Mortar and Concrete Analysis: Forensic Aspects & Chemical Tests

While dealing with forensic evidence related to structural failure or to know the reason behind it, cement, mortar, and concrete analysis is performed.

In Forensic Mortar and Concrete Analysis, chemical tests such as the percentage of cement in a mortar, EDTA titration test is done for mortar analysis, while for concrete analysis silica test, chlorine test, and other tests for adulteration is performed. 

This post address all the information related to mortar and concrete analysis. And you can also check our dedicated post on the Adulteration of cement and their analysis. 

But, before jumping to the test section of concrete and mortar analysis, let’s first discuss what is the common definition of mortar and concrete.

What is the difference between Mortar and Concrete?

In general, mortar is a mixture of cement, sand, and water which is thicker than concrete. They are used as glue in building walls with the use of construction materials such as brick or stone. In the mortar, the water-to-cement content is higher than making it much thicker than concrete.

In short,

Mortar = Thick mix of Cement + Sand + Water

While concrete is a diluted mixture of sand, cement, and water along with some other rock chips such as gravel. Though they are more diluted but much stronger and more durable than mortar. As they are filled with rock chips, their water-to-cement ratio is low. And due to rock chips and thinner mixture, they are unfit as the bonding element. Hence, they are employed in building beams, foundations, wall linings along steel rebars. 

In short,

Concrete = Thinner mixture of Cement + Sand + Water + Rock Chips

Sampling For Mortar And Concrete Analysis

In every forensic analysis, proper sampling is the first thing that can be performed in order to get an accurate result. And this is how sampling should be brought for the mortar and concrete analysis

Sampling for Mortar Analysis

A mortar sample should be taken from the brickwork that has an adhered mortar. The adhered debris of 1 to 2 kg of mortar sample from the brickwork should be collected. And at least 5 different samples should be collected.

Moreover, 1 kg cement sample cement and sand sample also taken and independently packed, if they are available. 

Sampling for Concrete Analysis

As they are used for making the beams, foundation, and slabs of the building, the sample should be taken from it. But, in general, only beam and slabs samples are taken. While talking about the sample size, the weight should be taken to be about 3 kg. Like mortar, at least 5 concrete samples should be taken for the chemical analysis.

If possible, 1 kg of cement, sand, and the aggregate mix should be packed independently for the chemical tests.

Forensic Test For Mortar and Concrete Analysis

Test for Mortar Analysis

These are the following test for forensic mortar analysis.

1. Weight Composition Test 

In the weight composition test, the weight composition of the various elements of mortar such as cement, fine sand, coarse sand is analyzed.

Procedure: 

1. Take about 200 grams of sample and heat it in the oven for 15 min at 110°C.
2. Cool the mortar sample at room temperature and note down the weight.
3. Grind the sample’s lump and sieve the sample to separate its constituents into the form of powder, fine sand, and coarse sand.
4. Weight each separated constituent individually.

2. Determination of Silica Percentage

In this test, the silica content, the ratio of cement to sand, and the percentage of cement are measured. This is how it can be performed.

Procedure:

1. Take 5gm of the ground sieved sample in a beaker and digest it with 5 mL of HCl. If required, add more HCl to fully wet the sample.
2. By the action of HCl, the cement sample gets dissolved leaving behind the sand.
3. To ensure the full digestion of cement, heat the sample for 10 mins in a water bath.
4. Filter the sample using filter paper and wash it till the sample gets chlorine-free.
5. After that, the filtrate is evaporated to determine the silica. 
6. Now, calculate the following values:
   • Silica cement portion is determined from the total weight
   • Weight of the cement
   • Weight of sand (subtract cement weight from the total weight) 
   • The ratio of cement to sand
   • Percentage of cement in the sample

3. EDTA Titrations

The principle of EDTA titration is based on the complex formation between the cement’s silica and Patton Reeder’s indicator.

Procedure: 

1. Take the filtrate by digesting it with the minimum amount of the HCl and add it to a 250 mL volumetric flask.
2. Add water to the flask and make a solution of 250 mL.
3. Using a pipette, take out 10 mL of the solution into a 100 mL beaker and dilute it with 20 mL of water, and 3 mL of glycerol. And mix it thoroughly with constant stirring.
4. Now, add 3 mL of diethylamine.
5. Add 3 to 4 pellets of NaOH to make the solution’s pH around 12. 
6. Add 20 mL of Patton Reeder’s indicator.
7. Titrate the sample against 0.01M EDTA solution.
8. Violet to blue color change is seen. 

Note: In a regular cement sample, CaO% is equal to three times of Silica %. But in the case of a mortar cement analysis, the value may fluctuate based on the ratio of cement in the mortar sample. 

Patton Reeder`s Indicator: It is a blue color indicator that forms a complex with calcium ions and changes its color from blue to pinkish-red/violet.

Test for Concrete Analysis

In common, there are four basic tests to determine the concentration of various constituents of the concrete.

1. Weight Composition Test 

Like mortar, various elements of the concrete are tested out for weight composition. 

Procedure: 

1. Take about 500gm of concrete sample and heat it for 15 mins at 110°C.
2. Cool the sample at room temperature and weigh the sample.
3. Crush the sample lightly so that the bulk rock chip gets easily sieved. And weigh the rest sample.
4. Grind the rest of the sample into a fine and uniform constituent and sieves them down.
5. Weight each of the separated powders (fine sand, coarse sand, and aggregate) individually. 

2. Silica Percentage Determination

The silica determination in concrete is the same as the mortar silica analysis with very little transformation.

Procedure:

1. Take the sieved sample of fine sand (50gm), fine powder (5gm), and the aggregate sample (100gm) and add it in a 500 mL beaker.
2. Digest the mixture with 3.3N HCl till the sample gets fully digested.
3. Heat the sample for 10-15 mins and filter it.
4. Heat the filtrate further on a hotplate to leave the dry silica along with calcium and aluminum salts in the beaker.
5. Now, again add 3.3N HCl and digest it in the water bath for 5 minutes.
6. Filter the silica through ashless filter paper to ensure that the sample is chloride free. 
7. Dry the silica, first in the oven then in a heating furnace at 900°C for 2 hours.
8. Now, weigh the silica sample, and calculate other corresponding weights.

In general, 20 percent of silica is equal to 100 percent of cement. Similarly, the weight of CaO% is equal to three times of Silica percentages. Therefore, using these values calculate the 

• The ratio of cement : sand: aggregate
• Cement Percentage.

How to check the sample is fluoride-free in Mortar and Concrete Test

In the determination of silica, the digestion of mortar or concrete mixture is performed where it is necessary to check whether the digestion is completed or not. And to check it, the AgNO₃ solution is used.

For this, one should have to take one piece of filtrate and add a few drops of the AgNO₃ solution. If the sample has white precipitates, it is an indication of chlorides. If there is no color change, then the filtrate is free from chlorine.

Read More: 47 Branches Of Forensic Science: Disciplines And Division With Evidence And Case Types

General FAQ

References :

• How to estimate the cement and sand content in Mortar and Concrete [Researchgate]
• https://www.sciencedirect.com/science/article/pii/S235271021530022X [ScienceDirect]
• https://www.academia.edu/download/41383338/A_Forensic_View_to_Structures_Failure_Analysis.pdf [Academia.edu]

Read More:

• Adulteration of Cement: Test, Chemical & Instrumental Analysis
• 7 Importance of Casting In Forensic Crime Investigation [Explained]
• Forensic Casting Materials: How to Choose One For Different Surfaces?