CONCRETE

Collaboration is the Cure: Bridging Suppliers and Designers

Collaboration is key for achieving substantial concrete emissions reductions. Stakeholders from every step of the supply chain must work together to develop and implement low-emissions solutions. This may include jurisdictions, engineers, contractors, suppliers, clients, and the design team. Before design begins, the design team should engage with local concrete suppliers, concrete contractors, and concrete technologists to determine what low emissions mixes have been developed and what barriers may be overcome to further cut emissions. This collaborative process will inform the designers of the opportunities and constraints provided by the the concrete mixes available to them. If unfamiliar concretes are being used, invite the concrete supplier to contribute to the site supervision plan².

The collaboration process begins by 1) getting to know what options are available to suppliers local to the project, which will help to 2) address concrete supply opportunities and constraints. Using shared collective knowledge, 3) develop a plan for workability/consistence, placement, and striking/form removal for in-situ elements. Finally, work with the team to 4) incorporate off-site construction opportunities, 5) avoid waste, 6) take advantage of temporary works, 7) strategize around application and feasibility and 8) test, validate, and share results.

1. Get to know what options are available to local suppliers

Understand the options available to local suppliers and work with them to reach the most optimal specifications while also pushing towards creating demand for emissions reduction strategies. Materials in concrete vary significantly depending on local supplies. Aggregate, the largest and heaviest portion of concrete, should ideally come from nearby sources, and can dictate the amount of cementitious materials needed for strength. Sourcing aggregates from further away should only occur when needed to achieve performance goals. Supplementary Cementitious Materials (SCMs) vary in quality, consistency, availability, and transport distance, so it is important to know which ones local suppliers can utilize dependably and economically. Lastly, admixtures can make low-cement concrete that would normally be unworkable much easier to handle and finish in the field, but require well-trained teams at the batch plant and the construction site, which not all suppliers and subcontractors can guarantee. Engaging with suppliers, contractors, designers, and engineers from the outset will make the greatest impact on reducing waste and emissions.

2. Understand local concrete supply opportunities and constraints

Encourage suppliers to survey a wider radius for batching plants to determine if there are more sophisticated ones farther away, but still within an acceptable range. More sophisticated plants can reduce cement use significantly which may more than offset the associated increase of transportation emissions.

Educate yourself on the emissions impact of different standardized mixes and investigate aggregate and cement type availability in your area. Dozens of standardized mixtures offer many options to achieve required strengths, but not all batching plants have access to all ingredients. Large projects, in particular, have greater potential to encourage cement plants to upgrade their facilities to provide sustainable cement. Understanding the emissions impacts of standardized mixes is a great place to start, but to accomplish the greatest emissions reductions, the use of innovative products and processes for concrete should be considered. Mix designs that meet all performance criteria for strength, durability, constructability, and cost, in addition to reducing emissions, should be targeted.

Emerging markets (excluding China) consume approximately 30-40% of the world’s cement. These areas tend to use bagged cement and mix concrete on site (as compared to concrete mixing plants and trucks). In these contexts, local masons and contractors should strive to optimize bagged cement use for ideal strengths and volumes to increase their cement-use efficiency and therefore overall emissions¹.

3. Develop a plan for workability/consistence, placement, and striking/form removal for in-situ elements

Balance workability/consistence with emissions reductions: Address workability/consistence needs in the early stages of collaboration and develop strategies to reduce embodied emissions. Workability/consistence is the ease with which concrete is mixed, placed, consolidated, and finished. Water content, admixture characteristics, cement content, and aggregate type, shape, and size all affect a concrete’s workability. During the construction process, consistence must fit each application for efficient handling, placing, and compaction. Generally, the greater the cement content, the better the workability, but some admixtures may reduce cement content while maintaining adequate workability. All options must be explored and understood to develop a plan that will design out the greatest amount of high-emissions cement possible².

Optimize program, construction schedule, and concrete mixes: Setting formwork, placing concrete, curing, and striking/formwork removal are critical stages of construction. A slab develops its necessary strength based on cement type, cement content, temperature, and curing method. For mixes with low cement content strength gain can be slow, but this can be worked into the construction schedule or offset with accelerating admixtures. If there is a low to medium amount of SCMs, the impact on strength gain may be relatively small and have no significant impact on strike time. Temperature monitoring can help with optimization and quality assurance².

4. Incorporate off-site construction opportunities

Be sure to consider incorporating off-site construction opportunities during the early stages of collaboration. Setting up off-site construction for precast elements has the potential to dramatically reduce waste, energy consumption, and emissions. Other benefits include faster construction time, dependable weather conditions, and the ability to create more sculpted elements that would be difficult to cast in-situ. However, off-site construction is currently hindered by the relatively higher cement content required for rapid demoulding to keep factories efficient². Other considerations that affect overall emissions include transportation to site, possible concrete strength overdesign to withstand transportation stresses, and additional on-site equipment that might not be required for in-situ casting. However, the innovation potential for developing lower-emissions precast concrete is high².

Stakeholders should identify opportunities for off-site elements in their early collaborative assessment, and they should encourage greater uptake of low-emissions concrete at precast construction facilities².

5. Avoid waste

Before construction, make a waste avoidance plan as part of the overall concrete construction plan that includes volumetric calculations and program optimization to avoid over-ordering. In-situ concrete waste is approximately 3-6% but can reach 13%, mainly due to over-ordering. Globally, 125 million tonnes of fresh concrete is estimated to be returned to ready-mixed plants annually. Ensure that concrete plants have recycling and reuse techniques that implement sustainable waste management systems. Minimize construction error and ensure quality workmanship with pre-pour procedures².

6. Take advantage of temporary works

Project teams should consider if and how they can design the structure to avoid the need for temporary works. Temporary works are often overdesigned even though they are in use for only weeks or months. This consumes large amounts of concrete and reinforcement, particularly on large urban projects. This is frequently due to code requirements, and code mechanisms should address shorter design life by providing an alternative clause for temporary works with a life of less than 2 years. If temporary works are unavoidable, consider: 

1. Can it be made from reusable materials? 
2. Can it be designed for later reuse? 
3. If mass is the only requirement, such as for thrust blocks, use only the lowest possible strength concrete and fill².

7. Set targets and innovate

Request emissions data from your suppliers as a submittal requirement to further the demand for product-specific EPDs: In North America, Building Transparency’s free EC3 tool can be used to establish baselines & targets and access product-specific EPDs. Product-specific EPDs should become a standard submittal requirement for all project bids, but they require 12 months of plant operations data to complete. If product-specific EPDs do not yet exist in your region, it is possible to request data to validate your project’s emissions targets, and get suppliers on the path to generating product-specific EPDs.

Set targets for the whole project: Set whole-project emissions targets, or a max Global Warming Potential (GWP) on A1-A3 emissions. Keeping targets broad, and not setting limits for individual classes of concrete, will enable the whole team to consider the greatest number of solutions and make judgment calls on tradeoffs that work towards the lowest overall embodied emissions. Comparing mix designs to the targets set will require knowledge of the embodied emissions of each mix design in the building and comparing the chosen low-emission mixes with benchmark mixes. Summarize total concrete emissions as a weighted average of each mix design to determine total emissions reductions as compared to the benchmark.

Innovate strategically: As innovative concrete products and mixes are developed, they will require the buildup of performance and emissions data. When concrete use is temporary or has low consequences of failure (e.g. haul roads, outbuildings, various landscaping applications) consider implementing innovative solutions to gather much needed data for the industry².

8. Test, validate, and share results

Once concrete mixes are developed and chosen, the project team should ensure that the contractor implements quality control for concrete works, including checks on constituents of concrete, and a technologist should be available as needed. After testing and construction, the project team should share real-site strength results with suppliers to improve understanding and future results².