We have been inside and outside a lot of problems during our combined 100-plus years of service to our industry. When we first started, the industry was staid—barely crawling along—and everyone wanted to make, and sell, bulk Type I portland cement—no bags. Aside from price, sales competition was usually based on strength, and so ensued the “grinding wars” (the finer the grind, the earlier and greater the strength) and strength became the buzzword of the industry.
The next big gun was admixtures. Slowly at first, and then more and more rapidly, they slid into our arsenal of things to make concrete better and perhaps less costly, an engineer's dream. But less cost almost always brings some disadvantages. One near farce was the use of high alumina cement for precast elements, a real cost advantage because it provides very rapid strength gain that allows faster reuse of forms. But the dreamers forgot one ultra-important word—conversion. Over time, calcium aluminate cement hydration products convert to lower hydrate forms, decreasing in volume and resulting in micro and macro cracking, and strength loss. The conversion phenomenon had been known for years, but apparently not to the “inventors” of the “new” process. But that's what keeps consulting concrete pathologists like us in business. God bless inventions!
Another innovation involved the use of Sorel cement, a mixture of magnesium oxide (periclase, MgO) and a solution of magnesium chloride. The result, when mixed with water, is very rapid setting and strength gain. In the 1930s there was even an ASTM standard. Interestingly, Sorel cement was rediscovered twice during Bill's life because prior failures were forgotten. One failure in using this material that we investigated involved exterior cladding panels with zinc jointing strips. Rapid stiffening due to the Sorel cement allowed in situ casting of the panels and rapid construction. But within several months distortion and corrosion was evident. You could grab the strips at the top of the joints and zip them downward like a zipper. The distortion was due to restrained expansion of the panels when the magnesium oxide component of the cement reacted to form magnesium hydroxide (brucite, Mg(OH)2), which is accompanied by an in situ 117 percent solid volume increase. The zinc strips corroded because of the chloride in the cement that reacted to form zinc-hydroxychloride. Use of the cement was a reinvention with a double whammy!
Finally, an error of fantastic consequences fooled an industry into accepting an admixture for masonry mortar that could have been a boon to a sluggishly moving brick masonry industry. The product allowed prefabrication of brick masonry beams and panels, much like precast concrete, so that once fabricated, they could be rapidly installed. Or, for conventional field brick lay-up, it allowed shelf angles to be spaced every two floors instead of every floor. The product was a specially formulated latex similar in composition to Saran wrap. When added to masonry mortar, it created tremendous brick-mortar bond, overcoming the greatest physical weakness of brick masonry, low bond strength. The manufacturer of the latex touted its use and provided engineering design criteria for its application, the masonry industry encouraged its use, and engineers accepted it. What endorsements!
The success was so overwhelming that within several years hundreds of short and tall buildings around the country displayed brick masonry facades using the latex mortar admixture. Unfortunately, the latex admixture released chlorides because of degradation of the latex by the highly alkaline portland cement environment. The chlorides destroyed the passivating effect of cement's alkaline environment, initiating corrosion of steel reinforcement, relief angles, and anchors. Brick panels cracked and fell from building facades. The number of failures was enormous; another major mistake that took decades to overcome!
These are some past plagues to our industry, wrought by what was considered to be progress. But all problems are eventually overcome and hopefully provide lessons. They emphasize the need for better evaluation of materials, material combinations and new products and processes, which unfortunately may mean slower progress in the future.
Bernard Erlin is president of The Erlin Company (TEC), Latrobe, Pa., and has been involved with all aspects of concrete for over 47 years.
William Hime is a principal with Wiss, Janney, Elstner Associates and began working as a chemist at PCA 53 years ago.