Aggregates for Concrete PDF

CHAPTER 6 AGGREGATES FOR CONCRETE AGGREGATE FOR CONCRETE ▪ The importance of using the right type and quality of aggregates cannot be overemphasized. ▪ The aggregates strongly influence the concrete’s freshly mixed and hardened properties. Design and Control of Concrete...

CHAPTER 6 AGGREGATES FOR CONCRETE AGGREGATE FOR CONCRETE ▪ The importance of using the right type and quality of aggregates cannot be overemphasized. ▪ The aggregates strongly influence the concrete’s freshly mixed and hardened properties. Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 6; 2 FINE AGGREGATE (F.A.) ▪ Sand and/or crushed stone ▪ Most particles < 5 mm ▪ F.A. content usually 35% to 45% by mass or volume of total aggregate Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 6; 3 COARSE AGGREGATE (C.A.) ▪ Gravel and crushed stone ▪ Most particles  5 mm ▪ Typically between 10 mm and 40mm Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 6; 4 ROCK AND MINERAL CONSTITUENTS IN AGGREGATES 1. Minerals 2. Igneous rocks 3. Metamorphic rocks 4. Sedimentary rocks Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 6; 5 NORMAL-DENSITY AGGREGATE – CSA A23.1 Most common aggregates: ▪ Sand ▪ Gravel ▪ Crushed stone Produce normal-density concrete 2200 to 2400 kg/m3 Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 6; 6 AGGREGATE CHARACTERISTICS AND TESTS (1) Characteristic Test* Resistance to abrasion CSA A23.2-16A, 17A, 23A and degradation ASTM C131, C535, C779 Resistance to freezing CSA A23.2-24A and thawing ASTM C666, C682 Resistance to CSA A23.2-9A disintegration by ASTM C88 sulphates Particle shape and CSA A23.2-13A surface texture ASTM C295, D3398 Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 6; 7 AGGREGATE CHARACTERISTICS AND TESTS (2) Characteristic Test* CSA A23.2-2A, 5A Grading ASTM C136, C117 Density CSA A23.2-10A, ASTM C29 Relative density (specific CSA A23.2-6A, 12A density) ASTM C127, C128 Absorption and surface CSA A23.2-6A, 11A, 12A moisture ASTM C128, C70, C127, C566 Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 6; 8 AGGREGATE CHARACTERISTICS AND TESTS (3) Characteristic Test* Compressive and flexural CSA A23.2-8C, 9C strength ASTM C78, C39 Definitions of constituents ASTM C125, C294 CSA A23.2-3A, 4A, 5A, 7A, 8A Aggregate constituents ASTM C142, C123, C117, C40, C87, C295 Resistance to alkali CSA A23.2-14A, 25A, 26A, reactivity and volume ASTM C227, ASTM C289, C295, C586, change C342, C1293, C1260 Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 6; 9 GRADING OF AGGREGATE ▪ Grading is the particle-size distribution of an aggregate as determined by a sieve analysis using wire mesh sieves with square openings ▪ CSA A23.1 ▪ F.A. – 8 standard sieves with openings from 80 μm to 10 mm ▪ C.A. – sieves with openings from 1.25 mm to 112 mm Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 6; 10 RANGE OF PARTICLE SIZES Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 6; 11 GRADING LIMITS Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 6; 12 Aggregates of various sizes are used to reduce the total volume of voids between aggregates thus requiring less paste to fill the voids. REDUCTION OF VOIDS Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 6; 13 COARSE AGGREGATE GRADING ▪ Maximum size ― is the smallest sieve that all of a particular aggregate must pass through ▪ Nominal maximum size ― is the smallest sieve size through which the major portion of the aggregate must pass ▪ The nominal maximum size sieve may retain 5% to 15% Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 6; 14 NOMINAL MAXIMUM SIZE OF AGGREGATE (1) Size should not exceed: ▪ 1/5 of the narrowest dimension between sides of forms ▪ 3/4 of the minimum clear spacing between rebars and between rebars and the form ▪ 1/3 depth of the slabs Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 6; 15 NOMINAL MAXIMUM SIZE OF AGGREGATE (2) ▪ For concrete exposed to: ▪ Earth/weather ― 2/3 specified cover* ▪ Chlorides ― 1/2 specified cover* ▪ The specified cover for concrete not exposed to earth/weather* ▪ 1/3 internal diameter of hose/pipe or 40 mm whichever is smaller when pumping Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 6; 16 BULK DENSITY, RELATIVE DENSITY AND DENSITY OF AGGREGATES ▪ Bulk density: the mass of aggregate required to fill a container of a specified unit volume (Aggregate & Voids). ▪ Relative density (Specific Gravity): ratio of the mass of a certain aggregate to the mass of an equal absolute volume of water. ▪ Density: Determined by multiplying the relative density of the aggregate by the density of water (Kg/m3) Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 6; 17 MOISTURE CONDITIONS OF AGGREGATE S.S.D. Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 6; 18 ABSORPTION AND SURFACE MOISTURE ▪ Measured so the total water content of the concrete can be controlled, and correct batch quantities determined. Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 6; 19 RESISTANCE TO FREEZING AND THAWING ▪ The cracking of concrete pavement caused by the freeze-thaw deterioration of the aggregate within the concrete is called D-Cracking. ▪ Water naturally accumulates at the base and sub- base layers under the concrete. When this water goes through freeze-thaw cycles, it wears on the durability of the concrete and begins to crack in the aggregate starting at the base of the concrete working its way to the surface. ▪ Since the cracking begins beneath the surface it is hard to detect D-Cracking before it becomes visible on the surface of the pavement. Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 6; 20 D-CRACKING D-CRACKING ALONG A FRACTURED CARBONATE TRANSVERSE JOINT AGGREGATE PARTICLE Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 6; 21 POTENTIALLY HARMFUL MATERIALS ▪ Organic impurities ▪ Silt ▪ Clay ▪ Shale ▪ Iron oxide ▪ Coal ▪ Lignite ▪ Low density and soft particles Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 6; 22  HARMFUL MATERIALS IN AGGREGATES (1) Substances Effect on concrete Test designation Affects setting and CSA A23.2-7A, 8A Organic hardening, may cause impurities ASTM C40, C87 deterioration Materials finer CSA A23.2-5A Affects bond, increases than the 80µm water requirement ASTM C117 sieve Coal, lignite, or other low- Affects durability, may cause CSA A23.2-4A density stains and popouts ASTM C123 materials Soft particles Affects durability ASTM C 235 Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 6; 23  HARMFUL MATERIALS IN AGGREGATES (2) Substances Effect on concrete Test designation Clay lumps Affects workability and CSA A23.2-3A, and friable durability, may cause ASTM C142 particles popouts Chert of less Affects durability, may cause CSA A23.2-4A than 2.40 popouts ASTM C295, C123 relative density CSA A23.2-14A, 25A, 26A Alkali-reactive Causes abnormal expansion, ASTM C227, C289, C295, aggregates map cracking, and popouts C586, C1293, C1260 Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 6; 24  POPOUTS Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 6; 25 IRON PARTICLES IN AGGREGATES Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 6; 26 ALKALI- AGGREGATE REACTIVITY (AAR) ▪ Is a reaction between the active mineral constituents of some aggregates and the sodium and potassium alkali hydroxides and calcium hydroxide in the concrete ▪ Alkali-Silica Reaction (ASR) ▪ Alkali-Carbonate Reaction (ACR ) Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 6; 27 TYPICAL INDICATORS OF ASR ▪ Network of cracks ▪ Closed or spalled joints ▪ Relative displacements ▪ Fragments breaking off of the surface of the concrete (popouts) Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 6; 28 ALKALI-SILICA REACTION MECHANISM 1. Alkali hydroxide + reactive silica gel  reaction product (alkali-silica gel) 2. Gel reaction product + moisture  expansion Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 6; 29 FACTORS AFFECTING ASR ▪ Reactive forms of silica in the aggregate, ▪ High-alkali (pH) pore solution ▪ Sufficient moisture ▪ Those three conditions need to be present for ASR to occur Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 6; 30 CONTROLLING ASR ▪ Use non-reactive aggregates ▪ Use of supplementary cementing materials or blended cements ▪ Limit alkali loading ▪ Limestone sweetening (~30% replacement of reactive aggregate with crushed limestone) ▪ Lithium-based admixtures Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 6; 31 HANDLING AND STORING AGGREGATES ▪ Aggregates should be handled and stored in a way that minimizes segregation and degradation and prevents contamination by deleterious substances. Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 6; 32  RECYCLED CONCRETE AGGREGATE HEAVILY REINFORCED CONCRETE RECYCLED-CONCRETE AGGREGATE STOCKPILE CRUSHED BY A BEAMCRUSHER Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 6; 33 RECYCLED CONCRETE AGGREGATE Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 6; 34 QUESTIONS? Design and Control of Concrete Mixtures, 8th Canadian Edition Ch. 6; 35