One of the drawbacks to committing your thoughts to paper is that "eating your words" becomes a very real possibility. I am not quite ready to put the finishing touches on my Hammermill-Bond Casserole, but I have learned some new things about concrete that require at least a clarification of several of my earlier articles. I reported a mortar flaking problem that some agencies were having with the KCMMB concrete in several past articles. I cited inadequate curing, failure to control evaporation and drying as a possible cause of the problem. This past winter, all of us experienced mortar flaking problems with the hard rock concrete and in some instances; I saw the same problem with limestone concretes. It may be that this past winter was unusually harsh on relatively new concrete, but in any case, the performance of our concrete pavements was unacceptable. At this year's ACPA paving conference, two Iowa State University professors made presentations. In one of the presentations, Dr. Jim Grove indicated that Iowa State acted as a kind of concrete S.W.A.T. team funded in part by an FHWA grant. He spoke about a tactical crew that Iowa State could send to examine and quickly determine the cause of a variety of concrete pavement problems. Facing mounting cases of mortar flaking, this seemed too good to be true. Our local ACPA chapter recruited Dr. Jim Cable, the other professor from Iowa State, to discuss our problem at the conference. He grimaced a little at the S.W.A.T. team reference, but confirmed that indeed Iowa State was given a federal grant to study problems in concrete and that he would be our S.W.A.T. team commander should Iowa State elect to help us. Before he left, we arranged for a tour of several problem projects and drafted a scope for the study. We agreed to provide the cores, and to promote Iowa State's pooled fund studies, and Iowa State agreed to provide us with a report that identified the cause of our problem and a set of recommendations to solve it. It turns out that these federal grants require some matching funds. The pooled fund provides the matching funds and just like federally funded road projects, the return on local investment is compelling. The website for The Center for Portland Cement Concrete Pavement Technology is http://www.pcccenter.iastate.edu. It is definitely worth a look. We took cores in projects that were exhibiting the mortar flaking problems. We took cores in areas that had not mortar flaked so that Iowa State could examine specimens that had not failed. As Dr. Cable pointed out, the surface would provide the answers, thus we needed samples where it was intact. We cored projects in Prairie Village, Mission, Merriam, Olathe, Westwood, Shawnee, Overland Park, and at Ash Grove's new concrete parking lot. The study found that in every case the cores had high water cement ratios at the surface. This could be the result of overworking the surface, of "blessing" the surface during finishing, or of applying the curing compound while the concrete was actively bleeding, trapping bleed water at the surface. Dr. Cable identified an FHWA Policy Memorandum that recommended limiting slag cement percentages to 25% where used in exterior concrete exposed to freezing and deicing salts. Many of our mixes substituted slag at percentages between 35 and 40%. The slag is used to mitigate a damaging chemical reaction between the alkalis in the cements and the siliceous materials in the aggregates (ASR). Slag cements when used with Portland cements mitigate this reaction. The report suggested a less conservative (more realistic) test for setting the minimum percentage of slag or other ASR mitigators and recommended several changes to the concrete specification including setting the maximum slag percentage at 25%. The final report is available for download: Iowa State Report John Wojokowski of KDOT has done some excellent research regarding bleeding with modern concretes, and has found that the slag cement concretes tend to bleed sooner than straight Portland cement concretes. This earlier onset of bleeding coupled with the lower water content may be masking the bleed process, making it more difficult to determine when to perform final finishing and curing. It also becomes more important to have the concrete placed and shaped (screeded) quickly as screeding while the concrete is actively bleeding will contribute to a high water cement ratio at the surface. I was very impressed with Dr. Cable and the Iowa State team. The Center for Portland Cement Concrete Pavement Technology gave us a practical solution to a complex problem relatively quickly. I would encourage anyone that uses concrete pavement (streets, curbs, sidewalks) to consider participation in one of the pooled fund studies. As for me, I still believe that evaporation control and curing are essential to construct durable concrete. However, our mortar flaking problem was not caused by drying of the surface. Therefore, it looks like I may be adding a little more fiber to my diet – my wife the nurse tells me I need it.