Development of Rainwater Filtration System with Porous Asphalt

Rainwater that is not properly collected causes stagnant water, where the water will be polluted by pollutants and contaminants. Thus, it is necessary to innovate to increase the availability of clean water using porous asphalt which is researched to reduce pollutants in polluted water. In this study, filtration of rainwater and stormwater runoff will be carried out using porous asphalt as a filter media with six different filtrate variations. Parameters analysed were pH, Total Dissolved Solids (TDS), and conductivity. The tests carried out were Optimum Asphalt Content (OAC) testing using the Marshall test method with a percentage of asphalt content used was 4-6%, Cantabro Loss testing, porosity, and permeability tests on porous asphalt specimens, as well as testing the filtration effect of porous asphalt. Rainwater and stormwater runoff that flowed through porous asphalt samples without the addition of filter media increased pH, TDS, and conductivity. In rainwater and stormwater runoff filtration, the highest increase in pH occurred in variation 3, namely porous asphalt + aggregate + limestone. The largest reduction in TDS and conductivity values occurred in Variation 7, namely porous asphalt + aggregate + coconut shell activated carbon + sponge + cotton.


Introduction
Stormwater runoff can disrupt the comfort of driving.The condition is caused by a clogged road, as well as poor drainage along the road.One way to solve this problem is by using a porous asphalt layer.Porous asphalt is a layer that can increase the resorption of rainwater on the soil and reduce the presence of water on the road surface [1].Porous asphalt is an open-graded road pavement layer that is dominated by coarse aggregate which amounts to around 70-85% of the total weight of the mixture, has a low percentage of fine aggregate ranging from 15-30% of the total weight of the mixture [2], and has voids which is greater by 18% compared to normal asphalt pavement.The need for clean water among the people is increasing.Therefore, it is necessary to innovate to increase the availability of clean water using porous asphalt which is researched to reduce pollutants in polluted water.In this study, filtration of rainwater and stormwater runoff will be carried out using porous asphalt as a filter media, it is hoped that after rainwater passes through porous asphalt it can improve the quality of the rainwater.So, if rainwater enters the Water Treatment Plant (WTP), it doesn't require too much treatment.1324 (2024) 012001 IOP Publishing doi:10.1088/1755-1315/1324/1/012001 2 2. Literature Rerview 2.1.Porous Asphalt Porous asphalt is designed to have large air voids that function to drain water vertically and horizontally, and as a reservoir medium that can drain and store rainwater into the ground.Porous asphalt pavements can drain water in a shorter time, thereby reducing the chances of hydroplaning or aquaplaning.In addition, porous asphalt can also remove pollutants and improve water quality.Porous asphalt has lower strength than conventional asphalt, has low stability which can result in large deformations.This happens because the composition of the porous asphalt mixture is dominated by coarse aggregate, so the mixture tends to be stiff and brittle.Porous asphalt mixtures tend to experience high pressure due to high void content which can result in rutting.

The Ability of Porous Asphalt to Filter Rainwater
Porous asphalt is effective in rainwater management, improves water quality, reduces rainwater inflow, and restores groundwater supplies.Rainwater flows onto the porous asphalt surface and is retained in cavities to reduce rainwater inflow.The retained water flows to the base surface and eventually restores the groundwater supply.At the time of absorption of rainwater, water quality improves, because the porous asphalt filters out contaminants such as pollutants.Several previous studies have measured high levels of reduction of Total Suspended Solid (TSS), Pb, Zn, and pH, as well as turbidity in rainwater using porous asphalt.A study conducted by Thives et al in 2018 showed that filtering rainwater and rainwater runoff using porous asphalt with two models could increase pH, there was no significant change in DO (Dissolved Oxygen) between models and controls, able to reduce ammonia concentrations.However, there was an increase in the concentrations of P, Fe, Zn, NO3, Cr, and Cu.The model tested shows that porous asphalt can filter out some of the pollutants from rainwater runoff and rainwater, but not all of them [3].A study conducted by Myers et al in 2007 examined the physical and chemical processes that occur in dolomite and calcite aggregates in porous asphalt structures.The use of dolomite and calcite aggregates reduced the content of heavy metals namely Cu, Pb, Zn and phosphorus by 90%, there was an increase in pH, alkalinity and TDS.Dolomite aggregate has a greater effect than calcite in improving water quality [4].

Material
The material used in this study is from local aggregates.Asphalt that will be used in this study is asphalt pen 60/70.Table 1 represents aggregate and asphalt testing specifications.Optimum asphalt content is obtained by calculating from the data that has been obtained to obtain VIM, VMA, and VFA values, as well as making comparisons between the calculation results that have been obtained with the specifications used in the study to obtain optimum asphalt content.

Cantabro Loss Test
The Cantabro Loss Test is a test conducted to determine the resistance of pavement layers to wear using a Los Angeles machine without using steel balls.The wear value is obtained by comparing the weight of the sample after it has been rotated for 300 revolutions with the original weight before being put into the Los Angeles machine [5].Based on AAPA (Australian Asphalt Pavement Association) specifications, the maximum value of Cantabro Loss for porous asphalt is 20%.

Porosity and Permeability Test
Porosity and permeability tests on asphalt samples were carried out using a falling head permeameter.From this test a permeability coefficient value will be obtained [6].The difference in hydraulic heads on the right and left sides of the permeameter makes water flow from a higher hydraulic head reach equilibrium.The time required for water flowing from a higher hydraulic head to reach equilibrium can be calculated to obtain the permeability coefficient.Based on the specifications of the AAPA (Australian Asphalt Pavement Association), the porosity value of porous asphalt is 18% -25%.Based on the AAPA (Australian Asphalt Pavement Association) specifications, the permeability coefficient value for porous asphalt is 0.1-0.5 cm/s.

Rainwater Filtration Test
Figure 1 shows the rainwater filtration test.A 4" diameter PVC pipe was cut 50 cm long as a filter pipe and closed using a pipe cap to obtain different contact time variations, namely 0 minutes, 15 minutes, 30 minutes and 45 minutes, and was equipped with a faucet to drain the filtered water.The diameter of the porous asphalt sample is 10 cm with a thickness of 7.5 cm.In addition, the thickness of the filter media used is 5 cm each.Rainwater collection is carried out by collecting rainwater which is collected directly and collecting rainwater that falls to the road surface (stormwater runoff).The mixture weight for one sample is 1200 grams.To make asphalt samples, aggregate gradation is first carried out, where the composition of each aggregate requirement will be obtained in accordance with the planned asphalt content, namely 4%, 4.5%, 5%, 5.5%, and 6%.Based on Figure 2, it can be seen that the design gradation is between the top and bottom gradations.Thus, it can be concluded that the aggregate gradation meets the specifications.Based on Figure 3, it can be seen that the horizontal line indicates the sample that was tested meets the specifications.The vertical line shows that the optimum bitumen content is found in the percentage of asphalt content of 5.5%.Thus, the asphalt content of 5.5% can be used for further testing.

Cantabro Loss Test Result
Based on Table 6, it can be seen that the Cantabro Loss value obtained is 17.41%, this indicates that the asphalt mixture with an asphalt content of 5.5% meets the AAPA specifications, namely the maximum Cantabro Loss value for porous asphalt is 20%.4 shows the relationship between porosity and permeability.The greater the porosity, the greater the permeability of the porous asphalt sample.This is because the greater the percentage of bitumen content, the volume of voids in the sample decreases, so that the time needed for water to flow through the sample is longer.7, the results of rainwater testing in the Taman Mini area, East Jakarta have a pH of 6.6, as well as TDS and conductivity with respective values of 19 mg/L and 38 µS/cm.The results of the stormwater runoff test have a pH of 6.5, as well as TDS and conductivity with respective values of 103 mg/L and 206 µS/cm.Therefore, it is necessary to carry out tests to increase pH, reduce TDS and conductivity of the water that has been stored.Tests were carried out using porous asphalt samples with variations in contact time of 0, 15, 30, and 45 minutes.The test was carried out three times with three different water samples to obtain a statistically significant result.Figure 5 and Figure 6 show the results of pH, TDS, and conductivity of rainwater and stormwater runoff that has flowed through a porous asphalt specimen, respectively.Figure 5 and Figure 6 show that the longer both rainwater and stormwater runoff water stayed in the porous asphalt specimen, the pH, TDS, and conductivity values increase.It shows that the water became more contaminated.Thus, it is recommended that the water needs to pass through the specimen as soon as possible.Figure 7 is the result of testing rainwater that has been flowed through 6 variations of filter media.Figure 8 is the result of testing stormwater runoff that has been flowed through 6 variations of filter media.The addition of limestone as a filter media can increase the pH, TDS, and conductivity.In rainwater and stormwater runoff filtration, the highest increase in pH occurred in variation 3 because limestone is able to increase pH, but also increase TDS and conductivity.
Variations 3, 5, and 6 are considered ineffective for use as filter media for rainwater filtration, because they can increase pH, TDS, and conductivity upon direct contact.Variations 1, 2, and 4 can be said to be effective for use as filter media for rainwater filtration, due to an increase in pH, decrease in TDS, and decrease in conductivity.After obtaining the results of the six filtrate variations, the next step is to conduct tests by making the most effective filter media arrangement (variation 7) with the composition of porous asphalt + aggregate + coconut shell activated carbon + sponge + cotton to increase pH, and reduce TDS and conductivity in rainwater.Limestone is not used for this filtration because in the previous results limestone has the effect of increasing pH, TDS, and high conductivity.Figure 9 is the result of testing rainwater and stormwater runoff that has been flowed through variation 7. From the research results, it can be concluded that in variation 7 there is an increase in pH, as well as a decrease in TDS and conductivity that is greatest.

Conclusions
The conclusions of this study are the porosity and permeability values of the porous asphalt sample are directly proportional, the greater the porosity of the porous asphalt sample, the greater the permeability of the sample.The highest increase in pH occurred in variation 3 because limestone is able to increase pH, but also increase TDS and conductivity.The highest decrease in TDS and conductivity occurred in the most effective variation of filter media.The most effective layer to improve the quality of filtered water is porous asphalt + aggregate + coconut shell activated carbon + sponge & cotton, due to an increase in pH, as well as a decrease in TDS and conductivity.

Figure 4 .
Figure 4. Relationship Between Porosity and Permeability

Table 2 .
Gradation Distribution Marshall TestThe Marshall Test was carried out to determine the stability to flow of a porous asphalt mixture.In Indonesia, the specifications used for the Marshall Test refer to SNI 06-2489-1991.The Marshall Test was carried out by reading the stability and melting dial on the Marshall machine, where the sample was first placed in a water bath at 60 ºC for 30 minutes.The stability value is obtained when the needle on the dial reverses or decreases on the stability dial.Meanwhile, yield is the value read on the flow dial when there is a deflection from the stability dial.From the Marshall Test, the results obtained were Marshall components, namely stability, melting, Void in Mineral Aggregate (VMA), Void in Mix (VIM), and Void Filled Asphalt (VFA).From these components, the Optimum Asphalt Content can be obtained.Table3is the Marshall Test specifications for porous asphalt based on the AAPA (Australian Asphalt Pavement Association) and NAPA (National Asphalt Pavement Association) specifications to obtain optimum asphalt content.

Table 3 .
Marshall Test Specification

Table 4 .
Variation of Filter Media

Table 5
is the result of aggregate and asphalt testing.It can be seen that the aggregate quality parameter tested is specific gravity, which consists of bulk, SSD, and apparent specific gravity, and aggregate absorption meets SNI specifications.For asphalt testing, the quality parameters tested are penetration, flash point and firing point, ductility, softening point, and specific gravity according to SNI specifications.

Table 5 .
Aggregate and Asphalt Test Result

Table 6 .
Cantabro Loss Test Result

Table 7 .
Rainwater and Stormwater Runoff Test Result Before Filtration