Unit- 2(1)_42190992_2024_08_31_10_18.pdf

JAI CIVIL Prashant Sir (M.Tech, JNTU Hyderabad) 8+ years of Experience...

JAI CIVIL Prashant Sir (M.Tech, JNTU Hyderabad) 8+ years of Experience 8102127991 CONCRETE TECHNOLOGY (3rd SEM) UNIT- 2 SYLLABUS Aggregates: 2.1 Aggregates: Source, Requirements of good aggregate, Classification according to size and shape. 2.2 Fine aggregates: Properties, size, specific gravity, bulk density, water absorption and bulking, fineness modulus and grading zone of sand. 2.3 Coarse aggregates: Properties, size, shape, surface texture, water absorption, soundness, specific gravity and bulk density, fineness modulus of coarse aggregate, grading of coarse aggregates, crushing value, impact value and abrasion value of coarse aggregates with specifications. AGGREGATES: 2.1 AGGREGATES:  Aggregates are the material basically used as filler with binding material in the production of mortar and concrete.  They give body to the concrete and occupy 70 to 80% of volume of concrete.  They should be clean, hard, strong, durable, and graded in size. 1  JAI CIVIL Prashant Sir (M.Tech, JNTU Hyderabad) 8+ years of Experience 8102127991 SOURCE: 1. Natural sources: The aggregate are found in natural sources like river basin, sea bed, bed rocks etc. Ex- Gravel, sand, crushed rock such as granite, etc. 2. Artificial sources: The aggregate are made by man from various waste materials like broken brick, air cooled blast furnace slag, sintered fly ash, bloated clay, etc. REQUIREMENTS OF GOOD AGGREGATE: A good aggregate should fulfill the following requirements: 1. Strength: A good aggregate should have high crushing strength.  This requirement of the aggregate is essential so that it can withstand safely the stresses developed in the road pavement due to traffic wheel road. 2. Hardness: A good aggregate should be sufficiently hard i.e. it should offer maximum possible resistance to abrasion. 2  JAI CIVIL Prashant Sir (M.Tech, JNTU Hyderabad) 8+ years of Experience 8102127991 3. Durability: A good aggregate should be more durable to resist the effects of weathering agencies. Like rain, variation of temperature, frost etc. 4. Workability: Aggregate should be high workable.  In the case, which we can work (mixing, transporting, placing, finishing) with mixture. 5. Shape of aggregate: It should have angular shape for strong interlocking of particular. 6. Texture: It should have rough texture for better bonding. 7. Water absorption: It should not absorb water more than 0.5 - 1% from added water to avoid variation in w/c ratio. 8. Purity: It should be clean i.e. free from any organic and inorganic impurities for good aggregate. CLASSIFICATION ACCORDING TO SIZE AND SHAPE: On the basis of size: 1. Coarse aggregate: The aggregate having size of more than 4.75 mm and less than 80 mm is called coarse aggregate.  Coarse aggregate range 4.75 mm to 80 mm.  These are obtained from natural disintegration or artificial crushing of rocks. 3  JAI CIVIL Prashant Sir (M.Tech, JNTU Hyderabad) 8+ years of Experience 8102127991 2. Fine aggregate: The aggregate having size of particle less than 4.75 mm is called as fine aggregates.  These are obtained from rivers, crushed stone etc.  Smallest size of fine aggregates (sand) is 0.075 mm.  Passing through 4.75 mm sieve (No. 4 sieve), and retained on 75 𝛍m (No.200 sieve).  The purpose of the fine aggregate is to fill the voids and to act as a workability agent. Fine aggregate Size Coarse sand 4.75mm – 2mm Medium sand 2mm – 0.425mm Fine sand 0.425mm – 0.075mm Silt 0.075mm – 0.002mm Clay Less than 0.002mm On the basis of shape: 1. Rounded aggregates: It is rounded smooth shape.  These are usually obtained from river or sea shore.  Rounded aggregates result in the minimum percentage of voids (32 – 33%). 4  JAI CIVIL Prashant Sir (M.Tech, JNTU Hyderabad) 8+ years of Experience 8102127991  Hence gives more workability.  They require lesser amount of water cement ratio.  They are not considered for high strength concrete because of poor interlocking behavior and weak bond strength. 2. Irregular aggregate: This type of aggregate have irregular shape, and not fully rounded.  Irregular aggregates may result in 35 -37% of voids.  These will give lesser workability when compared to rounded aggregate.  The bond strength is slightly higher than rounded aggregates but not as required for high strength concrete. 3. Angular aggregate:  These have sharp, angular and rough shape. 5  JAI CIVIL Prashant Sir (M.Tech, JNTU Hyderabad) 8+ years of Experience 8102127991  And these are obtained by crushing the rocks.  Angular aggregate result maximum percentages of voids 38 - 40%.  It is impart low workability.  They gives 10-20% more compressive strength due to development of stronger aggregate mortar bond. 4. Flaky aggregate: When the aggregate thickness is small when compared with width and length of that aggregate is called flaky aggregate.  In the other work, when the least dimension of aggregate is less than 60% of mean dimension is called flaky aggregate.  For e.g. length of aggregate = 5cm, width =4cm, thicknessis 2cm,  So its least dimension is 2cm,  So when this least dimension (2cm) less than 60% of its mean dimension, i.e. (5+4)/2 =4.5 cm,  And 60% of this 4.5 x 0.60 = 2.7 6  JAI CIVIL Prashant Sir (M.Tech, JNTU Hyderabad) 8+ years of Experience 8102127991 5. Elongated aggregate: When the length of aggregate is larger than other two dimension then it is called elongated aggregate.  In other word, the length of aggregate is greater than 180% of its mean dimension is called elongated aggregate. 7  JAI CIVIL Prashant Sir (M.Tech, JNTU Hyderabad) 8+ years of Experience 8102127991 2.2 FINE AGGREGATES: The aggregate having size of particle less than 4.75 mm is called as fine aggregates. PROPERTIES: SIZE: The size of fine aggregate should be equal to or less than 4.75mm.  Using the largest size will give more dense concrete, but a mixture of all sizes is more desirable and more economical.  If cement mortar is prepared for masonry work or plastering work, very fine types of sand used. SPECIFIC GRAVITY: It is the ratio of density of aggregate to the density of water.  The specific gravity of fine aggregate (sand) to be around 2.65 to 2.67. BULK DENSITY: It is the ratio of weight of aggregate (including voids) to its unit volume.  The density of sand varies according to its condition (dry, wet or compacted).  The density of sand may change, if it is in dry or wet condition as well as loose and compacted state.  When sand is compacted, sand particles are forced to come closer which result in decrease in the volume.  When sand is in wet condition, water is present in sand particles that change the volume of sand.  The average density of sand in a different state are as follows:  Density of loose sand: 1442 kg/m3. 8  JAI CIVIL Prashant Sir (M.Tech, JNTU Hyderabad) 8+ years of Experience 8102127991  Density of compacted sand: 1602 kg/m3.  Mechanically compacted sand: 1660 kg/m3.  Water saturated sand: 1895 kg/m3. WATER ABSORPTION &BULKING OF SAND: Bulking of sand means increase in volume of sand due to surface moisture.  Increase in the volume of a given fine aggregate caused by the presence of water is known as bulking.  The free moisture in fine aggregate (sand) make the film (thin layer) on the surface of sand particle.  Bulking is due to adsorption of moisture on individual sand grains in the form of thin film (layer) the film of moisture keep the sand grain away from each other.  Bulking depend upon the percentage of moisture present in the sand, in ordinary sand bulking varies from 15 to 30%.  Volume increases with water content up to a certain point 4 – 6%, after that film on the surface break and volume start decreasing. 9  JAI CIVIL Prashant Sir (M.Tech, JNTU Hyderabad) 8+ years of Experience 8102127991 Note: 1) Bulking will be more in case of find sand. Note: 2) Bulking will be maximum at 5% of water content. FINENESS MODULUS: Fineness modules is a number which gives idea about fineness of coarse aggregate and fine aggregate (sand).  It may be defined as the sum of cumulative percentage retained on each ten sieve 80 to 150 micron and divided the sum by 100.  Fineness modulus (FM) =(sum of cumulative percentage retained)/100  Fineness modulus: a) Fine sand- 2.2 to 2.6 b) Medium sand- 2.6 to 2.9 c) Coarse sand- 2.9 to 3.2  Fineness modulus of coarse aggregate small than 40mm lies between 6.75 to 8. Question: 1) calculate the fineness modulus of a sample of coarse aggregate (15kg). Sieve 80 40 20 10 4.75 2.36 1.18 600 300 150 size mm mm mm mm mm mm mm micron micron micron Retained weight 0 1.5 6 4.5 3 0 0 0 0 0 (kg) 10  JAI CIVIL Prashant Sir (M.Tech, JNTU Hyderabad) 8+ years of Experience 8102127991 % % Sieve Weight Cumulative weight Cumulative size retained weight retained weight 80 mm 0 kg 0% 0 0% 40 mm 1.5 kg 10% 1.5 kg 10% 20 mm 6 kg 40% 7.5 kg 50% 10 mm 4.5 kg 30% 12 kg 80% 4.75 mm 3 kg 20% 15 kg 100% 2.36 mm 0 0% 15 kg 100% 1.18 mm 0 0% 15 kg 100% 600 0 0% 15 kg 100% micron 300 0 0% 15 kg 100% micron 150 0 0% 15 kg 100% micron 740% Fineness modulus = sum of % cumulative retained/100 = 740/100 = 7.4 GRADING ZONE OF SAND: Grading of aggregate means determination of particle size distribution of aggregate.  Grading of aggregate is an important factor for concrete mix. 11  JAI CIVIL Prashant Sir (M.Tech, JNTU Hyderabad) 8+ years of Experience 8102127991 As per IS 383 specifications:  There are 4 types of grading zones for fine aggregates (sand) namely grading zone I, II, III and IV.  All grading zones and their recommended value for different sieve size are given below. IS SIEVE ZONE 1 ZONE 2 ZONE 3 ZONE 4 SIZE 10 mm 100 100 100 100 4.75 mm 90-100 90-100 90-100 90-100 2.36 mm 60-95 75-100 85-100 95-100 1.18 mm 30-70 55-90 75-100 90-100 600 𝛍 15-34 35-59 60-79 80-100 300 𝛍 5-20 8-30 12-40 15-50 150 𝛍 0-10 0-10 0-10 0-15 JAI CIVIL DIPLOMA - ALL SEMESTER ONLINE AND OFFLINE RAJIV NAGAR, PATNA 12