Strength, fracture and fatigue of pervious concrete

Construction and Building Materials 42 (2013) 97–104

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Strength, fracture and fatigue of pervious concrete Yu Chen a,b,⇑, Kejin Wang b, Xuhao Wang b, Wenfang Zhou a a b

School of Traffic and Transportation Engineering, Changsha University of Science & Technology, Changsha 410004, China Department of Civil, Construction and Environmental Engineering, Iowa State University, Ames, IA 50010, USA

h i g h l i g h t s " The strengths of pervious concrete are much higher than what has been reported elsewhere. " The paper is aimed at filling research gap on fracture and fatigue behavior of pervious concrete. " Significant effect of specimen size on compressive strength of pervious concrete is found.

a r t i c l e

i n f o

Article history: Received 5 April 2012 Received in revised form 26 December 2012 Accepted 7 January 2013 Available online 13 February 2013 Keywords: Pervious concrete Strength Size effect Fracture toughness Fatigue life

a b s t r a c t Pervious concrete is increasingly used in the pavements and overlays subjected to heavy traffic and in cold weather regions. In the present study, strength, fracture toughness and fatigue life of two types of pervious concrete, supplementary cementitious material (SCM)-modified pervious concrete (SPC) and polymer-modified pervious concrete (PPC), are investigated. The results indicate that high strength pervious concrete (32–46 MPa at 28 days depending upon the porosity) can be achieved through both SCMmodification, using silica fume (SF) and superplasticizer (SP), and polymer-modification, using polymer SJ-601. For both SPC and PPC, porosity significantly affects compressive strength, but it has little effect on the rate of strength development. Flexural strength of pervious concrete is more sensitive to porosity than compressive strength. Pervious concrete has more significant size effect than conventional concrete. PPC demonstrates much higher fracture toughness and far longer fatigue life than SPC at any stress level. Ó 2013 Elsevier Ltd. All rights reserved.

1. Introduction Pervious concrete consists of a carefully controlled amount of paste and an aggregate system with a uniform particle size or a narrow particle size distribution and with little or no sand [1–3]. The paste in pervious concrete forms a thick coating around the aggregate particles, binding all the particles together while remaining a substantial amount (15–25%) of interconnected macro-voids in the concrete [4,5]. As a result, pervious concrete is highly permeable, having a water flow rate typically around 0.34 cm/s (480 in./h). Because of its environmental benefits, pervious concrete is increasingly used to a variety of infrastructures, including the pavements and overlays subjected to heavy traffic and in cold weather regions. These extended applications have demanded pervious concrete have superior strength and durability. Unfortunately, due to its high porosity and low cement/mortar content, ⇑ Corresponding author at: Department of Civil, Construction and Environmental Engineering, Iowa State University, Ames, IA 50010, USA. Tel.: +1 515 708 6868; fax: +1 515 294 2152. E-mail address: [email protected] (Y. Chen). 0950-0618/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.conbuildmat.2013.01.006

pervious concrete generally has significantly reduced strength when compared with conventional concrete (CC). Research has shown that the major factors that affect pervious concrete strength include the concrete porosity, water-to-cementitious material ratio (w/cm), paste characteristic, and size and volume content of coarse aggregates [5–9]. The mechanical properties of pervious concrete can be greatly improved by using proper concrete materials and mix proportions [10,11]. Yang and Jiang [12] demonstrated that use of silica fume (SF) and superplasticizer (SP) could enhance pervious concrete strength substantially. Kevern [13] reported that the addition of polymer (styrene butadiene rubber) could improve pervious concrete workability, strength, and permeability as well as freeze–thaw resistance. In addition, the performance of laboratory, field produced pervious concrete mixtures and field cores were evaluated and compared through laboratory performance tests, including air voids, permeability, compressive and split tensile strengths, as well as Cantabro and freeze–thaw durability tests by Shu et al. [14]. Although extensive work has been done, most previous research focuses on permeability, strength, frost resistance and abrasion resistance of pervious concrete [15–17], and limited study has been conducted on the fracture and fatigue behavior of

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Y. Chen et al. / Construction and Building Materials 42 (2013) 97–104

pervious concrete, which are especially important for pavement concrete subjected to heavy traffic and to severe seasonal temperature change. Being a brittle material, the mechanical behavior of pervious concrete is critically influenced by its crack propagation, or fracture behavior. Subjecting repeated traffic and environmental loads, concrete pavements often fail under fatigue cracking. A better understanding of fracture and fatigue behavior of pervious concrete can help to improve pavement design procedures. For compressive strength tests, Chinese standard GT/B 500812002 (standard for test method of mechanical properties in ordinary concrete) [18] requires using the specimen size of 150  150  150 mm3. However, researchers in China often use smaller specimens (100  100  100 mm3) for convenience. For pervious concrete, due to the difficulties in compaction of small specimens, 200  200  200 mm3 specimens are sometimes used. There is little or no research on the effect of specimen size on the pervious concrete compressive strength measurements. The present study is aimed at filling the above-mentioned research gap, and it is to investigate the mechanical responses (such as the compressive and flexural strength, fracture toughness, and fatigue properties) of the high-strength pervious concrete through use of supplementary cementitious materials (SCMs) or polymer modification. Besides, the effects of specimen size on the concrete compressive strength measurements are also discussed. 2. Experiment program 2.1. Materials and properties ASTM Type I ordinary Portland cement (OPC) is used as a primary binder, and its major properties are presented in Table 1. SCMs, such as Class C fly ash (CFA) and SF, are used as a cement replacement to modify the binder properties, and their properties are listed in Table 2. A polymer, SJ-601, which is a mixture of vinyl acetate ethylene (VAE) and acrylic emulsion, is also employed as an additive to modify the binder properties. Table 3 lists the main properties of SJ-601. In addition, a sulfonated naphthalene-formaldehyde condensate SP is used to improve workability of the pervious concrete made with OPC and SCMs. Granite aggregate is used in all the pervious concrete mixes studied. It is a blend of two sizes of the aggregate retained on 4.75 mm sieve and 9.5 mm sieve, and the blend ratio is 4 (4.75 mm): 6 (9.5 mm).

2.2. Mix proportions As known, the porosity of pervious concrete depends on the volume of the voids among the aggregate particles and the volume of paste/mortar that fills the voids. For given aggregate, with a given particle distribution and a given void ratio, the paste amount must be reduced accordingly so as to obtain high porosity. Based on this concept, two sets of pervious concrete mixes, (1) SCM-modified pervious concrete (SPC) and (2) polymer-modified pervious concrete (PPC), are designed, and their mix proportions are presented in Table 4. These pervious concrete mixes have porosity ranging from 15% to 25%. The SJ-601 dosages ranging from 8% to 12% are used based on the recommendation provided by previous research [1,19].

Table 1 Properties of OPC. Major chemical compositions (%) SiO2

Al2O3

CaO

MgO

Fe2O3

SO3

K2O

22.1

5.1

62.5

1.5

4.2

2.9

0.4

Specific gravity (g/cm3)

Blaine fineness (m2/kg)

3.07

391

Table 3 Properties of SJ-601. Solid content (%)

Viscosity (Pa s)

pH

Density (g/ml)

47 ± 3

0.03–0.04

5

1.08 ± 0.03

2.3. Specimens and test methods Different sizes of specimens are prepared for the 21 pervious concrete mixes (12 SPC mixes and 9 PPC mixes) as described in Table 4. The specimens are tested for the concrete porosity, compressive strength, flexural strength, fracture toughness, and flexural fatigue life. Table 5 lists the numbers and sizes of the specimens used for the designed tests. To cast a cubic specimen for compressive strength test or a beam specimen for fracture and fatigue tests, a half of the steel mold (Fig. 1) is firstly filled with fresh pervious concrete and placed on a standard vibration table to vibrate for 60 s. Then, while vibrating, more fresh pervious concrete is added into the mold until the mold is over-filled. This process takes approximate another 60 s. After placing and vibrating, the specimen is pressed by a press machine under a pressure of 2.0 MPa for 3 min. At 24 h, the mold is removed and the specimen is stored in a standard curing room (T = 23 °C, and RH = 95%) to the designated days. After cured for 28 days, porosity of the pervious concrete specimens is measured according to the cold-water saturation method (ASTM C642, standard test method for density, absorption, and voids in hardened concrete [20]). The compressive strength tests are performed according to GT/B 50081-2002. The effect of specimen sizes on concrete compressive strength is investigated using three different sizes of cubic specimens, 100  100  100 mm3, 150  150  150 mm3 and 200  200  200 mm3. Third-point loading simple beam in accordance with ASTM C78/C78M-10 [21] is conducted to assess the flexural strength, fracture toughness, and fatigue life of pervious concrete. 40  40  160 mm3 beam specimens are notched at the mid span with a depth of 20 mm and used for fracture toughness test. The specimens are loaded under the controlled strain rate of 0.1 mm/min. The fracture toughness, KIC, stress intensity factor, is then calculated according to the following equation [22,23]:

K IC ¼

PL BH3=2

  1=2  a 3=2  a 5=2  a 7=2  a 9=2  a  2:9  4:6 þ 21:8  37:6 þ 38:7 H H H H H ð1Þ

where L, B, H represents the specimen span, width and height respectively; a is the notch depth; and P is the maximum load. An electro-hydraulic servo-type material testing machine is used for measuring the flexural fatigue life of pervious concrete. Three stress levels of sine wave loading (that is 0.90, 0.80 and 0.70) with 0.1 of cycling eigenvalue, 10 Hz of frequency and zero time gaps, are adopted. The number of the cyclic load that the tested specimens are subjected until failure is recorded.

3. Results and discussions 3.1. Strength Table 6 provides the compressive and flexural strengths of all the pervious concrete mixes studied. As seen in the table, SPC and PPC mixes produced in this research all have good strengths (higher than 32 MPa), even for the mixes having porosity close to 25%. More detailed analyses of the strength results are presented below. 3.1.1. Strength development Fig. 2 illustrates the difference in rates of the strength development between SPC and PPC containing similar porosity. It is observed that the SPC mixes had more rapid strength development at early ages but slower strength development at later ages when

Table 2 Properties of SCMs. Major chemical compositions (%)

CFA SF

SiO2

Al2O3

Fe2O3

CaO

MgO

SO3

K2O

Na2O

61.8 98.2

26.4 –

5.0 –

1.10 –

0.40 –

0.42 –

0.80 –

0.54 –

Specific gravity (g/cm3)

Ignition loss (%)

2.37 1.98

2.07 0.61

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Y. Chen et al. / Construction and Building Materials 42 (2013) 97–104 Table 4 Mix proportions per 1 m3 pervious concrete. Mix ID

Aggregates (kg)

Cementitious materials

SJ-601 (%)

Water-to-binder ratio w/b

–

0.33

Total (kg)

OPC (%)

CFA (%)

SF (%)

SP (%)

80

14

6

0.2

76

16

8

0.3

0.32

0.4

0.30

0.28

SPC1 SPC2 SPC3 SPC4 SPC5 SPC6 SPC7 SPC8 SPC9 SPC10 SPC11 SPC12

1450 1472 1500 1532 1570 1591 1611 1637 1654 1668 1690 1702

440 432 416 410 394 390 378 366 345 330 325 320

PPC1 PPC2 PPC3 PPC4 PPC5 PPC6 PPC7 PPC8 PPC9

1500 1547 1581 1606 1643 1677 1692 1700 1712

380

72

18

10

0.5

100

–

–

–

8

0.34

10

0.32

12

0.30

Table 5 Pervious concrete specimens for designed tests. Mix ID

Number of specimens

Specimen size (mm3)

Tests

SPC1  SPC12

12  6 12 1 63 12 12

150  150  150 150  150  550 40  40  160 100  100  400 100  100  100 200  200  200

Compressive strength at 3 days, 7 days, 14 days, 28 days, 56 days and 90 days Flexural strength at 28 days Flexural fracture toughness at 28 days 28-day flexural fatigue at 3 stress levels Compressive strength at 28 days

PPC1  PPC9

96 9 2 63

150  150  150 150  150  550 40  40  160 100  100  400

Compressive strength at 3 days, 7 days, 14 days, 28 days, 56 days and 90 days Flexural strength at 28 days Flexural fracture toughness at 28 days 28-day flexural fatigue at 3 stress levels

Fig. 1. Steel moulds used to cast pervious concrete specimens.

compared with the PPC mixes. The rapid strength development of the SPC mixes at early ages may be contributed to the use of SF together with SP. The aggregate particles are rapidly wrapped and cemented together by a stiff paste to form the skeleton-pore structure, obtaining quite strong resistance to the destructive load at early ages. However, due to the small amount of cementitious paste used and slow hydration process, there is no remarkable strength gain at later ages (Fig. 2a). In the PPC mixes, cement hydration at early ages may be retarded due to the addition of the polymer SJ-601, the particles of which may adsorb on the cement particle surfaces and prevent the cement from contacting with water. Because of high relative

humidity in the paste, the polymer particles are also difficult to aggregate. Therefore, neither cement nor polymer can develop sufficient strength at early ages. However with time, the layer of the polymer coated on cement particles is destroyed by Brownian motion of water molecular and/or by the redistribution of gradually produced cement hydration products. As a result, more cement starts to hydrate. At the same time, the polymerization of SJ-601 speeds up with the decreasing relative humidity in the paste. Thus, cement hydration products and polymer films begin to intertwine, interpenetrate, and build up a network microstructure that can firmly bind aggregate particles together, shown as Fig. 3. The synergetic effect of cement particles and polymer particles provides

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Table 6 Results of strength test. Porosity (%)

3 days

7 days

14 days

28 days

56 days

90 days

SPC1 SPC2 SPC3 SPC4 SPC5 SPC6 SPC7 SPC8 SPC9 SPC10 SPC11 SPC12

15.2 16.3 17.6 18.4 18.9 19.5 20.1 21.1 22.8 23.2 24 24.7

23.8 24.8 23.9 26 22.7 24.8 21 19.7 22.2 22.6 19.1 20.4

38.3 36.1 35.9 34.2 34.4 35.6 32.8 32.7 31.5 33.1 28.8 29.9

42.6 40.6 38.5 40.6 37.8 38.2 36.5 35.9 36.2 33.8 34 32.4

46.7 45.1 43.3 42.7 42 41.4 40.5 39.4 38.9 37.6 36 35.2

48.1 48.1 45.5 48.7 44.5 43.5 41.7 42.2 40.4 41 37.1 36.3

PPC1 PPC2 PPC3 PPC4 PPC5 PPC6 PPC7 PPC8 PPC9

15.8 17 19.3 19.7 21.2 22.5 23.4 24.3 25

11.8 13.1 13.2 11.5 14.7 11.5 9.2 9.8 9.6

22.4 19.1 17.8 18.9 20.3 15.7 16.1 13.5 15.1

30.7 32.2 29.4 28.8 31.2 28.3 26 24.3 21.8

43.9 43.5 42.7 41.2 40.5 38.2 36.6 33.7 32.1

50.9 48.7 48.6 47.2 44.1 43.9 39.9 39.6 38.2

Compressive strength (MPa)

Mix ID

Compressive strength (MPa)

Flexural strength at 28 days (MPa)

Ratio of flexural to compressive strength at 28 days

49 49.1 46.3 51.1 45.8 46 43.3 43 42 41.9 38.5 36.7

6.1 5.9 5.6 5.4 5.4 5.3 5.1 5 4.8 4.7 4.4 4.2

0.131 0.131 0.13 0.127 0.129 0.128 0.127 0.127 0.124 0.125 0.121 0.119

51.8 50.5 48.7 48.9 46.7 44.3 41.0 40.1 39.2

7.3 7.4 7 7.2 6.3 6.2 5.5 5 4.8

0.166 0.157 0.163 0.17 0.156 0.162 0.151 0.149 0.148

60 50 40 30

SPC1: 15.2% of porosity

20

SPC6: 19.5% of porosity 10

SPC12: 24.7% of porosity

0

0

7

14 21

28 35 42

49 56 63

70 77

84 91

Age (days)

(a) SPC Compressive strength (MPa)

60 50 40

Fig. 3. Microstructure of the matrix in PPC.

30

PPC1: 15.8% of porosity

20

PPC4: 19.7% of porosity 10

PPC9: 25.0% of porosity

0 0

7

14

21

28

35

42

49

56

63

70

77

84

91

Age (days)

(b) PPC Fig. 2. Compressive strength development of SPC and PPC with different porosity.

PPC evident strength growth after 14 days. At later ages such as 56 and 90 days, the further improved strength of PPC may be attributed to the pore refinement, resulting from the aggregated polymer particles and cement hydration products that keep filling micro-pores in the paste, and attributed to the paste–aggregate

bond improvement in the concrete, resulting from the strong, cohesive polymer modified paste. It is worth to note that to benefit both cement hydration and SJ601 polymerization, it is favorable for PPC to be wet-cured at least 3 days to promote cement hydration, and then to be stored at a dry environment with relative humidity less than 70% for a better film formation of the polymer. 3.1.2. Effects of concrete porosity Fig. 4 demonstrates the effect of porosity on strength of the SPC and PPC mixes. As observed in the figure, although porosity plays a crucial role in controlling pervious concrete strength, it appears to have less effect on concrete strength at the early ages (3 and 7 days, Fig. 4a and b) when compared with at the later ages (28, 56 and 90 days, Fig. 4d–f). Fig. 4 also shows that SPC gains strength much more rapidly than PPC before the age of 14 days. As the time passed, the strength difference between SPC and PPC becomes smaller with concrete

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Y. Chen et al. / Construction and Building Materials 42 (2013) 97–104

50

Compressive strength (MPa)

Compressive strength (MPa)

30 25 20 15 10 5 0 14

SPC 16

PPC 18

20

22

24

15

SPC

10

PPC

5 16

18

20

22

24

26

24

26

55

Compressive strength (MPa)

Compressive strength (MPa)

20

(d) at 28 days

25 20 15 10

SPC 16

PPC 18

20

22

24

50 45 40 35 30 25 20 15

SPC

PPC

10 5 0

26

14

16

18

20

22

Porosity (%)

Porosity (%)

(b) at 7 days

(e) at 56 days 55

Compressive strength (MPa)

45

Compressive strength (MPa)

25

(a) at 3 days

30

40 35 30 25 20 15

SPC

PPC

16

18

5 0 14

30

Porosity (%)

35

10

35

Porosity (%)

40

0 14

40

0 14

26

45

5

45

20

22

24

26

50 45 40 35 30 25 20 15 10 5 0 14

SPC

PPC

16

18

20

22

Porosity (%)

Porosity (%)

(c) at 14 days

(f) at 90 days

24

26

Fig. 4. Compressive strength of SPC and PPC at different ages.

curing age. At the age of 28 days, there is little or no difference in strength between SPC and PPC. At the later ages (56 and 90 days), the strength of PPC is slightly higher than that of SPC. To further evaluate the rate of the pervious concrete strength development, the compressive strengths of all mixes are also expressed as a percentage of their 28-day strength as shown in Fig. 5. It is observed that at a given age, the strength percentages of specimens made with different mixes, or with different porosity, are very close. That is, porosity does not significantly affect the rate of both SPC and PPC strength development.

those of the SPC at 28 days. A possible reason is that polymer SJ601 strengthens both the interfacial transition zone (ITZ) between the paste and aggregate and the matrix microstructure of pervious concrete, and makes the concrete less brittle, thus having excellent resistance to flexural damage. With the increasing of porosity, both flexural and compressive strengths decrease, however, the most ideal trend lines in Fig. 6 exemplify that the ratios of flexural-tocompressive strength of SPC and PPC definitely decrease too. So it suggests that the flexural strength of pervious concrete may be more sensitive to porosity change than the compressive strength.

3.1.3. Relationship between compressive and flexural strength As seen in Table 6, PPC has evidently higher flexural strength than SPC at the same porosity level, and the ratios of flexural to compressive strength of the PPC mixes are also much higher than

3.1.4. Effect of specimen size on compressive strength Test results of the 28-day compressive strength of cubic specimens with different sizes are presented in Table 7. A size conversion factor (d) is calculated as the ratio of the 28-day com-

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Y. Chen et al. / Construction and Building Materials 42 (2013) 97–104

while those of 200  200  200 mm3 specimens are all much higher than 1.05 for all SPC mixes. Since no sufficient mortar/paste to fill the voids between aggregate particles, pervious concrete has much more significant size effect than conventional concrete, especially when porosity of pervious concrete is high. Fig. 7 shows that the size conversion factor (d) of specimens changes with pervious concrete porosity. From the data regression, the exponential function lines are derived as follows and displayed in Fig. 7: For 100  100  100 mm3 specimens,

Strength percentage (%)

140 120 100 80 60

SPC1

SPC2

SPC3

SPC4

40

SPC5

SPC6

SPC7

SPC8

SPC9

SPC10

SPC11

SPC12

20

d ¼ 1:111e0:012p ;

R2 ¼ 0:9417

0 0

7

14

21

28

35

42

49

56

63

70

77

84

91

Age (days)

R2 ¼ 0:9218

ð3Þ

where d is the size conversion factor, and p means the porosity of pervious concrete. When the non-standard cubic specimens are used for compressive strength test of pervious concrete, the size conversion factor can be determined using Eqs. (2) and (3).

140

Strength percentage (%)

For 200  200  200 mm specimens,

d ¼ 0:9862e0:0058p ;

(a) SPC

ð2Þ

3

120 100 80 60

PPC1 PPC4 PPC7

40

PPC2 PPC5 PPC8

3.2. Fracture toughness

PPC3 PPC6 PPC9

20 0 0

7

14

21

28

35

42

49

56

63

70

77

84

91

Age (days)

(b) PPC Fig. 5. Strength development process of pervious concrete.

Ratio of flexural to compressive strength

0.18 SPC

0.17

PPC

0.16 0.15 0.14 0.13 0.12

The mixes with similar porosity (i.e. around 19.5%), such as mixes SPC6, PPC3 and PPC4, are chosen to be tested for the fracture toughness. Among these mixes, PPC3 and PPC4 mixes have 8% and 10% of polymer SJ-601 addition, respectively, and SPC6 has no polymer addition. The fracture toughness results are given in Table 8. It can be seen that the fracture toughness of pervious concrete apparently increases with the increasing of polymer dosage. In comparison with SPC6, the fracture toughness of PPC3 and PPC4 increases 45.3% and 56.9% respectively. This implies that addition of the polymer improves the concrete resistance to cracking and crack propagation, and therefore it requires more fracture energy to fracture PPC than to fracture SPC. Besides, the improvement of PPC fracture toughness can also be attributed to that SJ-601 particles gather and polymerize in the region of ITZ with the polymer films tightly bonding the cement paste matrix and aggregate together, as illustrated in Fig. 8. Different from conventional pervious concrete, which generally fractures around aggregate particles due to the weak ITZ between the aggregate and paste, PPC fractures through aggregate particles, which indicates a good bond between aggregate and paste.

0.11

3.3. Flexural fatigue property

0.10

14

16

18

20

22

24

26

Porosity /% Fig. 6. Ratios of flexural to compressive strength of pervious concrete.

0 pressive strength (fc;0 ) of the specimens with standard size (150  150  150 mm3) to the 28-day compressive strength (fc0 ) of the specimens with non-standard size (100  100  100 mm3 0 or 200  200  200 mm3). That is, d ¼ fc;0 =fc0 . (Note: 3 150  150  150 mm is a standard size of specimens to be used for compressive strength test as prescribed in GB/T 50081-2002). For conventional concrete, it is specified by GB/T50081-2002 that the size conversion factors are 0.95 when 100  100  100 mm3 specimens are used and 1.05 when 200  200  200 mm3 specimens are used for compressive strength tests. Table 7 evidences the clear size effect of pervious concrete on compressive strength because the size conversion factors (d) of 100  100  100 mm3 specimens are all much lower than 0.95,

Results from the flexural fatigue tests of selected SPC and PPC mixes are listed in Table 9. It is found that PPC has by far longer flexural fatigue life than SPC at all stress levels, since the polymer helps reduce cracking or delay cracking growth. In Fig. 9, the most ideal trend lines based on the calculated data from Eq. (4) illustrates that for both SPC and PPC mixes, the fatigue lives decrease with the increasing porosity and the stress level sustained by the specimens. There exists an excellent linear relationship between the fatigue life of pervious concrete and its porosity. Fatigue life of a concrete material is often expressed by a twoparameter Weibull probability function [15,16]. In general, twoparameter Weibull probability function is established as:

LnS ¼ Lna  cLnN

ð4Þ

where S refers to the stress level sustained by concrete specimen; a and c are coefficients related to the concrete material properties. N means the number of cyclic loads sustained by concrete specimen at any stress level before failure.

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Y. Chen et al. / Construction and Building Materials 42 (2013) 97–104 Table 7 28-day compressive strength of SPC specimens with different sizes. Mix ID

SPC1 SPC2 SPC3 SPC4 SPC5 SPC6 SPC7 SPC8 SPC9 SPC10 SPC11 SPC12

100  100  100 mm3

150  150  150 mm3

fc0

d

0 fc;0

0.921 0.924 0.908 0.910 0.899 0.872 0.875 0.858 0.855 0.847 0.837 0.836

46.7 45.1 43.3 42.7 42.0 41.4 40.5 39.4 38.9 37.6 36.0 35.2

(MPa)

50.7 48.8 47.7 46.9 46.7 47.5 46.3 45.9 45.5 44.4 43.0 42.1

200  200  200 mm3

(MPa)

d

fc0 (MPa)

d

1.000

43.4 41.8 39.9 39.1 38.1 37.2 36.2 35.2 34.7 33.4 31.9 31.0

1.076 1.079 1.085 1.092 1.102 1.113 1.119 1.119 1.121 1.126 1.129 1.135

1.16

7.0

1.12

6.0

1.08

5.0

PPC; 0.9 of stress level

1.04

4.0

SPC; 0.8 of stress level

3.0

PPC; 0.8 of stress level

LnN

Size conversion factor

Note: fc0 – 28-days compressive strength of 100 mm or 200 mm cubic specimen; 0 fc;0 – 28-days compressive strength of 150 mm cubic specimen; 0 d – The size conversion factor, d = fc;0 / fc0 .

100mm cube

1.00

200mm cube

SPC; 0.9 of stress level

SPC; 0.7 of stress level

0.96

2.0

0.92

1.0

0.88

0.0 14

PPC; 0.7 of stress level

0.84 0.80 14

16

18

20

22

24

26

Porosity (%) 16

18

20

22

24

26

Fig. 9. Relationship of LnN and porosity of pervious concrete.

Porosity (%) Fig. 7. Size conversion factor (d) of specimens with different porosity.

Table 9 Number (N) of cyclic loads sustained by pervious concrete before failure.

Table 8 Effect of polymer on fracture toughness of pervious concrete.

Mix ID 1/2

Mix ID

SJ-601 (%)

P (N)

KIc (MPa m

SPC6 PPC3 PPC4

0 8 10

289 390 440

0.327 0.475 0.513

Fig. 8. Microstructure of ITZ in PPC.

) SPC1 SPC3 SPC5 SPC8 SPC10 SPC12

Stress levels of SPC 0.90

0.80

0.70

651 478 379 295 204 107

15,311 10,178 70,145 3422 930 395

230,158 101,134 57,894 31,490 20,158 8345

Mix ID

PPC1 PPC3 PPC4 PPC6 PPC7 PPC9

Stress levels of PPC 0.90

0.80

0.70

1054 815 707 426 315 187

20,014 14,331 12,067 9015 3088 801

604,121 371,580 248,741 112,055 30,851 12,334

Based on test data listed in Table 9, the two-parameter Weibull probability functions of both SPC and PPC under different failure probabilities can be derived. Zheng et al. [24] provided the same two-parameter Weibull probability functions of some typical concrete materials, including conventional concrete, lean concrete, and conventional pervious concrete under 50% of failure probability (Fig. 10). To compare with previous study, the functions of SPC and PPC under 50% of failure probability are also illustrated in Fig. 10. Each line represents the typical two-parameter Weibull probability distribution of different concretes under 50% of failure probability. It appears that for the same failure probability, conventional concrete has the longest fatigue life, followed by lean concrete; while pervious concrete generally has much shorter fatigue life. However, when compared with conventional pervious concrete [24], the high-strength SPC and PPC presented in this study have quite longer fatigue lives. Besides, it seems that the fatigue property of PPC can be comparable to or even higher than that of lean concrete, especially at low stress levels.

Y. Chen et al. / Construction and Building Materials 42 (2013) 97–104

LnS

104

0.05 0.00 -0.05 -0.10 -0.15 -0.20 -0.25 -0.30 -0.35 -0.40 -0.45 -0.50

Conventional concrete Lean concrete conventional pervious concrete [19] PPC SPC

0

1

2

3

4

5

6

7

8

LnN Fig. 10. LnS–LnN of different concretes under 50% of failure probability.

4. Conclusions

References

Compressive and flexural strength, fracture toughness, and fatigue life of two types of pervious concrete, (1) SCM-modified pervious concrete (SPC) and (2) polymer-modified pervious concrete (PPC), are investigated. The following conclusions can be drawn:

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(1) High strength pervious concrete, 32–46 MPa at 28 days depending upon the porosity, can be achieved through both SCM-modification using silica fume (SF) and superplasticizer (SP), and polymer-modification, using polymer SJ-601. (2) For both SPC and PCC, porosity significantly affects compressive strength of pervious concrete, but it has little effect on the rate of strength development. SPC gains compressive strength rapidly at early ages, while its strength increments are rather low after 28 days. Differently, PPC gains strength slowly at early ages, but its development accelerates at later ages, probably due to the continuous hydration of cement and film-forming of polymer materials. (3) PPC has both higher flexural strength and higher flexural-tocompressive strength than SPC at the same porosity level at 28 days. The ratios of flexural-to-compressive strength of both PCC and SPC decrease with increasing porosity, which indicates that flexural strength is more sensitive to porosity than compressive strength of pervious concrete. (4) Pervious concrete has more significant size effect than conventional concrete. The size conversion factors (d) for 100  100  100 mm3 specimens and for 200  200  200 mm3 specimens recommended from the present study may be considered in future when different size cubic specimens are used for the compressive strength tests of pervious concrete. (5) Both high-strength SPC and PPC produced in this study have improved fatigue property than conventional pervious concrete. PPC displays much higher fracture toughness and far longer fatigue life than SPC at any stress level, which suggests that PPC has improved resistance to cracking and crack propagation.

Acknowledgements The present study is sponsored by the Department of Hunan Highway Administration. All experiments are carried out in Key Laboratory of Ministry of Transportation for Road Materials and Structures in Changsha University of Science and Technology.