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Behaviour of Sand-Rubber Mixtures

Siemens Research Competition 2014

Abstract

Scrap tire disposal rates have increased and has posed a threat to the environment.

There have been research efforts to find ways in which scrap tires can be used in

civil engineering, by reusing the rubber (Lee, Changho, Hosung Shin, and Jong‐Sub

Lee, 2014) . Civil engineers have discovered different applications of the rubber and

one of the ongoing efforts is that of Sand-Rubber Mixtures. Sand is brittle, but was

found to be more ductile with rubber mixed. The research I conducted dealt with the

behaviour of the sand-rubber mixtures and was specifically geared towards studying

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its dynamic properties, one of which was its density, to be able to use the

information to implement it in constructions sites. Some tests that were taken

included the calculation of water content, determination of specific gravity, and

developed a procedure to create adequate and uniformed test samples. Through this

extensive research it was found that the density gave a negative correlation to the

volume ratio percentage of rubber mixed in a sample. Data on other dynamic

properties of the Sand-Rubber Mixtures are still yet to be recorded.

Introduction

The increase of scrap tire is critically affecting us globally. It is through civil

engineering that we find most of the rubber use applications that include recreational

park facilities, roadways, and railways. It is using rubber such as the ones found in

car tires, a resource that is disposed of improperly, and reusing them in different

ways. The research in Sand-Rubber mixtures is fairly new and there have been

studies to see how Sand-Rubber Mixtures could be able to be applied at construction

sites. Sand is known for being a very brittle material to work with, but recent

research such as (Neaz Sheikh, M., Mashiri, M., Vinod, J., & Tsang, H., 2013)

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suggest that mixing it with rubber could provide some beneficial outcomes. The

rubber is seen to reinforce the stability of the sand meanwhile it still keeps its

lightweight ability. It could certainly be advantageous in a construction site, not only

by being able to support an infrastructure but also through its eco-friendly material.

The research gives a more in depth look at the aspects of the mixture researchers

have to take into consideration that of which includes the density and how forces

may affect it. It has data that shows several test done on the amount of force that it

was able to handle and how it compared to other mixtures. The research was done in

a controlled environment and looked at the differences between pure sand deposits

and sand-rubber mixtures. It also tries to explain specific uses and is trying to be

approved as a method of building foundations on construction sites. Research was

able to provide some insightful information into the properties that sand-rubber

mixtures, but failed to test out every factor that may go into the construction of

foundations. It showed that sand-rubber mixture were quite strong compared to

simply pure sand and gave further details as to how much pressure it could handle

under specified circumstances. The research did not look at how the difference in

just how much rubber content could be mixed with sand before it could give way to

other problems. The research gave new data that is now being used to look at sand-

mixtures and the rest of the factors that contribute to its establishment as material in

construction sites. The data presented gave leeway to in depth research as to how

liable the Sand-Rubber Mixture could be when creating new foundation and lead to

other research.

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Materials and Methods

I began my research with a general idea of the civil engineering field and specifically

studied the structure of foundations and their properties. The research was started by

finding a specific method in which we would be able to find the density of samples

accurately in the most uniformed manner. Below is a list of materials used for

specific experiments that proved more influential for my research.

● Sand - It is pure sand collected in small grains all of one type.

● Rubber - It is tire shredded rubber that is mixed into the sand.

● Funnel - Used to drop the sand and rubber into the sample base and gave the

procedure a uniformed manner of placing the materials.

● LoadTrac-II, Cyclic-RM, FlowTrac-II - This mechanism was used to

calculate the density of the sample in the chamber.

● FlowTrac Cell/Base – This was the base of the sample and is the what is

inserted in the testing chamber.

● Porous Stone (2) - These stones are placed between the samples to mimic the

pressure of bedrock.

● Rubber Membrane – The rubber was used to create the sample and gave the

sample a malleable material to give way to pressure and other factors when

testing it.

● O Rings (2) – These were put at the base and top of the sample to keep the

sample enclosed and water from entering the sample.

● Top Cap – Used to enclose the sample to keep the test constant.

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● Cans – These were used in the water content experiment to determine its

percentage.

Procedure for Making Samples (See Figure 1)

The main focus on the research conducted was finding a procedure to make a

sample, simply because you wanted it to be as uniformed as possible. To begin,

attach the Rubber Membrane at the base of the cell and enclose it with the iron

encasing for sample module. Pull the rubber membrane tightly against the wall of the

module and vacuum the air out, getting closer to the inner wall, to enclose the

sample. Place a porous stone at the bottom and an O-Ring around; ensure it is

attached tightly around the indentation in the sample base. Measure a set amount of

pure sand using a weight consistently throughout the procedure. Pour sand into

funnel in a circular motion, keeping an even amount of sand pouring in. Use funnel

to mimic sand falling naturally and uniformly. Create layers, stop half-way when

pouring to level it out (with the same amount of hits each time) and then pour in the

rest, after two layers create small vibrations on the outside of the cell to level out the

sand and flatten down evenly across the sample. Keep it as consistent as possible to

ensure the results are uniformed. Once you have reached the top of the sample

flatten it out yet again evenly, with the same amount of hits each time. and put the

porous stone on top. Take the top cap and cover the sample, also cover top cap with

rubber membrane and seal it with an O-Ring (Make sure the sample is sealed tight).

Release the vacuum and remove the iron encasing showing the sample in the rubber

membrane. Study sample and look at layering before further testing, check to see if

layers are uniformed. Each time you create a sample look for improvements on

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making future samples. The sample is then ready for further testing on the LoadTrac-

II for force and load tests. After you have tested the pure sand you then make

samples that include sand and rubber mixtures at different levels, 5% rubber, 20%

rubber, 50% rubber, . . . etc, and repeat the process.

Figure 1: A test sample was made of pure sand and has

eight layers about one and a half inches apart.

Finding Water Content

Start by measuring the weight of three cans, it doesn't’ matter what size, and

record your data. Pour some wet sand into the can and measure the weight of the can

with the sand. The amount of sand does not matter, at this time record your data. Do

this to all three cans and record your data for each. Afterwards proceed to putting

them into a dry oven. At this point you wait a certain period of time to give the

sample ample time to dry off, make it as dry as possible for better results. It is then

that you take the samples out of the dry oven and measure their weight in respect to

their previous weight. Record your data. The weight of each sample should be far

less heavier than before, it is then that you record the difference between the weight

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of your wet sand and can sample and the mass of the dry sand and can sample,

record your data. When finding the difference of the dry soil do not forget to deduct

the weight of the can from the total weight of both measurements, then record your

data. This, in turn, will give you the mass of the moisture trapped in the sand

samples, record your data. Once you have found these measurements you divide the

mass of moisture and dry sand to get the water content. Average out all of the water

content measurements from the other cans. Convert the water content into a

percentage giving you roughly the same percentage overall from all the other three

samples. (See Figure 2)

Figure 2: This data table shows the approximate average water content

percentage.

Calculating Specific Gravity (See Figure 3)

We then proceeded to calculate the specific gravity of the pure sand used. You

would need a volumetric flask making sure it is dry. Fill the flask with distilled water

up to 500 ml. Measure the mass of the flask and the water, insert the thermometer

into the flask with water and determine the temperature of the water. Put

approximately 100 grams of air dry sand into an evaporating dish. Transfer the sand

into the volumetric flask. Add distilled water to the flask containing the sand to

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make it about two-thirds full. Remove the air from the san-water mixture, by

applying the vacuum until all the air is out. Add de-aired, distilled water to the flask

until the meniscus touches the 500ml mark. Dry the outside of the flask ad inside of

the neck of the meniscus. Determine the combined mass of the flask and the sand-

water mixture. Pour the sand and water into the evaporating dish into an oven to dry

to a constant weight. Find the mass of the dry sand in the evaporating dish.

Figure 3: The flask has the sand inside while the air

is being vacuumed out of the flask.

Discussions

Many variables were taken into consideration when trying to come up with a reliable

method to make a sample that was as uniformed as possible. Every factor was

looked into some of which included:1) How much sand was poured into each layer

in the sample, 2) the height at which it was dropped from, How many times the

sample was pounded down, how to control the excess sand from falling out of the

sample, etc.. As the research continued we discovered other small methods in which

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it could provide more uniformed results. We measured the amount of sand by weight

(in kg) to keep it constant, we added, We measured increments of approximately 1.5

in. in distance every time we moved the funnel upwards. We counted about thirty

strikes on the sand when leveling it out, and added a cylindrical cone around the

sample to keep the excess sand from falling out. One of the main concepts to keep in

mind while conducting the research was studying the density differences between

pure sand and sand-rubber mixtures. This is where you must look at the water

content of the sand sample and eventually of the sand and rubber sample. Through

background information it is known that rubber is a lighter material than sand so the

density is expected to decrease, from this a problem arose, sand and rubber are not

the same density so when mixed they will not as uniformed. It was important to

understand in the research that the percent of rubber put in a sample was calculated

through its volume ratio.

Results

When conducting the water content experiment it presented numbers that were

approximate to the actual water content percentage of pure sand. The water content

received from the test was approximately 8.52%. (See Figure 4) There was a small

difference that could have been resulted due to the moisture in the air, if it isn’t

weighed quickly enough the air will moisten the sand. This data was then compared

to the actual water content percentage given to me my mentor. The number was

approximately the same and was found to be conclusive data to be used in the

research.

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Figure 4: This specific table shows the approximation of the water

content in the pure sand.

The specific gravity of most common minerals found in soils are within a range of

2.6 to 2.9. The specific gravity of sandy soil may be estimated at about 2.65. So, the

soil that was measured at about 2.606 and would fall into an average specific gravity

value. The specific gravity gave us the approximate specific gravity for the pure sand

and would use this data to be able to calculate more of its properties (one of which is

calculated through the LoadTrac-II).

Figure 5: This table shows the approximation of the pure sand’s specific

gravity through several calculations.

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Figure 6: This data sheet gives data that came directly from the

LoadTrac-II data log sheets.

The LoadTrac-II was able to give detailed results (See Figure 6) regarding the

samples density. Through all the experiments and test we were able to conclude that

the density of the Sand-Rubber mixtures would decrease as the rubber percentage

increased.

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Conclusion

The data was put into an excel data sheet and recorded it on a graph

where the trend is seen to decrease and was calculated by putting the average

density over the percentage of rubber. The research specified on the dynamic

properties that need to be taken into account to look at other factors of the Sand-

Rubber Mixtures. The research gave an insight to how civil engineering would be

able to apply a method to make foundations and make them available in construction

sites. Future work is still needed on the other dynamic properties Sand-Rubber

Mixtures could have in different conditions. It is through this research that we

advance our understanding of the Sand-Rubber mixtures density characteristics, but

are many other aspects that must be further studied.

Citations

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Lee, Changho, Hosung Shin, and Jong‐Sub Lee. "Behavior of sand–rubber particle

mixtures: experimental observations and numerical simulations."

International Journal for Numerical and Analytical Methods in

Geomechanics (2014).

Lee, J., Salgado, R., Bernal, A., & Lovell, C. (1999). Shredded tires and rubber-sand

as lightweight backfill. Journal of Geotechnical and Geoenvironmental

Engineering, 125(2), 132-141.

Neaz Sheikh, M., Mashiri, M., Vinod, J., and Tsang, H. (2013). ”Shear and

Compressibility Behavior of Sand–Tire Crumb Mixtures.” J. Mater. Civ.

Eng., 25(10), 1366–1374.

Pierce, CE, and MC Blackwell. "Potential of scrap tire rubber as lightweight

aggregate in flowable fill." Waste Management 23.3 (2003): 197-208.

Senetakis, Kostas, Anastasios Anastasiadis, and Kyriazis Pitilakis. "Dynamic

properties of dry sand/rubber (SRM) and gravel/rubber (GRM) mixtures in a

wide range of shearing strain amplitudes." Soil Dynamics and Earthquake

Engineering 33.1 (2012): 38-53.

Youwai, S., & Bergado, D. T. (2003). Strength and deformation characteristics of

shredded rubber tire sand mixtures. Canadian Geotechnical Journal, 40(2),

254-264.