Balancing Structural Integrity with Eco-Friendly Mortar, Cement and Concrete Practices

30th Jan 2024 -

As environmental concerns around climate change continue to mount, the building industry is increasingly looking for ways to balance structural integrity with more eco-friendly practices when working with concrete and its composite materials like cement and lime mortar. 

In this article, we look at new ways to make concrete construction more environmentally friendly without compromising safety. We examine the benefits and limitations of greener alternatives to ordinary Portland cement, including geopolymers, magnesium oxides and limestone calcined clay cement mixture.

What are the challenges with traditional materials?

The production of traditional Portland cement and ready mix concrete comes with immense environmental baggage. From the mining of raw materials to the energy-intensive manufacturing process, they have many detrimental impacts. Here are the top 5 environmental challenges with conventional concrete mix.

1. High CO2 emissions

The production of traditional cement mortar releases staggeringly high amounts of carbon dioxide (CO2) emissions. Every tonne of cement production emits close to 1 tonne of CO2. People widely use concrete, and it contributes to about 8% of global CO2 emissions.

2. Intensive energy requirements

To reach the high temperatures of over 1400°C (2552°F) required to produce cement, huge amounts of fuels like coal and natural gas are burned in cement kilns. This fossil fuel consumption results in even more greenhouse gas emissions beyond just the CO2 from the limestone conversion process.

3. Finite raw materials

Limestone and clay are the finite raw ingredients needed for cement production. Extracting these through mining and quarrying causes environmental damage. At current usage rates, it is predicted that global limestone reserves could run out in the next 100-150 years.

4. Air and water pollution

Cement facilities release large amounts of dust and other particulate matter emissions that pollute local air quality. Runoff from quarries can also contaminate nearby water resources. Facilities near rivers, lakes and oceans can also adversely impact water quality.

5. Habitat destruction

The landscape scarring from limestone and clay quarrying destroys natural habitats and reduces biodiversity. Vegetation clearing and soil removal disrupt local plant and animal ecosystems. Proper reclamation methods are not always followed after quarrying activities cease.

5 eco-friendly alternatives to concrete production

As outlined above, the environmental impacts of standard concrete materials have led to promising adoption of greener alternatives. From novel binders to renewable heating methods, new techniques are emerging to reduce the carbon footprint of concrete production. Below are 5 eco-friendly alternatives.

1. Supplementary cementitious materials

Industrial byproducts like fly ash and blast furnace slag can replace up to half of the typical Portland cement content in concrete mixes. Requiring less processing than cement, these supplementary materials reduce the overall carbon footprint of concrete.

2. Alternative binders

New binder chemistries using magnesium oxide or calcium sulfoaluminate are being developed to produce concrete with lower-temperature manufacturing methods and fewer emissions. Geopolymer concrete uses fly ash as the binder instead of Portland cement.

3. Renewable fuels

Heating cement kilns with renewable biomass instead of fossil fuels like coal and gas cuts down on carbon emissions from concrete production. Solar or plasma heating methods could also be on the horizon to improve energy efficiency. 

4. Recycled materials

Substituting recycled concrete from construction and demolition debris for newly mined aggregates reduces the need for additional resource extraction.

5. Carbon capture and storage

Research shows promise for integrating captured CO2 into concrete mixes. This potentially creates carbon sink concrete that is stronger and more durable. 

Structural integrity issues with eco-friendly materials

While greener concrete alternatives promise environmental benefits, they must meet the same performance standards as conventional concrete. Here are the key structural integrity challenges with eco-friendly concrete alternatives. 

• Lower early strength: Alternative cement mix using fly ash or slag gains strength more slowly compared to traditional Portland cement concrete. This requires adjustments to curing times and delaying the removal of formwork.
• Reduced durability: The alternatives can be more prone to freeze/thaw damage as water penetrates pores more easily. Resistance to chloride penetration from de-icing salts and alkali-silica reactivity also needs verification.
• Higher shrinkage and creep: Cement with higher slag contents showcases increased dry shrinkage which can lead to more cracking over time. Concrete creep also increases, requiring changes to structural design parameters.
• Less uniformity: Recycled concrete has more variability in gradation, porosity and impurities compared to new aggregates which can impact overall concrete performance batch-to-batch.
• Unfamiliar practices: Contractors’ lack of familiarity with curing and field testing requirements for newer alternative concretes can result in underperforming structures if not properly executed.
• Code compliance: Alternative cement and concrete typically have less historical data compared to traditional materials like brick mortar mix. This poses challenges for approval under current structural design codes until more data is available.
• Appearance: Recycled concrete results in more colour variability. There is likely to be a small amount of exposed imperfections on finished concrete surfaces compared to consistent newer aggregates.

What is the compliance standard for eco-friendly practices?

When considering eco-friendly mixed mortar, concrete and cement alternatives, it is reasonable to question whether adoption is practical compared to proven traditional methods. The British Standards Institution (BSI) sets out 9 relevant areas and codes to meet.

1. Compressive strength (BS EN 12390)

Must meet the minimum strength classes stipulated in UK Building Regulations and structural design standards like BS 8500 for the particular structural application (e.g. foundation wall, slab, tiles, etc). Lower strength can compromise capacity.

2. Tensile strength (BS EN 12390-6)

Resistance to cracking is vital for durability. Cracking allows water ingress that can corrode rebar and undermine integrity over time. Testing measures tensile capacity.

3. Elastic modulus (BS 1881)

The modulus value factors into reinforced concrete calculations and flexibility which impact structural engineering design. 

4. Bond strength (BS EN 1542)

Developing an adequate bond between rebar reinforcement and the concrete matrix is crucial for composite interaction and load transfer. Standard pull-off testing examines bond strength. 

5. Drying shrinkage (BS ISO 1920-8)

Uncontrolled shrinkage of concrete can lead to excessive cracking over time which hinders durability. Testing verifies the chances of concrete crack repair work in the future. 

6. Freeze-thaw (BS 5075)

Repeated freezing and thawing degrade concrete in outdoor UK conditions. Testing evaluates resistance to saturation, freezing damage and scaling.

7. Sulphate resistance (BS EN 12390-10)

Exposure to sulphates in soils chemically attacks concrete foundations. Immersion testing proves resistance.

8. Chloride ingress (BS EN 13396)

Chlorides penetrate concrete and corrode rebar over time, which can weaken structures. Testing limits allowable amounts.

9. Alkali-silica reactivity (BS 812-123)

Expansive reaction between cement and aggregates causes cracking. Accelerated testing identifies susceptible mixes.

How to balance structural integrity and eco-friendly goals

Careful planning and execution are needed to achieve an improved environmental footprint while maintaining structural performance. The following suggestions can guide contractors in effectively blending traditional concrete practices with greener options.

Blend mixes

Use a ratio of 70-85% traditional Portland cement and 15-30% alternatives such as fly ash, slag or limestone. This reduces the carbon footprint while meeting strength and durability needs if properly tested.

Start with non-structural uses

Initially use eco-concrete alternatives for non-structural applications. This could be pathways and non-load-bearing walls. It builds confidence before using it for structural members.

Evaluate construction impacts

Analyse how using eco-alternatives will impact your construction processes including pouring, finishing, curing and scheduling. Be sure to account for those impacts in plans and budgets.

Monitor early results

Closely monitor the performance of the first few pours using new sustainable mixes. When monitoring results, make any adjustments immediately to avoid large-scale issues at a later stage.