The City of Winnipeg’s Public Works department has issued new specifications for Portland cement concrete pavement works, including new concrete categories, updated concrete material properties, updated requirements for cold and hot weather concreting and new requirements for concrete mix design, concrete suppliers approval and concrete placement.
“There have been extensive discussions between industry representatives and the department’s engineering division on these new specifications, and we will continue to discuss as the industry makes the necessary adjustments in the field,” MHCA President Chris Lorenc said.
A lot of the discussion centred around the new requirements for hot and cold weather concreting, which includes maintaining internal concrete temperatures and protection of the concrete.
The CW3310-R18 – PORTLAND CEMENT CONCRETE PAVEMENTS WORKS specification will be posted to the City of Winnipeg Materials Management website.
Below is a summary of the changes from the department:
- New concrete categories based on application;
- Updating the concrete material properties;
- The material properties have been updated considering supplier recommendations where they do not adversely affect the intended material characteristics.
- The absorption limit was adjusted to 2% for 2023. We will continue to monitor in 2023 and adjust as needed in 2024.
- New concrete mix design requirements (Cementitious content, w/c, fly ash dosage, etc.);
- Allowing new types of cement (General Use Limestone (GUL) cement and High-early-strength Portland cement (HE)).
- Updating fly ash type to meet the requirements of CSA A3001 Class F and increasing fly ash dosage based on concrete type.
- Updating the Concrete Suppliers Approval requirements;
- The Concrete suppliers can either submit the QC testing based on compressive or flexural strength.
- Introducing new testing to evaluate the durability of concrete.
- The time for RCPT testing was set at 91 curing days. We will continue to monitor in 2023 and adjust as needed in 2024.
- Updating the requirements for Hot and Cold Weather Concreting;
- The Contractor is responsible for the methods of protecting the concrete regardless of the concrete quantity. Table CW 3310.6 provides recommended minimum protection methods using insulated tarps.
- The Contractor shall maintain the internal concrete temperature above 10 °C for a minimum of five (5) days after completion of placing operations, and until the concrete has developed a minimum compressive strength of 24 MPa.
- Protection method(s) may be removed after three (3) days when the concrete has achieved its design strength (35 MPa). Based on 2022 results, there is a risk that the concrete will be susceptible to differential temperatures and will crack if the protection is removed after three days. We recommend the concrete remain covered for five days.
- Updating the requirements for reinforcement installation;
- Hand placement of tie bars into the plastic concrete shall not be permitted.
- Tie bars shall be drilled after the concrete has hardened and developed a minimum of 20 MPa compressive strength.
- Updating the requirements for concrete placement;
- The Contract Documents shall identify where double lane-at-a-time paving is required.
- Hand placement shall be minimized wherever possible.
- New requirements for protecting concrete from adverse weather conditions;
- Updating requirements for finishing concrete surfaces;
- New requirements for curing. Two applications of curing compound are required to ensure proper coverage;
- New quality assurance testing and frequency, and where cores are required, they will be collected after the specified Curing days. Curing Day is defined as a day when the average ambient air temperature is above 5 °C according to the nearest official meteorological office;
- New acceptance/rejection criteria. All pay adjustments are set at 0.0 in 2023 except the rejection and removal criteria. Payment adjustments should still be tracked by our design teams and reported to the City.