Tests on Portland Cement

Transcription

1 Tests on Portland Cement Dr. Kimberly Kurtis School of Civil Engineering Georgia Institute of Technology Atlanta, Georgia Composition Chemical Name Tricalcium silicate Chemical Formula 3CaO SiO 2 Shorthand Notation C 3 S Mass (%) Dicalcium silicate 2CaO SiO 2 C 2 S Tricalcium aluminate 3CaO Al 2 O 3 C 3 A 5 10 Tetracalcium aluminoferrite 4CaO Al 2 O 3 Fe 2 O 3 C 4 AF 5 15 Calcium sulfate dihydrate CaSO 4 2H 2 O CSH 2 ~ 5 1

2 Composition The relative quantities of each of these phases affects: setting time rate of strength development overall strength durability color It is important, then, to know the composition of the cement. Tests on Portland, Blended & Hydraulic Cements Chemical Properties Chemical analysis Compound composition Chemical limits Physical Properties Fineness Soundness Consistency Setting time False set and flash set Compressive strength Heat of hydration Loss on ignition Density Bulk density Sulfate expansion 2

3 Belite, C 2 S Alite, C 3 S Width of field = 0.31 mm 3

4 Chemical Analysis SiO 2 Silicon dioxide Al 2 O 3 Aluminum oxide Fe 2 O 3 Ferric oxide CaO Calcium oxide MgO Magnesium oxide SO 3 Sulfur trioxide LOI Loss on ignition Na 2 O Sodium oxide K 2 O Potassium oxide TiO 2 Titanium dioxide P 2 O 5 Phosphorus pentoxide ZnO Zinc oxide Mn 2 O 3 Manganic oxide Sulfide sulfur ASTM C 114 Standard Test Methods for Chemical Analysis of Hydraulic Cement Major components Separate determinations Insoluble residue Free calcium oxide CO 2 (carbon dioxide) Watersoluble alkali Chloroform soluble organic substances Minor components 4

5 Oxide Analysis Oxide % ASTM C114 Oxide Shorthand Common Name CaO C lime SiO Al 2 O Fe 2 O CaO 63.9 MgO 1.53 K 2 O 0.73 Na 2 O 0.15 SO LOI other trace elements 90 95% SiO 2 S silica Al 2 O 3 A alumina Fe 2 O 3 F ferric oxide MgO M magnesia K 2 O K alkalis Na 2 O N SO 3 S sulfate CO 2 C carbonate H 2 O H water Compound Composition Bogue Composition C 3 S = 4.07C 7.60S 6.72A 1.43F 2.85S C 2 S = 2.87S 0.75C 3 S C 3 A = 2.65A 1.69F C 4 AF = 3.04F (Only valid when A/F 0.64) 5

6 Bogue Composition: Example Oxide Analysis Calculated Phase Composition Oxide % SiO Al 2 O Fe 2 O CaO 63.9 MgO 1.53 K 2 O 0.73 Na 2 O 0.15 SO LOI 1.58 C 3 S = 4.07(63.9) 7.60(20.6) 6.72(5.07) 1.43(2.90) 2.85(2.53) = 58.1 C 2 S = 2.87(20.6) 0.754(58.1) = 15.6 C 3 A = 2.65(5.07) 1.69(F 2.90) = 8.5 C 4 AF = 3.04(2.90) = 8.8 Bogue Potential Composition: C 3 S 58% C 2 S 16% C 3 A 9% C 4 AF 9% Typical Chemical Composition of Portland Cement Oxide Analysis Oxide % SiO Al 2 O Fe 2 O CaO 63.9 MgO 1.53 K 2 O 0.73 Na 2 O 0.15 SO LOI 1.58 Sodium equivalent, Na 2 Oe Na 2 Oe = Na 2 O + (0.658 x K 2 O) Na 2 Oe = (0.658 x 0.73) Na 2 Oe = 0.63% + other trace elements 6

7 Bogue Composition The Bogue equations are based on the following assumptions: 1) All 4 phases are pure 2) All the F present occurs as C 4 AF, and the quantities of A = 0.64(%F) and C = 1.40 (%F) are subtracted from the appropriate totals. 3) The remaining Al 2 O 3 is combined as C 3 A and a further quantity of C = 1.65 (% Al 2 O 3 ) is subtracted fromt eh total remaining CaO. 4) The SiO 2 combines initially with CaO to form C 2 S giving a provisional C 2 S figure. The CaO combining with SiO 2 = 2.87%(SiO 2 ) is subtracted from the total CaO figure, and the remaining CaO is then combined with a part of the C 2 S = 4.07(%CaO) to form C 3 S. As a result, Bogue compositions may be off by as much as 10% compared to XRDdetermined compositions. Bogue XRD 7

8 Chemical Limits ASTM C 150 Portland Cement Chemical Requirements Cement Type I II III IV V SiO 2, min. % 20.0 Al 2 O 3, max. % 6.0 Fe 2 O 3, max. % MgO, max. % SO 3, max. % C 3 A 8% C 3 A > 8% LOI, max. % n/a n/a n/a 3.0 Insoluble residue, max. % Chemical Limits ASTM C 150 Portland Cement Chemical Requirements Cement Type I II III IV V C 3 S, max. % 35 C 2 S, min. % 25 C 3 A, max. % C 4 AF + 2 C 3 A, max. % 25 8

9 Chemical Limits ASTM C 150 Portland Cement Optional Chemical Requirements Cement Type I II III IV V C 3 A, max. % 8 C 3 A, max. % 5 C C 3 A, max. % 58 Na 2 Oe, max. % Chemical Limits ASTM C 595 Blended Cement Chemical Requirements Cement Type I(SM), I(SM) A, IS, ISA S, SA I(PM), I(PM)A, P, PA, IP, IPA MgO, max. % 6.0 Sulfur reported as SO 3, max. % Sulfide sulfur (S), max. % Insoluble residue, max. % LOI, max. % Watersoluble alkali, max. % 0.03 * * Only required when cement is specified to be nonstaining to limestone 9

10 Fineness Fineness of cement is also important; it affects: rate of hydration rate of setting rate of hardening durability (ASR) rate of carbonation during storage cost rate of gypsum addition bleeding Fineness However, later strength is not directly affected. Neville, Fig

11 Fineness Approx. 95% 45 microns Average diameter ~ 15 microns Those retained on the No 200 sieve (75 microns) will never hydrate completely Those retained on the No 325 sieve (45 microns) will be difficult to hydrate completely Type III >> Type I, II, V > Type IV Fineness is generally described as the specific surface of the cement, which is the surface area expressed in m 2 /kg 11

12 Lea and Nurse Air Permeability Relates flow of fluid (air) through a bed of granular material (cement) to the specific surface area of that granular material By knowing ρ cement, a bed 10mm thick with porosity of 4.75% is made; air is passed through at constant velocity; pressure drop is measured. S w = 14 [(ε 3 Ah 1 )/(KLh 2 )] 0.5 ρ(1ε) Blaine Air Permeability With the Lea Nurse method, air passes through the bed at a constant rate Blaine Air Permeability (ASTM C 204) In the Blaine test, a known volume of air passes at a constant pressure through the bed The rate of flow decreases steadily The time for flow to occur is measured for a given apparatus and a standard porosity of 5% (0.500). S w = K 2 t

13 Wagner Turbidimeter Wagner Turbidimeter (ASTM C 115) Uses a photoelectric cell to measure light passing through cement particles suspended in kerosene Test is based on Stoke s Law that states that a sphere will obtain a constant velocity under the action of gravity Allows calculation of particlesize distribution (psd) Blaine, in general, is 1.8X Wagner Laser Particle Size Analyzer Laser particle size analyzer Particlesize distribution (psd) 13

14 Cement Fineness ASTM C 430 Sample washed over 45µm (# 325) sieve Used in production Limits for pozzolans and slag (ASTM C 595) Cement Fineness Requirements for Type I, II, IV & V (No requirements for Type III) Air Permeability Turbidimeter Minimum, m 2 /kg ASTM C 150 & AASHTO M Maximum, m 2 /kg AASHTO M Typical values, m 2 /kg Type I Type III No limits for blended cement (ASTM C 595) or hydraulic cements (ASTM C 1157) but values must be reported on mill test reports 14

15 Soundness Soundness ability of hardened paste to maintain volume after setting Unsoundness (abnormal expansion) caused by hardburned CaO or MgO CaO + H O Ca(OH 2 ) 2 MgO + H O Mg(OH 2 ) 2 ASTM C 151 Standard Test Method for Autoclave Expansion of Portland Cement Expansion for all portland, blended & hydraulic cements 0.80% Consistency Consistency of Cement Paste Penetration of 10 ± 1 mm of Vicat plunger ASTM C 187 Standard Test Method for Normal Consistency of Hydraulic Cement Consistency of Mortar Flow table ASTM C 1437 Standard Test Method for Flow of Hydraulic Mortar 15

16 Setting Time Initial Set Final Set Time from moment water is added until the paste ceases to be fluid and plastic Time from moment water is added for the paste to acquire a certain degree of hardness Setting Time: Standard Test Vicat Needle ASTM C 191 Standard Test Method for Time of Setting of Hydraulic Cement by Vicat Needle Initial set occurs when needle penetrates after 30s 25 mm (1 inch) into paste Final set occurs when there is no visible penetration 16

17 Setting Time: Field Measurements Concrete penetrometer, measures resistance to penetration in sieved mortar samples Pocket penetrometers Setting Time: Standard Test Gillmore Needles ASTM C 266 Standard Test Method for Time of Setting of HydraulicCement Paste by Gillmore Needles Setting determined as time when paste resists indentation by needles 17

18 Setting Time ASTM C 150 Portland Cement Initial Set, not less than (h:min) Final Set, not more than (h:min) ASTM C 595 Blended Cement Initial Set, not less than (h:min) Final Set, not more than (h:min) ASTM C 1157 Hydraulic Cement Initial Set, not less than (h:min) Final Set, not more than (h:min) Vicat Needle 0:45 6:15 0:45 7:00 0:45 7:00 Gillmore Needles 1:00 10:00 Setting Time Type I Type II Type III Initial Final Type IV Type V Time of Set (Minutes) Vicat Method 18

19 False Set and Flash Set Early Stiffening False Set Loss of plasticity shortly after mixing little heat Due to hemihydrate (plaster) in cement hydrating to gypsum Workability restored by additional mixing False Set and Flash Set Early Stiffening False Set Loss of plasticity shortly after mixing little heat Due to hemihydrate (Plaster) in cement hydrating to Gypsum Workability restored by additional mixing Flash Set Rapid & early loss of workability significant heat Due to rapid reaction of aluminates when insufficient sulfate present Workability cannot be restored 19

20 Compressive Strength ASTM C 109 Standard Test Method for Compressive Strength of Hydraulic Cement Mortars. 50mm (2inch) mortar cubes Sand:Cement = 2.75:1 Water/Cement = for portland cement (0.460 for airentraining portland cement) Sufficient water for flow 110 ± 5 for blended (ASTM C 595) and hydraulic (ASTM C 1157) cements 20

21 Compressive Strength ASTM C 150 Standard Specification for Portland Cement Minimum Strength Requirements, MPa (psi) Age Cement Type I II III IV V 1 day 3 days 7 days 28 days 12.0 (1740) 19.0 (2760) 10.0 (1450) 17.0 (2470) 12.0 (1740) 24.0 (3480) 7.0 (1020) 17.0 (2470) 8.0 (1160) 15.0 (2180) 21.0 (3050) Lower strengths permitted for airentraining cements (Types IA, IIA & IIIA) and when heat of hydration option is specified for Type II cement Compressive Strength ASTM C 595 Standard Specification for Blended Hydraulic Cements Minimum Strength Requirements, MPa (psi) Age Cement Type 3 days 7 days 28 days I(SM), IS, I(PM), IP 13.0 (1890) 20.0 (2900) 25.0 (362) IS(MS), IP(MS) 11.0 (1600) 18.0 (2610) 25.0 (3620) S 5.0 (720) 11.0 (1600) P 11.0 (1600) 21.0 (3140) Lower strengths permitted for airentraining cements (with suffix A) 21

22 Compressive Strength ASTM C 1157 Standard Specification for Hydraulic Cement Minimum Strength Requirements (MPa) Age Cement Type GU HE MS HS MH LH 1 day 10 3 days days days Compressive Strength ASTM C 1157 Standard Specification for Hydraulic Cement Minimum Strength Requirements (MPa) Strength Range Minimum Strength, MPa (psi) Maximum Strength, MPa (psi) 5 (725) 15 (2175) 10 (1450) 20 (2900) 17 (2465) 30 (4350) 25 (3625) 40 (5800) 35 (5075) 60 (8700) 45 (6525) 22

23 Heat of Hydration Heat evolution in portland cement tested by conduction calorimetry Heat of Hydration Heat of Solution Test ASTM C 186 Standard Test Method for Heat of Hydration of Portland Cement Conduction Calorimetry 23

24 Heat of Hydration ASTM C 150 Portland Cement Moderate Heat of Hydration Type II (Option) 290 kj/kg at 7 days Low Heat of Hydration Type IV 250 kj/kg at 7 days 290 kj/kg at 28 days Heat of Hydration ASTM C 150 Portland Cement ASTM C 595 Blended Cement Moderate Heat of Hydration Type II (Option) 290 kj/kg at 7 days Suffix MH 290 kj/kg at 7 days 330 kj/kg at 28 days Low Heat of Hydration Type IV 250 kj/kg at 7 days 290 kj/kg at 28 days Suffix LH 250 kj/kg at 7 days 290 kj/kg at 28 days 24

25 Heat of Hydration ASTM C 150 Portland Cement ASTM C 595 Blended Cement ASTM C 1157 Hydraulic Cement Moderate Heat of Hydration Type II (Option) 290 kj/kg at 7 days Suffix MH 290 kj/kg at 7 days 330 kj/kg at 28 days Type MH 290 kj/kg at 7 days Low Heat of Hydration Type IV 250 kj/kg at 7 days 290 kj/kg at 28 days Suffix LH 250 kj/kg at 7 days 290 kj/kg at 28 days Type LH 250 kj/kg at 7 days 290 kj/kg at 28 days Loss on Ignition ASTM C 114 Standard Test Methods for Chemical Analysis of Hydraulic Cement Loss on ignition LOI Sample ignited at 900 to 1000 C (1650 to 1830 F) High LOI indicates prehydration and/or carbonation Improper or prolonged storage (transportation) ASTM C 150 Portland Cement LOI 3.0% (2.5% for Type IV) ASTM C 595 Blended Cement LOI % ASTM C 1157 Hydraulic Cement No limit must be reported 25

26 Density Le Chatelier flask ASTM C 188 Standard Test Method for Density of Hydraulic Cement Range= 3100 to 3250 kg/m 3 Average = 3150 kg/m 3 (196 lb/ft 3 ) Not indicator of quality Used for mixture proportioning calculations Relative density (specific gravity) = 3.15 Helium pycnometer Bulk Density Bulk density of cement varies between 830 kg/m 3 (52 lb/ft 3 ) and 1650 kg/m 3 (103 lb/ft 3 ). 26

27 Sulfate Expansion ASTM C 452 Standard Test Method for Potential Expansion of PortlandCement Mortars Exposed to Sulfate Gypsum added to cement to yield 7.0% SO 3 (by mass of cement + gypsum) Mortar bars stored in water Length change monitored periodically Only applicable to portland cements ASTM C 150 Portland Cement Optional requirement for Type V SulfateResisting Portland Cement Expansion 0.040% at 14 days Limits for C 3 A, C 4 AF + 2C 3 A, SiO 2 & Fe 2 O 3 not required 27