Effects of Cementitious Slag Content and Aggregate Type on Properties and Durability of Portland Blast-Furnace Slag Cement Concretes


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Title: Effects of Cementitious Slag Content and Aggregate Type on Properties and Durability of Portland Blast-Furnace Slag Cement Concretes

Author(s): G. J. Osborne and M. D. Connell

Publication: Special Publication

Volume: 192


Appears on pages(s): 119-140

Keywords: aggregates; blast furnace slag; carbonation; compressive strength; oxygen; pereability; portland cement

Date: 4/1/2000

A series of nine large concrete blocks (750 mm cube), stored outside on an industrial site at the Appleby Frodingham works at Scunthrope in N.E. England were assessed at 7-8 months, 30 months and 7.5 and 10.5 years of age. The concrete contained a normal total cementitious content of 390kg/m and had different levels of ground granulated blast furnace slag in the range 0, 30, 50 and 70% by weight as replacement material for portland cement. Some of the concretes were prepared using gravel and others with crushed limestone as aggregate. The quality and performance of these concretes were determined at each age by testing drilled cores taken from the side face of the blocks, partly protected form driving rain. The assessment involved early hear release data; measurements of the depth of carbonation; oxygen permeability and compressive strength. Comparisons were made between the different concretes on the basis of their comentitous slag content an aggregate types. The results showed that concretes containing 100% normal portland cement or 50% slag have hardly carbonated, although carbonation had progressed to 5 to 6 mm at 2.5 years where 70% slag was used, but there was little change thereafter. Gas permeability decreased slightly as the slag replacement levels were reduced from 70% to 50% and the coefficient of oxygen permeability (ko) values for the inner concrete were in the range .5 to 9 by 10 to the -18th. M2 by 2.5 years which indicated that all concretes had low permeability. Impressive compressive strength gains were realize with time for the slag cement concretes which at 7.5 years were in the rang 82.5 to 105 MPa compared with the plain portland cement concrete at 67.5 MPa, clearly demonstrating the beneficial long term effect of slag on strength development. Benefits were also derived form the use of water reducing admixtures and from using crushed limestone as aggregate. These are discussed in relation to the longer-term performance of the concretes at 10.5 years.