Civil Engineering Materials SAB 2112

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1 CONTENT SCHEDULE 1 st Meeting Civil Engineering Materials SAB 2112 Physical & Mechanical Properties of Aggregates Dr Mohamad Syazli Fathi 1. Introduction, cement manufacturing process, types of cement, chemical composition of OPC 2. Hydration of cement, testing of cement, types of aggregates, g physical and mechanical characteristics of aggregates 3. Size distribution and testing of aggregates, water in concrete, types of chemical admixtures Department of Civil Engineering RAZAK School of Engineering & Advanced Technology UTM International Campus July 25, 2010 CONTENT SCHEDULE 2 nd Meeting Aggregate 1. Types of pozzolanic admixtures, water-cement ratio and its effect in concrete 2. Workability, test of fresh concrete, segregation and bleeding in concrete 3. Concrete on site - method of production, concrete strength and grade 4. Concrete proportions - standard, nominal; Hardened concrete tests- destructive and non-destructive tests Aggregate: the inert filler materials, such as sand or stone, used in making concrete added up to 80% by volume in ordinary concrete to provide bulk Characteristic - Must clean & durable & Free from organic impurities & dust (WHY?) - it may prevent the cement paste from coating the aggregate properly - preventing bonding - reduce strength of the concrete 1

2 Aggregate Quality Aggregate Cleanliness Aggregate should not contain materials which are likely to Decompose/change in volume (eg coal, clay) React with cement paste (eg certain siliceous compounds (ASR)) Affect appearance of concrete (eg salt, pyrites) Should be free from dust, clay, etc Sea dredged aggregate may be contaminated with chlorides Excessive washing is costly and may wash away fines Shape will affect workability and durability Grading - involves seiving to find out the proportions of different sized aggregate (eg continuously-graded, gapgraded etc) 9 10 Aggregates Gravels, crushed rock, and sands, etc, which are mixed with cement and water to make concrete. Will influence all aspects of the concrete, eg Durability Structural performance Cost Two main categories Fine < 5mm Coarse > 5mm Types of Natural Aggregates Fine Aggregates natural sand crushed rock crushed gravel that pass 5mm BS Sieve Dry vary in character depending on their location, method of extraction & grading. Sharp sand has angular grains used mainly for concrete Soft sand has smaller rounded grains used for mortars & renderings Coarse Aggregate materials that retained on a 5mm sieve when dry. 10mm for small section work with a lot of close reinforcement 20mm for general work mm for large reinforced pours All in Aggregate mixture of coarse & fine aggregate either as extracted / delivered not allowed for structural purposes Graded Aggregates natural agg. consist of different size of stones randomly mixed. 11 2

3 Other Types of Aggregates (may be naturally occurring or industrial products) 1. Normal density aggregates (most widely used) 2. Lightweight i aggregates (eg pumice, expanded dclay - Leca, PFA - Lytag, Expanded Slag - Pellite ) 3. High density aggregate (eg, lead) 4. Fibres (eg asbestos, wood, steel, glass, polymers) 14 Source: BS EN :2009 Tests for mechanical and physical properties of aggregates. Determination of the polished stone value Concrete = 25-40% cement (absolute volume of cement = 7-15% ; water = 14-21%) Up to 8% air (depending on top size of coarse aggregate) 1. BS EN describes the test method for mechanical and physical properties of aggregates. 2. This part of the BS EN 1097 series of standards concentrates on determining the polished stone value (PSV) of a coarse aggregate used in road surfacing. 3. PSV is a measure of the resistance of coarse aggregate to the polishing action of vehicle tyres under conditions similar to those occurring on the surface of a road. 4. For other purposes, in particular factory production control, other methods may be used provided that an appropriate working relationship with the reference method has been established. 5. This standard also describes an optional method for the determination of the aggregate abrasion value (AAV). The AAV method should be used when particular types of skid resistant aggregates (typically those with a PSV of 60 or greater) which can be susceptible to abrasion under traffic, are required. Contents of BS EN : Foreword 1 Scope 2 Normative references 3 Definitions 4 Principle 5 Sampling 6 Materials 7 Apparatus 8 Preparation of test specimens 9 Conditioning of the rubber-tyred wheel 10 Accelerated polishing of specimens 11 Friction test procedure 12 Calculation and expression of results 13 Test report Physical Properties of Aggregates: 1.Unit Weight and Voids 2. Specific Gravity 3P 3. Particle til Shape and dsurface Texture 4. Shrinkage of Aggregates 5. Absorption and Surface Moisture 6. Resistance to Freezing and Thawing Unit Weight (unit mass or bulk density) The weight of the aggregate required to fill a container of a specified unit volume. Volume is occupied by both the aggregates and the voids between the aggregate particles. Depends on size distribution and shape of particles and how densely the aggregate is packed Loose bulk density Rodded or compact bulk density Normal-weight concrete bulk density of aggregate is approximately lb per cubic foot. 3

4 Weight Examples of Aggregates Used Uses for the Concrete Voids ultra-lightweight vermiculite, ceramic can be sawed or nailed, also used for its insulating properties Void content affects mortar requirements in mix design; water and mortar requirement tend to increase as aggregate void content increases. lightweight normal weight heavyweight expanded clay, shale or slate, crushed brick crushed limestone, sand, river gravel, crushed recycled concrete steel or iron shot; steel or iron pellets used primarily for making lightweight concrete for structures, also used for its insulating properties used for normal concrete projects used for making high density concrete for shielding against nuclear radiation Void content between aggregate particles increases with increasing aggregate angularity. Void contents range from 30-45% for coarse aggregates to about 40-50% for fine aggregates. Total volume of voids can be reduced by using a collection of aggregate sizes. Specific Gravity (Relative density) Absolute: the ratio of the weight of the solid to the weight of an equal volume of water (both at a stated temperature) refers to volume of the material excluding all pores Apparent: ratio of the weight of the aggregate (dried in an oven at ºF for 24 hours) to the weight of water occupying a volume equal to that of the solid including the impermeable pores volume of solid includes impermeable pores (but not capillary pores) The cement paste requirement for concrete is proportional to the void content of the combined aggregate. Used for calculating yield of concrete or the quantity of aggregate required for a given volume of concrete. Particle Shape and Surface Texture Particle Shape and Surface Texture Rough textured, angular, elongated particles require more water to produce workable concrete than do smooth, rounded, compact aggregates. Aggregates should be relatively free of flat and elongated particles (limit to 15% by weight of total aggregate). Important for coarse and crushed fine aggregate - these require an increase in mixing water and may affect the strength of the concrete, if cement water ratio is not maintained. 4

5 Shrinkage of Aggregates: Large Shrinkage = Low Shrinkage = fine grained sandstones, slate, basalt, trap rock, clay-containing quartz, limestone, granite, feldspar What happens if abnormal aggregate shrinkage occurs? Absorption and Surface Moisture 1. Excessive cracking 2. Large deflection of reinforced beams and slabs 3. Some spalling (chipping or crumbling) If more than 0.08 percent shrinkage occurs, the aggregate is considered undesirable. If water content of the concrete mixture is not kept constant, the compressive strength, workability, and other properties will vary from batch to batch. Moisture Conditions of Aggregates 1. Oven dryfully absorbent 2. Air dry- dry at the particle surface but containing some interior 3. Saturated moisture surface dry (SSD) neither absorbing water nor contributing water to the concrete mixture 4. Wet or moist- containing an excess of moisture on the surface 5

6 Resistance to Freezing and Thawing Absorption Capacity: maximum amount of water aggregate can absorb Absorption Capacity (%) = [(W SSD W OD )/W OD ] X 100 Surface Moisture: water on surface of aggregate particles Surface Moisture (%) = [(W WET W SSD )/W SSD ] X 100 Important for exterior concrete (for cold countries). Affected by an aggregate's high porosity, absorption, permeability and pore structure. If aggregates g or concrete absorbs so much water that when the water freezes and expands the concrete cannot accommodate the build up of internal pressure, pop outs may occur. Moisture Content: of an aggregate in any state Moisture Content (%) = [(W AGG W OD )/W OD ] X 100 Aggregate Gradation Types of Gradations Measurement Gradation is usually measured by a sieve analysis. In a sieve analysis, a sample of dry aggregate of known weight is separated through a series of sieves with progressively smaller openings. Once separated, the weight of particles retained on each sieve is measured and compared to the total sample weight. Particle size distribution is then expressed as a percent retained by weight on each sieve size. Results are usually expressed in tabular or graphical format. The typical graph uses the percentage of aggregate by weight passing a certain sieve size on the y-axis and the sieve size raised to the n th power (n = 0.45 is typically used) as the x-axis units. The maximum density appears as a straight line from zero to the maximum aggregate size (the exact location of this line is somewhat debatable, but the location shown in the next Figure is generally accepted). * Uniformly graded - Few points of contact - Poor interlock (shape dependent) - High permeability * Well graded - Good interlock - Low permeability * Gap graded - Only limited sizes - Good interlock - Low permeability 34 Aggregate Gradation Typical Aggregate Gradations Use 0.45 Power Gradation Chart Blend Size Definitions maximum size nominal maximum size Gradation Limits control points restricted zone 35 Source: 6

7 Aggregate Gradation Typical Gradations (see Figure) 1. Dense or well-graded. Refers to a gradation that is near maximum density. 2. Gap graded. Refers to a gradation that contains only a small percentage of aggregate particles in the mid-size range. The curve is flat in the mid-size range. These mixes can be prone to segregation during placement. 3. Open graded. Refers to a gradation that contains only a small percentage of aggregate particles in the small range. This results in more air voids because there are not enough small particles to fill in the voids between the larger particles. The curve is flat and near-zero in the smallsize range. 4. Uniformly graded. Refers to a gradation that contains most of the particles in a very narrow size range. In essence, all the particles are the same size. The curve is steep and only occupies the narrow size range specified. Other Gradation Terms 1. Fine aggregate (sometimes just referred to as "fines"). natural or crushed sand passing the No. 10 sieve and mineral particles passing the No. 200 sieve. 2. Coarse aggregate. as hard, durable particles or fragments of stone, gravel or slag retained on the No. 10 sieve. Usually coarse aggregate has a toughness and abrasion resistance requirement. 3. Fine gradation. A gradation that, when plotted on the 0.45 power gradation graph, falls mostly above the 0.45 power maximum density line. The term generally applies to dense graded aggregate. 4. Coarse gradation. A gradation that, when plotted on the 0.45 power gradation graph, falls mostly below the 0.45 power maximum density line. The term generally applies to dense graded aggregate. 5. Mineral filler. as a finely divided mineral product at least 65 percent of which will pass through a No. 200 sieve. Pulverized limestone is the most commonly manufactured mineral filler, although other stone dust, silica, hydrated lime, portland cement and certain natural deposits of finely divided mineral matter are also used (Asphalt Institute, 1962). Mechanical Properties of Aggregates There are many tests which are conducted to check the quality of aggregates. (Aggregates are very important component of concrete, so the quality really matters when it comes to aggregates). Various test which are done on aggregates are listed below. 1. Sieve Analysis 2. Water Absorption 3. Aggregate Impact Value 4. Aggregate Abrasion Value 5. Aggregate Crushing Value Other Info to Share Other Info to Share 7

8 Other Info to Share Other Info to Share Questions -? More info: