Cement - Module 1 - PDF

Module 1: Cement Main compounds: Concrete - Most important: 𝐶3𝑆 (alite) and 𝐶2𝑆 Basic Components: (belite) -...

Module 1: Cement Main compounds: Concrete - Most important: 𝐶3𝑆 (alite) and 𝐶2𝑆 Basic Components: (belite) - Cement, Water, Aggregates (Coarse - 𝐶3𝑆 is responsible for strength at early [gravel] or fine [sand]) - Others (Admixture) ages. An artificial stone made by binding particles of - 𝐶2𝑆 is responsible for strength at late inert materials with a paste of cement and water. ages. From “opus caementitium”. - 𝐶3𝐴 is responsible for the combination of cement + water = cement paste lime and silica. cement + aggre (fine) = mortar - 𝐶4𝐴𝐹 responsible for silicates (𝐶3𝑆 and cement + aggregates (coarse) = concrete (water is the adhesive) 𝐶2𝑆). - Gypsum prevents “flash setting”. Cement A material with cohesive and adhesive properties capable of bonding mineral fragments into a compacted whole. Portland cement (where it came from), Hydraulic cement (property being Hydraulic) calcareous material + argillaceous material - calcium (from limestone), silicon (sand), aluminum(clay, shale) iron (clay, slag, limestone) Portland Cement 1824, Joseph Aspdin Heated finely ground limestone and clay. Resembled quarried stone found in Isle of Portland. Hydraulic Cement Set and become adhesive due to the chemical reaction between dry ingredients and water. This allows setting in wet conditions or underwater and further protects the gardened material from chemical attack. Retains strength and stability even underwater. Production of cement consumes approx. 6% of the world's energy. Hydration of Cement The cement industry produces 5% of the global man-made CO2 emission. Hydration Products: When limestone is heated: - Calcium-Silicate-Hydrate Gel (C-S-H gel) 𝐶𝑎𝐶𝑂3 + Heat => CaO + 𝐶𝑂2 - Calcium Hydroxide (𝐶𝑎(𝑂𝐻)2) - 𝐶3𝑆 hydrates faster than 𝐶2𝑆. Manufacturing of Cement Four main processes: - 𝐶3𝑆 produces more C-S-H gel than 𝐶2𝑆. - Grinding raw materials - 𝐶2𝑆 produces less 𝐶𝑎(𝑂𝐻)2. - Mixing raw materials - 𝐶3𝐴 hydrates fastest. - Burning materials to from clinker - Grinding materials into powder Heat of Hydration Main components: The quantity of heat per gram of unhydrated - calcium (from limestone) cement evolved upon complete hydration at a - silicon (sand) given temperature. - aluminum(clay, shale) “Exothermic” - iron (clay, slag, limestone) Dependent on chemical composition of cement.  Types of Portland Cement Properties of Cement 1. Fineness Blaine Air Permeability Method - “Specific surface” - Affects: rate of hydration, cost of grinding, gypsum requirement, long term behavior of concrete. Sieve Analysis 2. Specific Gravity Density of Hydraulic Cement SG = Dcement / Dwater Sg = m / V Uses Le Chatelier flask Uses kerosene or naphtha Standard SG of cement = 3.15 3. Setting Time Selective hydration of silicates + temperature Additional Types of Portland Cement rise Type IA, IIA, and IIIA are cements used to make 4. Soundness air-entrained concrete. Ability of cement to not undergo a large change Same properties as types I to III, but with the in volume. exception of possessing small quantities of Expansion due to reactions from: Free Lime, air-entrained materials shared and combined Magnesia, Calcium Sulphate with them. Autoclave test 5. Strength Types of Blended Cement Tests done on Mortar Type IS-Portland blast furnace slag cement Compressive Strength (ASTM C 109) (Lower early strength, lower heat of hydration) Tensile Strength (ASTM C 190) Type IP and Type P-Portland-pozzolan cement Flexural Strength (ASTM C 348) (Cheaper) Type I(PM) - Pozzolan-modified portland cement Different kinds of Cement Type S-Slag cement Type I(SM) - Slag-modified portland cement. Portland cement and blended cement - Blended hydraulic cements are Pozzolans produced by intimately and uniformly Are siliceous/ aluminous materials which intergrinding or blending two or more possess little or no cementitious value but which types of fine materials. will, in finely divided form and in the presence of - Primary materials are portland cement, water, react chemically with calcium hydroxide ground granulated blast furnace slag, fly at ordinary temperature to form compounds ash, silica fume, calcined clay, other possessing cementitious properties. pozzolans, hydrated lime, and pre-blended combinations of these materials.  - lacks bond between smooth Module 2: Aggregates surface and cement paste - Angular: Aggregates - exhibits a better interlocking Occupies 3/4th of the volume of concrete. effect good for use in roads and Inert and inexpensive material dispersed pavements throughout the cement paste. - higher bond strength due to Affects: Workability -> Strength -> Durability larger surface area Natural: Sand, Gravel, Crushed rock - due to high surface area, it Artificial: Broken brick, slag, sintered fly ash requires more water for certain Properties based from parent rock: workability (thus high w/c) - Chemical and mineral composition - Crushed aggregates with cubical - Petrographic classification shapes are ideal for high strength - Specific gravity concrete - Hardness - Some specialized crusher are created - Strength for this purpose (e.g. hydrocone - Physical and chemical stability crusher) - Pore structure - Color Classification by Texture Properties that differ from parent rock: Depends on: - Particle shape - Hardness, grain size, and pore structure - Particle size of parent rock - Surface texture - Degree of weathering - Absorption - Closely associated with shape (rounded Classified by type, size, shape, and texture. – smooth, angular – rough) Classification by Size Coarse aggregates ≥ 5 mm Fine aggregates < 5 mm but > 0.07 mm Maximum size: - ⅕ narrowest form dimension - ⅓ slab depth - ¾ clear distance between bars Classification by Shape Roundness measures the relative sharpness or angularity of the edges and corners of a particle. Affected by: - Strength and abrasion resistance Mechanical Properties - Amount of wear Have something to do with strength performance. Listed below are the mechanical properties of aggregates: - Bond - Due to the interlocking of the aggregate and the paste owing to the roughness and area of the surface of the aggregate. - No existing test method. - Strength - Compressive strength of Affects: concrete cannot significantly - Void content exceed that of the major part of - Bond area the aggregate contained - Water requirement therein. - Durability - Tested indirectly: Some claims about shape and texture: - Crushing strength of - Round -> smooth textured rock samples and bulk - yields poor concrete aggregates  - Aggregate performance - Tested indirectly -> aggregate crushing value Bulk density (unit weight) - measures the - is the ratio of the weight of aggregate to resistance of aggregate its compacted volume. The aggregate is against a gradually dry, and the volume includes the spaces applied compressive in between particles. load (allowed: 25% , - In kg/m^3 45%). - Concrete mix proportioning uses bulk - Toughness density - Resistance to impact. - Together with specific gravity, void ratio - Hardness of a sample can be determined - Resistance to wear. - ASTM C 29 - Relating aggregate strength to concrete - Depends on: Method and extent of strength: compaction, Shape and size distribution - Concrete strength is not directly of aggregates related to aggregate strength - Porosity - Strong aggregate -> strong - Affects: concrete - Bond between constituents - depends on the - Resistance to freezing and strength quality of thawing cement paste and bond - Chemical stability between paste and - Resistance to abrasion aggregates. - Specific gravity - Weak aggregates -> weak - Also affects workability and durability concrete Soundness - Ability of aggregates to resist excessive Physical Properties changes in volume as a result of Moisture content changes in physical conditions (freezing - Amount of moisture present in the & thawing, variation in temp, alternate aggregate. wetting & drying) - Affects water requirements. - Effect: Local scaling -> surface cracking - ASTM C 566, ASTM C 70 -> disintegration Absorption Alkali-aggregate reaction (ASR/ACR) - The ratio of the increase in weight of the - Due to reactions: saturated sample to the weight of the - Alkali in cement + active silica oven-dried sample. - Alkali in cement + carbonate Specific gravity (results to formation of alkali - Specific gravity (SSD) silicate gel which swells - Specific gravity (OD) unlimitedly) - Apparent specific gravity Grading - Coarse aggre (ASTM C 127), fine aggre - Mortar – max. 55% aggregate by (ASTM C 128) volume - Most useful in concrete design mix - Concrete – max. 85% aggregate by - Allows for the conversion of volume into volume weights, vice versa - has an important role in concrete’s - Ave SG for rocks = 2.6 to 2.8; Ave SG workability and its finishing for sand = 2.4 to 2.6 characteristics - Most important in producing workable concrete is aggregate’s graduation Sieve Analysis Basic method to determine grading Simple orientation of dividing an aggregate sample into fractions, each consisting of particles of the same size Grading Curve  Graphical representations of the results of sieve Set Retarders analysis - Admixture that SLOWS DOWN the Grading affects workability more than strength hydration so that concrete would remain plastic and workable for a longer period Fineness Modulus - Delay the setting and hardening of The sum of the cumulative percentages retained concrete on the sieves of the standard series Water-Reducers (Plasticizers) Sieves for FA: 10, 5, 2.5, 1.2, 0.6, 0.3, 0.15 mm - Increases workability without excess Sieves for CA: 40, 20, 10, 5, 2.5 mm use of water - Surface-active agents Module 3: Water & Admixtures - creates repulsion effect between the particles and Water results in stabilizing their Usually water is specified only in terms of dispersion quantity rather than quality - Effects: A good concrete mix usually have about 140 to 1. Reduce water content 200 liters / cu.m. but depend on size of 2. Increase workability aggregates 3. Improve hydration Potable water is acceptable 4. Increase early strength No impurities must be present Superplasticizer - High range water reducing agent Seawater (HRWRA) there is an increase in study that explores the - Permits reduction of water up to 30% possibility of using seawater for concrete mixing w/o reduction in workability Potential: - Effects: Increase in early strength, - Does not significantly reduce concrete workability is improved for short duration strength Others - Slightly accelerates the early strength of - Air-Entraining (Gas-Forming) concrete - Permeability Reducing (Air-Detraining) Minor concern/s: - Waterproofing - Slightly reduces the 28-day strength by - Expansion Producing 10-15% - Anti-bacterial - May cause efflorescence and persistent dampness Mineral Admixtures - Not advisable for plastering purpose Includes Pozzolans (refer to module 1) Main concern (under debate): Pozzolanic Reaction - Corrosion in reinforced concrete - Pozzolan + Calcium hydroxide + water = members C-S-H - Reaction is slow Admixtures in Concrete - Heat of hydration and strength Compliance: development is slow 1. Water reduction and setting time Effects of Pozzolan modification: ASTM C494M; - Reduce bleeding and segregation 2. Producing flowing concrete: ASTM - Reduce temperature rise C1017M; - Improve resistance to concrete attack 3. Air entertainment: ASTM C260M; (i.e. ASR, sulphate attack, seawater) 4. Inhibiting chloride-induced corrosion: - Improve workability ASTM C1582M. - Increase strength at later age - Lower the heat of hydration and thermal Chemical Admixtures shrinkage Accelerator - Increase the watertightness - accelerate the hardening or the Types of Pozzolan development of early strength of - Natural concrete - either a raw or calcined natural - Benefits: permits earlier removal of material that has pozzolanic forms, reduces required period of properties curing, advances the time that a - volcanic ash or pumicite, structure can be made in service, opaline, metakaolin, shales and emergency repair works, etc. some diatomaceous earths  - Artificial mixture so that their distribution - Fly-Ash: is no longer uniform - a by-product of coal - Two forms: separation of combustion, a finely divided coarser particles; of grout residue, most widely used - Causes: pozzolanic material ➔ Difference in aggregate - Silica Fume: sizes - a by-product resulting from the ➔ Manner of transporting, reduction of purity quartz with handling, and placing of coal to produce silicon or concrete ferrosilicon alloys ➔ Improper vibration - Available in: As-produced silica - Segregation resistance: Ability fume, Silica fume slurry of the concrete to remain ,Densified silica fume, uniform for a period of time Pelletized silica fume - Cohesion: Intermolecular attraction by which the particles Module 4: Properties of Fresh Concrete of a body are united throughout the mass Fresh Concrete 5. Bleeding A freshly mixed material that can be molded in - a form of segregation which any shape some of the water in the mix Characterized by: tends to rise to the surface of 1. Workability freshly placed concrete - The amount of useful internal - Caused due to the inability of work necessary to produce full solid constituents to hold all of compaction the mixing water when they - Internal work: the work or settle energy required to overcome 6. Setting time the internal friction between the - Time required for the mortar to individual particles in concrete reach the specified value of - The ability to be easily placed resistance to penetration onto forms - Initial setting time -> final setting - The ability to easily compact or time consolidate concrete - Penetrometer test - Slump, flow, flow table, ball 7. Shrinkage penetration test - Caused by loss of water by - FACTORS affecting: evaporation or by hydration of ➔ Water content cement and carbonation ➔ Maximum size of - Types: aggregate ➔ Plastic: Caused by loss ➔ Aggregate grading, of water by evaporation ➔ shape, and texture and suction by dry Initial setting time cement ➔ Temperature and ➔ Autogeneous: Loss of Humidity (loss of water) water used up in 2. Density hydration - Test method in ASTM C 138 ➔ Drying - If the density is known, the volume of concrete can be Module 5: Fresh Concrete Operations found from the mass of the ingredients 1. Batching 3. Air Content Preparing or measuring quantities of the - Entrained air or entrapped air concrete constituents - Test methods: gravimetric, Two methods: volumetric, pressure - By weight 4. Cohesion and Segregation - By volume - Segregation: separation of the 2. Mixing constituents of a heterogeneous Objectives:  - To coat the surface of - Agitator trucks aggregate particles with cement - Water is added at paste central plant and mixing - To blend concrete ingredients occurs during into a uniform mass transportation Manual Mixing - Transit mixers - Mixing by hand - Water is added while Machine Mixing being transported - Tilting Drum Mixer For handling: - Either one-bagger or - Buckets two-bagger - Wheelbarrow - Chamber or the drum is - Concrete buggies TILTED for discharging - Belt conveyors (even during the mix) - Portalifts Pumping - Non-Tilting Drum Mixer - Crane and bucket (Reversing drum) 4. Placing - Axis of the drum is Deposit concrete as close as possible to ALWAYS horizontal its final position to avoid segregation - Chute is used during and obtain full compaction discharge Methods: Chute, Tremie, Flexible drop - Rotation can also be chute reversed to discharge 5. Compacting and Vibrating - Susceptible to Purpose of vibrating: segregation - To remove entrapped air - Pan-Type mixer - Filing up the forms - Efficient with stiff and - Ensure uniform mix cohesive mixes Methods: - Scraping action at the - Manual and mechanical means sides of the mixer (due By hand: by rodding or ramming to its revolving star of Internal vibrators blade (scrapes or - Poker or immersion vibrators paddles) - 12000 cycles per minute - Terminologies: External vibrators - Charging the mixer: - For precast or thin in-situ putting the ingredients sections in the mixer - Rigidly clamped onto the - Buttering: coating the formwork resting in an elastic sides of the mixer with support so both form and an initial amount of concrete are vibrated mortar - 3000-6000 cycles per minute - Mixing Time Vibrating tables - Dependent on: - Formwork is clamped to a vibrator in - Size and type of mixer precast concrete or in testing - Speed of mixer rotation - 1500-7000 cycles per minute - Quality of blending of Revibration the ingredients - For concrete placed in layers Intermittent Mixing - Purposes: Reduce settlement cracks; - Does not affect strength and internal effects of bleeding durability 6. Curing - Workability decreases with time procedures used for promoting unless loss of moisture is hydration of cement prevented in the mixer Consists of: - Retempering: adding - Control of temperature water to restore - Moisture movement to and from workability the concrete 3. Transporting/Handling Purpose: For transporting: Methods: Ponding, Plastic sheets, - Dump trucks waterproof paper, spraying, wet burlaps, - for short distances etc. Ready-Mixed Concrete Poisson’s Ratio Types: - Ratio of transverse strain to the strain in - Central-mixed the direction of uniaxial loading - Batched and mixed at central - Range: 0.15 to 0.20 plant Tensile Strength - Transit-mixed - Tensile strength develops faster than - Batched at central plant and compressive strength mixed in mixer trucks - Range: 10-15% of fc’ at 14 days Advantages - Method: Splitting Tensile Test - Close quality control of batching 𝐹𝑟 = 0. 62 𝑓𝑐' - Use on congested site Shear Strength - Use of agitator trucks to ensure care of - Pure shear seldom occurs transportation - Diagonal tension: combination of shear - Convenience when small quantities of and flexure concrete or intermittent mixing is - Range: 35 - 80% of fc’ required Impact Strength Disadvantages - Important for concrete piles, foundations - Maintaining workability up to the time of for machines, or when accidental impact placing is possible - Cost is relatively higher - Range: 30 - 80% greater than compressive strength Creep Module 6: Properties of Hardened Concrete - Long term deformation due to application of sustained loads Strength Shrinkage Gives an overall picture of the quality of - Drying shrinkage: due to loss of concrete because it is directly related to the adsorbed water structure of cement paste - Most detrimental property of concrete Strength of concrete comes from: - Strength of cement - Strength of aggregate - Strength of bond Mechanical Properties Compressive Strength - Tested on concrete cylinders or cubes - Usually 6” by 12” (as per NCSP) Stress-Strain Diagram - Behaves elastically until 50%fc’ - Nonlinear afterwards due to microcracking - fc’ usually attained at 0.002 to 0.003 strain - Concrete would experience permanent strain after unloading Modulus of Elasticity - Influenced by aggregate properties - The higher the aggregate modulus of elasticity, the higher concrete modulus of elasticity - Moisture condition is a factor - A wet specimen has higher modulus of elasticity 1.5 𝐸𝑐 = 𝑊𝑐 0. 04 𝑓𝑐' - For normal weight concrete: 𝐸𝑐 = 4700 𝑓𝑐' Examples for Quizzes and Notes: