Cement is made from a chemical mixture of calcium, silicon, aluminium, iron ore, and other materials such as fly ash, minor amounts of gypsum, limestone, and clay that is carefully managed.
The Main Constituents of Cement are:
|Di calcium Silicate||2CaO.SiO2||30%|
|Tri calcium Silicate||3CaO.SiO2||40%|
|Tri calcium Aluminate||Ca3Al2O6, or 3CaO·Al2O3||11%|
|Tetracalcium Alumino Ferrite||4CaO. Al2O3 Fe2O3||11%|
Types Of Cement
- Ordinary Portland Cement (OPC)
- Portland Pozzolana Cement (PPC)
- Rapid Hardening Cement
- Quick setting cement
- Low Heat Cement
- Sulfates resisting cement
- Blast Furnace Slag Cement
- High Alumina Cement
- White Cement
- Colored cement
- Air Entraining Cement
- Expansive cement
- Hydrographic cement
Common Adulterants of Cement
|Blast Furnace||Silver Grey|
|Furnace Ashes||Coarse And Gritty, With A Medium To Dark Gray Color.|
|Dessert Sand||Very Light Reddish-Yellow Color, With 2-3 Mm Of Particle Size With Brittle Edges|
|River Bed Sand||Rounded Particles, And May Contain Clay Or Other Impurities. And A Saturated Yellow Color.|
Adulteration in Cement
Adulteration of cement refers to the addition of non-cement elements to the cement’s raw sources. It may result in:
1.) Loss in cement strength.
2.) Formation of lumps
3.) The mixing percentage will be incorrect.
4.) Bonding will be porous owing to contaminated cement.
Forensic Analysis of Cement
- Preliminary analysis
- Laboratory Chemical analysis
- Instrumental analysis
Sample of cement should be collected maintaining chain of custody. It should be stored in an airtight plastic jar/Steel Jar with the collecting officer’s signature and the necessary details. The batch number or specifics of a cement bag, as well as the written data on the cement bag: firm name, kind of cement, should be documented for future reference of the collected sample.
Field and Laboratory Test
Colour Test and luminescence
Take 1 gm of the sample and evenly put it on a petridish or plate under normal conditions. Adulterants in cement may include ashes or burned bone. When the cremated bone was illuminated with a wavelength of 450 nm and examined through a yellow long-pass filter, it turned a dark purple colour.
The finer the particle, the better the quality guarantees against adulterants such as sands. Take a little sample between your fingers and feel it, if it’s a case of unaltered cement, squeezing it should feel smooth. If it doesn’t feel smooth and uninform in nature it may possible that it’s been contaminated with sand.
Adulterants such as ashes, pounded clay, and silt have an earthy odour, and if the cement smells earthy, it indicates that a significant amount of sand or silt have been added as an adulterant.
Lumps are described as the hardening of cement as a result of moisture application. The amount of water that reacts with cement is determined by the size of the lumps. Take a 100 gm sample and inspect it for visible lumps. It’s also noticeable while compressing the cement sample, where little lumps feel like sands. When using a spatula to smash these lumps, they are readily crushed.
Take roughly 500g of sample and dip your hand into it while wearing rubber gloves to sense the temperature. If it feels chilly to the touch, it might be pure cement. In comparison to cement, it seems warmer if it is mixed with sand and ashes.
Take 1 gm of the sample and heat it on a steel plate for around 20 minutes. The colour of the sample changes when it is composed of adulterated cement.
Spread a few gm of cement over 100 ml of the clear beaker filled with water. Unadulterated cement should float on the surface for a while before shrinking and then settling on the beaker’s bottom.
Particle-like ashes in adulterated cement begin to shrink immediately.
Make a paste using 10gm of cement sample and water. Make a firm and sharp-edged cake. Place the prepared paste in another 250ml beaker containing water and let aside for 24 hours.
If the cement sets without cracking, it might be an indicator of pure cement and an excellent result.
A cement block measuring 25mm x 25mm x 200mm is constructed and then submerged in water for seven days. Then one side of the cement block is secured with a hook, while the other is fastened to 34 kg of weight stings.
If the cement does not shatter, it is likely that it is pure of adulterants.