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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Jan 04

Minimize Rebounding in Shotcrete

Shotcrete, a.k.a gunite, is a wet mix technique that produces a high velocity cone-shaped spray pattern via pneumatic mechanism onto a horizontal or vertical surface. Increase the air from the shotcrete nozzle to increase the velocity and the compaction of the particles and produce a denser concrete. Shotcrete uses either aggregates or mortar.

When to use shotcrete?
When you need to apply concrete vertically but do not want to deal with formwork and poured in concrete. Shotcrete works best for covering or repairing curved surfaces like swimming pools, bridges, tunnels, dams, slope reinforcement…

Strength of Shotcrete
Shotcrete uses a wet mix so the water/concrete ratio is very important and controlled by the nozzle man. It needs to be low (under 0.5) to obtain a denser and water-resistant mix.  This will also help reduce shrinkage and lower permeability in the finished product.

What is rebound?
One of the problems with shotcrete is the loss of material from concrete ricochets off the target surface due to the high velocity of the spray. This causes having to use more concrete, longer application times etc. The result can be vastly different when it comes to the properties of the in-placed concrete mix. If you use steel fibers as a distribution solution, the problem is even more problematic than with aggregates. According to Austin and Robins (1995), aggregates rebound is about 20-30% whereas with steel fibers, rebounding can reach 35-78% (Morgan et al., 1987; Banthia et al., 1992) with dry-mix shotcrete. With such high rebound, compaction is reduced and the concrete strength ends up greatly compromised.  The rebound of non-adhering material during a gunite operation (using a dry process) is greater than during a shotcrete job (wet process) because gunite requires a much larger air compressor. On a gunite job, the rebound material can be reused, whereas, on a shotcrete job, the non-adhering material is wasted. Removing it is time consuming, slows progress and can be costly. So choosing the right technique for the job is essential.

Thick or thin applications?
It turns out that the percentage of loss is affected by the thickness of the layer sprayed. In other words, the thinner the layer of shotcrete, the larger the percentage loss. The highest amount of rebound happens in the first spray on concrete. With subsequent coats, rebound diminishes. Another factor affecting the rate of rebound is aggregate density. A lower density will result in lower rebound rate.

Some solutions
Some polymer additives (Etonis) or modified starches can improve the adhesion and flow properties of concrete and reduce crack formation.

What pump is best for your job?
 If you are not sure what concrete pump is best for your next job, call Dick Hibbard at (503) 283-2105. With over 40 years experience in all things concrete, no question is too simple or too complex for him!

Some great pumps he recommends are:

Schwing WP 1000 concrete pump

A Schwing Wp-1000X

 

 

 

 

 

A Reed B-50 or C50Hp

Reed B50 and C50HP concrete pumps

 

 

 

 

 

 

Check all the great deals he has on Mayco, Schwing, Olin, Reed and Putzmeister used shotcrete pumps on United Equipment Sale’s website:
If you you need a gunite machine, check our site for our latest great deals.

Reference material
Parametric Studies on Fiber Rebound in Dry-Mix Shotcrete
The American Shotcrete Association
Polymer modification of shotcrete

 

Dec 13

United Equipment Sales Saves The Day in El Salvador!

We all know that building tunnels can be challenging! But making sure they don’t leak can turn into a real nightmare.

We were recently approached by a construction company in El Salvador that had built a 4000 feet tunnel but ran into a big problem when ground water started running down the hill and eventually leak into the tunnel through the rocks.

Tunnel Repair Engineering Drawing

The company first hired a contractor who ended up charging them 1 million USD but failed to fix the problem. Then, they contacted us to see if we could help them find a solution to their problem and work within their budget and source the appropriate equipment for the job.  After a series of meetings with their team of engineers going over the site, dimensions, challenges, limitations, we were able to together design a plan that not only would incorporate a permanent fix, work within their budget but also save them over $150K! This was achieved not only with the equipment we sold them but with the actual solution we came up with. In today’s economy, any savings goes a long way, but $150K, for any construction company is pretty extraordinary!

Worthington 650 CFM compressor

One of the reason the previous contractor didn’t succeed in fixing the problem was that he didn’t use a large air compressor. We suggested and sold them a Worthington 650 CFM compressor that would do the job. The compressor will be placed at the end of the tunnel connected to 4000 feet of heavy duty concrete pipes to be able to cover the length of the tunnel.

Concrete Pipes

So we prepared 400, 3”x 10” feet sections and equipped them with clamps.

Then, we devised a solution for shotcreting the tunnel wall. It required both a Blastcreeter 5000 and a Reed C50HP pump to get the job done.  To shotcrete the seams of the rocks, they would need to mix the concrete with a Bobcat at the end of the tunnel, then dump it into a mixer to mix it up, then dump it into the high pressure concrete pump’s hopper.

Reed C50 HP

The Reed C50HP can shotcrete 1000 to 2000 feet with a robot arm.  The pump is also equipped with a shotcrete nozzle 650 CFM, using air pressure to blow wet concrete between the rocks. The pump would be moved 1000 feet at a time through the tunnel until the job is completed.

Blastcreeter 5000

So how were we able to not only solve their problem but also save $150K? We will do the math for you. A Blastcreeter 5000 costs about $60K new, we were able to sell them a refurbed one for $30K. A Reed C50HP, goes for $106K brand new, we had a used one on our lot for $42K. That’s almost $100K of savings, right there. The solution we came up with also saved them an additional $60-90K, because we worked it out so that they only had to purchase 2 pumps instead of 4.

This is a great example showing how combining real expertise on the ground, with in-depth knowledge of equipment performance with the ability to source discounted dealer certified refurbed equipment, can make the difference in a bid won and a project executed in time and within budget.

Do you have a tricky concrete job or a problem to solve? Check out our Troubleshooting article, our special deals on shotcrete equipment   or call us at 503- 283-2105, we can work with you on any job you have. Give us a chance and we will show you how you too can save and deliver quality results!
Or visit us at: Unitedequipmentsales.com to check our latest deals.

Dec 03

World Construction Forecast: 2014 and beyond…

World Construction

With 2013 soon to come to an end and the Christmas holidays fast approaching, we thought it would be a good idea to take a look at what experts are telling us are the new trends and what to expect in the short and medium term future for the world of construction.

As the story goes, “There is good news and bad news, which one do you want first?” We will cut to the chase and go back a little to 2012 since we have actual numbers we can build on. According to Reportlinker.com¹, the global construction market was valued over US$99 billion in 2012, the Asia-Pacific region accounted for 42.5% of it and China, as one could expect, had the lion share of that market with 66.1% in 2012.

In second and third position were Europe and North America, accounting for 26.9% and 20.8%. Growth projections for these regions are expected to reach 22.7% and 20% respectively in 2017 and 47.6% for the Asia-Pacific region with a noted slowdown in China and India. With the exception of Germany and Scandinavia which are leading the pack in terms of construction and growth, no impressive recovery is to be expected in 2014 for Europe and the market should remain -20% below peak.

Brazil the Leader in Emerging Markets

EMERGING MARKETS
They offer growth prospects in the areas of energy and infrastructure. Being the host of the summer Olympics and the World Cup, Brazil leads all of Latin America in construction. It will aggressively continue to expand its infrastructure and invest in urban development, commodities and renewable energies etc. Chile, Panama and Peru are also good growth contenders but represent smaller long-term markets.

Demand in the Middle East and Africa remains unstable and unpredictable and commodity-price driven. The impact of the Arab Spring was felt in the business and political climate. No single country is taking the lead but some cities are experiencing a growth explosion (See list below).

Other numbers are being circulated, according to Global Construction Perspectives and Oxford Economics, the global construction industry is expected to grow to $9.4 trillion in 2015. Since developing countries have well established infrastructures, reparation and upgrade will constitute most of the construction work. To alleviate traffic congestions in large cities, governments will have to upgrade or create new mass transit systems that will also fuel the projected growth. So where else and in what areas will this growth take place?

Based on population growth rate and GDP below are some of the fastest growing cities:

  • Brasilia (Brazil)
  • Riyadh (Saudi Arabia)
  • Jeddah (Saudi Arabia)
  • Hyderabad (India)
  • Bandung & Jakarat (Indonesia)
  • Pune (India)
  • Wuhan (China)
  • Delhi & Bangalore (India)

Closer to home, The US Department of Commerce reported that sales of single family houses in August 2013 were up 12.6 percent from August 2012. We are noticing that “Every major segment of nonresidential construction exhibited job growth for a second consecutive month, a positive indication after the sector posted consecutive losses for the five previous months” declares Anirban Basu, chief economist at Associated Builders and Contractors. The 2014 Dodge Construction Outlook² predicts that construction starts are expected to increase by 9% and reach $555 billion in 2014.

So, while we are far from out of the tunnel, signs of recovery are on the horizon and the construction industry will continue to expand and address the needs of an ever growing population.

So if you are doing residential construction in the US or abroad, and want to find out about great deals on new or used concrete pumps and other construction equipment, call United Equipment Sales at (503)283-210, visit us online and check out our new facility
We have been in the market for over 42 years and can help you find just what you need for your next job.

REFERENCES
¹ Complete market study can be found at: Global Construction Aggregates Market – Key Trends and Opportunities to 2017
(http://www.reportlinker.com/p01593393/Global-Construction-Aggregates-Market-–-Key-Trends-and-Opportunities-to-2017.html#utm_source=prnewswire&utm_medium=pr&utm_campaign=Building_Material)

² Dodge Construction Outlook complete report

Nov 14

Are We Really In a Building Recovery ?

Single-family home

Since the burst of financial and real estate markets in 2007, a major shake up has taken place in the construction world. We have all experienced it, as property owners, developers, builders, real estate agents… Demand for construction of new homes plummeted, access to construction loans just about stopped and as a result many small home builders went under.

In Europe, even large, well established companies, like Putzmeister and Schwing, two German leaders in the construction industry, were bought in 2012 by Chinese companies: Sany Heavy Industries and Xuzhou Construction Machinery Group. By taking advantage of the debt crisis and the slowing down of the market, China further established its position as new leader in the construction machinery industry.

Housing Market Recovery?  We hear on television and read in articles, that the residential market is finally starting to show signs of recovery: prices have gone up 12% per year, bidding wars are happening again, the inventory is low …

So is this really a sign that things are getting better? What is really causing this increase? It could be the result of several factors:

  1.  Interest rates are the lowest they have ever been (even though they have gone up a little.)
  2. Bidding wars are happening but mostly where inventory is really low

However, if we were really talking recovery, why then, is “the inventory of newly constructed homes is essentially at a 50-year low”, according to Lawrence Yun, Chief Economist at the National Association of Realtors?  And by the looks of it, no increase is to be expected any time soon!

Let’s look at some data…

Housing Market Data US Census

Looking at the above charts from the Census Bureau, we can see that single-family home starts is pretty much flat and there is a slight increase in the number of multifamily housing starts but well below 2008 and even 2012 levels.

Could it be that the government (read Fanny Mae & Freddy Mac) is sitting on a record high inventory of millions of foreclosed houses that are being slowly released on the market? So many, in fact, that new constructions cannot take off? Add to this, excessive government regulations and the virtual impossible access to construction loans, you get the picture!

Multi-family and single-family units are up 21% in 2013 from 2012. However, new constructions are well below the long-term average of 1.5 million new homes each year.

Building Permit Data Building permits show a slow progressive increase back to the level of 2008.  This being said, a closer look at the US census data², shows that only single family housing rose and hit a five-year high! On the other hand, 2-4 units, 5+ and multi-family are below 2008 levels. Apartments and condos went down 11.1%.

In terms of regions, the South leads, followed by the West, then the Midwest and the North East.

Cities with the most construction permits (2011-12)

Houston, Dallas, Washington, DC, New York, Austin, Los Angeles, Phoenix, Seattle, Atlanta, San Antonio.

Cities with the most construction activities (2011-12)

El Paso, Austin, Raleigh, Houston, Charleston, Dallas, Little Rock, Baton Rouge, Washington, DC, Columbia (SC)

Cities with the least construction activities (2011-12)

Detroit, Long Island, Providence, Springfield, Chicago, Cleveland, New Haven, Dayton, Toledo, Ventura County.

Cities that are building have two things in common: Besides being metro areas, all have enjoyed better than average job growth in the past 10 years and none saw real estate prices plummet during the crash. So informed builders are investing in the South, in Houston, Phoenix and Atlanta and building single-family homes to address the market needs.

So, whether you are a builder in a growing market or even a flat market, one thing is for sure, you are going to need to efficiently allocate your budget on your construction equipment to win bids and get the most out of your job.  United Equipment Sales is one of the few equipment supplier, still left standing and growing. As a result, we can guaranty to save you thousands of dollars on your next construction job. Check out our special deals this month or have your pumps repaired by us. It could cost you less to ship it to us for repair than buying a new pump. The good news is that partnering with United Equipment Sales gives you affordable options. Why wait? Call us now at (503)283-2105!
REFERENCES:

http://www.theatlanticcities.com/housing/2012/05/top-us-cities-new-home-construction/1935/

http://www.census.gov/construction/nrc/pdf/newresconst.pdf

http://economistsoutlook.blogs.realtor.org/2013/08/16/latest-housing-starts-data/

http://www.nahb.org/fileUpload_details.aspx?contentTypeID=3&contentID=45409&subContentID=154674

http://www.reuters.com/article/2013/09/18/us-usa-housing-starts-idUSBRE98H0HH20130918

Oct 03

Pumping Concrete Troubleshooting: How to avoid Blockages

 

Troubleshooting Concrete Pumping ProblemsAnyone who has ever pumped concrete will have encountered, at some point, problems with pump line blockages. They are a part and parcel of the job, especially in the beginning when operators are learning the ropes. So learning what cause them is a first order on the agenda for any operator. The good news is that most blockages can all be traced back to 3 main causes:

1. Problem with the mix (think batter recipe)
2. Problem with the pipe line (think capacity & maintenance)
3. Operator error (think proper handling)

1)   MIXING ISSUES:

Problem: Insufficient mixing
Insufficient mixing of the concrete can result in segregation or separation of heavier particles moving to the bottom of the concrete.
Solution: Ensure proper coating of cement grout and lubrication of the mix. Also avoid overworking cement that is prone to bleeding.

Problem: Concrete Bleeding
Concrete can sometimes bleed, meaning that the aggregates  (solid components) do not evenly retain the mixing water. This could come from the sand not being well graded and the water flowing through the tiny channels or floats to the surface of fresh material (since water is the lightest of all the mix constituents).

Solution: Use a different sand, more cement, entrained air or fly ash to reduce bleeding. Avoid remix the bleed water during the finishing of the surface. Instead wait until it has evaporated. Make sure that the evaporation is not faster than the rate of bleed, otherwise plastic shrinkage cracking could happen.

Problem: Premature setting
If, for some reason, the temperature on the site is high on that day or the pumping is delayed due to site issues or traffic, your concrete can set too quickly. This means that the mix could become too thick to pump, not fill the chambers and as a result put undue pressure on the equipment.
Solution: Plan ahead. Check the weather for the week, make sure everything is ready on the site to avoid delays, use the proper mix for the job and if all else fails, use ad mixers (for cold or hot weather).

2)   PROBLEM WITH THE PIPE LINE 

Sizing the system for the job is essential to avoid common problems. Here are some common pitfalls:

  • You have insufficient pump capacity and motor horsepower to push the concrete through the entire pipeline.
  • The aggregate you use is too large for your line so you will need to switch to a larger diameter to solve the problem.
  • Did you forget to properly clean your pipes on your last job?
    This will most likely result in blockages where the old concrete hardened, not to mention causing segregation and bleeding. Don’t cut corners, even if it means working overtime!
  • Are your couplings, gaskets and weld collars are in working conditions? If not, you risk grout loss. Not good!
  • How many short and sharp bends do you have in your pipeline? Do you have reductions in your pipeline’s diameter? Bends, on the one end, increase the pressure while reductions, on the other, slow the flow. But both increase the risk of blockages wherever they occur. So now you know: check and recheck your line.

3)  OPERATOR ERROR

Novice concrete pump operators may not know that hoses and pipes should only be removed and not added once the pour is in progress. Adding a new hose with dry internal walls could cause a blockage.

Then, there is poor handling of flexible hoses that can result in kinking and rock jam where the kink occurred. This is a double whammy, because not only will you halt or delay the job trying to clear the jam but the constricted aggregate in the line will contribute to wear and tear of the hose leading to an eventual hose rupture.

So make sure you have the right equipment for the job and that it is in good working condition. Using more cement or a larger diameter pipe will increase the cost of the job. So plan your work and work your plan. It will save you money on manpower and equipment cost over time.

For more information on concrete pumping and equipment sizing, give us a call at (503) 283-2105. If you have an older concrete pump that needs some TLC, we have a complete repair shop. Need new couplings, gaskets? We have it all. Check us online at UnitedEquipmentSales.com.

Sep 17

Concrete Safety Procedures

When it comes to safety, we have all heard many wise sayings and one-liners like: “Prepare and prevent, don’t repair and repent. A casual attitude toward safety = CASUALTY, Chance takers are accident makers”… Some of our favorite sayings are: “Think Safety: some accidents last a lifetime and Work safely: do it for you, also do it for your family” because one moment can shatter one’s life and one ounce of prevention… you can fill out the rest! Another great motto to have on the job is:

                                                SAFE:

                                                   Staying
                                                    Accident
                                                      Free
                                                       Everywhere

 

Any successful business owner will tell you that to succeed, you have to “Plan your work and work your plan!” Pumping concrete, is no exception and considering the amount of things that could go wrong, this is something that should not be under estimated. Working with machinery/equipment also requires a systematic approach when it comes to operating, maintenance etc. Cut corners and you are guaranteed that you stand to pay for that omission sooner than later and the impact in this case will not only be financial but more importantly, could result in severe injuries for the crew on the job and property damage.

Safety checklist

Safety checklist

So we have put together a few suggestions you can use as a checklist when going on your next job. Whether you are a veteran or a rookie in the art of pouring concrete, you will appreciate this checklist because no matter how experienced you are, under time pressure, it is easy to forget something really important and often not even realize it until it is too late.

BEFORE LEAVING FOR THE JOB

Safety is as simple as ABC: Always Be Careful.

Perform a quick inspection of the concrete pump, truck before leaving. If you use your equipment 5 days a week, you should do this pre-inspection every time. It may take an additional 15-20 minutes to complete, so plan your day accordingly. It will go faster if you can split the check list with another person.

On the pump:

  • Check the engine and hydraulic oil levels
  • Radiator and flush box water
  • Safety covers (make sure is properly closed)

For a more complete list, see more great tips in this article on How to save money on concrete pumps.

On the Trailer:

  • Make sure the hitches are closed and locked
  • The safety chains are properly placed and secured (you would not want to lose your equipment on the road!)
  • Lights are working (that’s a great way to get a ticket on the way to your job!)

On the truck (once a week): 

  • Check all fluids (radiator, power steering, brakes, transmission, engine oil)
  • Check system hoses & connections
  • Check all tires & lights are working properly
  • Check for safety cones, fire extinguisher and first aid kits
  • Secure the outrigger and strap the boom of the pumping unit during transportation of the pumping unit
  • Truck registration, proof of insurance and driver’s license
Safety on the job

Safety on the job

Safety & protective equipment for the crew

  • Safety goggles, hard hats, work gloves and boots, reflective vest
  • Safety chains and cables (one per every device hanging from the boom)
  • Tools and grease guns
  • Extra hose fittings, pipes
  • Clean-out equipment

ON THE JOB
Note: Below is only a partial list but it covers the absolute must on your checklist. You may want to add a few more items depending on the specifics of your job and requirements of your equipment. Remember: “KISS: Keep it Safe and Sound.”

  • When setting up for your job, make sure to park in a secure zone.
  • Go over your plan with the team and walk the area before setting up so that you can identify all potential hazards (power lines, walls, ditches, vegetation, underground utilities etc) that may require reworking your plan.
  • Make sure that area under the pumper and mixers can handle the high weight and load of these machines
  • Once the spot has been found, use the parking brake, lock all outriggers in place and stabilize the equipment with pads (make sure they don’t sink when raising the pump with outriggers)
  • Safely fasten all the hoses with cables or straps
  • Make sure the grate is always placed on top of the hopper
  • Identify an area for clean-up and place concrete washout containers per the NPDES (National Pollutant Discharge Elimination System) requirements
  • Establish a mandatory 17-foot minimum clearance from all power lines
  • Select the signal person that will direct the operator (only one please!)

FINISHING THE JOB

Even though the actual pouring is completed, the job isn’t over until you have completed cleaning up of the equipment and the area and packed your equipment. This means:

  • Remember to retract the outriggers and secure the equipment before moving the truck (may seem obvious but has been done before!)
  • Clean out the boom with a ball or sponge
  • Always follow the manufacturer’s instruction to clean your equipment
  • Clear the area

Note: The suggested recommendations above are very detailed and may seem too time consuming for some people. Don’t be overwhelmed and as a results, go from all to nothing approach. You will need to select the routine and the frequency you will commit to follow and stick to it, no matter what happens on the job. This way, you will plan going through this checklist as part of your routine and as a result anticipate needed maintenance and operate more safely. Because, in the end, safety, is in your hands.

Lessons from experience

Most accidents happen when you are tired, pressured to finish before a certain time, on a tight budget, short of manpower, trying to use equipment that may not be really designed for the job size, or getting old… So if you find yourself in a situation where any or all of the above is the case, you should go through your list even more thoroughly because the odds of something going wrong are much higher. So always plan ahead, so that you have bandwidth to accommodate for unknown surprises because in the end, safety doesn’t slow the job down but mishaps do.

We suggest you read manufacturer’s instructions when buying new or used equipment. Call us at (503)283-2105 if you have any question on concrete equipment, maintenance tips etc.

Additional suggested reading material & reference
American Pumping Associate, Certification of Concrete Pump Operators Manual.

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.

May 15

Save Money on Concrete Hose Accessories

Concrete hoses

Concrete and plaster pumping equipment and hoses especially, get a lot of wear and tear over the course of many jobs. Replacing hoses can be expensive and is not always necessary. Did you know that you can have your used hoses repaired for a fraction of the price of a new one? This goes beyond the usual servicing, because needed parts are actually replaced and tested.

United Equipment Sales can save you money on your existing concrete equipment by having us do any of the following repairs:

 Install a new weld-on end (metal ring part) to convert your regular hose to a heavy duty hose out of it. We fill the grove with steel so it takes longer to wear it through. They come in different sizes from 5” to 1 1/2 “ to fit all your needs. There are different types: heavy-Duty, Metric, Grooved, Male/Female. Each one is machined on computer-controlled equipment from quality carbon steels.

Install a new clamp and snap couplings
Grooved, heavy-duty & metric, both non-adjustable and some adjustable sizes. All of our clamps have been redesigned with very “user-friendly” handles and come with gaskets and safety pins. They are also all steel construction (not ductile iron), for added strength and gold colored zinc coating or painted green.

Install a ferrule (metal end) When have a bad end, we cut off the hose behind the original ferule and replace it with a new stem and internally expand it into the ferule (which grabs the hose on both sides so that it can’t back up).   We can use a heavy duty or a threaded end. If you need an adaptor, we also manufacture our own with threaded end, with coupling. Size vary from 2 “ to 1 ½”.

Slabjacking accessories

You can also replace different sizes of shotcrete nozzles for shotcreting tunnels and swimming pools. They come in 2 sizes: 1 ½” to 2 ½” nozzles with tips. They can get really worn out after many jobs.

 
NOTE: a clean out ball should always be used after every job to make sure that you get 99,9% of the cement out of the hose. This will extend the life of your hose and equipment.

The good news is that we ship anywhere in the world. Most of the cases we can turn around your order in less than 3 days depending on the amount the work needed. Accessories can be shipped the same day.

See video on our UnitedEquipmentSales Youtube channel.

Check our complete list of pump accessories at: http://unitedequipmentsales.com/ConcreteAccessories.php 

Or call our repair service at (503)283-2105 to get an estimate or more information.

Apr 09

How To Repair Broken Concrete

Cracked concrete

damaged concrete slab

If you live in a house that is over 50 years old, chances are you have cracked concrete somewhere on your property or a slab sinking. Whether the problem is in a foundation, a sunken sidewalk, a concrete patio surface, a damaged pool deck, concrete stairs, a parking lot or a factory floor, uneven and cracked concrete floors are not only unsightly and potentially dangerous but they also decrease property values and in some case can even result in safety hazards. The reason why so many people don’t ever address the problem is that the idea and the cost of pouring a brand new concrete pad can be too much for most property owners and especially in tough economic times. So what is one to do? Is there a lesser painful and costly alternative?

There is and it is called slabjacking, a.k.a mudjacking.  Considering that you can do a permanent foundation repair and re-level your floor for less than half the cost of pouring new concrete, this is great news. Wait, there is more, you are not only saving on cost, but you don’t have to pay for the usual demolition, removal and dumping. This means that not only you can repair the problem in record time (it can be done in one day because you don’t have to wait for the grout to cure), for about half the price and with a lot less disruption in the area (think costly damage to your landscape)!

How to repair damaged concrete slab:

Let’s say that you decided to mudjack your driveway. All you need to do is drill holes through the slab and pump a sand/cement mixture under the slab until it is filled. Complete the job by sealing up the holes with a cement mix to conceal them. Job done! Over time the strength of the repaired slab is similar to having poured a brand new concrete slab.

What equipment should I use?

Mudjacking equipment

For a big jobs you may need a full size trailer line pump.
For smaller jobs like smaller walk-ways and slabs, you may want a gas model machine with variable displacement (50-900psi).

The only green solution

Mudjacking is not only quicker, cheaper and faster it is also greener because not you are not wasting all the additives to do the job like fuel to operate equipment, manpower, waste removal & dumping of all the broken concrete. Mudjacking is a great affordable solution for everyone in need of durable and practical repair.

To find out more about equipment to get the job done at an affordable price visit http://unitedequipmentsales.com/ MudjackingPumps.php , or call (503)283-2105.

Watch pros do it here!