ACEC-BC Member Bulletin
ACEC-BC Member Bulletin:
Member Bulletins are articles developed by ACEC-BC Committees and Working Groups and published for use by consulting engineering companies as a general resource. The information provided highlights relevant issues and practices for the industry and should not be construed as legal advice.
Recently the BC Ministry of Transportation and Infrastructure (MoTI) announced that “to support the increased use of lower-carbon cement in British Columbia, we will now accept the use of Portland Limestone Cement (PLC), aka GUL, in all BC Ministry of Transportation and Infrastructure project components with the exception of pre-stressed elements.” Concrete mix design parameters for the use of mixes with GUL cement on MoTI structures are given in the latest edition of the MoTI Supplement (S6:19) to the Canadian Highway Bridge Design Code (CHBCDC) (Ref 1).
The MoTI Standards Specifications for Highway Construction also contain specifications for the use of GUL cement.
As many transportation stakeholders look to the Ministry standards and guidelines for support, the ACEC BC Transportation Committee in collaboration with the Sustainability Committee has developed this bulletin to provide additional context to the use of GUL cement in concrete.
What is GUL?
General Use Limestone Cement (GUL) is a type of blended Portland Limestone Cement (PLC) that contains between 5% and 15% of unprocessed (raw) ground limestone. This addition of raw limestone along with the addition of up to 5% gypsum or other minor additives occurs during the clinker grinding phase. This reduces the percentage of clinker present in the cement. GUL cement is typically ground finer than GU cement which results in similar compressive strength gain properties.
History of GU and GUL in BC
GU “General Use” Cement has historically been the most common cement used in BC. This changed in November 2010 when the BC Buildings and Safety Branch amended the BC Building Code to allow for the use of General Use Limestone (GUL). The Canadian Standards Association has allowed the use of GUL since 2008 in CSA A23.1 (Ref 2).
The Ministry of Transportation and Infrastructure (MoTI) have historically only allowed the use of GUL cement by consent request on a project-by-project basis with varying restrictions. In the latest supplement to the CHBDC (S6:19) published in July of 2022 the Ministry now provides parameters for the use of GUL in structures except in prestressed concrete elements.
Most research papers indicate no significant change in the long-term creep behaviour of GUL cement in comparison to GU cement. However, several validation projects have been initiated locally in BC to further confirm that there is no significant increase in creep of GUL cement based concretes in comparison with concrete manufactured with GU cement.
For very severe sulphate exposure the Ministry requires additional consultation for mix designs regardless of cement type.
Over 50% of the CO2 emissions related to cement production are released in the preheating stage of the clinker (at ~750oC) (Ref 3). The use of PLC’s reduces CO2 emissions due to the lower clinker content required in the cement that is subjected to the precalciner/preheating stage. This is in line with the government of Canada / Cement Association of Canada Roadmap to Net-Zero Carbon Concrete by 2050 (Ref 4).
GUL in BC now and into the future
It is expected that production of regular Portland Cements (including GU) will continue to decline in BC over the next few years. There are already ready-mix plants in BC that only use GUL cement, often due to only having one cement silo on hand.
The industry may push for a higher limestone addition rate than what is allowed at present. Further research on the durability of concrete with such cements would be required to support this.
How to Decrease Carbon Footprint of Concrete
The adoption of GUL cement has provided environmental benefit. However, there exists further opportunities to reduce the carbon footprint of concrete on new projects such as:
- using concrete mix design parameters to maximize service life,
- allowing for a performance based concrete specification designed to suit the structure and exposure, when there is confidence that the testing done at the time of construction will be sufficient to demonstrate long-term performance,
- optimizing mix designs to use supplementary cementitious materials (e.g. fly ash, slag and silica fume),
- optimizing structural design to limit the mass of concrete used in elements,
- consider specifying 56-day strengths instead of 28-day strength as appropriate, and
- consider transportation and local availability when specifying mix parameters.
Effect on Current and Ongoing Transportation Projects
Presently there may be concrete supply issues in BC as many ready-mix producers are not able to source both GU and GUL cement in a timely fashion.
This should be considered when specifying concrete mix requirements for projects as the option of allowing the use of either GUL or GU cement could reduce supply chain delays for concrete suppliers.
For projects which are in progress and have not allowed the use of GUL cement there may need to be a consent process to consider modifying the contractual requirements of the project.
On future projects there may be cost and project schedule implications if GUL cement is not permitted as concrete suppliers may need to import alternate cements and incur costs for additional on-site storage.
- Use of GUL cement is part of the Cement Association of Canada Action Plan for Canada’s cement and concrete industry to achieve its carbon emissions reduction goals by making cement net-zero by 2050.
- Expect supply and availability of GU cement to decrease in the next 2 to 3 years.
- Contractual issues may arise on projects where the use of GUL cement has not been permitted by the specifications.
- If high sulphate concentrations are present in the soil, then some projects may require special concrete mix considerations.
Ref 1: https://www2.gov.bc.ca/gov/content/transportation/transportation-infrastructure/engineering-standards-guidelines/structural/standards-procedures/volume-1
Ref 2: CSA A23.1 – Concrete Materials and Methods of Concrete Construction
Ref 3: https://ised-isde.canada.ca/site/clean-growth-hub/sites/default/files/documents/2022-11/roadmap-net-zero-carbon-concrete-2050_0.pdf
Ref 4: Rubenstein, M., 2012. Emissions from the Cement Industry. https://news.climate.columbia.edu/2012/05/09/emissions-from-the-cement-industry/ [Accessed 26 05 2023].
Ref 5: CSA S6:19 Canadian Highway Bridge Design Code