Acid-Resistant Bricks: Properties, Types, Tests, and Advantages

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Acid-resistant bricks are made of clay or shale, with low lime and iron content, and are vitrified at high temperatures in ceramic kilns.

Acid-resistant bricks are used to construct floorings vulnerable to acid attack, the lining of chambers and towers in chemical plants, the lining of sewers carrying industrial effluents, etc., to prevent deterioration of the surface by acids. 

Standard Properties of Acid-Resistant Bricks

1. Dimensions

The standard dimensions for acid-resistant bricks shall be 230 x 114 x 64 mm. The permissible tolerances on the dimensions shall be as per the table below:

	Dimensions in mm	Tolerances in mm
Length	230	±3.5
Width	114	±2.0
Depth	64	±1.0

2. Finish

The finished brick, when fractured, must appear fine-grained in texture, dense and homogenous. The brick shall be true to shape, sound, flat, and free from flaws and other manufacturing defects affecting its utility.

Types of Acid-Resistant Bricks

The acid-resistant bricks shall be manufactured in two classes:

1. Class I Bricks

These acid-resistant bricks are recommended for severe conditions of corrosive environments, as seen in pickling tanks, storage tanks, and heavy-duty floors subject to frequent contact with corrosives liquids. 

2. Class II Bricks

These types of acid-resistant bricks are recommended for working areas and floors subject to occasional spillage of fumes, acids, and chemicals in fertilizer silos. These are also used for skirting and lining silos.

Test for Acid-Resistant Bricks

The tests conducted for acid-resistant bricks are:

1. Water absorption
2. Flexural strength
3. Compressive strength
4. Acid resistance

The first three tests shall be carried out as per the test for regular bricks. The links for the tests are given below:

Types of Tests on Bricks for Building Construction Works

Water Absorption Test on Bricks – Values and Procedures

Compressive Strength Test on Bricks

Test for Acid Resistance

1. Preparation of Test Specimen

The test specimen for the acid resistance test shall be prepared from individual bricks, and a minimum of five bricks shall be tested. Each brick is crushed to powder in a stoneware mortar. 

The sample powder from each brick is taken and passed through an 850-micron sieve and is retained on a 600-micron sieve. The powdered sample shall be washed free from dust as follows:

1. A specimen of 30 g is placed in a porcelain basin, and 150 ml of distilled water is added to it.
2. Place the basin on a sandbath and heat the mixture in the basin until it starts boiling. 
3. Care must be taken to avoid loss of specimen by spurting while boiling, and heating shall be continued for one hour. 
4. Decant the water, and rinse the particles with cold, distilled water. 
5. Dry the material to constant weight by keeping it in an oven maintained at a temperature of 110°C.

2. Reagents

The reagents used for the test shall be:

1. Concentrated Nitric Acid 
2. Concentrated Sulphuric Acid
   

3. Test Procedure

1. 25 g of the prepared specimen is weighed and placed in a porcelain basin.
2. A mixture of 13 ml sulphuric acid, 7 ml nitric acid, and 65 ml distilled water is added to the specimen. 
3. The basin and its contents are placed on a sand bath and heated carefully, and spurting is avoided until all nitric acid is evaporated and sulphuric acid starts fuming profusely.
4. The basin and its contents are cooled to 27± 2°C, and 10 ml of nitric acid and 90 ml of distilled water are added into it. 
5. The heating process is repeated until the sulphuric acid starts to fume again strongly.
6. The basin and contents are cooled, and the acid is decanted carefully. 150 ml of cold distilled water is added and heated up to boiling.
7. The cycle of addition of freshwater, boiling, and decantation shall continue until the decanted liquid is found to be free from sulphuric acid when tested with barium chloride solution. No particle shall be lost during the process. 
8. After the final decantation, dry the sample in an oven maintained at 110°C to constant weight.

4. Calculation and Report

Loss in weight shall be calculated as follows:

Criteria for Conformity for Performance Requirement of Acid-Resistant Bricks

Sl No	Requirement	Class I Bricks	Class II Bricks
1	Water Absorption	≤ 2%	4%
2	Flexural Strength	≥ 100kg/cm2	70 kg/cm2
3	Compressive Strength	≤ 700kg/cm2	500 kg/cm2
4	Resistant to Acid	≤ 1.5%	4%

Advantages of Acid-Resistant Bricks

The advantages of acid-resistant bricks are:

1. It possesses features of high acid resistance, low water absorption rate, is not easily oxidized under room temperature, and does not get contaminated easily.
2. It is used in chemical industries, such as ditch puzzle acid, acid wells, acid storage libraries, and acid impacted ground.
3. It is a  cost-saving material when the special metals and alloys become uneconomical due to chemical attacks at high temperatures.
4. These acid-proof brick liners can lower concentration and temperature levels by making it feasible to use less expensive alloys.

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