Aggregates 1.2 PDF

1.2 Aggregates Aggregate Concrete Cement paste Aggregate (Coarse + fine) – granular material (or rock) that are suitable to use in concrete or asphaltic mixture  Classification of Aggregate 1. By Source A. Natural-result of a) weathering e.g. sand...

1.2 Aggregates Aggregate Concrete Cement paste Aggregate (Coarse + fine) – granular material (or rock) that are suitable to use in concrete or asphaltic mixture  Classification of Aggregate 1. By Source A. Natural-result of a) weathering e.g. sand and gravel or b) crushing (crushed stone). Come from 3 major groups of rock: Igneous rocks Sedimentary Metamorphic B. Artificial. By product of other industrial process e.g. slag from blast furnace Manufactured for special purpose 2. By Mineral Composition 3. By size  Igneous Rocks Igneous – formed from molten rock either above or below the earth’s surface i. extrusive – formed above the earth’s where they cool quickly to form small crystals. Some cool so quickly that they form an amorphous glass. - dark in color, fine grained, vesicular structure ii. Intrusive-formed below the earth’s surface (slow cooling) and the slow cooling allows large crystals to form. e.g. granite Igneous Rocks  Sedimentary Rocks Sedimentary-formed from disintegration of other rocks and deposited as sediments e.g. sandstone, limestone, shale Sedimentary rocks are produced by the weathering of preexisting rocks and the subsequent transportation and deposition of the weathering products. Weathering refers to the various processes of physical disintegration and chemical decomposition that occur when rocks at Earth’s surface are exposed to the atmosphere (mainly in the form of rainfall) and the hydrosphere. Sedimentary Rocks Sedimentary Rocks  Metamorphic Rocks Metamorphic-igneous or sedimentary rocks that have crystallized with heat and pressure. Hard and dense e.g. quartz, marble Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock (protolith) is subjected to temperatures greater than 150 to 200 °C (300 to 400 °F) and, often, elevated pressure of 100 megapascals (1,000 bar) or more, causing profound physical or chemical changes. There are two basic types of metamorphic rocks. Foliated metamorphic rocks have a layered or banded appearance that is produced by exposure to heat and directed pressure. Non-foliated metamorphic rocks do not have a layered or banded appearance. Metamorphic Rocks Aggregate B. Artificial i. By product of other industrial process e.g. slag from blast furnace-sp.g.of slag 2.0- 2.5 sp. G. of natural aggregate 2.3- 3.2 ii. Manufactured for special purpose e.g. lightweight aggregate 2. By Mineral Composition 3. By size i. coarse aggregate – larger than No. 4 sieve (4.75 mm or 3/16”) ii. fine aggregate – smaller than NO. 4 sieve Aggregate Functions of Aggregate in concrete: Economy Strength Reduces shrinkage or expansion Characteristics of Aggregates Hard, strong and durable Free of organic impurities Low alkali reactivity with cement Proper gradation Aggregate Aggregate Beneficiation-process to remove deleterious material from aggregate Washing-fine particles coatings are washed away by water Heavy media separation(or sink float method)- aggregates are passed through an artificial heavy liquid composed of water and magnetite or ferrosilicon. Lighter particles float to the top and can be removed. Lighter material float to the top Aggregate Jigging-upward pulsations of water or air is applied through aggregate kept in a box with perforated. Organic impurities (ASTM C40). Determines the presence of injurious organic compounds in natural sands. Soaking sand in sodium hydroxide. Classes of Aggregates Density of water  Terminologies A=mass of oven dry test sample in air, g B=mass of saturated surface dry test sample in air, g C=apparent mass of saturated test sample in water., g. W=density of water at certain temperature absorption, n—the increase in mass of aggregate due to water penetration into the pores of the particles during a prescribed period of time, but not including water adhering to the outside surface of the particles, expressed as a percentage of the dry mass. Average Absorption Value—When the sample is tested in separate size fractions, the average absorption value is the average of the values as computed above, weighted in proportion to the mass percentages of each size fraction present in the original sample. A1,2,n=absorption percentages for each size fraction P1,2,n = mass percentages of each size fraction present in the original sample.  Terminologies oven-dry (OD), adj— related to aggregate particles, the condition in which the aggregates have been dried by heating in an oven at 110 ± 5 °C for sufficient time to reach a constant mass. saturated-surface-dry (SSD), adj—related to aggregate particles, the condition in which the permeable pores of aggregate particle are filled with water to the extent achieved by submerging in water for the prescribed period of time, but without free water on the surface of the particles. density, n—the mass per unit volume of a material, expressed as kilograms per cubic meter, or gram per cubic centimeter (pounds per cubic foot).  Terminologies density (OD), n—the mass of oven dry aggregate per unit volume of aggregate particles, including the volume of permeable and impermeable pores within the particles, but not including the voids between the particles. density (SSD), n—the mass of saturated-surface-dry aggregate per unit volume of the aggregate particles, including the volume of impermeable pores and permeable, water-filled pores within the particles, but not including the voids between the particles.  Terminologies apparent density, n—the mass per unit volume of the impermeable portion of the aggregate particles. relative density (specific gravity), n—the ratio of the density of a material to the density of distilled water at a stated temperature; the values are dimensionless. relative density (specific gravity) (OD), n—the ratio of the density (OD) of the aggregate to the density of distilled water at a stated temp  Terminologies relative density (specific gravity) (SSD), n—the ratio of the density (SSD) of the aggregate to the density of distilled water at a stated temp. apparent relative density (apparent specific gravity), n—the ratio of the apparent density of aggregate to the density of distilled water at a stated temperature. Aggregate Dry rodded unit weight Used in mix design calculation  Aggregate Tests to characterize aggregates: Tests to Characterize Description Fine Coarse Aggregates Aggregates Aggregates Sieve Analysis Grading of ASTM C136 ASTM C136 Aggregates/fineness modulus Unit Weight Specific gravity and ASTM C128 ASTM C127 absorption Natural Moisture Content Total Evaporable Moisture ASTM C566 ASTM C566 Content of Aggregate Bulk Density Test Dry rodded unit weight ASTM C29 ASTM C29 Resistance to Degradation resistance to degradation ASTM C131 using the Los Angeles testing machine Sieve Analysis  Fineness Modulus of Fine Aggregates Fineness modulus – the sum of the cumulative percentages retained on #4, #8,#16, #30, 350 and #100 sieve divided by 100. Used only on sand passing 3/8” sieve. Example: Sieve size Cumulative % Cumulative % retained passing 3/8” 100 0 #4 98 2 #8 91 9 #16 63 37 #30 38 62 #50 15 85 #100 4 96 SUM 291 FINENESS MODULUS 291/100=2.91  Fineness Modulus of Fine Aggregates Fineness modulus of fine aggregate varies from 2.0 to 3.5mm. Various values of fineness modulus for different sands are detailed below. Type of sand Fineness modulus range Fine sand 2.2 – 2.6 Medium sand 2.6 – 2.9 Coarse sand 2.9 – 3.2 Fine aggregate having fineness modulus more than 3.2 should not considered as fine aggregate.