Ground granulated blast…

Ground granulated blast furnace slag or fly ash or a combination of the two materials and shall be restricted to the following proportions by mass of the total cementing material:
a) Slag up to 25%.
b) Fly ash up to 10%, except for silica fume overlays and HPC where up to 25% is permitted.

c) A mixture of slag and fly ash up to 25%, except the amount of fly ash shall not exceed 10% by mass of the total cementing materials, in concrete other than silica fume overlays and HPC.
For tremie concrete, the minimum cementing material content shall be 415 kg per cubic metre of concrete.

• The specified limits on slag and fly ash content are highly prescriptive and restrict the ability to optimize concrete mixtures based on performance.
• CSA A23.1 is fundamentally performance-based and allows flexibility in the selection and proportioning of supplementary cementing materials to meet specified durability and strength requirements.
• Imposing fixed percentage limits on SCMs conflicts with the intent of CSA A23.1 and may prevent the use of more sustainable and durable mix designs.
• The restriction on combined slag and fly ash content, particularly limiting fly ash to 10% in most applications, is not aligned with current industry practices or CSA provisions.
• The prescribed minimum cementing material content for tremie concrete further reinforces a prescriptive approach rather than allowing performance-based design in accordance with CSA A23.1.
• As this is a design-build standard, it is expected that CSA A23.1 governs material selection and mixture proportioning, with performance requirements taking precedence over prescriptive limits.
• Typical MTO prescriptive requirements should therefore be superseded by CSA A23.1 to allow innovation, optimize durability, and support GWP reduction objectives.