Critical Thinking

Perlite Turkish Liras with current unit price of

Perlite is a kind of volcanic glass
that is formed from obsidian. It is quite dense material and contains about 3%
water in it and density of perlite is about 1050 kg/m3. However, when
perlite heated up to about 1000 °C, the water in it vaporizes suddenly which
causes expanding on perlite. It became almost twenty times bigger than its
original size. As a result of this process, expanded perlite’s loose weight
density is about 35-45 kg/m3. Therefore, it became very
distinguishing material for construction industry. It is used in masonry and
plastering process for insulation, fire resisting and reducing the noise
transfer purposes. It is also used for the creating lightweight aggregate
concrete. The mixing process is same as the normal concrete except air
entraining admixture because the expanded perlite has very low density, mixing
with water is very difficult. Hence, admixtures are used for this purpose.

According to experimental study, expanded perlite light weight concrete have air
dry density between 560 and 1710 kg/m3. The compressive strength
values vary between 3.4 and 30.0 MPa at 28-day. (Jedidi,
Benjeddou, & Soussi, 2015) Unit price of lightweight concrete
made by expanded perlite is between 93.1 and 98.6 Turkish Liras with current
unit price of the materials in Turkey. (Table 3) (Jedidi
et al., 2015)

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Pumice is a volcanic lightweight
aggregate which has voids in its structure. That voids sourced from combining
of outflow gases and magma. The reason of having lightweight is that porous
structure. Pumice is the first used lightweight aggregate in the history and
nowadays it is widely used to have lightweight concrete in the world. (Parhizkar,
Najimi, & Pourkhorshidi, 2012) (Anwar
Hossain, 2004) Pumice aggregate’s  most important constituents are of SiO2 and
Al2O3. In order to produce the aggregates crushing and
blasting process are not applied unlike normal aggregates, only gradation and
washing operations are applied. The process to creating concrete with pumice
aggregate is not different than the concrete with normal weight aggregate. According
to study that is done by L. Gündüz, lightweight concrete with pumice aggregate
has air dry unit weight between about 1000 – 1300 kg/m3 and
compressive strength values are varies between 1.97 and 11.48 MPa. Modulus of
elasticity of the lightweight concrete with pumice aggregate is changes from
1.6 and 10 GPa. Moreover, in the same study, price of pumice aggregate concrete
per 1 m3 is varies from about 20 to 50 Turkish Liras for the concrete
that air dry unit weights between 1052 and 1272 kg/m3. (Table 2)  (Gündüz
& U?ur, 2005) The unit prices of pumice aggregate
and cement are updated according to current values in Turkey.

Foam concrete is a type of
lightweight and cellular concrete. It is produced with generating a void in a
cement paste with admixtures. Foam concrete has become very popular in recent
years however it has a quite long history. The first foam concrete that made
with Portland cement is discovered by Axel Ericsson in early times of 1920s.

Cement, water, sand and foam agent are the main components of the foam
concrete.(Thakrele,
2014) While mixing the concrete, firstly
foam agent and water are mixed together in the foam generator to produce foam then
the freshly produced foam and cement paste are blended together. Sand or other
necessary admixtures can be added to the mixture. In the mixture, foam agent is
the significantly important because it is the source of air bubbles that causes
to have lower density on the concrete. Foam agents are generally protein or
synthetic based. Protein based foam agents causes a lot of small bubbles
however synthetic based foam agents causes few but bigger bubbles because of
that, protein foam agents causes better compressive strength on the concrete
compared to the synthetic ones.(Amran,
Farzadnia, & Ali, 2015) Unit weight of foam concrete varies
between 240 and 1900 kg/m3 and its compressive strength values have
also wide range which is between 0.48 and 43 MPa. Also studied showed that
modulus of elasticity of the foam concrete is changes from 1.0 to 8.0 kN/mm2.

(Ramamurthy,
Kunhanandan Nambiar, & Indu Siva Ranjani, 2009). According to Sircontec that producer
company of lightweight concrete in USA, price of foam concrete per m3
is between 62.7 and 91.0 Turkish liras. Unit prices of cement and foam agent is
updated with the current values in Turkey. (Table 1)

In order to decrease
unit weight of the concrete, pores in the concrete must be increased. There are
mainly three methods to increase pores in the concrete; using porous aggregate,
using only coarse aggregate and creating a void in the paste. Using porous
aggregate in the concrete instead of the normal weight concrete is the most
effective method to decrease unit weight of the concrete because 60-70 percent
of concrete’s volume is covered by aggregates. The concretes produced with this
method is called lightweight aggregate concrete. The other method is making
concrete with only normal weight coarse aggregate and cement paste.  Not using fine aggregate causes to have void
in the concrete and decreases the weight of concrete up to three tenths. This
concrete type could be used when the permeability is relevant. The final method
creating porous in the paste which can be done with using prepared foam or
generating gas in the cement paste. Concretes made by with this method called
cellular concrete. (Bogas
& Cunha, 2017)

Concrete, which has
lower unit weight than 2000 kg/m3, are called lightweight concrete
and it has less thermal conductivity than the normal concrete. They have
different properties than normal concrete. Therefore, when the insulation or
lightness is desired in construction, lightweight concrete becomes the ultimate
solution. Lightweight concrete is separated into the three different categories
with respect to their basic physical characteristic. First one is structural
lightweight concrete, which has unit weight between 1120 and 1900 kg/m3.

It must also have at least 17 MPa compressive strength. That kind of
lightweight concrete can be used in load carrying structural elements such as
columns, beams or retaining walls. Second type of lightweight concrete is
called “moderate strength concrete”. Its unit weight is between 2000 and 800
kg/m3 and compressive strength is usually between 3.4 and 17 MPa.

Moderate strength concrete can be used for building walls, roofs and floors or
production of the masonry block. The last lightweight concrete type according
to its physical properties is low-density lightweight concrete. This type of
concrete has unit weight smaller than 800 kg/m3 and compressive
strength below from 3.4 MPa. This low density concretes can be used for the
“non-structural fills” or for some insulation purposes since it has much lower
compressive strength. (Bogas
& Cunha, 2017)

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