Raw Material Analysis

Soil Sample 1: Red Soil: This clay is not pure. It has grass roots, tree roots, and small stones. The wet bulk specific gravity is 1.0040g/cm3,the natural water content is 23.55%


Soil Sample 2: Wheat Colored Soil: This type has wet bulk specific gravity of 1.1120g/cm3 the natural water content is 8.26%


Third sample is Fly Ash.


     The chemical analysis of raw materials


Raw material SiO2 Fe2O3 Al2O3 CaO MgO Loss on ignition
Sample 1 62.03 7.05 9.17 1.08 0.56 10.79
Sample 2 62.41 1.10 16.13 1.54 2.33 5.20
Fly ash 59.28 6.57 23.30 1.85 1.44 6.57


The physical property of raw material


Liquid limit 
Plastic limit  
 The index of plasticity
 Moisture content
 Drying property   
 Coefficient of drying sensitivity Critical moisture content    Drying linear shrinkage rate
 Soil 1#  41.2  25.6  15.6  32.47  1.09  15.5 7.04
 Soil 2#  27.2  19.8  7.4  23.87  0.36  17.6  3.20


The plastic limit of item reflect the forming performance, according to above chart, the index of plasticity of soil 1# is more than 15,this is high plastic material, can add some low plasticity materials. The index of plasticity of soil 2# is more than 7 and less than 15, this is medium plastic material, it was suitable to making clay bricks.

Regarding drying performance, the coefficient of drying sensitivity of soil sample 2 is less than 1, we called it low coefficient of drying sensitivity material, this material is not easy to appear crack, it's suitable to adopt speedy drying


We use small double stage de-airing extruder to produce sample bricks, the chart show the performance of extrusion as following:


 Item  Extrusion pressure
Vacuum degree
Moulding moisture
(dried bricks) 
 Soil 1  2~4  -0.082  20.37  the surface of bricks are smoothly, the bricks are strength but lack tenacity
 Soil 2  4~6  -0.082 22.66



The soil sample 2 is suitable for speedy drying.



  a)Room temperature----400oC: temperature rise speed at150oC/h;
    400oC--400oC: preserve heat for 20 minutes;
    400oC--800oC: temperature rise speed at 150oC/h;
    800oC--800oC: preserve heat for 20 minutes;
    800oC--100oC: temperature rise speed at 150oC/h;
    1100oC--1100oC: preserve heat for 30 minutes;


After firing, natural cooling.


Conclusion and Suggestion

Soil Sample 1 is high plastic raw material, can add some low plasticity materials, soil sample 2 is medium plastic raw materials, both are good performance in forming, the red bricks are all high strength, it's good for making clay bricks.