Q.: There is no clear-running stream or other good source of mixing water near one of the sites planned for our portable batch plant, though there is a small lake which is more like a big pond. The trouble is that it contains a lot of green stuff that is reported to be algae. Can we use the water in making concrete?

A.: Not while it contains algae, because they cause great reduction in strength. It is reported that algae can reduce the rate of hydration, so for that reason you may not get the strength required. Algae can also cause a great amount of air to be entrained, and this could reduce the strength even more drastically. Another problem is that algae tend to deposit on aggregate particles and interfere with the bond between the aggregate and the cement paste, making the problem still worse.