Sorry for the delay, I hope…

Sorry for the delay, I hope my comments are considered.

We have been working for MTO projects for many years, and we usually encounter additional challenges in MTO projects for the following reasons (some of them have been discussed already and there are plans address them)

1) Reduced slump range +- 20 in standard mixes (example 80+-20). This is too restrictive and increases risk for rejected loads. Using the standard range (80+-30) will create less issues on site and will not affect performance of concrete. MTO mixes are designed with very high overdesign. MTO projects have higher risk and rejected loads need to be reduced in possible, provided that performance is not affected. The overdesign of MTO mixes is generally 10-15 MPA. Setting the slump range to +-20 will not make any improvement and cause many issues. The rate of rejected loads in MTO is significantly higher than high risk private jobs.

2) Mixes with 30 and 35 MPa and RCP 2500 at 28 days. The requirement of RCP 2500 with 25% slag max forces us to increase cement content significantly more that required for 30 or 35 MPA. The average strength for those mixes in about 50MPA. If the request is RCP 2500 and 80+-20 slump, the mix becomes very unstable and difficult to adjust. Those mixes should be plasticized.

3) Form A and B should be revised and indicate RCP targets, to avoid misunderstanding. Form A and B needs to reflect all specs required for the mix

4) GUL should be considered the default cement. Very few cement producers are still manufacturing GU.

5) OPSS 1350 is still requesting super P on site in some situations. The vast majority of concrete producers do not add super P on site and this is a reason for frictions with contractors. Reasons to avoid super P on site are as follows:
• Manually handling admixtures should be always avoided due to safety reasons. We had incidents due to this in the past that could have been avoided with super P at the plant.
• The addition of super P at the plant is more precise, and reduces the risk of contamination and human errors.
• Super P added at the plant allows for traceability of all the constituents added to the trucks.
• Super P added at the plant allows for better cement dispersion, resulting in better cement efficiency, lower RCP, better durability.
• Super P at the plant improves slump retention, exceeding 2 hs hours, without affecting any of the concrete properties.
• The addition of super P on site caused unnecessary delays on site that can be avoided adding super P at the plant.
• Super P at the plant improves air control. Air is strongly correlated to slump and making a drastic change of slump on site usually have an impact on air.

6) Limiting to 90 min for acceptance of concrete adds unnecessary constrains. Concrete producers are accountable for performance and with current admixtures is easy to achieve 120 min of slump retention.

7) Normal initial setting time of concrete is 4-6 hours not 3 hs. We need to use accelerants in all our concrete if 3 hs setting time is required. Fast setting time is not advisable because risks of cold joints will increase.

8) To allow for better GHG, more supplementary materials needs to be allowed and 56 days should be accepted in some cases (depending on the element).

9) Changing the requirements of RCP automatically from 2500 to 1000 when SF is used is not beneficial for MTO since prevent using mixes with small amounts of SF in combination with slag. One good example are sidewalks in bridges exposed to freeze-thaw and deicing salts. We have mixes with low SF and low slag that meets requirements of C1 and with excellent resistance to scaling that cannot be used in MTO due to this clause.

MTO is a very valuable customer and we want to provide the best quality as possible. Some of the rules in OPSS 1350 are an obstacle to provide the best quality, as expected by MTO.
Thanks