New Pervious Concrete Construction Material for Carbon Dioxide Sequestration
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Synonyms
Definition
Pervious concrete: porous material composed of cement, aggregates and water (Wang et al. 2019). Additives: crumbs incorporated in concrete mix of the modified pervious concrete (Lori et al. 2019). Finite elements analysis: method for solving differential equations, which consists of discretizing the material into several small particles (Wang et al. 2020).
Introduction
Additives used in the pervious concrete
Year | Additives | Author |
|---|---|---|
1995 | Superplasticizers | Ghafoori and Dutta (1995) |
2003 | Silica fume Vinyl acetate ethylene Polyvinyl alcohol Formaldehyde hydrosol | Yang and Jiang (2003) |
2010 | SBS latex Polypropylene fiber | Huang et al. (2010) |
2010 | Silica fume | Lian and Zhuge (2010) |
2016 | Silica fume | Chandrappa and Biligiri (2016) |
2016 | TiO2 | Barnhouse and Srubar III (2016) |
2018 | MgCl2 Fiber | Zhong and Wille (2018) |
2018 | Plasticizer | Kovac and Sicakova (2018) |
2018 | Polypropylene fibers Rubber Silica fume Styrene butadiene latex | Aliabdo et al. (2018) |
Ec – Young’s modulus (MPa)
ω – density of water (kg/m3)
fc – compressive strength (kg/cm2)
A descriptive statistical analysis was performed with data from the results of density, compressive strength tests and Young's modulus using the SPSS computer program, as presented in Table 6. Statistical analysis of the results of the density, compressive strength tests and Young modulus of the modified pervious concrete specimens provided 9 quartiles of each physical property, which were used in the Ansys R1 2019 software, academic version, to create 9 types of prototype materials, aiming to perform finite element discretization simulations to study structural behavior when prototypes are subjected to dynamic vertical loads. The 9 virtual prototypes have the dimensions of 1000 × 1000 mm, with a thickness of 50 mm. The loads to be applied will be of the order of 5,000 N, simulating a distributed load to be applied to the pavement under the conditions of compression strength.
A virtual prototype of pervious concrete to be used in the finite element structural calculation
The 9 virtual prototypes built in the computer environment of the Ansys program were subjected to loading simulations to collect data regarding the structural deformation of the materials with the application of vertical dynamic loads in the center of the prototypes. The results of maximum strain and maximum stress in virtual prototype materials are presented in Table 4.
Findings
The ratio 1:0.30:4 with lower amount of additive presents a greater variation of density
Figure 2 presents the results of the density tests performed with the three groups of specimens with the proportions of 1:0.3:4 (cement:Ca(OH)2:pebble), 1:0.5:4 (cement:Ca(OH)2:pebble), and 1:0.8:4 (cement:Ca(OH)2:pebble), all with a water/cement factor of 0.30, which show an increase in resistance when the additive ratio goes from 0.3 to 0.5 and a reduction when an increase in additive increase to 0.8 occurs. This is because with the addition of additive in the mixture, the material becomes more compact, with an increase in density, but the excess of additive makes the material fragile and weak, with disintegration of its structure 0.8. Excessive additive impairs cement adhesion between aggregate particles, causing material disintegration. However, a reduced amount of additive improves the material’s environmental properties as it absorbs CO2 from the atmosphere as shown in the CO2 volume monitoring tests; this way you should find an optimal additive value to be added to the new material mix so as not to impair the density properties. Figure 2 shows the results of an initial 3% density increase, which is natural as the additive fills the pores of the new material, and an 8% reduction in density demonstrating the disintegration of the new material’s internal structure, because the additive impairs the action of cement as a bonding element between aggregate particles.
The material gains resistance with the Ca(OH)2 additive because the carbonation produces CaCO3, but the material becomes brittle
Figure 3 presents results of the compressive strength of the specimens of the proportion of 1:0.3:4 (cement:Ca(OH)2:pebble), 1:0.5:4 (cement:Ca(OH)2:pebble), and 1:0.8:4 (cement:Ca(OH)2:pebble), all with a water/cement factor of 0.30, consistent with the results of the density tests performed on the specimens shown in Figure 2, because initially there is an increase in compressive strength and subsequently a reduction in this property. The addition of the additive makes the new material more compact; however, the excess additive ultimately makes the material brittle with little compressive strength. This phenomenon occurs because initially the additive fills the pores of the new material, making the material more compact, but excess additive impairs the cement which disintegrates the internal structure of the new material, rendering the material without compressive strength as it is added more additive to your mix. A material with low compressive strength cannot be used as a pavement or structural part, as it compromises the safety of the work, so the results of Fig. 3 demonstrate the need for strict control on the amount of additive to be added to the mix in the new material. The results demonstrate the need for further testing with specimens in order to find an optimized proportion of additive that allows the new material to be used as urban road pavement and maintains its CO2 sequestration properties. However, this negative feature of the new material of loss of density and loss of compressive strength does not predict its use as a sidewalk for pedestrians and garden floors that do not require structural strength of the material. Figure 3 initially shows an average 20% increase in compressive strength from 12.00 MPa to 15.10 MPa, but this 15.10 MPa is reduced to 12.90 MPa followed by a 14.5% reduction, indicating that excess additive contributes for the disintegration of the modified pervious concrete material, as it affects the binder action of the cement next to the aggregates. From that point on, the material loses compressive strength as the addition of additive to the mixture is increased, such that the internal structure of the new material becomes unstable and the new material cannot be used as urban road pavement or structural parts because it is very fragile. This loss of physical properties of the modified pervious concrete, with additive incorporated into the mixture, starts from a limit that configures the excess additive to be incorporated into the material. Tests shall be carried out to strike a balance between the additive limit and the maintenance of physical properties allowing the structural use of modified pervious road pavement concrete capable of absorbing CO2 into the atmosphere. An economical solution found in this research is a virtual simulation of nine prototypes of the new material being used as urban pavement and subjected to 5,000 N dinamic loads through the finite element calculation. The simulation is built using the modulus of elasticity data found in the test results of the density and compressive strength specimens performed in the laboratory.
The 1:0.80:4 ratio was the most efficient because it took less time to capture the same amount of CO2
The stoichiometric chemical calculation for calculating the Ca(OH)2 mass required to capture 1,000 L of CO2 from the atmosphere at an ambient temperature of 27 ° C (300 K) and atmospheric pressure of 0.20 atm is performed with n = 8,333 moles of CO2, as the molar ratio is 1: 1: 1, we have Ca(OH)2 = 8.33 × (40 + 2 × 16 + 2 × 1) = 616.42 g to be incorporated into the mixture of modified permeable concrete on each specimen. This CO2 sequestration property of the new material is very important for the environment, especially in climate control, air quality, and reduction of athermic pollution. Therefore this environmental benefit cannot be neglected, despite the negative points of reduction of density and compressive strength properties presented in the results of Figs. 2 and 3. The absorption of CO2 is accelerated with the addition of additive in the new material, but the results show that the material completely loses its physical properties, eventually disintegrating due to the lack of adhesion of cement to aggregates. An optimal ratio must be found so that there is a balance between CO2 absorption by the new material and its ability to be used as a building material, such as urban road pavement. The use of this new material as urban road pavement is important because it would cover an area of the city that would absorb toxic gases emanating from urban transport vehicles, which justifies the continuity of the research and laboratory tests being carried out. The results shown in Figure 4 have a positive environmental benefit that should be balanced against the negative results in density, Figure 2, and compressive strength, Figure 3, in such a way that the environmental and physical properties of the new material can be maximized. This equilibrium can be found with further research through laboratory testing with a larger number of specimens and new mixing ratios within the additive range without the destruction of the structure of the new material, manufactured from conventional pervious concrete with changes in the mix made in the laboratory.
The 1:0.30:4 ratio exhibits a greater variation of Young’s modulus, and the ratio 1:0.80:4 shows the smaller variation of Young’s modulus, demonstrating the influence of the additive on the structure of the material
Young’s modulus and density data used in the simulations
Quartiles | Pervious concrete Ratio 1:0.30:4 | Pervious concrete Ratio 1:0.50:4 | Pervious concrete Ratio 1:0.80:4 | |
|---|---|---|---|---|
Young’s modulus (MPa) | Quartile 1 | 992.21 | 1,445.58 | 1,178.88 |
Quartile 2 | 1,215.99 | 1,553.20 | 1,198.64 | |
Quartile 3 | 1,460.72 | 1,632.07 | 1,264.66 | |
Density (kg/m3) | Quartile 1 | 1,780.11 | 1,897.02 | 1,766.21 |
Quartile 2 | 1,903.06 | 1,963.33 | 1,822.53 | |
Quartile 3 | 2,086.72 | 2,153.63 | 1,851.39 |
Nine prototypes were used in the simulations
Prototypes | Young’s modulus (MPa) | Density (Kg/m3) |
|---|---|---|
P1 | 992.21 | 1,780.11 |
P2 | 1,445.58 | 1,897.02 |
P3 | 1,178.88 | 1,766.21 |
P4 | 1,215.99 | 1,903.06 |
P5 | 1,533.20 | 1,963.33 |
P6 | 1,198.64 | 1,822.53 |
P7 | 1,460.72 | 2,086.72 |
P8 | 1,632.07 | 2,153.63 |
P9 | 1,264.66 | 1,851.39 |
Nine prototypes were used in the simulations
Prototypes | Maximum deformation (mm) | Maximum Elastic Strain (mm/mm) |
|---|---|---|
P1 | 3.0575 × 10−8 | 1.6074 × 10−6 |
P2 | 2.0990 × 10−8 | 1.1035 × 10−6 |
P3 | 2.25748 × 10−8 | 1.3536 × 10−6 |
P4 | 2.4964 × 10−8 | 1.3124 × 10−6 |
P5 | 1.9785 × 10−8 | 1.0402 × 10−6 |
P6 | 2.5318 × 10−8 | 1.331 × 10−6 |
P7 | 2.0774 × 10−8 | 1.0922 × 10−6 |
P8 | 1.8585 × 10−8 | 0.9776 × 10−6 |
P9 | 2.3996 × 10−8 | 1.2615 × 10−6 |
Table 4 presents the results of maximum strain and maximum stress occurred in the nine virtual prototypes of finite elements created with the characteristics of the new material when subjected to vertical loading simulation. The prototype that was most deformed was P1 and the least deformed was P8 as shown in Table 4. The deformations occurred at the edges, which is structurally justified by the stress concentration at the edges of the materials. Deformations at the center of the prototypes were small, which is a positive factor as it indicates that the use of the new material does not tend to flexural rupture during loading, although the load was applied at the center of the prototype. The results of the structural analysis of the simulations showed that Prototype P8 presented the most efficient results, with the lowest deformations and tensions, according to Table 3.
Properties of the Prototype P8 used in the simulations
Prototype P8 | |
|---|---|
Ratio | 1:0.50:4 |
Young’s modulus | 1,632.07 MPa |
Density | 2,153.63 kg/m3 |
Descriptive statistics for the treated group (30 specimens) in the SPSS
Treated samples | Compressive strength (kg/cm2) | Density (kg/m3) | Sequestration volume CO2 (ppm/s) | Young’s modulus (kg/cm2) |
|---|---|---|---|---|
Mean | 13.83 | 1911.36 | 9.83 | 1338.40 |
Std. deviation | 2.57 | 193.33 | 2.46 | 246.11 |
Median | 13.05 | 1873.18 | 10.00 | 1305.89 |
Variance | 6.65 | 37,376 | 6.07 | 60570.85 |
Minimum | 8.70 | 1475 | 5.00 | 815.47 |
Maximum | 19.40 | 2284.94 | 14.00 | 1776.02 |
Skewness (statistic/error) | 0.50/0.43 | 0.29/0.43 | −0.08/0.43 | −0.098/0.427 |
Kurtosis (statistic/error) | −0.05/0.83 | −0.08/0.83 | 0.97/0.83 | −0.611/0.833 |
Maximum deformations in red color and located at the ends of Prototype P8
Among the nine virtual prototypes modeled by finite elements, P8 presented the minors deformations as shown in Fig. 6. The results of the tests performed with the prototypes submitted to dinamic load of 5,000 N presented deformations in the order of 0.00018585 mm (maximum) represented by the red color in the caption of Fig. 6. The P8 prototype showed the lowest deformations compared to the other prototypes, as shown in Table 4, which means that the P8 prototype material presented the best deformation results. The dimensions of the deformations that emerged in prototype P8 are noticeable only at the microscopic level. These results originate from a virtual simulation performed using finite element software, which does not rule out the need for field tests to prove the theoretical results presented here in the simulations. The results presented by the finite element software are positive and point to a possibility of using the new material as urban road pavement provided that there is a strict control of the additive mixture addition of the new material under study in this research and made from normal pervious concrete.
Minimum tensions in P8 is located in the center of the prototype
The displacements and deformations occurred in the prototype, through the structural loading simulations, allowed to verify the possibility of using the material researched as urban porous pavement and the choice of the best mixing ratio of the pervious concrete with the additive Ca(OH)2. The simulations performed in the computational program of structural analysis showed that the pervious concrete with additive, Prototype P8, supports well the loads applied in its structure, because it presented acceptable deformations and tensions in the structural field. The applied loads simulated a vehicle of 2,000 N on the surface of the pervious concrete pavement of a parking lot or urban road. For higher loads the material does not support the loading and should be replaced by a more resistant pavement. The addition of additive in the pervious concrete mixture causes an excess of deformations in its material, rendering the material unsuitable for structural use. The equilibrium between the environmental and structural qualities of the new pervious concrete with Ca(OH)2 additive is possible, but it is also fragile; therefore, more laboratory and field studies are needed to improve the material. The continuity of the studies should be carried out through field experiments that prove the studies carried out in the structural analyses of loading simulations on the prototype of pervious concrete with additive.
Conclusions
The results obtained in the structural simulations showed that it is possible to use the new pervious concrete with Ca(OH)2 additive as urban road pavement, with the most efficient performance obtained with the ratio of 1:0.50:4 (cement:Ca(OH)2:pebble), with modulus of elasticity of 1,632.07 MPa, and with density of 2,153.63 kg/m3. The results shown in Figure 2 show a 7% reduction in average density from 1,950.00 kg/m3 to 1,810.00 kg/m3, in Figure 3 a 15% reduction in average compressive strength from 15.10 MPa to 12.80 MPa and in Figure 5 a 22% reduction in Young’s Average Module from 1,200.00 kg/cm2 to 1,550 kg/cm2. These reductions in the physical properties of modified pervious concrete indicate that the additive impairs the action of cement as a binder, so it is not possible to use large portions of the additive incorporated in the modified pervious concrete mixture. The CO2 monitoring results demonstrated a positive environmental benefit with an increase in atmospheric CO2 absorption time of around 25% on average. The use of this new material as urban road pavement is important because it would cover an area of the city that would absorb toxic gases emanating from urban transport vehicles, which justifies the continuity of the research and laboratory tests being carried out, despite the reduction in the physical properties of density, compressive strength, and Young’s modulus because the cement action is impaired by the addition of additive in the new material mix. Future research should be conducted to find a balance between the positive environmental benefits of the new material with the disadvantages of loss of physical properties important for the structural strength of the new material, but nothing prevents the new material from being used as a pedestrian walkway or garden walkways that do not require structural strengths.
Cross-References
Notes
Acknowledgments
The authors wish to thank Fernando Pessoa University, Porto, Portugal, for the guidance provided and to the construction company J. Nasser Engenharia for the use of its concrete laboratory facilities.
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