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Ductility Test of Bitumen – Procedure, Apparatus & Limits (IS Method) Home › Bitumen Tests › Ductility Test of Bitumen Ductility Test of Bituminous Material – IS Standard Procedure 1. OBJECTIVE To determine the ductility of bituminous material, which measures the distance a bitumen sample can stretch before breaking. 2. APPARATUS Ductility testing machine Briquette moulds Hot knife 3. PROCEDURE Melt the bitumen sample to 75–100°C above its softening point until it becomes fully fluid. Strain the material through a 90-micron sieve, pour into the mould assembly, and place on a brass plate after applying a mixture of glycerine and dextrin to all mould surfaces. Allow it to stand for 30–40 minutes, then place the mould assembly in a water bath maintained at 27°C for 30 minutes. Remove mould from water bath and level the surface using a hot knife to cut off excess material. After trimming, place the specimen back in the water bath at 27°C for 85–95 minutes. Remove sides of mould and attach the clips to the ductility machine carefully without applying initial strain. Start the machine, setting pointer to zero, and apply tension at a uniform speed of 50 ± 2.5 mm/min. Ensure the sample remains immersed in water at a depth of at least 10 mm throughout the test. Record the distance (in cm) at which the bitumen thread breaks. This is the ductility value. 4. RESULTS The ductility value is the distance stretched (in centimeters) by the moving end of the briquette specimen at the point where the bitumen thread breaks. 5. LIMITS (ACCORDING TO IS REQUIREMENTS) A35 & S35 Grade Bitumen: Minimum ductility = 50 cm at 27°C All Other Grades: Minimum ductility = 75 cm at 27°C

Concrete Cube Casting & Compressive Strength Testing (IS:516) 1. Objective To prepare, cast, cure, and test concrete cube specimens of size 150 × 150 × 150 mm or 100 × 100 × 100 mm to determine compressive strength of concrete at specified ages (usually 7 days and 28 days). 2. Apparatus Required Cube moulds – 150 mm or 100 mm Mixing tray and scoop Tamping rod (16 mm diameter) Trowel Concrete mixer (if required) Curing tank (27 ± 2°C) Compression Testing Machine (CTM) 3. Preparation of Cube Moulds Clean moulds to remove dust and hardened mortar. Assemble moulds properly and tighten bolts. Apply thin uniform oil layer on internal faces. Check alignment and squareness of mould. 4. Sampling and Mixing of Concrete Sample concrete from freshly mixed batch. Mix thoroughly until uniform colour and consistency are achieved. Start casting immediately to avoid loss of workability. 5. Casting of Concrete Cubes Fill mould in three equal layers. Distribute concrete evenly around mould. 6. Compaction of Concrete Compact each layer by rodding or vibration. Manual compaction: 35 strokes per layer. Rods to penetrate into the previous layer. Tap mould sides gently to remove air voids. Finish top surface smoothly using trowel. 7. Identification and Initial Storage Date of casting Grade of concrete Cube number / location Store cubes undisturbed for 24 hours at 27 ± 2°C. 8. Curing of Concrete Cubes Demould cubes after 24 ± ½ hours. Immediately immerse in clean water. Maintain curing temperature at 27 ± 2°C. Continue curing till testing age. 9. Compression Testing of Cubes (IS:516) Remove cube from curing tank (SSD condition). Clean cube and CTM platens. Measure dimensions (nearest 0.2 mm). Place cube centrally on CTM platen. Apply load gradually at ≈140 kg/cm²/min. Record maximum load at failure. Note: Improper centring causes eccentric loading and wrong test results. 10. Calculation of Compressive Strength Compressive Strength (N/mm²) = Maximum Load at Failure ÷ Loaded Area 11. Cube Size – Area – Thumb Rules Cube Size Loaded Area 150 mm Cube 225 cm² 100 mm Cube 100 cm² Fast Site Calculation Rules 150 mm cube → Load (kg) ÷ 225 | Load (kN) ÷ 22.5 100 mm cube → Load (kg) ÷ 100 | Load (kN) × 10 12. Sampling Frequency (IS Practice – Simplified) Concrete Quantity No. of Samples Total Cubes 1 – 5 m³ 1 3 6 – 15 m³ 2 6 16 – 30 m³ 3 9 31 – 50 m³ 4 12 Each additional 50 m³ +1 +3 13. Reporting of Results Calculate strength of each cube. Round off to nearest whole number. Average of 3 cubes = representative strength. Variation limits must be satisfied. Concrete Strength Acceptance Criteria (±15% Rule Explained) Basic Rule For any set of 3 cubes (one sample): Calculate average strength Each cube must lie within: 0.85 × Average (−15%) 1.15 × Average (+15%) If even one cube is outside this range, the sample is REJECTED, irrespective of average strength. Key Strength Values – M25 Concrete Characteristic strength (fck) = 25 N/mm² Standard deviation (assumed) = 4 N/mm² Target mean strength = fck + 1.65 × S = 25 + (1.65 × 4) = 31.6 N/mm² CASE–1: Single Sample (Small Quantity Concrete) Concrete Quantity = 5 m³ As per IS practice → 1 sample (3 cubes) Acceptance Criterion (Special Case) When only one sample is available: Average strength ≥ fck + 4 = 29 N/mm² Cube Strengths (N/mm²) Average 0.85 × Avg 1.15 × Avg 19, 26, 16 20.3 17.3 23.3 Reasons for Rejection ❌ Average strength less than 29 N/mm² ❌ Cubes 26 and 16 N/mm² outside ±15% range Final Decision: ❌ CONCRETE REJECTED CASE–2: Multiple Samples (Normal Quantity Concrete) Concrete Quantity = 28 m³ Samples required = 3 samples (9 cubes) Acceptance Criteria Each cube ≥ fck − 2 = 23 N/mm² Overall average ≥ fck + 4 = 29 N/mm² ±15% variation satisfied for each sample Sample-wise Results Sample Cube Strengths (N/mm²) Average 0.85 × Avg 1.15 × Avg 1 33, 29, 32 31.3 26.6 36.0 2 24, 32, 28 28.0 23.8 32.2 3 25, 29, 32 28.7 24.4 33.0 Overall Average Strength (31.3 + 28.0 + 28.7) ÷ 3 = 29.3 N/mm² Acceptance Check (As per IS Acceptance Criteria) ✅ ±15% Variation Check: All individual cube strengths fall within the permissible range of 0.85 × Average to 1.15 × Average for their respective samples. This confirms uniformity in batching, mixing, compaction, and curing of concrete. ✅ Minimum Individual Strength Check: Each tested cube has achieved a compressive strength greater than or equal to fck − 2, i.e. 23 N/mm² for M25 concrete. No cube strength is below the minimum permissible limit. ✅ Average Strength Check: The overall average compressive strength of all samples is 29 N/mm² or higher, which satisfies the requirement of fck + 4 for acceptance of concrete under normal sampling conditions. ✅ Quality and Compliance Confirmation: Since variation, individual strength, and average strength criteria are all satisfied, the concrete meets the strength acceptance requirements prescribed under IS practice for M25 grade. Final Decision: ✅ CONCRETE ACCEPTED One-Line Site Memory Rules Single sample → Average ≥ fck + 4 Multiple samples → Each cube ≥ fck − 2 ±15% variation is compulsory Final Takeaway Concrete cube testing is the backbone of quality control. Correct casting, curing, testing, and acceptance checks ensure strength, durability, and compliance with IS standards. ✅ Why Concrete is ACCEPTED Uniform Strength: All cube test results lie within ±15% of their respective sample averages, indicating proper batching, mixing, compaction, and curing. Sufficient Individual Strength: No cube strength is below fck − 2 (23 N/mm² for M25), ensuring minimum safety at the individual specimen level. Adequate Average Strength: The overall average compressive strength is ≥ fck + 4 (29 N/mm²), satisfying IS acceptance requirements. Statistical Reliability: Multiple samples provide confidence that at least 95% of concrete will achieve the characteristic strength. ❌ Why Concrete is REJECTED (When Failure Occurs) One or more cube values fall outside ±15% of the sample