Drainage

Drainage and sustainability have been an issue since the beginning of urban living. Concrete covers 80% of all metropolitan areas in the world. However, this poses a problem when rain comes to town. Standard concrete is made so that it doesn’t absorb or allow water to pass through it, allowing for more structural integrity when the freezing and thawing process occurs. However, as a side effect, stormwater is collected on its surface. In the event of extreme rainfall flooding, our current drainage system is not well enough prepared to handle this issue, creating a large safety and infrastructure concern.

 Our current drainage system is also responsible for many environmental issues:

The first of which is groundwater replenishment. Groundwater is the water found in cracks and soil deep throughout the ground. Currently, groundwater levels are low in urban areas because of concrete; this has a large effect on the ecosystem in an area because many rivers and streams feed off the groundwater and, therefore, would disappear without it. This could then destroy ecosystems and affect species in this area. Furthermore, groundwater provides water for one-third of all Canadians, and in rural areas, this number increases to 80%. Also groundwater is used in abundance for agricultural irrigation worldwide.

Another issue caused by current concrete options is the effects of the current drainage system. Currently, all water drains into storm ponds, wetlands, streams, or rivers. This leads to a build-up of water that can have large impacts on ecosystems. I have quite a bit of personal connection to this, as my local wetland that had a small creek has developed into an enormous swamp. This greatly impacts the recreational use of the area, all due to its use as a drainage area. This also can have a large effect on infrastructure in case of overflowing storm waters.

 

 

These drainage concerns are currently being addressed by many concrete corporations right now there is one product on the market that allows for permeability. It is a regular mixture of concrete however, it was adapted in the following ways: it was created without sand, with very limited amounts of water, and gravel aggregate. However, there are some large issues with this product that are greatly affecting its success. One of which is durability, currently, this is the largest impediment in the spread of this product's usage as it cannot be used on roads or busy parking lots as it will easily wear down. Therefore, this product is only being used on bike and walking paths or driveways. The other main concern or issue with this product is the fact that it cannot be used in environments that reach temperatures below zero. If the cement isn’t properly installed, it may trap water in the actual cement, not the drainage layer beneath in which the water is supposed to be stored, causing cracks during the freezing and thawing, making it structurally unsound.

 

The Heat Island Effect

Another way that traditional concrete is harming our environment is known as the heat island effect. The heat island effect is a reaction that occurs in highly urbanized areas due to the use of heat-absorbent materials. Because of this material, urban areas can generate up to 3.9 C more than the surrounding, more rural areas. This increase in heat can lead to higher use of air conditioning in highly populated areas and can affect carbon emissions. However, using more reflective or higher albedo materials can play a large role in preventing this problem, and since about 30% of all urban areas are covered by pavement, a white alternative concrete could greatly help the environment.

 

Carbon Emissions

The final key way in which concrete negatively impacts the environment is through carbon emissions. Concrete production, refinery, and distribution made up 8% of all carbon dioxide emissions globally in 2021. Concrete is crucial for economic and industrial growth globally. Therefore, nearly 4 billion tons of cement are produced each year in a very energy-intensive process, largely due to the refining of limestone, which is a large ingredient in modern-day concrete. It has been calculated that for one ton of concrete produced, 0.8-1 ton of carbon dioxide is emitted, to put this into perspective, that is equivalent to running a car for 2,500 miles or 4,023 kilometres. This means that if concrete production were to be compared to countries' carbon emissions, it would rank third in the world. Despite this, some alternative materials can be used to reduce emissions, an example of this is volcanic ash, which I will be using In my prototypes. But there are also calcined (dry clay) and fly ash, which can be substituted for part of the cement mix. However, these two ingredients are not available enough to be used on a large scale, but volcanic ash is, meaning it would be the most viable alternative.

 

Costs

Currently, concrete is the most common building material in the world and is vital to building nearly everything in our world. However, concrete is currently made predominantly in China. Nearly half of the global production comes from China, and the costs and times of shipping can be very impactful on underdeveloped countries that need this material. Therefore, by using more locally available materials that may have been considered waste materials, it is possible to reduce the costs and increase the availability.

 

Throughout this testing, I have three main aims for my prototypes:

1. To be able to withstand the forces needed to be able to be a realistic alternative to current products
2. To be a more environmentally friendly alternative that solves the three main problems (groundwater, drainage, and carbon emissions)
3. It needs to be an affordable alternative; it can not be too expensive that it affects its usage

 

Research

To meet these aims, I have researched some possible materials that I can include or substitute into existing recipes.

Volcanic Ash 

Volcanic ash has been included in the formulation of concrete for centuries, aging back to the age of the Romans. The Romans are the crafters of many incredible historic structures, many of which are still standing today. This was an impressive feat, and therefore, scientists have been trying to reverse-engineer their recipe for quite some time. Eventually, it was found that their mixture used volcanic ash and lime in combination to create a chemical reaction called the pozzolanic reaction, which would strengthen the concrete. Along with adding strength, volcanic ash is a possible substitute for Portland cement. This is a large pro to this material and if it can be avoided, it is best not to use Portland cement as its production is an extremely large carbon emitter. 

 

 

Fibres 

The inclusion of short fibres in concrete formulations is a great material to use to add strength and durability to the mix. This material will be very important, as one of the main aims of the product is to be strong and durable enough to hold in place under the forces of daily use. Usually, the fibres used in concrete are either glass or steel fibres. However, I aim to create my prototypes with carbon fibre. The reason I am going to do this is the availability of this resource. A material known as bitumen is a byproduct of crude oil drilling. Recently, it has been found that this product can be used to create carbon fibre and an organization known as Alberta Innovates is working towards creating the necessary machinery to turn this waste product into a usable resource.

 

 

Super Plasticizers

Superplasticizers are a material that is commonly used in concrete. They are a group of additives that have many significant benefits to concrete production. The main four advantages of superplasticizers are added durability, reduction of water in the recipe, increased fluidity, and added strength throughout the freeze and thaw process to limit cracks. These are very important for my prototype, as strength and cracking are two of the large issues with current permeable concrete options. Along with this, reducing water usage in concrete production has a positive environmental impact, especially as permeable concrete already uses very small amounts of water, which means there would be very little water needed.

 

 

Air Entraining Agents

Air-entraining agents are concrete additives that allow the creation of microscopic air bubble formation. These air bubbles will also connect with the void gaps already made by the permeable concrete mixture to allow for more permeability. This additive also allows for more strength throughout the freeze and thaw process.

 

 

Plan

 

Mixes and Moulds

In order to build and test my prototype concrete solutions, I have the following plan to ensure fair and proper experimentation:

The first part of my method was creating the mould for the concrete, when building this, I had to ensure that it met the needs of both my testing and my resources. I found that the best way to create these moulds was with wood. Using wood, I created a square mould that is 1ft by 1ft on the outside. I constructed this out of 1.5 by 4-inch pieces of would screw into a square that was then screwed onto a piece of plywood. I then use a sheet of plastic to ensure the concrete doesn’t dry into the wood. The final inner volume of the boxes I made was 180 square inches. This method of construction was perfect for the needs of my experiment, as this is a large enough slab for it to be an accurate model of its real-life application. However, it will not use too many of my materials with one prototype. 

For the actual concrete mixes and recipes, I will be following this template: 

• 14 cups aggregate
• 5 cups cement
• 2 ½ cups water 
• 1 cups sand

 

Additives will be included as per the manufacturer’s instructions; if large sums of additives are used, I may need to increase the amount of water. Any cement substitutes will be added 40/60 to the Portland cement. 

Testing

For the permeability test, I followed the following steps:

I made sure that the edges of the mould were not allowing any water through by taping them off. I would then place the bottomless mould on top of an empty one, which I made specifically for this purpose to be sure there weren't any leaks or holes, this would act as a water collection system. Then I poured 2 cups or 473 millilitres of water onto the mould, and once all of the water was touching the surface, I would start a 30-second timer. Once the 30 seconds was up, I immediately removed the concrete and placed it on a bowl. I then poured the collected water back into the original measuring cup, recorded the amount of water it let through in both millilitres and cups, and then converted it into a percent.

To test for the concrete impact-resistant strength, I followed the following steps:

I knew that for this test I wouldn’t be able to break the prototypes using a stationary force, however, dropping a weight onto it would add a lot of complexity to the process. To combat the issues that arose with using a falling weight, we built a wooden chute to ensure that the weight would consistently land flat onto the concrete. Also, to ensure that we could effectively calculate the PSI generated by the falling weight. Using this chute, I then dropped a twenty-pound dumbbell 5 times, starting at one foot and making my way up in 1-foot increments. After each drop, I would check for any damages and note them, however I continued until a substantial breakage occurred. Once there was a breakage, I used an AI calculator to figure out how much force that weight generated and then divided that by 7.5 inches as that was the surface area of the head of the weight.

 

 

 

Looking at the results, the most successful mixture in the porosity portion of our testing was the base mixture. This wasn’t necessarily what I had expected from the testing. However, I knew that the volcanic ash would affect the porosity. However, I didn’t know whether it was going to be an increase or decrease in porosity. I believe that the reason for the decrease was due to the change in viscosity due to the addition of the ash. Because the mixture became more fluid, it settled at the bottom more than the base, and therefore, there were much fewer gaps for the water to pass through that would lead all of the way through the slab. Along with this, more water got caught in dead-end pathways, decreasing the amount of water that could get through. The reason that the mixture with the additives worked better was most likely because it slowed this flow toward the bottom of the mould.

 

On the contrary to the results of the porosity testing, the strength testing went as I had predicted. The prototypes went up throughout the test by a noticeable margin, and the PSI was as I had expected. Usually, concrete needs to be approximately 3,00 to 5,000 PSI to be used in heavy traffic areas. The base tests showed a result of approximately 1,072 PSI, which was as expected, as I used a large aggregate to amplify the results of all the testing so that they would be more definitive. So, taking this into account by mixing it more thoroughly to eliminate some void space and using a smaller aggregate would allow for more bonds between each piece of aggregate, meaning that you could double the strength of the mix. So, using this information, we can infer that the base mix wouldn’t meet the needed requirements to be used in high-traffic areas, which is exactly the issue that is currently impacting the popularity of permeable concrete. However, the incorporation of the volcanic ash made it a more viable yet still not a great option, but the final mix that includes the additives is well over the threshold. Through this, I can infer that the pozzolanic reaction did take place as the volcanic ash was more successful than just the concrete alone. Along with this, I can infer that the additives that I included did positively affect the concrete's durability.

 

My concrete prototype was able to solve many of the problems with modern-day concrete. Through the incorporation of the volcanic ash in my prototype, I was able to reduce the overall amount of carbon emissions by 16%, meaning that if all concrete globally were to use this method, it would save 608,000,000 tonnes of carbon each year. Along with this, volcanic ash is a cheap ‘waste material’ that doesn’t have many other uses outside of concrete, and it is available locally in approximately 30 of the 130 developing countries in the world. Therefore, in these countries that are often struck by natural disasters, they could use volcanic ash to prolong their materials and save money by using it 50/50 with regular cement. Along with this, the incorporation of the additives has allowed me to formulate a stronger and, therefore, more viable permeable concrete, which could save governments billions worldwide on drainage infrastructure, and it can significantly help to aid any flooding. 

 

Despite these accomplishments, there were still areas in which I could have improved within both my testing and what I put into my final product. The first key flaw was within my prototype, I was unable to acquire titanium dioxide, which was the best option for dyeing the concrete white. It goes into the mix and isn’t a stain, which is better as stains add extra time and, therefore, more labour costs. However, his problem could be easily solved, but titanium dioxide wasn’t available to me, however, if this recipe were to be implemented on a large scale, it would have been better to include this material. Another possible flaw occurred within the strength testing portion of the experiment, to find the strength of the mixes, we dropped a 20-pound dumbbell from various heights and then calculated the force that it took to break it. However, the result that we got is most likely inaccurate in some way, as there was no way to know if the previous drop had weakened it, and therefore, it did not survive the following one. Also, we dropped the weight at one-foot increments, so I know the range in which it could hold. However, I do not know the maximum force it would have been able to support. Despite this being a flaw, it doesn’t affect my ability to compare the tests to one another, however, it did affect my ability to compare the results of one test to others in the real world with certainty. The only way that I could have solved this issue would have been by using a professional grade hydraulic press that provides a constant force onto the subject and goes up in controlled and slow increments that are accurately measured to give a very exact force that the concrete was able to withstand.

 

Sources

Solving Cement's Massive Carbon Problem | Scientific American. 

Cement and Concrete: The Environmental Impact — PSCI 

What Are the Fibres Used in Concrete | Bisley & Company Pty Ltd 

Researcher engineers a better way to produce carbon fibre from bitumen | Folio.

 Air Entraining Admixtures for Concrete 

Cities of the future may be built with locally available volcanic ash | MIT News 

PIP 4 – Guide to Pervious Concrete Mix Design 

Urban Surfaces and Heat Island Mitigation Potentials). 

A Cooler Future Means a World With Less Pavement | The Nation 

 

Images

What is Groundwater? – Spokane Aquifer Joint Board 

Cement and Concrete: The Environmental Impact — PSCI 

Solving Cement's Massive Carbon Problem | Scientific American. 

Urban heat island | World Meteorological Organization 

What Is an Urban Heat Island? | NASA Climate Kids 

Uncovering the Roman recipe for self-repairing concrete

What Is Volcanic Ash, Its Effects, and How to Mitigation Them | Geology Base  

Ultimate Guide To What Superplasticizer Does Do To Concrete

Asphalt Bitumen Concrete Reinforcement Polyester Pet Fibre  

Air Entraining Admixtures | Modernization of Concrete - Structural Guide

Air Entraining Admixtures - CivilWeb Spreadsheets