Figures - uploaded by D. P. Bentz

Author content

All figure content in this area was uploaded by D. P. Bentz

Content may be subject to copyright.

ResearchGate Logo

Discover the world's research

  • 20+ million members
  • 135+ million publications
  • 700k+ research projects

Join for free

Concrete international

/ MAY 2010 35

BY NARAYANAN NEITHALATH, DALE P. BENTZ, AND MILANI S. SUMANASOORIYA

Predicting the

Permeability of

Pervious Concrete

Advances in characterization of pore structure and transport properties

The use of pervious concrete is on the rise due to its

environmental advantages, such as reducing tire-

pavement interaction noise, moderating storm-water

runoff, and limiting the pollutants entering groundwater.1-4

The fundamental material characteristic that makes

pervious concrete a sustainable material with respect to

its noise-absorbing and water-transport characteristics

is its open pore structure (primarily the connected

porosity and the larger pore sizes), which is facilitated

by proportioning the concrete with gap-graded coarse

aggregates and little to minimal amounts of fine aggregates.

The characterization of the pore structure thus becomes

important in the evaluation and prediction of pervious

concrete performance.

POROSITY AND PERFORMANCE OF

PERVIOUS CONCRETE

Currently, mixture proportioning of pervious concrete

is primarily focused on obtaining a necessary pore

volume. It's common to relate the performance of pervious

concrete to its porosity because it's a relatively easy

quantity to measure, aided by the millimeter-sized pores

in the material. Figure 1 shows the porosity-permeability

relationships of pervious concretes from a few reported

studies. A general trend of increasing permeability with

increasing porosity can be observed (although, clearly,

porosity alone doesn't determine permeability). To design

the material for specific performance requirements (such

as permeability), an understanding of the features of the

pore structure (porosity being one of them) that determine

the performance is important. It's also important to

understand how the material design parameters affect

the pore structure. This article summarizes the current

understanding and the advances made in pore structure-

performance relationships in pervious concrete.

A Contribution from ACI Committee 236

Fig. 1: Porosity-permeability relationships for several pervious

concretes as provided in the indicated references. As the data

show, porosities typically range from 15 to 30%

36 MAY 2010 /

Concrete international

While porosity is undeniably one of the most important

features of pervious concrete pore structure, it's a

structure-insensitive property of the material—porosity

doesn't depend on the configuration of the various

elements in the structure. The question, then, is whether

such a property alone can be relied upon to determine

the performance of the material. Figure 2 shows the

permeability and acoustic absorption coefficient (an

index of the ability of the material to absorb acoustic

energy) as functions of the aggregate size for three

different pervious concrete mixtures having very similar

values of porosity (about 20%). These mixtures were

proportioned with carefully graded coarse aggregates:

■Passing No. 4 (4.75 mm) sieve and retained on No. 8

(2.36 mm) sieve;

■Passing 3/8 in. (9.5 mm) sieve and retained on No. 4

(4.75 mm) sieve; and

■Passing 1/2 in. (12.7 mm) sieve and retained on 3/8 in.

(9.5 mm) sieve.

The permeability was measured using a falling head

permeameter.1,9 The normal incidence acoustic absorption

coefficients were determined on pervious concrete

cylinders using an impedance tube in accordance with

ASTM E1050, up to a frequency of 1600 Hz. Details on

acoustic absorption coefficient measurements can be

found elsewhere.9,10

For the same porosity, an increase in aggregate size

from No. 8 to 3/8 in. (2.36 to 9.5 mm) is found to increase

the permeability by as much as a factor of two and

reduce the acoustic absorption coefficient to about half.

This shows that pore structure features other than porosity

are also influential in dictating material performance.

Because permeability is found to increase with increasing

aggregate sizes and the accompanying pore sizes

(because there is typically a linear relationship between

particle size and pore size11 ), the size of the pores can be

considered an important pore structure feature. In

addition, the transport of water through or sound waves

into the material requires that the pore system be

connected. Therefore, connectivity is another significant

pore structure characteristic. Both are discussed in the

following sections.

PORE SIZES, CONNECTIVITY, AND IMPACT

ON TRANSPORT PROPERTIES

One of the significant challenges in porous material

characterization is obtaining relevant features of the

three-dimensional (3D) pore structure from two-dimensional

(2D) images. Geometrical-statistical methods (also called

stereology12 ) are generally applied for this purpose.

Image acquisition and analysis procedures have been

elucidated in earlier publications.9,13

Figure 3 shows representative planar images of

pervious concrete sections from specimens made using

the three aggregate sizes described previously. The

complexities of the pore space in pervious concretes are

evident from these images. Even though the porosities are

similar, the pore sizes, their distributions, and likely their

connectivities are very different. In these planar images,

there are fewer and larger "pores" in the specimen made

with larger aggregate. Also, for a given pervious concrete

specimen, there are a multitude of apparent pore sizes in

the 2D images of the material. This complicates the

selection of a "characteristic" pore size that is represen-

tative of the pervious concrete mixture that could be

used in the estimation of performance properties. A few

methods to choose such a characteristic pore size are

briefly discussed herein. Readers are directed to the

corresponding references for more details.

Different methods of obtaining

characteristic pore sizes

If a statistically significant number of random planar

images from a particular pervious concrete mixture are

used, then the area fraction of pores can be used as an

unbiased estimator of (volumetric) porosity. Based on a

2D image, a direct representation of the equivalent pore

sizes can be obtained through the use of an area histogram.

The pore size corresponding to 50% of the cumulative

frequency distribution13 d 50 can be used as a characteristic

pore diameter from area histograms. This is a particularly

straightforward method of pore size estimation.

Fig. 2: Permeability and acoustic absorption coefficients of

three pervious concrete mixtures having similar porosities5,6 as

a function of the aggregate sizes in the mixture. Aggregate

sizes are denoted by the sieve sizes in which particles are

retained. The error bars correspond to one standard deviation

on three replicate specimens

Concrete international

/ MAY 2010 37

Binary images similar to the ones shown in Fig. 3 can

be subjected to certain transformations to obtain a

quantitative description of the features of interest, such

as the pore size. One such method is the use of a two-

point correlation (TPC) function.13-15 TPC is obtained by

randomly throwing line segments of length l with a

specific orientation into a binary image and counting the

fraction of times both end points of the segment fall in

the phase of interest.16 The features of the TPC function

along with the porosity can be related to a representative

pore size dTPC .

Another method that involves transformation of the

images to determine the pore size distribution is a

granulometric opening function. Structuring elements

(SEs) of increasing sizes are used to "open" the pore

phase. Figure 4(a) shows an original image and the

images obtained by "opening" using SEs of two different

sizes. The size distribution is obtained by plotting the

area fraction of the pore space remaining after opening

by SEs of gradually increasing size, as shown in Fig. 4(b).

For normal cement pastes (pore size distributions often

obtained by mercury intrusion), a critical pore size dcritical

is defined, associated with the inflection point in the pore

size distribution curve. In a similar manner, the first peak

of the derivative curve of the granulometric opening

distribution (Fig. 4) can be considered as the critical pore

radius for pervious concrete rcritical that corresponds to

the smallest pore that completes the first connected

pathway in a material. Because this size relates to the

percolation threshold, it could be used to determine the

permeability of pervious concretes. Changes in the pore

structure during service, such as clogging, can reduce the

critical pore size, thus reducing water transport.

A comparison of the pore sizes obtained using the

previously mentioned methods from a few pervious

concrete specimens made using single-sized aggregates

or chosen blends of these sizes9,10,13 are shown in Fig. 5.

The pore diameters corresponding to 50% of the cumulative

frequency distribution d 50 are plotted on the x-axis, and

the corresponding pore sizes obtained from granulometry

and TPC functions are plotted on the y-axis.

A reasonably good 1:1 correlation can be seen between

the pore sizes determined using all three methods for

the limited number of specimens evaluated. TPC and

granulometry provide characterizations of the pore sizes

based on mathematical morphology (quantifications

(a) (b) (c)

20 mm 20 mm 20 mm

Fig. 3: Representative planar images from pervious concrete

specimens of aggregate size: (a) 2.36 mm; (b) 4.75 mm; and

(c) 9.5 mm. The pores appear black in these images (1 mm =

0.039 in.)

Radius of structuring element (SE), mm

Derivative of area fraction

Area fraction of porosity

0.0 0.5 1.0 1.5 2.0 2.5

0.00

0.04

0.08

0.12

0.16

0.20

0.24

0.00

0.04

rcritical

0.08

0.12

0.16

0.20

Opened

using SE of

radius 0.5 mm

Original

image

Opened

using SE of

radius 1 mm

(a) (b)

Area fraction

Derivative

critical

Equivalent pore diameter d50 , mm

12345

1

2

3

4

Granulometry

TPC

R2 = 0.96

R2 = 0.87

Fig. 4: A granulometric opening function is defined using

structuring elements (SEs) of increasing sizes to "open" the pore

phase: (a) original image and the resultant images after opening

using SEs of 0.5 and 1 mm radii; and (b) critical pore radius rcritical

is defined using the first peak of the derivative curve of the

granulometric opening distribution (1 mm = 0.039 in.)

Fig. 5: Comparison of the characteristic pore size determined

using different methods. The error bars correspond to one

standard deviation on at least three images from a particular

specimen (1 mm = 0.039 in.)

38 MAY 2010 /

Concrete international

based on changes in images when subjected to certain

transformations), whereas d 50 is a statistical quantity

based on idealizing the observed 2D image structures

into circles. While advanced characterization techniques

such as TPC or granulometry are preferred to extract the

pore sizes, the relationships in Fig. 5 show that in the

absence of these techniques, d 50 could also be used as a

characteristic pore size of pervious concrete.

Connectivity of pore structure

Pervious concrete specimens filled with a conducting

electrolyte (such as sodium chloride solution) can be

approximated as a medium with a single electrically

conducting phase (solid phase has a much lower conductivity

as compared with the electrolyte-filled pore space). Therefore,

the specimen conductivity σ can be expressed as

σ = σ0 φβ (1)

where σ 0 is the conductivity of the electrolyte filling the

pores of the specimens, φ is the porosity, and β is the

pore connectivity factor. The lumped parameter φβ can

be used as a single quantity that represents the combined

effect of the amount of pore space and its connectivity.

A simple measurement of the conductivity of the pervious

concrete cylinder or core when filled with a conducting

solution of known electrical conductivity (for example,

3% sodium chloride solution has a conductivity of 4.4 S/m)

provides the value of the lumped pore structure parameter.9

Pore structure and its effect on water transport

It's instructive to examine the relative influence of

porosity, pore size, and pore connectivity on the

permeability of pervious concretes. Even though these

factors are equally critical in acoustic absorption, this

application is not detailed here for brevity.

The pore sizes chosen for this examination correspond

to the values obtained from the granulometric distribution,

as it's hypothesized that this provides a representative

size of the percolated pores. Figure 6 shows the contour

plot of measured permeability as a function of φβ and the

critical pore size.

An increase in either the pore size or the pore structure

factor φβ is found to result in increased permeability. For

the same value of φβ, an increase in pore size results in

increased permeability as expected, especially at lower

values of φβ. Increasing the pore size (typically by using

larger aggregates) at the same porosity is definitely a

means of obtaining higher permeability, as was also

observed in Fig. 2. At higher values of φβ, pore size does

not seem to influence the permeability significantly as

seen from contour lines that are essentially parallel to

each other. A higher value of φβ can be obtained by

increasing either the porosity or the connectivity factor.

Very high porosities (typically more than 25 to 30%)

are generally undesirable from a viewpoint of mechanical

properties. It has also been shown in an earlier study that

higher porosities are not necessarily required to obtain

higher connectivity factors.9 It's suggested that the

connectivity factors be increased by careful aggregate

gradations and/or blending to obtain desirable transport

properties.

The pore structure parameter φβ, which is equal to the

normalized conductivity σ/σ 0 from Eq. (1), as well as the

characteristic pore size d from any of the methods described

previously, can be used in the Katz-Thompson equation17

shown in Eq. (2), which is a well-established method of

the permeability k prediction of porous materials. The

empirical constant (1/226) employed by Katz and Thompson 17

was to provide a best fit to experimental data for a

variety of rock specimens and, hence, this value could

very well change for pervious concretes as

(2)

X-RAY MICROTOMOGRAPHY AND 3D PORE

STRUCTURE RECONSTRUCTION

Three-dimensional visualization of the pore space of

pervious concrete can be accomplished through the use

of X-ray microtomography. Several horizontal slices

through the pervious concrete specimen (at 1984 by

1984 pixels with a spatial resolution of approximately

Porosity × pore connectivity φβ

Pore diameter (2rcritical from granulometry), mm

Pemeability ×10-10 m2

1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

0.010

0.015

0.020

0.025

0.030

0.035

0.040

10.0 8.0 6.0 4.0

2.0

0.0 12.0

Fig. 6: Permeability as a function of critical pore size and the

product of porosity and pore connectivity (1 mm = 0.039 in.)

Concrete international

/ MAY 2010 39

0.026 mm/pixel and a signal resolution

of 8 bits) were obtained at the

National Institute of Standards and

Technology (NIST) using a commer-

cially available X-ray microtomography

unit and an image analysis procedure

employed in all of the slices to

produce requisite contrast between

the pore and solid phases. These

horizontal images were then stacked

to obtain the volumes shown in Fig. 7.

The pore space in each of the

horizontal slices that make up this

image (about 420 of them) can be

tracked vertically to visualize and

quantify the connected pore network,

and in turn relate its characteristics

to the permeability.

Because the availability of X-ray

microtomography units is still

somewhat limited, a recent study15

used a correlation filter-based 3D

reconstruction algorithm to produce

digitized virtual pervious concretes.

Computer programs were used to

compute the permeabilities and

conductivities of the digitized 3D

material structure. The permeability

and conductivity values predicted

from the digitized material structures

matched reasonably well with the

experimental values.

More recently, studies have been

conducted using actual 2D images

from several pervious concrete

specimens to reconstruct the 3D

pore structure and predict the

permeability using computer

programs developed at NIST.18

Figure 8 shows a starting 2D binary

image of a pervious concrete

specimen, the reconstructed 3D

structure, and representative 2D

slices from the reconstructed

structure. Once again, comparisons

between predicted and measured

permeabilities were favorable.18

Material structure models for

pervious concrete can be useful in

achieving better material design

and proportioning toward targeted

performance characteristics as

well as in predicting the material

performance.

SUMMARY

Increasing use of pervious

concrete has led to an emphasis on

mixture proportioning methods and

test methods for performance. For

a macroporous material such as

pervious concrete, mixture propor-

tioning methods must aim at achieving

desired pore structure features that

dictate the required performance.

Characterization of the pore structure

thus becomes important in material

design and performance evaluation.

This article has provided details on

methods for characterizing pore

structure features such as porosity,

pore size, and pore connectivity.

Fig. 7: X-ray microtomography images of a typical pervious concrete specimen:

(a) a grayscale image; and (b) a color-thresholded image, with the pore space

represented in red

Fig. 8: 3D reconstruction of pervious concrete material structure from 2D images

The relative influence of the pore

structure features on the transport

behavior has been brought out.

Recent studies using X-ray microto-

mography for visualization of the

pore space, and computational

models for 3D reconstruction and

permeability prediction of pervious

concrete from real 2D images

promise to further advance quantitative

structure-property relationships for

this important class of materials.

References

1. ACI Committee 522, "Pervious

Concrete (ACI 522R-06)," American Concrete

Institute, Farmington Hills, MI, 2006, 25 pp.

(a) (b)

O

riginal 2D image

Reconstructed 3D image

Representative slices

from the 3D image

40 MAY 2010 /

Concrete international

ACI member Narayanan Neithalath is an

Associate Professor in the Department of

Civil and Environmental Engineering at

Clarkson University, Potsdam, NY. He

received his MS in civil engineering from

the Indian Institute of Technology, Madras,

Chennai, India, and his PhD in civil

engineering from Purdue University, West

Lafayette, IN. He is a member of ACI

Committees 123, Research and Current Developments; 232, Fly

Ash and Natural Pozzolans in Concrete; and 236, Material

Science of Concrete; and he is the Secretary of Committee 522,

Pervious Concrete. His research interests include hydration and

microstructure of cementitious systems, enhanced porosity

concretes, noninvasive sensing, and sustainable materials.

ACI member Dale P. Bentz is a Chemical

Engineer in the Materials and Construction

Research Division, National Institute of

Standards and Technology, Gaithersburg,

MD. He is a member of ACI Committees 231,

Properties of Concrete at Early Ages; 236,

Material Science of Concrete; and 308,

Curing Concrete. Bentz was a co-recipient

of the 2007 ACI Wason Medal for Materials

Research. His research interests include experimental and

computer modeling studies of the microstructure and performance

of cement-based materials.

ACI member Milani S. Sumanasooriya is a

Graduate Student in the Department of Civil

and Environmental Engineering, Clarkson

University, Potsdam, NY. She received her

bachelor's degree from the University of

Perandeniya, Perandeniya, Sri Lanka. Her

research interests include the characterization

and modeling of macroporous concretes.

2. Meininger, R.C., "No-Fines Pervious Concrete for Paving,"

Concrete International, V. 10, No. 8, Aug. 1988, pp. 20-27.

3. Tennis, P.D.; Leming, M.L.; and Akers, D.J., Pervious Concrete

Pavements, Portland Cement Association, Skokie, IL, 2004, 36 pp.

4. Deo, O.; Bhayani, B.; Holsen, T.M.; and Neithalath, N., "Modeling

the Retention of Oil in Enhanced Porosity Concretes," 2008 Concrete

Technology Forum Conference Proceedings (CD-ROM), National

Ready Mixed Concrete Association, 2008, 10 pp.

5. Low, K.; Harz; D.; and Neithalath, N., "Statistical Characterization

of the Pore Structure of Enhanced Porosity Concrete," 2008

Concrete Technology Forum Conference Proceedings (CD-ROM),

National Ready Mixed Concrete Association, 2008, 10 pp.

6. Neithalath, N., "Development and Characterization of Acoustically

Efficient Cementitious Materials," PhD thesis, Purdue University,

West Lafayette, IN, 2004, 269 pp.

7. Montes, F., and Haselbach, L., "Measuring Hydraulic Conductivity

on Pervious Concrete," Environmental Engineering Science, V. 23,

No. 6, 2006, pp. 960-969.

8. Wang, K.; Schaefer, V.R.; Kevern, J.T.; and Suleiman, M.T.,

"Development of Mix Proportion for Functional and Durable

Pervious Concrete," 2006 Concrete Technology Forum Proceedings

(CD-ROM), National Ready Mixed Concrete Association, 2006,

12 pp.

9. Neithalath, N.; Weiss, J.; and Olek, J., "Characterizing Enhanced

Porosity Concrete Using Electrical Impedance to Predict Acoustic

and Hydraulic Performance," Cement and Concrete Research, V. 36,

No. 11, Nov. 2006, pp. 2074-2085.

10. Marolf, A.; Neithalath, N.; Sell, E.; Wegner, K.; Weiss, J.; and

Olek, J., "Influence of Aggregate Size and Gradation on Acoustic

Absorption of Enhanced Porosity Concrete," ACI Materials Journal,

V. 101, No. 1, Jan.-Feb. 2004, pp. 82-91.

11. Neithalath, N.; Weiss, J.; and Olek, J., "Reducing the Noise

Generated in Concrete Pavements through Modification of Surface

Characteristics," Portland Cement Association R&D Serial No. 2878,

Portland Cement Association, Skokie, IL, 2004, 122 pp.

12. Underwood, E.E., Quantitative Stereology, Addison-Wesley

Publishing Co., Reading, MA, 1970, 284 pp.

13. Sumanasooriya, M.S., and Neithalath, N., "Stereology- and

Morphology-Based Pore Structure Descriptors of Enhanced Porosity

(Pervious) Concretes," ACI Materials Journal, V. 106, No. 5, Sept.-Oct.

2009, pp. 429-438.

14. Berryman, J.G., and Blair, S.C., "Use of Digital Image Analysis

to Estimate Fluid Permeability of Porous Materials: Application of

Two-Point Correlation Functions," Journal of Applied Physics, V. 60,

1986, pp. 1930-1938.

15. Bentz, D.P., "Virtual Pervious Concrete: Microstructure,

Percolation, and Permeability," ACI Materials Journal, V. 105, No. 3,

May-June 2008, pp. 297-301.

16. Torquato, S., Random Heterogeneous Materials: Microstructure

and Macroscopic Properties, Springer Science and Business Media,

2002, 701 pp.

17. Katz, A.J., and Thompson, A.H., "Quantitative Prediction of

Permeability in Porous Rock," Physical Review B, V. 34, No. 11, 1986,

pp. 8179-8181.

18. Sumanasooriya, M.S.; Bentz, D.P.; and Neithalath, N.,

"Predicting the Permeability of Pervious Concretes from Planar

Images," 2009 Concrete Technology Forum Conference Proceedings

(CD-ROM), National Ready Mixed Concrete Association, 2009, 11 pp.

Note: Additional information on the ASTM standards discussed

in this article can be found at www.astm.org.

Received and reviewed under Institute publication policies.

... pervious concrete properties such as strength and permeability while Lian and Zhuge [6] proposed an optimal mix design for enhanced permeability concrete with sufficient compressive strength and permeability. It is known from porositypermeability relationship developed in the literature that there is a general trend of increasing permeability with porosity and porosity alone cannot determine permeability [8]. In fact, it was found from the literature that the actual volume of interconnected voids in pervious concrete mixtures is the key parameter that directly affects permeability characteristics of pervious concrete pavements [8,9]. ...

... It is known from porositypermeability relationship developed in the literature that there is a general trend of increasing permeability with porosity and porosity alone cannot determine permeability [8]. In fact, it was found from the literature that the actual volume of interconnected voids in pervious concrete mixtures is the key parameter that directly affects permeability characteristics of pervious concrete pavements [8,9]. ...

Pervious concrete is a special class of concrete with sufficient continuous void structure resulting in the increase of drainage, skid resistance and acoustic characteristics. The paper attempts to investigate the effect of pore network properties obtained using advanced image processing techniques on the non-Darcy permeability characteristics of pervious concrete samples obtained from the same batch mixing process. Twelve different pervious concrete samples for a single pervious concrete mixture were produced in the laboratory using batch mixing and its internal pore network structure was obtained using medical X-ray computed tomography (XRCT) and digital image processing. The pore network structure from the XRCT scan is then adopted into a finite-volume computational fluid dynamics permeability simulation model to evaluate how pore network characteristics can affect non-Darcy permeability coefficients. The key microstructural parameters of the pervious concrete air voids and solids were analyzed in the paper, and it was found that an increase in non-Darcy permeability coefficient can be attributed to higher effective porosity, mean effective pore volume, throat area and coordination number properties. Overall, the findings presented in the paper can help in future optimization of pervious concrete mixture design and provide an understanding towards future works on pavement mixture quality control.

... The optimum pervious concrete mix was determined by casting pervious concrete cubes to obtain optimum cement content, size of coarse aggregate, and water-to-cement ratio (w/c) based on compressive strength and water permeability. According to ACI (2010) and previous studies [39], pervious concrete was made according to the cement/coarse aggregate ratio by mass (1:3, 1:4, 1:5, 1:6, and 1:7), size of coarse aggregate (5e10, 10e14, and 14e20 mm), and w/c ratio (0.25, 0.30, 0.35, and 0.4). All specimens were molded into 100 Â 100 Â 100 mm cubes. ...

Waste palm oil products can be recycled in the production of pervious geopolymer concrete (PGC) for long-term sustainable development. PGC is a non-slip porous pavement concrete that allows water to pass through. Biomass aggregate (BA) is produced by burning palm oil biomass and is introduced as a replacement for natural aggregate (NA). BA is mixed with fly ash (FA) and alkaline liquid (AL) and heated in an oven at 80 °C for 24 h to produce coated biomass aggregate (CBA). PGC containing CBA is commonly used as a cement substitute in concrete. This study aims to develop and evaluate the effect of rainfall intensity on the ability of PGC to reduce stormwater runoff. Coating BA with geopolymer paste resulted in improved properties, better Aggregate crushing value (ACV), Aggregate impact value (AIV), water absorption and higher compressive strength compared with BA. Results indicated, a PGC with a FA/CBA ratio of 1:7, CBA of 5–10 mm, NaOH molarity of 10 M, Na2SiO3/NaOH ratio of 2.5, and AL/FA ratio of 0.5 when cured in an oven for 24 h at 80 °C, gave the optimum ratio for compressive strength of 13.7 MPa and water permeability of 2.1 cm/sec. Both BA and CBA revealed a viable alternative aggregates for producing PGC and that the compressive strength of PGC made with CBA was 51% greater than cement pervious concrete containing NA. The results also showed that the reduction in runoff was due to the permeable concrete and decreased runoff with the increased rainfall intensity.

... Figure 12 shows nonlinear relationship between the porosity and permeability for 19 subsets. This trend is in common with exponential porosity-permeability curve obtained by NeithAlAth et al. (2010) in macroporous media such as concrete and Tan et al. (2020) which was found power relationship between permeability and porosity after dissolution in carbonate sample. Furthermore, Gueven et al. (2017) showed the nonlinear trend for porosity-permeability curve; again, there was a nonlinear trend, but by increasing permeability, the porosity increased. ...

  • Fateme Shamsi
  • Saeid Norouzi-Apourvari Saeid Norouzi-Apourvari
  • Saeed Jafari

Image-based simulations at pore scale provide direct insight into the impact of the microstructure on flow and transport processes in porous media. Diffusion is an important mechanism of mass transfer in gas or liquid phases, confined in porous media. Similar to fluid flow, the diffusive transport in porous media is a strong function of pore size and structure. Although the effect of porosity, pore connectivity and constrictivity of homogeneous porous media on macroscopic properties is clear, this is not well understood for heterogeneous porous media. This study uses a dual-structural-scale medium to analyze the effect of topological and morphological parameters on effective properties such as permeability and the effective diffusivity. A synthetic porous medium was created by two sizes of small and large glass beads, and 3D pore structure image of the sample was captured by X-ray computed tomography technique. The Stokes and diffusion equations were directly solved on the extracted pore geometry of sample, using a finite element method. The results show a strong nonlinear relationship between constrictivity, as a morphological parameter, with permeability and effective diffusivity. Based on the results obtained from pore-scale imaging and modeling, the connectivity of the pore space is increased by decreasing the Euler number and consequently the permeability and effective diffusivity is increased. Good agreement between image-based computed effective diffusivity with that estimated by van Brakel and Heertjes empirical relation confirms the reliability of this relation for heterogeneous porous medium, which includes constrictivity in addition to porosity and tortuosity, as three important morphological properties.

... Figure 3a shows the microstructure of the porous layer with the porosity in black and Figure 3b the same picture thresholded with the porosity in white. The porosity is evaluated at around 30% in the porous layer for the four concrete references and this value is in good agreement with pervious concrete specifications [15]. The observation of the surface shows that most of the pores seem to be inter-connected and suggests potential high value in terms of water permeability in this porous layer (even if this parameter was not quantified experimentally). ...

... Therefore, a single value of pore size alone might not be sufficient to characterize the material behaviour. Indeed, a variety of studies have demonstrated that the mechanical, hydraulic and acoustic performance of PC are dependent on the PSD of the pore system [19,21,30]. Mercury intrusion porosimetry (MIP) is generally used to determine PSD of CIC. ...

Pervious concrete (PC) has gained renewed interest in the past decade due to its positive environmental impacts. Extensive research employing a variety of strategies has been conducted to improve the overall performance of PC. Numerous literatures have been published. With the advances in high performance pervious concrete (HPPC), widespread application of this material has been made possible. This paper reviews the state-of-the-art and state-of-the-practice research and application of PC. Emphasis has been laid on the pore system characterization (PSC) and its influence on the mechanical, hydraulic and acoustical properties of PC. Among the various applications of PC, this review focuses on its application as a sustainable pavement construction material.

Computational microstructure characterisation and reconstruction of materials with a cementitious nature are essential for understanding their behaviour and predicting properties in the macro scale. Modelling cementitious materials with a representative spatial scale with precise characterisation has troubled researchers for decades. Although numerous physical descriptors have been applied for the characterisation of cementitious materials, only a few of them describe high-order information within the microstructure such as spatial arrangements. In this work, we demonstrated the capturing of the spatial correlation in cementitious material using deep convolutional neural networks at multiple scales based on imaging data with nanoscale resolution. Our results revealed the presence of a spatial correlation in the cementitious system and give the first indication of its distribution among the diverse features of the microstructure. We also propose functions of the discovered correlation for representative scale determination of cement materials and suggest the implications for the reconstruction of the cement microstructure based on its spatial correlation.

The permeability characteristics is one of the most important properties of pervious concrete (PC), which represents the ability of water on the surface to drain through the pervious pavement structure. Its measuring is a sensitive key on the pervious concrete. Thus, this paper presents the experimental results of two commonly used laboratory test methods to measure the permeability of pervious concrete; namely falling-head (FH) method and constant-head (CH) method, to investigate the relationship between the examined methods and select the reliable method. Moreover, study the effect of aggregate gradation and ratio of cement to aggregate on the permeability of PC. Therefore, thirty-six groups of pervious concrete specimens with twelve different types of gradation and three kinds of ratios of cement to aggregates were prepared in this study. The comparison between the two methods to evaluate which method is more suitable includes: the precision, the cost of the experimental equipment, the convenience of the test operation process and the time required for the test. The results showed that the permeability values measured by the falling-head method were significantly higher than those measured by the constant-head method and it is more convenient compared to the constant-head method. Effect of aggregate gradation on porosity and permeability was examined in this study. Correlation between porosity and permeability was investigated, and a new model between FH and CH methods was established.

This paper presents a focused study on properties of porous concrete to widen its application to structural engineering. Mechanical properties like compressive strength, indirect tensile strength, flexural strength and physical properties like density, permeability and porosity are studied. To determine those parameters, twenty-seven cubes, cylinders and prisms were tested. Also, three polymer impregnated porous concrete slabs were tested under pure bending moment to study the efficiency of selected resin to integrate particle of concrete to achieve a new generation in using porous concrete in structural engineering. Three different cement content specimens of porous concrete were considered, studied cement contents are 200 kg/m 3 , 300 kg/m 3 and 400 kg/m 3. The results show that, increasing the cement content can increase the compressive strength, indirect tensile strength and flexural strength. Density of porous concrete is less than conventional concrete by 21% but permeability factor recorded higher value compared to conventional concrete by sixteen times. Increasing the cement content has no significant effect on either ultimate load or maximum deflection of polymer impregnated porous concrete slabs but the results recorded an achievement to use this concrete in structural engineering applications and give an easy way to cast special concrete like polymer concrete without special tools.

Both the porosity-based method and the paste coating thickness-based method are aimed to design pervious concrete with target porosity. However, the properties of pervious concrete are partially related to its porosity, leading to their poor precision and repeatability. Actually, the skeleton structures of pervious concrete, which govern the permeability of pervious concrete, can be characterized by the number of contact zones, the width of contact zones, and the paste thickness between neighboring aggregates, and the mechanical properties are also influenced by the strengths of cement paste and aggregate. Therefore, the relationships between fundamental properties and the skeleton structures of pervious concrete must be clarified prior to the mixture proportion design. In the present study, structurally-designed pervious concretes were prepared by rationally changing their skeleton structures. Then the compressive strength and permeability of pervious concretes were measured and corelated to their skeleton structures and the strength of cement paste. Based on the empirical equations established, a new mixture proportion design method for pervious concrete was proposed to achieve the target compressive strength and permeability. Experimental validation presented that the design method has higher reliability, precision, and adaptability.

  • Junbo Sun
  • Junfei Zhang Junfei Zhang
  • Yunfan Gu
  • Guowei Ma

Pervious concrete is a widely used construction material thanks to its good drainage characteristics. Before application, its most important properties, i.e. the permeability coefficient (PC) and 28-day unconfined compressive strength (UCS) are required to be tested. However, conducting PC and UCS tests with multiple influencing variables is time-consuming and costly. To address this issue, this paper proposed, for the first time, an evolved support vector regression (ESVR) tuned by beetle antennae search (BAS) to accurately and effectively predict the PC and UCS of pervious concrete. To prepare the dataset of the ESVR model, 270 specimens in total were prepared and casted in a controlled environment in the laboratory. The water-to-cement (w/c) ratio, aggregate-to-cement (a/c) ratio, and aggregate size were selected as the crucial influencing variables for the inputs, while PC and UCS were the outputs of this model. The results indicate that both the PC and UCS firstly increased and then decreased with increasing w/c ratio. As the a/c ratio increased, PC increased, while UCS decreased. Moreover, BAS is more reliable and efficient than random hyper-parameter selection for hyper-parameter tuning. A low root-mean-square error (RMSE) and high correlation coefficient (R) indicate a relatively high predictive capability of the proposed ESVR model. The sensitivity analysis (SA) suggests the a/c ratio and aggregate size were the most sensitive variables for UCS and PC, respectively. This pioneering work provides a simple and convenient method for evaluating PC and UCS of pervious concrete.

Portland cement pervious concrete (PCPC) mixes made with various types and amounts of aggregates, cementitious materials, fibers, and chemical admixtures were evaluated. Porosity, water permeability, strength, and freezing-thawing durability of the concrete were tested. The results indicated that the PCPC made with single-sized coarse aggregates generally had high permeability but not adequate strength. Addition of a small amount of fine sand (approximate 7% by weight of total aggregate) to the mixes significantly improved the concrete strength and freezing-thawing resistance while maintaining adequate water permeability. Addition of a small amount of fiber to the mixes increased the concrete strength, freezing-thawing resistance as well as void content. Based on these results, performance-based criteria are discussed for proportioning functional and durable PCPC mixes.

  • Paul Tennis Paul Tennis
  • Michael L. Leming
  • David J. Akers

Pervious concrete as a paving material has seen renewed interest due to its ability to allow water to flow through itself to recharge groundwater and minimize stormwater runoff. This introduction to pervious concrete pavements reviews its applications and engineering properties, including environmental benefits, structural properties, and durability. Both hydraulic and structural design of pervious concrete pavements are discussed, as well as construction techniques.

  • D. P. Bentz D. P. Bentz

As the usage of pervious concrete continues to increase dramatically, a better understanding of the linkages between microstructure, transport properties, and durability will assist suppliers in mixture proportioning and design. This paper presents various virtual pervious concrete microstructural models and compares their percolation characteristics and computed transport properties to those of real world pervious concretes. Of the various virtual pervious concretes explored in this study, one based on a correlation filter three-dimensional reconstruction algorithm clearly provides a void structure closest to that achieved in real pervious concretes. Extensions to durability issues, such as freezing-and-thawing resistance and clogging, that use further analysis of the virtual pervious concrete's void structure are introduced.

This paper presents results from an investigation aimed at identifying whether enhanced porosity concrete (EPC) may have the potential to be used for sound mitigation purposes. Toward this end, EPC mixtures were prepared using single sized aggregates as well as blends consisting of two different aggregate sizes. In addition, mixtures were prepared to determine the influence of sand content and silica fume on the measured acoustic characteristics and mechanical properties of EPC. All mixtures were tested for sound absorption using an acoustic impedance tube and flexural strength using three-point bending. An image analysis procedure was used to characterize the total porosity and size of the pores for each mixture. Differences in aggregate grading were observed to result in variations in both the acoustic absorption and flexural strength. These variations are directly related to both total porosity and pore size. The results of this research indicate that EPC mixtures with single sized aggregates provide substantial improvement to sound absorption as compared to conventional concrete. Blending aggregates in correct proportions enables the pore size and overall porosity to be controlled resulting in an improvement in the acoustic absorption. The influence of specimen length on the frequency at which maximum absorption is achieved is discussed and a simple conceptual model is used to illustrate the influence of pore structure on the sound absorption properties.

  • Narayanan Neithalath Narayanan Neithalath

Tire-pavement interaction noise is one of the significant environmental issues in highly populated urban areas situated near busy highways. The understanding that methodologies to reduce the sound at the source itself is necessary, has led to the development of porous paving materials. This thesis outlines the systematic research effort conducted in order to develop and characterize two different types of sound absorbing cementitious materials--Enhanced Porosity Concrete (EPC), that incorporates porosity in the non-aggregate component of the mixture, and Cellulose-Cement Composites, where cellulose fibers are used as porous inclusions. The basic tenet of this research is that carefully introduced porosity of about 15%-25% in the material structure of concrete will allow sound waves to pass through and dissipate its energy. The physical, mechanical, and acoustic properties of EPC mixtures are discussed in detail. Methods are developed to determine the porosity of EPC. The total pore volume, pore size, and pore connectivity are the significant features that influence the behavior of EPC. Using a shape-specific model, and incorporating the principle of acoustic wave propagation through semi-open cells, the acoustic absorption in EPC has been modeled. The pore structure and performance of EPC is characterized using Electrical Impedance Spectroscopy. Using a multi-phase conducting model, a pore connectivity factor has been developed, that correlates well with the acoustic absorption coefficient. A falling head permeameter has been designed to ascertain the water permeability of EPC mixtures. A hydraulic connectivity factor is proposed, which could be used to classify EPC mixtures based on their permeability. Electrical conductivity is shown to be a single measurable parameter that defines the performance of EPC. Preliminary studies conducted on the freezing and thawing response of EPC are also reported. From several porous, compliant materials, morphologically altered cellulose fibers are chosen to be used as inclusions. The "macronodule" (aggregate-like, 2-8 mm in size) fibers are shown to be the most effective among the various morphologically altered cellulose fibers considered. The physical and mechanical properties (porosity, flexural and compressive strengths, modulus of elasticity), acoustic absorption, and the energy dissipating capacity (specific damping capacity) are evaluated. Composite mixing relations have been used to model the loss modulus and loss tangent of these composites. The response of these composites to extreme exposure conditions has also been studied.

  • Richard C. Meininger

Results of a laboratory study of no-fines pervious concrete for paving are presented. Conclusions are drawn regarding the percent air voids needed for adequate permeability, the optimum water-cement ratio range, and the amounts of compaction and curing required. Recommendations are made regarding appropriate uses for this type of concrete.

  • Felipe Montes
  • Liv M. Haselbach Liv M. Haselbach

A computerized falling head permeameter system was used to measure hydraulic conductivity of pervious concrete from samples taken from three different field-placed slabs with known porosities. Important differences between samples were found, and these follow the same trend as differences in porosity. The relationship between porosity and hydraulic conductivity is suggested as a tool for designing pervious concrete pavements as a stormwater pollution best management practice. A quantitative relationship between porosity and hydraulic conductivity was established based on the Carman-Kozeny equation for the samples tested. Samples with porosities less than 15% presented limited hydraulic conductivity. Important considerations on the measurement of hydraulic conductivity of pervious concrete samples are discussed, and the Ergun equation is used to explore the flow regime inside pervious concrete samples.

  • Salvatore Torquato

Motivation and overview * PART I Microstructural characterization * Microstructural descriptors * Statistical mechanics of particle systems * Unified approach * Monodisperse spheres * Polydisperse spheres * Anisotropic media * Cell and random-field models * Percolation and clustering * Some continuum percolation results * Local volume fraction fluctuation * computer simulation and image analysis * PART II Microstructure property connections * Local and homogenized equations * Variational Principles * Phase-interchange relations * Exact results * Single-inclusion solutions * Effective medium approximations * Cluster expansions * Exact contrast expansions * Rigorous bounds * Evaluation of bounds * Cross-property relations * Appendix A Equilibrium Hard disk program * Appendix B Interrelations among 2-3D moduli* References * Index

  • James G Berryman James G Berryman
  • S.C. Blair

Scanning electron microscope images of cross sections of several porous specimens have been digitized and analyzed using image processing techniques. The porosity and specific surface area may be estimated directly from measured two‐point spatial correlation functions. The measured values of porosity and image specific surface were combined with known values of electrical formation factors to estimate fluid permeability using one version of the Kozeny‐Carman empirical relation. For glass bead samples with measured permeability values in the range of a few darcies, our estimates agree well (±10–20%) with the measurements. For samples of Ironton‐Galesville sandstone with a permeability in the range of hundreds of millidarcies, our best results agree with the laboratory measurements again within about 20%. For Berea sandstone with still lower permeability (tens of millidarcies), our predictions from the images agree within 10–30%. Best results for the sandstones were obtained by using the porosities obtained at magnifications of about 100× (since less resolution and better statistics are required) and the image specific surface obtained at magnifications of about 500× (since greater resolution is required).

Enhanced Porosity Concrete (EPC) is manufactured by gap grading coarse aggregates to create interconnected porosity in the system. The porosity and physical features of the pore network are characterized in this paper using Electrical Impedance Spectroscopy (EIS). Porosity alone was found to be an inaccurate indicator of the electrical conductivity of the sample. While several studies have shown that a conventional form of Archie's law can describe porous systems, it was observed that Archie's law did not completely describe the electrical conductivity of the EPC system. Therefore, a modified version of Archie's law was used that incorporated the matrix conductivity, which described the system more accurately than the conventional form. The pore connectivity factor determined using EIS is found to be linearly related to the acoustic absorption of the material. Similarly, conductivity results determined from EIS were used with total porosity to compute the hydraulic connectivity factor. This factor was related to intrinsic permeability calculated from hydraulic conductivity (measured using a falling head permeameter). Based on these studies, it appears that a single electrical impedance test could provide information for the design, quality control/quality assurance, and utilization of EPC.