superior appearance: fly ash makes beautiful, lighter coloured, “architectural” concrete; fewer bug holes and less honeycombing result in a smoother surface
Why use EcoSmart™ concrete?
Some technical advantages that make EcoSmart concrete a choice construction material:
EcoSmart concrete is easier to place, pump, and finish. When fly ash is used, workability of fresh concrete is improved. The glass spheres in fly ash improve lubrication by attaching themselves to cement particles, and diffuse electrical charge that causes cement particles to clump together. This increases responsiveness of the mix during pumping, placing and vibration.
Enhances long-term strength
The early strength developed in EcoSmart concrete is slightly less than that of a conventional design mix, but over time, higher compressive strengths are generally achieved. The slower strength gain is generally in the first several hours or a few days, depending on the mix. For a given 28-day design strength, the longer-term strength of EcoSmart concrete will be, in general, significantly higher than that of conventional concrete.
SCMs have a different particle size distribution than Portland cement and some have added pozzolanic properties that generate additional cementing compounds, both of which better fill the pore space, and thus, reduce the permeability of hardened concrete. Some SCMs reduce the water demand of the concrete mixture thereby reducing the capillary weak zones.
The slower hydration of some SCMs in EcoSmart concrete mixtures also results in a more gradual strength gain, which in turn generates less heat and thermal stress, thus leading to less cracking and more impervious concrete.
EcoSmart concrete can be less permeable, have less cracks, have less free lime in the hardened concrete, and be more resistant to alkali-silica reactions and sulphate attack, which result in more durable concrete.
Reduces thermal stress and cracking
By reducing the amount of Portland cement, lowering water-to-cementing materials ratios to achieve similar workability and gaining strength more gradually, EcoSmart concrete mixtures generate less heat and thermal stress, so are less likely to crack. These characteristics contribute to increased long-term performance of EcoSmart concrete.
Results in less bleeding
Because of the greater volume of finer particles and lower water content, weak zones from bleeding are less likely to occur.
Improves resistance to sulphate and other chemicals
The supplementary cementing materials in EcoSmart concrete react with the calcium hydroxide (which is susceptible to sulphate attack) to form calcium silicate hydrate, a stronger and more chemically resistant binder.
Improves control over alkali-silica reactions (ASR)
SCMs have proven to be efficient at controlling alkali-silica reactions (ASR) in concrete. However, their effectiveness is dependent on the properties (i.e., pozzolanic reactivity) and chemical composition (i.e., CaO and alkali contents) of the SCM.
Gives a superior appearance
Fewer bug holes and honeycombing result in a smoother surface. Typically, fly ash makes lighter coloured, “architectural” concrete.
When properly proportioned, and especially in applications where high early-age strength is not crucial, using EcoSmart concrete can reduce construction costs. Supplementary cementing materials are generally cheaper than Portland cement, since they are industrial by-products. Designs that take advantage of the higher ultimate strength of EcoSmart concrete can lead to further materials cost savings (e.g., EcoSmart concrete which continues to gain strength beyond 40 MPa after 56 days may cost 10% less than a standard mixture of 40 MPa at 28 days).
A life cycle cost analysis may show the financial advantages of using EcoSmart concrete, since it becomes stronger and more impermeable with time compared to conventional concrete of similar 28-day strength, and may not need to be repaired or replaced as often.
EcoSmart concrete has been found to be easier to place and to have fewer bug holes and honeycombing requiring patching, while the decreased amount of bleed water requires moist curing to commence sooner, and greater quality control for surface finishing. The lower cost of placing of EcoSmart concrete, and the lower labour costs associated with patching, can offset the potentially higher slab finishing costs.
Is environmentally sound
Partially reducing the Portland cement content of EcoSmart concrete by replacing it with supplementary cementing materials reduces the greenhouse gas emissions associated with the production of the concrete.
Using EcoSmart concrete also saves natural resources because fewer raw materials are extracted for cement production, reducing energy use and greenhouse gas emissions. Using industrial by-products such as fly ash and slag reduces the demand for landfilling and the associated costs.
Contributes to achieving LEED® credits
EcoSmart concrete contributes significantly towards achieving the Materials and Resources Credits 4.1 and 4.2 under the LEED® Canada Green Building Rating System. The recycled content formula takes into consideration the weight of supplementary cementing materials (SCMs) as a percentage of total cementing materials (rather than the weight of concrete). This is because SCMs are very light compared to the weight of concrete (approx. 5% by mass), but their use in partially replacing Portland cement in the concrete mix can reduce the “GHG signature” of concrete by up to 45 or 70%, depending on the SCM (fly ash or slag).
LEED Canada also adds the cost of formwork for cast-in-place concrete to the cost of concrete materials. This brings the cost of cast-in-place concrete more in line with the cost of pre-cast concrete or steel, both of which already include the cost of the formwork as part of the cost for the pre-fabricated materials delivered to site. As a result, the contribution of using EcoSmart concrete towards achieving the LEED MRc4.1 and MRc4.2 also increases.