This chapter delves into the effects of polymer paste content on the porosity and strength of pervious polymer concrete, a lightweight concrete variant known for its porous structure and excellent permeability. The study uses unsaturated polyester resin as a binder, aiming to enhance the strength characteristics while maintaining high porosity. The research methodically assesses the influence of varying polymer paste content on both the total and connected porosity, revealing a significant decrease in porosity as the polymer paste content increases. Additionally, the study demonstrates that the compressive and flexural strengths of the pervious polymer concrete are substantially higher than those of conventional pervious cement concrete, highlighting the superior bond strength provided by the polymeric binder and cross-linking agent. The chapter also explores the inverse exponential relationship between porosity and strength, offering valuable insights into the optimization of pervious polymer concrete for various structural and non-structural applications. The findings of this study have the potential to contribute to the commercialization of porous polymer concrete, making it a must-read for professionals interested in advanced concrete materials and their applications.
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Abstract
This study investigates the effect of polymer paste content on the porosity and strength of pervious polymer concrete made of unsaturated polyester resin, fly ash filler, and crushed coarse aggregate. The porosity (total porosity and connected porosity) and strength (compressive and flexural strengths) for different polymer paste contents were investigated. The polymer paste content was chosen as an experimental variable because it determines the cost-effectiveness and has a significant impact on various material properties. The results showed that the total and connected porosity fell between 37.5–8.8% and 34.2–7.2%, respectively, when the polymer paste content increased from 7 to 19.5 wt.%. The porosity tended to decrease as the polymer paste content increased. The compressive and flexural strengths ranged from 14.5 to 41.5 MPa and 4.3 to 16.1 MPa, and the strengths increased as the paste content increased. In particular, the strengths were much higher than those of many existing studies on conventional portland cement concrete due to the enhanced adhesion of the polymer binder upon the addition of the cross-linking agent.
1 Introduction
Pervious concrete is a sort of lightweight concrete, which is also called porous concrete, permeable concrete, or no-fines concrete [1]. Most of the voids in pervious concrete are large and interconnected because the coarse aggregates are in point-to-point contact via mortar or paste, resulting in a lower unit weight than conventional cement concrete. Coarse aggregate is the main component of the skeleton structure of pervious concrete, which bears a substantial amount of load [2]. In particular, one of the primary advantages is that the hydrostatic pressure applied to pervious concrete is relatively low, typically 1/3 of that applied to conventional cement concrete [3]. In addition, previous concrete undergoes less drying shrinkage due to its larger void size, and the moisture movement by capillary action is minimal. More importantly, the unit weight of the pervious concrete is quite low, which makes it lightweight and has excellent insulation performance. A former study reported that the life-cycle cost (LCC) of a surface course made with pervious concrete is lower than that made with conventional concrete since the cost required for underline pipes can be significantly reduced when using pervious concrete [4]. Given the benefits, pervious concrete has been widely used for water-permeable blocks and pavement, sound-absorbing concrete, and eco-concrete. Despite such advantages, pervious concrete has been limitedly used for non-structural applications because it inherently has a low strength, and the strength even becomes lower as the porosity increases.
The main goal of this study is to develop pervious concrete using polymeric resin as a binder in place of conventional portland cement to improve the strength characteristics while ensuring the highly porous nature of typical pervious concrete. Particularly, this study focuses on assessing the effect of polymer paste content on the strength and porosity of porous polymer concrete made of unsaturated polyester (UP) polymeric resin. The outcomes of this study will contribute to the commercialization of porous polymer concrete for various structural and non-structural applications.
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2 Materials and Methods
2.1 Materials
Unsaturated polyester resin.
An ortho-type UP resin (Aekyung Chemical Co., Ltd., Korea) added with a cobalt-based curing accelerator was used. The UP resin had a specific gravity of 1.13 at 25 ℃, viscosity of 3.0 ± 0.4 at 25 ℃, acid value of 20.0, gel time of 7–11 min at 25 ℃, and styrene content of 40%.
Initiator.
An initiator composed of 55% MEKPO and 45% DMP (KeumJungCo., Ltd., Korea) was used. Because the UP used in this study was premixed with an accelerator, the hardening reaction began upon the addition of the initiator.
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Cross-linking agent.
To enhance the bond between the polymer matrix and inorganic aggregate, silane (Hansol Chemical, Korea) was used as a cross-linking agent, of which specific gravity and viscosity were 1.03 and 2.41 mm2/sec, respectively.
Filler.
Fly ash was added as a filler to formulate polymer paste. The fly ash had a specific gravity of 2.20, SiO2 content of 51.9%, loss on ignition of 3.3%, and specific surface of 3,648 cm2/g.
Crushed coarse aggregate.
The crushed coarse aggregate (GyeonginMaterials Inc., Korea) used in this study had a grain size of 5–20 mm, which was dried to keep the moisture content below 0.5 wt.%. The coarse aggregate had a specific gravity of 2.63, absorption capacity of 2.67%, abrasion resistance of 24.3%, and soundness of 3.95%. The result of a sieve analysis is presented in Table 1.
Table 1.
Sieve analysis of crushed coarse aggregate
Sieve size (mm)
Passing (%)
2.5
0
5
0.3
10
29.5
20
99.0
25
100.0
2.2 Mixing
The polymeric resin content often falls within the range of 10–20 wt.% of polymer concrete [5], and the optimum resin content depends on the properties of the aggregate. As the aggregate size becomes smaller, more polymer content is required since the specific surface area of the aggregate increases [6, 7]. In this study, only 3–8% polymeric binder content was used to achieve the target void ratio of 10–35%, while the mixing ratio between the polymeric binder and filler was fixed at 1:1.5 by weight. Table 2 summarizes the mixture proportions of the pervious polymer concrete tested in this study. Wet mixing was done at 60 rpm for 3 min after dry mixing coarse aggregate and filler for 3 min.
Table 2.
Mixture proportions of pervious polymer concrete
Polymer paste content (wt.%)
Target porosity (%)
Polymeric binder (kg/m3)
Fly ash (kg/m3)
Coarse aggregate (kg/m3)
Unit weight (kg/m3)
7.0
35
48
72
1,600
1,720
9.5
30
67
101
1,600
1,768
12.0
25
88
132
1,600
1,820
14.5
20
108
162
1,600
1,870
16.0
15
132
198
1,600
1,930
19.5
10
156
234
1,600
1,990
2.3 Specimen Preparation
Polymer concrete was placed in three layers for cylindrical specimens (Φ100 mm × 200 mm) while placed in two layers for cube specimens (200 mm × 200 mm × 60 mm). All the specimens were cured for 7 days at 25 ± 2℃ and 50–60% RH. The top surface of the cylindrical specimens was flattened with polymer paste to avoid possible eccentricity when loaded as shown in Fig. 1. Three replicates were prepared for each test.
Fig. 1.
Appereance of flattened loading area
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2.4 Methods
Total porosity.
The total porosity was computed as follows [8, 9]:
where Vp is the total porosity (%), W1 is the weight of the saturated specimen underwater, W2 is the weight of the specimen oven dried at 60 ± 3℃ for 24 h, and V is the volume of the specimen (cm3).
Connected porosity.
The connected porosity is key to ensuring the required permeability and strength. The connected porosity can be computed as follows [8, 10]:
where Vcp is the connected porosity (%), W1 is the weight of the saturated specimen underwater, W3 is the weight of the saturated surface dry-conditioned specimen, and V is the volume of the specimen (cm3).
Compressive strength.
Φ100 mm × 200 mm cylindrical specimens were tested at 7 days as per the test procedures specified in KS F 2405:2010.
Flexural strength.
Flexural strength was measured at 7 days using 200 mm × 200 mm × 60 mm cube specimens in accordance with KS F 4419:2016.
3 Results and Discussion
3.1 Porosity
Figure 2 shows that the total porosity gradually decreased from 37.5 to 8.8% as the polymer paste content increased from 7 to 19.5%. This is because as the polymer paste content increases, more voids are filled with polymer paste. Mounika et al. [11] reported that the total porosity was about 13–28% of the total volume of concrete (no-fines concrete) when the cement-aggregate ratio was between 1:3 and 1:9. Another study by Muthaiyan et al. [12] revealed that the total porosity fell between 18.68–28.70% and 18.19–26.47% for pervious cement concrete and pervious fly ash-cement concrete, respectively. Liu et al. [13] found that the total porosity of pervious concrete made with 5–20 mm natural and recycled aggregates fell between 15 and 33%. Xia et al. [14] used 15–30 mm artificial gravel aggregate to fabricate grass-planting concrete, and the effective porosity was found to be 20–31.8%. Sriravindrarajah et al. [15] used two single-sized natural coarse aggregates ranging from either 5 to 13 mm or 13 to 20 mm in pervious concrete and showed that the total porosity was 26.8–28.1% for 13–20 mm aggregate and 33.3–36.1% for 5–13 mm aggregate. ACI 522R [16] reported that the total porosity of pervious concrete usually ranges from 15 to 35%.
Figure 2 also indicates that the connected porosity decreased from 34.2 to 7.2% as the polymer paste content increased from 7 to 19.5%, which showed a very similar trend to the total porosity. The connected porosity was approximately 91.2–81.8% of the total porosity. A former study by Muthaiyan [12] revealed that the connected porosity was 17.85–27.23% for pervious cement concrete and 15.01–24.79% for pervious fly ash-cement concrete. Yao et al. [2] reported a 14–32% connected porosity for pervious concrete made with 9.5–26.5 mm coarse aggregate. Some discrepancies in measured porosity were noted between this study and the previous studies. The possible reason appeared to stem from the type and content of paste/mortar and the maximum size and gradation of coarse aggregate used.
Fig. 2.
Effect of polymer paste content on the porosity
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3.2 Strength
Figure 3 shows the effect of polymer paste content on the compressive and flexural strengths. The compressive strength increased from 14.5 to 41.5 MPa as the polymer paste content increased from 7 to 19.5%. Geethanjali et al. [15] reported that the 28-day compressive strength of pervious concrete was 16.85 MPa. Liu et al. [13] found that the compressive strength of porous concrete with 5–20 mm natural aggregate and recycled aggregate fell between 7 and 25 MPa. Yao et al. [2] reported a 28-day compressive strength of 3–12 MPa for porous concrete made with 9.5–26.5 mm coarse aggregate. Lori et al. [3] reported a compressive strength of 23.45 MPa for pervious concrete containing 60% copper slag. Lang et al. [18] demonstrated that the 28-day compressive strength of magnesium phosphate cement steel slag pervious concrete was between 29.5 and 36.0 MPa.
As can also be seen in Fig. 3, the flexural strength tended to increase from 4.3 to 16.1 MPa as the polymer paste content increased from 7 to 19.5%. The flexural strength was about 29.6–38.7% of the compressive strength. Given the flexural strength of pervious concrete from many former studies typically fell within the range between 1.44 and 1.88 MPa [12], 0.3 and 1.7 MPa [2], 6.02 and 7.75 MPa [17], 3.15 and 3.80 MPa [9], 1 and 3.8 MPa [2], and 5.0 and 8.0 MPa [18], The flexural strength of the pervious polymer concrete developed in study was significantly higher (14.5 MPa to 41.5 MPa) than that of the previous research studies.
Consequently, the compressive and flexural strengths observed in the present study were much superior to those reported in the previous studies since the polymeric binder provided a stronger bond strength, and the cross-linking agent further improved the bond.
Fig. 3.
Effect of polymer paste content on the strengths
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3.3 Porosity vs. Strength
The strength of pervious concrete is closely related to its total porosity [19]. Figure 4 presents the relationship between the total porosity and strength of the pervious polymer concrete. As noted in the results, there was an inverse exponential relationship between the strength and total porosity with a high coefficient of determination (R2) of 0.9927; as the total porosity increased, the compressive strength was dramatically reduced. This trend was similar to the results of a previous study by Jia Hao et al. [20].
Fig. 4.
Relation between total porosity and compressive strength
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4 Conclusions
This study investigated the effect of polymer paste content on the strength and porosity of pervious polymer concrete made with an unsaturated polyester (UP) resin. The following conclusions can be drawn from the findings of this study.
As the polymer paste content increased, the total and connected porosity substantially decreased. The connected porosity was approximately 81.8–91.2% of the total porosity.
The porosity appears to be closely related to the type and content of paste/mortar and the maximum size and gradation of coarse aggregate used.
The strength of the previous polymer concrete was found to be much higher than that of conventional pervious cement concrete. The strength tended to increase as the polymer paste content increased. The flexural strength was about 29.6–38.7% of the compressive strength.
The strengths of porous polymer concrete were much superior to those of conventional pervious cement concrete because the polymeric binder and cross-linking agent enhanced the bond between the polymer matrix and aggregate.
A strong exponential relationship existed between the porosity and strength with a high coefficient of determination.
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