Question

Properties/Characteristics

You are to write down as many properties and/or characteristics of materials as you can think of (not just for one material, but any and all materials). Try to get one that starts with each letter of the alphabet…!    

General principles in Construction for landscape architecture

A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
Q
R
S
T
U
V
W
X
Y
Z

Answer 1

• Characteristic and properties of brick
• A) Brick should be uniform in color, size and shape. Standard size of brick should be maintained.
• B) The should be sound and compact.
• C) They should be free from cracks and other flaws such as air bubbles, stone nodules etc. with sharp and square edges.
• D)Bricks should not absorb more than 1⁄5of their own weight of water when immersed in water for 24 hours (15% to 20% of dry weight).
• E) The compressive strength of bricks should be in range of 2000 to 5000 psi (15 to 35 MPa).
• F) Salt attack hampers the durability of brick. The presence of excess soluble salts in brick also causes efflorescence. The percentage of soluble salts (sulphates of calcium, magnesium, sodium and potassium) should not exceed 2.5% in brunt bricks.
• G) Brick should not change in volume when wetted.
• H) Bricks should neither overburnt nor under-brunt.
• I) Generally, the weight per brick should be 6 lbs. and the unit weight should be less than 125 lbs. per cubic ft.
• J) Th thermal conductivity of bricks should be low as it is desirable that the building built with them should be cool in summer and warm in winter.
• K) Bricks should be sound proof.
• L) Brick should be non-inflammable and incombustible.
• M) Bricks should be free from lime pitting.
• Characterustic and properties of cement
• N) The colour of cement should be uniformly grey with greenish shade. It gives an indication of excess of lime or clay and the degree of burning.

• O) It should feel smooth when touched or rubbed in between fingers.

  P) If hand is inserted in a bag of cement or in a heap of cement, it should feel cool and not warm.

  Q) It should be free from any hard lumps.

  R) It should not contain excess silica, lime, alumina or alkalies.

• S) Physica Properties of Cement:

• Following are the important physical properties of good cement which primarily depend upon its chemical composition, thoroughness of burning and fineness of grinding:

• (i) It gives strength to the masonry.

  (ii) It is an excellent binding material.

  (iii) It is easily workable.

  (iv) It offers good resistance to the moisture.

• ix) The particles should have uniformity of fineness. To get an idea of fineness, specific surface area of cement particles is calculated. The specific surface area is a measure of the frequency of particles of average size, which should not be less than 2250 cm2/gm.

  (x) The consistency of cement should be checked with Vicat apparatus. If the settlement of plunger is between 5 mm to 7 mm from the bottom of mould, the water added is correct, otherwise repeat the process with different percentages of water till the desired penetration is achieved.

  (xi) The initial setting time for ordinary cement is about 30 minutes. The initial setting time is the interval between the addition of water to cement and the stage when the square needle of Vicat apparatus ceases to penetrate completely.

  (xii) The final setting time for ordinary cement is about 10 hours. The final setting time is the difference between the time at which water was added to cement and time required for needle with annular collar of Vicat apparatus ceases to make an impression on test block.

  (xiii) The cement should be tested for soundness using Le Chatelier apparatus. This test is to detect the presence of uncombined lime in cement. The expansion of cement after heating and cooling the mould, should not exceed 10 mm.

  U) Mechanical properties of Cement:

  (i) The compressive strength at the end of 3 days should not be less than 11.5 N/mm2and that at the end of 7 days should not be less than 17.5 N/mm2.

  (ii) The tensile strength at the end of 3 days should not be less than 2 N/mm2 and that at the end of 7 days should not be less than 2.50 N/mm2.

  V)Chemical Properties of Cement:

  (i) The ratio of percentage of alumina to iron oxide should not be less than 0.66.

  (ii) The ratio of percentage of lime to alumina, iron oxide and silica, known as Lime Saturation Factor (LSF) should not be less than 0.66 and should not be more than 1.02.

  (iii) Total loss on ignition should not be more than 4 per cent.

  (iv) Total sulphur content should not be more than 2.75 per cent.

  (v) Weight of insoluble residue should not be more than 1.50 per cent.

  (vi) Weight of magnesia should not exceed 5 per cent.

• Characteristics and properties of aggregate

• W) Composition

• Aggregates consisting of materials that can react with alkalies in cement and cause excessive expansion, cracking and deterioration of concrete mix should never be used. Therefore it is required to test aggregates to know whether there is presence of any such constituents in aggregate or not.

  X) Size and shape of aggregate

  Maximum size of aggregate should be less than

  • One-fourth of the minimum dimension of the concrete member.
  • One-fifth of the minimum dimension of the reinforced concrete member.
  • The minimum clear spacing between reinforced bars or 5 mm less than the minimum cover between the reinforced bars and form, whichever is smaller for heavily reinforced concrete members such as the ribs of the main bars.

  Remember that the size & shape of aggregate particles influence the properties of freshly mixed concrete more as compared to those of hardened concrete.

  Y). SURFACE TEXTURE

  The development of hard bond strength between aggregate particles and cement paste depends upon the surface texture, surface roughness and surface porosity of the aggregate particles.

  If the surface is rough but porous, maximum bond strength develops. In porous surface aggregates, the bond strength increases due to setting of cement paste in the pores.

  Z) . SPECIFIC GRAVITY

  The ratio of weight of oven dried aggregates maintained for 24 hours at a temperature of 100 to 1100C, to the weight of equal volume of water displaced by saturated dry surface aggregate is known as specific gravity of aggregates.

  Specific gravities are primarily of two types.

  • Apparent specific gravity
  • Bulk specific gravity

  Specific gravity is a mean to decide the suitability of the aggregate. Low specific gravity generally indicates porous, weak and absorptive materials, whereas high specific gravity indicates materials of good quality. Specific gravity of major aggregates falls within the range of 2.6 to 2.9.

  Specific gravity values are also used while designing concrete mix.

  5. BULK DENSITY

  It is defined as the weight of the aggregate required to fill a container of unit volume. It is generally expressed in kg/litre.

  Bulk density of aggregates depends upon the following 3 factors.

  • Degree of compaction
  • Grading of aggregates
  • Shape of aggregate particles

  6. VOIDS

  The empty spaces between the aggregate particles are known as voids. The volume of void equals the difference between the gross volume of the aggregate mass and the volume occupied by the particles alone.

  Also read: Bulk Density & Void Test of Aggregate

  7. POROSITY & ABSORPTION

  The minute holes formed in rocks during solidification of the molten magma, due to air bubbles, are known as pores. Rocks containing pores are called porous rocks.

  Water absorption may be defined as the difference between the weight of very dry aggregates and the weight of the saturated aggregates with surface dry conditions.

  Depending upon the amount of moisture content in aggregates, it can exist in any of the 4 conditions.

  • Very dry aggregate ( having no moisture)
  • Dry aggregate (contain some moisture in its pores)
  • Saturated surface dry aggregate (pores completely filled with moisture but no moisture on surface)
  • Moist or wet aggregates (pores are filled with moisture and also having moisture on surface)

  8. BULKING OF SAND

  It can be defined as in increase in the bulk volume of the quantity of sand (i.e. fine aggregate) in a moist condition over the volume of the same quantity of dry or completely saturated sand. The ratio of the volume of moist sand due to the volume of sand when dry, is called bulking factor.

  Fine sands bulk more than coarse sand

  When water is added to dry and loose sand, a thin film of water is formed around the sand particles. Interlocking of air in between the sand particles and the film of water tends to push the particles apart due to surface tension and thus increase the volume. But in case of fully saturated sand the water films are broken and the volume becomes equal to that of dry sand.

  Also read: Bulking of Sand – What, Why & How

  9. FINENESS MODULUS

  Fineness modulus is an empirical factor obtained by adding the cumulative percentages of aggregate retained on each of the standard sieves ranging from 80 mm to 150 micron and dividing this sum by 100.

  Fineness modulus is generally used to get an idea of how coarse or fine the aggregate is. More fineness modulus value indicates that the aggregate is coarser and small value of fineness modulus indicates that the aggregate is finer.

  Also read: Fineness Modulus of Aggregate – What, Why & How

  10. SPECIFIC SURFACE OF AGGREGATE

  The surface area per unit weight of the material is termed as specific surface. This is an indirect measure of the aggregate grading. Specific surface increases with the reduction in the size of aggregate particle. The specific surface area of the fine aggregate is very much more than that of coarse aggregate.

  Also read: How to Calculate Total Surface Index of Aggregate

  11. DELETERIOUS MATERIALS

  Aggregates should not contain any harmful material in such a quantity so as to affect the strength and durability of the concrete. Such harmful materials are called deleterious materials. Deleterious materials may cause one of the following effects

  • To interfere hydration of cement
  • To prevent development of proper bond
  • To reduce strength and durability
  • To modify setting times

  Deleterious materials generally found in aggregates, may be grouped as under

  • Organic impurities
  • Clay , silt & dust
  • Salt contamination

  12. CRUSHING VALUE

  The aggregates crushing value gives a relative measure of resistance of an aggregate to crushing under gradually applied compressive load. The aggregate crushing strength value is a useful factor to know the behavior of aggregates when subjected to compressive loads.

  13. IMPACT VALUE

  The aggregate impact value gives a relative measure of the resistance of an aggregate to sudden shock or impact. The impact value of an aggregate is sometime used as an alternative to its crushing value.

  14. ABRASION VALUE OF AGGREGATES

  The abrasion value gives a relative measure of resistance of an aggregate to wear when it is rotated in a cylinder along with some abrasiv

• The size and shape of the aggregate particles greatly influence the quantity of cement required in concrete mix and hence ultimately economy of concrete. For the preparation of economical concrete mix on should use largest coarse aggregates feasible for the structure. IS-456 suggests following recommendation to decide the maximum size of coarse aggregate to be used in P.C.C & R.C.C mix.