Week 4 Chapter 4 Lec. SCM 2 PDF

2024-02-06 CIVI321 ENGINEERING MATERIALS Chapter #4 Supplementary Cementing Materials A.M. Soliman, PhD, P.Eng Assistant Professor Department of Building, Civil & Environmental Engineering (BCEE) 1 Supplementary Cementing Materials (SCMs) A material that, when used with Portland cement contributes t...

2024-02-06 CIVI321 ENGINEERING MATERIALS Chapter #4 Supplementary Cementing Materials A.M. Soliman, PhD, P.Eng Assistant Professor Department of Building, Civil & Environmental Engineering (BCEE) 1 Supplementary Cementing Materials (SCMs) A material that, when used with Portland cement contributes to the properties of the hardened concrete through: Hydraulic Activity or Pozzolanic Activity or Both. 2 1 2024-02-06 Supplementary Cementing Materials Pozzolans A siliceous or alumino-siliceous material that, in a finely divided form and in the presence of moisture, chemically reacts with a hydration product of Portland cement to form compounds possessing cementing properties. Fly Ash Silica fume Natural Pozzolans A natural material which may also be calcined and/or processed Volcanic Rise Husk 3 Pozzolanic Reaction 4 2 2024-02-06 Heat of Hydration Cement C3S C2S Water Hydration Products H 2O CSH CH + C 3A C4AF + Heat Others CSH (Calcium Silicate Hydrate): is the binder (glue) responsible for strength CH (Calcium Hydroxide): does not have an important contribution to strength. 5 6 3 2024-02-06 C3S C2S H2O + CSH CH + S CSH CSH SCMs Addition of supplementary cementing materials (SCMs) provide reactive amorphous silica (S) leading to Pozzolanic reaction (A reaction between S and CH to form CSH) Enhancement to mechanical properties and durability SCMs ⇒ Refinement of porosity Densification of aggregate-cement paste interface 7 Physical Filler Effect 8 4 2024-02-06 Aggregate Cement Paste Time Liquid state Soil state Cement Paste Voids Aggregate 9 Effect 2- Physical Filler Effect Cement Paste Aggregate Time Liquid state Soil state Cement Paste Voids Aggregate 10 5 2024-02-06 Effect 2- Physical Filler Effect Cement Paste Aggregate Time Liquid state Soil state Cement Paste Aggregate 11 Effect 2- Physical Filler Effect SCMs with adequate particle size distribution can lead to a physical filler effect (reduction of porosity between cement grains). 12 6 2024-02-06 Densification of AggregateCement Paste Transition Zone 13 ? WHAT is Transition Zone? 14 7 2024-02-06 Cement Paste Aggregate Interfacial Transition Zone (ITZ). Transition zone is a thin layer between the bulk hydrated cement paste and the aggregate particles in concrete. This zone is the weakest component in concrete, and it is also the most permeable area. 15 Wall Effect Wall Effect Wall Effect 16 8 2024-02-06 Effect 3- Densification of AggregateCement Paste Transition Zone Fine pozzolans play a significant role in the transition zone through both their physical and chemical effects. Wall Effect Transition zone is more porous due to wall effect 17 Portland cement alone CH Crystals Porous and crystalline Transition Zone Voids Portland cement + Silica fume Filler effect + Pozzolanic reaction Dense and non-crystalline transition zone 18 9 2024-02-06 Supplementary Cementing Materials (SCMs) Silica Fume 19 Silica Fume Smoke by-product from furnaces used in the production of ferrosilicon and silicon metals Very fine non-crystalline silica (Amorphous Silica) - High Silica (S) content, - Extremely small particle size, - Large surface area - Highly reactive pozzolan Before installation of equipment to collect Silica Fume. Also known as: - Condensed silica fume - Microsilica. - Silica dust - Volatilized silica 20 10 2024-02-06 Silica Fume Production A B C D (Si) SiO2+ 2C = Si + 2CO A Raw material C Wood-chips QUARTZ SiO2 C D B Coal (Si) 21 Silica Fume Product Forms As-produced powder Extremely fine and dusty Self-agglomerating /create small lumps Silica fume slurry 50 - 52% solids (as-produced silica fume dispersed in water) Densified silica fume Reversible agglomeration process Bulk transportation economical 22 11 2024-02-06 Physical Properties of Silica Fume Physical Property Particle size Bulk density - As-produced - Slurry - Densified Specific gravity Silica Fume Cement < 1 µm 15 µm (Average) 130 to 430 kg/m3 1320 to 1440 kg/m3 480 to 720 kg/m3 830to 1650kg/m3 2.2 3.1 to 3.25 (3.15) Surface area (BET) 13,000 to 30,000 m2/kg 300 to 370 m2/kg At 15 % silica fume replacement of cement: “About 2,000,000 particles of silica fume for each grain of portland cement”. (ACI 234R-96 ) 23 Chemical Characteristics of Silica Fume Property SiO2 Content Pozzolanic Activity (with cement, %)* Silica Fume Cement 85- 97 20-25 120 - 210 N/A *The Pozzolanic activity is a measure for the reaction rate between a pozzolan and CH in the presence of water. It is expressed in terms of a strength activity index 24 12 2024-02-06 C3S C2S H2O + CSH CH + S CSH CSH SCMs CSH (Calcium Silicate Hydrate): is the binder (glue) responsible for strength Strength activity index = (A/B) × 100 A = average compressive strength of blended cement mixture cubes B = average compressive strength of pure cement mixture cubes. 25 This figure shows the reduction in calcium hydroxide (CH) content of a mature cement-silica fume paste with a water-cement ratio of 0.60. (CH consumed to make more CSH!) CH CSH ? Strength ? 26 13 2024-02-06 Silica-Fume Concrete: Typical Strengths Compressive strength 27 150-200 MPa 60-100 MPa 25-35 MPa NC HPC UHPC Using high strength concrete can lead to savings in space and steel 28 14 2024-02-06 Example Mixture Binder 1 2 Pure Cement Cement + SF 56.2 78.3 ?? ?? Compressive strength (MPa) Activity Index (%) Strength activity index = (A/B) × 100 A = average compressive strength of blended cement mixture cubes B = average compressive strength of pure cement mixture cubes. 29 Effect of SCMs on Concrete Permeability Cement Particles Voids Space Permeability (How easy solutions can pass) Pure Cement 30 15 2024-02-06 Pure Cement Cement + SF Cement Particles Cement Particles Space Space Silica Fume Voids Adding SF Permeability Voids Permeability ? 31 Water Cement Silica Fume SF Hydration product Cement Hydration product Pure Cement Hydration + Hydration Cement + SF Silica fume reduces permeability of concrete and diffusion of chlorides, which substantially enhances durability to corrosion provided that adequate curing is provided to eliminate drying shrinkage cracks. 32 16 2024-02-06 Chloride ions (CL) 33 Silica-Fume Concrete: Typical Chloride Penetration Values Silica fume (by mass of cement) 0% RCP (Coulombs) > 3,000 Compressive Strength (MPa) = 35 7-10% > 10% < 1,000 < 500 > 50 > 60 The total charge passing through the specimen (in Coulombs) 34 17 2024-02-06 Drying shrinkage cracks Water Evaporate Preventing drying shrinkage cracks is key to achieving enhanced durability of silica fume concrete. Moist curing Generally, 7-days of moist curing are required. 35 Increased Abrasion Resistance Abrasion-erosion damage to the stilling basin of Kinzua Dam, Western Pennsylvania 36 18 2024-02-06 Segregation Because of the silica-fume addition and the low w/cm ratio, silicafume concrete is cohesive and less prone to segregation. 37 Summary A by-product from the production of ferrosilicon and silicon metals SF is finer than cement Particle size < 1 µm Vs. 15 µm (Average) for cement Surface area 13,000 to 30,000 m2/kg Vs. 300 to 370 m2/kg cement Pozzolanic activity is a measure for the reaction rate between a pozzolan and CH in the presence of water. Silica fume: Increases Strength (S+CH =CSH) Reduces permeability ≈ Enhance durability Increases concrete cohesiveness Good curing 38 19 2024-02-06 Supplementary Cementing Materials (SCMs) Fly Ash 39 Fly Ash By-product of coal burned power plants Made mostly of spherical particles 40 20 2024-02-06 Two classes of fly ash Class F fly ash Class C fly ash Low calcium oxide fly ash High calcium oxide fly ash Produced by calcination of Produced by calcination subbituminous coal or lignite. of bituminous coal. Has pozzolanic properties Has pozzolanic + cementitious properties 41 Fly Ash Production 42 21 2024-02-06 Fly ash has a filler effect, less effective than silica fume The particle sizes in fly ash vary from 100 μm Typical particle size measuring under 20 μm. 10% to 30% of the particles by mass are > 45 μm. 43 Physical Properties of Fly Ash Physical Property Fly Ash Cement Particle size < 1 µm to >100 µm 15 µm (Average) Bulk density 540 to 860 kg/m3 830to 1650kg/m3 2.65-2.38 3.1 to 3.25 (3.15) 200 to 700 m2/kg 300 to 370 m2/kg Specific gravity Surface area (BET) Finer fly ash has higher pozzolanic activity 44 22 2024-02-06 Chemical Characteristics of Fly Ash Property SiO2 Content Pozzolanic Activity (with cement, %)* Class F Class C Cement 52 35 20-25 85-110 85-110 N/A *Based on compressive strength with 20% by mass of cement is replaced by Fly Ash 45 Setting Time Fly ash usually hydrates slowly Setting time is moderately or severely extended depending upon properties of fly ash, temperature and mixture proportions. Finer fly ash results …………………..shorter setting time Higher CaO content …………………..shorter setting time 46 23 2024-02-06 Effect of Fly Ash on Workability With FA With FA Fly ash addition generally improve the workability of concretes. At similar slump fly ash concrete is more workable than normal concrete 47 Effect on Compressive Strength Strength (MPa) OPC +FA concrete OPC concrete - Fly ash concrete tends to gain strength at a slower rate than concrete without fly ash - The long term strength (90 days and after) is usually higher. Age (Days) 48 24 2024-02-06 Permeability Rate Fly Ash act as a filler (reduce space ) Pozzolanic effect of fly ash: creates more impermeable hydration products. 49 Chloride Diffusion Fly ash increases the resistance After 30 years of concrete to chloride ingress extending the service life of reinforced concrete exposed to OPC concrete OPC +FA concrete a chloride environment. Mixture Coulomb Range Chloride Perm. w/c >0.6 >4000 High w/c 0.4 - 0.5 2000-4000 Moderate w/c< 0.4 1000-2000 Low Cement/Fly Ash (30%) 100-1000 Very low 50 25 2024-02-06 Alkali-Silica Reaction “The quantity of fly ash necessary to prevent expansive damage due to alkali-aggregate reaction may be greater than the amount necessary for strength and workability properties of concrete.” 51 Alkali-Silica Reaction “Class F fly ash may be used at 20-25 percent or higher mass replacement as a general preventive measure.” 52 26 2024-02-06 Expansion Due to Sulfates Expansion (%) Sulfates in soil or groundwater can attack the cement hydrates OPC OPC +20%FA Time (months) Low-calcium fly ash can increase the sulfate resistance of concrete. High calcium fly ashes are less effective in this role. 53 HEAT OF HYDRATION Massive concrete elements may experience significant thermal differentials between the core and the rapidly cooling surface while curing. 54 27 2024-02-06 Temperature change (°C) Heat gradient can cause crazing, surface cracks, and more extreme failure. Reducing the core temperature reduces the heat differential. Time after placing (days) Replacing cement with fly ash can reduce the heat of hydration in concrete. 55 Summary A by-product of coal burned power plants Particle size Surface area (BET) < 1 µm to >100 µm 15 µm (Average) 200 to 700 m2/kg 300 to 370 m2/kg Fly Ash: Increases later Strength (S+CH =CSH) Reduces permeability ≈ Enhance durability Increase workability Reduce heat of hydration Increase concrete Alkali-Silica Reaction Increase concrete sulfates resistance Good curing 56 28 2024-02-06 Supplementary Cementing Materials (SCMs) Slag 57 Slag and Slag Cements By-product of the metallurgical industry. The most used in cement is iron blast furnace slag Quickly cooled blast furnace slag 58 29 2024-02-06 - Conventional slag is crystalline and used as aggregate or disposed as waste. Blast Furnace Slag Modern steel mills produce slag that is glassy and can be used as a hydraulic binder Granulated Blast Furnace Slag (GBFS) - Hydraulic slags give similar hydration products to OPC but react slowly with water Slag cement 59 Effect on Fresh Properties GBFS : angular particles like cement, but smoother. GBFS density is 2.9: lower than that of cement 3.1. Replacement by weight leads to higher paste volume and better workability At low temperatures, setting time is increased (slower hydration of GBFS) They are low-heat of hydration cements. 60 30 2024-02-06 Mechanical Properties Strength development of slag cement is slower at early age than that of OPC but faster at later ages. At one year slag cement achieves significantly higher strength. Rate of strength gain depends on type of slag, cement replacement rate, temperature, activation technique used, etc. They give comparable strength to OPC at 28 days 61 Slag improve the concrete resistance to fire damage 62 31 2024-02-06 Reinforcement corrosion Slag concrete has significantly much lower chloride ion (Cl) penetrability than OPC concrete. Penetration resistance increases with increased slag content and curing duration. 63 Alkali Aggregated Reaction There is much evidence that the expansion due to the AAR in concrete decreases as the slag addition increases (same trend for fly ash) Expansion (%) 45% 55% Time (days) 64 32 2024-02-06 Summary A by-product from iron blast furnace slag Fly Ash: Increases later Strength (S+CH =CSH) Reduces permeability ≈ Enhance durability Increase workability Reduce heat of hydration Increase concrete Alkali-Silica Reaction Good curing 65 Supplementary Cementing Materials (SCMs) Natural Pozzolans 66 33 2024-02-06 Natural Pozzolans Have been in use for many centuries. Name originates from town of Pozzuoli near Naples in Italy (Roman time). Overshadowed by more popular recycled pozzolans (fly ash, slag, silica fume, etc.) Two types: 1- RAW Example: Ash from volcanic eruptions is a source of natural Pozzolans. 67 2- Calcined natural pozzolans Example: Calcined clays, including Metakaolin SEM Micrograph of Calcined Clay Particles 68 34 2024-02-06 Other Mineral Admixtures There are several other supplementary cementitious materials and pozzolanas that are not all discussed herein. The example of rice husk ash is mentioned briefly. 69 Rice Husk Ash Each ton of rice produced leads to 200 kg of rice husk by-product. (Total of 100 million tons of rice husk worldwide) Rice husk Rice grain + Combustion of 1-ton of rice husk produces energy = ½ ton of coal + 20% ash containing more than 90% silica. Village market use power generated from rice husk 70 35 2024-02-06 Under controlled combustion conditions silica is amorphous. Also high surface area, highly reactive like silica fume when finely ground. SEM Micrograph showing skeletal structure of RHA 71 Effect on 28-day strength 72 36 2024-02-06 Effect on chloride diffusion Very Low Low ASTM Limits 73 Summary 74 37 2024-02-06 Summary 75 38