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/

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Aug 21

Air-Placed Concrete

The concrete industry is constantly looking into innovative techniques that can improve the product quality, its lifetime and sometimes cut cost.  If you live in an area of the world that is known for harsh and long winters, as a concrete contractor, you are facing additional factors and challenges that, let’s say, a contractor in California or Florida, does not’t have to worry about.  These external factors are not only harsh to the local residents but also to the concrete structures and can significantly shorten their strength, look and lives.

Air-placed concreteA new technique called ‘air-placed’ or ‘entrained air’ concrete, invented about 50 years ago, is helping reducing the impact of frequent freezing and exposure to deicing chemicals on concrete and improve its resistance.  Anyone who has ever accidentally placed a can of soda in their freezer and forgotten about it, knows that contraction and expansion can be messy! The same goes for concrete! Water expands when freezing and breaks the tensile strength of concrete, resulting in cracks and scales. This problem not only affects the aesthetics of what was built but also its structural quality, which is a bigger problem.

THE PROCESS

As its name implies, added air is incorporated in fresh concrete mixtures (using a proportioned combination of Portland cement, aggregates and water) and used to expel the material. The force of the air jet compacts the material. This process creates extra tiny spaces (we are talking smaller than the head of a pin) or bubbles that lessens the pressure that occurs with the expansion of water when it freezes and after it thaws off.

This process can be achieved a number of ways:
1. By using air-placed Portland cement
2. With a shearing action of mixer blades breaking up the air into tiny bubbles
3. By delivering compressed air at the nozzle by a separate air line
4. By adding entraining admixtures to stabilize the air voids

The process does require careful supervision during the mixing of the concrete. If you are using a separate air line, you will need a nozzleman helper, responsible for the air lance, to blow out excess material in the forms, steel etc. Always start at the bottom, when shooting walls, beams. You will know you have reached the maximum height and thickness, when the material begins to sag!

How much entrained air should be added to the mix? Anywhere between 5-8 percent of the volume of the concrete, with some variations are allowed if other conditions require it. It is recommended to take a sample every 75 m³ (100 yd³). You should have a minimum of 0.028 m³ (1 ft³).  Avoid using the first and last batch for the sample.

WHERE TO USE IT

While it has mostly been used in regions with harsh winters, air-placed or entrained air can be used virtually in all concrete applications and structures.  It is now being used in very hot countries where extreme high temperatures are also causing concrete to expand and contract. In terms of applications, entrained air concrete is found in heavy constructions, bridges, roads, large structures but also for water control, water storage, slope protection and special architecture features etc.

ADVANTAGES

Air-placed concrete adhered well to structural steel and provides great protection against corrosion. It improved the steel’s rigidity. The usage of entraining admixtures not only produces a finished product that is highly resistant to wetting  and drying, freezing and thawing cycles, but it also provides greater workability and durability. Something that could be used on all jobs!

EQUIPMENT TO USE

Mayco Concrete Line Pump

Mayco Concrete Line Pump

Concrete line pumps is what  you will need to make air entrained concrete.
You will also need an air compressor capable of producing a minimum of 100 cu ft. of air per minute per nozzle.

OTHER VARIABLES TO CONSIDER

The ways concrete is batched, mixed, the time and speed of mixing, transport, finishing and temperature can also affect the air content of concrete. To find out more about the effects of Concrete Ingredients on Air Content or the effects of Production and Construction Variables on Air Content, go to : http://www.cement.org/tech/pdfs/PL981.pdf.
You can also order the Manual on Control of Air Content in Concrete (EB116), published in 1998 by NRMCA and PCA.

Visit United Equipment Sales, and check out their special deals on used and new line pumps or call us at: (503)283-2101, if you have more questions.