How to determine the pH value of the water sample for use in concrete/mortar?

Objective

To determine the pH value of the water sample for use in concrete/mortar.

 

Theory and Scope     

Water plays an important part in deciding the quality of the final product. The pH value of water is an indication of its acidity/alkalinity, the property that directly affects the strength of concrete, due to its chemical reaction with the ingredients of cement.

The test determines the quality of water for use in concrete/mortars.

 

Apparatus   

Litmus paper pack

 

Procedure   

Step 1: Collect the water sample representing water to be used for concreting or otherwise for any use involving its mixing with the cement during construction.

 

Step 2: Insert a litmus paper strip into a water sample. Allow a reaction time of 10 to 20 seconds.

 

Step 3: Observe the change in colour and match it with the reference coloured cover strip. The colour will change according to the level of concentration of acidic and alkaline substances in water.

Reference coloured cover strip colour matching.

 

Observations

The pH value of the water sample is …………..; water is suitable/unsuitable for the construction job.

 

Precautions

1. The sample of water taken for testing should be representative of water proposed to be used for concreting, taking into consideration the seasonal variation.

 

2. The sample shall not receive any treatment before testing other than that envisaged in the regular supply of water proposed for use in concrete.

 

3. The sample shall be stored in a clean container previously rinsed out with similar water.

Determination of pH value of water sample

 

Discussion

The test results are sufficiently accurate for determining the quality of water for use in concrete/mortars. Ac-  curate testing is possible by the use of pH meter shown typically in Fig. 5.1(c) which is based on potentiometric measurement of hydrogen ion concentration in a sample.

 

pH meter It consists of a glass probe which is placed in the water. Inside the thin glass bulb at the end of the probe, there are two electrodes that measure voltage. One electrode is contained in a liquid that has a  fixed acidity or pH value. The other electrode responds to the H+ concentration of the water sample. The pH electrode produces a voltage that is proportional to the concentration of the H+ concentration, and making measurements with a pH meter is, therefore, a form of potentiometry. A voltmeter in the probe measures the difference between the voltages of the two electrodes and translates it into pH and displays it on the little screen on the meter.

 

Before taking a pH measurement, the meter must be ‘calibrated’. The probe is immersed in a solution that has a known and stable pH (a ‘buffer solution’). The knobs on the box are used to adjust the displayed pH value to the known pH of the solution, thus calibrating the meter.

 

The water for construction purposes should be of neutral nature, i.e., pH from 6.0 to 8. In case of high pH of 10 to 12 or a low pH of 4 to 6, the water will need suitable treatment for correction of pH value.

 

NATIONAL STANDARDS

IS 3025(Part 11) - 1983 (reaffirmed 2003): Methods of Sampling and Test (physical and chemical) for  Water and Wastewater; Part 11: pH Value

 

IS 3025 (Part 17) - 1984 (reaffirmed 2002): Methods of Sampling and Test (physical and chemical) for  Water and Waste Water; Part 17: Non-filterable Residue (total suspended solids)

 

IS 3025 (Part 18)-1984 (reaffirmed 2002): Methods of Sampling and Test (physical and chemical) for  Water and Waste Water; Part 18: Volatile and Fixed Residue (total, filterable and non-filterable)

 

IS 3025(Part 24) - 1986 (reaffirmed 2003): Methods of Sampling and Test (physical and chemical) for  Water and Wastewater; Part 24: Sulphates

 

IS 3025 (Part 32) - 1988 (reaffirmed 2003): Methods of Sampling and Test (Physical and Chemical) for  Water and Wastewater; Part 32: Chloride

 

REFERENCES

1 Gambhir, M. L., Concrete Technology, 4th Edition, McGraw-Hill Education (India), 2009

 

2. Gambhir, M. L. and Neha Jamwal, Building Materials: Products, Properties and Systems, McGraw-Hill  Education (India), 2011.

 

FAQ

What is the pH value of water is used for concrete?

The pH value of the water should be between 6.5 and 8.5. The pH value of the water should not be less than 6. If that type of water is used in concrete, it is corrosive because if the pH value is 11 the cement will hold all the concrete ingredients.

 

How pH value in the concrete is determined?

The in situ leaching method for measuring pH in concrete is based on inserting a glass micro pH electrode into a hole drilled in a concrete sample [4]. An Ag/AgCl electrode was used as the reference electrode