Aggregates. Introduction. Inert, granular, inorganic materials, which normally consist of stone or stone-like solids.

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1 Introduction Inert, granular, inorganic materials, which normally consist of stone or stone-like solids. Usage: Alone road bases, fill, drainage layers Particulate Composites - Portland cement concrete - Asphalt concrete Typical Proportions (by Volume): Portland Cement Concrete: 70-80% Asphalt Concrete: 90% or more

2 General Properties Functions: Economy inexpensive filler Dimensional Stability shrinkage/expansion control Durability wear resistance, chemical attack Classification by Specific Gravity: Heavyweight (>3.5) Normal-weight ( ) Lightweight (<1.0) 90% of N.A. concrete General Properties Classification by Source Natural: Naturally Occurring (sand, gravel) Modified (crushing, washing, sieving) Artificial: Industrial wastes (blast furnace slag) Man-made (lightweight) Reclaimed (recycled concrete)

3 General Properties Igneous: Formed during the cooling of molten rock Examples basalt, granite Sedimentary: Formed by deposition and consolidation of particles Examples shale, limestone, sandstone Metamorphic: Formed from sedimentary rock by heat and pressure Examples slate, marble, quartzite General Properties Desirable Characteristics: ti Hard, strong, durable Free of undesirable impurities Chemical stability (or beneficial reactivity) Important Properties: Sh d t t Shape and texture Size gradation Moisture content Specific gravity Bulk unit weight

4 Shape & Texture Aggregate shape and texture directly affect the workability of fresh concrete. Sufficient paste is required to coat the aggregates in order to provide lubrication and decrease interactions between aggregate particles during mixing. Ideal aggregate particle for workability would be: Spherical (no corners, low surface-to-volume ratio) Smooth (less friction between particles) Shape & Texture High inter-particle contact and friction. Paste acts as lubricant between particles.

5 Shape & Texture Shape & Texture Mechanical properties of concrete are also affected by particle shape and texture. Higher surface-to-volume ratio increases the amount of surface area available for bonding. Extreme changes in shape can induce stress concentrations. Rough, textured surfaces improve mechanical bond.

6 Shape & Texture Shape & Texture

7 Size Gradation Particle size distribution determines paste requirements: Uniform Grading Continuous Grading Size Gradation Particle size distribution determines paste requirements:

8 Other possible gradations: Size Gradation Gap Grading No-Fines Grading Size Gradation

9 Size Gradation How big is it????? Size Gradation How can we determine a 3-D particle s diameter?

10 Sieve Analysis Sieve Analysis

11 How big is it????? Sieve Analysis d i Three-Dimensional Object = L x W x D How big is it????? Sieve Analysis d i-1 Particle is retained on the d i-1 sieve. Particle belongs to the d i d i-1 size fraction.

12 Sieve Analysis Maximum Aggregate Size The maximum size of the coarse aggregate influences the paste requirements of the concrete. Optimum grading depends on maximum aggregate size. Maximum Aggregate Size = The smallest sieve opening through which the entire aggregate sample will pass. Nominal Maximum Aggregate Size = ASTM allows 5-10% retention on the largest sieve size.

13 Maximum Aggregate Size The choice of nominal maximum aggregate size is determined by job conditions i to ensure consistency: 1/5 Narrowest dimension between forms 1/3 Depth of slabs 3/4 Clear spacing between reinforcing and/or forms Most concrete will be limited it to 1½" or less but mass structures t can use much larger sizes (up to 6"). Concrete testing equipment can normally only handle 1½" or smaller aggregate. Size Gradation Particle size distribution determines paste requirements: Uniform Grading Continuous Grading Increased Maximum Aggregate Size

14 Maximum Aggregate Size A larger maximum aggregate size reduces paste requirement: Grading Curves Grading Curve: Graphical plot of the distribution of particle sizes in an aggregate sample. Plotted as: Cumulative % Passing Sieve vs. Sieve Size. Since successive standard sieve sizes are incremental by a Since successive standard sieve sizes are incremental by a factor of 2 (i.e. #4, #8, #16, etc) this effectively produces a semilog plot.

15 Grading Curves Grading Curves

16 Grading Curves Grading Curves

17 Grading Curves Optimum combined grading. Grading Curves Fuller's Maximum Density Curves Theory based on spherical particle packing.

18 Grading Curves Fuller's Maximum Density Curves Handling & Storage Avoid Segregation!!! Do not store in tall cone-shaped piles.

19 Handling & Storage Avoid Segregation!!! Be wary of windy conditions. Handling & Storage Avoid Segregation!!! Do not let aggregate run down slope.

20 Fineness Modulus A single parameter that describes the grading curve of a fine aggregate. Used to check the uniformity of grading between aggregate samples. cumulative % retained on standard sieves FM = 100 Increasing FM = Coarser Aggregate Fineness Modulus

21 Fineness Modulus Fineness Modulus Two aggregates with the same FM are not necessarily identically graded. FM is not normally used for coarse aggregate since: -Less relevant -Very high values -Low sensitivity FM of the fine aggregate is required for mix proportioning since sand gradation has the largest effect on workability. Finer sand increases workability and allows an increase in the proportion of coarse aggregate.

22 Moisture States: Moisture Content Oven Dry (OD) All pores are empty of water. Heated in oven at 105 o C to constant weight. Air Dry (AD) All moisture is removed from the surface but internal pores are partially full. Saturated Surface Dry (SSD) All pores are filled with water but there is no film of water on aggregate surface. Wet All pores are filled with water and there is a film of water on aggregate surface. Moisture Content

23 Moisture Content Moisture Content Only OD and SSD correspond to specific moisture contents. The AD and wet states represent the variable moisture contents present in stockpiled aggregate. SSD is used as the reference state for calculating moisture contents instead of OD because: It is the equilibrium moisture content. It is the equilibrium moisture content. Moisture contents in the field are much closer to SSD. Bulk specific gravity (BSG) more accurate using SSD. Moisture content can be calculated directly from apparent specific gravity (ASG).

24 Moisture Content Absorption (A): The maximum amount of water that t the aggregate can absorb. b W A = W W SSD OD OD 100% Effectively, the amount of water in the aggregate at SSD as a proportion of the dry aggregate weight. Normal-Weight Aggregate: A = 1-2% Lightweight Aggregate: A = 10% plus Moisture Content

25 Moisture Content Effective Absorption (EA): The amount of water needed d to bring the aggregate from the AD state to the SSD state: W EA = W W SSD SSD 100% The amount of water needed can be calculated as: W abs = The weight of AD aggregate batched must be W agg in SSD state less W abs while the mix water is increased by W abs AD ( EA) W 100% agg Moisture Content Surface Moisture (SM): The amount of water in excess of the SSD state: t W SM = W W wet SSD SSD The additional water can be calculated as: W add = ( SM ) W 100% 100% The weight of wet aggregate batched must be W agg in SSD state plus W add while the mix water is decreased by W add agg

26 Moisture Content Moisture Content Adjustments: The goal here is to adjust the mix water such that the moisture absorbed by or shedded by the aggregates is accounted for and the amount of water specified in the concrete mix design is unaffected. With wet aggregates, the excess water is immediately available. Preferable Condition With AD aggregates, the amount of water absorbed is a function of time. Use 30 min Absorption Bulking of Sand: Moisture Content Stockpiled coarse aggregate is generally in the AD state with an EA of less than 1% Stockpiled fine aggregate is often in the wet state with a SM typically in the range of 2-6% Due to its small particle size, fine aggregate can hold water in the interstices between particles. Menisci tend to form which push the particles apart and increase the apparent volume of the aggregate.

27 Moisture Content When saturated, the menisci are destroyed and bulk volume returns to normal. are batched by weight and unit weights are determined on OD basis. Moisture Content

28 Specific Gravity The specific gravities of the aggregates are required in mix proportioning i to establish weight-volume relationships. density of solid SG = density of water In practice, aggregates are not solid materials. They contain pores that either connect to the surface (permeable) or are sealed within the solid material (impermeable). Impermeable pores are considered to be part of the solid material when determining specific gravity. Specific Gravity Apparent specific gravity (ASG) refers only to the solid material excluding permeable pores: ASG = mass of aggregate (solid only) volume of aggregate (solid only) 1 ρ water Bulk specific gravity (BSG) includes the permeable pores in the aggregate volume: mass of aggregate (solid + pores) 1 BSG = volume of aggregate (solid + pores) ρ water

29 Specific Gravity BSG is the most realistic value since the effective volume that aggregates occupy in concrete includes the pores. When the pores are filled with water, there is additional mass that is absent in the OD state: ASG > BSG SSD > BSG OD Since the porosity of most rocks is 1-2%, these values are very similar. Exception lightweight aggregate (BSG a function of MC) Unit Weight Unit weight is simply the weight of a given volume of graded aggregate. g Sometimes called bulk density. Volume includes both the solid aggregate particles and the space between them. Affected by degree of compaction and moisture content of aggregate.

30 Unit Weight Maximum unit weight typically occurs at a fine aggregate content of 35-40% by weight of total aggregate g. Durability Aggregate durability is a critical issue since they make up the largest proportion of the volume of concrete. Of the various testing approaches available for measuring aggregate durability, preference should be given in the following order: 1. Field performance of concrete 2. Tests that evaluate aggregates in concrete 3. Tests on the aggregates themselves

31 Soundness Durability are said to be unsound if the volume changes that accompany environmental changes lead to deterioration of the concrete. Volume changes can be induced by freezing and thawing or from repeated wetting and drying. There are two forms of freeze-thaw deterioration due to aggregate unsoundness pop-outs and D-cracking. Durability Soundness Aggregate Deterioration

32 Soundness Popouts Durability Soundness D-Cracking Durability

33 Soundness Shrinkage Durability Wear Resistance Durability play an important role in determining the resistance of concrete to surface abrasion and wear. Particles must be hard, dense, strong, and free of soft, porous, or friable particles.

34 Chemical Resistance Durability Most chemical durability problems result from a reaction between reactive silica in aggregates and alkalis contained in the cement. Other detrimental reactions include: Iron pyrite reacts expansively with CH Excessive gypsum causes sulfate attack Zinc or lead delay setting and hardening Deleterious Substances Durability

35 Deleterious Substances Durability Deleterious Substances Iron oxide in aggregate: Durability

36 Nonstandard If an aggregate does not meet ASTM standards, certain processes may be able to help: These will increase cost and are usually only done where aggregate supplies are scarce. Nonstandard The use of solid waste materials as aggregates is becoming more common:

37 Nonstandard Nonstandard

38 Nonstandard When dealing with the implementation of waste materials as aggregates, four major factors must be considered. 1. Economy 2. Compatibility with other materials 3. Concrete properties 4. Consistency Successful usage depends on anticipating potential problems and the ensuing properties of the concrete, and developing uses that comply with these restraints. Lightweight Nonstandard

39 Lightweight Nonstandard Expanded Clay Expanded Shale Heavyweight Nonstandard