Protocol to Compare Two Water Reducing Admixtures

1. Objective

The objective of this protocol is to compare the performance of two water-reducing agents (WRAs) by measuring their effect on initial slump, slump retention over time, and compressive strength to determine which admixture maintains workability better and ensures that compressive strength requirements are met.

2. Materials and Equipment

Materials:

• Portland cement (Type I/II)
• Fine aggregate (sand)
• Coarse aggregate (gravel)
• Water
• Two different water-reducing agents (WRAs)

Equipment:

• Concrete mixer
• Slump cone and rod
• Stopwatch or timer
• Measuring tape or ruler
• Thermometer
• Weighing scale
• Measuring cylinders
• Compression testing machine
• Molds for compressive strength specimens (cylinders or cubes)
• Curing tank

3. Sample Preparation

Concrete Mix Design:

1. Control Mix: Prepare a control mix without any WRA to establish baseline properties.
2. Test Mix 1: Prepare a mix with WRA 1 at the recommended dosage.
3. Test Mix 2: Prepare a mix with WRA 2 at the recommended dosage.

Keep the water-cement ratio and all other mix design elements constant to ensure a fair comparison.

4. Mixing Procedure

1. Batching: Measure all materials accurately based on the mix design.
2. Mixing: Follow a consistent mixing procedure for all batches:

• Add coarse aggregate, fine aggregate, and cement into the mixer.
• Start mixing and add 80% of the mixing water.
• Add the WRA and the remaining water while mixing.
• Continue mixing until a homogeneous mix is achieved (usually 3-5 minutes).

5. Testing Procedures

Initial Slump

1. Conduct the Slump Test Immediately After Mixing:

• Fill the slump cone in three layers, each layer compacted with 25 strokes of the tamping rod.
• Lift the slump cone carefully and measure the slump.
• Record the initial slump value for each mix.

Slump Retention at 30 Minutes

1. Set a Timer for 30 Minutes

• Keep the mixed concrete in a covered container to prevent evaporation.
• Stir the concrete briefly before testing to ensure uniformity.

2. Perform the Slump Test Again at 30 Minutes:

• Follow the same procedure as the initial slump test.
• Record the slump value at 30 minutes.

Slump Retention at 60 Minutes

1. Set a Timer for an Additional 30 Minutes (Total 60 Minutes):

• Keep the mixed concrete in a covered container.
• Stir the concrete briefly before testing to ensure uniformity.

2. Perform the Slump Test Again at 60 Minutes:

• Follow the same procedure as the initial slump test.
• Record the slump value at 60 minutes.

Compressive Strength

1. Specimen Preparation:

• Cast concrete specimens (cylinders or cubes) from each mix immediately after the initial slump test.
• Cure specimens in a controlled environment (typically in water at 20°C) for specified durations (7 and 28 days).

2. Testing:

• Test the compressive strength of cured specimens at 7 and 28 days using a compression testing machine.
• Ensure all specimens meet the required compressive strength standards for the intended application.

6. Data Analysis

1. Initial Slump Comparison:

• Compare the initial slump values of Test Mix 1 and Test Mix 2.

2. Slump Retention Analysis:

• Calculate the percentage slump retention at 30 minutes and 60 minutes for each test mix.

• Use the formula:

  • Slump Retention (%) = (Slump at Time T / Initial Slump) × 100

3. Compressive Strength Comparison:

• Compare the compressive strength results at 7 and 28 days for both WRAs.
• Verify that all mixes meet the required compressive strength standards.

7. Reporting

1. Summary of Results:

• Present the initial slump, slump at 30 minutes, and slump at 60 minutes in tabular format.
• Include percentage slump retention and compressive strength results for both WRAs.

2. Comparative Analysis:

• Provide a detailed analysis of which WRA performs better in terms of initial slump, slump retention, and compressive strength.

3. Recommendations

• Recommend the WRA that shows better workability retention and ensures that all mixes meet the required compressive strength standards.

8. Quality Control

1. Repeatability:

• Repeat tests for a subset of mixes to ensure consistency and reliability of results.

2. Standard Compliance:

• Ensure all tests comply with relevant standards (e.g., ASTM, EN, ISO).

9. Implementation Timeline

Day 1: Collect materials and set up the laboratory.

Day 2: Define mix designs and prepare materials.

Day 3: Conduct initial mixing, slump tests, and cast compressive strength specimens. Perform slump retention tests at 30 minutes and 60 minutes for both WRAs. Record and analyze the results. Cure compressive strength specimens.

Day 10: Perform compressive strength tests at 7 days for initial analysis.

Day 10-11: Analyze data, compare the performance of the two WRAs, and prepare the final report.

Day 31: Perform 28 days compressive strength tests to validate results.