1. INTRODUCTION
⌅According
to ACI, Pervious Concrete is a highly porous concrete that can be used
combinedly as a pavement and drainage system. In recent times, pervious
concrete has been the most significant development in concrete
technology and had a profound environmental benefit. It is a special
type of concrete made with or without the inclusion of fine aggregate
content than a normal conventional type of concrete. It is widely used
in pedestrian footpaths, car parks, sidewalks, car washing areas,
efficient sanitization systems, and slope stability in hilly areas and
other low-traffic areas (1-41.
Wang, H.; Li, H.; Liang, X.; Zhou, H.; Xie, N.; Dai, Z. (2019)
Investigation on the mechanical properties and environmental impacts of
pervious concrete containing fly ash based on the cement-aggregate
ratio. Constr. Build. Mater. 202, 387-95. https://doi.org/10.1016/j.conbuildmat.2019.01.044.
2.
Nguyen, D.H.; Boutouil, M.; Sebaibi, N.; Baraud, F.; Leleyter, L.
(2017) Durability of pervious concrete using crushed seashells. Constr. Build. Mater. 135, 137-50. https://doi.org/10.1016/j.conbuildmat.2016.12.219.
3. Calkins, J.; Kney, A.; Suleiman, M.T.; Weidner, A. (2010) Removal of heavy metals using pervious concrete material. World Environ. Wat. Res. Cong. 37, 74-83.
4.
Gaedicke, C.; Marines, A.; Miankodila, F. (2014) A method for comparing
cores and cast cylinders in virgin and recycled aggregate pervious
concrete. Constr. Build. Mater. 52, 494-503. https://doi.org/10.1016/j.conbuildmat.2013.11.043.
).
Pervious concrete provides many advantages when used as pavement
material, it recharges the groundwater, and it eliminates the need for a
2 to 3% slope to prevent ponding (55.
Ali, T.K.M.; Hilal, N.; Faraj, R.H.; Al-Hadithi, A.I. (2020) Properties
of eco-friendly pervious concrete containing polystyrene aggregates
reinforced with waste PET fibers. Innov. Infrastruct. Solut. 77, 1-16. https://doi.org/10.1007/s41062-020-00323-w.
). It minimizes the heat island effect (6-96.
Nazeer, M.; Kapoor, K.; Singh, S.P. (2023) Strength and microstructural
properties of pervious concrete made with different powder to aggregate
ratios. Eur. J. Environ. Civ. Eng. 1-25. https://doi.org/10.1080/19648189.2023.2168763.
7.
Ramkrishnan, R.; Abilash, B.; Trivedi, M.; Varsha, P.; Varun, P.;
Vishanth, S. (2018) Effect of mineral admixtures on pervious concrete. Mater. Today Proc. 5 [11], 24014-24023. https://doi.org/10.1016/j.matpr.2018.10.194.
8.
Lu, G.; Liu, P.; Wang, Y.; Fabender, S.; Wang, D.; Oeser, M. (2019)
Development of a sustainable pervious pavement material using recycled
ceramic aggregate and bio-based polyurethane binder. J. Clean. Prod. 220, 1052-1060. https://doi.org/10.1016/j.jclepro.2019.02.184.
9. Yang, J.; Jiang, G. (2003) Experimental study on properties of pervious concrete pavement materials. Cem. Conc. Res. 33 [3], 381-386. https://doi.org/10.1016/S0008-8846(02)00966-3.
).
Moreover, pervious concrete as pavement material generates less noise
from traffic and low thermal conduction as compared to asphalt or
conventional rigid pavement (1010.
Aman, A.M.N.; Selvarajoo, A.; Chong, S.; Teo, F.Y. (2022) Comparative
life cycle assessment of pervious concrete production in Malaysia with
natural and recycled aggregate. Innov. Infrastruct. Solut. 7, 211. https://doi.org/10.1007/s41062-022-00801-3.
, 1111.
Zhang, Y.; Li, H.; Abdelhady, A.; Yang, J. (2020) Effect of different
factors on sound absorption property of porous concrete. Transp. Res. Part D. 87, 102532. https://doi.org/10.1016/j.trd.2020.102532.
).
For its diverse environmental benefits, it was also tagged as the best
stormwater mechanism by Environmental Protection Agency (EPA) and Low
Impact Development (LID) system (12-1412.
Ibrahim, A.; Mahmoud, E.; Yamin, M.; Chowdary, V. (2013) Experimental
study on Portland cement pervious concrete mechanical and hydrological
properties. Constr. Build. Mater. 50, 524-529. https://doi.org/10.1016/j.conbuildmat.2013.09.022.
13.
Wang, H.; Li, H.; Liang, X.; Zhou, H.; Xie, N.; Dai, Z. (2019)
Investigation on the mechanical properties and environmental impacts of
pervious concrete containing fly ash based on the cement-aggregate
ratio. Constr. Build. Mater. 202, 387-395. https://doi.org/10.1016/j.conbuildmat.2019.01.044.
14.
Neptune, A. (2008) Investigation of the effects of aggregate properties
and gradation on pervious concrete mixtures. Thesis. 1-154. Retrieved
from: https://tigerprints.clemson.edu/cgi/viewcontent.cgi?article=1460&context=all_theses.
).
As per reports of ACI, the normal size of pores in pervious concrete
fluctuates between 2-4 mm and it may vary due to several aspects such as
powder to aggregate ratio, water to cement ratio, and size and shape of
aggregates (15-1715. Kia, A.; Wong, H.S.; Cheeseman, C.R. (2019) High-strength clogging resistant permeable pavement. Int. J. Pavement Eng. 22 [3], 271-282. https://doi.org/10.1080/10298436.2019.1600693.
16.
Liu, R.; Chi, Y.; Chen, S.; Jiang, Q.; Meng, X.; Wu, K. (2020)
Influence of pore structure characteristics on the mechanical and
durability behavior of pervious concrete material based on image
analysis. Int. J. Concr. Struct. Mater. 14, 29. https://doi.org/10.1186/s40069-020-00404-1.
17.
El-Hassan, H.; Kianmehr, P.; Zouaoui, S. (2019) Properties of pervious
concrete incorporating recycled concrete aggregates and slag. Constr. Build. Mater. 212, 164-175. https://doi.org/10.1016/j.conbuildmat.2019.03.325.
).
Moreover, the porosity of pervious concrete ranges between 15% to 30% (1818. Wang, K.; Schaefer, V.R.; Kevern, J.T. (2015) Development of mix proportion for functional and durable pervious concrete. NRMCA Con. Tech. Forum. 1-12.
, 1919. Mulyono, T.; Anisah, M.T. (2019) Properties of pervious concrete with various types and sizes of aggregate. MATEC Web Conf. 276, 01025. https://doi.org/10.1051/matecconf/201927601025.
).
However, there is serious concern that due to high turbid runoffs
containing fine silt, sand, and clay and frequent erosion of organic and
inorganic fine particles from surroundings, temporary chocking of
pervious concrete pavement. This temporary accumulation of these fine
materials inside the pores leads to the clogging of pavement made with
pervious concrete (20-2220.
Lim, E.; Hwee, K.; Fang, T. (2013) Effect of mix proportion on strength
and permeability of pervious concrete for use in pavement. J. East. Asia Soc. Tran. Studies. 1-11.
21.
Yeih, W.; Fu, T.C.; Chang, J.J.; Huang, R. (2015) Properties of
pervious concrete made with air-cooling electric arc furnace slag as
aggregates. Constr. Build. Mater. 93, 737-745. https://doi.org/10.1016/j.conbuildmat.2015.05.104.
22.
Chopra, M.; Asce, M.; Kakuturu, S.; Asce, A.M.; Ballock, C.; Asce, A.M.
(2010) Effect of rejuvenation methods on the infiltration rates of
pervious concrete pavements. J. Hyd. Eng. 15 [6], 426-33. https://doi.org/10.1061/(ASCE)HE.1943-5584.0000117.
). Therefore, the efficacy of pervious concrete when used as pavement decreases due to diminishing hydraulic permeability (2323.
Singh, D.; Singh, S.P. (2020) Influence of recycled concrete aggregates
and blended cements on the mechanical properties of pervious concrete. Innov. Infrastruct. Solut. 5, 66. https://doi.org/10.1007/s41062-020-00314-x.
).
Thus, the problem of serviceability and premature degradation starts at
an early age and cuts the service life of pervious concrete pavement.
When a significant percentage of pores in the previous concrete pavement
gets clogged, water starts pooling on the surface and causes
waterlogging of pervious concrete pavement. Moreover, the standing water
over the road surface for a long time accelerates the deterioration of
the pervious concrete pavement and sometimes causes unpleasant nuisance
and water-borne diseases (24-2724.
Aliabdo, A.A.; Abd Elmoaty, A.E.M.; Fawzy, A.M. (2018) Experimental
investigation on permeability indices and strength of modified pervious
concrete with recycled concrete aggregate. Constr. Build. Mater. 193, 105-27. https://doi.org/10.1016/j.conbuildmat.2018.10.182.
25. Sun, Z.; Lin, X.; Vollpracht, A. (2018) Pervious concrete made of alkali activated slag and geopolymers. Constr. Build. Mater. 189, 797-803. https://doi.org/10.1016/j.conbuildmat.2018.09.067.
26. Aydin, S.; Yazici, H. (2010) Effect of aggregate type on mechanical properties of RPC. J. Mod. Tech. Eng. 107 [5], 441-449.
27.
Zhang, Z.; Zhang, Y.; Yan, C.; Liu, Y. (2017) Influence of crushing
index on properties of recycled aggregates pervious concrete. Constr. Build. Mater. 135, 112-118. https://doi.org/10.1016/j.conbuildmat.2016.12.203.
).
However, a small amount of research is available on averting the
clogging problems in pervious concrete pavement systems. Different
maintenance and rejuvenation techniques such as vacuuming, pressure
washing, and sweeping have been adopted (28-3028. Sun, Z.; Lin, X.; Vollpracht, A. (2018) Pervious concrete made of alkali activated slag and geopolymers. Constr. Build. Mater. 189, 797-803. https://doi.org/10.1016/j.conbuildmat.2018.09.067.
29.
Kayhanian, M.; Anderson, D.; Harvey, J.T.; Jones, D.; Muhunthan, B.
(2012) Permeability measurement and scan imaging to assess clogging of
pervious concrete pavements in parking lots. J. Environ. Manage. 95 [1], 114-23. https://doi.org/10.1016/j.jenvman.2011.09.021.
30.
Deo, O.; Asce, M.; Sumanasooriya, M.; Asce, M.; Neithalath, N. (2010)
Permeability reduction in pervious concretes due to clogging:
experiments and modeling. J. Mat. Civil Eng. 22 [7], 741-751. https://doi.org/10.1061/(ASCE)MT.1943-5533.0000079.
). However, all these techniques show limited results as these were effective only to a depth of 15- 20 mm (3131. Bean, E.Z.; Hunt, W.F.; Bidelspach, D.A. (2007) Field survey of permeable pavement surface infiltration rates. J. Irrig. Drain. Eng. 133 [3], 249-255. https://doi.org/10.1061/(ASCE)0733-9437(2007)133:3(249).
).
Some
authors have investigated surface cleaning with pressurized water and
air-blowing techniques and suggested that the air-blowing technique is
the best practice to de-clog the choking (3232.
Sandoval, G.F.B.; de Moura, A.C.; Jussiani, E.I.; Andrello, A.C.;
Toralles B.M. (2020) Proposal of maintenance methodology for pervious
concrete (PC) after the phenomenon of clogging. Constr. Build. Mater. 248, 118672. https://doi.org/10.1016/j.conbuildmat.2020.118672.
).
Others have investigated that the combined effect of sand and clay
produces a flash downfall in permeability as seen for single loaded
sediment such as single sand or single clay cycle of runoff, however,
complete blocking of pores was seen between 2 to 13 cycles of artificial
runoff (3333.
Winston, R.J.; Al-Rubaei, A.M.; Blecken, G.T.; Viklander, M.; Hunt,W.F.
(2016) Maintenance measures for preservation and recovery of permeable
pavement surface infiltration rate - The effects of street sweeping,
vacuum cleaning, high pressure washing and milling. J. Environ. Manage. 169, 132-44. https://doi.org/10.1016/j.jenvman.2015.12.026.
).
Gersson studied the effect of fine sediments over the clogging of
pervious concrete and found that fine sediment is more damaging for a
reduction in hydraulic conductivity due to the smaller size of sediments
(3434.
Sandoval, G.F.B.; Galobardes, I.; Toralles, B.M. (2020) Assessing the
phenomenon of clogging of pervious concrete (Pc): Experimental test and
model proposition. J. Buil. Eng. 29, 101203. https://doi.org/10.1016/j.jobe.2020.101203.
).
Haselbach performed the clogging of pervious concrete using clay
sediments and found that the rate of clogging depends on the density of
rinsing runoff. Moreover, it was observed that less cohesive sediments
can be removed easily by applying sweeping as compared to more cohesive
soils (3535. Haselbach, L.M.; Asce, M. (2010) Potential for clay clogging of pervious concrete under extreme conditions. J. Hydr. Eng. 15 [1], 67-69. https://doi.org/10.1061/(ASCE)HE.1943-5584.0000154.
).
Alalea Kia found the critical condition of clogging happens due to
choking of top surface pores and traveling of fine particles to the
lower strata of samples. It was also mentioned that all the
rehabilitation techniques reestablish the permeation volume partially
and rehabilitation cannot work if choking happens a few centimeters
below the top surface of pervious concrete (3636. Kia, A.; Wong, H.S.; Cheeseman, C.R. (2017) Clogging in permeable concrete: A review. J. Environ. Manage. 193, 221-233. https://doi.org/10.1016/j.jenvman.2017.02.018.
).
2. RESEARCH SIGNIFICANCE
⌅Based on the literature survey presented in the preceding section indicates that a lot of research has been done to examine the strength and hydraulic properties of pervious concrete made with single grade proportion of aggregates. However, the information on clogging potential for pervious concrete made with different aggregate grade proportions is scanty. Therefore, an investigation has been developed on the effect of grade aggregate proportions on the clogging phenomenon of pervious concrete. In this study, three grades proportion of aggregates (P, Q, and R) were prepared from four aggregates proportions (A: B: C: D) such as 2.36 mm, 4.75 mm, 6.3 mm, and 10 mm. Moreover, to stimulate the actual sediment load conditions and to calculate actual load percentages, sieve and hydrometer analyses have also been done. Furthermore, other properties such as porosity, permeability, and compressive strength have been evaluated at 28 and 56 days of curing. Additionally, a visual inspection test through the half-cut method, dry cut method, and slicing method is performed to check the flow and depth of clogging sediment.
3. EXPERIMENTAL PROGRAMME
⌅The experimental program in this study was divided into two general findings. The first aim involves the determination of porosity, water permeability, and compressive strength. secondly, the clogging performance of pervious concrete was evaluated using three different sediment cloggers.
3.1. Materials
⌅The different materials utilized in this experimental study have been discussed in the following sub-sections.
3.1.1. Cement
⌅Ordinary Portland Cement (OPC) 43 grade, according to IS: 8112 (3737. IS: 8112-1989 (2013) Specification for 43 grade ordinary portland cement. Bur. Indian Stand. 1-17.
)
was used as a primary binder. The consistency was 32.5%, and the
fineness of 6% was determined as material properties in the present
investigation as per guidelines of IS 4031 (Part 2 and 4) (3838.
IS: 4031 (Part 2)-1999 (2004) Methods of physical tests for hydraulic
cement, Determination of fineness by specific surface by Blaine air
permeability method. Bur. Indian Stand. 1-13.
, 3939. IS: 4031-1988 (1988) Methods of physical tests for Hydraulic cement. Bu.r Indian Stand. 1-6.
).
The physical properties such as specific gravity (3.15), initial
setting time (40 minutes) and final setting time (240 minutes) were also
determined as preliminary testing of OPC binder.
3.1.2. Aggregates
⌅The three
different grades (P, Q, and R) of Natural Coarse Aggregates (NCA) and
Natural Fine Aggregates (NFA) have a size of 12-10 mm, 10-6.3 mm,
6.3-4.75 mm, and 4.75-2.36 mm were used in the ratio of A:B:C:D. The
different grades were used in the ratios of, 0:40:40:20, (i,e 0% of 2.36
mm, 40% of 4.75 mm, 40% of 6.3 mm, and 20% of 10 mm) for P, 10:40:40:10
(i,e 10% of 2.36 mm, 40% of 4.75 mm, 40% of 6.3 mm, and 10% of 10 mm)
for Q, and 20:40:40:0 (i,e 20% of 2.36 mm, 40% of 4.75 mm, 40% of 6.3
mm, and 0% of 10 mm) for R, respectively. Natural Fine Aggregates, 2.36
mm was obtained locally and was utilized in the ratios of 0%, 10%, and
20% as per IS 383 guidelines (4040. IS: 383-1970 (1970) Specification for coarse and fine aggreagtes from natural sources for concrete. Bur. Indian Stand. 1-24.
). The particle distribution for all three grades (P, Q, and R) is plotted as per IS 2386 (part 1) (4141. IS: 2386- Part I (2002) Method of test for aggregate for concrete. Particle size and shape. Bur. Indian Stand1-26.
) and presented in Figure 1. Moreover, the different physical properties and their standards are presented in Table 1.
| Aggregate properties | 2.36 mm (NFA) | 4.75 mm (NCA) | 6.3 mm (NCA) | 10 mm (NCA) | Testing standards |
|---|---|---|---|---|---|
| Impact value (%) | - | 13.36 | 13.10 | 13.00 | IS:2386-Part-IV (5353. IS: 2386-Part IV. (2016) Methods of test for aggregates for concrete: Mechanical properties. Bur. Indian Stand. New Delhi. 1-37. ) |
| Abrasion value (%) | - | 20.86 | 19.00 | 18.03 | ASTM C 131 (5454.
ASTM C131M-20. (2014) C131/C131M-14 Standard test method for resistance
to degradation of small-size coarse aggregate by abrasion and impact in
the Los Angeles Machine. 5-8. ) |
| Water absorption (%) | 2.10 | 0.56 | 0.57 | 0.98 | ASTM C127 (5555. ASTM C 128-01 (2001) Standard test method for density, relative density (Specific gravity), and absorption. 1-6. ) |
| Soundness (%) | - | 5.70 | 5.68 | 5.30 | IS:2386-Part-V (5656.
Bureau of Indian Standards (BIS) (2002) IS:2386-Part V-1963: Methods of
test for aggregates for concrete. Indian Stand. 1-14. ) |
| Apparent density (kg/m3) | 2490 | 2445 | 2420 | 2410 | ASTM C127 - 15 (5757. ASTM C 127-01 (2001) Standard test method for relative density (Specific gravity) and absorption of coarse. 88, 1-6. ) |
| Bulk density (kg/m3) | 1795 | 1780 | 1765 | 1750 | ASTM C29/C29M (5858. ASTM C29/C29M − 17a. (2017) Standard test method for bulk density (Unit weight) and Voids in aggregate. 1, 5-9. ) |
3.1.3. Sediment load
⌅Sediment load for clogging was selected from the actual road dust sample and the particle size distribution is shown in Figure 2. It was seen from the results of the hydrometer that 70% of particles present in finer dust were clay and only 30% were silt. The loading rate of sediments used in this study was of the order of 50 grams of fine sand, 150 grams of kaolin clay, and 200 grams of sand and clay in combination were used as for sand (S), clay (C), and Combined “Sand & clay” (S & C) respectively.
3.2. PC mix proportions
⌅The mix proportions of the different pervious concrete mixes are presented in Table 2. All the quantities (cement and aggregates) are measured by taking the overall unit weight of pervious concrete as 1920 kg/m3. The basic mix proportions for all the mixes were taken following ACI-522R-s2010 (4242. NRMCA. Guide to Specifying Pervious Concrete.
). The pervious concrete mixes were made using a tilting drum mixer in the lab at the authors’ institute as shown in Figure 3.
A sufficient number of specimens were cast to conduct all the tests for
this study. Cylindrical samples (100×200 mm) were cast for porosity,
permeability, and clogging. However, for compressive strength testing,
cubes measuring 150 mm in size were cast.
| Mix Notation | Aggregate proportion (AP) | AP Notation | W/C ratio | P/A ratio | 2.36 mm (A) | 4.75 mm (B) | 6.3 mm (C) | 10 mm (D) | OPC Kg/m3 | Water Kg/m3 |
|---|---|---|---|---|---|---|---|---|---|---|
| P-A0 | 0%A+40%B+40%C+20%D | P | 0.35 | 1:5 | 0 | 640 | 640 | 320 | 320 | 112 |
| P-A10 | 10%A+40%B+40%C+10%D | Q | 0.35 | 1:5 | 160 | 640 | 640 | 160 | 320 | 112 |
| P-A20 | 20%A+40%B+40%C+0%D | R | 0.35 | 1:5 | 320 | 640 | 640 | 0 | 320 | 112 |
3.3. Test methods
⌅After 24 hours of casting, the specimen was demoulded and placed in a curing tank for 7, 28, and 56 days at room temperature conditions (20 ± 1°C while as humidity was maintained over 95%. All the testing procedures are discussed in the following sub-sections.
3.3.1. Porosity
⌅ASTM C1754 (2012) was used to evaluate the porosity of the pervious concrete (4343.
ASTM C1754/C1754-12. (2012) Standard test method for density and void
content of hardened pervious concrete. ASTM Stand. 1-3.
). The initial mass of the sample is taken in submerged condition as W1. The sample was then dried in an oven for 24 hours at 105 °C, and the dry mass of the sample in the air was taken as W2.
The porosity of three samples from each batch of pervious concrete was
taken and the final porosity was calculated as the average of the three
values. The porosity (P) was calculated using Equation [1].
Where P is the porosity of cylindrical sample, %; W1 is the mass of sample in dry condition, g; W2 is the mass of sample in submerged condition, g; V represents volume specimen, cm3; and ρw represents the density of water, g/cm3.
3.3.2. Permeability
⌅A falling head permeability apparatus as shown in Figure 4, was used to measure the permeability of pervious concrete. A cylindrical sample is fitted inside the black collar and a water head of 90 cm is maintained in a graduated PVC tube. A fabric inch tape and thin transparent pipe also adhere for head reading and piezometer purposes respectively. To ensure that the pervious concrete sample is saturated, valve (v1) is kept open initially and a trial is performed between a preliminary head (h1) of 90 cm and a bottom head (h2) of 30 cm. As the sample is saturated fully, the permeability test is performed by calculating the time (t) that it took from head (h1) to head (h2) using a stopwatch. Finally, the permeability was calculated using Darcy’s Equation [2].
Where K is permeability, A1 is the area of the head pipe, A2 is the specimen area, L is specimen length and ‘t’ is the time required for water to drop from the preliminary head h1 to bottom head h2.
3.3.3. Compressive strength
⌅A compressive strength test on pervious concrete was performed according to IS 516 (1959), (4444. IS: 516 (1959) Method of tests for strength of concrete. Bur. Indian Stand. 1-30.
). A compression testing machine with a 2000 kN maximum loading capability
was used to perform the compressive strength test of pervious concrete.
A sample size of 150 mm cube was loaded till failure at a rate of 5.2
kN/sec.
3.3.4. Clogging potential
⌅3.3.4.1. Permeability reduction
⌅The falling head permeability apparatus used for measurement of permeability was used to evaluate the outcome of artificial clogging in pervious concrete. Three cloggers (S, C, and S&C) were used to produce artificial runoff and permeability reductions are calculated using Darcy’s Equation [2].
3.3.4.2. Visual observation of clogging
⌅To know whether the blockage in the pore channel was at the top, bottom, or center, a visual inspection is necessary to perform. In this study visual inspection was performed through three techniques. a) Half-cut method: In this method, the clogged samples of pervious concrete are cut into two halves as shown in Figure 5 and the weight of each half is taken. It provides an idea of whether cloggers are present only on the top surface half or on the lower half. b) Dry cut method: It is a visual inspection in which a clogged sample is transversely cut into two halves as shown in Figure 6 to know the location of sediments inside the clogged sample. The sample is cut under CTM using upper and lower steel strips. C) Slicing method: Diamond saw cutter is used to cut the clogged sample into four halves as sown in Figure 7 to know the distribution and tortuosity of sediment flow.
3.3.4.3. Image Processing of clogging
⌅With the help of a high-resolution micro-focus X-ray computed tomography (X-CT) system and filter 7 image processing software, the exact presence of sediment was predicted with clear visuals. Moreover, the clogging of clogged sample was predicted through X-CT at three sections, top, mid, and bottom respectively.
3.3.4.4. Rejuvenation of clogging
⌅Two rejuvenation techniques are used to un-clog the clogged samples of pervious concrete are:
Eureka Forbes vacuum cleaner having a suction capacity of 2300 mm of WC (0.022 MPa) was used for vacuum treatment of clogging. Both the nozzles, floor cum carpet, and crevice nozzle were used to remove the sediment particles from cylindrical samples. Whereas, a car service pressure washer having 20.7 MPa (3,000 psi) pressure of water was used pressure washing treatment of clogging. Both the rejuvenation methods are intended to wash out the ingressed materials and regain the hydraulic functionality of clogged pervious concrete samples.
4. EXPERIMENTAL RESULTS AND DISCUSSION
⌅4.1. Porosity
⌅The porosity of all the mixes of pervious concrete made with different grade aggregate proportions is presented in Figure 8.
Porosity obtained in this study was in the range of 18 - 20% which is
in the qualified range of results observed in the literature (15-35%) (45-4845.
Haselbach, L.M.; Valavala, S.; Montes, F. (2006) Permeability
predictions for sand-clogged Portland cement pervious concrete pavement
systems. J. Environ. Manage. 81 [1], 42-49.
46. Ramadhansyah,
P.J.; Y M.I.M.; Hainin, M.R.; Warid, M.N.M.; Ibrahim, W. (2014) Porous
concrete pavement containing nano-silica: Pre-review. 911, 454-458.
47.
Yao, A.; Ding, H.; Zhang, X.; Hu, Z.; Hao, R.; Yang, T. (2018) Optimum
design and performance of porous concrete for heavy-load traffic
pavement in cold and heavy rainfall region of NE China. Adv. Mater. Sci. Eng. 2018, 7082897. https://doi.org/10.1155/2018/7082897.
48.
Ni, T.Y.; Jiang, C.H.; Tai, H.X., Zhao, G.Q. (2014) Experimental study
on sound absorption property of porous concrete pavement layer. Appl. Mech. Mater. 507, 238-241. https://doi.org/10.4028/www.scientific.net/AMM.507.238.
).
It was observed from the results that porosity of pervious concrete
across all the curing ages decreases marginally with changing the
aggregate grade proportion from P to R. For example, in the mix P-A10,
in which aggregate gradation Q was used having 10% of NFA content,
relative to pervious concrete control mix, P-A0 having 0% NFA, the
reduction in the porosity was 3% and 2.5% at 7 and 28 days respectively,
which is significant. However, for the mix containing R type of
aggregate gradation in which 20% of NFA was included, I,e mix P-A20, the
porosity reduction relative to control mix P-A0 at the curing age of 7
and 28 days was 8% and 10.25% respectively. The behavior is similar to
that observed in pervious concrete where similar reductions in porosity
have been reported in literature upon the inclusion of NFA with NCA (4949.
Neithalath, N.; Marolf, A.; Weiss, J.; Olek, J. (2005) Modeling the
influence of pore structure on the acoustic absorption of enhanced
porosity concrete. J. Adv. Concr. Technol. 3 [1], 29-40.
, 5050.
Neithalath, N.; Weiss, J.; Olek, J. (2015) Improving the acoustic
absorption of enhanced porosity concrete with fiber reinforcement. Int. RILEM. Symp. Concr. Sci. Eng. 1-16.
). It is obvious that porosity is a volumetric property, therefore the
volume of the void will depend upon a few parameters like the size of
aggregates, the proportion of fines, the amount of binder content, etc.
Generally, the pervious concrete prepared with a higher p/a ratio had
lower porosity due to the reduction of cement content than the mix
prepared with a lower p/a ratio. The increase in cement content
increases the packing density of the matrix, thereby reducing the
porosity of pervious concrete. Similarly, the effect of aggregate
gradation has the same effects on porosity that as the amount of fine
content is increased porosity decreases due to an increase in apparent
density of pervious concrete. The apparent density of mix containing 0%
of NFA (I, e mix P-A0) was 1960 kg/m3, while as the mix containing 10% and 20% of NFA have the apparent densities of the order of 1984 kg/m3 and 2009 kg/m3 respectively, which is 1.2% and 2.5% higher than the control mix.
Therefore, with increasing the values of apparent densities, porosity of
pervious concrete decreases significantly.
Furthermore, it was also observed from Figure 8 that at two different curing ages, a marginal decrease in the porosity of pervious concrete was seen. On comparing porosities of mix P-A0 at 7 and 28 days, a borderline decrease of 1% was seen at 28 days age of curing as compared to porosity seen at 7 days. This marginal decline in porosity after 28 days was due to further strength gain due to which the micropores of paste get filled and a marginal reduction in porosity is observed. Similarly, for mixes P-A10 and P-A20, a small decrease in the porosity of pervious concrete at 7 and 28 days was observed. A decrement of 0.5% and 0.3% in porosity of mix P-A10 and P-A20 respectively was seen at 28 days as compared to porosity observed at 7 days of curing age.
4.2. Permeability
⌅The water permeability tests on pervious concrete were performed at 7 and 28 days of curing age and are presented in Figure 9.
Here we assume the meaning of PC conferring to the American Concrete
Institute which mentions the working range of permeability coefficient
from 0.13-1.2 cm/s (5151. Committee ACI. (2015) ACI 522R-10 Report on pervious concrete. 10, 1-44.
). It can be seen from Figure 9 that pervious concrete shows a declinement in permeability with the
change in aggregate grade proportion from P to R. A maximum permeability
of 0.92 cm/s was seen for control mix P-A0, in which aggregate grade
proportion R was used, having 0% NFA content. A significant decrease in
permeability was seen for mix P-A10, in which Q type aggregate grade
proportion was included, having 20% NFA. For mix P-A10, a decrease of
4.5% and 5% at 7 and 28 days of curing was observed as compared to
control mix P-A0, which is a significant drop. Moreover, for mix P-A20,
in which R type aggregate grade proportion was used having 20% content
of NFA as compared to control mix P-A0. A significant drop in
permeability of pervious concrete was observed at 22% and 23% at the
curing ages of 7 days and 28 days as compared to the permeability of
control mix P-A0. It was further observed from the results of
permeability that a marginal drop in permeability was seen for all the
mixes of pervious concrete after 28 days of curing. For example, for the
control mix, P-A0, in which the NFA percentage was 0%, a reduction of
0.5% was seen at 28 days as related to 7 days. Moreover, a reduction of
0.5% and 1% in permeability was seen for mix P-A10 and P-A20
respectively after 28 days of curing as compared to 7 days of
permeability. This marginal drop in permeability at 28 days of curing
was due to the development in the microstructure of pervious concrete
which is also confirmed by enhancement in compressive strength after 28
days of curing. Therefore, readjustment of micropores is seen at higher
curing age due to which permeability drop is seen.
Furthermore, a relationship was developed between permeability and porosity of all the mixes as shown in Figure 10. It was observed from the relation that R2 holds a decent range of 0.9. Therefore, the permeability of pervious concrete can be projected from the initially calculated porosity.
4.3. Compressive strength
⌅The compressive strength results of the pervious concrete mixes made with three aggregate grade proportions are presented in Figure 11 which shows that the compressive strength of all the mixes increases
significantly with changing the aggregate grade proportions from P to R.
For example, significant development of 8%, 10% and 3% in compressive
strength was seen for mix P-A10 in which Q series of aggregate grade
proportion was used at curing age of 7, 28 and 56 days, relative to mix
P-A0, which is control mix. The significant development in the results
of compressive strength at all the curing ages was due to the inclusion
of 10% of NFA in the Q series of aggregate proportion, thereby due to
which the development in paste density magnifies the results of
compressive strength. However, for the mix containing R type series of
aggregates having 20% NFA content I, e mix P-A20, the strength
development relative to controller mix at 7, 28, and 56 days was 21%,
24%, and 15%, which is more prominent. A similar trend in the
development of compressive strength has been reported in the literature
that due to substitution of a fine up to 5% increases the mechanical
strength of pervious concrete (5252.
Ćosić, K.; Korat, L.; Ducman, V.; Netinger, I. (2015) Influence of
aggregate type and size on properties of pervious concrete. Constr. Build. Mater. 78, 69-76. https://doi.org/10.1016/j.conbuildmat.2014.12.073.
).
The significant increment in compressive strength with incorporation of
different percentages of NFA was due to the overall development in
apparent density of pervious concrete. It was observed from the results
that with incorporation of 10% of NFA, apparent density of pervious
concrete increases by 1.2% relative to mix containing 0% of NFA.
Moreover, a maximum increment of 2.5% in apparent density of pervious
concrete can be seen for mix containing 20% of NFA relative to P-A0,
containing 0% of NFA. Therefore, with increasing the apparent density of
pervious concrete, compressive strength increases significantly.
Furthermore, the development of compressive strength in pervious concrete shows optimum results at 28 days of curing for each mix as compared to the compressive strength of pervious concrete at 7 and 56 days. A prominent development of 43% in compressive strength was seen for the control mix, at 28 days as compared to 7 days strength. Nevertheless, the increase in strength for the same control mix, P-A0 at 56 days was only 17% as compared to compressive strength at 28 days. Moreover, the same increment in compressive strength for pervious concrete was seen for mix P-A10 and P-A20, in which aggregate grade proportion of Q and R type was used having 10% and 20% of NFA respectively. An increment of 45% and 46% was observed for mix P-A10 and P-A20 at 28 days as compared to compressive strength at 7 days. However, a marginal development of 9% and 6% in compressive strength was seen for the same mixes of P-A10 and P-A20 at 56 days as compared to compressive strength at 28 days. This shows that on increasing the curing period from 7 to 28 days, maximum hydration of pervious concrete mix occurs at 28 days because of higher creation of C-S-H which contributes to more compressive strength. The increase in strength was also attributed to the more pozzolanic and filler effect of pervious concrete by incorporating more NFA which increases the overall density of pervious concrete. For pervious concrete mix in the varied graded proportion of aggregates.
4.4. Clogging of pervious concrete
⌅4.4.1. Permeability reduction
⌅The falling head permeability apparatus used for measurement of permeability was used to evaluate the outcome of artificial clogging in pervious concrete as shown in Figure 12. The test was started by calculating the initial permeability of pervious concrete without any sediment load which acts as reference permeability. As the preliminary permeability was calculated, dry sediment was progressively added evenly to the top surface of the specimen before adding extra water to simulate the clogging phenomenon. It can be seen from Figure 13 (a) that the permeability of each sample reduces after each cycle of runoff. For the control mix, P-A0, the initial average permeability was 0.92 cm/s and it starts declining as compared to initial permeability after progressive sand-laden runoff cycles as 7.6%, 23%, 36%, 58%, 71%, 86%, 92%, 94% and 100% for 10 cycles in total, however, the working limit of permeability ends at the 7th cycle where clogging was almost 80% and remaining permeability of sample was only 0.12 cm/s. For the same control mix, on applying the clay-laden runoff, permeability declinement was more gradual than sand-laden runoff. The reduction percentage of permeability was 3%, 7%, 20%, 41%, 60%, 75% 85%, 95%, and 100% for 9 cycles. However, 80% of clogging was done after the 7th cycle at which the remaining permeability of pervious concrete was below the permissible limits. Moreover, for the same mix, combined (S and C) laden runoff shows a quick declinement in permeability. The decrease in permeability was seen at 38%, 55%, 70%, 85%, 97% and 100% for 6 cycles of combined sand and clay runoff. Moreover, the permissible limit of permeability was crossed in the early 4th cycle of runoff at which 85% of clogging was seen. This quick declinement in permeability for the combined laden runoff was due to the formation of a mud lid over the surface of the sample. Therefore, flocking of clay with fine sand particles causes early blocking of surface pores of pervious concrete by forces of Van der Waals.
From Figure 13 (b) the initial average permeability for mix P-A10 was 0.90 cm/s and it starts declining after progressive sand-laden runoff cycles as compared to initial permeability of 14%, 20%, 33%, 46%, 58%, 70%, 82%, 93% and 100% for 9 cycles in total, however, the working limit of permeability ends at the 7th cycle where clogging was almost 82% and remaining permeability of sample was only 0.12 cm/s. For the same control mix, on applying the clay-laden runoffs, permeability declinement was more gradual than sand-laden runoff. The reduction percentage of permeability was 4%, 12%, 24%, 41%, 57%, 69% 80%, 86%, 94% and 100% for 10 cycles. However, 80% of clogging was done after the 7th cycle at which the remaining permeability of pervious concrete was below the permissible limits. Moreover, for the same mix, combined (S and C) laden runoff shows early clogging in pervious concrete. The decrease in permeability when compared to initial permeability was seen as 32%, 52%, 66%, 74%, 86% and 93%, 98%, and 100% for 8 cycles of combined sand and clay runoff. Moreover, the permissible limit of permeability was crossed at the early 5th cycle of runoff at which 86% of clogging was observed. Furthermore, the reduction in permeability for mix P-A20 was faster as compared to previous mixes due to low porosity (18%) as shown in Figure 13 (c). Moreover, 80% clogging in pervious concrete occurs at the 5th, 6th, and 3rd cycle after performing sand, clay, and combined runoff cycles respectively. However, the complete (100%) clogging of pervious concrete occurs on the 7th, 8th, and 5th for sand, clay, and combined runoff laden.
4.4.2. Visual observation of clogging
⌅It can be seen from Figure 13 that the permeability of pervious concrete was initially highest but decreased exponentially due to the choking of pores. However, the exact reason for the blockage of pores was observed from visual inspection. It was observed from the half-cut method of clogging that samples clogged with fine sand show a significant weight difference between the upper half and lower half. From the results it was observed that the upper half weight for the sand clogged sample was more than the lower half, indicating that major sediment was accumulated on the upper half of pervious concrete. Moreover, no weight difference was seen in samples clogged with clay, as it was observed from the dry cut method that clay sediment was seen evenly through the whole depth of the sample. Moreover, the samples clogged with both sand and clay showed a clear presence of sediment only on the upper top 5 cm, which was also confirmed from the half-weight method of pervious concrete.
It was also analyzed from the slicing method of visual inspection that the clay clogger was evenly distributed over the whole length of the sample. However, peripheral sand sediment was seen at the outer periphery of cylindrical samples clogged with sand only as shown in Figure 14. It indicates that sandy clogger flows with water through the shortest radial flow path. Therefore, in general, it can be concluded that clogging due to clay is critical because of its cohesive nature, makes a strong bond inside the pores, and is difficult to unclog through rehabilitation techniques.
4.4.3. Image processing of clogging
⌅The image processing techniques such as X-CT tomography and filter 7 image processing were used and are shown in Figure 15 and Figure 16. To know the actual depth of sediment, X-CT tomography of clogged cylindrical sample was performed at three different sections (top, mid, and bottom). A 200 mm cylinder was cut into three equal discs and X-CT of each 65 mm disc was performed separately. It can be seen from Figure 15 (a) that distribution of sediment particles for sand clogged sample were more on the top section of the sample. The intensity of sediment particles for the sample starts decreasing with the depth of sample. Therefore, it confirms the visual examination of above section that sand sediment flows through shortest outer periphery path. Moreover, X-CT of cylindrical sample clogged with clay alone as seen in Figure 15 (b), shows that distribution of clay particles was seen evenly throughout the depth of sample. It can be further seen from the same tomography that clay particles predominantly clinged with each other with the help of weak vander waals forces due to sticky nature. Furthermore, the tomography of cylindrical sample clogged with combined sediment load shows that sediment was only present on the top section of clogged sample. Therefore, with the variable charged particles of sand and clay, a mud lid was formed on the top of sample shows that choking of voids is only to the top section of pervious concrete. Therefore, clogging with clay shows chocking through all the over the depth, which could be more severe and critical. Moreover, image processing filter 7 was used to counter check the presence of clay sediment which is considered to be more critical. It can be seen from Figure 16 that distribution of sediment load was evenly distributed over the whole depth of sample, which is in full agreement with the above study of tomography technique.
4.4.3.1. Rejuvenation of clogging
⌅Vacuuming as shown in Figure 17 was performed on all the mixes of pervious concrete through carpet and crevice nozzle for a minute after drying the sample in the oven for 24 hours at 60 0C. It was observed from the results of this treatment that sand clogged sample shows a maximum recovery of 80% regain in permeability. Moreover, a worst rate of recovery of the order of 10% was observed for the samples clogged with clay alone. Whereas, recovery against combined (S & C) clogger was observed as 40%. However, aggregate pervious concrete mix combination made with P-type of aggregate gradation shows optimum results against both the rejuvenation techniques relative to other mix combinations made with Q, and R-type of aggregate gradations. This optimum recovery for P-type of mix combination could be due to higher porosity relative to other mix combinations. Vacuuming extracts, the ingressed material of clogging from the sample, therefore mix having more voids enables large suction cavity through maximum depth of sample.
Moreover, pressure washing as shown in Figure 17 (a) pushes out or washes the impurities through the pervious concrete sample. A maximum recovery of pressure 50% was seen for samples clogged with combined (S&C) clogger sediment. This could be possible that combined sediment forms the mud lid over the top surface of sample, which stops maximum amount of sediment on the top surface without blocking the internal path of voids. However, results of pressure washing against sand shows worst results (20% recovery) due to secondary clogging of lower section. Due to pressure washing sand particles easily move down the top section of sample and settles in the lower section of sample. However, using pressure washing in the opposite direction for the same sample shows some development in de-clogging but the development was marginal. Furthermore, pressure washing against clay clogged shows a recovery rate of 30%, which is acceptable. Pressure washing dissolves some loose part of clay and drains out on the other side of sample. It was further, observed that the overall recovery of pressure washing was optimum for mix combinations made with R-type of aggregate gradation due to higher ranges of porosity relative to other combinations of pervious concrete.
5. CONCLUSIONS
⌅The present study was designed to determine the influence of different aggregate grade proportions on the clogging potential of pervious concrete. Based on the results obtained, a few conclusions are drawn.
-
Relative to the control mix, made with P-type of aggregate gradation, the 28-day compressive strength increased significantly by 10% and 24% for mixes P-A10 and P-A20 in which Q and R type aggregate grade proportion was used respectively. Therefore, the inclusion of NFA up to 20% in pervious concrete increases the compressive strength significantly at 28 days of curing age due to increasing the overall density of concrete matrix.
-
Clogging done by combined sand and clay clogger shows an 80% loss in permeability in 4 to 5 cycles for all three mixes. However, clogging through clay alone take highest number of cycles (99. Yang, J.; Jiang, G. (2003) Experimental study on properties of pervious concrete pavement materials. Cem. Conc. Res. 33 [3], 381-386. https://doi.org/10.1016/S0008-8846(02)00966-3.
-1010. Aman, A.M.N.; Selvarajoo, A.; Chong, S.; Teo, F.Y. (2022) Comparative life cycle assessment of pervious concrete production in Malaysia with natural and recycled aggregate. Innov. Infrastruct. Solut. 7, 211. https://doi.org/10.1007/s41062-022-00801-3.
) to reach 80% of clogging, therefore could show worst case of clogging due to even filling of pores through whole length of sample. -
All the visual observations supported by image processing shows that clogging due to clay alone could show critical results of clogging as the sediment of clay was evenly distributed over the whole depth of sample. Whereas, clogging due to combined sediment shows least clogging due to formation of mud lid on the top of sample.
-
Rejuvenation treatment shows that a maximum 80% recovery of permeability was observed for sand clogged samples against vacuuming treatment. Whereas, a maximum recovery of 50% in permeability was seen for combined clogged samples against pressure washing. However, in general it was observed that pervious concrete mix made with R-type of aggregate gradation shows optimum results of recovery against both the rejuvenation techniques.