Synthesis of Expanded clay aggregate pellets by using local raw materials

This study assesses the possible use of local raw materials (clays) for producing expanded clay pellets and test the product with American standard for test materials (ASTM) and according to ASTM C 330.For using them as lightweight aggregate in different construction applications, like thermal insulation, lightweight structural concrete , decoration pieces ,etc. The clay was collected from AlAnbar province. The clay was bloated at 1150 C° without adding any impurities ,just mechanical treatment and perfect firing program, in order to obtain good bloating coefficient that is related with firing parameters (access time, temperature, socking time). We got the results of the match determined by the American specification (ASTM C330) and in which is considered lightweight aggregate. We got density about (280 kg / m 3 ) which is much less than that determined by ASTM where the aggregate lightly if the density is less than (880 kg / m 3 ).


1.Introduction
The expanded clay pellets as a lightweight aggregates are an important and versatile materials , used in concrete mixtures to make lightweight concrete (LWA), which used in different applications such as curtain walls , shell roof floors , pre-cast and pre-stressed concrete [Satish Chandra and Leif Berntsson,2004].
Today, lightweight aggregates are available in wide range of densities, size and strength.This makes designers capable to design concrete with more options of densities and strengths for different applications.
Expanded clay is a powdery building material with good thermal insulation properties and resistance to the external impacts.It is obtained by feeding clay in a rotary kiln at a temperature of (1150 ) .In this temperature raw materials start bloat turning into light pellets with a porous and firm structure.Properties of the obtained product depend not only on the properties of the start materials , but also on its additives and production technology [Giedrius Vaickelionis and Aras Kantautas, 2011].

2.Study objective
The objective of this research is to produce the lightweight expanded clay pellets from the local raw materials and compare to the specifications (ASTM C330).

Materials
Clay sample supplied by " state company for mining industries -Department of materials extraction" the clay was collected from Al-Anbar province.The table (1) show the chemical composition of this study.The clay through several processes to prepare it for producing expanded clay pellets

Crushing and milling
The raw materials was supplied as rock form .The mechanical treatment was applied to produce clay powder with and average surface area (SSA= 0.4-0.7 m 2 /kg), by using crushing and milling machine that shown in Figure (1) at university of Babylon/college of materials engineeringdepartment of ceramic and building materials.

XRD diffraction
Table (2) shows the XRD results for the sample, that contain quartz, calcite, dolomite and small amount of feldspar.Behind that the figure (2) show the phases of XRD test for clay.X-ray diffraction (XRD) type (Shimadzu 6000, Japan) shown in

Plastic and liquid limit
This test measured the plastic and liquid limits of the clay samples used in this study.The liquid limit (LL) is arbitrarily defined as the water content, in percent.By using Liquid Limit Device (mechanical device) show in figure (5).Amount of clay mixed with water and put in a standard cup, then cut by a groove of standard dimensions after this the clay subjected to 25 shocks from the cup being dropped 10 mm with a rate of one shock per second, to find the liquid limit of the clay samples, this test according to ASTM( D 4318 ) .
The plastic limit (PL) is the water content, in percent, at which a soil can no longer be deformed by rolling into 3.2 mm, diameter threads without crumbling , according to ASTM( D 4318 ) .
The plasticity index (PI) of a soil is the numerical difference between its liquid limit and its plastic limit, and is a dimensionless number.Both of the liquid and plastic limits are moisture contents.Table (3

Molding
Mechanical treatment, milling and mixing with water and finally molding by using extruder.The shape of sample shows in the figure (6) , the mixer shows in figure (7) and the extruder shows in the figure (8).

Drying and firing program
The next steps of producing expanded clay pellets are drying and firing, the Figure

coefficient of bloating
In this study clay formed, 8 mm in diameter using a laboratory piston press and cut into specimens, 10 mm long.The specimens, dried at a temperature of 105 °C, then weight and volume are calculated.
Afterward, the dry specimens were heated at a temperature of 200 °C for 20 min and fired at high firing rate by using a laboratory electrical furnace to a temperature of 1050 °C -1150 °C and stay in the furnace for 25 min.Bloating tests were performed at temperatures differing between (20-50 °C) until the semi-melt temperature of the specimens was attained.After heating , the specimens are taken out of the furnace , cooled at the room temperature, then weighted and submersed into a water for 24 hours by flooded them.
The specimens are removed from water, wiped with a cloth then weighted, the volume (V 2 ) is measured .According to the obtained data, bloating coefficients K p are measured by using equation below.Table (4) shows the coefficient of bloating of clay pellets.

Bulk density
The bulk density of expanded clay pellets that was produced from clay was measured according to American standard ASTM (C 29/C 29M -97) , shown in the table (6).
The clay has big amounts of calcite that produce more gases during firing that make density is low.

Porosity measurements
Table (7) shows the results of porosity for expanded clay as lightweight aggregate that produced in this study by using clay.The results show that the structure of expanded clay have high porosity, that means the weight will be decreased and thermal conductivity will be also decreased.The porosity of clay caused by the structure of clay contain amounts of calcite, that release gases during firing that make the structure more porous.

Specific Gravity
The results of specific gravity are very important because of identifying the expanded clay whether it is lightweight or not, after compare the results with ASTM C330, it is found that the expanded clay is lightweight aggregate.Table (8) shows the results of specific gravity.
The results of specific gravity are very important because of identifying the expanded clay whether it is lightweight or not, after compare the results with ASTM C330, it is found that the two types of expanded clay are lightweight aggregates.

Water absorption
Absorption calculations shown in the following, as well as comparing the results with the specification and find out the validity of the product in the table (9).Note that the test was conducted according to standard (ASTM C 127).These value show that clay pellets has low water absorption percentage because of the shield that covers the surface of pellets such a glass that prevents water from enters inside pellets.

Sieving
Table (10) shows the grading of expanded clay pellets as lightweight aggregate according to ASTM (C 136), the results refer to the aggregates that have the grading (4.75-19 mm)

Conclusions
In this study for the first time , the expanded clay pellets has been produced equal in quality with the expanded clay pellets that manufactured outside the country, by using the available local raw materials and by simple technology .During the study of mechanical properties , the expanded clay as lightweight aggregate has been according to ASTM C 330 .Through laboratory tests, it is considered successful by all standards and can be used to produce lightweight concrete.

Table (7) shows the results of porosity
Table (8) shows the results of specific gravity.Table (9) shows the results of water absorption.
Table (10) shows the grading of expanded clay pellets.

Figure ( 3
Figure (3) at the Babylon University / Collage of Materials Engineering -Department of Ceramics and Building materials was used to characterize the structure of clay samples .

Figure
Figure (4) of clay ) shows the results of clay.The next equations used to calculate LL, PL and PI.LL=W (N/25) 0.12 PL = (Weight of water/ Weight of oven -dry soil)*100% Plasticity Index = Liquid Limit -Plastic Limit PI=LL-PL Where, N : number of shocks W : weight percentage of water

( 9 )
show the electrical furnace that used for drying and firing clay samples which used many programs for drying and firing clay samples but the best program is shown in Table (4).
Figure (1)  shows the crushing and milling machine.

Figure ( 2
Figure (2) shows the phases of clay sample by XRD test.

Figure ( 4
Figure (4) show the DTA curve of clay sample.

Figure ( 5
Figure (5)  show the mechanical device used to calculate LL.

Figure ( 6
Figure (6)  show the shape of sample.
Figure (1) shows the crushing and milling machine

Figure ( 5
Figure (5) show the mechanical device used to calculate LL.

Figure ( 6
Figure (6) show the shape of sample.Figure (7) show the mixer.

Table ( 1
) shows the chemical composition of clay sample.

Table ( 3
) Shows the results of PL, LL, PI clay.

Table ( 8
) shows the results of specific gravity.

Table ( 9
) shows the results of water absorption Table(10)shows the grading of expanded clay pellets