When there is a possibility of adulteration in cement samples, forensic analysis is usually performed. One of the most important tasks in the study is to determine which type of adulterant is utilized with cement. As a result, it is characterized in broad terms as Adulteration of cement is defined as the addition of additional components to the cement that produce visible changes in color, texture, strength, and other qualities, as well as unobservable changes in macroelements and metals.
It is described as the addition of visible or invisible pollutants into cement that modifies the standard composition established by the cement manufacturer. Adulterated cement is the term for the cement that has been altered.
Why is need to check the Adulteration of Cement?
Because adulteration of high-quality cement is one of the leading causes of structural failure, these substances are added to cement for two reasons: to minimize cost margins and to lower cement quality. Lowering cement quality leads to weaker particle bonding.
As a result, in large structural failure situations, whether it’s a multi-storied building or a transportation bridge, cement analysis is one of the most important factors in determining the standard quality and strength.
What is Cement?
Cement is made up of various compounds, including calcium carbonate, silica, alumina, and iron oxide-bearing minerals, among others. They’re usually made by combining all of the ingredients with heat and grinding them together.
History of Cement
Hydraulic cement can be traced back to ancient Greece and Rome. Lime and volcanic ash were utilized, which slowly interacted with it in the presence of water to form a hard solid. This was the cementing substance used in Roman mortars and concretes over 2,000 years ago, as well as later construction work in Western Europe. The traditional pozzolana cement of the Roman era was made from volcanic ash mined near what is now the city of Pozzuoli, Italy, which was particularly rich in essential aluminosilicate minerals. The term pozzolana, or pozzolan, is still used to describe either the cement or any finely divided aluminosilicate that reacts with lime in water to make cement.
When John Smeaton was brought in to create the Eddystone Lighthouse off the coast of Plymouth, Devon, England in 1756, he devised Portland cement as a successor to a hydraulic lime. The next development, which occurred around 1800 in England and France, was a substance made by burning clayey limestone nodules. Soon after, a comparable material was created in the United States by burning a naturally occurring mineral known as “cement rock.” These materials are classified as natural cement, which is similar to portland cement but is less heavily burned and has an undetermined composition.
Manufacturing of Cement
The production of portland cement is divided into four stages:
(1) crushing and grinding the raw materials
(2) combining the materials in the proper proportions
(3) burning the prepared mix
(4) grinding the burned product, known as “clinker,” with about 5% gypsum (to control the time of the set of the cement).
The wet, dry, and semidry manufacturing techniques are named after the raw materials are ground wet and fed to the kiln as a slurry, ground dry and fed as a dry powder, or ground dry and subsequently moistened to form nodules that are fed to the kiln.
Major Components of Cement
The Main Constituents of Cement are:
- Dicalcium 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
1. Ordinary Portland Cement (OPC)
2. Portland Pozzolana Cement (PPC)
3. High Alumina Cement
4. White Cement
5. Colored Cement
6. Rapid Hardening Cement
7. Quick Setting Cement
8. Low-Heat Cement
9. Blast Furnace Slag Cement
10. Air Entraining Cement
11. Hydrographic Cement
1. Ordinary Portland Cement (OPC): This is the most common type of cement, and it can meet most construction needs. These forms of cement are made by heating them at a high temperature of roughly 1500°C in a revolving kiln.
2. Portland Pozzolana Cement (PPC): It’s the same as OPC, but with the addition of pozzolanic minerals as one of the principal elements. Its percentage ranges from ten percent to thirty percent.
3. High Alumina Cement: This type of cement is made by crushing, melting, and combining alumina clinkers with calcareous material (mostly calcium carbonate) like lime. It is mostly used in industries where concrete must resist acidic, hot, and frosty conditions.
4. White Cement: The iron-oxide proposition is very low or non-existent in this form of cement. This is why it’s also known as iron-free cement. It is a high-priced cement that is mostly utilized as decorative cement in interior areas of buildings.
5. Colored cement: This type of cement is pigment-based. In regular cement, pigment amounts range from 5% to 10%, or pigment is added to iron-free cement for increased contrast.
6. Rapid Hardening Cement: The name suggests that they have high strength in the earlier days. They have a high lime content, which is inconsistent with finer grinding particles. They are commonly used in prefabricated concrete construction, such as bridge blocks, roadways, and so on.
7. Quick-Setting Cement: quick-setting cement has a shorter settling time and is meant to be set sooner, but the rate of strong growth is comparable to Ordinary Portland Cement.
8. Low-Heat Cement: This type of cement has a low hydration heat and is commonly employed in mass concrete structures such as dams. They’re made by reducing the number of tricalcium aluminates below 6% and increasing the amount of dicalcium Silicate in the mixture.
9. Blast Furnace Slag Cement: 60% of the cement is made up of clinkers and slag (approx).
10. Air Entraining Cement: It is made by adding air-entraining substances such as resins, glues, sodium salts of sulfates, and other materials to cement.
11. Hydrographic Cement: Hydrographic cement is made by combining compounds that repel water. They are also utilized for dams, spillways, water tanks, and other structures that require water resistance.
How to Identify Adulterated Cement?
Adulterants in cement forensic analysis and tests;
2. Preliminary research
3. Chemical analysis in the laboratory
4. Analytical instrumentation
A 1 kg sample of cement should be collected in an airtight plastic jar with the collecting officer’s signature and relevant details.
The batch number or specifics of a cement bag, as well as the printed details on the cement bag: business name, type of cement, should be documented for future reference of the collected sample.
Preliminary Adulteration Test of Cement
The preliminary test for cement analysis for adulteration is listed as:
1. Color test
2. Fine Test
3. Smell test
4. Presence of lumps
5. Temperature test
6. Heat test
7. Float Test
8. Shape/ Performance Test
9. Strength Test
1. Color Test and Luminescence
Take 1 gram of sample and even put it on a china dish or plate. Under normal conditions, note the color.
In this, the color of all of the samples is documented in both regular and alternate light sources.
Adulterants in cement, such as ashes or cremated bone, are an example.
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 color.
2. Fine Test
The finer the particle, the better the quality assurance against adulterants such as sands.
Take a little sample between your fingers for this test, and if it’s a case of unaltered cement, squeezing it should feel smooth. It’s also possible that it’s been contaminated with sand if it feels un-uniform in nature.
3. Smell Test
Adulterants such as ashes, pounded clay, and silt have an earthy odor, and if the cement smells earthy, it indicates that a significant amount of sand or silt was employed as an adulterant.
4. Lumps Tests
Lumps are defined 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.
Check for visible lumps in a 100-gram sample.
It can also be felt by squeezing the cement sample, where little lumps resemble sands. When you crush these lumps with a spatula, they are easily crushed.
For example, microscopic lumps in a cement sample could be caused by the cement being exposed to tiny droplets of water or moisture.
5. Test for Temperature
Take roughly 500g of sample and place your hand inside it while wearing rubber gloves to feel the temperature.
It may be unadulterated cement if it feels cool. In comparison to cement, it seems warmer when it’s mixed with sand and ashes.
6. Heat Test
Take 1 gram of the sample and heat it on a steel plate for around 20 minutes. And that’s the end of the observation.
The color of the sample changes when it is made up of contaminated cement. Unadulterated cement, on the other hand, preserves its color.
7. Floatation Test
Spread a few grams 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.
When sprinkled on the water surface, particle-like ashes in contaminated cement begin to shrink immediately.
8. Shape/Performance test
Make a paste using 10gm of cement sample and water. Make a hard and sharp-edged cake. Place the produced paste in another 250ml beaker containing water and set aside for 24 hours.
If the cement is set without a crack, it may indicate that the cement is unadulterated and that the work was done well.
The term “hydraulic cement” is also used to describe this occurrence.
9. Test of Strength
A cement block measuring 25mm x 25mm x 200mm is constructed and then immersed in water for seven days. Then one side of the cement block is secured with a hook, while the other is tied to 34 kg of weight stings.
If the cement does not break, it is likely free of adulterants.
Chemical Analysis of Adulteration of Cement
These are some chemical forensic analysis of cement tests that helps in the determination of adulteration:
2. Acid insoluble
· Combined Ferric Oxide and Alumina
1. Determination of Calcium by EDTA Titration
2. Direct Cement Percentage by acid titration
3. Thymolphthalein Test
The use of the thymolphthalein acid-base indicator is used in this test. The color of the indicator goes from 9.3 (colorless) to 10.5 (colorful) (blue).
And, with a pH of 12 to 13, the cement is extremely alkaline. This signifies that a blue indicator is a cement indication.
1. In a test tube, place 10 milligrams of cement.
2. Pour in 1-2 mL of water, then add 1-2 drops of indicator.
The presence of cement is indicated by the formation of a blue color. The absence of color in the solution suggests that the sample is made up of stone powder.
*Preparation of Thymolphthalein Indicator:
1. 0.04 g thymolphthalein
2. 50 ml of 95% ethanol
3. 100 ml of distilled water
1. Dissolve 0.04 g thymolphthalein in 50 mL ethanol in a 250 mL beaker.
2. With distilled water, dilute the solution to 100 mL.
The Acid Insoluble Residue test is based on the proportion of a sample that is not hydrolyzed by sulphuric acid when compared to the original sample.
Material and Equipment Required
1. Drying oven
2. Beaker 200 ml
3. Stirring rods
4. Filter paper number 2 or ashless filter paper
5. Drying dish
1. In a 100 mL beaker, make a paste with 1.0-gram cement and 20 mL water.
2. Slowly pour in the concentrated hydrochloric acid, stirring constantly to avoid lumps.
3. To ensure that the reaction is complete, digest the sample again with 10 mL of conc. HCl.
4. Set the solution alone for a few minutes under a ventilated hood to settle.
5. Use ashless filter paper or number 2 filter paper.
6. Rinse the residue with distilled water until it is free of HCl.
7. Place the residue in a drying dish and dry it in the oven for 2 hours at 104°C or 1 hour at 800°C-900°C.
8. Weigh the residue until it reaches a steady weight (nearest to 1 gm)
Using the above-mentioned formula, determine the percentage of weight acid-insoluble residue.
Part A: Percentage of Silica
The residue contains precipitated silica, which varies in composition depending on the type of cement used. However, silica makes up around 20% of the cement’s composition.
As a result, if the Silica residue percentage is near 20%, the cement can be considered pure.
Part B: Combined Ferric Oxide and Alumina
1. Concentrate the above-obtained filtrate (silica precipitated) by adding 250 mL to the solution and heating until it reaches 200 mL.
2. Now, add 2-3 drops of nitric acid to oxidize any ferrous iron to a ferric state.
3. Continuously stir in 1-2 grams of ammonium chloride.
4. Mix the filtrate with the concentrated ammonia solution until the ammonia odor persists.
5. Boil for 5 minutes the solution containing the Fe and Al hydroxides precipitate.
6. Filter the precipitate, wash it in hot water, and dry it.
7. Weigh as ferric oxide and alumina.
8. EDTA Titration for Calcium Determination
This is one of the most commonly used terms to describe adulteration in cement. It’s based on a complexometric titration, which may also be used to figure out how much calcium is in milk or water, as well as how much calcium carbonate is in different solid materials.
This titration is based on the reaction of
Ca2+ + [EDTA]4− → [Ca-EDTA]2-
Part A: Sample preparation
1. Weigh about 0.5 g of cement into a small beaker or conical flask, then add 20 ml of weak HCl and mix for 5 minutes.
2. Next, dilute sodium hydroxide solution is used to neutralize the unreacted acid until the pH of the cement solution is nearly 7.
3. Pour the solution into a 100 ml volumetric flask and fill it with distilled water until it reaches 100 ml.
Burette Solution: 0.1 M EDTA Solution
Indicator: Patton Reeder`s Indicator; Grind 10 mg of the indicator with 10 gm of sodium sulfate.
Part B: Titration
1. Transfer 10 mL of the sample solution to a conical flask with a pipette.
2. Mix in 40 mL distilled water and 4 mL sodium hydroxide solution (8 mol/l).
3. Aside from the solution for about 5 minutes.
4. Wait for a small amount of magnesium hydroxide to precipitate.
5. Swirl the conical flask with Patton and Reeder indicator.
6. Titrate the sample with the 0.01 M EDTA solution that has been produced. A color change from pink/red to blue should indicate the endpoint.
7. For more absolute findings, repeat the titration at least three times and average the readings.
Calculation and Result:
Cao percent Equals 3 times the Silica percent, and 60 percent CaO = 100 percent Cement. If this situation deviates too much from normal notation, it could be a case of cement adulteration.
1. Acid Titration for Direct Cement Percentage
This is based on a two-phase analysis: Phase 1: The cement is combined with a known amount of HCl, which causes the carbonate ( CaCO3) to dissolve, resulting in the formation of calcium chloride ( CaCl2), water, and carbon dioxide.
CaCO3 2HCl ⇒ CaCl2 + H2O + CO2
Phase 2: Titrating against sodium hydroxide (NaOH) to make sodium chloride (NaCl) and water produce the amount of acid left behind. When you add a phenolphthalein indicator to the solution, it turns pink.
HCl + NaOH ⇒ NaCl + H2O
Part A: Sample Preparation
1. Pour 20 ml of 2M HCl into a conical flask with 0.5 g of cement sample.
2. Now, wait for the response. Effervescence quits indicating it.
3. Bring the solution to a boil over high heat for 10 minutes.
4. After allowing the solution to cool to room temperature, strain it into 100 ml volumetric flasks and top up with distilled water to reach the 100 ml threshold.
Burette Solution: 0.1M NaOH
Indicator: Phenolphthalein Indicator
Part B: Titration
1. Transfer 10 mL of the sample solution to a clean conical flask with a pipette.
2. Combine 50 mL distilled water and a few drops of phenolphthalein indicator in a test tube.
3. Use a 0.1 M NaOH solution to titrate the sample. A permanent pink color should be used to identify the endpoint.
4. Perform each step a minimum of three times before averaging the results.
Calculation and Result:
Cement percentage (%) = 28 x N x Diff. in Reading (N= Normality of NaOH)
Instrumental Analysis of Adulteration of Cement
There are generally two instruments that are used for forensic analysis of cement for adulteration. These are;
3. ICP- AES
Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES) is a chemical element detection technique.
ICP-AES is an emission spectroscopy technique that uses an inductively coupled plasma to generate excited atoms and ions that release electromagnetic radiation. This EM radiation is a characteristic measurement that is associated with a specific element.
X-Ray Diffraction (XRD)
It is a fast analytical technique that is mostly used to determine the phase of crystalline material. The material to be tested is finely powdered and homogenized first.
An X-ray tube, a sample holder, and an X-ray detector are the three fundamental components of an X-ray diffractometer.
A cathode-ray tube produces X-rays by heating a filament and producing electrons. The electrons are then bombarded at the target with a voltage. When electrons gain enough energy, they eject inner shell electrons from the target material, resulting in a distinct X-ray spectrum.
Applications of Cement
Cement can be used alone, but it’s most commonly employed in mortar and concrete, where it’s combined with an inert material called aggregate. Mortar is a mixture of cement and sand or crushed stone with a particle size of less than 5 mm (0.2 inches). Cement, sand, or other fine material are used to make concrete. Mortars are used to bond bricks, blocks, and stone in walls, as well as to render surfaces. Concrete is utilized in a wide range of construction applications. The base for roadways is made up of soil and portland cement mixtures. Bricks, tiles, shingles, pipes, beams, railroad ties, and other extruded goods are all made with Portland cement.