Jim Klinger, concrete construction specialist The Voice Newsletter October 2022

Question: We poured a cast-in-place concrete residential basement wall one week ago. The mix was a standard 6-sack footing and wall mix typically specified in our local market, 3000 psi at 28 days with a design water-cementitious ratio of 0.55. We stripped the walls this morning, and were surprised to see the wall surfaces stained blue as depicted in the photos below. We have been using the same type of form panels and form release for years and have never seen such discoloration. The homeowner is demanding an explanation. What can ASCC tell us?

Answer: Our review of your approved mix design submittal indicates that the concrete mix has been proportioned with 366 lbs. of Type II cement (ASTM C150) and 198 lbs. of Grade 120 slag cement (ASTM C989). Put another way, this is a 35 percent slag mix, and therein lies our answer. According to the Slag Cement Association (SCA) "Info Sheet IS-10", the mottled green or blue-green areas you are seeing are known as "greening", caused by a chemical reaction between sulfide sulphur in the slag cement and compounds in the straight cement. Greening is cosmetic only; the temporary discoloration does not affect strength, permeability or durability. No special treatment needs to be applied to make this go away.

Greening typically disappears once the concrete surface is exposed to air and direct sunlight. The key is giving the wall a chance for the surface to oxidize. Conditions that may cause slower oxidation rates could include cold, wet weather, sealed surfaces, and so on. In most cases, however, the exterior surfaces should return to normal within a week. The interior of the wall section, however, since it isn't exposed, could stay blue indefinitely.

The Slag Cement Association website currently has 29 technical "Info Sheets" that can be downloaded for free, covering all aspects of working with slag cement from mix design proportioning to sawcut joints to greening. All should be of interest to ASCC members. 
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Question: We experienced readymix material shortage delay issues at the end of 2021 and the first part of 2022 as described by Cory Lee in the September 2022 ASCC VOICE. We are currently trying to close out a project and have requested an equitable price adjustment from the Owner in an attempt to recover cost impacts associated with supply-chain issues that were totally out of our control. The Owner is asking us to provide proof that there was indeed a break in the supply-chain that caused our project to be delayed. Does ASCC have literature or articles from that time that can show this was a real shortage?

Answer: We searched for literature you might use to support your position. The best way to proceed is to document the shortage or supply-chain issues through your readymix supplier and the cement sources identified in your approved mix design submittals, since those would be the most project-specific.

For regional information regarding cement economic trends, the Portland Cement Association (PCA) website has a wealth of resources available in various media. Some of the economic reports have a subscription-type paywall, but there are many complimentary reports that may contain the regional data you are seeking.

What you are going to find straightaway is the PCA economic reports are extremely comprehensive in scope, covering monetary policy, wage trends, fuel trends, housing market trends and other factors that either directly or indirectly affect the supply, demand and distribution of cement.

There are no doubt other ASCC members who have similar experiences with tight cement market conditions. After reviewing the information from your suppliers and the PCA reports, please let us know how your negotiations turned out.

We also recommend you sending a copy of the recently-published ASCC Position Statement #45 titled "Managing Concrete Projects: Concrete/Steel Price and Delivery Volatility Risks" to the Owner, which is a reminder that there are indeed unpredictable and unstable market factors beyond the control of the concrete contractor that are fair game for an equitable price adjustment.