Aggregates PDF

UCC302 AGGREGATES Arpit Goyal Assistant Professor Civil Engineering Department Thapar Institute of Engineering and Technology, Patiala  Aggregates for concrete Aggregation of solid particles other than paste Makes nearly 80 – 85% weight of concrete Why aggre...

UCC302 AGGREGATES Arpit Goyal Assistant Professor Civil Engineering Department Thapar Institute of Engineering and Technology, Patiala  Aggregates for concrete Aggregation of solid particles other than paste Makes nearly 80 – 85% weight of concrete Why aggregates? Economy and efficiency Dimensional stability: shrinkage and thermal changes Provides strength and stiffness 15 billion tons of aggregates in concrete used worldwide Challenges – environmental concerns; Major Conditions: shortage and alternative resources Change of river course Must be inert Disturbance to geological structure Inexpensive Availability of industrial waste Recycling of old concrete as aggregate  Classification of aggregates Based on… Size Source Shape and texture Petrographic Weight  Size Coarse Vs. Fine aggregates Dividing sieve size is 4.75 mm Typical concrete aggregates: Coarse aggregate: 40 (generally 20 mm) – 4.75 mm Fine aggregate: size ranges from 4.75 mm to 0.075 mm River sand (well graded,) crushed stone sand (made by crushing stone to sand size) Manufactured sand Expressed in terms of square size sieve Analysis is carried out with a series of sieves with a quotient of linear dimension as 2  Terminology based on size Maximum size of aggregate: The smallest sieve through which 100% of the aggregate pass (eg. 10 mm MSA) Nominal max size of aggregate: Largest sieve that retains any of the aggregate, generally not more than 10% Generally, MSA is one sieve larger than nominal MSA  Source Natural See IS383 for approved sources of aggregate - From river beds (called gravel) - From quarries (called crushed stone) Manufactured – Fly ash based lightweight aggregate, blast furnace slag aggregate, etc. Aggregates made from steel slag are heavyweight (used in radiation shields) Aggregates made from Styrofoam are lightweight (used for insulations etc.) Fly ash aggregate Quarried aggregates  Shape Rounded vs. angular (River gravel vs crushed rock) Roundness will depend upon strength, abrasion resistance and type of wear undergone Crushed rocks are generally angular. Why?? Flakiness (Length >> width >> thickness) and elongation (Length >> other dimension) Flaky and elongated aggregates have to be avoided in large quantities why? Flakiness (Elongation) index: %age of flaky (or elongated) particles by mass of sample IS 383: 2016: Combined flakiness + elongation index < 40% Affects properties such as: Workability Paste aggregate bond strength Rounded Angular Flaky Packing and compaction Flaky and Elongated elongated Example of flaky aggregates: from laminated rocks Flat and Elongated 9  Surface texture Related to degree to which the particle surfaces are polished Smooth vs. rough Related to hardness of grain, porosity of parent rock Rough texture improves bonding and increase interparticle friction  Petrographic classification In terms of minerals present Requirement: Some aggregates are reactive Can lead to ASR (silica reacting with alkalies in cement to form gel which can adsorb water to increase volume  cracking) Eg. Opal Weight of aggregates Heavy weight agg.: Hematite, Magnetite Specific Gravity, Gs > 2.8 Normal weight agg.: Gravel, sand, crushed stone 2.8 < Gs < 2.4 Light weight agg.: Expanded perlite, burned clay Gs < 2.4 12  Ultra-lightweight Aggregates can be sawed or nailed used for its insulating properties Vermiculite 250 to 1450 kg/m3 Perlite Pumice Scoria Diatomite 13  Lightweight Aggregates Expanded clay Expanded shale used primarily for making lightweight concrete for structures Also used for its insulating properties 1350 to 1850 kg/m3 Crushed Brick 14  Normal weight aggregates used for normal concrete projects River gravel Crushed Limestone Crushed Concrete Normal weight aggregates can be further classified as natural aggregates and artificial aggregates. 15  Heavyweight Aggregates used for making high density concrete for shielding against nuclear radiation Magnetite Magnetite-sand 16 Properties of aggregates Why study properties of aggregate: 1. The mineral character of aggregate affects the strength, durability, elasticity of concrete. 2. The surface characteristics of aggregate affects the workability of fresh mass & the bond between the aggregate & cement paste in hardened concrete. If it is rough, workability decreases & bond increases. 3. The grading of aggregate affects the workability, density & economy. 18  Relevant properties of aggregates Crushing strength Modulus of elasticity Hardness, impact and crushing resistance Specific gravity Gradation Bulking of fine aggregate Soundness Presence of impurities Tests for aggregate covered in IS 2386 Properties of aggregates Depends on parent rock: Chemical and mineralogical composition Porosity Tests for aggregate: IS 2386 Strength Part I: Particle Size and Shape Hardness Part II: Estimation of Deleterious Materials and Organic Impurities Thermal properties Part III: Specific Gravity, Density, Voids, Absorption and Bulking Does not depend on parent rock Part IV: Mechanical Properties Part V: Soundness Size Part VI: Measuring Mortar Making Properties of Fine Shape Aggregate Part VII: Alkali Aggregate Reactivity Surface texture Part VIII: Petrographic Examination Strength of aggregates Strength of concrete does not exceed the strength of aggregates Aggregate strength inside concrete is different from that as a rock Usual range of compressive strength of aggregates: 35 MPa to 350 MPa Difficult to test crushing strength of individual aggregates Indirect test: Crushing strength of bulk aggregates Force required to compact bulk aggregates Performance of aggregates in concrete  Crushing value test Tested as per IS 2386 (Part 4) Sample of weight A: aggregate passing a 12.5-mm and retained on 10 mm Sieve Condition of sample: SSD or over dry for 4 hours Crushed under 400 kN in 10 minutes Sieved through 2.36 mm sieve: (fraction passing B) Crushing value: B/A x 100 Another variant: 10% fines IS 383: Crushing value < 30% test Lower crushing value aggregate is better Aggregate Impact value Aggregate Abrasion value Aggregate passing a 12.5-mm For concrete flooring and retained on 10 mm Sieve Test set-ups: Condition: SSD or over dry for 4 Deval machine hours Los Angeles machine Standard hammer falling 15 times under self weight Sieved through 2.36 mm sieve IS 383:  Stiffness Large difference in E of aggregates and paste  mismatch! Cracking can occur at low load levels Cracking is more when aggregates are angular and rough From: Concrete: Structure, Properties and Materials, by P.K. Mehta and P.J.M. Monteiro  Specific gravity: weight-volume characteristic of aggregates SG = density of substance / density of water Not important indicator of aggregate quality, but important for concrete mix design Three types: Bulk- dry Saturated surface dry Apparent Design purposes – SSD is typically used  Coarse aggregates Fine aggregates Pycnometer: constant vol flask Weight of sample = 500 gm 1.Basket + SSD sample while suspended in water = W1g. 2. Weight of empty basket in water= W2 g. 3. Weight of SSD = W3 g 4. Weight of dry agg=W4 g Specific gravity = W3 / (W3– (W1– W2)) Natural aggregates: 2.6 to 2.7 Aggregates having low specific gravity are generally weaker than those with higher specific gravity values Absorption and moisture content of aggregates Absorption: water contained in the aggregates at SSD condition Moisture content: water present in excess of SSD condition IS: 2386 (Part III) Surface moisture of CA < 1% Surface moisture in FA: can be as high as 10%  Bulking of fine aggregate Increase in volume by uptake of water between grains of sand More of a problem with manufactured sand Could lead to difficulties in volume batching of ingredients Important to measure moisture content before use in concrete!! IS: 2386 (Part III) QUESTION A sample of sand has the following properties: Moist mass = 625.2 g Dry mass = 589.9 g Absorption = 1.6 % Determine (a) saturated surface dry mass (b) total moisture content and (c) free moisture content. SOLUTION a. Absorption = (SSD-Dry mass)/ Dry mass (SSD- 589.9)/ 589.9 = 1.6/100 SSD = 599.3 g b. Mass of water = 625.2 - 589.9 = 35.3 g Total moisture content 35.3/589 * 100 = 6.0% c. Free moisture = 6.0 - 1.6 = 4.4% Question Calculate the specific gravity of aggregate for 1kg specimen. The empty weight of pycnometer is 551 gm. The weight of water filled pycnometer was 1.528 kg. The weight of pycnometer after filled with water and aggregate was 2111.5 gm. Solution Weight of pycnometer + Water + Aggregate W1; Empty pycnometer weight = 551 gm W3 = 2111.5 gm Weight of Pycnometer + Sample; W2 = 1551 gm Weight of Aggregate Weight of water S.G. = (W2 – W1) filled pycometer; ------------------- W4 = 1528 gm (W4-W1) – (W3-W2) Weight of equal volume of water S.G. = (1551-551) ---------------------------------- (1528 - 551) – (2111.5 - 1551) S.G. = 2.40 Question Calculate the specific gravity of 20mm aggregate. The surface saturated dry weight of 20mm aggregate is 3 kg. The weight of bucket while in water was 1.3485 kg. The same weight goes up to 3.225 kg when aggregate added. Solution W2, Weight of bucket + aggregate in water = 3225 gm W1, SSD = 3000 gm W3 , Weight of bucket in water = 1348.5 gm S.G. = W1 -------------- W1 – ( W2 – W3) S.G. = (3000) ----------------- 3000 – (3225-1348.5) S.G. = 2.67 Question Calculate the specific gravity of 10mm aggregate. The surface saturated dry weight of 10mm aggregate is 3 kg. The weight of bucket while in water was 1.360 kg. The same weight goes up to 3.22 kg when aggregate added. Solution W2, Weight of bucket + aggregate in water = 3220 gm W1, SSD = 3000 gm W3 , Weight of bucket in water = 1360 gm S.G. = W1 -------------- W1 – ( W2 – W3) S.G. = (3000) ----------------- 3000 – (3220-1360) S.G. = 2.63  Gradation Defines particle size distribution of aggregates Important from the point of view of aggregate packing Large aggregates: economical since require less binder But, makes the mix harsher Evaluated by sieve analysis Sieve analysis IS 2386 (Part I) Set of sieves Fine aggregates Coarse aggregates  Results of sieve analysis test Results are represented in: Tabular form Grading curves: Semi-log gradation charts Recommended grading of coarse aggregates IS 383 Recommended grading of fine aggregates Absolute division of zones is carried out at 600µ sieve. Why?? Particles finer than 600µ has larger influence on workability Zone 1 sand is harsher Proportioning of FA: CA is done based on zone of sand. More proportion of CA will be used in Zone 4 sand Fineness modulus Measure of fine aggregates gradation Used in concrete mix design Defined as 1/100th of sum of cumulative percentage weight retained on 10 mm, 4.75, 2.36, 1.18 mm and 600, 300, 150 micron sieves test procedure is given IS: 2386 (Part I) A fineness modulus of 3.0 can be interpreted to mean that the third sieve i.e., 600 m is the average size. Generally value ranges from 2 to 3.5 As value increases: indicates coarser sand and harsh mix Question A 1.2 kg sample of fine aggregate is taken and passed through the sieves designated by IS code. The weight retained against the IS Sieve is given below. Calculate the F.M of the aggregate. Also, identify the sand belongs to which ZONE as per IS 383:2016. Solution Wt. %age cumulative wt. IS Sieve Retained retained retained wt passed %age passing 10mm 0 0 0 1200 100 4.75mm 16 1.33 1.33 1184 98.67 2.36mm 154.5 12.88 14.21 1029.5 85.79 1.18mm 270.5 22.54 36.75 759 63.25 600 micron 304 25.33 62.08 455 37.92 300 micron 290 24.17 86.25 165 13.75 150 micron 117 9.75 96 48 4 pan 48 4 0 0 1200 100 296.62 4840.5 403.38 Fineness Modulus = 296.62 ------------------- = 2.96 100 Solution : Continue…… Wt. %age IS Sieve Retained Passing 10mm 0 100 4.75mm 16 98.67 2.36mm 154.5 85.79 1.18mm 270.5 63.25 600 micron 304 37.92 300 micron 290 13.75 150 micron 117 4 pan 48 0 1200 403.38 Answer : ZONE II  100 80 %age Passing 60 40 20 0 150 μm 300 μm 600 μm 1.18 mm 2.36 mm 4.75 mm 10 mm Sieves Upper Limit Lower Limit Obtained Values Question Solution Question Solution  Soundness of aggregates Ability to retain volume when concrete is subjected to frost Related to porosity of aggregate High porosity  more absorption, greater chance of volumetric expansions (either on freezing or on exposure to chemicals) Checked by soaking the aggregates in Na2SO4 or MgSO4 solution  Deleterious materials Impurities such as organic matter – interfere with hydration Coatings like clay  affect paste-aggregate bond IS 383 allows maximum 5% Weak and unsound particles deleterious matter  Alkali reactivity Aggregate reactivity: Alkali-silica reaction when aggregates have amorphous silica… Need effective testing to screen deleterious aggregates Test: Mortar bar method Thank you