composite cement material

COMPOSITE CEMENTSUse of Supplementary Cementations Material (SCM) +Limestone

-RBS-Jakarta, 27 Juni 2013

Indonesia Cement & Concrete Institute

Introduction & HistoryComposite/Blended cement is an old component of concrete mixtures. Pozzolanic cement was standardised in Italy in 1929. Blast-furnace slag cements were produced in Germany, France, Luxembourg and Belgium for more than a century. Cements containing fly ash appeared in France in 1950.However, the importance of mineral additions has notoriously rose in the last decades due to cement industry requirements, as well as the need of longer service life for concrete structures.The use of mineral additions in cement production implies a reduction in consumption of fossil fuel, mineral natural resources and the gas emissions that contribute to the green-house effect. Consequently, partial replacement of Portland clinker is a feasible solution from an economic, ecological and technical point of view.


Technical DescriptionsCement mixtures containing ordinary portland cement (OPC) and at least one Supplementary Cementitious Material (SCM) are called blended cements. Binary cements contain OPC and one SCM, e.g. blended cements containing 85% OPC and 15% Class C fly ash.Ternary cements contain OPC and two SCMs, e.g. blended cements containing OPC, 15% Class C fly ash and and 20%, 25%, or 35% slag.


Potential Benefits of Blended CementsSupport sustainable cement development policy.Improved concrete workability.Lower risk of thermal cracking.Improved concrete durability and long-term strength.Reduced overall concrete cost.


Range of ApplicationsComposite cements for general applications (clinker replacement 10-30%)

Special concrete applicationsMass constructionHydraulic constructionIndustrial construction (Chemical attack, heat attack)(Ultra) high performance concrete (example: M2C Obourg Origny using 80% slag)Self Compacting Concrete

Special bindersRoad bindersSoil stabilisationSealing wallsEtc.


Supplementary Cementitious Material (SCM)Most common and widely used is Fly AshReady-to-use productClinker replacement around 20% (max. 55% EN 197-1)Slags produced in blast furnaces, steel converters, non-ferrous industries, or municipal waste incinerators.Milling/granulation is generally requiredOnce milling plant installed easy to produce composite cementClinker replacement around 35% (max. 95% En 197-1Rice Husk Ash (RHA)Pozzolans Natural (volcanic ashes, sediments, etc.)By-product/waste (burned clays, dusts e.g. Cement Kiln Dust, silica fume)


Global Fly Ash & Slag Production(in million ton/year)Global volumes:FA+S in Cement: 603 mio t/yFA+S in Aggregates: 257 mio t/y Cement Production: 1500 mio t/y


Introduction of SCM in cement industry


CharacteristicsBlended cements either blended or interground at cement plants are generally more uniform and produce better results than blended concrete mixtures combined at the concrete mixer.Concrete performance varies with the source and proportion of cementitious materials used.Fly ash can function as a water-reducing agent in cement mixtures. As a result, ternary cement concrete can achieve the same flowability as OPC concrete.Fly ash replacement in binary cements generally increases paste/concrete set time when compared with OPC concrete.Slag replacement in ternary cements can either increase or decrease the set time, depending on the type of clinker used when compared with binary cement concrete.


Initial Set Times


Effect of SCM on Strength


Pozzolanic Materials


Criteria of Using Pozzolanic Materials1. Quarry informationGeographic locationLegal situationGeologic history and set-upExact sampling location2. MoistureBetween 2% and 5%3. Mineralogical composition Low degree of rock heterogeneitySmall particle sizes (< 150 mm)High porosity (> 20%)High amount of vitreous phasesLow amount of minerals (except zeolites)No clays and xenoclasts4. Chemical composition High sum of SiO2+Al2O3+Fe2O3 (> 70%)High amount of reactive SiO2 (> 25%)Low LOI (< 10%)Low amount of SO3 (< 1%)Low amount of Cl (< 0.1%)


Testing the Reactivity of Pozzolans(According to EN 196-5)Materials with pozzolanic properties contain glassy silica and alumina that will, in the presence of water and free lime, react with the calcium in the lime to produce calcium silicate hydrates (cementitious compounds).


Metallurgical Slag


Metallurgical SlagsMetallurgical slags are disposed as waste from the ferro-manganese and ferro-manganesesilicon alloys manufacturing plants and in the smelting of non-ferrous metals such as lead, zinc and copper.The slags are found in two types, i.e. granulated and air-cooled (lumpy).They find little use unlike blast furnace slags from steel plant, although in Canada, some steel alloy slags are being used as an additive in cement raw materials


Characterisation of raw materialsIt can be chemically classified as the high MnO slag contains 33% MnO and the low MnO slag has 15% MnO.The specific gravity: 3.20 g/cm3 , whereas there was a variation in the bulk density, with low MnO slag having 1.73 g/cm3 and high MnO slag having 2.05 g/cm3.High silica (39%) in the low MnO slag indicates the possibility of a partial replacement for cement.


Physical Properties and Compressive Strength


FLY ASH 490 million ton produced in 2002 worldwide


Fly AshFly ash is defined in Cement and Concrete Terminology (ACI Committee 116) as "the finely divided residue resulting from the combustion of ground or powdered coal, which is transported from the firebox through the boiler by flue gases." Fly Ash primarily contains a silico-alumino material capable of reacting with calcium hydroxide at room temperature to form compounds having cementitious propertiesFly ash is commonly known as a by-product of coal-fired power plants.The characteristics of a fly ash depend on the nature of the coal used and the type of operating furnaceFly ash to be used in blended cement must meet the requirements of ASTM C618


ASTM standard forblended cementASTM has introduces performance standard for blended cement, C 1157.ASTM C595(1) defines two blended cement products in which fly ash has been added: 1) Portland-pozzolan cement (Type IP), containing 15 to 40 % pozzolan or2) Pozzolan modified Portland cement (Type I-PM) containing less than 15 % pozzolan.


Global Fly Ash Production (in million ton/year)


Fly ash classification according ASTM C 618Class F, referred to low-calcium fly ash, usually produced by burning anthracite or bituminous coal.Class C, usually produced by burning sub-bituminous coal or lignite.Both types of fly ash are pozzolanic and contain a substantial amorphous phase. The difference between Class F and Class C fly ash is the amount of calcium and the silica, alumina, and iron content.In Class F fly ash, total calcium typically ranges from 1 to 12 %, mostly in the form of calcium hydroxide, calcium sulfate, and glassy components in combination with silica and alumina. In contrast, Class C fly ash may have calcium oxide contents as high as 30 to 40%.Another difference between Class F and Class C is that the amount of alkalis (combined sodium and potassium) and sulfates (SO4) are generally higher in the Class C fly ashes than in the Class F fly ashes. It is important to stress that not all fly ashes are able to meet ASTM C618 requirements and that could be acceptable for applications other than concrete.The American Concrete Institute (ACI) recommends that Class F fly ash replace from 15 to 25 % of the Portland cement and Class C fly ash replace from 20 to 35 %


Quality of fly ash according to JIS-A 6201


Physical Properties of Fly AshFly ash consists of fine, powdery particles that are predominantly spherical in shape, either solid or hollow, and mostly glassy (amorphous) in nature. The specific gravity of fly ash usually ranges from 2.1 to 3.0, while its specific surface area (measured by the Blaine air permeability method) may range from 170 to 1000 m2/kg. The carbonaceous material in fly ash is composed of angular particles. The particle size distribution of most bituminous coal fly ashes is generally less than a 0.075 mm or No. 200 sieve.


Physical Properties of Fly Ash (contd)The color of fly ash can vary from tan to gray to black, depending on the amount of unburned carbon in the ash.The lighter the color, the lower the carbon content. Lignite or subbituminous fly ashes are usually light in color, indicating relatively low amounts of carbon as well as the presence of some lime or calcium. Bituminous fly ashes are usually some shade of gray, with the lighter shades of gray generally indicating a higher quality of ash. Subbituminous coal fly ashes are are generally slightly coarser than bituminous coal fly ashes.


Chemical composition of fly ash of different coal types (% w/w)


Fly Ash FinenessFineness is the primary physical characteristic of fly ash that relates to pozzolanic activity. As the fineness increases, the pozzolanic activity can be expected to increase. Current specifications include a requirement for the maximum allowable percentage retained on a 0.045 mm (No. 325) sieve when wet sieved. ASTM C618 specifies a maximum of 34 % retained on a 0.045 mm (No. 325) sieve. Fineness can also be assessed by methods that estimate specific surface area, such as the Blaine air permeability test commonly used for Portland cement.


Fly ash TreatmentFly ash must be in a dry form when used as a mineral admixture.Fly ash quality must be closely monitored when the material is used in blended cement. Fineness, loss on ignition, and chemical content are the most important characteristics of fly ash affecting its use in concrete. Fly ash must also have sufficient pozzolanic reactivity and must be of consistent quality.


Fly Ash StorageFly ash is typically stored dry in silos, from which it can be used or disposed of in a dry or wet form. Water can be added to the fly ash to allow for stockpiling or landfilling in a conditioned form (approximately 15 to 30 % moisture), or for disposal by sluicing into settling ponds or lagoons in a wet form. Approximately 75 % of the fly ash produced is handled in a dry or moisture-conditioned form, making it much easier to recover and use. The main advantage to the conditioning of fly ash is the reduction of blowing or dusting during truck transport and outdoor storage.


Fly Ash Quality ControlFly ash used in concrete should be as consistent and uniform as possible. Fly ash to be used in concrete should be monitored by a quality assurance/quality control (QA/QC) program that complies with the recommended procedures in ASTM C311.These procedures establish standards for methods of sampling and frequency of performing tests for fineness, loss on ignition (LOI), specific gravity, and pozzolanic activity such that the consistency of a fly ash source can be certified. ASTM C618 specifies a maximum allowable moisture content of 3.0 %.Due to concern of air-entraiment, many users specify a maximum LOI value that does not exceed 3 or 4 percent, even though the ASTM criteria is a maximum LOI content of 6%.


Quality-compromised fly ashAsh from a reserve powerplant. Ash from plants burning different coals or blends of coal. Ash from plants burning other fuels (wood chips, tires, trash) blended with coal. Ash from plants using oil as a supplementary fuel. Ash from plants using precipitator additives, such as ammonia. Ash from start-up or shut-down phases of operation. Ash from plants not operating at a "steady state." Ash that is handled and stored using a wet system.To Ensure the quality of fly ash being used, the following sources of fly ash should be avoided:


TRASS


Mineral Composition & Oxides


Effect on Strength (case study)


LIMESTONE


Introduction & History


Grinding of Limestone Cement


Effect of Limestone


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