How to use set retarders with CSA cements in concrete countertop mixes

All CSA products are inherently fast setting. In order to boost the work time, chemical retarders are often used. Unlike portland cements, CSA cements can use ordinary citric acid, often at doses of 0.2% to 0.4%.

Straight CSA cements such as Rapid Set Cement actually benefit from moderate retardation. The structural silicate crystal growth occurs more slowly, and like old-growth wood, results in better concrete with higher strengths.

Another way to increase work time when using CSA cement is to substitute ice for some of the mix water. Generally 1/4 to 1/3rd of the mix water is ice, and the melting ice absorbs heat from the other ingredients. The advantage of thermally retarding the mix with ice is that once the mixture warms up to ambient temperatures, its normal setting rate return, so early strength is far less affected than when citric acid is used.

Both ice and citric acid can be used together for very long work times. I have achieved over an hour of working time with Rapid Set Cement in 90 degree weather when citric acid was used along with ice. Ice can also be used with “plain” portland cement based concretes, as this is a time tested technique used in the construction industry for hot weather concreting.

Ice to cool and retard the concrete

Ice to cool and retard the concrete

Note: CSA additives are different. (See article here.) Since CSA additives are blended with portland cement, you may use citric acid to extend working time, but that may also reduce early strength development of the portland cement it’s blended with. Dosages vary depending upon CSA additive amounts and upon the amount of working time desired.

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