Cement – Specification and Performance Hugh Wang Eduardo Caballero CEMEX USA hugh.wang@cemex.com

Use of cement: Cement is ONLY one of the ingredients in any applications – well cementing or construction concreting. The specified quality parameters of cement are tested without considering other ingredients. Lessons learned from concrete mixtures - interaction of cement with other ingredients can be critical to performance.

Production of quality well cement involves: Chemistry Ca, Si, Al, Fe Proportioning Physical fineness, strength, TT, FF etc Grinding Mineral C3S, C2S, C3A, C4AF Burning

Mineral Desired clinker characteristics for well cement: C3S, C2S, C3A, C4AF Well crystallized alite; Optimize burning condition in order to minimize f-CaO content; Generally very low in C3A content – a challenge for kiln operation.

Physical Physical properties requirements: Fineness; Thickening time (TT); Free fluid (FF). Physical fineness, strength, TT, free fluid, etc Potential conflicting response: Fineness vs TT; Fineness vs FF.

Specifications - ASTM vs API : Fineness: ASTM lowered the limit from 280 to 260 m2/kg; SO3: ASTM adopted performance based specification; D It is permissible to exceed the values in the table for SO3 content, provided it has been demonstrated by Test Method C1038 that the cement with the increased SO3 will not develop expansion exceeding 0.020 % at 14 days. C3S: No requirement for MSR and HSR cements. C4AF+2C3A: 24 API vs 25 ASTM.

Mineral calculation – ASTM:

Mineral calculation – ASTM:

Mineral calculation – API 10A:

Mineral calculation – API vs ASTM:

Discussions – ASTM vs API Minimum blaine 400 m2/kg for API Class-C: if high blaine is intended for early strength, its benefit may be potentially reduced due to the higher water demand. Minimum blaine for other types of cements should be harmonized with ASTM requirements from 280 to 260 m2/kg;. This will improve thickening time performance. Why ASTM revised cement SO3 content? Critical in the mixtures containing supplementary cementitious materials (SCM) and chemical admixtures. Construction industry has gone through the learning process. Potential incompatibility problems in the mixtures shall be considered when complex components are used in slurry.

Cement hydration rate profile I II III IV V Stage I: dissolution Stage II: induction (dormant) Stage III: acceleration Stage IV: deceleration Stage V: steady Time in hours Energy release rate mW/g Maximum heat release rate On-set of acceleration stage Conversion of ettringite to mono-sulfate

Cement hydration heat release – strength indication

Incompatibility: uncontrolled early hydration

Incompatibility: slow strength development

Well cement examples:

Hydration rate at 23˚C (73˚F) TA03 TA05

Hydration heat at 23˚C (73˚F)

Hydration rate at 38˚C (100˚F) TA03 TA05

Hydration heat at 38˚C (100˚F)

Example: cement and fly ash combination

Well cement with 50% Class-C fly ash (C-FA) Viscosity increase

Well cement with 50% C-FA and 1.5% gypsum

Viscosity profile comparison Gypsum addition eliminates high viscosity during early stages

SO3: Supply - Demand Rule SO3 demand false normal flash

If SO3 supply is greater than demand SO3 demand false normal flash

If SO3 supply is greater than demand SO3 demand false normal flash

If SO3 supply is less than demand SO3 demand false normal flash

If SO3 supply is less than demand SO3 demand false normal flash

Recommendations In order to make well cement more robust for slurry mixtures containing SCM and chemical admixtures, the cement SO3 needs to be optimized. The 280 m2/kg blaine requirement needs to be revised to 260 m2/kg, this will help to improve thickening time. The minimum blaine 400 m2/kg for Class-C cement may be eliminated by specifying the strength requirement. Harmonize cement mineral phase calculation to reflect lasted advance in understanding cement chemistry. 30

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