ETC 1250 Lesson 04b - Lesson 4b ETC1250 - Properties of...

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Unformatted text preview: Lesson 4b ETC1250 - Properties of Materials 0 Chapter#4 « Pgs 161 - 186 Mixing Water lmpure water used for washing aggregates may coat the aggregates with chemicals Water should be free of especially — Organic material — Clay — Salts such as chlorides or sulfates Potable water or water with up to 3.5% salt may be used in the mixing of cement Questionable water may be used for concrete if mortar cubes made with the water have T and 28 day strengths equal to at least 90 percent of the strength of cubes made with water from a known source Aggregate Weight Barites. Iimonite. magnetic iron. and iron particles — Heavyweight concretes with weights going as high as 400 lb per cu ft Sand, gravel, and crushed stone — Normal-weight concrete weighing 135 to 180 lb per cu ft Expanded shales and clays — Structural lightweight concrete haying unit weights ranging from 85 to 1 15 lb per cu tt Vermiculite. pumice, and perlite — Lighter concretes weighing 15 to 90 lb percu fl — Insulating concretes Introduction « Concrete Ingredients — Mixing Water — Aggregates - Aggregate Shape - Aggregate Size — Admixtures « Proportioning Ingredients Aggregate = Strength - 60-80% of total volume — Aggregate transfers Load as shear and compressive torce components — The shear component IS resisted through a combination of friction and interlocKing of particles - Mix of large and small aggregate — fine material is used to fill the voids without separating the larger particles from contact with each other - Portland Cement — Binds with aggregate to form concrete holding the particles together Agg regates Shape and Size Matter - Particle shape and surface texture influence the properties of freshly mixed concrete more than the properties of hardened concrete Rough-textured, angular, and elongated particles require more water to produce workable concrete than smooth, rounded compact aggregate. Why? Consequently, the cement content must also be increased to maintain the water-cement ratio Agg regates Shape and Size Matter - Abrasion and skid resistance of an aggregate are essential when the aggregate is to be used in concrete constantly subject to abrasion as in heavy-duty floors or pavements Harder aggregate can be selected in highly abrasive conditions to minimize wear. Aggregate Size Max aggregate size for non-reinforced slabs on grade = 1;“3 depth of slab. Example g = 2.0-" ‘1 3 Use 2" maximum aggregate size Admixtures - Admixtures are any material other than Portland cement, aggregates, and water added to a concrete or mortar mix before or during mixing. - Admixtures are used to modify Portland cement concretes, used to improve — workability. — increase durability, — to retard or increase setting time and — improve resistance to freeze-thaw damage. — etc Aggregate Size Max aggregate size used in concrete for non-reinforced walls = 15 minimum wall thickness. Example: [Haul 15"= 3.0" 5 Use 3" maximum aggregate size Aggregate Size Max aggregate size for reinforced beams = 3M the clear space between rebar or rebar and forms. Member width 14" 2 - 1 1:2” covers -3" my. mm. 2 - U4" stirrups -1f2" 4 - #5 rebar -£ 1.4“ stirrup clear space 7 11’2" 7 132”:r 3 spaces =2-1f2'U’space Cover space = 1 1!2" Cover space is smaller 3:4"Rehau- 1 11’2" x 3M" = 1 11’8" |—14"—l Use 1" maximum aggregate Admixtures - Most popular are air-entraining elements, accelerators, retarders, and water retarders - Some admixtures perform more than one function. When air-entraining admixture is used, — increased resistance to freeze-thaw cycles — A reduction in bleedwater — and increased workability in the fresh concrete. - Sometimes the admixture produces adverse reactions — Some finely powdered workability admixtures tend to increase drying shrinkage Admixtures Air-entraining Admixtures — Increase The Workability OfThe Wet Concrete, — Reduce Freeze-thaw Damage, — Create Very Lightweight Nonstructural Concretes — With Thermal Insulating Properties. Water-reducing Admixtures — Allow A Reduction In The Amount OfMixing Water While Retaining The Same Workability, Which Results In A Higher— strength Concrete. Superplasticizers (High-range Water-reducing Admixtures} Organic Compounds That Transform Stiff Concrete Mix Into One That Flows Freely — Facilitate Placement OfConcrete Under Difficult Circumstances — Reduce The Water Content Of A Concrete Mix In Order To Increase Its Strength Admixtures Silica fume, also known as microsilica A byproduct of electronic semiconductor chip manufacturing. A powder of silicon dioxide approximately 100 times finerthan ortland cement — roduces extremely high strength concrete — Very low permeability. Blast furnace slag Is a byproduct of iron manufacture — Improve concrete workability, Increase strength, Reduce permeability, Reduce temperature rise during curing, Improve sulfate resistance. Pozzolans Are various natural or artificial materials that react with the calcium hydroxide in wet concrete to form cementing compounds. Reduce the internal temperatures of curing concrete Reduce the reactivity of concrete with aggregates containing sulfates. Improve' the workability of concrete Admixtures Freeze protection admixtures 7 Allow concrete to cure satisfactorily at temperatures as low as 20 degrees Fahrenheit Extended set-control admixtures — Delay the curing reaction in concrete for any period upto several days 7 Include two components: - The stabilizer component, added at the time Of initial mixing, defers the onset of curing indefinitely. - The activator component, added when desired, reinitiates the curing process Coloring agents Dyes and pigments used to alter and control the color of concrete — For building components whose appearance is important Admixtures - Accelerating Admixtures — Cause Concrete To Cure Rapidly - Retarding Admixtures — Slow Curing Time. - Fly Ash A Fine Powder Waste Product From Coal—fired Power Plants Increase Concrete Strength, Decrease Permeability, Increases Sulfate Resistance, Reduces Temperature Rise During Curing, Reduces MiXing Water, Improves Pumpability And Workability Of Concrete Admixtures - Workability agents — Improve the plasticity ofwet concrete to make it easierto place in forms and finish. — Includes pozzolans and air—entraining admixtures, along with certain fly ashes and organic compounds. - Corrosion inhibitors — Reduce rusting of reinforcing steel in structures that are exposed to road deicing salts or other corrosion-causing chemicals. - Fibrous admixtures Are short fibers, usually of glass, steel, or polypropylene — Act as microreinforcing. — Reduce plastic shrinkage cracking that sometimes occurs during curing ofslabs. — Glass—fiber—reinforced concrete (gfrc), used forcladding panels Proportioning Concrete Ingredients Four main ingredients in Concrete - Water - Cementitious Material — Portland Cement — Pozzolans — Etc - Fine Aggregate - Course Aggregate — Typically sand — Typically gravel or crushed rock I.._ _ 6"; Air ' *- ' fl— _" 11% Pornand Cement 41°, Gravel 04 Crushed Slone {Coarse Aggregate! 26'. Sand [Fine Aggregate: Preportiening Concrete Ingredients Waten'Cementetiens Mfltfllifll Ratie - Rule efthurnb = [3.45m 0.58 ' Strength IE ii'l'k'Ei‘E El‘j' propeniunal tD water EDI‘IEEI'It _ Farm ('1 [3-1 renur.tinn in the retie results in 1mm Increase nl' 3'3 day strengh Approximate propertiening fer the nun-engineer. Use 1:2:3 ‘1 part —Cementitieus Material - 2 parts ‘ Fine Aggegete - 3 parts —ceurse Aggregate MAE Himmfim l1"!- Gui-13H?" mm M ICU-ulsefiwum: “j MSaI-tllfinefiwwm __ 1W Assignment ' Page 224 Review Questions 5, E, 'r', 'ICIe, E: ‘Iflb If you do not understand a guestiem email me at temlinmfighecedu erthreugh myPHCfledu ...
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This note was uploaded on 01/05/2011 for the course DRAFTING A ETC 1250 taught by Professor Tomlinson during the Spring '10 term at Pasco-Hernando Community College.

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ETC 1250 Lesson 04b - Lesson 4b ETC1250 - Properties of...

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