It appears that some of the concrete suppliers in the western part of the state do not understand or have issues with KDOT's specifications. We have created this discussion board for you to post any comments or suggestions regarding this issue. All comments can be posted anonymously.
Next week, KDOT will meet with the Kansas Ready Mixed Concrete Association's TQC Committee to discuss these issues as well. We invite anybody who wants to participate to attend. The meeting will be next week, August 26th at 9:30 AM in the Basement Conference Room at 800 SW Jackson St. in Topeka, KS. Please click here to RSVP for the meeting.
Below you will various comments that have already been made about the concrete specifications from other parties.
KDOT: "Every time a new spec book comes out, the price of concrete increases even though the specification are supposedly only getting easier?
We went out and tried to explain it to them. We have actually made several trips out there since 2007. I do not think it is helping.
I think we need a different plan."
IM: "The main problem we have out west is that most ready mixes only have two aggregate bins and one cement silo. In order to meet the new MA requirements, additional coarse aggregate has to be added to the mix. Our old mixes primarily used 30% coarse aggregate. We are now having to use anywhere from 35% to 60%. The main reason for this is to meet the requirement of the actual workability being within 5% of the target workability. A third aggregate would be useful in many cases but the ready mixes do not have the capability to add the third aggregate. We are also having difficulty meeting the permeability requirements and have had to switch to a fly ash blended cement. This is a higher priced cement and is only supplied by Ash Grove at the present time.
Another thing that I think needs to be looked at is the amount of and size of coarse aggregate in the mix. If you try to use a MA-3, MA-4, or MA-5 aggregate, you have to retain material on the ¾” sieve. This is requiring problems with the present design clearances on RCB’s and RCSH bridges. The bottom mat on RCSH bridges is only 1” and many times this gets slightly less with the bar chairs pushing into the plywood or squashing slightly. With the larger aggregate and more of it, we are starting to see voids left between the forms and the steel.
The addition of the extra coarse aggregate, the change of cement, and the requirement that the concrete suppliers design their own mixes has increased the cost substantially. Many of the ready mixes just don’t want to deal with it and thus are going to add a lot of money to their quote if they do. My problem with all of it is that we are paying a lot for the new concrete and are not getting anything better for it. For local bridges, especially RCB’s with earth fill, I just don’t see the need to worry about the permeability of the concrete."
