasticizer is increased.

Habeeb et al. [34] produced ashes with fineness of 27.4 m2/g, 29.1m2/g and

30.4 m2/g by grinding ashes at intervals of 180, 270 and 360 min, respectively.

The results of their study showed that the finer the ash particles, the more superp-

lasticizer is needed to achieve the same slumps. Since in this study more than 10%

of RHA in concrete, has made the slump toolow even with heavy use of superplast-

icizer, it seems that the most desirable amount of RHA is 10% which requires a rea-

sonable amount of plasticizer. It should be noted that the RHA is a waste material

but too much superplasticizer is needed to achieve the desired slump, economically

justifiable. Also, high percentages of RHA reduce the concrete strength and slump.

3. Analysis of results

3.1. Effect of fiber type on mechanical properties

3.1.1. Compressive strength

Fig. 4shows the effect of fiber type (glass, steel and PPS) with-

out RHA on the compressive strength of pervious concrete in accor-

dance with the results of series A, B and C, respectively. In w/cratio

of 0.27, compressive strength, compared to the control concrete

(without fibers), increases by 32%, 24% and 28% for glass, steel

and PPS fibers, respectively. In the w/c ratio of 0.33, with glass,

steel and PPS fibers the compressive strength is increased by

46%, 40% and 50% compared to the control concrete (without fi-

bers), respectively. Moreover in w/c ratio of 0.4 the compressive

strength increases by 36%, 26% and 30% when glass, steel andPPS fibers are used, respectively. It is clear that when the vertical

compressive force is exerted to the concrete element, the specimen

inclines to show lateral strain increase. Due to high flexibility and

length of PPS fibers and also their proper placement and distribu-

tion in the concrete mixture which makes better interlocking be-

tween the fiber and the paste, the lateral strain is delayed and

consequently the compressive strength increases. It should be

Fig. 3. The constructed device for permeability test.

Table 4

Mixes with w/cratio of 0.27 (Series A).

Component RHA

0 2 4 6 8 10 12

PPS fiberVf= 0.3% Cement (kg) 340 333.2 326.4 319.6 312.8 306 299.2RHA (kg) 0 6.8 13.6 20.4 27.2 34 40.8

Gravel (kg) 1395 1395 1395 1395 1395 1395 1395

Sand (kg) 105 105 105 105 105 105 105

Water (kg) 93 93 93 93 93 93 93

SP (kg) 0 1.8 2.3 2.7 3.1 3.5 4

Steel fiberVf= 0.5% Cement (kg) 340 333.2 326.4 319.6 312.8 306 299.2

RHA (kg) 0 6.8 13.6 20.4 27.2 34 40.8

Gravel (kg) 1395 1395 1395 1395 1395 1395 1395

Sand (kg) 105 105 105 105 105 105 105

Water (kg) 93 93 93 93 93 93 93

SP (kg) 0 1.8 2.3 2.7 3.1 3.5 4

Glass fiberVf= 0.2% Cement (kg) 340 333.2 326.4 319.6 312.8 306 299.2

RHA (kg) 0 6.8 13.6 20.4 27.2 34 40.8

Gravel (kg) 1395 1395 1395 1395 1395 1395 1395

Sand (kg) 105 105 105 105 105 105 105

Water (kg) 93 93 93 93 93 93 93

SP (kg) 0 1.8 2.3 2.7 3.1 3.5 4

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noted that because of high flexibility and length of PPS fibers and

also their proper placement, the pull strength is also increased as

well as the compressive strength.

3.1.2. Tensile strength

Fig. 5 shows the effect of fiber type (glass, steel and PPS)

without RHA on the tensile strength of pervious concrete in

accordance with the results of series A, B and C, respectively. Asshown in the figure, tensile strength is increased by increasing

the amount of fibers, similar to the compressive strength trend at

presence of fibers. In the w/cratio of 0.27, tensile strength, com-

pared to the control concrete (without fibers), increases 31%, 27%and 28% when glass, steel and PPS fibers are used, respectively.

Table 5

Mixes with w/cratio of 0.33 (Series B).

Component RHA

0 2 4 6 8 10 12

PPS fiberVf= 0.3% Cement (kg) 340 333.2 326.4 319.6 312.8 306 299.2

RHA (kg) 0 6.8 13.6 20.4 27.2 34 40.8

Gravel (kg) 1395 1395 1395 1395 1395 1395 1395

Sand (kg) 105 105 105 105 105 105 105

Water (kg) 112 112 112 112 112 112 112

SP (kg) 0 1.8 2.3 2.7 3.1 3.5 4


RHA (kg) 0 6.8 13.6 20.4 27.2 34 40.8

Gravel (kg) 1395 1395 1395 1395 1395 1395 1395

Sand (kg) 105 105 105 105 105 105 105

Water (kg) 112 112 112 112 112 112 112

SP (kg) 0 1.8 2.3 2.7 3.1 3.5 4


RHA (kg) 0 6.8 13.6 20.4 27.2 34 40.8

Gravel (kg) 1395 1395 1395 1395 1395 1395 1395

Sand (kg) 105 105 105 105 105 105 105

Water (kg) 112 112 112 112 112 112 112

SP (kg) 0 1.8 2.3 2.7 3.1 3.5 4

Table 6

Mixes with w/cratio of 0.40 (Series C).

Component RHA

0 2 4 6 8 10 12

PPS fiberVf= 0.3% Cement (kg) 340 333.2 326.4 319.6 312.8 306 299.2

RHA (kg) 0 6.8 13.6 20.4 27.2 34 40.8

Gravel (kg) 1395 1395 1395 1395 1395 1395 1395

Sand (kg) 105 105 105 105 105 105 105

Water (kg) 135 135 135 135 135 135 135

SP (kg) 0 1.8 2.3 2.7 3.1 3.5 4


RHA (kg) 0 6.8 13.6 20.4 27.2 34 40.8

Gravel (kg) 1395 1395 1395 1395 1395 1395 1395

Sand (kg) 105 105 105 105 105 105 105

Water (kg) 135 135 135 135 135 135 135SP (kg) 0 1.8 2.3 2.7 3.1 3.5 4


RHA (kg) 0 6.8 13.6 20.4 27.2 34 40.8

Gravel (kg) 1395 1395 1395 1395 1395 1395 1395

Sand (kg) 105 105 105 105 105 105 105

Water (kg) 135 135 135 135 135 135 135

SP (kg) 0 1.8 2.3 2.7 3.1 3.5 4

Table 7

Mixes containing RHA (Series D).

Component RHA

0 4 8 12

FiberVf(%) = 0 % Cement (kg) 340 326.4 312.8 299.2RHA (kg) 0 13.6 27.2 40.8

Gravel (kg) 1395 1395 1395 1395

Sand (kg) 105 105 105 105

Water (kg) 93 93 93 93

SP (kg) 0 2.2 2.8 3.5

CompressiveStren

gth(MPa)

Control PPS Fiber Steel Fiber Glass Fiber

Fig. 4. Bar chartcompressive strength of pervious concrete containing fibers (Series

A, B and C).


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Also inw/cratio of 0.33, with glass, steel and PPS fibers the tensile

strength is increased 28%, 33% and 37%, compared to the control

concrete (without fibers), respectively. Moreover in w/c ratio of0.4, the tensile strength increases 19%, 30% and 31% when glass,

steel and PPS fibers are used, respectively. As a conclusion, the ef-

fect of PPS fibers is much better than the glass and steel fibers be-

cause the PPS fibers have more interlock in the matrix of cement

due to their suitable flexibility and appropriate placement within

the concrete. Therefore the resultant tensile strength is higher

compared to the concrete containing glass and steel fibers.

3.1.3. Flexural strength

Fig. 6shows the effect of fiber type (glass, steel and PPS) with-

out RHA on the flexural strength of pervious concrete in accor-

dance with the results of series A, B and C, respectively. As

shown in the figure, flexural strength is increased by increasingthe amount of fibers, similar to the tensile and compressive

strengths trends at presence of fibers. In the w/cratio of 0.27, flex-

ural strength, compared to the control concrete (without fibers),

increases by 24%, 22% and 21% when glass, steel and PPS fibers

are used, respectively. Also in w/cratio of 0.33, with glass, steel

and PPS fibers the flexural strength is increased by 17%, 19% and

21%, compared to the specimen control concrete (without fibers),

respectively. Moreover inw/cratio of 0.4, the flexural strength in-

creases by 7%, 13% and 17% when glass, steel and PPS fibers are

used, respectively. As a conclusion, the effect of PPS fibers is much

better than the glass and steel fibers because the PPS fibers have

more interlocking in the matrix of cement due to their suitable

flexibility and appropriate placement within the concrete.

Therefore the resultant flexural strength is higher compared tothe concrete containing glass and steel fibers.

3.2. Effect of RHA on compressive strength

In terms of microstructure, concrete is composed of three

phases: aggregate, cement and transition zone. Although most of

the concrete is aggregate and cement phase, the transition zone

is more effective on the mechanical properties of concrete in spite

of its smaller proportion than the two other phases and thus plays

a critical role in the concrete structure [35,36]. In pervious concrete

without admixtures, concrete failure generally occurs on the sur-

face of the hardened paste or the transition zone between the

aggregates and the paste [37]. Pozzolanic properties of rice husk,

as well as its role as a chemical filler improves the physical struc-

ture of the cement and makes the cement paste denser. The RHA as

a pozzolan reacts with calcium hydroxide in the hydration process

and improves aggregate-paste connectivity and hence reduces

transition zone thickness between aggregate and cement paste.

This causes the failure occurs in the through aggregate which is in-

tended because this phase has definitely higher strength than the

transition zone and improves the mechanical properties of the con-

crete including compressive, tensile and flexural strengths. The ef-

fect of RHA on the concrete compressive strength is shown in Fig. 7

based on the results of concrete containing RHA (series D). As ob-

served, the compressive strength of concrete containing RHA is 29%

more than control concrete and a RHA of 8% was considered as

optimum.

3.3. Combined effect of fiber and RHA on the mechanical properties of

concrete

Due to the low pull strength of fibers in pervious concrete con-taining fiber (Series A, B, C), it appears that the total capacity of the

0

0.5

1

1.5

2

2.5

3

Tensile

Strength(MPa)

w/c=0.27 w/c=0.33 w/c=0.40


Fig. 5. Bar chart tensile strength of pervious concrete containing fibers (Series A, B

and C).

0

0.5

1

1.5

2

2.5

3

3.5

FlexuralStrengt

h(MPa)

w/c=0.27 w/c=0.33 w/c=0.40


Fig. 6. Bar chart flexural strength of pervious concrete containing fibers (Series A, B

and C).

10

12

14

16

18

0 2 4 6 8 10 12CompressiveStrength(MPa)

Rice husk ash (%)

Mix containing RHA

Fig. 7. The compressive strength of concrete containing RHA without fibers (Series

D).

10

15

20

25

30


Rice Husk Ash (%)

Mix With Glass Fiber Mix With Steel Fiber

Mix With PPS Fiber

Fig. 8. The compressive strength of concrete containing RHA and fibers inw/cratio

0.27 (Series A).

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fiber is not used. However, due to the low value of fine aggregate,

cement matrix of pervious concrete is poor. Thus the interlocking

between fibers and concrete components should be improved

through strengthening the cement paste. However, it should be ta-

ken into account that the volume of the cement paste cannot be in-

creased since this would affect the permeability of the concrete

which contradicts the nature of pervious concrete. Thus, a propor-

tion of the existing cement can be removed and the same amount

of RHA can be substituted so that pozzolanic property of RHA is

utilized. RHA has a high pozzolanic activity and is commonly used

as pozzolanic materials in concrete.

Increase in the strength and durability of concrete contain-ing RHA is due to strengthened the transition zone, void structure

reformation, blocking large voids in the hydrated cement paste be-

cause of pozzolanic reaction. Another important pozzolanic mate-

rial is silica. Improvement of the mechanical properties and

reduction of the permeability of concrete containing micro-silica

is due to the reduction of the thickness of the transition zone be-

tween aggregate and cement paste [38]. Hence, because fine mi-

cro-silica is extremely fine and has high pozzolanic reactivity,

this material decreases the permeability of concrete and reduces

the amount of calcium hydroxide. Since micro-silica is finer than

RHA, it reduces the porosity of the transition zone and further im-

proves the mechanical properties of the concrete compared to RHA[39].

10

15

20

25

30

0 2 4 6 8 10 12Compressive

Strength(MPa)

Rice Husk Ash (%)


Mix With PPS Fiber

Fig. 9. The compressive strength of concrete containing RHA and fibers inw/cratio

0.33 (Series B).

10

15

20

25

30


Rice Husk Ash (%)


Mix With PPS Fiber

Fig. 10. The compressive strength of concrete containing RHA and fibers in w/c

ratio 0.40 (Series C).

2

2.4

2.8

3.2

3.6

0 2 4 6 8 10 12

TensileStrength(MPa)

Rice Husk Ash (%)


Mix With PPS Fiber

Fig. 11. The tensile strength of concrete containing RHA and fibers in w/cratio0.27

(Series A).

2

2.4

2.8

3.2

3.6

0 2 4 6 8 10 12

TensileStre

ngth(MPa)

Rice Husk Ash (%)


Mix With PPS Fiber

Fig. 12. The tensile strength of concrete containing RHA and fibers in w/cratio 0.33

(Series B).

2

2.4

2.8

3.2

3.6

0 2 4 6 8 10 12

TensileStrength(MPa

)

Rice Husk Ash (%)


Mix With PPS Fiber

Fig. 13. The tensile strength of concrete containing RHA and fibers in w/cratio 0.40

(Series C).

1

2

3

4

5

0 2 4 6 8 10 12

FlexuralStrength(MPa)

Rice Husk Ash (%)


Mix With PPS Fiber

Fig. 14. The flexural strength of concrete containing RHA and fibers in w/cratio

0.27 (Series A).


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Nielsen [40] using the X-ray analysis technique reported that

RHA replacement to the cement causes reduction in the relative

concentration of calcium hydroxide in the transition zone.

The properties of rice husk can be studied from two aspects,

chemically and physically, both of which improve the mechanical

properties of concrete. The most important feature of RHA thatcauses pozzolanic reaction to occur is its amorphous material. Pro-

duction of RHA can lead to the formation of about 8595% amor-

phous silica[41]. In the cement hydration process, large amounts

of calcium hydroxide crystals are formed. These crystals that are

hexagonal and are mainly formed at the transition zone between

the aggregates and cement paste have been crucial in the concrete

permeability. The term Chemical property of the RHA means that

due to its large specific surface area, it is highly reactive. It can re-

act to with calcium crystals hydroxide quickly and produce CSH

gel. Therefore, the dimensions and quantity of calcium hydroxide

crystals are reduced and instead CSH gel fills voids on the con-

tact surface of cement paste with aggregates making it denser.

The physical effects of RHA include improvement of interlock-

ing between solid materials and filling the space between cementparticles. In other words, minute RHA particles are finer than

cement particles and fill the space between them. So, all these pro-

cesses will strengthen the microstructure and result in a denser ce-ment paste.

1

2

3

4

5

6

0 2 4 6 8 10 12FlexuralS

trength(MPa)

Rice Husk Ash (%)


Mix With PPS Fiber

Fig. 15. The flexural strength of concrete containing RHA and fibers in w/c ratio

0.33 (Series B).

1

2

3

4

5

0 2 4 6 8 10 12

FlexuralStrength(M

Pa)

Rice Husk Ash (%)


Mix With PPS Fiber

Fig. 16. The flexural strength of concretecontainingRHA andfibers inw/cratio0.40

(Series C).

Table 8Percentage of compressive strength increase for optimum RHA amount compared to

control concrete.

w/c PPS fiber Steel fiber Glass fiber

0.27 47 43 41

0.33 36 37 34

0.4 41 37 30

Table 9

Percentage of tensile strength increase for optimum RHA amount compared to control

concrete.


0.27 37 41 30

0.33 28 30 31

0.4 32 33 38

Table 10

Percentage of flexural strength increase for optimum RHA amount compared to

control concrete.


0.27 59 54 48

0.33 69 63 64

0.4 53 57 63

0

5

10

15

20

25

30

CompressiveStrength

(MPa)

Rice Husk Ash (%)

Glass Fiber

W/C=0.27 W/C=0.33 W/C=0.4

0 108642 12

0

5

10

15

20

25

30

CompressiveStrength

(MPa)

Rice Husk Ash (%)

Steel Fiber

W/C=0.27 W/C=0.33 W/C=0.4

0 108642 12

0

5

10

15

20

25

30

35

CompressiveStrength(MPa)

Rice Husk Ash (%)

PPS Fiber

W/C=0.27 W/C=0.33 W/C=0.4

0 108642 12

Fig. 17. The compressive strength of concrete containing RHA and fibers with

differentw/cratios.

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3.3.1. Compressive strength

The results of the compressive strength test are shown in

Figs. 810. As it can be seen, the compressive strength increased

with increasing the amount of RHA, but using more of them re-

duces the strength. Therefore, the range of 810% of RHA can be

considered as the optimal value and leads to significant improve-

ment in strength. As it can be seen in Table 8, the compressive

strength values increase 3041% for glass fiber, 3743% for the

steel fibers and 4147% for the PPS fibers. It should be noted that

due to reduction of porosity, the amount of calcium hydroxideand the thickness of the transition zone between aggregate and ce-

ment paste, and also increase of RHA up to optimum value (810%)

the compressive strength increases compared to the control con-

crete (concrete containing fiber) and then decreases with the fur-

ther increase of RHA. This is because workability and lack of

required water.

3.3.2. Tensile strength

The results of the tensile test are shown by Figs. 1113. It can be

seen that, as it was detected for compressive strength trend, gener-

ally while the rate of cement replacement with RHA particles in-

creases, the tensile strength has an increasing trend at first, but

it decreases after a while. As it can be seen in Table 9,the tensile

strength values increase 3038% for glass fiber, 3041% for thesteel fibers and 2837% for the PPS fibers. It can be said that in-

crease of RHA strengthens the cement paste. In other words, the

used fibers have better performance in the presence of RHA than

when the concrete exclude RHA particles. Other reasons why ten-

sile strength is increased is the small size of RHA particles and their

filling effect. Habeeb et al. [34] reported that the finer the RHA par-

ticles, the more the tensile strength is improved.

3.3.3. Flexural strength

The results of the flexural test are shown in Figs. 1416. As ob-

served, generally while the rate of cement replacement with RHA

particles increases, the flexural strength has an increasing trend

at first, but it decreases after a while. The increase in flexural

strength could be due to the improvement of the bond betweenthe cement matrix and aggregate in the presence of RHA. As it

can be seen inTable 10, the flexural strength values increase 48

63% for glass fiber, 5463% for the steel fibers and 5369%

for the PPS fibers. Gemma [25] reported that the use of RHA

results in significant improvement in the flexural strength of

concrete.From the above results, it can be seen that, as previously men-

tioned, the optimum percentage of RHA in series D (without fibers)

is 8% while the optimum percentage of RHA in specimens contain-

ing fiber series (A, B and C) is between 8% and 10%. The difference

of RHA amount between two types of specimens is negligible. This

means that the addition of fibers to concrete containing RHA does

not affect the optimal amount considerably. It also can be seen that

the curve slope, for all w/c ratios, before the optimum of RHA is

steeper than the slope after the optimum RHA amount. In fact,

using 12% of RHA slightly decreases the compressive, tensile and

flexural strengths, compared to the 10% RHA, while considerably

increasing the permeability which is economic and practical. As

it is obvious, combination of fiber and RHA increases the compres-

sive strength in comparison with concrete containing RHA andwithout fibers (series D).

Table 11

Porosity and permeability percentage in different w/cratios.

w/c Fiber PPS Steel Glass

RHA Porosity

(%)

Perme-

ability

(cm/s)

Porosity

(%)

Perme-

ability

(cm/s)

Porosity

(%)

Perme-

ability

(cm/s)

0.27 0 23.2 0.25 23.3 0.25 22.9 0.24

2 20.5 0.202 20.2 0.22 19 0.22

4 19.5 0.18 17.5 0.186 18 0.19

6 18.2 0.165 15 0.16 16 0.17

8 16.6 0.14 12.5 0.12 13.5 0.145

10 14.8 0.108 21.1 0.23 20.5 0.2

12 23.7 0.26 27 0.28 24 0.25

0.33 0 21.5 0.21 22 0.21 19 0.19

2 19.4 0.18 20 0.19 19.5 0.16

4 18 0.19 17.5 0.17 16 0.13

6 17.5 0.15 15 0.14 14 0.14

8 15.5 0.12 12.5 0.12 11 0.1

10 12 0.095 10 0.09 9 0.08

12 19 0.21 20 0.23 21 0.24

0.4 0 28 0.45 26 0.41 29 0.48

2 25 0.41 23 0.37 25 0.45

4 22 0.38 21 0.33 22 0.39

6 20 0.35 20 0.3 21 0.33

8 18 0.3 16 0.26 17 0.3710 14 0.36 13 0.21 25 0.39

12 24 0.38 21 0.32 29 0.47

0

0.05

0.1

0.15

0.2

0.25

0.3

Per

meability(cm/s)

Rice Husk Ash (%)

w/c=0.27 (Series A)

Mix With PPS Fiber Mix With Steel Fiber

Mix With Glass Fiber

0 108642 12

0

0.05

0.1

0.15

0.2

0.25

0.3

Permeability(cm/s)

Rice Husk Ash (%)

w/c=0.33 (Series B)

Mix With PPS Fiber Mix With Steel Fiber Mix With Glass Fiber

0 108642 12

0

0.1

0.2

0.3

0.4

0.5

0.6

Permeability(cm/s)

Rice Husk Ash (%)

w/c=0.4 (Series C)


0 108642 12

Fig. 18. Permeability of pervious concrete containing RHA and fibers with different

w/cratios (Series A, B and C).


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3.4. Effect of water to cement ratio

In order to evaluate the effect of the w/c ratio on the

mechanical properties of fibers and concrete containing RHA, a

bar graph for compressive strength is depicted in Fig. 17. As

can be seen the specimens with w/cratios of 0.27 and 0.40 have

lower strengths compared to a w/c ratio of 0.33. It may be con-

cluded that, for thew

/c

ratio of 0.27 the failure has occurred on

cement paste that is due to insufficient water content to operate

the hydration. The w/c ratio of 0.33 leads to increased workabil-

ity of the mixture which causes full hydration of the cement

paste and consequently generates stronger mixes. In the w/c ra-

tio of 0.4, there is high-water content in the cement paste that

causes the formation of small pores in the cement paste and

thus the compressive strength will be reduced. According to

the tests carried out by Lian and Zhuge [37] on the pervious

concrete, increasing the w/c ratio to a value of 0.34 increases

the compressive strength and then further increase of the w/c

ratio will decrease the compressive strength.

3.5. Porosity and permeability test results

The results of the porosity and permeability tests with the w/c

ratios of 0.27, 0.33 and 0.4 are shown in Table 11. As it can be seen,

the permeability is roughly 0.080.48 cm/s and porosity is in the

range of 929%, which are high enough and can be used as a drain-

age layer in pavement. As shown in Fig. 18 for the permeability and

Fig. 19for porosity with differentw

/c

ratios, fiber does not have

considerable effect on the permeability while using RHA leads to

rapid decrease in porosity and the permeability. However, porosity

and permeability decrease when RHA is increased to 810%, and

then it increases for more RHA contents. This is opposite to the

compressive strength trend where it increases when RHA increases

to 810% and then decreases. As it is clear, the permeability and

porosity have a direct relationship with each other [42]in which

the permeability coefficient increases when porosity is increased.

As previously mentioned, the thickness of the transition zone de-

creases with increasing RHA and so the porosity and permeability

will be reduced to the optimization point and after that compres-

sive and tensile strengths are reduced while porosity and perme-

ability are increased as shown in Fig. 18. As shown inFig. 18, the

permeability, in the w/c ratio of 0.27, is more than that of 0.33

but far less than the case related to the w/cratio of 0.40.

0

5

10

15

20

25

30

Porosity(%)

w/c=0.27 (Series A)Mix With PPS Fiber Mix With Steel Fiber

Mix With Glass Fiber

0

5

10

15

20

25

Porosity(%)

Rice Husk Ash (%)

w/c=0.33 (Series B)


Rice Husk Ash (%)

0

5

10

15

20

25

30

35

Porosity(%)

Rice Husk Ash (%)

w/c=0.4 (Series C)


Fig. 19. Porosity pervious concrete containing RHA and fibers with different w/cratios (Series A, B and C).

2

2.2

2.4

2.6

2.8

3

3.2

3.4

15 17 19 21 23 25TensileStrength(MPa)

Compressive Strength (MPa)

w/c=0.27 (Series A)

PPS Fiber Steel Fiber Glass Fiber

2

2.2

2.4

2.6

2.8

3

3.2

3.4

3.6

20 22 24 26 28 30



w/c=0.33 (Series B)


2

2.2

2.4

2.6

2.8

3

3.2

3.4

15 17 19 21 23 25



w/c=0.4 (Series C)


Fig. 20. Relationship between tensile strength and compressive strength indifferentw/cratios (Series A, B and C).

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As previously mentioned, RHA reacts with calcium hydroxide in

the hydrationprocess and the amount of RHA is reduced, leading to

the production of the CSH gel. Thus porosity and permeability

increase and the compressive strength decreases with the increase

of RHA. Although, using a further amount of RHA causes reduction

in the compressive strength. From this stage on, the RHA had a

negative effect on the hydration of cement and results in an in-

crease of porosity in the cement paste and consequently increases

concrete porosity and permeability. This is because high specific

surface area of RHA and lack of required water absorption by

RHA particles cause the compressive strength to reduce and conse-

quently increase the permeability and porosity.

3.6. Relations between mechanical properties

Figs. 2022 show the relationship between the physical and

mechanical properties of the specimens containing glass fiber, steel

fiber, PPS fiber and RHA with w/cratios of 0.27, 0.33 and 0.4. These

relationships are similar to normal concrete[43].

Fig. 20 shows the relationship between compressive and tensile

strengths of pervious concrete. As it is obvious, by increasing com-

pressive strength, the tensile strength also increases and the rela-tionship between them is almost linear. As it can be seen, curve

slopes of the specimens containing PPS is more than that of steel

and glass fibers. Fig. 21shows the relationship between the void

content and permeability of pervious concrete. It can be concluded

that the permeability of the pervious concrete is related linearly

with the amount of air. As it is apparent, permeability of concrete

increases with increasing the amount of air and this trend contin-

ues until the optimum value is reached and then the amount of airincreases and compressive strength is reduced. One of the chal-

lenges of using pervious concrete is to achieve an acceptable bal-

ance between the permeability and high compressive strength.

As is clear from Fig. 22, increasing the amount of RHA decreases

the amount of air while increasing compressive strength. That is

because when RHA is mixed with concrete, the compressive

strength increases due to chemical reactions and after the opti-

mum point the compressive strength is reduced while porosity is

increased.

4. Conclusion

In this study the results of the experimental tests to investigate

the physical and mechanical properties of pervious concrete con-taining fibers and RHA is as follows:

0.05

0.1

0.15

0.2

0.25

0.3

0.35

10 15 20 25 30

Permeability(cm/s)

Void Content (%)

w/c=0.27 (Series A)

PPS Fiber Steel fiber Glass Fiber

0.05

0.1

0.15

0.2

0.25

10 12 14 16 18 20 22 24

Permeability(cm/s)

Void Content (%)

w/c=0.33 (Series B)


0.05

0.15

0.25

0.35

0.45

0.55

10 15 20 25 30

Permeability(cm/s)

Void Content (%)

w/c=0.4 (Series C)


Fig. 21. Relationship between void content and permeability in differentw/cratios

(Series A, B and C).

10

12

14

1618

20

22

24

26

28

10 15 20 25 30Compressive

Strength(MPa)

Void Content (%)

w/c=0.27 (Series A)


10

15

20

25

30

35

8 13 18 23Compressive

Strength(MPa)

Void Content (%)

w/c=0.33 (Series B)


10

1214

16

18

20

22

24

26

10 15 20 25 30

CompressiveStrength(MPa)

Void Content (%)

w/c=0.4 (Series C)


Fig. 22. Relationship between compressive strength and the void content in

differentw/cratios (Series A, B and C).


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1. The optimum percentage of RHA in the specimens without

fibers (series D) is 8% while it is between 8% and 10% in the

specimens with fiber series (A, B and C). This indicates that

the addition of fibers to the concrete containing RHA does not

considerably affect the optimal amount.

2. The compressive, tensile and flexural strengths in concrete with

12% of RHA were found to be slightly lower than those of 10% of

RHA, as the optimum RHA amount, while its permeability is

considerably higher than that of 10% of RHA. Hence, it seems

that 12% of RHA can be more suitable for concrete pavements.

3. The mechanical properties including the compressive, tensile

and flexural strengths were found to be the maximum for w/c

ratio of 0.33.

4. For 810% replacement of RHA andw/cratio of 0.33, the com-

pressive strength of pervious concrete containing fibers and

RHA increases by 34%, 37% and 36% for glass, steel and PPS

fibers, respectively. Also, for the above-mentioned mix design,

the tensile strength increases by 31%, 30% and 28% for glass,

steel and PPS fibers, respectively. Finally, the flexural strength

undergoes a 64%, 63% and 69% increase when glass, steel and

PPS fibers are used, respectively.

5. In three w/c ratios of 0.27, 0.33 and 0.4, a similar trend was

observed for the compressive, tensile and flexural strengths of

concrete containing both RHA and fiber but the range of opti-

mum percentage of RHA was different. Moreover for all cases,

the compressive, tensile and flexural strengths rises at a rapid

slope before the optimum percentage and drops gradually after-

wards. The same trend is detected when for concretes with

fibers and without RHA.

6. The pervious concrete permeability was obtained to be between

0.08 cm/s and 0.48 cm/s, and the porosity is in the range of 9%

and 29%, which are appropriate for a drainage layer of pave-

ment to be used.

7. The compressive strength of the pervious concrete increases

linearly with the increase of the tensile strength.

8. The permeability of concrete decreases with the increase of

RHA amount until the optimum RHA amount is reached. Afterit, the permeability increases and the strengths are reduced.

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