Effect of zeolite and pumice powders on the environmental and physical characteristics of green concrete filters

Construction and Building Materials 240 (2020) 117931

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Effect of zeolite and pumice powders on the environmental and physical characteristics of green concrete filters Armin Azad a, Amir Saeedian a, Sayed-Farhad Mousavi a, Hojat Karami a,⇑, Saeed Farzin a, Vijay P. Singh b a b

Faculty of Civil Engineering, Semnan University, Semnan, Iran Department of Biological and Agricultural Engineering & Zachry Department of Civil Engineering, Texas A & M University, College Station, TX, USA

h i g h l i g h t s
Using zeolite enhances the filter ability in reducing pollution parameters of wastewater types.
Using pumice enhances the filter ability in reducing pollution parameters of wastewater types.
Using zeolite and pumice materials do not deteriorate the physical properties of porous concrete.

a r t i c l e

i n f o

Article history: Received 23 December 2018 Received in revised form 29 August 2019 Accepted 20 December 2019

Keywords: Water pollution Urban and industrial runoff Adsorbent Cementitious materials

a b s t r a c t Green porous concrete (GPC) is a porous concrete (PC) with minimum amount of cement. This study investigated the effects of zeolite and pumice, as cementitious materials, on the physical properties of PC and the enhancement of its ability to reduce urban and industrial runoff pollution. GPC specimens were prepared by replacing cement with zeolite and pumice in different portions (10–40%). Results indicated that pumice had a better physical performance but zeolite had a greater ability to enhance GPC performance in improving wastewater quality. Furthermore, zeolite and pumice reduced the apparent density of concrete up to 181 and 92 kg/m3, respectively. Also, GPC performed well in eliminating TSS and turbidity. The use of 40% zeolite improved the ability of PC to reduce chemical oxygen demand (COD), Zinc (Zn), Copper (Cu), Cadmium (Cd) and Lead (Pb) by 38.6, 99, 99, 99 and 99%, respectively. The reductions in these water quality parameters due to the addition of 40% pumice were 25.4, 98, 96, 99 and 99%, respectively. Ó 2019 Elsevier Ltd. All rights reserved.

1. Introduction Increasing temperature, decreasing precipitation, rising population, and growing demand for water are some of the reasons for over-exploitation of groundwater resources. Artificial recharge is a well-known method for recharge and retrieval of groundwater resources [1,2]. In this system, storm runoff, drainage water from agricultural fields, and urban and industrial runoffs are collected into stilling basins and returned to groundwater resources [3]. Meanwhile, urban storm-runoff has significant amounts of contaminants, such as microorganisms, total dissolved solids (TDS), total suspended solids (TSS), turbidity, COD, and salinity, due to the existence of organic and inorganic substances on the streets.

⇑ Corresponding author. E-mail addresses: [email protected] (A. Azad), Saeedian_amir@yahoo. com (A. Saeedian), [email protected] (S.-F. Mousavi), [email protected] (H. Karami), [email protected] (S. Farzin), [email protected] (V.P. Singh). https://doi.org/10.1016/j.conbuildmat.2019.117931 0950-0618/Ó 2019 Elsevier Ltd. All rights reserved.

Runoff may also contain heavy metals, such as Cd, Cu, Pb and Zn [4]. Porous concrete (PC) is an eco-friendly and cost-effective material for improving water and wastewater quality, which is applicable almost everywhere. This type of concrete has many applications, such as in the pavements of streets and sidewalks, as a substrate for patios and greenhouses, and for reducing flow during floods and improving road drainage. Furthermore, PC contributes to the recharge of groundwater resources [5]. This kind of concrete can be used for drainage of agricultural and industrial runoff, or as a filter in the recharge basins. In all of these cases, PC slightly improves the quality of drained runoff (qualitative behavior), in addition to rapid disposal of runoff and controlling floods. Some of the water quality parameters are trapped during the drainage of wastewater, thus, the quality of wastewater will be improved [6]. Despite the ability of PC to improve wastewater quality, in many cases, the level of water contamination is far from the standard level for disposal to groundwater resources [7]. Therefore,

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some new methods should be developed to enhance the ability of the PC system in reducing water pollution. Mineral adsorbents (additives) are inexpensive and easily available materials for this purpose. Many studies have been conducted to investigate the effectiveness of some minerals, such as zeolite, pumice, vermiculite, kaolin and dolomite in removing various harmful substances from wastewater [8–13]. In this respect, studies have also been conducted using mineral adsorbents as aggregates in PC. Abedi Koupai et al. (2016) added iron slag aggregate to PC, which increased its ability to improve the quality of urban storm-water runoff. In order to improve the ability to reduce total suspended solids (TSS) in water, a filter (sand column), 200 mm high, was used under concrete samples [6]. Saghaian Nejad et al. (2017) reported that addition of zeolite, as fine aggregate, improved the performance of PC in the pollution reduction of urban storm-water runoff [7]. Kim et al. (2017) indicated that the use of ash aggregates increased the ability of PC to reduce water pollution [14]. In this respect, Azad et al. (2018) examined the application of vermiculite and quartz as aggregate substitute in porous concrete. Their results showed that these adsorbents had a good effect on the performance of concrete to remove COD, TSS, and turbidity [15]. However, using PC and improving its ability to reduce water pollution with the abovementioned methods has several disadvantages, which should be considered in the future studies. Cement is known as a non-eco-friendly material due to the emission of CO2 (as one of the greenhouse gases) in its production process, which is harmful to the environment [16]. Furthermore, the cement slurry covers the surface of additives (such as zeolite, pumice, perlite, iron slag, etc.) during the mixing process of PC and eliminates a significant portion of its ability to improve water quality. On the other hand, using mineral additives as fine grains reduces the permeability and draining ability of PC [2]. Green porous concrete (GPC) refers to a type of porous concrete in which the portion of cement usage has been minimized. In this type of concrete, an attempt is made to minimize the dependence of concrete on cement, considering the physical properties of PC and using nonharmful and suitable cementitious materials. The GPC is thus an attempt to improve the environmental characteristics of PC. In recent years, some studies have been conducted on the use of some cementitious materials, as a substitute for cement, which have the ability to improve water quality. These studies aimed to select materials which increase the ability of PC to improve water quality, and simultaneously make minimal change in the physical properties of PC. Ong et al. (2016) improved the ability of PC to reduce urban storm-water runoff pollution by replacing limestone powder and fly ash for part of the cement [17]. López-Carrasquillo and Hwang (2017), Homles et al. (2017), and Shabalala et al. (2017) used fly ash and obtained positive effects on the ability of PC to remove heavy metals from water [18–20]. In recent years, numerous studies have been performed on the application of these minerals as cementitious materials for physical properties of various types of concrete [21,22]. Zeolite and pumice are eco-friendly and well-known substances in water purification [23,24]. Zeolite, which is primarily an aluminosilicate mineral, has an ability to improve the quality of water, especially to remove heavy metals, due to its high surface area, high superficial pores, and ion exchange capacity [25]. The properties of this material have led to the use of zeolite as a cement substitute in various types of concrete [26]. On the other hand, pumice has been used in many studies to improve water quality due to its porous structure [27]. It has also been used as a cementitious material in all kinds of concrete (except PC), because of its high surface area, low specific weight, and a substitute for cement in the concrete [28]. The main reason for using these minerals was to find a suitable cementitious material as a substitute for cement,

focusing on physical properties and reducing the harmful environmental impacts of cement. However, the impact of these cementitious materials on the physical and qualitative behavior of PC has not been investigated before. Based on the authors’ knowledge, less attention has been paid on the physical and environmental advantages of the two mentioned minerals if they are properly used. In this research, using the two cementitious materials (zeolite and pumice) in GPC was examined from three aspects: i) effect of using these materials as a substitute for cement in the concrete filter in order to improve runoff quality by reducing some parameters, such as COD, TSS, TDS, and turbidity; ii) potential of the mentioned materials in concrete to remove such heavy metals as Zn, Cu, Cd and Pb, from industrial runoff; and (iii) to study the effect of zeolite and pumice on physical properties of GPC. 2. Materials and methods In the present study, zeolite and pumice were used in the PC mixtures. Both zeolite and pumice were Iranian types, which were obtained from some mines in Semnan and East-Azerbaijan provinces, Iran, respectively. Tables 1 and 2 show the XRF and mineral components analysis, as well as their physical properties, respectively. Crushed gravel and Portland cement type 5 were used to prepare the PC. Selection of this type of cement is due to the possible use of GPC where there may be the danger of sulfate attacks. 2.1. Mixing proportions of PC Characteristics of PC mixtures are listed in Table 3. Initially, control specimens (without zeolite and pumice) were mixed on the basis of ACI 211 3R standards and previous studies [17,29,30]. The water-to-cement ratio (W/C) of these samples

Table 1 XRF analysis and some physical properties of cement, zeolite and pumice. Chemical parameter

Cement

Zeolite powder

Pumice powder

SiO2 Al2O3 Fe2O3 CaO MgO SO3 Na2O K2O Apparent density (kg/m3) Color

22.6 4.4 4.4 63.1 1.70 1.50 0.2 0.5 3300 Gray

0.69 0.10 0.049 0.035 0.005 0.005 0.0073 0.01 2215 Light-green-green-yellow

63.45 17.24 2.86 3.22 1.73 0.16 2.01 2.16 2380 White

Table 2 Mineral components of zeolite and pumice [[49], with permission]. Zeolite

%

Pumice

%

Clinoptilolite KNa2Ca2(Si29Al7)O7224H2O Cristobalite (Ca,Na)(Si,Al)4O8 Anorthite (Ca,Na2,K2)Al2Si10O24,7H2O Orthoclase KAlSi3O8

66

Albite (Na,Ca)(Si,Al)4O8 Amorphouse

25

6

Mordenite (Ca,Na2,K2)Al2Si10O24,7H2O Dolomite CaMg(CO3)2 Other minerals

4

Quartz SiO2 Hornblende Ca2(Fe.Mg)4Al(Si7Al) O22,(OH)2 Calcite CaCO3 Dolomite CaMg(CO3)2 Other minerals

14 7 5

2 1

55

8

4 1 2

was 0.35, and the amounts of cement and aggregates were 330 and 1400 kg=m3 , respectively. Subsequently, based on the volume of cement, samples were mixed by replacing zeolite and pumice in different portions (10, 20, 30 and 40%). Each mixture had 3 replications. The cubic PC specimens had dimensions of 150  150  150 mm in order to conduct compressive strength tests and dimensions of 100  100  100 mm in order to perform permeability, air voids (porosity), and water quality tests. All specimens were cured in a water pond (surface of the samples was kept moist by a 5-cm layer of water) for 42 days due to the use of type 5 cement. The relative humidity and average air temperature were about 40% and 22 °C, respectively, during the curing period. Finally, physical and water quality characteristics of all mixtures were tested after the curing period. Properties of the used aggregates are presented in Table 4.

32 31 32 32 32 32 31 32 31 36.1 34.6 35.2 34.7 35.6 35.4 35.9 34.7 36.2 10.05 10.47 9.88 7.28 7.49 12.03 10.20 9.48 9.82 1400 1400 1400 1400 1400 1400 1400 1400 1400 0 0 0 0 0 23.80 47.60 71.40 95.20

Permeability (cm/min) Aggregate (kg/m3)

2.2.1. Compressive strength The test was conducted according to BS 1881 standard. Each mixture consisted of 3 replications and the compressive strength value reported for each treatment was the mean strength of the 3 specimens [31].

330 297 264 231 198 297 264 231 198 0.36 0.36 0.37 0.38 0.39 0.36 0.36 0.36 0.36

0 22.15 44.30 66.45 88.60 0 0 0 0

2.2.2. Permeability This experiment was performed on 100  100  100 mm specimens, using an apparatus made according to the ACI 522R standard (Fig. 1) [32]. The permeability of each specimen was tested using two filters (sand and gravel) at the bottom of the PC samples, in order to bring the test conditions closer to the actual conditions. The gravel used in the gravel filter had the same diameter range as the aggregates (4.75 to 9.6 mm) utilized in PC mixtures; so, it did not have a significant effect on the permeability of specimens; while the sand filter (grain size range of 0.4 to 1 mm) had some effect. Therefore, for each specimen, there were two permeability results (with and without sand filter). 2.2.3. Air voids The total air voids (porosity) of the PC samples was measured by using an Archimedes balance according to ASTM C1754 standard. Three samples for each PC type were tested to calculate the mean value. According to Eq. (1), the air voids value was obtained by dividing the difference between the initial mass of the specimen in water (W2) and the ultimate mass measured following air drying for 24 h (W1), divided by the sample volume (V) and the density of water (qw Þ [33,34]:

15 15 15 15 15 15 15 15 15

        

15 15 15 15 15 15 15 15 15

        

15 15 15 15 15 15 15 15 15

0 10 20 30 40 10 20 30 40

Cement (kg/m3)

   W2  W1  100 At ¼ 1  qw  V

CPC* = Control porous concrete.

3 3 3 3 3 3 3 3 3 CPC* Z10 Z20 Z30 Z40 P10 P20 P30 P40

–– Zeolite Zeolite Zeolite Zeolite Pumice Pumice Pumice Pumice

Cube Cube Cube Cube Cube Cube Cube Cube Cube

Replacement level (%) Dimensions (cm) Geometry Number of specimens Replaced cementitious material Specimens’ name

Table 3 Porous concrete mixing proportions and results.

3

2.2. Physical characteristics

Water/ cement (w/c)

Zeolite (kg/m3)

Pumice (kg/m3)

Compressive strength (MPa)

Total void (%)

A. Azad et al. / Construction and Building Materials 240 (2020) 117931

ð1Þ

2.2.4. Unit weight The unit weight describes the density of fresh porous concrete. It is an indicator offered to test the quality of porous concrete [17]. The unit weight of concrete can be determined according to ASTM C1688 [35]. It is noted that unit weight is used to estimate the compressive strength of porous concrete because there is a relationship between void ratio and compressive strength [36]. 2.3. Water quality tests The performance of different treatments (GPC mixtures) was evaluated for improving the urban and industrial runoff quality. The runoff used in this study had some of the most important pollutants of urban and industrial runoff, namely TSS, TDS, COD, turbidity, Cd, Pb, Cu, and Zn. In order to perform qualitative tests, a

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GPC specimen was first inserted in the apparatus shown in Fig. 1. Then, the contaminated runoff was drained from the specimen. Finally, some of the drained runoff was collected to perform the qualitative tests. The synthetic runoff was prepared by mixing water with clay, NaCl salt, and potassium hydrogen phthalate powder (KHP) for TSS, TDS, and COD tests, respectively. For heavy metals, specific salts for each parameter were used. Table 5 presents runoff characteristics of the quality tests.

Table 4 Physical properties of aggregates. Characteristic

Value

Gradation (mm) Unit weight (kg/m3) Apparent density (kg/m3) Water adsorption (%)

9.5–4.75 1550 2480 1.2

2.3.1. Measurement of urban runoff parameters TSS, turbidity, COD, and TDS are present in various types of runoff. However, due to the wide application of PC in the drainage of urban storm-water runoff, these parameters are classified under urban runoff. In order to measure COD by dichromate reflux method, a COD reactor, and a spectrophotometer (DR-2010) were used [37]. This instrument has the ability to measure concentrations between 0 and 800 ml/L with an accuracy of ±2 nm [38]. For TDS, a HANNA HI-2040 apparatus was used, in which the electrode was placed in the drained runoff of each treatment for 10 s and readings were recorded. The device was able to measure the concentration between 0 and 14.99 g/L with an accuracy of ±1%. A HACH turbidimeter 2100 N was used for the estimation of turbidity [39]. This apparatus was calibrated with 5 standard solutions ranging from 0 to 400 NTU (nephelometric turbidity unit). Finally, the paper filter method was used to determine the TSS concentration in the input and output runoff. The difference between these two values was reported as the ability of each treatment to reduce TSS. 2.3.2. Measurement of Cd, Pb, Zn, and Cu Many industrial wastewaters and runoff contain Cd, Pb, Zn, and Cu. In the present study, atomic absorption spectrometry (Shimadzu–AA-6300) was used to measure the concentration of these heavy metals in the input and output runoff. The apparatus had the ability to measure wavelength within a range of 185– 900 nm, with a resolution of 0.2–2 nm. 3. Results and discussion 3.1. Physical properties of GPC

Fig. 1. Permeability measurement and urban/industrial runoff draining apparatus.

Table 5 Concentration of runoff quality parameters.

COD (mg/l) TSS (mg/l) EC (dS/m) Turbidity (NTU) Cu (mg/l) Pb (mg/l) Zn (mg/l) Cd (mg/l)

Control porous concrete

GPC-Za

GPC-Pb

300 ± 65 750 + 280 6.10 ± 0.25 250 ± 52 1.75 ± 0.2 3.70 ± 0.3 2.51 ± 0.2 4.00 ± 0.10

300 ± 80 750 + 260 6.10 ± 0.3 250 ± 48 175 ± 0.1 3.70 ± 0.25 2.51 ± 0.2 4.00 ± 0.15

300 ± 97 750 + 260 6.10 ± 0.35 250 ± 56 1.75 ± 0.25 3.70 ± 0.15 2.51 ± 0.10 4.00 ± 0.20

a, b: GPC-Z and GPC-P = Green porous concrete containing zeolite or pumice, respectively.

3.1.1. Effect of pumice and zeolite on compressive strength Several studies have been carried out to improve environmental properties of concrete by replacing some cementitious materials which have appropriate physical properties. The compressive strength results of the mixtures containing pumice (GPC-P) showed that overall the use of this mineral had no significant negative effect on the compressive strength of GPC. However, in the mixture with 10% pumice (GPC-P10), the compressive strength improved up to about 20% (Fig. 2). According to the authors’ knowledge, the effect of pumice, as a cementitious material, on porous concrete has not been examined before. Reports on other types of concrete show that pumice appropriately performs on the various physical properties of the concrete. Demirel and Kelestemur (2010) reported that although the increase of pumice usage, as a cement substitute, culminated in a bit compressive strength reduction, the resistance to temperature was enhanced [40]. In another study, pumice was suggested as an apt cement alternative to make normal concrete somehow lightweight [41]. Proper performance of pumice is due to its porous structure, high surface area, as well as appropriate pozzolanic activity of this material with cement paste [42]. The porous structure and surface cavities cause pumice to react better with cement particles and aggregate surfaces, resulting in good adhesion between concrete elements. Fig. 3 shows the cavities of Iranian pumice. Also,

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A. Azad et al. / Construction and Building Materials 240 (2020) 117931

Compressive strength (MPa)

14 12

Zeolite

Pumice

Linear (Zeolite)

Linear (Pumice)

y = -0.831x + 11.497 y = -0.288x + 11.164

10 8 6 4 2 0 0

10

20

30

40

Replacement level (%) Fig. 2. Effect of using various replacement levels of zeolite and pumice on the compressive strength of GPC.

Fig. 3. SEM pictures of Iranian natural pumice [[44], with permission].

appropriate chemical reaction of pozzolanic material with cement is another reason for acceptable results of GPC-P specimens [43]. Pozzolanic materials, such as pumice and zeolite, have silicon compounds with amorphous structure, which have high reactivity with alkaline substances, including lime released in the cement hydration reaction. This reaction leads to the production of calcium silicate hydrate, which improves the physical and chemical resistance

of concrete [44]. The pumice XRD analysis showed that most peaks had low angles and suitable gradients which reflected the amorphous structure of the pumice mineral (Fig. 4). In XRD analysis, low angles are a sign of amorphous structure. Results showed that GPC containing zeolite also had an acceptable performance in the physical properties (Fig. 2). The average compressive strength of zeolite samples (GPC-Z) was about 12% lower than that of control mixtures. However, this lower strength was justifiable and negligible, due to the benefits of decreasing the amount of cement as well as the higher ability of GPC-Z to improve the quality of urban and industrial runoff [45]. Like pumice, the proper function of zeolite is due to its high surface area, high superficial pores, amorphous structure, and calcium silicate hydrate production (Figs. 5 and 6). Results of the current study are similar to those of previous published reports about using zeolite as a cementitious material in different types of concrete. Ranjbar et al. (2013) proposed zeolite as an appropriate cement alternative in self-compact concrete [46]. According to their results, although the compressive strength of mixtures containing zeolite was up to 15% less than of other samples, these specimens had some compensating benefits [46]. Samimi et al. (2017) reported that the compressive strengths of normal concrete containing zeolite in all replacement levels were about 5–15% lower than non-zeolite specimens [24]. Although the effects of zeolite on some physical factors, like resistance to chloride penetration, durability and sulfate resistance, were not examined in the present study, other studies have shown that zeolite has a good effect on various physical parameters of different types of concrete [24,46,47]. Based on these studies, the use of natural pozzolans not only reduces the harmful effects of cement, but also improves the resistance of concrete to corrosive and sulfated agents [48]. This can be noticed in GPC, which is always exposed to corrosive agents, bacteria, and sulfate conditions [49]. Table 6 shows analysis of variance for the compressive strength of suggested materials which suggests that there is no significant relationship between porous concrete containing zeolite and pumice at various replacement levels. The XRD analysis of zeolite and pumice showed that zeolite had a higher slope than pumice at various angles (Figs. 4 and 5). Figs. 4 and 5 show that the tendency of pumice material to have amorphous structure was more than that of zeolite. This could be a reason for better performance of pumice in the chemical reaction with cement, and as a result, better physical properties. Another reason for lesser compressive strength of zeolite mixtures is the higher ratio of water/cement

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A. Azad et al. / Construction and Building Materials 240 (2020) 117931

Fig. 4. XRD analysis of Iranian natural pumice.

Fig. 5. XRD analysis of Iranian natural zeolite [[49], with permission].

Fig. 6. SEM pictures of Iranian natural zeolite [[50], with permission].

Table 6 Analysis of variance (ANOVA) for physical properties of porous concrete. Physical property

Condition

Total

Mean Square*

F

P-value

F critical

Compressive strength Air voids Permeability

— — Without filter With filter —

17.90 0.0004 3.54 0.15 30,504

2.80 0.00007 0.70 0.01 5462.1

2.10 3.73 4.69 0.92 3.86

0.21 0.09 0.06 0.51 0.08

5.19 5.19 5.19 5.19 5.19

Weight

* Mean square is reported for between groups. To calculate mean square of within groups, F should be multiplied by the presented mean square.

(W/C) used in zeolite specimens [24]. The amount of water needed to achieve proper workability of GPC-P mixtures was similar to that of the control GPC. Therefore, it was not necessary to change

the W/C ratio when using different pumice levels. However, the amount of water needed for GPC-Z mixtures to achieve the desired workability was more than that of the control specimens [24].

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38

Pumice

6.5

Zeolite

Pumice

Zeolite

20

30

6

Permeability (cm/min)

Permeability (cm/min)

36 34 32 30 28 26 24

5.5 5 4.5 4 3.5

22

3

20 Control PC

10

20

30

Control PC

40

Replacement level (%)

10

40

Replacement level (%)

(a)

(b)

Fig. 7. Permeability of various PC samples: a) samples without filter, b) samples with filter.

Zeolite

0.35

Pumice

0.3

Air void

0.25 0.2 0.15 0.1 0.05 0 Control

10

20

30

40

Replacement level (%) Fig. 8. Air voids of various mixtures.

Thus, an increase in the zeolite content increased the W/C ratio to allow the cement paste to reach an acceptable workability. This can be considered as an advantage of pumice over zeolite. Although this weakness of zeolite can be compensated for by using superplasticizers, it was decided that superplasticizers should not be used due to economic and environmental reasons, nonconventional use of superplasticizers in GPC, and negative effects on this type of concrete, such as a sharp decrease in permeability and reduced ability of GPC in draining runoff water. 3.1.2. Effect of zeolite and pumice on permeability and air voids Permeability (hydraulic conductivity) shows how fast the GPC is able to drain runoff. Permeability in the GPC is directly related to its air voids. Results of this study showed that the use of zeolite and pumice at various replacement levels did not have any considerable negative effect on the values of permeability and air voids (Figs. 7 and 8). In fact, the cement was replaced by zeolite and pumice powder, and the void ratio of GPC specimens was not changed, so the permeability of GPC was not decreased. Fig. 7 shows that both systems with/without filter had an acceptable performance for the drainage of runoff water. Table 6 shows statistical analysis of air voids and permeability, with/without filter. It further shows that permeability and air voids of no mixture were statistically significant. It is because when zeolite/pumice replaces part of cement, approximately no change would occur in the volume of concrete. In this case, there would be very small changes

which are mostly based on laboratory errors; as a result, there is no expectation to see a significant relationship between results. 3.1.3. Effect of zeolite and pumice on the weight of specimens Results indicated that apparent density of GPC-P and GPC-Z specimens was significantly less than that of typical PC. By replacing 10, 20, 30 and 40% of the cement by the additives, the apparent density of zeolite mixtures was reduced by 75, 82, 147, and 181 kg/ m3, respectively, and the pumice samples became lighter by 34, 45, 83, and 92 kg/m3, respectively. These results were due to the lower apparent density of zeolite and pumice than that of cement. Indeed, replacement of lightweight cementitious materials with cement resulted in a reduction in the final apparent density of porous concrete (Table 1). On the other hand, results showed that the average apparent density of GPC-Z samples was less than that of pumice, which was due to the lower apparent density of zeolite powder than that of pumice (Fig. 9). 3.2. Effectiveness of GPC in water quality control 3.2.1. Improvement of urban runoff quality Results showed that GPC was more suitable than conventional PC to reduce COD from storm-water runoff. Also, an increase in the replacement level of zeolite and pumice improved the ability of GPC specimens to reduce COD. Using 10, 20, 30 and 40% zeolite increased the ability of PC to reduce COD from 14% in the control

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1700 Control sample

Pumice

Zeolite

1650

Weight (kg/m3)

1600 1550 1500 1450 1400 1350 1300 Control PC

10

20

30

40

Replacement level (%) Fig. 9. Effect of zeolite and pumice on the weight of porous concrete.

45

Pumice

40

Zeolite

COD Remocal (%)

35 30 25 20 15 10 5 0 Control sample

10

20

30

40

Replacment level (%) Fig. 10. Effect of various replacement levels of zeolite and pumice on the performance of GPC to reduce COD.

Fig. 11. SEM pictures of Iranian zeolite and pumice minerals: a) pumice and b) zeolite [[47] and [51], with permission].

sample to 15.3, 22, 29, and 38.6%, respectively (Fig. 10). The GPC specimens containing pumice had similar results to the GPC-Z specimens. At the replacement levels of 10, 20, 30, and 40%, the ability of GPC-P in reducing COD increased from 14% in the control sample to 14.5, 16.9, 21.7 and 25.4%, respectively. Table 6 indicates that these results are statistically significant. The reason for better performance of GPC samples is their porous structure, higher specific surface, and more superficial pores of zeolite and pumice

as compared to cement [25]. During the drainage of runoff water, pollutants are trapped inside the cavities and pores of the zeolite and pumice particles, so the drained runoff had a lower amount of COD (Figs. 5, 6, and 11). TSS and turbidity are two other common contamination parameters in runoff. Based on the previous studies, zeolite and pumice, as cementitious materials, do not have considerable effect on the ability of PC to reduce TSS and turbidity. The size of suspended

9

A. Azad et al. / Construction and Building Materials 240 (2020) 117931 Table 7 Analysis of variance (ANOVA) for water quality properties of porous concrete. Water quality parameter

Condition

Total

Mean Square*

F

P-value

F critical

COD TSS

— Without filter With filter Without filter With filter —

579.56 39.15 91.069 88.7 38.8 4.69

113.30 2.45 5.02 10.35 6.13 0.32

4.48 0.41 0.35 1.09 2.14 0.48

0.05 0.79 0.83 0.45 0.21 0.75

5.19 5.19 5.19 5.19 5.19 5.19

Turbidity TDS

* Mean square is reported for between groups. To calculate mean square of within groups, F should be multiplied by the presented mean square.

Fig. 12. Effect of fine aggregates on the PC pores. a) PC sample without fine aggregates and b) PC sample with fine aggregates. In a and b, voids are indicated in blue and aggregate particles are red. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

particles in runoff (TSS and turbidity) is generally much larger than the particles of dissolved parameters (COD, TDS, heavy metals). Therefore, zeolite and pumice pores cannot reduce TSS and turbidity of urban runoff. These points were confirmed by statistical analysis which did not show any significant relationship between various mixtures and the level of TSS and turbidity removal (Table 7). Results of a study showed that the most important factor in the reduction of TSS and turbidity was the voids’ size of the used filter (the porous concrete with sand filter) [6]. The PC voids’ size depends on the grading range of the coarse aggregates and the use or non-use of sand and fine aggregate materials. Fig. 12 shows the voids in a PC specimen and also how the use of fine aggregates reduces the volume of voids, and improves the ability of PC in the reduction of TSS and turbidity in runoff. In the present study, powder pumice and zeolite were applied to the cement. Therefore, there was no change in the voids volume of GPC. Results of preliminary experiments showed that all samples with different replacement levels of pumice and zeolite had a similar ability to reduce TSS and turbidity. The mixtures containing zeolite reduced TSS and turbidity by 48 and 55 percent, and samples containing pumice decreased TSS and turbidity by 46 and 57 percent, respectively. Results of control specimens were similar to GPC-Z and GPC-P specimens, and this mixture decreased TSS and turbidity by 46% and 56%, respectively. In addition to the abovementioned tests, a 300 mm filter (100 mm gravel and 200 mm sand) was added to the system to better improve the ability of GPC specimens for reducing these parameters. Results indicated a significant improvement in the ability of the system to decrease these parameters, such that the average ability of pumice specimens to reduce the TSS and turbidity increased from 46% and 57% in samples without filter to 92% and 97%, respectively. This improvement was obtained for the zeolite samples. In these samples, the ability to remove TSS and turbidity was improved by about 93% and 98%, respectively (Fig. 13).

TDS is considered as a parameter of water salinity [52]. High values of this parameter causes some problems for humans and in agriculture. Fig. 14 presents the performance of different mixtures in reducing the TDS content of runoff. None of the treatments had a good performance in decreasing TDS. In fact, there are some anions and cations in these cementitious materials which are added to water during drainage. Although part of TDS may be trapped in adsorbents’ cavities, their effect was neutralized by adding cations or anions available in the concrete to runoff. This is probably why Table 7 did not show significant results in this respect. Besides, other studies have pointed out the inability of PC to reduce salinity [6,7] (Fig. 15). 3.2.2. Improvement of industrial-runoff quality Results indicated that both applied adsorbents were suitable for increasing the performance of GPC in reducing heavy metals’ concentration and improving the quality of industrial runoff. By replacing 10, 20, 30, and 40% of the cement by zeolite, the ability of GPC to reduce Zn, Cu, Cd, and Pb contents was improved from 78, 80, 76, and 86% to 94, 92, 99, and 97%; 95, 94, 99, and 98%; 96, 96, 99, and 99%; and 99, 99, 99, and 99%, respectively. In pumice specimens, replacing 10–40 percent of the cement with pumice improved the ability of GPC to reduce Zn, Cu, Cd, and Pb contents by 93, 91, 94 and 94%; 94, 92, 96 and 96%; 98, 92, 97, and 97%; and 98, 96, 99, and 99%, respectively. Table 8 confirms these significant results statistically. High specific area, porous structure, and superficial pores of the additives influenced the ability of suggested porous concretes to reach these results. Furthermore, wide ranges of pore size and air voids of zeolite and pumice were another reason for the adsorption of heavy metals. Results also showed that zeolite was more effective in adsorbing heavy metals than pumice. This can be due to the high ion exchange of zeolite, which increases the ability of this mineral [25].

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A. Azad et al. / Construction and Building Materials 240 (2020) 117931

TSS

Without filter

100

With filter

90

TSS Removal (%)

80 70 60 50 40 30 20 10 0 Control PC

GPC-P

Turbidity

GPC-Z Without filter

With filter

100

Turbidity Removal (%)

90 80 70 60 50 40 30 20 10 0 Control PC

GPC-P

GPC-Z

Fig. 13. Average performance of various treatments in reducing TSS and turbidity from urban runoff.

6 GPC-Z

GPC-P

TDS Removal (%)

5 4 3 2 1 0 Control PC

10

20

30

Repleacment level (%) Fig. 14. Performance of various GPC mixtures in reducing TDS in urban runoff.

40

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A. Azad et al. / Construction and Building Materials 240 (2020) 117931

The GPC samples containing Zeolite Heavy metals Removal (%)

100 95 90 85 80 75 Zn

Cu

Cd

Pb

Heavy metal parameters GPC-Z10

GPC-Z20

GPC-Z30

GPC-Z40

Control PC

GPC samples containing Pumice Heavy Metal Removal (%)

100 95 90 85 80 75 Zn

Cu

Cd

Pb

Heavy metals parameters GPC-P10

GPC-P20

GPC-P30

GPC-P40

Control PC

Fig. 15. Performance of GPC-Z and GPC-P samples in reducing heavy metals from industrial runoff.

Table 8 Analysis of variance (ANOVA) for industrial wastewater quality of porous concrete. Wastewater parameter

Total

Mean Square*

F

P-value

F critical

Zn Cu Pb Cd

546.1 367.6 228.9 782.40

135.65 88.15 55.1 190.85

193.7 29.3 32.41 50.22

** ** ** **

5.19 5.19 5.19 5.19

* Mean square is reported for between groups. To calculate mean square of within groups, F should be multiplied by the presented mean square. ** P-value was less than 0.001.

4. Conclusion Green porous concrete (GPC) is a new system for improving the quality of polluted waters, and restoring it to the groundwater resources. Results of the present study revealed that: 1) Pumice had no negative effect on the compressive strength of GPC. 2) Physical properties of zeolite were weaker than those of pumice. However, the average compressive strength of zeolite specimens (GPC-Z) was only about 12% less than that of the control treatment. 3) All GPC specimens had acceptable permeability and ability for the drainage of urban and industrial runoff.

4) Using zeolite and pumice as cementitious materials reduced the apparent density of GPC, such that the apparent density of lightest mixtures containing zeolite and pumice was 181 and 92 kg/m3, respectively, less than those of the control specimens. 5) Both zeolite and pumice had an appropriate performance in improving GPC’s ability to reduce urban and industrial runoff contamination. Using 40% zeolite increased GPC’s ability to reduce COD, Zn, Cu, Cd and Pb up to 38.6, 99, 99, 99 and 99%, respectively. Using 40% pumice improved the performance of GPC control specimens to remove these parameters by 25.4, 98, 96, 99 and 99%, respectively. In addition, the GPC-Z and GPC-P treatments had a good ability in eliminating TSS and turbidity, and on average, reduced these

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parameters up to about 46% and 56% in treatments without filter, and 93% and 38% in specimens with filter, respectively. Finally, TDS was the only parameter in the runoff which GPC could not reduce it notably. Taking into account the cause and effect as well as results seen in this research, some suggestions could be highlighted for future research: (i) Using combination of zeolite and pumice in order to obtain an optimized mixture which benefits from both adsorbents; (ii) Trying other types of wastewater runoff, such as mining seeps or leachates, to examine the ability of the suggested green concrete filter in improving other water quality parameters; and (iii) with respect to local resources, examination of some other adsorbents, such as vermiculite, kaolin and talc, in order to find other acceptable adsorbents for the use in green concrete filters. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. References [1] L.K. Singh, M.K. Jha, V.M. Chowdary, Multi-criteria analysis and GIS modeling for identifying prospective water harvesting and artificial recharge sites for sustainable water supply, J. Cleaner Prod. 142 (2017) 1436–1456. [2] A. Azad, S.F. Mousavi, H. Karami, S. Farzin, Application of talc as an eco-friendly additive to improve the structural behavior of porous concrete, Iranian J. Sci. Technol. Trans. Civ. Eng. 43 (2019) 443–453. [3] A.G. Selvarani, G. Maheswaran, K. Elangovan, Identification of artificial recharge sites for Noyyal River Basin using GIS and remote sensing, J. Indian Soc. Remote Sens. 45 (1) (2017) 67–77. [4] H.M. Leung, N.S. Duzgoren-Aydin, C.K. Au, S. Krupanidhi, K.Y. Fung, K.C. Cheung, M.T. Tsui, Monitoring and assessment of heavy metal contamination in a constructed wetland in Shaoguan (Guangdong Province, China): bioaccumulation of Pb, Zn, Cu and Cd in aquatic and terrestrial components, Environ. Sci. Pollut. Res. 24 (10) (2017) 9079–9088. [5] A. Azad, S.F. Mousavi, H. Karami, S. Farzin, Using waste vermiculite and dolomite as eco-friendly additives for improving the performance of porous concrete, Eng. J. 22 (5) (2018) 87–104. [6] J. Abedi Koupai, S. Saghaian Nejad, S. Mostafazadeh-Fard, K. Behfarnia, Reduction of urban storm-runoff pollution using porous concrete containing iron slag adsorbent, J. Environ. Eng. 142 (2) (2016) 04015072. [7] S. Saghaian Nejad, J. Abedi-Koupai, S. Mostafazadeh-Fard, K. Behfarnia, Treatment of urban storm water using adsorbent porous concrete. Proceedings of the Institution of Civil Engineers-Water Management, 2017; doi:10.1680/jwama.16.00093. _ Çifçi, S. Meriç, A review on pumice for water and wastewater treatment, [8] D.I. Desalin. Water Treat. 57 (39) (2016) 18131–18143. [9] Z. Ma, Q. Zhang, X. Weng, C. Mang, L. Si, Z. Guan, L. Cheng, Fluoride ion adsorption from wastewater using Magnesium (II): Aluminum (III) and Titanium (IV) modified natural zeolite: Kinetics, thermodynamics, and mechanistic aspects of adsorption, J. Water Reuse Desalin. (2017). jwrd2017037. [10] E. Ranjbar, R. Ghiassi, Z. Akbary, Lead removal from groundwater by granular mixtures of pumice, perlite and lime using permeable reactive barriers, Water Environ. J. 31 (1) (2017) 39–46. [11] B. Silva, E. Tuuguu, F. Costa, V. Rocha, A. Lago, T. Tavares, Permeable biosorbent barrier for wastewater remediation, Environ. Process. 4 (1) (2017) 195–206. [12] M. Belhachemi, S. Djelaila, Removal of amoxicillin antibiotic from aqueous solutions by date pits activated carbons, Environ. Process. 4 (3) (2017) 549– 561. [13] S.S. Salih, T.K. Ghosh, Preparation and characterization of chitosan-coated diatomaceous earth for hexavalent chromium removal, Environ. Process. 5 (1) (2017) 1–17. [14] G.M. Kim, J.G. Jang, H.R. Khalid, H.K. Lee, Water purification characteristics of pervious concrete fabricated with CSA cement and bottom ash aggregates, Constr. Build. Mater. 136 (2017) 1–8. [15] A. Azad, S.F. Mousavi, H. Karami, S. Farzin, V.P. Singh, The effect of vermiculite and quartz in porous concrete on reducing storm-runoff pollution, ISH J. Hydraul. Eng. (2018) 1–9, https://doi.org/10.1080/09715010.2018.1528482. [16] D.F. Velandia, C.J. Lynsdale, F. Ramirez, J.L. Provis, G. Hermida, A.C. Gomez, Optimum green concrete using different high volume fly ash activated systems, in: Concrete Durability, Springer International Publishing, 2017, https://doi.org/10.1007/978-3-319-55463-1_8. [17] S.K. Ong, K. Wang, Y. Ling, G. Shi, Pervious Concrete Physical Characteristics and Effectiveness in Stormwater Pollution Reduction, CTRE, Iowa State University, Ames, Iowa, USA, 2016.

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