Ihab Saad – Concrete Equipment
AI: Summary ©
AI: Transcript ©
Music, hello and welcome again to another lecture on construction
equipment, and today we're going to be talking about equipment
involved in concrete in general, whether it's mixing or placing or
finishing the concrete. So let's see what are the concrete
different operations, and what kind of equipment is involved in
these operations. First of all, what's concrete? Concrete is a
flexible construction material. We call it flexible because, again,
in its initial form before gaining a strength before setting. It's
sort of a fluid mixture that can fill any form it's placed in. It's
used to build structural components in many shapes or
strong pavements to withstand surface abrasion.
It's produced by mixing Portland cement with water aggregates, and
sometimes that mixtures to improve properties such as workability,
strength, weight and resistance to elements, including freezing and
thawing, and including attacks by sulfates or chlorides or any other
chemicals that might affect the concrete. The
different concrete operations include
the process of manufacturing, placing concrete, whether plain or
reinforced. Of course, the difference is adding the rebar,
and it consists of the following operations, batching, which is
basically calibrating and weighing the different components of the
mixture, mixing, transporting, after that concrete has been
mixed, transporting it to the construction site, placing, which
is putting the concrete or removing the Concrete from the
transportation means to its final place, consolidating or vibrating
to remove any air pockets in the concrete which are going to reduce
its strength, finishing the surface of concrete. And finally,
curing. And curing is primarily to distinguish the difference between
curing and setting. Some people confuse the two issues. The
reaction, the chemical reaction that results in concrete gaining
strength, is called an exothermal
reaction. Exothermal means it emits heat. So when it emits heat,
it sort of evaporates the water that include that's included in
the concrete itself.
That's why that water is going to be evaporating through very fine
channel. Channels are called the capillary channels, that if not
treated properly, are going to result in hair cracks on the
surface of concrete, which would weaken the concrete, and later on,
would allow moisture and water or other chemicals to penetrate
through the concrete and attack the rebar, which is going to cause
it to rust and corrode and separate from the concrete itself.
So in order to avoid all of that, we are going to replenish that
water inside the concrete by keeping the concrete moist for
about three to five days after it has been placed. This can be very
simply done by just wetting the concrete with a water hose, or
covering the concrete with a wet surface, like wet burlap, for
example, or even applying certain chemicals to seal the concrete and
prevent that water from evaporating. This is the process
of curing.
Batching. Is the process of proportioning the ingredients of
the concrete mix.
Most specifications require a batching accuracy between one and
3% and this is going to be included in the specifications of
the concrete that's going to tell you about the concrete mix and the
trial mix that's going to be subject to testing to make sure
that it produces the final stresses or resistance that the
concrete should withstand before it breaks concrete, especially in
large volumes, is usually best in the central batch plant. We're
going to see a sample of these batch plants. Some central batch
plants, mix the concrete, while others only batch, measure and
calibrate the ingredients. The product can be either a dry, dry
mix without adding water, just including the sand, cement and
gravel and any other additives, dry additives, or it could be a
wet mix by adding water and any other fluid additives or
admixtures as well.
These are different modes of mixing the concrete, batching and
mixing the concrete. So we can here see, for example, here, a
central batch plant that can produce anywhere between 275, and
450, cubic yards per hour, huge production. This is a portable
mixer where you're going to pour the cement, sand and gravel and
add water. And this is this drum mixer is going to mix the
concrete, and it has a capacity of five to 10 cubic yards per hour.
Relatively small, but it has the mobility. And here are side batch
plants, for example, that can produce anywhere between 165
230,
cubic yards per hour, where you have the silos, and these belt
conveyors can transport the gravel and the sand and so on. They are
mixed. The silo usually holds the cement, and then they're going to
be added to this transit mixer that's going to transport the
concrete to the site. Here we have a pavement batch plant for
concrete pavements and again, here's the drum of that transit
pixel where it's going to be mixed and transported to the site
can produce up to 600 cubic yards per hour, so a very high capacity.
Now we're going to have a look quickly at two video clips, one
representing a portable or a movable batch plant, and the other
one talks about one of the innovations in how to reuse the
concrete, or how to have a zero waste in concrete. So let's watch
these two clips.
I President, our system is being used to build a 1 million square
foot shopping mall, an airport parking lot, and a 200 turbine
wind farm at Wash Creek. A plant is a footprint approximately the
size of an 18 wheeler, self erecting and pouring within a day,
we bring our professional staff, including an experienced patcher,
to the customer's job site. We take the rain mixture off of the
road, producing a more environmentally friendly product.
We are able to work to the customer's schedule, including
evenings, weekends and last minute jobs. The aggregate for the batch
plant can be stored as required, anywhere on the job site. In some
cases, we can also produce the gravel on site instead of the
customer holding it away.
Vancouver, ready mix mobile batch plant has three bins, which are
typically used for sand and two different sizes of graft, such as
28 and three quarter inch. We have two ready mix trucks, and on
really high volume days of over 500 meters, we bring in a third
truck. The truck is loaded in five minutes and delivers a concrete to
the pump or the specific area on the job site. Our control system
can handle hundreds of mixed designs. All of the mixed designs
for the customer's job are in the system before the job starts.
Having a voucher on site makes it easy to change or add mixed
designs to fulfill the requirements of the job. Our
control system handles the precise Wayne to the cement aggregates,
water and atom mixtures. We have all of the admixtures on site that
the customer's job may require. Mobile plant has a 400 gallon way
bin that can always be primed with hot water, a 660 gallon water
surge bin and a 2000 gallon storage tank. We also have a 100
horsepower diesel engine to supply the power required to run the
plant.
We also have a 75 ton self erecting saddle, which can be used
to store more cement or along with a 58 ton saddle, can be used to
store cement and fly ash. We can produce high strength or
specialized concrete. Our mobile batch plant can be used to build
office buildings, apartment buildings, tilt up, warehouses,
large subdivisions and its ideal for both locations. Give us a call
at 604-533-0052,
to learn more about our plants capabilities and how we can help
you with your next problem.
So as you can see here, it mentioned something about adding
hot water, and this is primarily going to be used in very cold
weather, because if you add just cold water to the concrete mix,
that water might freeze and is going to defeat the purpose of
having that water in the first place, because it's not going to
properly react with the cement and give the concrete its strength.
Therefore, you're gonna have to use hot water. That's gonna take
some time to cool down, and you can, you can mix the concrete
properly. In this case, on the other hand, if you're gonna be
working in a very hot climate, then in this case, we're gonna use
chilled water, or even add ice to the concrete mix, to slow down the
process of of setting of that concrete, because you don't want
the concrete to set in a transit mixer or before reaching its final
destination. Therefore it's not going to have the required
strength from that concrete. Now let's look at the second video
clip, which is going to talk about the Zero Waste concrete. And this
is a system that has been adopted in Australia. I don't know if
that, if it has been used here in the US, but let's, let's have a
look at what they're talking about, sustainable
concrete, introducing the Zero Waste concrete plant, in keeping
with its focus on maximizing the environmental sustainability
of its business operations, a CT based concrete supplier elfin
group has created what is believed to be Australia's first zero waste
concrete
utilizing a range of state of the art processing equipment from.
Handy Creek recycling, Proprietary Limited elven group has managed to
effectively recover and recycle all of the waste concrete from its
Canberra batch plants, whilst at the same time recycling up to
12,000 liters of water per hour
located in a purpose built truck washout area, the concrete
Reclaimer captures the washout material in a large trough behind
the truck. From here, it is washed into the unit separation chamber,
where the sand and aggregate components of the concrete are
separated into high quality resource streams ready for reuse.
The the new zero waste system incorporates two major components,
a concrete Reclaimer and an automated water treatment system.
These two components work together in tandem to reclaim the vertical
solid resources from the waste material and treat the rung of
water for every use,
the cement binder material, which remains suspended in the process
water, is sent to the water treatment segment of the zero
waste system. Here the process water, together with run of water
from the truck washing and matching area, is sent to a
primary agitator, where a flocculent is added to aid with
the separation process.
The water is then pumped to a separation silo from where it is
gravity fed into the final filter. The clean water is then returned
to a storage tank for reuse in the concrete matching process for
truck washing and in water tankers. Interestingly, the high
quality dewatered filter cake generated by the water treatment
process is suitable for use in a range of manufacturing processes
and products, including brick and pavers, and can also be used in
road based material, thereby closing the loop completely on the
resource stream. I
so as you can see, they have used every part of the concrete, sort
of recycling the concrete and having zero waste. Why the
concrete is still fresh? Because once the concrete has been
consolidated, when it's gained the strength, especially when you're
demolishing a building or something like that, well it's
very hard to recycle that concrete, except for using it as
sort of gravel for highway construction or something like
that. But other than that, this is the only way they have been able
to recycle the water, the cement, the sand and the gravel as well.
The second step is going to be transporting, or the third step
actually, after batching and mixing, it's going to be
transporting. And it's usually performed using a transit mixer or
a truck to transport the concrete, whether it's wet or dry mix. If
it's wet, water has already been added. If it's if it's a dry mix,
then it can travel for longer distances, because now the
concrete is not going to set. And then you add the water as you
approach the construction site. So they're used to transport the
concrete from that plant to the construction site. If travel type
exceeds 30 minutes, if you have a remote site, then usually we're
going to use the dry mix with water added as the truck
approaches the construction site, and it's going to have to mix it
for certain number of revolutions to allow for the concrete
ingredients to mix together. Otherwise, the wet mix would be
loaded in the drum, and the drum rotates to keep mixing the
concrete and preventing segregation. Segregation is the
separation of the heavier particles from the smaller ones,
basically the separation of the gravel from sand that creates
inconsistent concrete, which is a major weakness in the concrete.
The drum capacity for the transit mixers is anywhere between six to
15 cubic yards. The trucks have an inclined access revolting drum
assemblies used for the concrete mixing. It may discharge concrete
from front or rear end. We're going to see a couple of pictures
on that. Rotating speed is about two to six revolutions per minute,
which is relatively slow, and mixing speed is six to 18
revolutions per minute,
maximum stay of concrete and the drum is one and a half hours, or
300 revolutions. Beyond 300 revolutions gonna create some
segregation. And beyond one and a half hours, concrete might
consolidate inside.
The drum rendering totally
unusable. In this case, you would lose the truck itself, or you
would lose the drum itself, and you have to do a major operation
to chip or break the concrete from inside the drum.
Here we have, for example, a transit mixer. As you can see, the
drum is tilted little bit. And here's the water tank that can be
adding water as the truck approaches the site. This one is a
transit mixer without water tank. So usually it's going to be used
for shorter distances, where you load it with the wet mix already.
And here you can see we have a chute at the end of the of the
drum that's going to be used to discharge the concrete, used, in
this case, for pavement. And here's another example of that
drum discharging the concrete in a loader that can carry it to
another distance
to place the concrete now that we have transported it to the site,
one of the media for you for placing the concrete includes
concrete buckets attached to a tower crane, so the concrete
buckets can be used in conjunction with tower cranes or helicopters
to place concrete in some cases, for example, well, these are
extreme cases. Let's say, like what happened in Japan last year
the, I think it was called fukujima reactor, where there was
some leakage. Now this reactor has to be encased in concrete. Of
course, you cannot approach that reactor, so you cannot use cranes.
In this case, you load the concrete in buckets that are
carried by helicopters, and drop this concrete to cover and in case
that reactor capacities for the buckets range for from point five
to four cubic yards for general purposes and up to 12 cubic yards
for special construction, usually used for heavy civil construction,
like dams or massive concretes for harbors and ports and so on. The
bucket is filled through the chute of the transit mixer or directly
from the batch plant and lifted to the required level for placing
concrete. Multiple buckets can be used to reduce the placing cycle
time. So you would have two buckets, for example, one being
filled while the other one being lifted to download the concrete
and as soon as the other one is returns back to its initial
position, you load the filled one, and so on and so forth. That's
going to expedite the concrete placing cycle.
We can also use concrete pumps you may have seen in some of the
cliffs that we've seen about the tallest building in the world, how
they place the concrete using concrete pumps. Because obviously,
for the tallest building in the
world, tower cranes are not going to be a feasible option. But in
this case, concrete pumps was where the selected mode concrete
pumps can be used to transport concrete under pressure to the
required level. And these can be either fixed pumps or mobile
pumps. The means of transport can be a rigid pipe, a flexible hose,
or a combination of both. So here, for example, we have these are
rigid pipes, and at the end we have a tremie or a flexible hose.
Concrete pumps are rated in cubic yards per hour. How many cubic
yards can they pump per hour? These pumps can be either
stationary. This one is relatively stationary because it's moved to
the construction site and remains there until the concrete is
pumped. Whereas this one is carried over a truck, so it moves
to the construction site on a regular basis, and it's followed
by the transit mixers, where the shoot of the transit mixer is
going to empty the concrete in another shoot, in the truck, in
the in the pump, and it's gonna pop that concrete to whatever
level is needed. Production can be up to 170
cubic yards per hour and reach up to 150 feet horizontally. That's a
relatively high reach.
Pumped concrete has to be more fluid the water cement content, or
through water cement content or plasticizers to make it easy to
overcome the friction within the pipes and move smoothly and be
pumped. And it's it's more fluid than regular concrete for smooth
pumping and reducing segregation as well.
Another way of placing concrete is concrete buggies that can move
concrete from the mixer trucks to the desired location or from the
dump area of a bucket on elevated levels. So for example, you might
have a large floor area for a high rise building, and the concrete
bucket is going to pour the concrete in a certain area, and
then you're gonna load that concrete on buggies that can
travel to the different corners of that floor. They can have.
Capacities of 10 to 30 cubic feet, and can travel at speed speeds up
to 15 miles per hour.
Now the fourth step is going to be the consolidation, or the
vibrating of the concrete. Concrete vibrators are used to
consolidate concrete, get rid of air pockets and make sure the
concrete engulfs the rebar to avoid honeycombing, which is
basically voids around the rebar, which are going to result in poor
and weak concrete. It they can be electrical powered, gasoline or
compressed air vibrators, external vibrators, might be installed on
the form or to shake the concrete over a wider area. So these are
going to be vibrators installed on the formwork itself, especially
for walls that are going to be able to shake that that formwork
so that concrete fills all the gaps around the rebar. The
next step, once the concrete has been placed and vibrated, is to
finish the surface. Power floats or travels are used for to embed
the surface, aggregate and smooth surface of the concrete. So again,
to flatten and have a smooth finish for the concrete. Some are
walked behind while other others are riding. This one, for example,
is a walk behind, so it's held from the handles by an operator
who walks and pushes them in front of him or her. And this one is a
riding right riding, a riding
finishing, concrete finisher. It's called the helicopter because it
has blades like those of helicopter, and again, using the
different controls, you can adjust the thickness and the height of
the finish and so on. Now we're going to have another look at
another video clip showing traveling of that concrete and
finishing it for a concrete
paving job.
So let's have a look at that.
You can see the concrete being
poured from the chute of a transit mixer. And this is something like
a driveway or a simple slab. And this is the trowel that has a
* on top of it, so it vibrates the concrete while
finishing its surface to have a flat finish. And you can see the
labor behind that trowel discrete is going to be used to level the
concrete while compacting it at the same time and vibrating it.
You see the concrete being cooled for a driveway, and in the back
there's a transit fixer that's pulling the concrete through the
chute. And then these labor try to level the concrete, while discrete
gives the final leveling and the final shape for the surface of the
concrete. Now you can see the chute in the back of the frame.
Additional patching might be needed later on. So for example,
in this part here, you can see that this was not done properly,
so later on, they can come back and patch it.
This concrete can be either reinforced with the welded wire
fabric, as most of the driveways would be. So here in at the
bottom, you're going to find the welded wire fabric, or welded wire
mesh. It can be either one layer or two layers, depending on the
design. Mostly it's going to be one layer.
You
now you can see that at the edge, the concrete is going to be
slightly lower than in the middle,
but this can be controlled by the speed of the motion of the screen,
Just to make sure that the concrete is level so
are trying to fill any holes before the street finishes the
surface.
You can see it can rather rather than.
Relatively be done at the relatively high speed so it didn't
take too long.
Concrete paving. We can have also something called slip forms that
are going to inject the concrete and mold it to the required shape.
So slip form pavers are used to distribute the concrete across the
surface to be paved and then to vibrate screed and finish the
concrete. So it's a one, one stop shop. It is very similar to the
asphalt pavers as well. But instead of using asphalt, we're
going to use concrete in this case. And here you can see it can
be done for a very narrow width, or for much wider areas. This is
going to be the street that's going to finish that concrete.
They can place concrete pavements up to 18 inches thick, 25 feet
wide, at speed of up to 18 feet per minute, relatively fast.
Now, how are we going to measure the production of a concrete
operation? Since several pieces of equipment are used in series to
achieve the concrete operations, for example, batch plant, followed
by a transit mixer, followed by maybe a tower crane with buckets,
followed by a crew of labor that are going to place and finish and
vibrate the concrete and so on. Optimization can be achieved to
produce the least cost or the shortest time, depending on the
amount of resources that you have, you have to have a balanced
operation so you're not going to use, for example, a very big batch
plant with only one transit mixer, because the production of the
batch plant is going to be limited by the transportation capacity,
which is going to be through the transit mixer. And if you have a
wide, a large, not a fleet of transit mixers, you're not going
to use only one bucket with the tower crane, because, again,
you're going to have a long queue of these transit mixers, which
again defeats the purpose and reduces the production rate. The
rate at which concrete is delivered may control the duration
of the operation, whereas in other cases, the rate of placing and
finishing might be the critical factor. So the number of labor and
crews that are going to be available for placing and
finishing might be the controlling factor in that operation.
The productivity of a concrete pump can be estimated from the
manufacturer's data sheets. The productivity of a crane, which is
going to tell you basically how many cubic yards you can produce
per hour. The productivity of a crane and bucket operation can be
estimated from bucket volume times operational efficiency divided by
cycle time, which is the same equation that we've used for every
other equipment, which is volume per cycle divided by cycle time,
or multiplied by number of cycles per hour, which is basically one
hour divided by the cycle time.
The productivity of concrete buggies can be estimated as,
again, body volume times operational efficiency divided by
cycle time and the cycle time, in this case going to include loading
time, travel time, dump time and return to be loaded one more time.
Let's look at a very simple example on concrete operations. We
have a concrete slab with dimensions of 90 by 120 feet, and
the thickness is 10 inches. It's to be constructed. The available
equipment include a 16 cubic foot buggy or a two cubic yard bucket.
The load and dump time for the buggy is 1.7 minutes,
and the average travel speed is 1.5 miles per hour, one loaded and
two and a half miles per hour, one empty. For the return trip, the
average travel distance is 250 feet. The Cycle Time for a
hydraulic crane to load lift, empty and return the bucket is
eight minutes. Operational efficiency for both operations is
50 minutes per hour. What's the estimated productivity for the
buggy and what's the estimated productivity of the bucket? So if
we were to choose the system to place concrete, which one are we
going to select based on production time, the criterion
that you're looking at, or the main factor, is we need to finish
that operation as soon as possible.
So for the buggy, the cycle time is going to be 1.7 minutes, which
is basically the load and dump time, which is fixed time, plus
the travel time, 250 divided by 1.5 miles per hour. And then we
have the factor to convert from feet to miles per hour plus 250
divided by two and a half miles per hour. That's the return trip.
So adding all of these together gives us a cycle time of 4.7
minutes. The productivity of the buggy is 16 cubic feet times 50
minutes per hour divided by 27 cubic feet per cubic yard, to
convert from cubic feet to cubic.
Yard divided by also the cycle time, which is 4.7 minutes, and
that gives 6.3 cubic yards per hour. So the production for the
buggy 6.3 cubic yards per hour, relatively low. Let's see what the
bucket is going to do.
For the crane and bucket, we have two cubic yards times 50 minutes
per hour divided by eight minutes, that's the operational efficiency
divided by eight minutes that the cycle time. So it gives 12 and a
half cubic yards per hour. So obviously, 6.3 12 and a half,
that's about twice as much concrete that you can place per
hour. So in this case, we're going to select the crane and bucket.
These are different examples of equipment used, again, to finish
the concrete. This is a a mixer, a portable mixer. This is a conveyor
belt to place the concrete in places where you cannot reach with
any other means. This is a transit mixer with the chute. And this is
a concrete finisher, especially for pavement, and it's also used
for asphalt. So it's either asphalt or concrete before the
concrete gains its initial setting, because otherwise it's
not going to be able to finish the surface.
And again, here are some examples of these different transit mixers.
We have seen this slide before with these four different
pictures. So these are examples of transit mixers with different
sizes for their jobs. This is basically our introduction or our
lecture on concrete equipment. As you have seen, it's quite simple.
Once we understand the operation and once we can balance the
different equipment to have the best productivity for this
equipment.