Aggregates for Portland Cement Concrete (PCC) PDF

AGGREGATES FOR Portland cement Concrete (PCC) Objectives of Lecture Classification of Aggregates Properties of Aggregates: (Physical and mechanical properties) Applications of aggregates  Aggregates Aggregates are inert materials which are mixed with binding ma...

AGGREGATES FOR Portland cement Concrete (PCC) Objectives of Lecture Classification of Aggregates Properties of Aggregates: (Physical and mechanical properties) Applications of aggregates  Aggregates Aggregates are inert materials which are mixed with binding material such as cement or lime for manufacturing of mortar or concrete. Aggregates are used as filler in mortar and concrete and also assist in cost reduction  Classification of Aggregates (1) Fine aggregates (2) Coarse aggregates Depending upon the shape of their particles aggregates are classified as: (1) Rounded aggregates (2)Irregular or partly rounded aggregates (3)Angular aggregates (4)Flaky aggregates (5)Elongated aggregates Construction aggregates (What are they?) Aggregates are fine and coarse material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates.  CLASSIFICATION OF AGGREGATES Coarse Aggregate (CA) Size: 4.75 mm to 37.5 mm(retained on No. 4 sieve) Fine Aggregate (FA) Size: 0.075 mm (0.003 in.) (retained on No. 200 sieve) to 4.75 mm to 37.5 mm Classification of aggregates Aggregates can classified as natural or artificial or industrial by products Natural sands and gravels are the product of weathering and the action of wind or water, Artificial (Manufactured) crushed fine aggregate and crushed stone coarse and fine aggregate are produced by crushing natural stone. Synthetic aggregates may be either by products of an industrial i.e. blast-furnace slag, or manufacture aggregates  Shape Classification Aggregates are categorized using following definitions : Roundness: relative angularity or sharpness of the corners and edges of a particle. Elongation: particles whose longest length is more than 3 x their thickness are described as being elongated or non-cubical Angular Possessing well-defined edges formed at the intersection of approximate planar faces.  Effect of Texture of Aggregates on Aggregates Workability: Aggregates with a smooth texture, such as natural river gravel, improve the workability of concrete. They reduce friction between particles, making the mix easier to handle and place Bond Strength: Rough-textured aggregates, like crushed stone, provide a better mechanical bond with the cement paste. This enhances the overall strength and durability of the  Effect of Texture of Aggregates on Concrete Water Demand: Smooth aggregates require less water to achieve the same workability compared to rough aggregates. This can help in reducing the water-cement ratio, which is beneficial for the strength and durability of the concrete Compaction: In asphalt mixtures, angular and rough-textured aggregates interlock better, providing higher stability and resistance to deformation under load. This is particularly important for road surfaces Skid Resistance: For pavements, rough-textured aggregates increase skid resistance, enhancing safety for vehicles Segregation: Smooth and rounded aggregates can lead to segregation in the mix, where the heavier particles settle at the bottom. Proper mix design and handling are required to mitigate this issue  Natural mineral aggregates Natural mineral aggregates, i.e., A. Sand and gravel have a bulk density of (1520 – 1680) Kg/m3 B. and produce Normal Weight Concrete (NWC). (2400 ) Kg/m3 C. Aggregates with bulk densities less than (1120 Kg/m3) are called Lightweight. Aggregates weighing more than (2080 Kg/m3) are called heavyweight aggregates  ORIGIN OF NATURAL AGGREGATES Physical and mechanical Properties of the aggregates depends on parent rock: (i) Strength (ii)relative density* (iii)hardness (iv)permeability (v)pore structure *Relative density, or specific gravity, is the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity usually means relative density with respect to water. The term "relative density" is often preferred in scientific usage DEFINITIONS Hardness is the property of a material that enables it to resist plastic deformation, usually by penetration, resistance to bending, scratching, abrasion or cutting Permeability s a measure of the ability of a porous material (often, a rock or an unconsolidated material) to allow fluids to pass through it.  PORE STRUCTURE OF SLAG AGGREGATES Permeability in fluid mechanics and the earth sciences (commonly symbolized as κ, or k) is a measure of the ability of a porous material (often, a rock or an unconsolidated material) to allow fluids to pass through it. Pore Structure of Aggregates Presence of air voids (entrapped air)  Artificial aggregates (I )Synthetic Aggregates Thermally processed materials, i.e. expanded clays and shale. (ii) Industrial wastes and municipal wastes Aggregates made from industrial by-products, i.e. blast-furnace slag & fly ash. Recycled Aggregates (iii) Recycled concrete from demolished buildings and pavements. NB: Problems: Cost of crushing, grading, dust AGGREGATES? What you must know……… Type and origin (rock source, type) affects its strength and durability and reactivity, surface hardness. Grading (effort to achieve consistency in aggregate size) affects the workability of the fresh concrete. Shape and texture - determined from the processes used to produce to materials (either natural or man-made). Porosity depending on its dryness and type of porosity can affect the strength and durability.  Important minerals found in aggregates Silica Ferromagnesium Mica Clay Carbonate Sulfate Sulfide Iron ore A mineral is different from a rock, which can be an aggregate of minerals or non-minerals and does not have one specific chemical composition  Why use aggregates Reduction of costs Minimization of the shrinkage of concrete Production of concrete with satisfactory plastic properties Manufacture of low density aggregates decrease foundation load as well as increase thermal insulation  Why use aggregates High –density concrete for radiation shielding (iron based aggregates) Improvement of fire resistance (limestone, light weight aggregates) Abrasion- resistance concrete for floors (granites or carborundum aggregates)  OTHER MAJOR CHARACTERISTICS OF AGGREGATES http://www.ce.memphis.edu/1101/notes/concrete/PCA_manual/Cha p05.pdf EXAMPLES OF HEAVYWEIGHT SOME PROPERTIES OF THE LIGHTWEIGHT CONCRETE Aggregates size and their applications  WHY GRADATION OF AGGREGATES? The particle size distribution, or gradation, of an aggregate is one of the most influential aggregate characteristics in determining how AGGREGATES will perform For Example the bulk density, physical stability, permeability the sieve analysis test . To determine the size distribution of particles, the sieve analysis test is conducted. In sieve analysis, the particle size distribution is defined using the mass or volume. Sieve methods exist as: -Manual sieving method, -mechanical sieving method, -dry sieving method and -wet sieving method According to: http://www.basiccivilengineering.com/2017/06/sieve-analysis-test.html  Fineness Modulus The Fineness Modulus (FM) is an empirical figure obtained by adding the total percentage of the sample of an aggregate retained on each of a specified series of sieves The fineness modulus helps in determining the proportions of fine and coarse aggregates in concrete mix designs A lower FM indicates finer aggregate, w hile a higher FM indicates coarser aggre  Importance of Fineness Modulus The fineness modulus (FM) of aggregates is crucial for several reasons: 1. Concrete Mix Design: FM helps in determining the proportions of fine and coarse aggregates in concrete mix designs. It provides a basis for estimating the amount of aggregate needed to achieve the desired workability and strength  Importance of Fineness Modulus Workability: The FM influences the workability of the concrete mix. A higher FM indicates coarser aggregate, which can reduce the workability, while a lower FM indicates finer aggregate, which can improve workability  Importance of Fineness Modulus  Water Demand: FM helps predict the amount of water required for the mix. Aggregates with a higher FM will generally require less water to achieve the same consistency compared to aggregates with a lower FM.  Importance of Fineness Modulus Consistency and Strength: Aggregates with the same FM will require the same quantity of water to produce a mix of the same consistency and strength. This Consistency is vital to ensure uniformity of concrete production  Importance of Fineness Modulus Gradation Control – It helps in controlling the grading of aggregates ensuring that the mix has the right balance of fine and coarse particles  Fineness (Determined by Fineness Modulus) Empirical figure obtained by adding the total percentage of the sample of an aggregate retained on each of a specified series of sieves, and dividing the sum by 100 Sieves sizes are: 150-μm (No. 100) 300-μm (No. 50)  600-μm (No. 30) 1.18-mm (No. 16) 2.36-mm (No. 8) 4.75-mm (No. 4)  9.5-mm (3/8-in.) 19.0-mm (3/4-in.) 37.5-mm (11/2-in.) Larger: increasing in the ratio of 2 to 1. Sample Calculation: Calculate the cumulative percentage of the weight retained and determine the Fineness Modulus of the Aggregates. Sieve Number Percentage of Weight Cumulative Value of Weight Cumulative Percentage of Retained Retained Weight Retained 4 90 8 100 16 120 30 160 50 140 100 140 Pan 250 Types of aggregates gradation Dense gradation – Narrow gradation – Gap gradation – Open gradation – Rich gradation – Types of gradation relatively to the aggragate nature Dense gradation – A dense gradation refers to a sample that is approximately of equal amounts of various sizes of aggregate. Most of the air voids between the materials are filled with particles. It results in an even gradation curve. Narrow gradation –has aggregate of approximately the same size. The curve on the gradation graph is very steep, and occupies a small range of the aggregate. Types of gradation relative to aggregate nature Gap gradation – A gap gradation refers to an sample with very little aggregate in the medium size range. This results in only coarse and fine aggregate. Types of gradation relatively to the aggragate nature Open gradation – An open gradation refers an aggregate sample with very little fine aggregate particles. Rich gradation – A rich gradation refers to a sample of aggregate with a high proportion of particles of small sizes. Types of Gradation  gradation Unsatisfactory gradation may lead to: 1. Segregation of the mortar from the coarse aggregates. 2. Bleeding of water below and around larger aggregates and on the surface of the concrete. 3. Settling of aggregates, leaving paste in the top layer of the concrete. 4. Use of chemical admixtures in order to restore workability to the concrete. 5. Increased use of cement. 6. Insufficient air entrainment and air-void distribution. 7. Excessive use of water. 8. High porosity of the hardened concrete. 9. High material costs. 10. Reduced service life.  Effect of Void Spaces between aggregates in concrete Strength and Durability: The presence of voids can reduce the overall strength and durability of concrete. Voids act as weak points where cracks can initiate and propagate, leading to structural failure  Effect of Void Spaces between Aggregates in Concrete Workability: The amount of void space affects the workability of concrete. More voids require more cement paste to fill the gaps, which can make the mix less workable. Conversely, fewer voids can improve workability but may compromise strength Effect of Void Spaces between Aggregates in Concrete Permeability: Increased void spaces can lead to higher permeability, allowing water and other harmful substances to penetrate the concrete. This can accelerate the deterioration process, especially in environments exposed to freeze- thaw cycles or chemical attacks  Effect of Void Spaces between aggregates in concrete Economy: The void content influences the amount of cement paste needed. A higher void content means more paste is required, increasing the cost of the concrete mix. Optimizing the aggregate size distribution to minimize voids can reduce costs while maintaining desired properties Effect of Void Spaces between aggregates in Concrete Thermal and Elastic Properties: Aggregates define the thermal and elastic properties of concrete. Voids can affect these properties by altering the density and homogeneity of the mix  Effect of Moisture Content of Aggregates on Concrete Workability: Aggregates with higher moisture content can improve the workability of the concrete mix. However, if the moisture content is too high, it can lead to segregation and bleeding  Effect of Moisture Concrete of Aggregates on Concrete Water-Cement Ratio: Excess moisture in aggregates increases the effective water-cement ratio, which can reduce the strength and durability of the concrete. Conversely, if the aggregates are too dry, they can absorb water from the mix, leading to a lower effective water-cement ratio  Effect of Moisture Content of Aggregates on Concrete Volume Stability: Changes in moisture content can cause volume changes in aggregates, leading to potential cracking and other structural issues in the concrete Mix Proportions: Accurate measurement of aggregate moisture content is essential for adjusting mix  Effect of Moisture Content of Aggregates on Content Strength and Durability: Properly controlled moisture content ensures that the concrete achieves its desired strength and durability. Variations in moisture content can lead to inconsistent concrete quality  Effect of Moisture Content of Aggregates on Concrete Volume Stability: Changes in moisture content can cause volume changes in aggregates, leading to potential cracking and other structural issues in the concrete Mix Proportions: Accurate measurement of aggregate moisture content is essential for adjusting mix AGGREGATES MOISTURE CONTENT The varying moisture contained on aggregates is one of the major causes of inconsistency in batching concrete from one batch to another. Moisture content can have dramatic effect on the concrete STRENGTH and DURABILITY influenced by the W/C ratio. Knowing the moisture content on aggregates Concrete can be Batched accurately by adjust the amount of water to be added to the mix. http://www.fiorigroup.com/concrete-facts/ why-it-is-so-important-tomeasure-moistur  Alkali Silica Reaction chemical reaction that occurs between the alkaline cement paste and reactive silica found in many common aggregates. This reaction causes expansion and cracking in concrete which leads to structural issues  Alkali Silica Reaction ASR is triggered by the reaction between hydroxyl ions in the alkaline cement pore solution and reactive forms of silica in the aggregate. This reaction produces a gel that e xpands when it absorbs water, exe rting pressure and causing cracks  Quality of aggregates Aggregate must posses: a high degree of strength; and stability to resist Degradation Static and dynamic Stresses Impacts and wearing action to which it is exposed  Common applications underlying material for foundations base course for pavements filler materials for Portland cement concrete up to 75 % of the volume and up to 85% of the weight filler materials for asphaltic concrete up to 80 % of the volume an dup to 96+ % of the weight drainage barrier behind retaining walls, etc  PROPERTIES OF THE RCA increased water absorption  decreased bulk density  decreased specific gravity  increased abrasion loss  increased crushability  increased quantity of dust particles  increased quantity of organic impurities if concrete is mixed with earth during building demolition  Possible content of chemically harmful substances, depending on service conditions in building from which the demolition and crushing recycled aggregate is obtained.  benefits from RCA No Landfill Dumping Charge Less Transport to landfill Lower air pollution Lower Gas emissions Lower energy consumption Less noise generated Separated steel from old concrete is resold. references TAYLOR, G.D. and Smith B. J. (1992) Materials in construction: 6th impression, Ed, Longman Scientific and Technical Harlow, Pearson Education Ltd. UK.pp 10-20 NEVILLE, A.M. and BROOKS, J.J (1987) Concrete technology. Longman Scientific and Technical, Harlow. Ch. 3. TAYLOR, G.D. (2001) Materials in construction: an introduction, 3rd Ed, Harlow, Pearson Education Ltd. pp 51-60. Relevant British Standards (as mentioned in text) available through the Construction Information Service or British Standards Online (electronic databases available through the Learning Centres web page).