Specialty Cements. Dr. Kimberly Kurtis School of Civil Engineering Georgia Institute of Technology Atlanta, Georgia.

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1 Specialty Cements Dr. Kimberly Kurtis School of Civil Engineering Georgia Institute of Technology Atlanta, Georgia Specialty Cements Portland cements do not always meet every need of the construction industry. Other specialty cements have been developed to meet these needs. Generally much smaller production, limited availability, and increased cost. modified portland cements some particular component has been added to portland cement to provide the desired quality In these cements, the calcium silicates continue to provide the strength, but changes are made to the aluminate and ferrite phases nonportland cements Do not rely on the calcium silicates for strength, but on the hydration of other phases

2 Today s Cements Wide range of portland, blended & other hydraulic cements available Sulfateresisting cements Lowheat cements Rapid strength gain cements ASR resistant cements Airentraining cements Blended cements White or colored cements Masonry cements Mortar cements Expansive cements Rapid setting cements Rapid hardening cements Oil well cements Biogenic cements Calciumaluminate cements White or Colored Cements Fe, Mg give clinker and cement gray color Can produce white cement if F<0.5% in raw materials Burn clean fuels Controlled cooling to retain Fe 2+ Use ceramic ball mill 2

3 White or Colored Cements Fe, Mg give clinker and cement gray color Can produce white cement if F<0.5% in raw materials Add pigments to white cement to achieve desired color: red, yellow, brown, black iron oxides green chromium oxide blue cobalt blue White cements are ~3x cost of ordinary portland cement Masonry & Mortar Cements Properties of masonry mortars: Workability Water retentivity Consistent rate of hardening Durability Compressive strength Bond Volume stability Appearance Composition of masonry mortars: Cementitious material Masonry sand Water 3

4 Masonry & Mortar Cements Masonry cement consists of: Portland cement or blended hydraulic cement Hydrated or hydraulic lime Other materials like talc, clay, fly ash, slag, air entrainers ASTM C 9 Standard Specification for Masonry Cement Mortar cement: Similar to masonry cement Lower air content Bond strength requirement ASTM C 329 Standard Specification for Mortar Cement Masonry & Mortar Cements Masonry & Mortar Cements: Type M Type S Type N ASTM C 9 Standard Specification for Masonry Cement Mortars: Type M Type S Type N Type O ASTM C 270 Standard Specification for Mortar for Unit Masonry ASTM C 329 Standard Specification for Mortar Cement 4

5 Masonry & Mortar Cements ASTM C 270 Property Specifications for LaboratoryPrepared Mortars Mortar Type Minimum 28day compressive strength, MPa (psi) Minimum water retention, % Maximum air content, % Masonry cement Mortar cement Or Cementlime M 7.2 (2500) S 2.4 (800) N 5.2 (750) 75 20* 4* O 2.4 (350) 75 20* 4* *2% lower if structural reinforcement is embedded in mortar Masonry & Mortar Cements Recommended Guide for Selection of Mortar Type Building Segment Exterior, above grade: Exterior, at or below grade: Interior: Load bearing Nonload bearing Parapet wall Load bearing Nonload bearing Type N or S N N or S S or M N or S O or N 5

6 Masonry & Mortar Cements ASTM C 270 Proportion Specifications Mortar type Portland or blended cement Parts by volume Masonry or mortar cement type M S N Hydrated lime or lime putty Sand M ¼ 2¼ to 3½ times the total volume of cement plus lime S ½ ¼ ½ N Masonry & Mortar Cements Requirements for Masonry and Mortar Cements (ASTM C 9 & C 329) Fineness Autoclave expansion Time of setting Compressive strength Air content Water retention Bond strength 6

7 Masonry & Mortar Cements Requirements for Mortar Cements (ASTM C 329) Property Type of Mortar Cement Compressive strength minimum, MPa (psi) M S N 7 days 2.4 (800) 9.0 (300) 3.4 (500) 28 days 20.0 (2900) 4.5 (200) 6.2 (900) Air content, volume % Minimum Maximum Bond strength minimum, MPa (psi) 28 days 0.8 (5) 0.7 (00) 0.5 (70) Expansive Cements Ordinary portland cements expand slightly during early hydration, but the effect is far outweighed by the amount of drying shrinkage that occurs early. 7

8 Expansive Cements Expansive Cements Expansive cements expand during the early setting period Can be used as: Shrinkage compensating cements induce a small (2500psi) selfstress in restrained members to offset drying shrinkage and avoid cracking Chemically prestressing or selfstressing cements induce a larger selfstress (500000psi) for prestressing precast elements Shrinkage compensating concrete at Love Airport taxiways 8

9 Expansive Cements Expansive cements are generally a blend of portland cement or calcium aluminate cement and some expansive component ASTM Type K Blend of Type II or V portland cement and the calcium sulfoaluminate Kleinite (C 4 A 3 S) C 4 A 3 S + 6C + 8CS + 96H > 3(C 3 A 3CS H 32 ) or 3(C 6 AS 3 H 32 ) Amount of Kleinite depends on degree of desired expansion (8 50% by mass) Ettringite produced by this reaction is believed to produce the expansion colloidal ettringite topochemical growth Typically good sulfate resistance Expansive Cements ASTM Type M Blend of portland cement, calcium aluminate cement, and calcium sulfate CA + 3CS + 2CH+ 30H > C 6 AS 3 H 32 Precast units made with solids in the ratio 66:20:4 ASTM Type S Portland cements with high C 3 A content (~20%) and suitable amounts of gypsum Difficult to control setting Rapid slump loss Sulfate durability problems 9

10 Expansive Cements: Influence of Curing Conditions Expansive Cements: Influence of Curing Conditions It is desirable for the ettringite to form after setting, rather than in plastic concrete, to maximize expansion. 0

11 Rapid Setting and Hardening Cements Type III cements harden rapidly, but may not set quickly enough for some applications, such as repair. Rapid setting and rapid hardening cements include: Calcium sulfoaluminate cements Calcium fluoroaluminate cements f c >000psi at hour Rapid Setting and Hardening Cements Calcium sulfoaluminate (or very high early strength) cements Typically contain more C 4 A 3 S than Type K cement C 4 A 3 S is formed during clinkering (rather than used as an addition, added after grinding) CS is added to feedstock or during grinding Contain little C 3 S and much C 2 S Contain little C, which is believed to produce nonexpansive ettringite with better strength

12 Rapid Setting and Hardening Cements Calcium fluoroaluminate or regulatedset cements C 3 A is replaced by C A 7 CaF 2 (2025%) C A 7 CaF 2 can be produced in kiln or added during grinding C A 7 CaF 2 reacts even more vigorously than C 3 A Use very soluble additives, such as citric acid and/or sodium sulfate, to control reaction rate Setting can be controlled to occur 240 min. Initial strength due to C A 7 CaF 2 hydration; later strength due to C 3 S Other Rapid Setting/Hardening Cements High iron cements (HIC) Use a combination of C 4 A 3 S and C 4 AF to produce ettringite Finely ground cements Type III cements ground to high fineness ( m 2 /kg) May contain chemical accelerators as well Mixtures of Type I cement and gypsum Magnesium phosphate cements Mixtures of calcium aluminate and portland cement Use of 2080% calcium aluminate cement in a blend can produce an almost instantaneous set Early strength will be very high, but late strength will be low 2

13 Oil Well Cements Make up 5% of portland cement used in US Not used for structural concrete Oil well cement slurries are used to: protect casing from damage from surrounding water give strength prevent fluid migration Oil Well Cements Extreme conditions exist: slurry must be flowable for hours and then set rapidly slurry may be pumped thousands of meters below the surface slurry may be exposed to high temperatures (00250C) at the bottom of the well (up to 300C) slurry may be exposed exposed to high pressure (>20,000 psi) 3

14 Oil Well Cements Eight classes: Class A general use, like Type I Class B sulfate resistant, like Type II Class C rapid hardening, like Type III Classes D, E, F sulfate resistant with set modifying admixtures; Class E can be used in hotter conditions than Class D, and Class F hotter still Classes G and H sulfate resistant with stringent thickening times; Class H is more coarsely ground Class J withdrawn, was a C 2 Sbased cement with silica flour (finely ground quartz) In US, Type H is most common Outside US, Type G is most common Oil Well Cements In addition, there are 3 grades: O ordinary MSR moderate sulfate resistant HSR high sulfate resistant Class A only grade O Class B only MSR, HSR Class C O, MSR, HSR Class D, E, F only MSR, HSR Class G, H only MSR, HSR 4

15 Oil Well Cements Oil Well Cements: Temperature Effects High temperatures during oil well applications can influence slurry properties and chemistry: Many retarders and water reducers decompose at T > 50C Cement hydration, particularly of C 2 S and C 4 AF phases, is accelerated at ~7090C Changes in CSH structure and strength can result >00C, CSH > αc 2 SH (crystalline, low f c, high permeability) >200C, αc 2 SH > C 6 S 2 H 3 (Jaffeite, similar properties) Silica flour is added to prevent strength retrogression initially form C 5 S 6 H 4 (tobermorite) >50C C 5 S 6 H 4 > C 6 S 6 H + C 2 S 3 H 2 (xonotlite and gyrolite) > 250C residual tobermorite and gyrolite form truscottite > 400C truscottite and xonotlite decompose 5

16 Biogenic Cements Rice hull ash (RHA) is most common source of biogenic silica for cement manufacture Rice hulls are an abundant byproduct in many developing countries Contain cellulose, lignin, and hemicellulose, but are also 020% silica by mass Rodrigues et al. have produced βc 2 S from biogenic silica at relatively low temperatures ( o C) Cements are typically doped with barium or manganese to increase reactivity. µm unhydrated 6% Ba 2+ βc 2 S Calcium Aluminate Cements Calcium aluminate cements or high alumina cements (HAC) or ciment fondu rely on hydration of calcium aluminate phases, rather than calcium silicates. Composed of: alumina ~40% lime ~40% ferric or ferrous oxides ~5% fused silica ~5% small amounts of titanium dioxide, silica, and magnesia Common applications are for refractory brick and where sulfate resistance is needed 6

17 Calcium Aluminate Cements Raw materials are bauxite and limestone Composition varies (iron rich vs. iron poor) Monocalcium aluminate (CA) is principal phase Calcium Aluminate Cements: Hydration <0C > CAH 0 CA + H 030C > C 2 AH 8 + AH 3 no CH >30C > C 3 AH 6 +2AH 3 In addition, xc 2 A 7 + yh > zc 2 AH 8 C 2 A 7 sets within a few minutes, but CA sets more slowly; CAC with higher C:A sets more rapidly Generally, setting time is comparable to portland cement However, strength gain is RAPID, achieving 80% ultimate f c at 24 hours 24 hour strengths for CAC are similar to 7 day strengths for PC Total heat evolved is similar to PC, but rate is 3x as fast Excellent sulfate resistance 7

18 Calcium Aluminate Cements: Conversion With these great properties why isn t CAC more widely used?!? CONVERSION Both of the primary hydration products are metastable at both normal and elevated temperatures. In the presence of moisture, 3CAH 0 > C 3 AH 6 +2AH 3 + 8H 3C 2 AH 8 > 2C 3 AH 6 + AH 3 + 9H The original hydration products have a lower density than the conversion products Thus, conversion leads to increased porosity and hence reduced strength and impermeability Calcium Aluminate Cements: Conversion 8

19 Calcium Aluminate Cements: Conversion Higher temperatures, higher concentrations of lime, and greater alkalinity all promote conversion. Calcium Aluminate Cements: Conversion Some have suggested that postconversion strength of CAC concrete with w/c<0.40 may be adequate for some structural applications. Current French recommendations require maximum w/c of 0.40 and minimum cement content of 400kg/m 3. 9

20 Calcium Aluminate Cements: Conversion Small variations in w/c can significantly affect strength after conversion 20