Construction and Building Materials 30 (2012) 366–371

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Construction and Building Materials

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Pervious high-calcium fly ash geopolymer concrete

Tawatchai Tho-in a, Vanchai Sata a,⇑, Prinya Chindaprasirt a, Chai Jaturapitakkul b

a Sustainable Infrastructure Research and Development Center, Dept. of Civil Engineering, Khon Kaen University, Khon Kaen 40002, Thailandb Dept. of Civil Engineering, King Mongkut’s University of Technology Thonburi, Bangkok 10140, Thailand

a r t i c l e i n f o

Article history:Received 13 July 2011Received in revised form 25 November 2011Accepted 4 December 2011Available online 30 December 2011

Keywords:Geopolymer binderPervious concreteFly ashCompressive strengthWater permeability

0950-0618/$ - see front matter � 2011 Elsevier Ltd. Adoi:10.1016/j.conbuildmat.2011.12.028

⇑ Corresponding author. Tel.: +66 4320 2846 127; fE-mail address: vancsa@kku.ac.th (V. Sata).

a b s t r a c t

This study evaluates the properties of pervious concrete made of high-calcium fly ash geopolymer binder.Pervious geopolymer concretes (PGCs) were prepared from lignite fly ash (FA), sodium silicate (NS),sodium hydroxide (NH) solution, and coarse aggregate. The FA to coarse aggregate ratio of 1:8 by weight,constant NS/NH ratio of 0.50, alkaline liquid/FA (L/A) ratios of 0.35, 0.40, and 0.45, and NH concentrationsof 10, 15, and 20 M were the PGC mix proportions. The curing temperature of 60 �C for 48 h was used toactivate the geopolymerization. The results showed that the high-calcium fly ash geopolymer bindercould be used to produce pervious concrete with satisfactory mechanical properties. The relationshipsof the density-void content, compressive strength-density, and compressive strength-void content ofthe PGCs were derived and found to be similar to those of conventional pervious concrete.

� 2011 Elsevier Ltd. All rights reserved.

1. Introduction

In the last decade, geopolymer binders have emerged as one ofthe possible alternatives to cement binders for applications in con-crete industry. Geopolymers can be produced by polymerization ofalumino-silicate oxides with alkali polysilicates yielding Si–O–Albonds [1]. The two main ingredients of geopolymer binder are al-kali liquids and source materials. The alkali liquids are usually so-dium or potassium based solutions. The source materials should berich in silicon (Si) and aluminum (Al) from geological origin orby-product materials such as clays, metakaolin, fly ash, bottomash, slag, and rice husk ash. The use of geopolymer involves a lesseramount of green house gas and is, therefore, a more environmen-tal-friendly binding material compared to the conventionalPortland cement [2]. In addition, geopolymers possess manyexcellent properties such as high early strength, excellent mechan-ical properties, low creep and shrinkage, and good resistance inacid and sulfate attacks [3–7].

Pervious concrete, also known as porous concrete or water-permeable concrete is a special concrete which contains a highvoid content to allow air or water to move through the concrete.Typically, pervious concrete has the connected pores ranging insize from 2 to 8 mm, void content between 18% and 35%, and com-pressive strengths between 2.8 and 28.0 MPa [8]. Pervious concretehas been in use for more than 30 years in many countries aroundthe world, especially in England and the United States [9]. It canbe used in the construction of park areas, areas with light traffic,

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ax: +66 4320 2846 102.

pedestrian walkways, tennis courts, greenhouse, and other civilengineering and architectural works [8–14]. Its high void contentmakes it possible for use in the other applications such as ther-mally insulating, acoustic absorption, concrete bed for vegetationor living organism, and water purification [15–19]. Therefore, per-vious concrete is environment friendly. The pervious concrete mix-ture is normally composed of binder material, coarse aggregate,little or no fine aggregates, water, and some admixture if needed.Generally, Portland cement is used as a binding material in pervi-ous concrete and there is still a lack of study on the use of otherbinding materials such as geopolymer binders in perviousconcrete.

Therefore, this study focuses on the use of a geopolymer binderfor making pervious concrete which comprises lignite fly ash, so-dium silicate and sodium hydroxide solution, and coarse aggregate.The physical and mechanical properties of the PGC were tested.The obtained data will undoubtedly be beneficial for the futureuse of fly ash geopolymer in the construction of pervious concretewhich will lead to the reduction of cement consumption and envi-ronmental problems.

2. Experimental details

2.1. Materials

Lignite fly ash (FA) was obtained from Mae Moh power station from LumpangProvince in Northern Thailand. Fig. 1 shows the scanning electron microscopy(SEM) and energy dispersive spectroscopy (EDS) of the FA. The particle shape ofFA was mainly spherical with the main chemical composition of 36.8% SiO2,15.2% Al2O3, 19.7% Fe2O3, and 19.4% CaO. A median particle size of FA was 50 lmwith a Blaine fineness of 2250 cm2/g, 45.0% retained on sieve no. 325 (45 lm)

Fig. 1. SEM/EDS micrograph of lignite fly ash particle.

T. Tho-in et al. / Construction and Building Materials 30 (2012) 366–371 367

and a specific gravity of 2.23. Sodium silicate solution (Na2SiO3, NS) with 15.32%Na2O, 32.87% SiO2 and 51.81% H2O, and sodium hydroxide (NaOH, NH) were usedas alkali activators. The single-size crushed limestone with 12.5–20.0 mm diameter,90% passing the No. 3/8’’ sieve, a fineness modulus of 7.1, and specific gravity of2.74 in saturated surface dry condition was used for making PGC.

2.2. Mix proportions, mixing, and casting

The FA to coarse aggregate ratio of 1.0–8.0 by weight, a constant NS/NH ratio of0.50, and the alkaline liquid/FA (L/A) ratio of 0.35, 0.40, and 0.45 were the mix pro-portions of PGC. In order to study the effects of NH concentration on the PGC prop-erties, three concentrations of NH viz., 10, 15, and 20 Molar (M) were used. The mixproportions are shown in Table 1. The symbol 40PGC10 stands for the PGC with theL/A ratio of 0.40 and NH concentration of 10 M.

The PGC mixing was done in a 25 �C controlled room. FA was mixed with NH for5 min in a pan-type mixer. Coarse aggregate was then incorporated and mixed for 4more minutes. This was followed by the addition of NS with a final mixing of 1 min.After being mixed, the PGC was placed in 100 mm in diameter and 200 mm inheight cylindrical molds and compacted by a vibrating table. The specimens werewrapped with a thin plastic sheet to minimize moisture loss and allowed to standfor 1 h at 25 �C. It was then cured at 60 �C for 48 h and stored in the controlled roomat 23 ± 2 �C and 50% RH until the testing age. Fig. 2 shows the typical PGC cylindricalspecimens.

2.3. Testing detail

2.3.1. Void content and water permeabilityThe void content and water permeability of PGC were tested using 100 mm in

diameter and 200 mm cylindrical specimens. The void content was determined inaccordance with the ASTM C 1688 [20] and calculated using Eq. (1). The reportedvoid contents were the average of three samples.

VT ¼ðT � DÞ100

Tð1Þ

T ¼ MS

VSð2Þ

where VT is the void content (%), T is the theoretical density of PGC computed on anair free basis (kg/m3), D is the density of PGC (kg/m3), MS is the total mass of allmaterial batched (kg), VS is the sum of absolute volumes of component ingredientsin the batch (m3).

Table 1Mix proportions of PGC.

Mix no. Mix proportion (kg/m3)

FA NS NH (10 M) NH (15 M) NH (20 M) Aggregate

35PGC10 221 25.5 51 – – 176835PGC15 221 25.5 – 51 – 176835PGC20 221 25.5 – – 51 176840PGC10 221 29.5 59 – – 176840PGC15 221 29.5 – 59 – 176840PGC20 221 29.5 – – 59 176845PGC10 221 33.0 66 – – 176845PGC15 221 33.0 – 66 – 176845PGC20 221 33.0 – – 66 1768

Note: NS/NH = 0.50.

After the void content test, the cylindrical specimens were placed in the PVCpipe and tightened by circular clamps. The water permeability of PGC was testedusing the constant head method [21,22] and the schematic diagram of the experi-mental test set-up is shown in Fig. 3. The permeability test was carried out when asteady state flow was reached. The coefficients of water permeability (k) were theaverage of three samples and calculated following Darcy’s law as shown in the fol-lowing equation:

k ¼ QLHAt

ð3Þ

where k is the coefficient of water permeability (cm/s), Q is the quantity of water col-lected (cm3) over time t (s), L is the length of specimen (cm), H is the water head(cm), A is the cross sectional area of specimen (cm2).

2.3.2. Compressive strength and splitting tensile strengthThe compressive strength [23] and splitting tensile strength [24] were tested at

the age of 7 days. Compression test cylinders were capped at both ends with a sul-fur capping compound. The reported strengths were the average of three results.

3. Results and discussion

3.1. Void content and water permeability

The results of the void contents and water permeability coeffi-cients of PGC are summarized in Table 2. The void contents of PGCwere relatively high between 28.7% and 34.4% which led to the highwater permeability coefficients between 1.92 and 5.96 cm/s. Gener-ally, the void content of Portland cement pervious concrete dependson the gradation of aggregate and the methods of compaction[25,26]. However, in this test, the gradation of aggregate and themethod of compaction were not varied. The results, however, indi-cated that the void content in this study slightly decreased withincreasing L/A. For instance, the void content of 35PGC20,40PGC20, and 45PGC20 concretes were 34.4%, 31.8%, and 29.9%,respectively. The adding of alkali liquid in the mixture increasedthe paste content and the excess paste filled the voids resulting ina relatively dense pervious concrete with low void content [27]. Atthe same L/A ratio, the void contents of the PGCs with different NHconcentrations but the same paste content were not very differentas shown in Fig. 4.

Fig. 5 shows the relationship between water permeability andL/A ratio at various NH concentrations for all PGCs. Similar to thatof void content, the water permeability tended to decrease whenthe L/A was increased. In addition, the significant increase in waterpermeability with increasing void content could be observed asshown in Fig. 6. The highest water permeability of 34.4% and high-est void content of 5.96 m/s were obtained with 35PGC20 concrete.There was a definite trend that the water permeability increasedwith the increase in the void content. However, the goodness offit of the relationship between void content and water permeabil-ity was not high due mainly to the narrow void content range

Fig. 2. PGC cylindrical specimens.

Fig. 3. Constant head water permeability test set-up.

Table 2Total void ratio and water permeability coefficient of PGC.

Mix Void content (%) Water permeability coefficient (cm/s)

35PGC10 30.5 2.2235PGC15 30.9 3.6135PGC20 34.4 5.9640PGC10 30.7 2.6640PGC15 28.8 2.9140PGC20 31.8 3.9645PGC10 28.7 3.6445PGC15 28.7 1.9245PGC20 29.9 2.39

20

25

30

35

40

45

Voi

d co

nten

t (%

)

0.35 0.40 0.45

L/A ratio

Fig. 4. Void contents of PGCs at various L/A ratios and NaOH concentrations.

0

2

4

6

8

10

0.450.400.35L/A ratio

Wat

er p

erm

eabi

lity

(cm

/s)

NaOH 10 MNaOH 15 MNaOH 20 M

Fig. 5. Water permeability of PGCs at various L/A ratios and NaOH concentrations.

368 T. Tho-in et al. / Construction and Building Materials 30 (2012) 366–371

(28.7–34.4%) resulted from the use of a single aggregate gradation.This was also related to the pore size distribution, pore roughness,and pore connectivity that affect the permeability of pervious con-crete in addition to the void content [25]. For normal Portland ce-ment pervious concrete, the permeability was found to increaseexponentially with the void content [9,28].

3.2. Compressive strength and splitting tensile strength

Table 3 summarizes the density, compressive strength, and split-ting tensile strength of PGCs. Because of the high void content, thedensities of PGC were quite low ranging from 1680 to 1820 kg/m3

which were nearly 30% lower than that of the conventional concrete(about 2400 kg/m3). The densities of these PGCs were, however,within the general densities of the normal Portland cement perviousconcretes which were between 1600 and 1900 kg/m3 [15,29,30].

The compressive strengths of PGCs were slightly lower thanthose of normal Portland cement pervious concretes [15,16,31].The relatively high strength Portland cement pervious concretewas obtained with the use of the high strength paste [26]. The highstrength geopolymer paste could also be obtained with the use offine fly ash [32]. In this study, the fly ash used was an as-receivedone and was rather coarse with the Blaine fineness of 2250 cm2/g.However, it was illustrated that the rather coarse high-calcium flyash geopolymer could be used to produce pervious concrete withacceptable compressive strengths between 5.4 and 11.4 MPa.

P = 0.0447e0.1388 (VT

)

R² = 0.53

0

1

2

3

4

5

6

7

8

20 25 30 35 40

Void content (%)

Wat

er p

erm

eabi

lity

(cm

/s)

Fig. 6. Relationship between water permeability and void content for all PGCs.

Table 3Density, compressive strength, and splitting tensile strength of PGC.

Mix Density(kg/m3)

Compressive strength(MPa)

Splitting tensile strength(MPa)

35PGC10 1780 8.5 1.035PGC15 1770 9.3 1.335PGC20 1680 5.4 0.740PGC10 1770 10.1 1.140PGC15 1820 9.9 1.340PGC20 1740 8.4 1.445PGC10 1810 10.2 1.145PGC15 1810 11.4 1.245PGC20 1780 9.6 1.2

T. Tho-in et al. / Construction and Building Materials 30 (2012) 366–371 369

As shown in Fig. 7, the compressive strength of PGC increasedslightly with an increase in the L/A ratio. At low L/A ratios of 0.35and 0.40, the PGCs contained low liquid and were difficult to com-pact. The PGCs with high void contents and low compressivestrengths were thus obtained. For example, the compressivestrengths of 5.4–9.3, 8.4–10.1, and 9.6–11.4 MPa were obtainedfor PGCs with L/A ratio of 0.35, 0.40, and 0.45, respectively. Thiswas consistent with Sathonsaowaphak et al. [33] work which re-ported the increase in compressive strength of lignite bottom ashgeopolymer mortar with the increase in L/A ratios from 0.325 to0.429. With regards to the NH concentration, the optimum NH con-centration to produce good strength PGC was 15 M. Increasing NHconcentration from 10 to 15 M increased the compressive strength.However, when the concentration of NH was 20 M, the compres-sive strength started to decline [34,35]. A maximum compressivestrength of 11.4 MPa was obtained with 45PGC15 concrete.

2.0

4.0

6.0

8.0

10.0

12.0

14.0

0.35 0.40 0.45

L/A ratio

Com

pres

sive

str

engt

h (M

Pa)

NaOH- 10 M

NaOH- 15 M

NaOH- 20 M

Fig. 7. Compressive strength and L/A ratios at various NaOH concentrations of PGC.

The splitting tensile strengths of PGCs as shown in Table 3 ran-ged from 0.7 to 1.4 MPa. The ratio of splitting tensile strength tocompressive strength ranged from 10.4% to 16.3% with the averageof 12.6%. These ratios were slightly higher than 10% for the conven-tional concrete and 9–14% for normal Portland cement perviousconcrete [36]. This was probably due to the stronger interfacialtransition zone between aggregate and geopolymer matrix com-pared to that of normal Portland cement matrix [37]. It should bepointed out that the increase in the tensile strength is beneficialto increase the service-life of the PCG products.

3.3. Relationship of density, void content, and compressive strength

The relationship between density and void content of PGCs isshown in Fig. 8. The density decreased linearly with an increasein the void content for all PGCs. For example, the density was1820 kg/m3 when the void content was 28.8%. While the void con-tent increased to 34.4%, the density reduced to 1680 kg/m3. A lin-ear relationship with high R2 of 0.98 could be derived as given inEq. (4). The results showed the same trend of relationship to thatof the normal Portland cement pervious concrete [27].

D ¼ 2481� 23:2ðVTÞ ð4Þ

where D is the density of PGC (kg/m3) and VT is the void content (%).Generally, the compressive strength of concrete is improved

when the density is increased. Similar to conventional concrete,the compressive strength of PGC was related to the density asshown in Fig. 9. Since the density is directly linked to the void inthe material, it is not surprising that the compressive strength ofPGC was linearly proportional to density. A relationship betweencompressive strength and density of PGC could be fitted in a linearline as shown in the following equation:

f 0C ¼ 0:035ðDÞ � 53:6 ð5Þ

where f 0C is the compressive strength of PGC (MPa) and D is the den-sity of PGC (%).

In addition, the relationship between compressive strength andvoid content could also be fitted using exponential curve as shownin Fig. 10 and Eq. (6). This equation is similar to the empiricalformulae of Portland cement pervious concretes which were re-ported by Chindaprasirt et al. [26,27] and Lian et al. [38].

f 0C ¼ 237:77e�0:107ðVT Þ ð6Þ

where f 0C is the compressive strength of PGC (MPa) and VT is the voidcontent of PGC (%).

This study

D = 2481-23.2(VT)

R2 = 0.98

Kevern et al. [29]

1500

1600

1700

1800

1900

2000

2100

20.0 25.0 30.0 35.0 40.0

Void content (%)

Den

sity

(kg

/m3 )

Fig. 8. Relationship between density and void content of PGC.

f c' = 0.035 (D) - 53.6

R2 = 0.81

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0

1500 1600 1700 1800 1900 2000

Density (kg/m3)

Com

pres

sive

str

engt

h (M

Pa)

Fig. 9. Relationship between compressive strength and density of PGC.

f c' = 237.77e-0.107(VT

)

R² = 0.84

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0

24.0 28.0 32.0 36.0 40.0

Void content (%)

Com

pres

sive

str

engt

h (M

Pa)

Fig. 10. Relationship between compressive strength and void ratio of PGC.

370 T. Tho-in et al. / Construction and Building Materials 30 (2012) 366–371

4. Conclusions

In order to expand the use of fly ash geopolymer binder, pervi-ous geopolymer concretes (GPCs) were prepared from alkali acti-vated lignite high-calcium fly ash binder and coarse aggregate.The void content, water permeability, compressive strength, andsplitting tensile strength of PGCs were determined. The compres-sive strengths between 5.4 and 11.4 MPa and splitting tensilestrengths between 0.7 and 1.4 MPa were obtained. The ratios ofsplitting tensile to compressive strength ranged from 10.4% to16.3% which were slightly higher than conventional concrete. Thehigh void contents at 28.7–30.4% led to the high water permeabil-ity coefficients between 1.92 and 5.96 cm/s. Because of the highvoid content, the densities of PGC were low between 1680 and1820 kg/m3 which were approximately 30% lower than that ofthe conventional concrete. In addition, the relationships of thedensity-void content, compressive strength-density, and compres-sive strength-void content of the PGCs were formulated and weresimilar to those of the conventional pervious concrete. It has there-fore been demonstrated that lignite high-calcium fly ash geopoly-mer binder could be used for fabricating pervious concrete withacceptable strength.

Acknowledgements

This work was supported by the Higher Education ResearchPromotion and National Research University Project of Thailand,Office of the Higher Education Commission, through the AdvancedFunctional Materials Cluster of Khon Kaen University. The authors

also would like to acknowledge the support of the Thailand Re-search Fund (TRF) under TRF Senior Research Scholar Grant No.RTA5380002.

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