Literature Review Revised 2.docx

Table of Contents Literature Review: ..................................................................................................................... 3 1. General: ........................................................................................................................... 5 2.

Origin and Nature of SCMs: ............................................................................................... 5 2.1.

What are SCMS? ......................................................................................................... 5

2.2.

History of Use: ............................................................................................................ 5

2.3.

Nature of some typical SCMs: .................................................................................... 6

2.4.

Fly Ash: ....................................................................................................................... 7

2.4.1.

Production of Fly Ash: ............................................................................................ 7

2.4.2.

Composition and Properties of Fly Ash: ................................................................. 7

2.4.3.

Classification of Fly Ash: ........................................................................................ 8

2.5.

3.

4.

5.

6.

Silica Fume:................................................................................................................. 9

2.5.1.

Production of Silica Fume: ...................................................................................... 9

2.5.2.

Composition and Properties of Silica Fume: ........................................................... 9

Properties of Fresh Concrete: ........................................................................................... 10 3.1.

Workability and Water Demand: .............................................................................. 10

3.2.

Setting Time: ............................................................................................................. 11

3.3.

Air Entrainment: ........................................................................................................ 11

3.4.

Bleeding: ................................................................................................................... 11

Chemical Reactions of SCMs in Concrete: ...................................................................... 12 4.1.

Pozzolanic Reactions: ............................................................................................... 12

4.2.

Effects of SCMs on Hydration of Portland Cement:................................................. 13

Mechanical Properties of Concrete: ................................................................................. 14 5.1.

Compressive Strength: .............................................................................................. 14

5.2.

Flexural and Tensile Strength: .................................................................................. 15

5.3.

Modulus of Elasticity: ............................................................................................... 16

Volume Stability: .............................................................................................................. 17 6.1.

Drying Shrinkage: ..................................................................................................... 17

6.2.

Creep: ........................................................................................................................ 17

7. Durability of Concrete: ................................................................................................. 18

8.

7.1.

Permeability: ............................................................................................................. 19

7.2.

Alkali-Silica Reaction: .............................................................................................. 20

Specifications: .................................................................................................................. 21 8.1.

ASTM Standards for SCMs: ..................................................................................... 21

8.2.

ASTM Standards for Hydraulic Cement: .................................................................. 21

References: ............................................................................................................................... 22

Figure 1 Production of Fly Ash ................................................................................................. 7 Figure 2 CaO content w.r.t Number of Sources......................................................................... 9 Figure 3 Composition of Silica Fume ........................................................................................ 9 Figure 4 Effect of Fly Ash on Water Demand ......................................................................... 10 Figure 5 Setting Time of Concrete containing Fly Ash ........................................................... 11 Figure 6 Heat Evolution in Concrete w.r.t Time ..................................................................... 13 Figure 7 Strength of Concrete w.r.t Days ................................................................................ 14 Figure 8 Relationship between W/C and the Compressive Strength ....................................... 15 Figure 9 Relationship between Compressive Strength and E .................................................. 16 Figure 10 Relationship between Drying Shrinkage and Age................................................... 17 Figure 11 Drying Shrinkage w.r.t Age..................................................................................... 18 Figure 12 Cracking of concrete due to ASR in (a) bridge abutment, (b) hydraulic dam, (c) retaining wall, (d) pavement, (e) bridge piers and beams, and (f) curb and gutter .................. 20

Table 1 Nature of some typical SCMs ....................................................................................... 6 Table 2 Chemical Composition of Fly Ash ............................................................................... 8 Table 3 Concrete Chemistry Nomenclature:............................................................................ 12 Table 4 Chemical and Physical causes for Concrete Detrition ................................................ 19 Table 5 Effect of the Fly Ash on permeability of Concrete ..................................................... 19 Table 6 Effect of Silica Fume on Permeability of Concrete .................................................... 20

Literature Review: 1. General: Supplementary cementing materials (SCMs) are wide employed in the assembly of concrete worldwide. The term covers a broad vary of materials, together with natural (and manufactured) pozzolans and industrial by-products, appreciate y ash, slag, and oxide fume. though the properties of the various sorts of SCM vary significantly, they share the flexibility to react with chemicals in concrete and manufacture building material compounds that supplement those created by the association of cement. suitably used, SCMs will improve several of the contemporary and hardened properties of concrete. the employment of SCMs in concrete isn't new, because the use of pozzolans, appreciate volcanic ash, has been copied back to Hellenic and Roman civilizations, and lots of of the structures designed victimisation pozzolans square measure still standing nowadays. The appropriate use of appropriate supplementary cementing materials (SCMs) will cause several enhancements within the contemporary and hardened properties of concrete, together with reduced water demand, higher workability, enhanced long-run strength, and improved sturdiness in aggressive environments. However, if SCMs don't seem to be used properly or poor quality SCMs area unit used, the contemporary and hardened concrete properties could also be adversely affected. This textbook provides elaborated descriptions of the various SCMs offered, the chemical reactions that they endure in concrete, the impact of those reactions on the event of the microstructure in concrete, and the way the utilization of SCMs nuances the properties of concrete.

2. Origin and Nature of SCMs: 2.1.

What are SCMS?

The term supplementary cementing materials (SCMs) defines a broad vary of materials that square measure wide utilized in concrete additionally to hydraulic cement.1 Associate in Nursing SCM could also be outlined as “a material that, once utilized in conjunction with hydraulic cement, contributes to the properties of the hardened concrete through hydraulic or pozzolanic activity, or both” (CSA A3001, 2003). intrinsically SCMs embody each pozzolans and hydraulic materials. SCMs that square measure normally utilized in concrete nowadays embody ash, ground coarse furnace scum, oxide fume, and a large vary of natural pozzolans, like volcanic ash, calcined clay or sedimentary rock, and ground. A pozzolan is outlined as “a siliceous or siliceous and aluminous material that in itself possesses very little or no building material price however which will, in finely divided type and within the presence of wet, with chemicals react with hydrated oxide (an association product of Portland cement) at normal temperatures to type compounds having building material properties” (ACI 74295018669000). Supplementary cementing materials is currently the popular term for the category of materials that wont to be known as mineral admixtures.

2.2.

History of Use:

It is documented that the utilization of natural pozzolans, corresponding to volcanic ash, to supply concrete dates back quite 2 millennia to the traditional civilizations of Greece and Rome, though it's been claimed that the old- Eastern Standard Time example of a hydraulic binder dates back quite six millennia and consisted of a combination of lime and a diatomite from the gulf (Malinowski and Frifelt, 1993). The Greeks made hydraulic bind- ers from mixtures of lime and volcanic ash from the Island of Santorini (Thera), and archaeologists have

uncovered concrete structures engineered as so much back as 600 b.c. victimisation these pozzolan-lime mixes (Efstathiadis, 1978). The Greeks passed the technology on to the Romans in regarding a hundred and fifty b.c., and therefore the Romans developed a large vary of pozzolans throughout their empire dur- ing their 600-year domination (ACI 232, 2012), together with Rhenish trass that was used throughout European country and a supply of volcanic ash from the village of Pozzouli, near Italy, that Lent its name to the materials we have a tendency to currently decision pozzolans. SCMs endure chemical reactions in concrete, and therefore the product of reaction square measure building material in nature; that's, the product facilitates bind the parts of the concrete along within the same manner because the reaction (or hydration) product of hydraulic cement. Consequently, SCMs square measure thought of to be a part of the cementing material part of the concrete, and they should be enclosed within the calculation of the water-to-cementing materials magnitude relation, W/CM, of the concrete. As such, SCMs ought to be differentiated from fnely divided mineral fillers, like ground stone or quartz, which square measure usually with chemicals inert in concrete and aren't thought of to be a part of the cementing material.

2.3.

Nature of some typical SCMs:

The chemical and physical properties of supplementary cementing materials (SCMs), the chemical reactions that occur with these materials, and the impact that they need on concrete vary wide among the various sorts of SCM. Table 1 describes the character of five unremarkably used SCMs: low calcium fly ash, high-calcium fly ash, slag, oxide fume. The chemical and mineralogical composition, the particle size, and therefore the morphology of the particles varies significantly among SCMs. each oxide fume and fly ash area unit preponderantly comprised of spherical particles, however the typical particle size of oxide fume is regarding a hundred times finer than that of fly ash. Slag and metakaolin each need grinding to create the fabric appropriate for use in concrete, and this produces angular particles. The fineness of these materials depends on the extent of grinding Table 1 Nature of some typical SCMs Low-CaO fly ash

High-CaO fly ash

Slag

Silica fume

Mineralogy

Al-Si glass, inert crystalline phases

Ca-Al-Si glass, some Ca-Al glass, crystalline C2S, C3S, CŜ, MgO, and lime

Ca-Al-Si-Mg glass

Silicate glass

Shape

Spherical

Spherical

Angular crushed particles

Spherical

5–20

2–20

5–20

0.1–0.2

300–500

300–500

400–650

15,000–25,000

1.9–2.8

1.9–2.8 130–430 (undensifed) Pozzolanic and hydraulic

2.85–2.95

2.2–2.3

Hydraulic

Pozzolanic

Property Chemical composition (see Table 2.2)

Median size (μm) Surface area (m2/kg) S.G. Bulk density (kg/m3) Nature of reaction

1200 Pozzolanic

Colour

grey to buff white

Grey

White

Dark grey to black

2.4. Fly Ash: 2.4.1. Production of Fly Ash: Fly ash could be a by-product of burning coal in Associate in Nursing electrical generating station. Figure 1 shows a typical layout of a coal-burning generating station. Coal is first smallgrained in grinding mills before being blown with air into the burning zone of the chamber. during this zone the flammable constituents of coal (principally carbon, hydrogen, and oxygen) ignite, producing heat with temperatures reaching just about 1500°C (2700°F). At this temperature the fireproof inorganic minerals related to the coal (such as quartz, calcite, gypsum, pyrite, feldspar, and clay minerals) melt and type tiny liquid droplets. These droplets are carried from the burning zone with the flue gases and funky chop-chop, forming tiny spherical

Figure 1 Production of Fly Ash

glassy particles as they leave the chamber. These solid particles area unit collected from the flue gases victimisation mechanical and electrical precipitators, or baghouses. The particles of ash that “fly” far from the chamber with the flue gases area unit referred to as fly ash, associated this material is used as an SCM in Portland cement concrete. ash is additionally referred to as powdered fuel ash (PFA) in some countries. Heavier turn ash particles drop to rock bottom of the chamber, and this material is termed bottom ash or chamber bottom ash; such material isn't typically appropriate to be used as a building material for concrete, however is employed within the manufacture of masonry block.

2.4.2. Composition and Properties of Fly Ash: The performance of fly ash in concrete is powerfully influenced by its physical, mineralogical, and chemical properties. The mineralogical and chemical compositions square measure dependent to an oversized extent on the composition of the coal, and since a large vary of domestic and foreign coals (anthracite, bituminous, subbituminous, and lignite) square measure burned in several generating stations in North America, the properties of the fly ash may be terribly completely different between sources and assortment strategies. The burning conditions within an influence plant also can have an effect on the properties of the fly ash.

The low-calcium fly ash results from the burning of associate jap coal, and also the highcalcium fly ash was produced from a subbituminous coal from the Powder basin. The range of fly ash composition encountered in Asia is shown in Figure 2, with metal contents locomotive anyplace from not up to I Chronicles\ CaO to over half-hour CaO. Table 2 Chemical Composition of Fly Ash Mineral name Quartz Mullite Hematite Magnetite

Anhydrite Tricalcium aluminate (C3A) Dicalcium silicate (C2S) Lime Periclase Melilite Merwinite Alkali sulfates Sodalite

Chemical formula SiO2 Al 6Si2O3 Fe2O3 Fe 3O4 CaSO4 Ca 3Al2O6 Ca2SiO4 CaO MgO Ca2(Mg,Al)(Al,Si)2O7 Ca 3Mg(SiO4)2

Comments These phases are inert in concrete and are the only crystalline phases in low-calcium fly ash. These phases are also present in lesser amounts in high-calcium fly ash. Many of these phases react with water to form solid products of hydration. The quantity of these phases generally increases as the calcium content of the fly ash increases. These phases are not found in fly ashes with low to moderate calcium content (<15% CaO).

(Na,K)2O4 Ca2(Ca,Na)6(Al,Si)12 O24(SO4)1–2

The metal content of the fly ash is maybe the most effective indicator of however the fly ash can behave in concrete (Thomas et al., 1999), though different compounds, corresponding to the alkalis (Na2O and K2O), carbon (usually measured as LOI), and salt (SO3), will have an effect on the performance of the fly ash. Low calcium fly ashes (<8% CaO) square measure invariably made from hydrocarbon coals and square measure preponderantly composed of aluminosilicate glasses (60 to 90%) with varied amounts of crystalline quartz, mullite, hematite, and magnetite (ACI 232, 2003). These crystalline phases square measure primarily inert in concrete, and also the glass needs a supply of alkali or lime (for example, Ca(OH)2) to react and kind building material hydrates. Such fly ashes square measure pozzolanic and show no significant hydraulic behaviour.

2.4.3. Classification of Fly Ash: The most wide used specification for fly ash in Asia is ASTM C 618: customary Specification for Coal ash and Raw or Calcined Natural Pozzolan to be used in Concrete (Equivalent to AASHTO M 295). This specification divides fly ash into 2 categories supported its supply of origin and composition, as shown in Table a pair of.5. several fly ashes made from humate or subbituminous coals meet the chemical demand of Class F fly ash (SiO2 + Al2O3 + Fe2O3 ≥ 70%). Such fly ashes could also be classed as category F or category C and area unit typically stated as category F/C or C/F fly ashes. In Canada, the specification covering fly ash is CSA A3001: building material Materials to be used in Concrete, that separates fly ash into 3 sorts supported the Ca content of the fly ash.

Figure 2 compares the Ca content with the total of the oxides (SiO2 + Al2O3 + Fe2O3) for identical fly ashes. Most fly ashes that meet CSA Type F or kind CH would be classified as, severally, category F and sophistication C by ASTM C 618.

Figure 2 CaO content w.r.t Number of Sources

2.5. Silica Fume: 2.5.1. Production of Silica Fume: Silica fume is that the ultrafine monocrystalline silicon dioxide created in electrical conduction furnaces as associate industrial by-product of the assembly of element metals and ferrosilicon alloys. silicon dioxide fume is additionally called condensed silicon dioxide fume or micro silica. A schematic of the method is shown in Figure two.11. In element metal production, a supply of high-purity silicon dioxide (such as quartz or quartzite), in conjunction with wood chips and coal, is heated to around 1800°C (3300°F) in an electrical arc chamber to get rid of the atomic number 8 from the silicon dioxide (reducing conditions). On heating the silicon dioxide (SiO2) and carbon (C) along, most of the SiO2 is reduced to element metal (Si), that is sporadically broach from the chamber. The remaining silicon dioxide is merely part reduced to SiO, and this is over excited with CO (CO) by the exhaust gases. As these gases ar drawn off from the chamber, the SiO oxidizes and returns to its original state of SiO2. because the temperature drops within the flue the silicon dioxide condenses into tiny droplets of silicon dioxide glass, that are off from the exhaust gases by a series of filter luggage. The collected product is observed as silicon dioxide fume (or micro silica).

2.5.2. Composition and Properties of Silica Fume:

Figure 3 Composition of Silica Fume

Silica fume consists of extremely fine, spherical, glassy particles with an average diameter of 0.1 to 0.2 μm. The average size of individual silica fume particles is approximately 100 times smaller than those of Portland cement or other SCMs. The specific surface area of silica fume is in the range of 15,000 to 25,000 m2/kg (measured by nitrogen absorption) compared with values of 300 to 600 m2/kg for other cementing materials. However, the surface area of silica fume is not measured by the Blaine apparatus typically used for other cementing materials, and the values are not directly comparable. The specific gravity of silica fume is approximately 2.2, but may be higher (up to 2.5) if the iron content is high. The colour of as-produced silica fume is dark grey to black, although the material can be processed to a white colour. The bulk density of the as-produced material is in the range of 130 to 430 kg/m3, but this is frequently increased by mechanically densifying the material.

3. Properties of Fresh Concrete: 3.1.

Workability and Water Demand:

The water demand of concrete refers to the number of water needed to achieve the required level of workability or consistency (slump). The water demand of a cement concrete is essentially controlled by the scale, shape, surface texture, and grading of the aggregates (particularly the coarse aggregate), however is additionally a perform of the number and fineness of the cement, and also the amount of entrained air gift. Workability and consistency also are full of temperature. Water-reducing admixtures and superplasticizers will be wont to significantly increase the workability and consistency, or cut back the water demand of concrete, and area unit wide utilized in concrete production these days. Supplementary cementing materials may have a significant impact on the workability, consistency, and water demand of the concrete. The effect depends on the sort of supplementary cementing material (SCM) and also the level of replacement, among alternative factors. The use of excellent quality fly ash with a high fineness and low carbon content improves the workability and reduces the water demand of concrete, and consequently, the employment of fly ash ought to allow the concrete to be made at a lower water content than a cement concrete of the same workability.

Figure 4 Effect of Fly Ash on Water Demand

Source: Effect of fly ash fineness on water demand of concretes proportioned for equal slump. (Data from Owens, P.L., Concrete Magazine, July 1979, pp. 22–26.)

3.2.

Setting Time:

The impact of SCMs on the setting behaviour of concrete depends not only on the composition, fineness, and amount of SCM used, but also on the sort and quantity of cement, the water-tocementitious materials ratio (W/CM), the sort and quantity of chemical admixtures, and the concrete temperature. It is fairly well established that low-calcium fly ashes extend each the initial and final set of concrete, as shown in Figure five.8, particularly once used at higher levels of replacement and in weather condition. Similarly, high levels of slag may end up in slower setting times at low temperatures. During weather condition, the utilization of fly ash and scoria, particularly at high levels of replacement, will cause terribly significant delays in each the initial and therefore the fnal set.

Figure 5 Setting Time of Concrete containing Fly Ash

Source: The Use of GGBS and PFA in Concrete, Technical Report 40, Concrete Society, Wexham, Slough, 1991

3.3.

Air Entrainment:

Concrete containing low-calcium (Class F) fly ashes usually needs a higher dose of airentraining admixture to realize a satisfactory air void system. this can be principally thanks to the presence of unburned carbon, which absorbs the admixture. Consequently, higher doses of air-entraining admixture area unit needed as either the fly ash content of the concrete increases or the carbon content of the fly ash will increase. The carbon content of the fly ash accustomed generate the information. The carbon content of fly ash is typically measured indirectly by determining its LOI. The redoubled demand for air-entraining admixture should not gift a significant downside to the concrete producer provided the carbon content of the fly ash doesn't vary significantly between deliveries. it's been shown that because the admixture dose needed for a specific air content will increase, the speed of air loss additionally will increase (Gebler and Klieger, 1983).

3.4.

Bleeding:

Bleeding is defined because the upward migration of blending water in contemporary concrete caused by the settlement of the solid materials and ends up in the event of a layer of water at the surface of recently placed concrete. Bleeding is normal, and provided it doesn't occur

overly, it's not prejudicial to the concrete and should be useful in reducing plastic shrinkage cracking. Excessive trauma happens once the quantitative relation of the quantity of water to the surface area of solids is high and should diminish the standard of the concrete due to (1) the build-up of bleed water beneath combination particles or embedded steel weakening the bond, (2) a rise within the W/CM at the surface, particularly if the finishing takes place once the bleed water is gift, (3) associate accumulation of bleed water and development of a weak layer below the surface if the surface is finished before trauma has ceased, (4) the development of bleed channels which will gift most well-liked pathways for the ingress of aggressive species, and (5) excessive settlement of the solid concrete. Excessive trauma might occur in improperly proportioned concrete and is exacerbated by high intermixture water contents, low cement contents, and also the use of aggregates deficient in fines. trauma is lower in airentrained concrete.

4. Chemical Reactions of SCMs in Concrete: 4.1.

Pozzolanic Reactions:

By definition, a pozzolan is “a oxide or oxide and aluminous material … that reacts with chemicals with hydrated oxide (lime) to make compounds having building material properties.” In early civilizations, natural pozzolans were mixed beside lime to provide hydraulic cements, whereas nowadays natural or artificial pozzolans area unit sometimes used beside Portland cement. The association of the atomic number 20 salt compounds, C3S (or elite) and C2S (or belite), in Portland cement produces bumper atomic number 20 hydroxide through the reactions depicted by Equations 4.1 and 4.2 2C3S + 11H → C3S2H8 + 3CH

(3.1)

2C2S + 9H → C3S2H8 + CH

(3.2)

Table 3 Concrete Chemistry Nomenclature: Abbreviation S A C F M N K

S C H

Formula SiO2 Al 2O3 CaO Fe2O3 MgO Na2O K 2O SO3 CO2 H 2O

The pozzolanic activity of a fabric defines the power of that material to react with lime. There are 2 parts to the current activity, the frst being the whole quantity of CH with that the fabric can mix and therefore the second being the speed at that the reaction with CH occurs. Massazza (1998) states that there's general agreement that the total quantity of CH with that a pozzolan will mix depends on the following factors: • • •

Nature of the reactive phases within the pozzolan Content of those phases SiO2 content of those phases

•

CH/pozzolan quantitative relation of the combo • length of action On the opposite hand, the speed of the reaction with CH can rely upon: • Specific area of the pozzolan • Water/solid quantitative relation of the combo • Temperature

4.2.

Effects of SCMs on Hydration of Portland Cement:

The use of supplementary cementing materials (SCMs) can accelerate the early-age hydration of elite when blended with Portland cement. Following are the stages involving the heat evolution in cement: Stage 1: A period of rapid heat evolution due to the initial hydrolysis of the cement. This stage starts as soon as the cement and water come into contact and ceases after about 15 minutes.

Figure 6 Heat Evolution in Concrete w.r.t Time

Source: Ogawa, K., et al., Cement and Concrete Research, 10(5), 683–696, 1980. Printed with permission of Elsevier Stage 2: A amount of relative inactivity called the dormant amount or the induction amount. this era results from the necessity for the ions in answer to succeed in a crucial concentration before nucleation happens and association begins. The period of this era is typical between 2 and four hours, however could also be altered by the presence of constituents that act as either set accelerators or retarders. This stage represents the period once contemporary concrete is often handled, placed, and consolidated. Stage 3: The association of C3S begins once more and accelerates, reaching a most at the tip of the acceleration amount. Stage 4: the speed of association decreases throughout the speed period thanks to the formation of C-S-H round the hydrated C3S grains, that acts as a barrier. Stage 5: The association reaches a gentle state and future association is diffusion controlled, because the mass transport of water and dissolved ions through the association barrier controls

future association. The rate of association slows because the barrier thickens and approaches completion asymptotically.

5. Mechanical Properties of Concrete: 5.1.

Compressive Strength:

The compressive strength of concrete containing supplementary cementing materials (SCMs) depends on an oversized variety of things, as well as the kind and quantity of the SCM used, the composition and quantity of the portland cement, alternative mixture proportions (especially W/CM and air content), age, temperature, and curing. Figure 7 shows typical strength–time relationships for concrete cylinders with W/CM = zero.45 cured in limesaturated water at traditional laboratory temperature. The concretes were created with numerous SCMs victimization replacement levels typical for that individual SCM. In these concretes, the cement was replaced with associate degree equal mass of SCM, the sand content was then adjusted to keep up unit volume, and also the dosages of air-entraining and waterreducing admixtures were modified to keep up the required air content (5 to 8%) and slump (75 to a hundred twenty-five metric linear units, 3 to 5 in.). No alternative changes to the mixture proportions were created. below these conditions, the utilization of twenty fifth Class F fly ash reduces the early-age strength of the concrete, however will increase the long-run strength. The fly ash concrete achieves parity with the management concrete while not SCM someday between twenty-eight and ninety-one days.

Figure 7 Strength of Concrete w.r.t Days

Source: Thomas, M.D.A., et al., in Proceedings of the Fifth CANMET/ACI International Conference on Fly Ash, Silica Fume, Slag, and Natural Pozzolans in Concrete, ed. V.M. Malhotra, SP-153, Vol. 1, American Concrete Institute, Farmington Hills, MI, 1995, pp. 81– 98 Concrete with Class C fly ash behaves in a very similar manner, however the extent of the early age strength reduction is a smaller amount associate degreed strength parity is achieved at an early age (typically fourteen to twenty-eight days). the utilization of thirty fifth scoria conjointly reduces early-age strength, however to a lesser extent than fly ash, and equal strength is commonly seen as early as seven days. The later-age strength of scoria concrete is additionally improved compared to the management. Concrete with silicon dioxide fume

behaves in a very totally different manner as a result of the comparatively speedy reaction of silicon dioxide fume, which is attributed to its terribly fine particle size. Strengths at three days and on the far side area unit usually improved significantly by the presence of silicon dioxide fume. The behaviour of concrete containing natural pozzolans can depend upon the character of the pozzolan. Concrete containing comparatively slowly reactive pozzolans, such as some calcined shales and volcanic ashes, can behave in a very similar manner as concrete with category F fly ash.

Figure 8 Relationship between W/C and the Compressive Strength

5.2.

Flexural and Tensile Strength:

There are various equations for predicting the flexural and tensile strength of concrete from the compressive strength. Such relationships include the following:

Where: fc′ = compressive strength (MPa or psi) fr′ = flexural strength or modulus of rupture (MPa or psi) fsp ′ = splitting strength (MPa or psi) These empirical equations have been developed from data for portland cement contents, but they are generally considered to be appropriate for concrete containing SCMs.

5.3.

Modulus of Elasticity:

The modulus of elasticity, Ec, can also be predicted from the compressive strength, fc′, of concrete, and the equations used in ACI 318 are as follows:

where wc = unit weight of concrete (kg/m3 or lb/ft3) Ec = modulus of elasticity (MPa or psi) The relationship between the modulus of snap and also the compressive strength of concrete is actually unaffected by the presence of SCMs, and the prognosticative equations area unit equally applicable to concrete with or while not SCM. Figure 9 shows strength and modulus information for twenty-one concrete mixtures with fly ash levels up to five hundredth (Ghosh and Timusk, 1981), and this information indicate that fly ash concrete is expected to possess an identical modulus as Portland cement concrete of equivalent strength. The modulus determined by testing during this study was systematically more than the modulus expected using the equations in ACI 318.

Figure 9 Relationship between Compressive Strength and E

Source: (From Ghosh, R.S., and Timusk, J., ACI Materials Journal, 78(5), 351–357, 1981. Printed with permission from the American Concrete Institute.)

6. Volume Stability: 6.1.

Drying Shrinkage:

Drying shrinkage refers to the reduction in volume caused by the loss of water from hardened concrete thanks to evaporation. The strains made by drying are significant (typically >400 μs) and should be accounted for in design and construction. for instance, contraction joints ought to be provided in pavements, driveways, and slabs to stop uncontrolled cracking of the concrete once it shrinks. Uneven drying can even cause warp and curling of concrete slabs. The shrinkage of concrete also will cause reductions in restressing, and these losses ought to be accounted for within the design stage. There are several factors that have an effect on cracking, the principal ones being water content, mixture volume, mixture sort, water-cement quantitative relation, moist curing amount, and surface area-to-volume quantitative relation. to attenuate the drying shrinkage in concrete, the subsequent ways ought to be considered: •

Maximize content (increase most aggregate size, optimize grading).

• cut back the unit water content (judicious use of water-reducing admixtures, fly ash). • cut back the W/CM. •

Extend the amount of wet activity.

•

Use shrinkage-reducing admixtures.

Figure 10 Relationship between Drying Shrinkage and Age

Source: Zhang, M.H., et al., Cement and Concrete Research, 33(10), 1687–1694, 2003.

6.2.

Creep:

Creep is that the term accustomed describe time-dependent deformation beneath a sustained load. The quantity of creep exhibited by a concrete mixture can depend upon the composition of the mixture and therefore the nature of the loading. The water content, W/CM, and combination volume of the concrete have the most important influence on creep; the sort of cement encompasses a secondary result. to reduce the creep of concrete, the subsequent changes to mixture proportioning ought to be considered:

•

Maximize content (increase most aggregate size, optimize grading).

• cut back the unit water content (judicious use of water-reducing admixtures, fly ash). • cut back the W/CM. •

Increase maturity before loading (delay loading, steam curing).

Figure 11 Drying Shrinkage w.r.t Age

Source: Fourth International Conference on Fly Ash, Silica Fume, Slag, and Natural Pozzolans in Concrete, SP-132, Vol. 2, American Concrete Institute, Farmington Hills, MI, 1992, pp. 1325–1341; Malhotra, V.M., et al., Condensed Silica Fume in Concrete, CRC Press, Boca Raton, FL, 1987 Based on tests on concretes with fly ash or silicon oxide fume, Luther and Hansen (1989) planned that there's no significant distinction between the specific creep of cement concrete, silicon oxide fume concrete, and fly ash concrete of an equivalent strength. Indeed, this is often in keeping with the statement in ACI 232.2R that “the effects of fly ash on creep strain of concrete square measure restricted primarily to the extent to that fly ash influences the final word strength.” This statement will seemingly be extended to all SCMs.

7. Durability of Concrete: Concrete is usually a sturdy material and may be expected to perform adequately for many years or maybe centuries in most environments, provided the following conditions area unit met: •

The constituent materials area unit appropriate for the supposed use.

•

The concrete is proportioned to fulfil the exposure surroundings.

•

The concrete is correctly mixed, transported, placed, consolidated, finished, and cured.

•

Adequate protection is provided wherever needed (e.g., low pH environments).

There are a unit variety of processes that may result in the premature deterioration of concrete, and therefore the commonest processes area unit listed in Table. The table categorizes the

processes as being either chemical or physical, but several processes have each a chemical and a physical element. For example, physical salt attack happens as a results of crystallization pressure or the cyclic hydration-dehydration of bound compounds, and these area unit very chemical processes that manufacture physical stresses. Table 4 Chemical and Physical causes for Concrete Detrition

Chemical Acid attack Sulphate attack Delayed ettringite formation Attack by other chemicals Corrosion of embedded metals Alkali-aggregate reactions

Physical Freezing and thawing De-icer salt scaling Abrasion and erosion Physical salt attack Fire

Source: Based on Mindess, S., et al., Concrete, 2nd ed., Prentice Hall, Englewood Cliffs, NJ, 2003.

7.1.

Permeability:

Concrete may be a porous material and fluids (liquids or gases) might flow through concrete underneath sure circumstances. The porousness of concrete to fluids is usually measured by applying a pressure gradient across a concrete sample and measurement the speed of fluid flow. The porousness of concrete to water, usually termed the hydraulic physical phenomenon, is usually measured on a water-saturated cylindrical sample of concrete by waterproofing the curved surface of the sample, applying water struggling to 1 flat face, and measurement the speed of water flowing out from the opposite face. The coefficient of water porousness is then calculated exploitation D’Arcy’s equation as follows:

where k = coeffcient of water permeability or hydraulic conductivity (m/s) Q = flow rate (m3/s) A = cross-sectional area of sample (m2) l = length of the sample in the direction of flow (m) Δh= difference in hydraulic head across the sample (m) Table 5 Effect of the Fly Ash on permeability of Concrete Fly ash % by mass 0 30 0.65 30 0.65

Ratio W/CM 0.75 0.70 1410 0.70 1880

Relative permeability 28 days 6 months 100 26 220 5 2 320 5 7

Source: Data from Davies, R.E., Pozzolanic Materials—With Special Reference to Their Use in Concrete Pipe, Technical Memo, American Concrete Pipe Association, 1954.

Table 6 Effect of Silica Fume on Permeability of Concrete

Days 100% Type V 10% silica fume 20% silica fume

Coefficient of permeability (×10–13 m/s) 7 28 91 6.3 3.8 1.3 10.0 0.9 0.6 6.3 <0.1 0.4

182 0.3 0.4 <0.1

Source: Data from Hooton, R.D., ACI Materials Journal, 90(2), 143–151, 1993

7.2.

Alkali-Silica Reaction:

There are 2 forms of alkali-aggregate reaction (AAR) presently recognized in concrete: alkalisilica reaction (ASR) and alkali-carbonate reaction (ACR). solely ASR and therefore the interference of damaging ASR exploitation supplementary cementing materials are going to be mentioned during this text. ACR isn't as widespread as ASR, and therefore the preventive measures wont to management ASR are usually not effective for ACR. Aggregates that have the potential to cause injurious ACR shouldn't be utilized in concrete. Alkali-silica reaction may be a reaction between the alkali hydroxides within the pore answer of concrete and bound silicon oxide minerals gift in some aggregates that may, beneath some circumstances, turn out injurious enlargement and cracking of concrete. cement is that the predominant supply of alkalis (Na and K) in concrete, however alternative conducive sources could embody supplementary cementing materials, admixtures, aggregates, and external sources like de-icing salts and water.

Figure 12 Cracking of concrete due to ASR in (a) bridge abutment, (b) hydraulic dam, (c) retaining wall, (d) pavement, (e) bridge piers and beams, and (f) curb and gutter

8. Specifications: There are many specifications worldwide for supplementary cementing materials (SCMs) and for blended cements containing SCMs. This chapter discusses American Society for Testing and Materials (ASTM) specifications only.

8.1.

ASTM Standards for SCMs:

SCMs that are used as a separate addition at the concrete mixer are covered by the following ASTM specifications: • •

8.2.

ASTM C 618 Standard Specification for Coal Fly Ash and Raw or Calcined Natural Pozzolan for Use in Concrete ASTM C 1240 Standard Specification for Silica Fume Used in Cementitious Mixtures

ASTM Standards for Hydraulic Cement:

The special properties of the different types of cement can be achieved with or without SCMs at the option of the producer. The different hydraulic cement types covered by ASTM C 1157 must meet a number of physical requirements (including strength), but there are no chemical requirements in the specification. The setting time, autoclave, and mortar bar expansion requirements are the same for all cement types (the latter two of these are intended to protect from unsoundness due to free lime, percales, and excess sulphate); otherwise, the requirements vary according to the type of cement as follows: • Type HE cement is the only cement that has a 1-day strength requirement; it also has a higher 3-day strength requirement than the other types. • Type MS and HS cements must meet sulfate resistance requirements. Type HS cements have lower early-age strength requirements, as lowC3A cements or blended cements that meet the requirements of Type HS often show slower strength development. • Type MH and LH cements must meet heat of hydration requirements, but there are lower early-age strength requirements for these cements. It is not possible to produce high early strength and low heat with portland cement-based cements

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