Concrete 101 – Debunking the Mag Myths
“Many ready-mix suppliers blame magnesium chloride for concrete failures such as surface spalling and scaling. It is my contention that if concrete is made, handled, and finished properly, mag does not have any detrimental effects on concrete, regardless of age.”
ESI is fortunate enough to have an insider with knowledge in both the cement and mag industry. Let me introduce you to Tim Pike who worked in the ready-mix industry for 10 years before joining us. He gives presentations on practices to contractors, has testified in court on proper concrete proportions, and is involved on countless troubleshooting calls to determine various causes of concrete failures. The following is based on Tim’s most recent presentation.
Concrete should be made with its end purpose in mind and the most crucial roles occur during its design, placing and finishing. In general, concrete that will be exposed to deicers should be made with water to cement (w/c) ratio of .45 or less and have an air content of between 5% and 8%. These quotients are critical to the longevity of the concrete, but even if both specifications are met, the concrete can still be ruined by improper finishing practices.
Water is required to hydrate the cement, but it can be both friend and foe. 9 times out of 10 the spalling or scaling of concrete is because the finisher has ruined the w/c ratio by adding water to the surface during finishing operations. The addition of water is done to make finish work easier, but there are other methods available that won’t destroy the w/c ratio.
Case-in-point, Tim actually demonstrated his claim by overseeing the construction of ESI’s Evans Plant in 2007. Tests were placed every 100 cubic yards to assure the concrete delivered was to his specifications. Cylinders were cast for strength data tested at 7 and 28 days after placement.
The Evans Plant is one of the few places in the US that handles such a vast amount of mag chloride on a daily basis. The concrete at Evans Plant is subject to this amount, yet in spite of this it remains today without any sign of fault.