Simplified Guide to Measuring Mortar Making Properties of Fine Aggregate (IS 2386 Part VI - 1963)

 IS.2386.6.1963

Simplified Guide to Measuring Mortar Making Properties of Fine Aggregate (IS 2386 Part VI - 1963)

The test described in IS 2386 (Part VI) - 1963 evaluates the compressive strength of fine aggregates in concrete by creating mortar specimens and testing their performance under compression. This is crucial for assessing how fine aggregates contribute to the quality and strength of concrete in structures like buildings, bridges, and pavements.

Why Test Mortar Making Properties?

Fine aggregates (sand) significantly affect the workability, strength, and durability of concrete. This test measures how well a fine aggregate performs in a mortar mix, ensuring it meets the requirements for producing strong and durable concrete. It is particularly important when the quality of the aggregate is uncertain or when comparing different sources of sand.

Test Overview

What It Measures

The test determines the compressive strength of mortar specimens made from fine aggregates, cement, and water at a fixed water-cement ratio (0.6 by weight). The mortar is prepared to a specific flow (workability) and molded into cubes, which are then tested for compressive strength after curing.

Why It Matters

  • Ensures fine aggregates produce mortar with adequate strength for concrete applications.
  • Helps compare the performance of different fine aggregates, especially when service records are unavailable.
  • Identifies aggregates that may negatively impact concrete quality due to poor particle shape, texture, or impurities.

Apparatus

  1. Flow Table and Flow Mould: Conform to IS 1273:1960 (Methods of Test for Pozzolanic Materials).
  2. Tamping Bar (per Amendment No. 2, 1991):
    • Made of non-absorbent, abrasion-resistant, non-brittle material (e.g., rubber with Shore A hardness of 35–40 or paraffin-treated teak wood).
    • Minimum length: 25 cm for 50-mm moulds, 20 cm for 75-mm moulds.
    • Tamping face: Flat and at right angles to the bar’s length.
  3. Trowel: Steel blade, 100–150 mm long, with straight edges.
  4. Tamping Rod: ~10 mm diameter, 100 mm long, with one end rounded to a 10-mm hemispherical tip.
  5. Cube Moulds (per Amendment No. 2, 1991):
    • 50-mm cube moulds, conforming to IS 4031:1962 (Specification for Moulds for Cement and Concrete Tests).
    • Note: The document mentions 700 cm cubes, likely a typo for 70-mm or 50-mm cubes, corrected to 50 mm in Amendment No. 2.
  6. Compression Testing Machine: Suitable capacity for testing cube specimens.
  7. Mixing Vessel and Spoon: For preparing mortar.
  8. Moist Closet and Storage Tank: Maintained at 27 ± 2°C for curing.
  9. Drying Oven: For drying sand at 105°C for 24 hours.
  10. Indicators: Phenolphthalein or litmus to check for sodium hydroxide residue.

Materials

  1. Cement: Standard cement for consistent results.
  2. Water: Clean, potable water for mixing and curing.
  3. Fine Aggregate:
    • Washed with sodium hydroxide solution (per IS 2386 Part II - 1963, clause 6.2.2) to remove deleterious materials and organic impurities.
    • Ensure no fines are lost during washing.
    • Check for complete removal of sodium hydroxide using phenolphthalein or litmus.
    • Dry at 105°C for 24 hours before use.

Sample Preparation

  1. Fine Aggregate:
    • Wash the sand with sodium hydroxide solution to remove impurities, ensuring no fines are lost.
    • Rinse thoroughly and check with an indicator (e.g., phenolphthalein) to confirm all sodium hydroxide is removed.
    • Dry the sand at 105°C for 24 hours to achieve a dry condition.

Test Procedure

  1. Mortar Preparation:
    • Mix cement and water at a water-cement ratio of 0.6 by weight in a suitable vessel.
    • Allow cement to absorb water for 1 minute, then mix into a smooth paste using a spoon.
    • Add a known weight of dried fine aggregate (3300–5300 g, depending on sand fineness; e.g., 3300 g for fine sand, up to 5300 g for coarse sand).
    • Mix until the mortar achieves a flow of 100 ± 5 (measured per step 2).
    • Continue mixing for 30 seconds after achieving desired consistency.
  2. Flow Test:
    • Clean and dry the flow table and place the flow mould at the center.
    • Place a 25-mm layer of mortar in the mould and tamp 20 times with the tamping bar (sufficient pressure to compact).
    • Add a second layer and tamp similarly.
    • Level the mortar surface flush with the mould top using a trowel’s straight edge in a sawing motion.
    • Clean the table, especially around the mould edge.
    • Lift the mould 1 minute after mixing and drop the table 10 times through a 12.5-mm height.
    • Measure the mortar’s diameter along four equally spaced axes and calculate the flow as a percentage of the original diameter.
    • If flow exceeds 100 ± 5, add more sand and repeat. If more than two trials are needed or the mortar is too dry, discard and prepare a new batch.
    • Record the final sand weight by subtracting the remaining portion from the initial sample.
  3. Moulding Test Specimens:
    • Immediately after the flow test, place mortar in 50-mm cube moulds in two layers.
    • Rod each layer with 25 strokes of the tamping rod.
    • Fill moulds to overflowing, then strike off to a smooth surface 3–4 hours after moulding.
    • Cure in a moist closet at 27 ± 2°C for 20–24 hours, then demould and store in water at 27 ± 2°C until testing.
  4. Testing Specimens:
    • Test cubes for compressive strength after curing:
      • For 2,4-Dichlorophenol specimens: Test immediately after removal from the moist closet.
      • For others: Test 4 days after water storage.
    • Surface-dry each specimen and remove loose sand or incrustations from faces contacting the testing machine’s bearing blocks.
    • If a specimen’s face is significantly curved, grind to a plane surface or discard.
    • Test in a compression testing machine, ensuring plane surfaces for accurate loading.
    • Note: Specimens must be tested quickly after removal from the moist closet to avoid drying, which could affect results.

Reporting Results

  • Flow Value: Report the flow (100 ± 5) achieved during the test.
  • Sand Quantity: Report the weight of sand used in the mortar mix.
  • Compressive Strength: Report the compressive strength of the cubes (in MPa or N/mm²) after testing.
  • Observations: Note any issues (e.g., specimen defects, curing conditions).

Real-Life Example

For a building project, you test fine aggregate from a local riverbed:

  • Mix: Use 1800 g cement, 1080 g water (water-cement ratio = 0.6), and 4000 g dried sand.
  • Flow Test: After mixing, the flow is 102, within 100 ± 5. The sand weight used is 3950 g (50 g remains).
  • Moulding: Prepare three 50-mm cubes, tamp each layer 25 times, cure in a moist closet for 24 hours, then store in water for 4 days.
  • Testing: Test cubes at 4 days; average compressive strength is 25 MPa.
  • Interpretation: Compare the strength to project specifications (e.g., >20 MPa for general concrete). The sand is suitable if it meets or exceeds the required strength.

Key Tips for Students and Engineers

  • Ensure Proper Flow: Achieving a flow of 100 ± 5 is critical for consistent mortar consistency. Adjust sand quantity carefully.
  • Control Curing Conditions: Maintain 27 ± 2°C in the moist closet and water storage to ensure reliable curing.
  • Clean Specimens Properly: Remove loose sand without damaging the surface layer to ensure accurate compressive strength results.
  • Use Correct Moulds: Per Amendment No. 2, use 50-mm cube moulds (not 70-mm or 7.06-cm, as mentioned in earlier versions).
  • Avoid Sodium Hydroxide Residue: Thorough rinsing and indicator checks are essential to prevent chemical interference with mortar properties.

Common Mistakes to Avoid

  • Incorrect Flow Adjustment: Adding too much sand or discarding batches unnecessarily can skew results.
  • Improper Tamping: Inconsistent tamping pressure can lead to uneven specimen density.
  • Curing Errors: Deviations from 27 ± 2°C or improper curing duration can affect strength results.
  • Surface Preparation: Failing to grind curved specimen faces or testing with loose sand can lead to inaccurate compressive strength readings.
  • Typographical Confusion: The document’s mention of “700 cm cubes” is likely a typo; use 50-mm cubes per Amendment No. 2.

Notes on Document Issues

  • Typographical Errors: The document contains errors like “18 2 2866” instead of “IS 2386” and “AGREGATES” instead of “AGGREGATES”. The mention of “700 cm cubes” is likely a typo for 50-mm cubes, corrected in Amendment No. 2 (1991).
  • Truncation: Large portions of the document are truncated, limiting procedural details. Consult the full IS 2386 (Part VI) - 1963 for complete information.
  • Amendments: Amendment No. 2 (1991) updates the tamping bar and mould specifications. Ensure compliance with these updates.
  • Reference Standards: Follow IS 1273:1960 (flow table), IS 4031:1962 (moulds), and IS 2386 (Part II) - 1963 (sodium hydroxide washing) for accurate testing.
  • Year Discrepancy: References to “2366” or “1968” are likely typos for IS 2386 and 1963, respectively.

For the complete procedure and additional details, refer to the full IS 2386 (Part VI) - 1963 document, including Amendments No. 1 and 2.

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