DCS-1 PPT Submitted By- Amandeep Singh Roll No

INDEX FINE AGGREGATES COARSE AGGREGATES GAP GRADED AGGREGATES FINENESS MODULUS SIEVE ANALYSIS

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 and 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.

Gap Graded Aggregate Aggregate is gap-graded when intermediate sizes are essentially absent from the gradation curve. Usual gap-graded mixes contain aggregate retained on a 3/4- or 1 1/4-inch sieve, and particles passing the No. 4 sieve. Gap-graded mixes are used to obtain uniform textures for exposed-aggregate concrete and can also increase strength and reduce creep and shrinkage. Though the intermediate sizes usually can be omitted without making the mix unduly harsh or prone to segregation, choose the fine-aggregate percentage with care for gap-graded concrete. Use about 25% by volume with rounded aggregate and 35% with crushed material.

Advantages of Gap Grading 1.Requirements of sand is reduced by 26 to 40%. 2.Specific area of 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 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). Fine aggregates range from a FM of 2.00 to Coarse aggregates smaller than 38.1 mm range from 6.50 to 8.00.

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) – 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 – 80mm, 63mm, 50mm, 40mm,31.5mm, 25mm, 20mm, 16mm, 12.5mm, 10mm, 6.3mm,4.75mm, 3.35mm, 2.36mm, 1.18mm, 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 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.