DCS1 PPT Submitted By Amandeep Singh Roll No

DCS-1 PPT Submitted By. Amandeep Singh Roll No. -140306

Fine Aggregate It is the aggregate most of which passes 4. 75 mm IS sieve and contains only so much coarser as is permitted by specification. According to source fine aggregate may be described as: • Natural Sand– it is the aggregate resulting from the natural disintegration of rock and which has been deposited by streams or glacial agencies • Crushed Stone Sand– it is the fine aggregate produced by crushing hard stone. • Crushed Gravel Sand– it is the fine aggregate produced by crushing natural gravel. According to size the fine aggregate may be

described as coarse sand, medium sand fine sand. IS specifications classify the fine aggregate into four types according to its grading as fine aggregate of grading Zone-1 to grading Zone-4. The four grading zones become progressively finer from grading Zone 1 to grading Zone-4. 90% to 100% of the fine aggregate passes 4. 75 mm IS sieve and 0 to 15% passes 150 micron IS sieve depending upon its grading zone. Coarse Aggregate It is the aggregate most of which is retained on 4. 75 mm IS sieve and contains only so much finer material as is permitted by specification. According to source,

coarse aggregate may be described as: Uncrushed Gravel or Stone– it results from natural disintegration of rock Crushed Gravel or Stone– it results from crushing of gravel or hard stone. Partially Crushed Gravel or Stone– it is a product of the blending of the above two aggregate. According to size coarse aggregate is described as graded aggregate of its nominal size i. e. 40 mm, 20 mm, 16 mm and 12. 5 mm etc. for example a graded aggregate of nominal size 20 mm means an aggregate most of which passes 20 mm IS sieve.

A coarse aggregate which has the sizes of particles mainly belonging to a single sieve size is known as single size aggregate. For example 20 mm single size aggregate mean an aggregate most of which passes 20 mm IS sieve and its major portion is retained on 10 mm IS sieve.

What is Gap Graded Aggregate? Generally we use well graded aggregate or continuous graded aggregate, which means representation of all the standard particle sizes in certain proportion. Assumption made in well gradation is that voids created by the higher size of aggregate will be filled-up by immediate next lower size of aggregate and again some smaller voids will be left out which will again be filled-up by next lower size aggregates.

Practically it has been found that voids created by a particular size may be too small to accommodate the very next lower size. Therefore the next lower size may not be accommodated in the available gap without lifting the upper layer of the existing size. Therefore, Particle Size Interference is created which disturbs the very process of achieving the maximum density. In fact the size of voids created by a particular size of aggregate can accommodate the second or third lower size aggregates only i. e. voids created by 40 mm will be able to accommodate size equal to 10 mm or 4. 75 mm but not 20 mm. This concept is called Gap Grading.

Advantages of Gap Grading 1. Requirements of sand is reduced by 26 to 40%. 2. Specific area of total aggregates will be reduced due to less use of sand. . 3. Point contact between various size fractions is maintained, thus reducing the dying shrinkage. 4. It requires less cement as the net volume of voids to a greater extent.

Fineness Modulus is defined as an index to the particle size not to the gradation. Fineness Modulus is calculated from the sieve analysis. It is defined mathematically as the sum of the cumulative percentages retained on the standard sieves divided by 100. The standard size sieves are 6” (150 mm), 3” (75 mm), 1 1/2” (37. 5 mm), 3/4” (19. 0 mm), 3/8” (9. 5 mm), No. 4 (4. 75 mm), No. 8 (2. 36 mm), No. 16 (1. 18 mm), No. 30 (600 μm), No. 50 (300μm), and No. 100 (150 μm). Always report the fineness modulus to the nearest 0. 01. In fineness modulus, the finer the material the more the

water demand is. It is used for the purpose of estimating the quantity of coarse aggregate to be used in the concrete mix design. The F. M. of fine aggregates should not be less than 2. 3 or more than 3. 1, or vary by more than 0. 20 from batch to batch. The American Concrete Institute (ACI) has developed Table A 1. 5. 3. 6. (page 2 - 16) which for various sizes of coarse aggregate, gives the volume of dry rodded coarse aggregate per unit volume of concrete for different fineness moduli of sand. If the maximum size of the coarse aggregate and the fineness modulus of the Fine Aggregate are known, the volume of the dry rodded coarse aggregate can be obtained from this table.

The volume relationship in the ACI Table actually relates to the total surface area of the aggregates, or water demand of the aggregate. For example, if the Fineness Modulus is constant, the volume of coarse aggregate increases with the size of the aggregate, or with the decrease in surface area of the coarse aggregate. Likewise, as the fine aggregate decreases for any one size of coarse aggregate, the volume of the coarse aggregate increases.

Sieve Analysis Sieve analysis helps to determine the particle size distribution of the coarse and fine aggregates. This is done by sieving the aggregates as per IS: 2386 (Part I) – 1963. In this we use different sieves as standardized by the IS code and then pass aggregates through them and thus collect different sized particles left over different sieves. The apparatus used are – i) A set of IS Sieves of sizes – 80 mm, 63 mm, 50 mm, 40 mm, 31. 5 mm, 20 mm, 16 mm, 12. 5 mm, 10 mm, 6. 3 mm, 4. 75 mm, 3. 35 mm, 2. 36 mm, 1. 18 mm, 600µm, 300µm, 150µm and 75µm.

ii) Balance or scale with an accuracy to measure 0. 1 percent of the weight of the test sample. The weight of sample available should not be less than the weight given below: -

The sample for sieving should be prepared from the larger sample either by quartering or by means of a sample divider. Procedure to determine particle size distribution of Aggregates. i) The test sample is dried to a constant weight at a temperature of 110 + 5 o. C and weighed. ii) The sample is sieved by using a set of IS Sieves. iii) On completion of sieving, the material on each sieve is weighed. iv) Cumulative weight passing through each sieve is calculated as a percentage of the total sample weight.

v) Fineness modulus is obtained by adding cumulative percentage of aggregates retained on each sieve and dividing the sum by 100. Reporting of Results The results should be calculated and reported as: i) the cumulative percentage by weight of the total sample ii) the percentage by weight of the total sample passing through one sieve and retained on the next smaller sieve, to the nearest 0. 1 percent. The results of the sieve analysis may be recorded graphically on a semi-log graph with particle size as abscissa (log scale) and the percentage smaller than the specified diameter as ordinate.