Aggregate Properties, Gradation, and Density PDF

Properties: 1) Gradation. 2) Relative density and absorption. 3) Hardness. 4) Durability. 5) Shape and surface texture. 6) Deleterious substances. 7) Crushing strength. 8) Soft and lightweight particles 9) Soundness. 1) Gradation: - Gradation or grain size analysis is the most c...

Properties: 1) Gradation. 2) Relative density and absorption. 3) Hardness. 4) Durability. 5) Shape and surface texture. 6) Deleterious substances. 7) Crushing strength. 8) Soft and lightweight particles 9) Soundness. 1) Gradation: - Gradation or grain size analysis is the most common test performed on aggregates. - Curve (a) ensures maximum density And strength. - Curve (b) uniform or single size aggregate. - Curve (c) gap-graded. - Curve (d) open-graded. See page 130  Dense and Well-Graded Aggregates: - Dense and well-graded aggregates are desirable for making concrete, as the space between larger particles is effectively filled by smaller particles to produce a well- packed structure. - A well-graded soil is a soil that contains particles of a wide range of sizes and has a good representation of all sizes.  Gap-Graded Aggregates - Gap grading is a kind of grading which lacks one or more intermediate size. - Gap graded aggregates can make good concrete when the required workability is relatively low. - Advantages of gap grading are more economical concrete, use of less cement and lower w/c ratios. - The resulting concrete has: Low workability. Difficult to handle and compact. Developing low strength and high permeability.  Uniform or Single-Size: - For uniformly graded aggregates, only a few sizes dominate the bulk material. With this grading, the aggregates are not effectively packed, and the resulting concrete will be more porous, unless a lot of paste is employed..  Open –Graded Aggregates: - Contain little or no fine aggregate. - Relatively large void spaces. - Good for places requiring high permeability such as backfill of retaining walls. - The fines content must be limited, the silt and clay particles (finer than 75 µm or No. 200) are relatively weak and weaken the bond between cement and those particles. - Washed sieve analysis are required when the amount passing 75 µm is important. - Washed sieve analysis : a) the sample is dried and washed. b) the wash water is poured out over a 75 µm sieve. c) the material retained in the sieve is retained to the sample. d) then dried again and dry-sieved. e) the total amount passing 75 µm is the sum of the amount lost in washing and passing the 75 µm. See Example 4.1 page 132  1 2 3 4 Dry Sieve Analysis - The maximum aggregate size is defined as the smallest sieve size that requires 100 % passing. - The nominal maximum aggregate size is defined as one sieve size smaller than the maximum aggregate size, or one sieve size larger than the first size to retain more than 10%. - Percent Passing 3/4" : 100% Maximum aggregate size 1/2" : 95% Nominal aggregate size 3/8" : 89% #4 : 63% #8 : 39%  What Is Specific Gravity? Specific gravity is a measure of density relative to the density of a reference substance. It's often abbreviated as sp gr. Specific gravity is also called relative density and is expressed by the formula: Specific Gravitysubstance = ρsubstance/ρreference The reference material could be anything, but the most common reference is pure water. The specific gravity is the ratio of of the weight to the weight of water of the same volume. Bulk density is different. A mass of a single stone size 1 m3 weighs 1600 kg. We call the specific gravity of the stone is 1600 kg/m3. But if this stone is crushed into samll peces called gravels, they will not fit in a 1 m3 container any more, because there are void in between gravels that accupy the container. May be only 1100 kg that fill the container. They say the bulk density is 1100 kg/m3. So the Bulk density of any bulk material will always less than its specific gravity.  The term “relative density” is dimensionless. In other words, it has no units. It’s a measurement of how many times the given material is denser than the reference material. Water is generally taken as the reference material for liquids. What is the difference between Relative Density and Specific Gravity? - Relative density and specific gravity are almost the same quantity. - Specific gravity also has another definition called apparent specific gravity, which is defined as the weight of a volume of a given substance divided by the weight of the same volume of the reference substance. - The modern scientific community prefers specific gravity over the badly defined relative density. Specific gravity is the new, more precise definition for the relative density. Relative density Example The dry mass of a sample is 2239.1gm. The mass in saturated surface dry condition is 2268.4gm. The net volume is 835.4 cm. Find 3 the relative density values? Solution 3 VN = 835.4 cm MD = 2239.1gm MW= 2268.4-2239.1=29.3gm MSS = MD+ MW=2239.1+29.3=2268.4 3 VW =29.3/1=29.3 cm 3 VB= VW+ VN=29.3+835.4=864.7 cm RDA = MD / VNxPW=2239.1/835.4x1=2.68 RDB = MD / VBxPW =2239.1/864.7 x1=2.59 RDSSD = MSSD / VBxPW =2268.4/864.7x1=2.623 %Abs = MW / MD = (29.3/2239.1)x100=1.31% Hardness=resistance to wear Pavement surfaces Friction rounded surface pavement less skid resistance Loss Angeles abrasion test %loss = (Mass before test – Mass after test) / Mass before test x100% Example Mass placed in abrasion machine = 5015gm Mass of intact particles left after test =3891gm %loss =(5015-3891) / 5015 x 100% = 22.4% Durability= resistance to weathering Freezing & thawing Soundness test %loss = (original mass - Mass after test) / original mass of sample x 100% Example Original mass = 2175 gm Mass after test = 1847 gm %loss = (2175-1847)/2175 x 100% = 15.1% 1-d 2-a 3-b 4-c 5-a 6-c 7-c 8-a 9-d