Developing a New Generation of Portable Concrete Barriers

Andrew Huonder Author

08/03/2020 Added

54 Plays

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Research on the development of portable concrete barriers

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[00:00:00.500]Hello, everyone.
[00:00:01.333]My name is Andrew Huonder
[00:00:02.800]and my research project over the summer
[00:00:04.950]was developing a new type of portable concrete barrier.
[00:00:08.410]Concrete barriers have changed minimally in recent years.
[00:00:11.500]The current barrier's called an F-shape type
[00:00:14.250]and it is pictured here.
[00:00:15.300]It has a sloped part on the sides
[00:00:17.460]and ends up being very steep in the middle.
[00:00:19.890]The two main issues with the current barrier are
[00:00:21.840]one, the barrier produces a large deflection
[00:00:25.090]when a vehicle impacts it.
[00:00:26.870]The vehicle is pushed far back
[00:00:28.389]and could possibly be pushed into oncoming traffic.
[00:00:31.770]The second big issue is due to the slope
[00:00:34.190]on the edge of the barrier.
[00:00:36.200]Vehicles tend to climb up the barrier and then roll over,
[00:00:38.770]possibly harming anyone on the other side of the barrier.
[00:00:40.637]So the objective of this research is to develop
[00:00:42.990]a new type of barrier that addresses the large deflection
[00:00:47.060]and the rollover while maintaining stability and durability.
[00:00:52.790]The new design features an almost vertical slope
[00:00:55.860]on either side in order to decrease the amount of rollovers.
[00:00:59.350]The new design also has a new type of connection
[00:01:02.680]that should reduce deflection.
[00:01:04.790]What I focused on mainly was the type of concrete
[00:01:07.760]to be used in the barrier.
[00:01:10.070]The main type of concretes researched were
[00:01:12.160]steel fiber reinforced concrete
[00:01:13.770]and polypropylene fiber reinforced concrete.
[00:01:17.690]Design criterias for the materials are it cannot decrease
[00:01:21.250]the compressive strength of the concrete,
[00:01:22.690]it needs to increase the tensile strength,
[00:01:24.620]flexural strength, and impact resistance to the concrete,
[00:01:27.140]and it can't increase the barrier cost
[00:01:29.100]to more than $100 per foot.
[00:01:31.606]This number was figured out through a survey done
[00:01:33.789]over many different state governments
[00:01:35.840]that commission portable concrete barriers.
[00:01:40.520]Right now, the average cost for portable concrete barriers
[00:01:43.887]is about $50 per foot
[00:01:46.340]and they said for a new, better barrier,
[00:01:48.140]their max would be $100 per foot.
[00:01:50.270]And the material also needs to maintain the workability
[00:01:53.330]of the concrete.
[00:01:55.800]Steel fibers, there's little strands of steel
[00:01:58.740]usually with hooked ends,
[00:02:01.080]they're typically 10 to 16 millimeters long
[00:02:03.140]and with a tensile strength
[00:02:04.120]about 1,000 to 3,000 megapascals.
[00:02:07.730]Polypropylene fiber, just strands of polypropylene,
[00:02:12.190]and they're a lot lower tensile strength than the steel,
[00:02:14.840]about 80 to 800 megapascals and are shorter
[00:02:18.200]with about 10 to 30 millimeters long.
[00:02:23.120]Other concrete additives that were looked into
[00:02:25.380]were polyester fiber and nylon fiber.
[00:02:29.380]Both of them were very expensive,
[00:02:31.460]so they weren't able to meet that $100 per foot of barrier.
[00:02:37.480]Two other that were looked into
[00:02:38.640]were polyvinyl alcohol fiber,
[00:02:40.370]which decreased the flexural and compressive strength,
[00:02:43.530]so it didn't meet the design criteria.
[00:02:45.660]We also looked into hemp fiber,
[00:02:47.010]which is an organic fiber made out of hemp plant,
[00:02:50.000]but adding it to the concrete didn't increase
[00:02:53.770]the mechanical properties at all.
[00:02:55.700]All the data gathered came from other research articles
[00:02:58.750]and falls under one of these five tests,
[00:03:01.390]a compressive strength test, tensile strength test,
[00:03:04.190]flexural strength test, impact resistance test,
[00:03:07.140]and a slump test,
[00:03:08.179]and these are all concrete-based tests.
[00:03:12.640]So a compressive strength test takes a cylinder of concrete
[00:03:15.357]and is put into a machine that applies compression
[00:03:18.970]to the cylinder.
[00:03:20.860]The force is increased until the cylinder breaks
[00:03:23.430]and then the compressive strength is able to be measured.
[00:03:28.110]Due to the fact that concrete has
[00:03:29.540]a very low tensile strength,
[00:03:32.670]the split tensile strength needs to be measured.
[00:03:34.697]And the way this is done is we had a cylinder of concrete
[00:03:38.530]is put horizontally in a machine
[00:03:40.020]that adds compression on either side
[00:03:42.050]and do the geometry of the cross-sectional circle,
[00:03:46.250]that force on one point on the top
[00:03:48.130]and one point on the bottom,
[00:03:50.420]force is applied until the cylinder breaks
[00:03:53.290]and then the tensile strength is able to be determined.
[00:03:57.420]Flexural strength test is just a beam of concrete
[00:04:00.100]that's put on two supports
[00:04:01.460]and then a force is applied in the center of the beam
[00:04:05.410]and then the force required to break the beam
[00:04:08.810]results in the flexural strength.
[00:04:11.124]To measure the impact resistance of concrete,
[00:04:13.710]a disk of concrete is hit with a hammer repeatedly.
[00:04:17.000]The hammer is delivering a very specific amount of force
[00:04:20.020]and this is done until the concrete breaks
[00:04:24.110]then the number of times
[00:04:25.430]the hammer needed to hit the concrete to break it
[00:04:27.620]multiplied by the force delivered is the impact energy,
[00:04:30.800]the amount of energy that is required to break the concrete.
[00:04:34.970]So slump test, like I said before,
[00:04:36.550]measures the workability of the concrete.
[00:04:39.320]What is done is wet concrete is put into a cone mold
[00:04:43.630]and then the mold is removed
[00:04:45.255]and the height difference
[00:04:46.450]between the original height of the cone
[00:04:48.560]and the mound left over is measured.
[00:04:51.680]A concrete that has a high workability,
[00:04:53.780]which means it's easier to form, the mound height is lower
[00:04:58.570]because it's able to go back to its original shape easier,
[00:05:02.090]while concrete with a lower workability
[00:05:05.740]maintains its shape more and is harder to mold.
[00:05:09.830]All these graphs are based off
[00:05:11.280]of the volume percentage of the fiber,
[00:05:13.840]whether it be steel fiber or polypropylene fiber.
[00:05:17.860]For compressive strength, steel and polypropylene show
[00:05:20.190]very similar trends that could be
[00:05:22.276]essentially interchangeable when it comes
[00:05:23.960]to compressive strength.
[00:05:25.470]For tensile strength,
[00:05:26.310]polypropylene and steel fiber both show very similar trends
[00:05:29.610]that can be used at similar capacity,
[00:05:33.150]although it's unsure whether polypropylene will follow
[00:05:36.230]the trend to a higher dosage of fiber.
[00:05:38.690]Considering the trend for flexural strength,
[00:05:42.260]polypropylene and steel show very similar trends
[00:05:44.610]with steel showing a little bit higher flexural strength
[00:05:48.940]at similar dosages
[00:05:50.045]but between tensile, compressive, and flexural strength,
[00:05:54.170]there is not much of a significant difference
[00:05:56.700]between the two.
[00:05:58.900]Moving on to impact resistance.
[00:06:01.170]As you can see, steel increases the impact resistance
[00:06:05.270]a lot faster than polypropylene does
[00:06:08.780]in terms of increase of fiber volume percentage
[00:06:13.030]but as you can see, polypropylene is kind of
[00:06:15.870]on an exponential curve so with a little higher dosages,
[00:06:19.250]it could be a much higher (indistinct),
[00:06:20.570]while steel fiber seems to do it's peaking out at
[00:06:23.400]about 7,000 megapascals.
[00:06:26.180]For workability, as fiber percentage increases
[00:06:29.140]for both steel and polypropylene,
[00:06:31.030]the workability decreases,
[00:06:33.430]but polypropylene decreases much faster than steel does.
[00:06:37.490]The most important factor of the concrete additive
[00:06:40.720]is how much it costs.
[00:06:42.460]So a rough estimate of the barrier is
[00:06:44.450]about 12 1/2 feet long, 32 inches high and 24 inches wide,
[00:06:49.290]so their total volume is about 66.7 cubic feet.
[00:06:53.250]So if we need a volume percentage of 1%,
[00:06:55.820]that means it's about .67 cubic feet.
[00:07:00.730]Steel fiber is about $750 per cubic foot
[00:07:04.590]while polypropylene fiber is about $70 per cubic foot,
[00:07:08.830]so polypropylene is about a tenth of the price
[00:07:11.570]of the steel fiber.
[00:07:13.080]Comparing the prices of the two fibers
[00:07:15.930]at different volume percentages.
[00:07:18.310]As you can see, steel's extremely expensive
[00:07:21.350]in considering the barrier is about 12 1/2 feet long,
[00:07:25.310]that's going around $2,550 per barrier.
[00:07:30.990]So already at like 2%,
[00:07:32.480]we're already getting really close to that.
[00:07:34.338]So polypropylene, we could have a lot higher dosages
[00:07:38.588]of fiber than steel for a cheaper price.
[00:07:44.070]So in conclusion,
[00:07:45.270]steel fiber increases the compressive strength,
[00:07:47.660]tensile strength, and flexural strength slightly more,
[00:07:50.580]if not the exact amount of polypropylene fiber,
[00:07:53.770]while it increases the impact resistance substantially more.
[00:07:59.140]It also doesn't decrease the workability
[00:08:01.090]as much as polypropylene does but when it comes to cost,
[00:08:05.650]even though steel might result in a better barrier
[00:08:09.640]at the same percentage dosage, it's gonna cost much more.
[00:08:14.530]So it might be better to go to polypropylene instead
[00:08:18.320]and have a higher dosage for a cheaper price.
[00:08:22.130]Thank you very much for listening to my research summary.

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Developing a New Generation of Portable Concrete Barriers

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