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Preparation and performance evaluation of an innovative pervious concrete pavement
Construction and Building Materials 138 (2017) 479–485
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Preparation and performance evaluation of an innovative pervious concrete pavement Jiusu Li a,⇑, Yi Zhang a, Guanlan Liu b, Xinghai Peng a a b
School of Traffic and Transportation Engineering, Changsha University of Science & Technology, 410114 Changsha, PR China Artie McFerrin Department of Chemical Engineering, Texas A&M University, College Station, TX 77843-3122, USA
h i g h l i g h t s High strength pervious concrete pavement based on reactive powder concrete. Solution of low strength, high likelihood clogging and inconvenient maintenance. Characteristics of high compressive strength and favorable permeability. Combination of efficient drainage and clogging-preventing in precast concrete pavement system.
a r t i c l e
i n f o
Article history: Received 9 December 2016 Received in revised form 26 January 2017 Accepted 30 January 2017
Keywords: Reactive powder concrete Permeable pavement High strength pervious concrete Permeability coefficient Prefabricated concrete pavement
a b s t r a c t The low strength, high likelihood for clogging and inconvenient maintenance are three main challenges for the wider application of pervious concrete pavement. To overcome these challenges, a high strength pervious concrete (HSPC) pavement was designed and prepared by introducing reactive powder concrete (RPC) as the matrix in addition to constructing accessible pores. Optimized mix proportion of RPC and the porosity were also evaluated in the design and preparation stage. After successful production of HSPC, its performance (e.g. compressive strength, permeability) was evaluated via multiple mechanical and physical tests. As for the experimental results for HSPC, its 7 days compressive strength peaked at 61.37 MPa together with a 13.02 mm/s corresponding permeability coefficient, which indicates a favorable performance for wide application. In addition, referring to current technologies of prefabricated concrete pavement, (e.g., Miller super-slab system, Michigan system), a tongue-and-groove connecting structure was designed and fabricated in the pervious concrete. Finally, a drainage system was designed to exclude the clogging dusts in the pores of the HSPC pavement efficiently, where the clogging dusts were excluded from bottom to top. This innovative high strength pervious concrete has the potential to allow of a wider application of this material. Ó 2017 Elsevier Ltd. All rights reserved.
1. Introduction Environmental issues, such as waterlogging, water pollution, atrocious climate and urban hot island phenomena, occur frequently and globally. The presence of impermeable pavement in highway and urban roads, which cuts off the moisture and heat exchange between earth and air, is one main reason for these environmental issues. Meanwhile, reported traffic accidents cause more than one million fatalities and nearly five hundred billion dollars’ loss globally every year. The lack of water permeability in traditional pavement, which radically weakens the pavement’s ⇑ Corresponding author. E-mail addresses: [email protected] (J. Li), [email protected] (Y. Zhang), [email protected] (G. Liu), [email protected] (X. Peng). http://dx.doi.org/10.1016/j.conbuildmat.2017.01.137 0950-0618/Ó 2017 Elsevier Ltd. All rights reserved.
skid resistance under rain or snow, is responsible for traffic accidents. Unlike impermeable concrete pavement, pervious concrete pavement (PCP) provides better rain-drainage and snow-melting to prevent drivers’ safety issues such as slippery, glare, mist and flood, under severe weather conditions. Additionally, the porous structure in pervious pavement can preliminarily purify the rain and serve as tunnels for atmosphere-pavement heat and moisture exchange, leading to positive environmental effects (maintaining water balance, relieving hot island phenomena and the protection of biodiversity, etc.) [1–4]. However, due to the high porosity, the two main types of permeable pavement (pervious concrete and permeable asphalt mixture pavement) are also suffering from several performance issues including concrete loose, pore clogging, lower strength and durability, and difficulty in maintenance. Besides physical and mechanical issues, asphalt oxidative aging
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fatigue, which is a chemical process relevant to porosity and pores structure, can significantly reduce the life span of asphalt mixture pavement as well [5–7]. Due to the deficiency in current pervious pavement technology, its application is limited to light loading constructions such as sidewalks, driveways, parking lots or residential streets. To utilize pervious concrete for heavier loading pavements and other relevant construction or transportation fields, demand for improved performance has increased significantly. The term of Sponge City was introduced in China in 2012, which reflects the consideration of water absorption, reservation, permeability, purification and release. From that time onward, building more pervious concrete pavements as well as permeable asphalt pavements became more widely encouraged and practiced. However, it is very intriguing but challenging to overcome the performance bottlenecks of traditional pervious concrete pavement, especially on its low strength (28d’s compressive strength hardly exceed to 35 MPa), high likelihood of clogging and inconvenient maintenance. The general methods to improve the strength of PCP are the optimization of aggregate quality [8–11], gradation [12–13] as well as the modification of binders by blending mineral and chemical admixtures [14–17] to strengthen the bond between the aggregates. Research on pervious concrete clogging is still premature, mainly focused on the pore characteristics and precipitates distribution [18–21]. Prefabricated concrete is believed to be an ideal solution for the difficulty in pervious concrete pavement maintenance. As a response to the demands of feasible maintenance for pervious concrete, the Strategic Highway Research Program 2 (SHRP2) includes the design, fabrication, installation and evaluation of prefabricated concrete as an important research objective [22]. Besides in the U.S., the investigation and application of prefabricated concrete also attracts researcher’s attention from the Netherlands, France, Russian, Japan, etc. Recently, it was reported over 32 km prefabricated concrete pavement toll way was constructed in Indonesia. In this research, reactive powder concrete (RPC, a developing composite material with characteristics of super-high strength, favorable toughness and durability) [23] is designed and manufactured to be the matrix of an innovative high strength pervious concrete (HSPC) pavement. Superior to the traditional technologies for pervious concrete preparation, this new method achieves water permeability by constructing physical interconnected pores for
prefabricated pervious concrete, based on mortar-similar materials but no-fines concrete, so, this paper considers pervious concrete in its untraditional form. The objectives of this study are to overcome the obstacles in traditional pervious concrete such as low strength, concrete clogging and maintenance difficulty, aiming a solution towards safe, durable, widely applicable and environmentally friendly pavement design and construction.
2. Materials and methods 2.1. Materials Ordinary Portland cement (P.O 52.5R, similar to Type III in ASTM C150-07 with a strength grade of 52.5 MPa) was employed to prepare the high strength pervious concrete. Silica fume (SF), fly ash (FA, Grade II) (selected as reactive powder, featured with pozzolanic activity) and U-type expansion agent (UEA) (which consists aluminum sulfate, aluminum oxide and aluminum potassium sulfate, with strong resistance to undesirable shrinkage) were selected as the mineral admixtures. A superplasticizer (water-reducing rate above 30%) was used to improve the product strength by reducing the water-binder ratio. River sand (passing through a square sieve size of 0.6 mm prior to use) was also used in this research. In addition, other additives including styrene-butadiene latex, silica sol and polypropylene fibers (PP) were applied, with the purpose to get favorable mechanical properties, especially toughness. 2.2. Methods The process of high strength pervious concrete preparation can be described as follows (Fig. 1) and the steps are fivefold: a) Materials preparation: In this step, the raw materials were prepared and weighted. b) Model design: The pore size, arrangement and shape were designed as shown in Fig. 2. To meet the mechanical and permeable properties requirement of the sample, the pore size selected was 3 mm in diameter and there were four different types of layouts (3 3, 3 4, 4 4 and 4 5). The sample was prepared by apical plate and pore making components.
Fig. 1. The process of HSPC preparation.
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Fig. 2. Schematic of pore-making model.
c) Casting and forming: After well-stirring, the materials were casted into pre-made model and cured to age I. The initial setting time was 165 min. d) Pore making: The pore-making components were inserted into formed matrix vertically to create straight pores that connects the upper and bottom. Then, the sample was cured to age II (setting time 1 day). e) Model removal: The model then was removed to check the pore quality. If necessary, the samples would be continuously cured to experimental age. To prepare performance satisfied matrix material, single factor and orthogonal experiments and analysis were implemented with the index of mechanical properties. Other properties were also tested for better understanding of the material and the process of HSPC preparation, e.g. initial/final setting time were tested for determining the pore-making time. And with the test of HSPC’s strength and permeability performance, the performance and feasibility were evaluated for the innovative pervious concrete pavement. Tests related to cement paste and mortar (initial/final setting time, compressive strength and flexural strength) were performed per JTG E30-2005/ISO 957-1989, ISO 679-1989 [24]. The compressive strength test of pervious concrete was conducted according to the hardened cement concrete section in standard JTG E30-2005/ ISO 4012-1978, where the sample size was prepared as 100 mm 100 mm 100 mm, and with the consideration of size effect, all compression strength results were deducted to a fraction of 0.95. The flexural strength testing specimen size was 40 mm 40 mm 160 mm. Lastly, the water permeability test was carried out by constant hydraulic testing method according to CJJT135-2009 [25].
3. Results and discussion 3.1. Mix design of high strength concrete As specified in China, high strength concrete (HSC) refers to concrete with a compressive strength of no less than 60 MPa. In this research, reactive powder concrete was introduced to make HSC, serving as the matrix of HSPC. So, in this section, the mix design was carried out with the goal of getting high strength concrete (not high strength pervious concrete). The initial mix proportion of HSPC was determined based on analyzing the compressive strength test results when water-binder ratio, SF dosage, FA dosage, fiber and superplasticizer dosage was regarded as the variables.
Table 2 Strength results of orthogonal test. №
Flexural strength(MPa) 7d
11d
7d
11d
1 2 3 4 5 6 7 8 9
8.75 11.48 10.25 9.36 11.70* 9.45 10.42 10.45 10.26
8.10 7.05 8.10 5.35 7.15 10.57 7.85 10.60 8.16
71.66 65.02 60.55 78.63 62.24 61.77 82.60 58.45 57.21
73.20 76.94 67.27 81.30 67.36 66.36 83.96 59.78 60.00
*
Compressive strength (MPa)
Exceeded equipment’s range.
Table 1 Orthogonal design plan for the optimal mix proportion. №
P.O 52.5R
FA
SF
Sand
PP
Superplasticizer
Water/binder
UEA
Silica gel
SBR
Curing*
1 2 3 4 5 6 7 8 9
100%
11.83%
5.92%
46.75%
0.08%
1.36%
0.24
4.00%(2) 4.00%(2) 4.00%(2) 3.00%(1) 3.00%(1) 3.00%(1) 5.00%(3) 5.00%(3) 5.00%(3)
0.00%(1) 0.70%(2) 1.50%(3) 1.50%(3) 0.00%(1) 0.70%(2) 0.70%(2) 1.50%(3) 0.00%(1)
0.00%(1) 1.30%(2) 2.60%(3) 0.00%(1) 1.30%(2) 2.60%(3) 0.00%(1) 1.30%(2) 2.60%(3)
1 2 3 2 3 1 3 1 2
* Curing method: 1 represents T = 40 ± 5 °C, humidity P80%; 2 represents soaking in normal temperature water; 3 represents soaking in 40 ± 5 °C water. The percentage shown in this table is mass percent.
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Table 3 Extremum difference analysis.
*
№
UEA
Silica gel
SBR
Curing
Compressive strength(MPa)
Flexural strength(MPa)
Flexural strength reduction(MPa)
1 2 3 4 5 6 7 8 9 Dj*
4.00% 4.00% 4.00% 3.00% 3.00% 3.00% 5.00% 5.00% 5.00% D1 = 1.32 D1 = 0.01 D1 = 0.97
0.00% 0.70% 1.50% 1.50% 0.00% 0.70% 0.70% 1.50% 0.00% D2 = 5.90 D2 = 0.22 D2 = 0.47
0.00% 1.30% 2.60% 0.00% 1.30% 2.60% 0.00% 1.30% 2.60% D3 = 5.64 D3 = 1.70 D3 = 1.90
1 2 3 2 3 1 3 1 2 D4 = 6.37 D4 = 1.24 D4 = 3.80
71.66 65.02 65.55 78.63 62.24 61.17 82.60 58.45 57.21 Compressive strength Flexural strength Flexural strength reduction
8.75 11.48 10.25 9.36 >11.70 9.45 10.42 10.45 10.26
0.65 4.43 2.15 4.01 4.55 1.12 2.57 0.15 2.10
Dj is the extremum difference of column ‘j’.
Orthogonal design experiment was carried out after the determination of the initial mix proportion. In this orthogonal experiment, there were four factors including curing condition plus dosages of UEA, silica sol and styrene butadiene rubber (SBR) latex. The experiment design and results (average value) are shown in Tables 1 and 2, respectively. All curing conditions were switched to natural condition (T = 25 °C/RH = 80%) after seven days. Table 2 indicated excellent 7d flexural strength for all nine groups of samples with many above 10 MPa. Especially, the flexural strength of sample group 5 even exceeded the equipment’s testing capacity. This result could be attributed to the role of dense microstructure and polypropylene fibers in those samples. However, the 11d flexural strength of most groups showed certain level of reduction, which could be explained by the decrease of the curing moisture. Additionally, different sample groups showed significant degree of variance on their compressive strength. For example, the 7d compressive strength ranged from 57.21 MPa to 82.60 MPa. The compressive strength of 11d was close to their 7d value, despite the curing condition switch (from constant curing to natural curing). Table 3 statistically evaluated the effect of each factor on the compressive, flexural strength and their deduction, via extremum difference analysis method. The results indicated that factors affecting the compressive strength of concrete could be summarized in descending order as curing condition > silica sol > SBR > UEA, and the optimum combination was 1, 2, 2, 3 (Table 3); while the factors affecting the flexural strength of concrete could be summarized as SBR > curing condition > silica sol > UEA, where the best combination was 1, 1, 2, 3 (Table 3). The factors affecting the deduction of flexural strength were curing condition > SBR > UEA > silica sol, where the effect of curing condition (D4) was overwhelming, and the optimum combination was 1, 2, 3, 1 (Table 3). Further investigation suggested that although the application of expansive agent would lead to strength reduction (Table 3), its effect was minor comparing to the water saturated curing condition (either 40 °C or room temperature). Especially, at the final natural curing stage, both temperature and humidity of sample were dramatically altered. To make a sum, the optimum mix proportion of HSPC is shown in Table 4. Comparing to the initial mix design, its 7d compressive strength was 10 MPa higher at the same curing condition, reaching 70 MPa at natural curing condition and above 80 MPa under constant curing condition (40 ± 5 °C, humidity P80%). Also, the flexural strength of high strength pervious concrete could reach 10 MPa with low strength reduction.
3.2. Pores design and fabrication of high strength pervious concrete As described previously, aggregate-aggregate contact is the traditional way to create permeable pores in Portland cement pervious concrete despite the various existing fabrication methods for porous ceramics (e.g., extrusion, particle accumulation, gas foaming, organic foam soaking) [26]. In the pores design and construction of HSPC, the processing technology of porous ceramic are referred. Aiming the pores’ interconnectivity while considering the effect of porous structure on strength and permeability, the initial design was proposed as following: select RPC as the matrix, create interconnected top-bottom pore path via physical pore processing, to implement satisfactory mechanical performance as well as excellent water permeability. The detailed procedures to fabricate pores are described below: First, determine the pore size and morphology. In traditional pervious concrete, the pore usually possess size distribution in the range of 2–4 mm [27], with obvious irregularity and uncertainty. From a morphological perspective, cylinder is recognized as the best interface shape because it is the ideal way to disperse interfacial force evenly. In this research, a cylindrical pore with a 4 mm diameter is selected. The second task is to determine the pore content. According to standard CJJT135-2009, the continuous void fraction should be no less than 10% for ordinary pervious concrete; however, considering that an interconnected pore structure possesses much more efficient water permeability than a disconnected skeleton pore structure, four lower interconnected pore contents were designed in this research, i.e. 1.246% (3 3 array), 1.617% (3 4 array), 2.216% (4 4 array) and 2.769% (4 5 array). Moreover, the initial and final setting time of HSPC was evaluated, and the initial and final setting times were 165 min and 9 h, respectively. Based on the quality of the pores, the optimum pore forming time was ±0.5 h within the initial setting time. At last, a pore fabricating model (Fig. 2) is designed to produce HSPC specimen with different pore fraction, as shown in Fig. 3. 3.3. Performance of high strength pervious concrete 3.3.1. Porosity and permeability The permeability coefficient, corresponding to the unit flow rate under certain water pressure, is a direct indicator to characterize the water permeability. For pervious concrete, national standard requires a permeability coefficient no less than 0.5 mm/s (specified in CJJT135-2009) [25]. However, even meeting this minimum requirement, the application of pervious concrete is still practically
Table 4 Optimum mix proportion of HSPC. P.O 52.5R
FA
SF
Sand
UEA
Superplasticizer
PP
Silica gel
SBR
Water
100%
11.83%
5.92%
46.75%
3.00%
1.36%
0.08%
0.70%
1.30%
28.44%
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Fig. 3. HSPC specimen and schematic.
Table 5 Permeability coefficient of HSPC with different porosity. Porosity (%)
0
1.246
1.617
2.216
2.769
Permeability coefficient (mm/s)
0 0 0 0
13.11 13.19 12.94 12.85
16.89 16.56 16.48 16.83
18.32 18.83 18.62 18.54
21.71 22.24 22.74 20.67
0
13.02
16.69
18.58
21.84
Mean (mm/s)
limited to certain locations. Moreover, although the total porosity of traditional pervious concrete can exceed 10%, its water permeability could be still inefficient due to its inhomogeneous pore size, rough pore surface, long and circuitous water path, etc. Table 5 shows the permeability coefficient testing results. The permeability coefficient varied from 13.02 mm/s (1.246% porosity) to 21.84 mm/s (2.769% porosity). This result is exciting because in comparison to the traditional pervious concrete (permeability coefficient usually under 15 mm/s), the high strength pervious concrete possessed more favorable water permeability even at much lower porosity. This excellent permeability could be attributed to the innovative physical structure inside the HSPC, i.e., the top-bottom interconnected pore path, which also strengthens the correlation between porosity and water permeability coefficient. As a reference, literature report indicated that the relationship between porosity and the permeability coefficient was non-linear in traditional pervious concrete [28]. However, the regression on
Fig. 4. Correlation between porosity and permeability coefficient.
the porosity and permeability coefficient in HSPC shows significant linearity (Fig. 4). The regression parameters were estimated based on statistical analysis, as shown in Eq. (1).
kt ¼ 1:695 þ 785:648 p
ð1Þ
where kt is permeability coefficient, p is the porosity. The R2 is 0.976, and p value is 0.004 (0.05), suggesting a statistically significant linear relationship. Compared to common pervious concrete, the porosity of prepared high strength pervious concrete is much lower, which guarantees the mechanical properties but also has negative effects on permeability. However, benefitting from the pores’ properties (which are characterized by straight shape, homogeneous and relatively large size (d = 4 mm)), the high strength pervious concrete showed favorable permeability as shown in table 5. As discussed above, it has the same effect to performance of anti-clogging too. As a comparison, common sense pervious concrete, featured with inhomogeneous pore size, rough pore surface, long and circuitous
Table 6 7d compressive strength of HSPC with different porosity. Porosity (%)
0
1.246
1.617
2.216
2.769
7d compressive strength (MPa)
74.22 71.66 73.58
59.72 63.80 60.58
58.92 56.71 54.37
54.99 53.33 51.38
49.94 48.93 53.50
Mean (MPa)
73.15
61.37
56.67
53.23
50.79
Fig. 5. Comparison of measured and calculated compressive strength.
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Fig. 6. Schematic diagram of prefabricated pavement design.
pore path, owns poor permeability and performance of anticlogging even with much higher porosity. That is to say, it is the pores’ properties (ability and efficiency to transmit water and plugs) that is critical for permeability and performance of anticlogging (not porosity).
3.3.2. Porosity and strength In most of the solid materials, the porosity and strength are inversely related [29], as expressed as Eq. (2):
S ¼ S0 ekp
ð2Þ
where S is the material strength under certain porosity (p), S0 is the strength of material without pores, k is a constant. In many cases, the direct application of Eq. (2) to ordinary concrete is inaccurate because of the presence of the interfacial transition zone and micro cracks. However, in this research, the particle sizes of HSPC raw materials are all below 0.6 mm (while most of the particle diameters are even below 50 lm), producing solid and homogenous RPC product. Thus, the application of Eq. (2) becomes reasonable. Non-linear regression based on Eq. (2) was done on the experimental data, aiming a descriptive explanation of porosity and strength of pervious materials. In this regression, the S0 was assumed to be 73.15 MPa, as shown in Table 6. Constant k was optimized to be 0.1411, and statistical analysis returned R2 of 0.9876, indicating a nice regression. Thus, the relation of porosity and strength in HSPC can be summarized as Eq. (3). Fig. 5 (plotted by Table 6 and Eq. (3)) validates the equation estimations with experiment results.
3.4. Prefabrication and drainage design of HSPC pavement system Precast concrete pavement system, as a new rapid maintenance technology, is recognized in favor of its improved weather tolerance, low time consumption and high quality [30]. Recently, precast concrete pavement system has been increasingly applied to rapid repair and temporary construction for pavement, airport, etc., especially in the urban road in occasion of heavy traffic and short construction window [31]. In this study, common precast concrete pavement systems (PCPS) all over the world were compared, including Fort Miller super-slab system, Michigan system (U.S., Canada, Indonesia), hexagonal PCPS (France), PAG XIV slab system (Russian) and PCPS containing hore device plus sliding dowel bar joint (Japan)[22,30]. Referring to the advantages of these widely applied technologies, a tongue-and-groove connection PCPS method specifically designed for high strength pervious concrete is introduced (Fig. 6). The innovations of this combined pavement system are: First, efficient combination of PCPS and HSPC extends the potential application of PCP, while overcoming its inconvenience in maintenance. Second, the technology for HSPC maintenance is creatively advanced, e.g., removing the slab when structural failure was observed (Fig. 6(a) and (c)), and cleaning clogging of pores from bottom to top which would be more feasible and efficient (Fig. 6(b) and (d)), comparing to the traditional way. According to the results of tests, the favorable performance (mechanical and permeability) of HSPC guarantees the feasibility of the tongue-and-groove connection PCPS, and as for applicability, it would be investigated in future studies.
4. Conclusion
S ¼ 73:15e0:1411p where S is the HSPC strength, p is the porosity in HSPC.
ð3Þ Aiming a solution towards the current deficient strength, durability and inconvenient maintenance in pervious concrete
J. Li et al. / Construction and Building Materials 138 (2017) 479–485
pavement, an innovative high strength pervious concrete was designed and prepared. Substantial performance evaluation indicated that HSPC possesses ideal compressive and flexural strength while maintaining excellent water permeability. Furthermore, an efficient drainage system and clogging-preventing paths from bottom to top were combined in the precast concrete pavement systems to overcome other technical bottlenecks in current pervious concrete technology. The key findings of this research are summarized as following: Optimum mix proportion of RPC was determined to guarantee performance of HSPC based on it. Results show that the optimized product possesses over 70 MPa of compressive strength and around 10 MPa of flexural strength. An innovative pore structure is designed and applied to HSPC, where interconnected pore path provides much excellent water permeability at relatively low porosity. Other important properties for ideal HSPC production such as pore size (4 mm), morphology (cylindrical), porosity/array design (1.246% (3 3 array), 1.617% (3 4 array), 2.216% (4 4 array) and 2.769% (4 5 array)) and optimum pore forming time (±0.5 h within the initial setting time) are also introduced. The relations between HSPC porosity, permeability and strength are investigated. The porosity (p) and permeability (kt) are linearly correlated in HSPC. Moreover, an exponential correlated is found between the 7d compressive strength (S) and porosity of HSPC. Performance characterization indicates both satisfactory strength and desirable permeability in HSPC. The permeability coefficients varied from 13.02 mm/s to 21.84 mm/s, with a corresponding strength ranging 61.37–50.79 MPa, which is obviously higher than the common sense pervious concrete performance level (compressive strength: 5.5–40 MPa, permeability coefficient: 0.3–14 mm/s [8–9,11]). A creative combination of precast concrete pavement system (PCPS) and innovative high strength pervious concrete (HSPC) is proposed. Efficient combination of PCPS and HSPC provides broad application and easy maintenance, as well as a feasible clog cleaning. Thus further extends the application possibility of HSPC.
Acknowledgement The authors thank Hunan Province Department of Education for the financial support in funding this research study (14A001). And the research is also supported by Hunan Provincial Innovation Foundation for Postgraduate (CX2015B352) and Water Resources Science & Technology Plan of Hunan Province ([2016]194-40). The authors declare that there is no conflict of interest. References [1] P. Starke, C. Wallmeyer, S. Rölver, et al., Development of a new laboratory evaporation measurement device as decision support for evaporationoptimized building, Build. Environ. 46 (2011) 2552–2561. [2] M. Uma, V.L. Maguesvari Narasimha, Studies on characterization of pervious concrete for pavement applications, Soc. Behav. Sci. 104 (2013) 198–207.
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Contents lists available at ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Preparation and performance evaluation of an innovative pervious concrete pavement Jiusu Li a,⇑, Yi Zhang a, Guanlan Liu b, Xinghai Peng a a b
School of Traffic and Transportation Engineering, Changsha University of Science & Technology, 410114 Changsha, PR China Artie McFerrin Department of Chemical Engineering, Texas A&M University, College Station, TX 77843-3122, USA
h i g h l i g h t s High strength pervious concrete pavement based on reactive powder concrete. Solution of low strength, high likelihood clogging and inconvenient maintenance. Characteristics of high compressive strength and favorable permeability. Combination of efficient drainage and clogging-preventing in precast concrete pavement system.
a r t i c l e
i n f o
Article history: Received 9 December 2016 Received in revised form 26 January 2017 Accepted 30 January 2017
Keywords: Reactive powder concrete Permeable pavement High strength pervious concrete Permeability coefficient Prefabricated concrete pavement
a b s t r a c t The low strength, high likelihood for clogging and inconvenient maintenance are three main challenges for the wider application of pervious concrete pavement. To overcome these challenges, a high strength pervious concrete (HSPC) pavement was designed and prepared by introducing reactive powder concrete (RPC) as the matrix in addition to constructing accessible pores. Optimized mix proportion of RPC and the porosity were also evaluated in the design and preparation stage. After successful production of HSPC, its performance (e.g. compressive strength, permeability) was evaluated via multiple mechanical and physical tests. As for the experimental results for HSPC, its 7 days compressive strength peaked at 61.37 MPa together with a 13.02 mm/s corresponding permeability coefficient, which indicates a favorable performance for wide application. In addition, referring to current technologies of prefabricated concrete pavement, (e.g., Miller super-slab system, Michigan system), a tongue-and-groove connecting structure was designed and fabricated in the pervious concrete. Finally, a drainage system was designed to exclude the clogging dusts in the pores of the HSPC pavement efficiently, where the clogging dusts were excluded from bottom to top. This innovative high strength pervious concrete has the potential to allow of a wider application of this material. Ó 2017 Elsevier Ltd. All rights reserved.
1. Introduction Environmental issues, such as waterlogging, water pollution, atrocious climate and urban hot island phenomena, occur frequently and globally. The presence of impermeable pavement in highway and urban roads, which cuts off the moisture and heat exchange between earth and air, is one main reason for these environmental issues. Meanwhile, reported traffic accidents cause more than one million fatalities and nearly five hundred billion dollars’ loss globally every year. The lack of water permeability in traditional pavement, which radically weakens the pavement’s ⇑ Corresponding author. E-mail addresses: [email protected] (J. Li), [email protected] (Y. Zhang), [email protected] (G. Liu), [email protected] (X. Peng). http://dx.doi.org/10.1016/j.conbuildmat.2017.01.137 0950-0618/Ó 2017 Elsevier Ltd. All rights reserved.
skid resistance under rain or snow, is responsible for traffic accidents. Unlike impermeable concrete pavement, pervious concrete pavement (PCP) provides better rain-drainage and snow-melting to prevent drivers’ safety issues such as slippery, glare, mist and flood, under severe weather conditions. Additionally, the porous structure in pervious pavement can preliminarily purify the rain and serve as tunnels for atmosphere-pavement heat and moisture exchange, leading to positive environmental effects (maintaining water balance, relieving hot island phenomena and the protection of biodiversity, etc.) [1–4]. However, due to the high porosity, the two main types of permeable pavement (pervious concrete and permeable asphalt mixture pavement) are also suffering from several performance issues including concrete loose, pore clogging, lower strength and durability, and difficulty in maintenance. Besides physical and mechanical issues, asphalt oxidative aging
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fatigue, which is a chemical process relevant to porosity and pores structure, can significantly reduce the life span of asphalt mixture pavement as well [5–7]. Due to the deficiency in current pervious pavement technology, its application is limited to light loading constructions such as sidewalks, driveways, parking lots or residential streets. To utilize pervious concrete for heavier loading pavements and other relevant construction or transportation fields, demand for improved performance has increased significantly. The term of Sponge City was introduced in China in 2012, which reflects the consideration of water absorption, reservation, permeability, purification and release. From that time onward, building more pervious concrete pavements as well as permeable asphalt pavements became more widely encouraged and practiced. However, it is very intriguing but challenging to overcome the performance bottlenecks of traditional pervious concrete pavement, especially on its low strength (28d’s compressive strength hardly exceed to 35 MPa), high likelihood of clogging and inconvenient maintenance. The general methods to improve the strength of PCP are the optimization of aggregate quality [8–11], gradation [12–13] as well as the modification of binders by blending mineral and chemical admixtures [14–17] to strengthen the bond between the aggregates. Research on pervious concrete clogging is still premature, mainly focused on the pore characteristics and precipitates distribution [18–21]. Prefabricated concrete is believed to be an ideal solution for the difficulty in pervious concrete pavement maintenance. As a response to the demands of feasible maintenance for pervious concrete, the Strategic Highway Research Program 2 (SHRP2) includes the design, fabrication, installation and evaluation of prefabricated concrete as an important research objective [22]. Besides in the U.S., the investigation and application of prefabricated concrete also attracts researcher’s attention from the Netherlands, France, Russian, Japan, etc. Recently, it was reported over 32 km prefabricated concrete pavement toll way was constructed in Indonesia. In this research, reactive powder concrete (RPC, a developing composite material with characteristics of super-high strength, favorable toughness and durability) [23] is designed and manufactured to be the matrix of an innovative high strength pervious concrete (HSPC) pavement. Superior to the traditional technologies for pervious concrete preparation, this new method achieves water permeability by constructing physical interconnected pores for
prefabricated pervious concrete, based on mortar-similar materials but no-fines concrete, so, this paper considers pervious concrete in its untraditional form. The objectives of this study are to overcome the obstacles in traditional pervious concrete such as low strength, concrete clogging and maintenance difficulty, aiming a solution towards safe, durable, widely applicable and environmentally friendly pavement design and construction.
2. Materials and methods 2.1. Materials Ordinary Portland cement (P.O 52.5R, similar to Type III in ASTM C150-07 with a strength grade of 52.5 MPa) was employed to prepare the high strength pervious concrete. Silica fume (SF), fly ash (FA, Grade II) (selected as reactive powder, featured with pozzolanic activity) and U-type expansion agent (UEA) (which consists aluminum sulfate, aluminum oxide and aluminum potassium sulfate, with strong resistance to undesirable shrinkage) were selected as the mineral admixtures. A superplasticizer (water-reducing rate above 30%) was used to improve the product strength by reducing the water-binder ratio. River sand (passing through a square sieve size of 0.6 mm prior to use) was also used in this research. In addition, other additives including styrene-butadiene latex, silica sol and polypropylene fibers (PP) were applied, with the purpose to get favorable mechanical properties, especially toughness. 2.2. Methods The process of high strength pervious concrete preparation can be described as follows (Fig. 1) and the steps are fivefold: a) Materials preparation: In this step, the raw materials were prepared and weighted. b) Model design: The pore size, arrangement and shape were designed as shown in Fig. 2. To meet the mechanical and permeable properties requirement of the sample, the pore size selected was 3 mm in diameter and there were four different types of layouts (3 3, 3 4, 4 4 and 4 5). The sample was prepared by apical plate and pore making components.
Fig. 1. The process of HSPC preparation.
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Fig. 2. Schematic of pore-making model.
c) Casting and forming: After well-stirring, the materials were casted into pre-made model and cured to age I. The initial setting time was 165 min. d) Pore making: The pore-making components were inserted into formed matrix vertically to create straight pores that connects the upper and bottom. Then, the sample was cured to age II (setting time 1 day). e) Model removal: The model then was removed to check the pore quality. If necessary, the samples would be continuously cured to experimental age. To prepare performance satisfied matrix material, single factor and orthogonal experiments and analysis were implemented with the index of mechanical properties. Other properties were also tested for better understanding of the material and the process of HSPC preparation, e.g. initial/final setting time were tested for determining the pore-making time. And with the test of HSPC’s strength and permeability performance, the performance and feasibility were evaluated for the innovative pervious concrete pavement. Tests related to cement paste and mortar (initial/final setting time, compressive strength and flexural strength) were performed per JTG E30-2005/ISO 957-1989, ISO 679-1989 [24]. The compressive strength test of pervious concrete was conducted according to the hardened cement concrete section in standard JTG E30-2005/ ISO 4012-1978, where the sample size was prepared as 100 mm 100 mm 100 mm, and with the consideration of size effect, all compression strength results were deducted to a fraction of 0.95. The flexural strength testing specimen size was 40 mm 40 mm 160 mm. Lastly, the water permeability test was carried out by constant hydraulic testing method according to CJJT135-2009 [25].
3. Results and discussion 3.1. Mix design of high strength concrete As specified in China, high strength concrete (HSC) refers to concrete with a compressive strength of no less than 60 MPa. In this research, reactive powder concrete was introduced to make HSC, serving as the matrix of HSPC. So, in this section, the mix design was carried out with the goal of getting high strength concrete (not high strength pervious concrete). The initial mix proportion of HSPC was determined based on analyzing the compressive strength test results when water-binder ratio, SF dosage, FA dosage, fiber and superplasticizer dosage was regarded as the variables.
Table 2 Strength results of orthogonal test. №
Flexural strength(MPa) 7d
11d
7d
11d
1 2 3 4 5 6 7 8 9
8.75 11.48 10.25 9.36 11.70* 9.45 10.42 10.45 10.26
8.10 7.05 8.10 5.35 7.15 10.57 7.85 10.60 8.16
71.66 65.02 60.55 78.63 62.24 61.77 82.60 58.45 57.21
73.20 76.94 67.27 81.30 67.36 66.36 83.96 59.78 60.00
*
Compressive strength (MPa)
Exceeded equipment’s range.
Table 1 Orthogonal design plan for the optimal mix proportion. №
P.O 52.5R
FA
SF
Sand
PP
Superplasticizer
Water/binder
UEA
Silica gel
SBR
Curing*
1 2 3 4 5 6 7 8 9
100%
11.83%
5.92%
46.75%
0.08%
1.36%
0.24
4.00%(2) 4.00%(2) 4.00%(2) 3.00%(1) 3.00%(1) 3.00%(1) 5.00%(3) 5.00%(3) 5.00%(3)
0.00%(1) 0.70%(2) 1.50%(3) 1.50%(3) 0.00%(1) 0.70%(2) 0.70%(2) 1.50%(3) 0.00%(1)
0.00%(1) 1.30%(2) 2.60%(3) 0.00%(1) 1.30%(2) 2.60%(3) 0.00%(1) 1.30%(2) 2.60%(3)
1 2 3 2 3 1 3 1 2
* Curing method: 1 represents T = 40 ± 5 °C, humidity P80%; 2 represents soaking in normal temperature water; 3 represents soaking in 40 ± 5 °C water. The percentage shown in this table is mass percent.
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Table 3 Extremum difference analysis.
*
№
UEA
Silica gel
SBR
Curing
Compressive strength(MPa)
Flexural strength(MPa)
Flexural strength reduction(MPa)
1 2 3 4 5 6 7 8 9 Dj*
4.00% 4.00% 4.00% 3.00% 3.00% 3.00% 5.00% 5.00% 5.00% D1 = 1.32 D1 = 0.01 D1 = 0.97
0.00% 0.70% 1.50% 1.50% 0.00% 0.70% 0.70% 1.50% 0.00% D2 = 5.90 D2 = 0.22 D2 = 0.47
0.00% 1.30% 2.60% 0.00% 1.30% 2.60% 0.00% 1.30% 2.60% D3 = 5.64 D3 = 1.70 D3 = 1.90
1 2 3 2 3 1 3 1 2 D4 = 6.37 D4 = 1.24 D4 = 3.80
71.66 65.02 65.55 78.63 62.24 61.17 82.60 58.45 57.21 Compressive strength Flexural strength Flexural strength reduction
8.75 11.48 10.25 9.36 >11.70 9.45 10.42 10.45 10.26
0.65 4.43 2.15 4.01 4.55 1.12 2.57 0.15 2.10
Dj is the extremum difference of column ‘j’.
Orthogonal design experiment was carried out after the determination of the initial mix proportion. In this orthogonal experiment, there were four factors including curing condition plus dosages of UEA, silica sol and styrene butadiene rubber (SBR) latex. The experiment design and results (average value) are shown in Tables 1 and 2, respectively. All curing conditions were switched to natural condition (T = 25 °C/RH = 80%) after seven days. Table 2 indicated excellent 7d flexural strength for all nine groups of samples with many above 10 MPa. Especially, the flexural strength of sample group 5 even exceeded the equipment’s testing capacity. This result could be attributed to the role of dense microstructure and polypropylene fibers in those samples. However, the 11d flexural strength of most groups showed certain level of reduction, which could be explained by the decrease of the curing moisture. Additionally, different sample groups showed significant degree of variance on their compressive strength. For example, the 7d compressive strength ranged from 57.21 MPa to 82.60 MPa. The compressive strength of 11d was close to their 7d value, despite the curing condition switch (from constant curing to natural curing). Table 3 statistically evaluated the effect of each factor on the compressive, flexural strength and their deduction, via extremum difference analysis method. The results indicated that factors affecting the compressive strength of concrete could be summarized in descending order as curing condition > silica sol > SBR > UEA, and the optimum combination was 1, 2, 2, 3 (Table 3); while the factors affecting the flexural strength of concrete could be summarized as SBR > curing condition > silica sol > UEA, where the best combination was 1, 1, 2, 3 (Table 3). The factors affecting the deduction of flexural strength were curing condition > SBR > UEA > silica sol, where the effect of curing condition (D4) was overwhelming, and the optimum combination was 1, 2, 3, 1 (Table 3). Further investigation suggested that although the application of expansive agent would lead to strength reduction (Table 3), its effect was minor comparing to the water saturated curing condition (either 40 °C or room temperature). Especially, at the final natural curing stage, both temperature and humidity of sample were dramatically altered. To make a sum, the optimum mix proportion of HSPC is shown in Table 4. Comparing to the initial mix design, its 7d compressive strength was 10 MPa higher at the same curing condition, reaching 70 MPa at natural curing condition and above 80 MPa under constant curing condition (40 ± 5 °C, humidity P80%). Also, the flexural strength of high strength pervious concrete could reach 10 MPa with low strength reduction.
3.2. Pores design and fabrication of high strength pervious concrete As described previously, aggregate-aggregate contact is the traditional way to create permeable pores in Portland cement pervious concrete despite the various existing fabrication methods for porous ceramics (e.g., extrusion, particle accumulation, gas foaming, organic foam soaking) [26]. In the pores design and construction of HSPC, the processing technology of porous ceramic are referred. Aiming the pores’ interconnectivity while considering the effect of porous structure on strength and permeability, the initial design was proposed as following: select RPC as the matrix, create interconnected top-bottom pore path via physical pore processing, to implement satisfactory mechanical performance as well as excellent water permeability. The detailed procedures to fabricate pores are described below: First, determine the pore size and morphology. In traditional pervious concrete, the pore usually possess size distribution in the range of 2–4 mm [27], with obvious irregularity and uncertainty. From a morphological perspective, cylinder is recognized as the best interface shape because it is the ideal way to disperse interfacial force evenly. In this research, a cylindrical pore with a 4 mm diameter is selected. The second task is to determine the pore content. According to standard CJJT135-2009, the continuous void fraction should be no less than 10% for ordinary pervious concrete; however, considering that an interconnected pore structure possesses much more efficient water permeability than a disconnected skeleton pore structure, four lower interconnected pore contents were designed in this research, i.e. 1.246% (3 3 array), 1.617% (3 4 array), 2.216% (4 4 array) and 2.769% (4 5 array). Moreover, the initial and final setting time of HSPC was evaluated, and the initial and final setting times were 165 min and 9 h, respectively. Based on the quality of the pores, the optimum pore forming time was ±0.5 h within the initial setting time. At last, a pore fabricating model (Fig. 2) is designed to produce HSPC specimen with different pore fraction, as shown in Fig. 3. 3.3. Performance of high strength pervious concrete 3.3.1. Porosity and permeability The permeability coefficient, corresponding to the unit flow rate under certain water pressure, is a direct indicator to characterize the water permeability. For pervious concrete, national standard requires a permeability coefficient no less than 0.5 mm/s (specified in CJJT135-2009) [25]. However, even meeting this minimum requirement, the application of pervious concrete is still practically
Table 4 Optimum mix proportion of HSPC. P.O 52.5R
FA
SF
Sand
UEA
Superplasticizer
PP
Silica gel
SBR
Water
100%
11.83%
5.92%
46.75%
3.00%
1.36%
0.08%
0.70%
1.30%
28.44%
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Fig. 3. HSPC specimen and schematic.
Table 5 Permeability coefficient of HSPC with different porosity. Porosity (%)
0
1.246
1.617
2.216
2.769
Permeability coefficient (mm/s)
0 0 0 0
13.11 13.19 12.94 12.85
16.89 16.56 16.48 16.83
18.32 18.83 18.62 18.54
21.71 22.24 22.74 20.67
0
13.02
16.69
18.58
21.84
Mean (mm/s)
limited to certain locations. Moreover, although the total porosity of traditional pervious concrete can exceed 10%, its water permeability could be still inefficient due to its inhomogeneous pore size, rough pore surface, long and circuitous water path, etc. Table 5 shows the permeability coefficient testing results. The permeability coefficient varied from 13.02 mm/s (1.246% porosity) to 21.84 mm/s (2.769% porosity). This result is exciting because in comparison to the traditional pervious concrete (permeability coefficient usually under 15 mm/s), the high strength pervious concrete possessed more favorable water permeability even at much lower porosity. This excellent permeability could be attributed to the innovative physical structure inside the HSPC, i.e., the top-bottom interconnected pore path, which also strengthens the correlation between porosity and water permeability coefficient. As a reference, literature report indicated that the relationship between porosity and the permeability coefficient was non-linear in traditional pervious concrete [28]. However, the regression on
Fig. 4. Correlation between porosity and permeability coefficient.
the porosity and permeability coefficient in HSPC shows significant linearity (Fig. 4). The regression parameters were estimated based on statistical analysis, as shown in Eq. (1).
kt ¼ 1:695 þ 785:648 p
ð1Þ
where kt is permeability coefficient, p is the porosity. The R2 is 0.976, and p value is 0.004 (0.05), suggesting a statistically significant linear relationship. Compared to common pervious concrete, the porosity of prepared high strength pervious concrete is much lower, which guarantees the mechanical properties but also has negative effects on permeability. However, benefitting from the pores’ properties (which are characterized by straight shape, homogeneous and relatively large size (d = 4 mm)), the high strength pervious concrete showed favorable permeability as shown in table 5. As discussed above, it has the same effect to performance of anti-clogging too. As a comparison, common sense pervious concrete, featured with inhomogeneous pore size, rough pore surface, long and circuitous
Table 6 7d compressive strength of HSPC with different porosity. Porosity (%)
0
1.246
1.617
2.216
2.769
7d compressive strength (MPa)
74.22 71.66 73.58
59.72 63.80 60.58
58.92 56.71 54.37
54.99 53.33 51.38
49.94 48.93 53.50
Mean (MPa)
73.15
61.37
56.67
53.23
50.79
Fig. 5. Comparison of measured and calculated compressive strength.
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Fig. 6. Schematic diagram of prefabricated pavement design.
pore path, owns poor permeability and performance of anticlogging even with much higher porosity. That is to say, it is the pores’ properties (ability and efficiency to transmit water and plugs) that is critical for permeability and performance of anticlogging (not porosity).
3.3.2. Porosity and strength In most of the solid materials, the porosity and strength are inversely related [29], as expressed as Eq. (2):
S ¼ S0 ekp
ð2Þ
where S is the material strength under certain porosity (p), S0 is the strength of material without pores, k is a constant. In many cases, the direct application of Eq. (2) to ordinary concrete is inaccurate because of the presence of the interfacial transition zone and micro cracks. However, in this research, the particle sizes of HSPC raw materials are all below 0.6 mm (while most of the particle diameters are even below 50 lm), producing solid and homogenous RPC product. Thus, the application of Eq. (2) becomes reasonable. Non-linear regression based on Eq. (2) was done on the experimental data, aiming a descriptive explanation of porosity and strength of pervious materials. In this regression, the S0 was assumed to be 73.15 MPa, as shown in Table 6. Constant k was optimized to be 0.1411, and statistical analysis returned R2 of 0.9876, indicating a nice regression. Thus, the relation of porosity and strength in HSPC can be summarized as Eq. (3). Fig. 5 (plotted by Table 6 and Eq. (3)) validates the equation estimations with experiment results.
3.4. Prefabrication and drainage design of HSPC pavement system Precast concrete pavement system, as a new rapid maintenance technology, is recognized in favor of its improved weather tolerance, low time consumption and high quality [30]. Recently, precast concrete pavement system has been increasingly applied to rapid repair and temporary construction for pavement, airport, etc., especially in the urban road in occasion of heavy traffic and short construction window [31]. In this study, common precast concrete pavement systems (PCPS) all over the world were compared, including Fort Miller super-slab system, Michigan system (U.S., Canada, Indonesia), hexagonal PCPS (France), PAG XIV slab system (Russian) and PCPS containing hore device plus sliding dowel bar joint (Japan)[22,30]. Referring to the advantages of these widely applied technologies, a tongue-and-groove connection PCPS method specifically designed for high strength pervious concrete is introduced (Fig. 6). The innovations of this combined pavement system are: First, efficient combination of PCPS and HSPC extends the potential application of PCP, while overcoming its inconvenience in maintenance. Second, the technology for HSPC maintenance is creatively advanced, e.g., removing the slab when structural failure was observed (Fig. 6(a) and (c)), and cleaning clogging of pores from bottom to top which would be more feasible and efficient (Fig. 6(b) and (d)), comparing to the traditional way. According to the results of tests, the favorable performance (mechanical and permeability) of HSPC guarantees the feasibility of the tongue-and-groove connection PCPS, and as for applicability, it would be investigated in future studies.
4. Conclusion
S ¼ 73:15e0:1411p where S is the HSPC strength, p is the porosity in HSPC.
ð3Þ Aiming a solution towards the current deficient strength, durability and inconvenient maintenance in pervious concrete
J. Li et al. / Construction and Building Materials 138 (2017) 479–485
pavement, an innovative high strength pervious concrete was designed and prepared. Substantial performance evaluation indicated that HSPC possesses ideal compressive and flexural strength while maintaining excellent water permeability. Furthermore, an efficient drainage system and clogging-preventing paths from bottom to top were combined in the precast concrete pavement systems to overcome other technical bottlenecks in current pervious concrete technology. The key findings of this research are summarized as following: Optimum mix proportion of RPC was determined to guarantee performance of HSPC based on it. Results show that the optimized product possesses over 70 MPa of compressive strength and around 10 MPa of flexural strength. An innovative pore structure is designed and applied to HSPC, where interconnected pore path provides much excellent water permeability at relatively low porosity. Other important properties for ideal HSPC production such as pore size (4 mm), morphology (cylindrical), porosity/array design (1.246% (3 3 array), 1.617% (3 4 array), 2.216% (4 4 array) and 2.769% (4 5 array)) and optimum pore forming time (±0.5 h within the initial setting time) are also introduced. The relations between HSPC porosity, permeability and strength are investigated. The porosity (p) and permeability (kt) are linearly correlated in HSPC. Moreover, an exponential correlated is found between the 7d compressive strength (S) and porosity of HSPC. Performance characterization indicates both satisfactory strength and desirable permeability in HSPC. The permeability coefficients varied from 13.02 mm/s to 21.84 mm/s, with a corresponding strength ranging 61.37–50.79 MPa, which is obviously higher than the common sense pervious concrete performance level (compressive strength: 5.5–40 MPa, permeability coefficient: 0.3–14 mm/s [8–9,11]). A creative combination of precast concrete pavement system (PCPS) and innovative high strength pervious concrete (HSPC) is proposed. Efficient combination of PCPS and HSPC provides broad application and easy maintenance, as well as a feasible clog cleaning. Thus further extends the application possibility of HSPC.
Acknowledgement The authors thank Hunan Province Department of Education for the financial support in funding this research study (14A001). And the research is also supported by Hunan Provincial Innovation Foundation for Postgraduate (CX2015B352) and Water Resources Science & Technology Plan of Hunan Province ([2016]194-40). The authors declare that there is no conflict of interest. References [1] P. Starke, C. Wallmeyer, S. Rölver, et al., Development of a new laboratory evaporation measurement device as decision support for evaporationoptimized building, Build. Environ. 46 (2011) 2552–2561. [2] M. Uma, V.L. Maguesvari Narasimha, Studies on characterization of pervious concrete for pavement applications, Soc. Behav. Sci. 104 (2013) 198–207.
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