How to Read a Portland Cement Mill Test Report

Transcription

1 How to Read a Portland Cement Mill Test Report David J. Imse, P.E. Skyway Cement Company, LLC

2 ASTM C150 Portland Cement Specification Mill Test Reports Due to overlaps in requirements and strength levels typically well above specification limits, some cements meet several types. This may show in some mill certificates as Type I/II or in extreme cases Type I/II/V. It is important to understand that the certificate is not an analysis of a particular shipment of cement (unless required by the purchaser) Results reported are for the average of a large number of different samples analyzed and performance-tested over the time period chosen. Thus, normal, day-to-day production variation is averaged out, and a certificate gives no indication of such variation. Also, the samples tested on each day are usually physical composites of several samples taken over a production period, such as a shift or the full day. In some cases, these may be as frequent as hourly, meaning that the physical tests could have been done on a blend of 24 different samples, while the chemical results would be a mathematical averaging of each hourly sample. ASTM C917 - Standard Test Method for Evaluation of Cement Strength Uniformity From a Single Source

3 ASTM C150 Portland Cement Specification Mill Test Reports There are no concrete tests reflected in the certificate, no tests with admixtures, no tests with supplementary cementitious materials (SCMs), and no tests at other-than-laboratory temperatures Cement manufacturers are challenged to offer a consistent product from materials that are dug out of the ground and by their very nature must be variable. To do that, mixture proportions of the raw materials must be continually adjusted. With such multicomponent raw materials, it is impossible to keep all composition factors the same. So the cement characteristics will vary, as will the characteristics of all concrete components.

4 Mill Test Report Physical Chemical Optional

5 Bogue Nomenclature C = CaO S = SiO 2, A = Al 2 O 3 F = Fe 2 O 3 Example C 3 A = 3CaO Al 2 O 3

6 Chemical Requirements Cement heated to 1,650 1,830 F. A high loss on ignition can indicate prehydration and carbonation, which may be caused by improper and prolonged storage or adulteration during transport or transfer Cement treated with hydrochloric acid a measure of non-cementing materials largely arising from gypsum impurities Bogue Equations

7 Bogue Equations The standard Bogue calculation refers to cement clinker, rather than cement The calculation assumes that the four main clinker minerals are pure minerals with compositions: Alite: C 3 S, or tricalcium silicate Belite: C 2 S, or dicalcium silicate Aluminate phase: C 3 A, or tricalcium aluminate Ferrite phase: C 4 AF, or tetracalcium aluminoferrite It is important to remember that these assumed compositions are only approximations to the actual compositions of the minerals.

8 Bogue Calculations C 3 S = CaO SiO Fe 2 O Al 2 O 3 C 2 S = SiO Fe 2 O Al 2 O CaO C 3 A = Al 2 O Fe 2 O 3 C 4 AF = Fe 2 O 3

9 Portland Cement Grain CaO MgO C 4 AF C 3 S - Alite C 3 A C 2 S - Belite A pictorial representation of a cross-section of a cement grain. Adapted from Cement Microscopy, Halliburton Services, Duncan, OK.

10 C 3 S - Alite C 3 S (tricalcium silicate) is the major strengthproducing phase in concrete curing and dominates through the first 28 days. Sometimes the C 3 S level may go down and the cement fineness may go up, or vice versa. These variations occur when the cement producer balances one factor with another to keep the performance as consistent as possible, and is to be expected.

11 C 2 S Belite Hardens slowly and contributes largely to strength at 28 days and beyond. C 3 S and C 2 S - require approximately the same amount of water for hydration, but C 3 S produces more than twice as much Ca(OH) 2 as is formed by the hydration of C 2 S

12 C 3 A Aluminate Phase Releases large amount of heat during the first few days of hardening Most highly reactive element in cement Calcium sulfate (CaSO 4 ) is added to cement to control this high-reactivity component Limited to 8% in Type II and 5% in Type V cements

13 C 4 AF Ferrite Phase This is a fluxing agent which reduces the melting temperature of the raw materials in the kiln (from 3,000 o F to 2,600 o F). It hydrates rapidly, but does not contribute much to strength of the cement paste. Affects cement color

14 Physical Requirements Air permeability test that is translated to Specific Surface of the cement particles in m 2 /g or cm 2 /g. Soundness Test - refers to the ability of a hardened 2 cement x 2 cubes paste made to retain with its volume w/c. after Strengths setting without 13% higher delayed than destructive 2:1 ratio size expansion. High steampressure accelerates hydration of magnesia and lime causing expansion.

15 Blaine - Fineness Cement Cell Top Mark Starting Point Stopping Point Air permeability test that is translated to Specific Surface of the cement particles in m 2 /g or cm 2 /g Filling Level Typical Values m 2 /kg ( cm 2 /g). ASTM C204

16 Blaine - Fineness Blaine (fineness) is determined by how fast air moves through a compacted pellet of cement Cement fineness controls early strength development Market has driven cement fineness higher for all types over the past several decades Fineness increases, concrete water demand generally goes up and may need adjustment. Admixture demand may follow the same pattern. As fineness increases 7 to 28-day strength gain experienced in the past may decrease

17 Optional Requirements Equivalent Alkalis - Na 2 Oeq (%) = Na 2 O (%) x K 2 O (%) False Set When concrete stiffens too early caused by gypsum in the cement that gets dehydrated during the grinding process. This can be overcome with additional mixing. Flash Set When concrete stiffens too early caused by a lack of gypsum in the cement. This cannot be overcome.

18 Alkali Content Equivalent alkali is the summation of the sodium oxide and potassium oxide content of the cement, expressed as a percentage of mass equivalent sodium oxide (often abbreviated Na 2 Oeq) Air-entrainment - more air is produced as the alkali content increases SCM reactivity (more reactivity as alkali content increases) Alkali-silica reactivity of aggregates. Concretes using low-alkali cements can still be problematic if the concrete has relatively high cement contents, depending on how reactive the aggregates are. Cement content times alkali content provides the alkali loading of the concrete.

19 Thank You!