contributed by the Portland cement and expressed in LBA ( lbs./cy) by multiplying the cement content of the concrete in lbs. /cy by the alkali content of the cement divided by 100. For example, for a concrete containing 500 lbs./cy with an alkali content of 0.81% Na2Oe, the value of LBA = 500 x 0.81/100 = 4.05 lbs. /cy. For this concrete, the minimum replacement level of silica fume for Level Y is 1.8 x 4.05 = 7.3 %.
only method of prevention.
cement used, therefore, where silica fume is used as the sole method of prevention, the maximum assumed alkali limit of the cement must be indica ted on the mix design.
if the concrete is not properly proportioned, finished , and cured.
2.c.1 The minimum replacement levels in Table G are appropriate for use with P ortland cements of moderate to high alkali contents (0.70% to 1.25% Na2Oe). Table H provides an alternative approach for utilizing SCMs if the alkali content of the P ortland cement is less than or equal to 0.70%.
Table H Adjusting the Minimum Level of SCM if using low alkali Portland cement Cement Alkalis (% Na2Oe) Level of SCM ≤ 0.70 Reduce the minimum amount of SCM given in Table G by one prevention level.(1)
Level W regardless of the alkali content of the Portland cement.
2.c.2 Requirements for Prevention Level Z . Where prevention Level Z is required, use the minimum level of SCM shown in Table G or use the minimum level of SCM and the maximum concrete alkali content indicated in Table I.
Table I Using SCM and Limiting the Alkali Content of the Concrete Prevention Level SCM as sole prevention Maximum Alkali Content, ( lbs./cy) and Minimum SCM Level Z Level Z from Table G Maximum Alkali Level Content: 3.0 AND minimum SCM Level Y from Table G
specified in Section 704.1(g), provide Portland cement, blended hydraulic cement, or Portland cement -SCM combinations as specified in Secti on 704.1(b) and the following:
3.a Portland Cement. Conforming to the optional chemical requirement in AASHTO M 85 for a m