Hands-on Activity Making "Magic" Sidewalks of Pervious Pavement

Learning Objectives

After this activity, students should be able to:

• Explain the materials that make a traditional concrete mix and how pervious pavement differs.
• Evaluate different ratios of materials to predict how infiltration rate changes with different mix combinations.
• Use everyday building materials to create pervious pavement.

Educational Standards

Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.

All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (www.achievementstandards.org).

In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.

NGSS: Next Generation Science Standards - Science

Common Core State Standards - Math

International Technology and Engineering Educators Association - Technology

State Standards

Materials List

Each group needs:

• 12-inch round, clear plastic planter liner, such as this 12.15 x 12.15 x 3.37-inch example for $1.08 at Home Depot http://www.homedepot.com/p/Vigoro-12-in-Deep-Plant-Liner-DL12HBDI/204400737
• 1-gallon native plant species
• 12-inch biodegradable coir hanging basket or planter; use the same planter filled with the media mix combination from the Does Media Matter? Infiltration Rates and Storage Capacities activity
• (2) 4-5/8" brick trowel or equivalent
• large mixing tub
• (2) measuring cups, volumetric cylinders or gallon containers
• (optional) 4 ounces liquid cement color
• stopwatch or smartphone, for measuring time
• 2 pairs latex gloves
• access to water and sink/drain
• Magic Sidewalk Worksheet, one per student

To share with the entire class:

• 50-lb. bag ¼-inch to 3/8-inch pea gravel, pond rocks, granite or limestone
• 50-lb. bag construction/playground sand
• 10-lb. bag Portland cement (do not use pre-mix cement)

Worksheets and Attachments

Introduction/Motivation

What happens to water when it rains? When it rains hard enough, rainwater begins to collect on surfaces such as roofs, sidewalks, driveways and even within our yards. This rainwater becomes stormwater runoff as it moves into the street and travels down the street gutters into the storm drain or storm sewer. Does anyone know where stormwater goes once it enters the sewer? That's right; after entering the storm sewer, stormwater typically goes into stormwater ponds, rivers and lakes. This water is also known as surface water and eventually makes its way into the oceans. Older cities have combined storm sewer and sanitary sewer systems. In these cases, the water is first directed to a wastewater treatment plant where it is treated (cleaned) and released back into surface water ecosystems.

A lot of pollutants collect on surfaces such as roofs, sidewalks, driveways and our yards, and these pollutants are carried away with the stormwater after it rains. These pollutants make their ways into the rivers, lakes, groundwater and oceans, and can negatively impact the health of the ecosystem, fishes, wildlife and humans.

Does anyone have a better idea of how we might reduce the amount of water that makes its way to the oceans when it rains? What if, instead of creating stormwater runoff from our homes, we were able to capture and provide treatment of pollutants before they enter the traditional stormwater infrastructure? One way to do just that is to create "magic" sidewalks—or concrete that permits water to pass through it.

Would it seem like magic if water went through a sidewalk? Well, Yes! Water can pass through a sidewalk if we change the materials that we use to make a sidewalk. (You may want to write the following four items on the board as you describe them.) Traditional materials that are used to create an impervious sidewalk—or a sidewalk in which water does not pass through—are a coarse aggregate consisting of ¼-inch to 3/8-inch limestone, pebble, granite or locally sourced material; fine grain sand such as construction, playground or beach sand; Portland cement, which is made of clay and limestone fines; and water.

To create pervious concrete, we need to eliminate one of the four materials used to create traditional concrete and determine the best design ratio mix for those materials. In this activity, we will keep track of the types of material used, the quantity of materials and the resulting infiltration rate of the final pervious pavement mix, and compare the results.

Pervious concrete may look a little different, but it serves the same purpose and helps protect the environment from the effects of pollution.

Procedure

Background

The objective of this activity is to create a pervious pavement that is structurally sound to walk on and also allows water to pass through it. Students begin by adding small amounts of water, aggregate (pea gravel, pond rocks, granite or limestone), and Portland cement and then mixing to the appropriate consistency. Adding too much water or cement results in a material that water will NOT pass through. The teacher may want to experiment with this mix to gain familiarity with what a successful mix feels and looks like before conducting this activity with the class. Expect a pervious pavement mix combination to feel very course and just be able to stick together. See Figure 1 for the appropriate consistency. When the mix is placed in a mold, expect to be able to see openings between the aggregate, so that water will be able to pass through.

Before the Activity

• Gather all materials and set them up at group lab stations, students' desks, classroom tables, or outside, prior to students arriving for class.
• Make copies of the Magic Sidewalk Worksheet, a two-page handout; page 1 for Day 1 and page 2 for Day 2. The porous concrete mixes must dry overnight before testing continues.
• Poke holes in the bottom of the plastic planter liner to permit water drainage. Do not poke holes in the center; the plant will be placed in the center.
• Note that students will need their completed worksheets and pervious pavement mixes for the next activity in this unit.

With the Students

1. Day 1: Ask the class the pre-assessment warm-up questions provided in the Assessment section. Then present the Introduction/Motivation content, having students think more deeply about some of its questions using the think-pair-share approach described in the Assessment section.
2. Then divide the class into groups of two or three students each, depending on class size and the availability of resources. Hand out the worksheets.
3. If conducting the experiment outside, direct students to record the date, time of day, temperature, humidity, dew point and weather conditions on the worksheet. Refer to an online weather website that provides localized weather conditions, such as Weather Underground at http://www.wunderground.com.
4. Start the activity by presenting the Introduction/Motivation content, which includes asking students what happens when it rains and describing the concept of impervious and pervious surfaces. If water can go through a sidewalk, would this be magic?
5. Explain that cement, sand, aggregate (such as gravel, pebbles, crushed limestone) and water are the four ingredients that make a traditional concrete sidewalk. Have students record these materials on their worksheets.
6. Tell students that the materials for making a traditional sidewalk are at each group's lab station. By removing one of these materials from the mix, they can create a "magic" sidewalk, that is, concrete that lets water pass through it.

   

7. Ask students to record on their worksheets the material they think they should remove to create the magic sidewalk.
8. Direct student teams to begin the challenge to create a "magic" sidewalk mix by removing one of the materials from the typical concrete sidewalk mix in their mixing tubs. To do this, groups need a measuring cup or volumetric cylinder, large mixing tub, brick trowel and mix materials. Remind students to keep track of the quantities of each ingredient in their mixes. Direct students to begin with small quantities of each material and complete several trials until they achieve a mix combination that they believe will result in a magic sidewalk.
9. Upon mix completion, have students answer the questions:

• Does the magic sidewalk mix stick together?
• Does the magic sidewalk mix look magical?
• Will the mix allow water to pass through?

10. Circulate through the groups and observe their mixes. Generally speaking, as they go through the trials, expect students to conclude that they must use a higher ratio of aggregate to cement and water. Keep hinting at this.

    

11. Next, have students in each group place their 1-gallon native plant species container in the center of the 12-inch planter liner and fill the surrounding area with the magic sidewalk mix, approximately 2 to 3-inches deep. If liquid cement color is available, incorporate it to the mix prior to filling the planter liner. Then, let the mix in the planter liner dry over night before testing to see if it is magic and determine its infiltration rate.
12. Students use the 12-inch planter liner and a 1-gallon plant container so that the magic sidewalk can be inserted into the basket/planter while allowing space for native plants to be inserted inside the opening. Prior to having students place their magic sidewalk mixes into the planter liner, poke several holes in the bottom of the liner except in the center area where the plant will be inserted. These holes allow excess water to drain from the pervious pavement mix. Hence, the plant container serves as a mold for the magic sidewalk mix and provides appropriate spacing for the plant within in the final personal rain garden assembly (created in the next associated activity, A Guide to Rain Garden Construction).

    

13. Day 2: The next day, the materials should be dry and ready to test to see if they are indeed "magic" sidewalks. Remove the magic sidewalk from the plastic liner and place it into the coir basket or planter. Use the coir basket/planter filled with the media mix combination from the Does Media Matter? Infiltration Rates and Storage Capacities activity. Place the magic sidewalk on top of the media layer in the hanging pot.

    

14. Remind students to have available their worksheets from the day before, so they can record new data and observations on page 2. If conducting the experiment outside, direct students to record the date, time of day, temperature, humidity, dew point and weather conditions on the worksheet.
15. Have teams test the magic sidewalks by filling a volumetric cylinder with a known volume of water and pouring the water directly over the magic sidewalk. Advise them to start with small quantities of water to ensure that all the water does infiltrate into the magic sidewalk. Have students keep track of the amount of water, the time it takes for the water to disappear from the surface of the magic sidewalk, and record on the worksheet this information and their observations. The infiltration rate is equal to the volume of water divided by the time it takes for the water to disappear from the surface.
16. Conclude by leading a class discussion to share, compare and review student results and recommendations. Write on the classroom board the different mix combinations and their infiltration rates. Examine the mix ratios of the different groups. What can we conclude about the common characteristics of the mixes with higher infiltration rates? Also ask the questions provided in the Assessment section. Collect and review the worksheets.

Vocabulary/Definitions

cement: A gray powder that serves as the bonding agent when sand and course aggregate are mixed with water to create concrete. Cement is composed of clay and limestone fines.

concrete: A "rock hard" mass that is made by mixing cement, sand, course aggregate and water. The resulting material is heavy and strong, and used for road paving, and slabs for structures like homes, bridges, foundations, basements, retaining walls and sidewalks.

Assessment

Pre-Activity Assessment

Warm-Up Questions: Ask students the following questions to gauge their base level of knowledge and warm up the class to the activity topic.

• Have you ever seen a hard surface, driveway, road or sidewalk that permitted water to go through it? If so, what did it look like? If you have not seen such a surface, what do you think one would look like? (Answer: Water can go through many everyday surfaces such as grass, pavement cracks, soil, rocks and pavers. Water follows the path of least resistance and will flow through any surface that provides openings for it to move through.)
• What is the technical term for a surface in which water can pass through? (Answer: Pervious surface.)
• What is the technical term for a surface in which water can NOT pass through? (Answer: Impervious surface.)

Activity Embedded Assessment

Think-Pair-Share: As part of the Introduction/Motivation presentation, ask students to think about the following questions with a partner, and then share with the class.

• What happens to water when it rains? (Answer: When it rains hard enough, rainwater begins to collect on surfaces such as roofs, sidewalks, driveways and even within our yards. This rainwater becomes stormwater runoff as it moves into the street and travels down the street gutters into the storm drain or storm sewer.)
• Where does stormwater go once it enters a storm sewer? (Answer: After entering the storm sewer, stormwater typically goes into stormwater ponds, rivers and lakes. This water is also known as surface water and eventually makes its way into oceans. Older cities have combined storm sewer and sanitary sewer systems. In those situations, water is first directed to a wastewater treatment plant where it is treated/cleaned and released back into surface water ecosystems.)
• Does anyone have a better idea of how we can reduce the amount of stormwater that makes its way to rivers, lakes, ponds and oceans when it rains? (Answer: Low-impact development [LID] and green infrastructure (GI) technologies can be utilized to reduce stormwater runoff at its sourced to restore the hydrology and water quality of developed sites to pre-development conditions. Examples of LID or GI are rain gardens or bioretention, pervious pavement, green roofs, bioswales, rainwater harvesting, green streets and alleys, planter boxes, urban tree canopies and downspout disconnection.)

Worksheet: Have students complete the two-day Magic Sidewalk Worksheet as they conduct the activity by answering questions, recording measurements and observations, and making calculations. Review their worksheets to gauge their depth of comprehension.

Post-Activity Assessment

Wrap-Up: Lead a class discussion to share, compare and review student results and recommendations, including the worksheet questions/answers. Ask the students:

• Where might this magic sidewalk material be used in the real world and how would engineers use this information? (Answer: A magic sidewalk could be used in areas that do not see a lot of heavy traffic. This includes driveways, sidewalks, bike paths, patios, parking lots, public plazas, outdoor basketball courts, and neighborhood streets and alleys. Engineers could use the testing results from this activity to specify the mix combination to be installed at a specific project, to design a stormwater management plan for new development, or to reduce areas of localized flooding within the existing urban environment.)
• What is the difference in materials between traditional pervious pavement and traditional pavement? (Answer: By mixing specific ratios of materials together to create permanent pore spaces, pervious pavement lets water pass through. Pervious pavement uses materials that are similar to traditional pavement mix materials—small aggregate, cement and water—but differs from traditional pavement in that finer grain size particles [such as sand] are eliminated. The ratio of small aggregate, cement and water is critical; too much of one material may create an impervious surface or a surface that is not structurally sound.)
• How does pervious pavement reduce stormwater runoff and pollution from affecting downstream ecosystems? (Answer: Reducing the volume of water entering into traditional stormwater infrastructure systems limits the mass of pollutant loading entering downstream ecosystems. Pervious pavement reduces stormwater runoff at its sources by promoting infiltration of stormwater into the ground.)

References

Copyright

Contributors

Supporting Program

Acknowledgements

This curriculum was developed by Water Awareness Research and Education (WARE) Research Experience for Teachers (RET) at the University of South Florida, funded by National Science Foundation grant number EEC 1200682. However, the contents do not necessarily represent the policies of the NSF, and should not be assumed an endorsement by the federal government.