Mini Slump Cone Test for Optimum Dosage of Superplasticizer

The mini slump cone test is performed to evaluate the flow characteristics of cementitious paste and determine the optimum dosage of a superplasticizer.

The test is useful for the following purposes:

• To compare the relative fluidity of different cementitious pastes by measuring their spread after lifting the mini slump cone.
• To determine the optimum dosage of a superplasticizer for a given cementitious system.
• To compare the effectiveness of different superplasticizers under identical test conditions.
• To identify the dosage at which the cement paste begins to exhibit bleeding, indicating excessive superplasticizer content.

Note: Use the calculator provided at end to find out optimum dosage of superplasticizer for you concrete.

Limitations

• The optimum dosage determined using cement paste cannot be directly adopted for concrete, even if the same binder composition is used. Concrete contains aggregates that significantly influence the required dosage.
• The results should be interpreted carefully for applications involving high shear mixing, as the performance of the superplasticizer may differ under such conditions.

Apparatus Required

• Mini slump cone
• Non-absorbent square base plate or glass plate (minimum size 400 mm × 400 mm) with center markings or measurement graduations
• Vernier caliper
• Wooden mallet

Precautions

Before conducting the test, ensure the following:

• Perform the test in a temperature- and humidity-controlled environment. Variations in environmental conditions can significantly affect the test results.
• Follow exactly the same mixing and testing procedure for every trial to obtain consistent and comparable results.
• If a liquid superplasticizer is used, determine its solid content and apply the necessary water correction while preparing the paste.

Test Procedure

Step 1: Prepare the Test Surface

Apply a thin layer of grease to the inside surface of the mini slump cone. Place the cone at the center of the non-absorbent base plate or glass plate.

Step 2: Fill the Mini Slump Cone

Prepare the cementitious paste according to the required mix proportions. Pour approximately 40 mL of the freshly prepared paste into the mini slump cone.

Step 3: Position the Test Setup

Ensure that the mini slump cone is placed vertically and remains stable on the base plate before proceeding with the test.

Step 4: Remove Entrapped Air

Gently tap the sides of the mini slump cone using a wooden mallet. This helps eliminate any entrapped air bubbles within the paste.

Step 5: Lift the Cone

Carefully lift the mini slump cone vertically upward in one smooth motion. Avoid any twisting, vibration, or lateral movement, as these may disturb the spread of the paste.

Step 6: Measure the Spread

Allow the paste to spread freely for 1 minute.

Measure the diameter of the spread in two mutually perpendicular directions using a Vernier caliper. For improved accuracy, measurements may also be taken along additional directions and averaged.

Step 7: Assess the Fluidity

The measured spread represents the fluidity of the cement paste. A larger spread indicates better dispersion of cement particles and improved performance of the superplasticizer.

Step 8: Repeat the Test with Different Dosages

Conduct the test for mixes containing different dosages of the superplasticizer while maintaining:

• Constant water-to-binder (w/b) ratio
• Fixed replacement level of mineral admixtures (by weight or volume), wherever applicable

Step 9: Record the Spread

Measure and record the spread diameter for each superplasticizer dosage.

Step 10: Determine the Optimum Dosage

Identify the dosage at which further increases in superplasticizer content produce only a marginal increase in spread. This dosage is considered the optimum dosage.

Also observe the paste for any signs of bleeding. If bleeding occurs at higher dosages, those dosages should be considered excessive and beyond the optimum level.

Step 11: Plot the Results

Prepare a semi-logarithmic graph with:

• X-axis: Superplasticizer dosage (% by weight of binder)
• Y-axis (log scale): Measured spread diameter

The graph helps visualize the relationship between dosage and fluidity and assists in identifying the optimum dosage.

Observations and Calculations

Record the following details before performing the calculations:

• Cementitious materials used: ____________________________
• Water-to-binder ratio (w/b): ____________________________

Record all measured spread values for the different superplasticizer dosages in the observation table for further analysis.

Superplasticizer Optimum Dosage Calculator

Example

Trial	SP Dosage (%)	Spread (mm)	Bleeding
1	0.20	118	No
2	0.40	156	No
3	0.60	184	No
4	0.80	201	No
5	1.00	206	No
6	1.20	208	Yes

Recommended Optimum Dosage: 1.00%