Roller-Compacted Concrete (RCC) – What is it? | Укладываем бетон без использования арматуры
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Roller-Compacted Concrete (RCC) – What is it? | Укладываем бетон без использования арматуры


Hello everyone, my name is Alex and you are
on MechanismOne channel, where I will be discussing engineering topics in a simple,
easy to understand, language. Today we will be talking about a complicated topic for any
person, who drives a vehicle – we will discuss a unique and quite uncommon technique
of placing concrete road pavement with no rebars. Is it possible? Would the concrete be as strong as the
usually used steel-reinforced concrete? How does one place such concrete? Today I will not just tell you about this technique but will
also show you the entire process of placing such concrete. Before we would start, please give me a thumbs up, if you
like this video, pretty simple deal for you, but it would significantly help me, and share this video
with your buddies. I also have an instagram account, subscribe, if you like
pictures and random short videos. Let’s go! First, let us clarify some terminology. The layman, who does
not have any involvement in construction, commonly get confused between two definitions –
concrete and cement. Gray-looking fine powder is called cement, which can easily
be found at any home improvement store in bagged form. When cement is mixed with different additives, such as sand,
water and other chemical ingredients – concrete is formed. Concrete is divided into different
classes and types, but that is a topic of discussion for another day. Concrete is a great durable material; however,
it has one problem – it is only good at withstanding compressional forces. If you would try to stretch or elongate concrete – it would
become extremely brittle and fail. It cannot withstand even a tiny tensional force. Steel, on the other hand, has the opposite behavior – it is greatly resistant to tensional forces; however, it is
not very effective when compressional forces are applied. Logically then, it would be obvious to conclude that the
combination of two materials such as these would form a new type of material, one that would be
resistant to both types of forces. That’s exactly what engineers in the past concluded, and
steel reinforced-concrete was invented. That is why today, at just about every construction zone, you might be able to see rebar which seemingly sticks out
from everywhere. But you might wonder, what causes concrete to stretch? Those forces exist everywhere, for example, when a car is
moving across the bridge girder – the girder bends under the weight of the car, and concrete
experiences compressional forces at the top side, and elongation at the bottom. That is why bridge guilders
are heavily reinforced at the bottom. However, this simple solution introduces two problems. First, steel installation is a very long
and labor-intensive process. Secondly, steel, as a material, is very costly. If steel can be removed from the construction process, it would significantly accelerate construction time and
reduce its cost. So, is it possible to remove steel from road construction?
The answer is yes! Roller-Compacted Concrete, or RCC for short, is the
technology that allows it to be done. RCC cannot be used in all applications, it is only used in
situations when concrete can be placed as a wide and thin layer, i.e. this technology can be used
for any type of road construction, airport landing stripes, warehouse floors and parking lots. In addition, RCC can be utilized for dam construction,
spillways and other hydro-infrastructure. Let’s start with some history about RCC.
RCC was invented in the 1960’s, when several dams utilized the process during construction. However, it did not gain wide recognition
and acceptance until Canadian logging companies started using it for yard paving Heavy logging trucks were making a mess
of the lay down yards and engineers were requested to develop an easy-to-place pavement that could support
heavy equipment and logging trucks. After this point, RCC began to be utilized more and more in
a wider variety of applications. Now, lets us see how regular concrete is made. First, engineers calculate the desired strength of the
concrete on a piece of paper. Concrete strength is driven by several factors:
cement-to-water ratio and the type and shape of gravel. As more water is added to the mix – the weaker the concrete.
Inversely, the lack of water will cause some cement to remain dry in the mix and the resulting concrete
would be defective. Amount of the cement should also be sufficeint because
cement acts as a connection bond between sand and gravel. Additionally, the gravel needs to be strong enough to
withstand projected stresses because it would be the first element in the mix to fail. Chemical additives, air bubbles, water quality, and the
gravel to sand ratio also affect concrete strength,
but these are secondary factors. In order to make a traditional concrete mix the following
steps should be taken: some water is added into mixer, cement is added,
following sand and gravel. All ingridients should be well mixed and final product is a
mixture that looks like a gelly. Water presense and excess can usually be clearly seen
in the mixture. RCC production is also significantly different from
traditional concrete as well. The amount of cement is reduced by about 30%. The water & cement ratio is also reduced and might be twice
as lower in comparison with traditional concrete mix. At the same time, coarse aggregate is completely removed, and only fine gravel and sand are present. If properly mixed RCC forms a relatively dry mix,
one that appears like wet beach sand. This is how well mixed RCC looks like. What strengths can RCC reach? Without too much of a headache
– 6,000 psi can be obtained, with some additional tweaking – up to 10,000 psi. Enough with theory let’s build it! RCC should be placed on a very well compacted subgrade. In order to obtain such subgrade, top soil is removed, and the bottom layer of the dirt is mixed
with limestone solution. This process is called subgrade stabilization. Additionally, limestone solution is used for moisture
content preservation. To stabilize the subgrade, it first needs to be fully
saturated with water. Then the limestone solution is sprayed all over
the saturated subgrade. Finally, the stabilizing machine slowly crawls afterwards. It has series of knives, like ones that are used
in agriculture, which rotate at high speed. Those knives can mill up to 10 inches of a soil forming
homogeneous mixture of dirt with water and limestone. After limestone stabilization, the subgrade is covered
with geotextile and then gravel is placed on the top. This gravel will help to drain any water. Then, more dirt is
placed on the top of gravel and it also is stabilized, but this time with cement, instead of limestone.
Now we are ready for RCC placement. This is how the sandwich looks like. At the bottom we have 8 inches of lime-stabilized soil, then the geotextile layer, then 4 inches of coarse gravel, then 12 inches of cement-stabilized soil, and then 18 inches of RCC, in two layers, 9 inches each.
All right, moving on. The RCC placement process is also significantly different
from traditional joint-reinforced concrete (JRC). and looks more like asphalt placement. A slip-form machine is not used, instead,
a high-compaction asphalt paver is used. This paver can achieve
90-96% density of the placed concrete. Asphalt roller-vibrators are also used, as they are
necessary in order to achieve 99% density. Since pavers cannot get such high density – rollers must
pick up the slack. Typical concrete vibrators are not used, as we mentioned
earlier – RCC does not have any residual water. Utilizing engineering terminology, RCC has “negative” slump,
as any excess water makes RCC defective. Thermal joints are also non-existent. For quite some time,
thermal joins were completely ignored, since they were believed to be unnecessary.
In recent times, however, engineering practice has slightly changed, and saw-joints
were introduced. Joins would be cut a few days after RCC placement
and then sealed with silicone In theory, thermal joints are not necessary at all, however, they do help somewhat in keeping the surface
of the concrete crack free. The surface of the concrete looks very different
in comparison with traditional concrete. It has some voids and open cracks; however, it is strong. Workers can freely walk on the surface right behind
the paver; light equipment can cross newly placed concrete as well.
No marks will be left on the pavement. Lab technicians are also right behind the paver – they are constantly checking density of the concrete, along
with moisture content. RCC can be placed at a much higher paste than the
traditional JRC, at the rate of about 10 ft/min, vs. 3 ft/min in average for JRC. Maximum pavement thickness of RCC is about 10 inches
with maximum lane width of 30 ft. Three days after RCC placement lab technicians
will take cores. The main purpose of these cores is to check the bond
strength between two layers of RCC. In addition, cores will also be checked for strength
of the concrete. Unlike traditional concrete, with 28-day curing period, RCC
pavement is ready for utilization just after 7 days. While I was at the library reading history of RCC I found
one particularly interesting book called Roller Compacted Concrete Dams.
It was published in UK in 2003. This book summarized the experiences of different people
utilizing RCC for various applications all around the world. One thesis contained in the book, was written by two Russian
professors, who were studying RCC in Moscow. They share their experience designing a gravity dam
in Angola, called Capanda Dam. This dam is 360 ft. tall and 4,900 ft. long. Total concrete
volume that was used to pour the body is 1.44M cu. yards. Dam was designed at the end of the Soviet era and
construction began in 1987.

8 Comments

  • Iskander

    Как здорово, что ты снова начал вести блог. Очень ждал продолжения в старом ЖЖ. Вот, дождался ))

  • TheRusbot

    Интересная технология. Как ведет себя такая дорога в условиях, когда зима 9 месяцев в году?

  • Oleg Chikhladze

    Если эта технология обладает всеми преимуществами железобетонной дороги, но дешевле и быстрее возводится, то какой смысл строить дороги с арматурой внутри? Почему эта технология полностью не выдавила альтернативу?

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