Q.: Is there any way to tell, after the concrete has hardened, whether a superplasticizer was added to the concrete? Is there a way to tell how much? How about the water-cement ratio?

A.: Yes, it is possible to determine whether a superplasticizer has been used in concrete, but few laboratories are equipped to do it. The process involves making a solvent extraction and then doing an infrared analysis of the extract to determine whether a melamine or a phenol formaldehyde system is present. Two laboratories capable of performing the work are the Erlin-Hime Division of Wiss, Janney, Elstner Associates, 330 Pfingsten Road, Northbrook, Illinois 60062, and the Concrete Technology Laboratories of the Portland Cement Association, 5420 Old Orchard Road, Skokie, Illinois 60077.

In some cases it is possible to make a quantitative determination. If you already know the specific identities of the chemicals used, it is possible to determine the amount of superplasticizer.

There are two possible methods for determining the water-cement ratio in a sample of hardened concrete. One is a linear traverse method described by Axon in a paper in the ASTM Proceedings (1962), pages 1068-1080. The other is a method described by Brown in a Building Research Station (United Kingdom) publication, Analysis of Concrete, published in July 1970. This latter method involves vacuum saturation of the concrete with carbon tetrachloride, but the method doesn't work on air-entrained concrete because some of the air voids take up carbon tetrachloride and consequently get counted as part of the water.

A good estimate of water-cement ratio can be made petrographically by measuring the size of the calcium hydroxide crystals. A petrographer familiar with the method might come up with an answer somewhere between 0.55 and 0.65 when estimating a concrete whose actual water-cement ratio is 0.60.