Nov 13

Fly Ash Concrete

Fly ash in concrete

FROM GREY TO GREENISH …

If you consider yourself a green person, you may think using fly ash, a by-product of burning coal, in your concrete mix rather sacro-saint! After all, coal plants are some of the biggest polluters and CO2 emitters.  In recent decades, in an attempt to minimize its environmental impact, the EPA forced coal-powered plants to trap particulate matter before it is released in the smokestacks, to properly capture and dispose coal ash, a.k.a. as fly ash, the residue found after smokestacks are cleaned. Disposal of fly ash is usually done by mixing it with water and placing it into open impoundments (that could be damaged by storms), storage ponds or buried in landfills that have been known to occasionally breach or leak as in the case of the December 2008 collapse at the Tennessee Valley Authority’s Kingston Fossil Plant, releasing 5.4 million cubic yards of coal fly ash into the Emory River! So how much are we reusing? Approximately 43-45% of all fly ash is being recycled today.

Electrical PoleWith 50% of all electricity in the US being generated by coal plants, one couldn’t begin to imagine the huge amount of fly ash produced by coal-powered plants daily. Capturing it and reusing it in a safe way would in fact prevent the inevitable spread of some of the heavy metals  it contains (depending on the coal bed makeup: arsenic, lead, chromium, mercury, dioxins etc.) in the atmosphere we breathe, the water we drink… So when the first attempts at substituting fly ash to Portland cement resulted in a concrete with greater strength and durability, what was once a worrisome problem looked like it could be turned into a solution for the environment and the construction industry. Recycling fly ash into concrete would not only reduce CO2 emissions but also neutralize the harmful effects of the known carcinogens it contains and the need to mine for new raw materials. Also called geopolymer concrete, this “green” concrete is cheaper to produce and is being widely adopted for all types of concrete applications.

2 TYPES OF FLY ASH
There are 2 classes and both can be used as a replacement for Portland cement or hydrated lime. They act as a filler providing contact points between larger aggregate particles in asphalt concrete mixes.

Class F: is made from burning anthracite and/or bituminous coal
Class C: is made from lignite or subbituminous coal

BENEFITS OF USING FLY ASH IN CONCRETE

Earth-Friendly-IconECO FRIENDLY?
The process of making cement is quite energy-intensive and could account for 5-8% of greenhouse gas emissions around the world. Factor in steady population growth and the number will continue to increase unless a massive adoption of greener alternatives happens. Fly ash concrete is one of them because of its abundant availability, cheap cost and the fact that it could reduce as much as 90% of CO2 emissions when considering the end to end process.

Green builders can gain points towards their LEED goals (Leadership in Energy and Environmental Design) if they can replace at least 40% of Portland cement with it. Bricks that are made with fly ash can even store CO2 from the atmosphere.

ALL AROUND BETTER CONCRETE
Fly ash is known to improve concrete’s workability, pumpability, chemical resistance, finish, strength, and durability. Fly ash particles are similar in size with Portland cement and as a result requires less water during the mixing stage. This means better surface finish, sharper edges in precast concrete. Its fine particles reduce bleeding and segregation and improve overall workability. This is especially helpful in extending working time in hot weather.

DECREASED PERMEABILITY:
Fly ash produces a concrete that is less porous than Portland cement. The pozzolanic effect of fly ash creates a denser product due to smaller pore sizes. It also reduces bleed channels and permeability in concrete.

Widely used in road projects, fly ash increases the stiffness of the asphalt, improving rutting resistance and mix durability.

EXAMPLES OF FLY ASH REUSE

In addition to replacing Portland cement, fly ash is being used in the following areas and the list keeps expanding:

  • Road construction: ideal self-compacting backfill material (as a replacement for compacted earth) for backfill, embankments, road sub base construction, mineral filler in asphaltic concrete, as a loose application on roads for ice control, in highway sound barriers…
  • Agriculture: fertilizer, soil amendment and stabilization.
  • Aggregate material substitute: for brick production replacing clay.
  • Dam construction: in roller compacted concrete dams.
  • Waste management: waste solidification and stabilization, conversion of sewage sludge into organic fertilizer or bio fuel.
  • Roofing material: tiles, granules.
  • Marine: pilings, artificial reefs
  • Binding agent: paints, undercoating.
    And much more

IN CONCLUSION

Only time will tell whether or not small amounts of heavy metals could leak from the concrete over time and if this new found durability is truly long lasting. Recent spills have prompted environmental groups to call for tougher regulations, so whether or not the EPA decide to classify it as hazardous  material remains to be seen. But until then and until coal powered plants are being phased out for greener alternatives, and the huge reserves of fly ash remains an environmental issue, the safe use of fly ash in concrete makes sense and should continue. 

United Equipment Sales

Sources:
Marc Boyer: How fly ash concrete works
Fly Ash on Wikipedia
Fly ash products
Fly ash suppliers

 

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May 09

Milestones in Concrete Construction

We thought we would take a trip into the past to find out some of the major milestones in the history of concrete construction. After all, how can we appreciate the technologies we have today, without knowing the work that countless individuals have contributed to this industry by giving their lives, passion and vision to better our world. The timeline below is by no mean everything but covers some of the most important milestones.

12,000,000 BC – It turns out that cement compounds can be found as a result of a natural process where limestone came in contact with oil shale in a process of spontaneous combustion. It was discovered in Israel.

5600 BC – First form of concrete discovered in Europe in the region of the Danube River in Yugoslavia. It was used to make floors in stone age huts providing a major upgrade in the quality of life for hunters and gatherers.

3000 BC – First known use of concrete-like material in China with the building of the Great Wall. Made from a mix of sand, pottery shards, bones and water, this cement was greenish-black.

Egyptian pyramid

2500 BC – The practice of binding bricks using mud mixed with straw appears. The addition of lime and gypsum mortar to the process can be seen in the Pyramids in Egypt.

800 BC – The first use of bitumen (a.k.a. asphalt), a semi-solid form of petroleum that can bind stones with bricks is credited to the Babylonians and Assyrians.

600 BC – Use of the first concrete that can harden under water and in the air was made by the Greeks, thanks to the discovery of pozzuolana (a.k.a. pozzolan or calcined lime) on the Island of Santorini.

Roman Colosseum

82 AD – The Colosseum in Rome is completed using tons of Roman concrete which bears no resemblance whatsoever to Portland cement, since it is never in a plastic state and is more like cemented rubble made by manually packing mortar around stones of various sizes.

AFTER 400 AD – With the fall of the Roman Empire, the art of concrete is lost for almost 1300 years, reverting to lime based mortars and concrete.

1756-1796 – Multiple patents are filed in England for hydraulic cement (stucco), hydraulic lime etc.

1825 – Creation of the Erie Canal launching the need for cement in the United States using hydraulic lime.

1828 – First application of Portland cement used to seal breaches in the Thames Tunnel.

1850s – Building of the first concrete roads in Austria, England, other European countries and the US.

1850-1880 – French builder, Francois Coignet popularizes the use of concrete in construction.

1856 – First patent filed for the use of reinforcement in concrete using iron bars and wire mesh in small rowboats by French gentleman farmer named Jean-Louis Lambot.

1891 – First concrete streets built in the US, in Ohio.

1904 – First concrete skyscraper is built in Cincinnati, Ohio.

1905 – The National Association of Cement users is created, which will later become the American Concrete Institute.

1911 – Shotcrete is invented, allowing for the first time placement of concrete on vertical or horizontal planes.

1913 – The first concrete pump patent is filed.

1936 –  The Hoover Dam and the Grand Coulee Dam, are the first concrete dams built.

1970s – The first fiber reinforced concrete appears on the market.

1983 –  Invention of Syndecrete™, a light weight concrete that combined cement with recycled materials such as coal fly ash (a byproduct of coal plants) with polypropolene fiber to provide reinforcement (from carpet manufacturers). The finished product is used in kitchen countertops, tile flooring and more.

1985 – Introduction of silica fumes or micro silica into cement to produce the strongest concrete with very low permeability.

1995 –  Insulated Concrete Forms (ICF) are being introduced to build homes and to hold concrete, providing greater insulation (temperature and sound) than common stud walls.

Concrete pumping has grown to become a vast industry that keeps expanding its boundaries, and possibilities. Looking back over the timeline, it is interesting to see that French and British have contributed a great deal to the progress of concrete in construction and Ohio leads the way in the US! So, it isn’t surprising that the American Concrete Pumping Association is based in Ohio!

Stay tuned for a future article on newer developments in the world of concrete and what the future of concrete holds. Until then, if you are looking for a great deal on a concrete pump for your next job, why don’t you give us a call at (503)283-2105. With over 40 years of experience in the industry, we can help you solve challenges and work within your budget. We always love to hear from you.

Suggested further reading:
http://excavatorheavyequipment.com/blog/2013/06/03/plaster-used-by-ancient-builders-still-used-today/

https://fp.auburn.edu/heinmic/ConcreteHistory/Pages/timeline.htm

Jan 21

What is Polyurethane Concrete Raising?

Difference between Mudjacking and Polyurethane Concrete Raising

Also called foam lifting, polyurethane for concrete raising has been in practice for about 20 years. However, the price of the equipment and polyurethane material made it way too expensive for private contractors to adopt and replace traditional mudjacking. It has mostly been used by the Department of Transportation to raise streets and highway roads. Well, until now! What changed?

1.The equipment:
Today, smaller and affordable basic trailer units can be bought for under $50K that contain everything needed to do the job. They can also be pulled by a simple pickup truck that can carry the equivalent of 5 cubic yards of material. The polyurethane can be shipped and stored in 55 gallon drums.

2.The material:
This used to be protected under a patent. By mixing a two-part polyurethane, a reaction is created and the material expands to fill voids and raise concrete slabs. On-demand instead of batched. The average cost of Polyurethane material at $153.00 per cubic yard.

3. The selection:
There are several types of foam depending on the job requirements:
Lightweight and fast reactive
High density foam (for heavy slabs on highways)
Single component polyurethane to bind and stabilize loose soil
(http://www.mudpumps.com/materials/)

Mudjacking Versus Polyurethane concrete raising

Both techniques are used for similar projects with settled concrete: garage floors, driveways, entry, porches, sidewalks, basement floors, pool decks etc.
Both achieve the same results and are cost effective alternative to pouring new concrete but the process is a bit different.

Mudjacking equipment:
As a minimum you will need a paddle mixer, a truck that can carry 5 cubic yards of material, a front end loader, a yard to store bulk materials!

Mudjacking material:
Lots of dirt! Pumping 100 lbs per cubic foot of sand mixed with Portland cement under the settled slab. Foam, on the other hand, weighs about 2 lbs per cubic foot! The cost of mudjacking material is less than $20.00 per cubic yard. So it is quite cheap.

Mudjacking, doing the work:
Mudjacking involves heavy work like shoveling material into a mixer, drilling lots of 1” holes and moving a pump around the job site.

Compared to mudjacking, polyurethane concrete raising is pretty light work, much less physically demanding. For one, no dirt to haul, one person can handle the job. Using a pickup truck you can move the trailer unit anywhere on the site, as close as you need to be, drill a few 5/8” holes, inject the liquid foam in them. 5/8” holes are very tiny compared to having to drill many 1” holes when mudjacking. So there is little patching to do.  The job is completed in record time and the surface is immediately ready to be used. In less than 15 seconds, the liquid turns into foam and reach its final volume. Once cured, it will never lose its density! You can cover a much larger area in less time than with mudjacking because of the material can easily be delivered in any area and cures so quickly.

So if you are tired of hauling dirt, heavy physical labor, ready for something new and cleaner, you might want to look into foam raising. It is here to stay and has a very promising future.

And, if you have mastered the art of mudjacking and are in need of a good concrete pump, check out our mudjacking pumps specials.
Or give us a call at: (503)283-2105

Reference Material:

Mudjacking 101: How to repair broken concrete
http://www.mudpumps.com/concrete-lifting-options-the-pros-the-cons/