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QUALITY CONTROL OF CONSTRUCTION MATERIALS (Cement) by K. RAMESH Research Officer, Engineering Materials Laboratory, A.P. Engineering Research Laboratories, Himayatsagar, HYDERABAD-500030.
Tests on cement(Physical Tests) • Standard consistency • Setting times (Initial and Final ) • Compressive strength • Fineness • Soundness • Specific Gravity
Standard consistancy • Standard consistancy of cement may be defined as the percentage of water (by weight of cement), to be mixed with the cement, to get a cement paste having some stiffness, which is arbitrarily fixed with the help of Vicat apparatus.
Name of the Test: Standard Consistency of Cement. [ IS : 4031 (Part.4) – 1988] 1. Weight of cement (A) = 500 g. 2. Observations: 3. Weight of water in g for Standard consistency (B) = (Note: For standard consistency the depth of Penetration of vicat plunger should be 5 mm to 7 mm.) 4. Standard consistency in % (P) = B/A * 100 = =
Setting times • The time at which the cement paste looses its plasticity is termed as initial setting time and the time at which the cement paste becomes hard mass is termed as the final setting time.
Name of the Test: Setting Times of Cement. • [ IS : 4031 (Part.5) – 1988] • Standard Consistency in % (P) = • Weight of cement (A) = 500 g • Weight of water in g = 0.85 x P/100 x A = • = • 4. Starting time (B) = • 5. Time at initial setting (C) = • (Note: The period elapsing between the time when water is added to the cement and the time at which the vicat needle fails to pierce the test block by 5mm + 0.5mm is termed as the initial setting time.) • 6. Time at final setting (D) = • (Note: The period elapsing between the time when water is added to the cement and the time at which the vicat needle makes an impression on the surface of the test block while the annular ring fails to do so, is termed as the final setting time.) • 7. Initial setting time in min = C – B = • 8. Final setting time in min = D – B =
Compressive strength • Size of the cube = 7.06 Cm. • Cement Mortar = 1 : 3 • Ages = 3, 7, 28 days • No. of cubes = 3 x 3 = 9 • Weight of cement = 200 g • Weight of Ennore sand = 600 g • Weight of water = (P/4 + 3) % where P = Standard consistancy of cement
Name of the Test: Compressive Strength of Cement. • [ IS : 4031 (Part.6) - 1988] • 1. Weight of cement for each cube of 7.06 Cm size = 200 g • 2. Weight of I.S. sand = 600 g • (Consisting of three grades, each of 200 g) • 3. Standard consistency of cement in % (P) = • 4. Weight of water in g = (P/4 + 3) x 800 / 100 = • = • Compressive strength: • a. Cross sectional area of the 7.06 Cm cube (A) = 50 Cm2 • b. Observations: (Note: For each age of testing minimum 3 cubes shall be tested.)
Fineness • Fineness of cement is a measure of the mean size of the cement grains. The rate of strength development of cement depends on the rate of hydration of cement which inturn depends on the fineness of cement.
Name of the Test: Fineness of Cement. [ IS : 4031 (Part.2) - 1988] 1. Specific gravity of cement ( ) = 2. Weight of cement in g = x V (1 – e) = = Where, V = Bulk volume of bed of cement in Cm3 = 1.89 e = Desired porosity of bed of cement = 0.50 3. Time required for fall of 5 Cm height in sec (T) (Average of 3 readings) = (T1+T2+T3) / 3 = = 4. Fineness in m2/Kg = 136.8 T / = =
Fineness (cm2/gm) Compressive strength at the age of (N/mm2) 7 days 28 days 90 days 1 year 1600 2000 2500 3000 23 26 29 30 32 35 37 38 38 40 41 41 41 42 42 42
Soundness • Certain cements undergo large expansion after setting causing disruption of the set and hardened mass. • Unsoundness in cement is due to excess lime or excess magnesia in cement • Unsoundness in cement due to excess lime is detected by the Lechatelier test. • Unsoundness in cement due to excess magnesia & excess lime is detected by the Autoclave test.
Specific gravity • Specific gravity of cement may by defined as the weight of cement to the weight of equal volume of water. • It is determined by using Lechatelier flask or 50ml specific gravity bottle.
Name of the Test: Specific Gravity of Cement. • [ IS : 4031 – 1988] • Weight of specific gravity bottle in g (W1) = • Weight of specific gravity bottle with about half filled cement in g (W2) = • 3.Weight of specific gravity bottle with about half filled cement & rest is filled with kerosene iin g.(W3) = • 4.Weight of specific gravity bottle completelyfilled with kerosene in g (W4) = • 5. Specific gravity of cement () • (W2 - W1) • = ---------------------------- x 0.79 • (W4 - W1) - (W3 - W2) • = • = • (Note : Specific gravity of kerosene is taken as 0.79)