Special-Uses-Alkali - Expanded Shale & Clay

educe its amount in the cement paste. Consequently, the ASR gels formed in concrete havelower swelling characteristics (2).The ACI 221 report identifies natural pozzolans either as a naturally occurring amorphoussiliceous material or a material that is processed to give the same general properties. Recentlymetakaolin has been proven effective in mitigating ASR, however the material properties arevery different from one another and no recommendations can be made without testing (2).2.3.2 Concrete InternationalConcrete International reported on ternary concrete in Canada. Ternary concrete is defined ashaving two SCMs in addition to Portland cement. These materials are generally silica fume witheither fly ash or slag cement. The test results using the ternary concrete mixes have shownincreases in compressive strength, and lower expansion (14). The substitution/addition of 4%silica fume and 25% slag resulted in an expansion of 0.006% compared to the baseline expansionof 0.238% using the ASTM C 1293 “Standard Test Method for Determination of Length ChangeDue to Alkali-Silica Reaction.”The long-term effects of these concrete mixes have been verified by field-testing in Ontario,Canada where slabs and beams were constructed with highly reactive aggregates and high alkalicements. After 10 years the slabs and beams that performed the best were constructed using3.5% replacement of cement with silica fume and 25% replacement with slag cement (14).These ternary concrete mixes have also shown good resistance to deicing salts when tested inaccordance with ASTM C672, “Standard Test Method for Scaling Resistance of ConcreteSurfaces Exposed to Deicing Chemicals”. There have been reported incidents of scaling ofsidewalks but further testing and investigation is underway to determine the actual cause of thescaling (14). A high replacement level of cement using slag has shown some problems with earlystrength development and scaling.12