Apr 09

Repairing Our Aging Bridges, a Concrete Dilemma!

Aging bridges

Aging bridges

In 2013, our nation’s bridges were rated and we got a C+ on our scorecard!  With the majority of our bridges approaching the ripe age of 42 years, United States is officially dealing with issues caused by an aging road infrastructure. We have over 607,380 bridges spread across the nation’s 102 largest metropolitan areas (where most of the traffic takes place with commuters and freight vehicles) and one out of nine bridges has been declared structurally deficient. The Federal Highway Administration has its work cut out for itself! The current annual budget of $12.8 billion won’t address the existing backlog by 2028! An additional $8 billion a year is needed to repair them appropriately, an additional budget that states and counties need to find to speed this process.

So what are the main issues with our aging bridges? They are either deficient, structurally deficient and/or functionally obsolete. So what’s does this mean? Well, a bridge that is considered structurally deficient will require significant maintenance, repair or even replacement and annual inspections. A deficient bridge is both structurally deficient and functionally obsolete.
A functionally obsolete bridge does not meet the current standards like load carrying capacity and width of lanes.

States that top the list of structural deficient bridges (with over 20%) are Pennsylvania followed by Iowa and Oklahoma. However, when you combined the number of bridges that have structural deficiency and are functionally obsolete, the District of Columbia leads all 50 states with 77%!

Concrete repair

Highway repair ahead!

The first signs of aging bridges are potholes, cracks, missing concrete chunks, posted signs with load restrictions and can extend in extreme cases to the closure of the bridge. The right bridge lane usually shows signs of damage faster that the left lane used for accelerating and decelerating, the shoulder lanes. To the naked eye, spalls or chips of concrete appear, they are usually caused by thermal strain due to rapid freeze thaw weathering. Dangerous explosive spalling can occur of refractory concrete and render the structure not usable as a result. Delamination or blisters is another common problem. When excess water and air in the mix are trapped under the surface mortar, voids are created along with weakened areas just below the surface that will come apart in the future. This problem stems from starting the finishing phase before the bleeding process is complete or when concrete is placed on cold substrates when ground temperatures are below 40F.

PROBLEMS:

Corrosion of steel reinforcements in concrete
This occurs when chloride ion that is found in sea water, ice melt water and deicer salts (made of sodium chloride and calcium chloride) starts corroding the concrete-steel contact surface. This can happen through drying shrinkage, cracking or the concrete’s pore water. The higher the temperature, the faster the corrosion! So regions like the Florida coast encounter constant and rapid degradation due to its warm temperatures and exposure to sea water. The corrosion produces rust which causes internal pressure and creates cracks, potholes…

Rust must be removed from the exposed reinforcing steel before repairing or the corrosion will continue under repaired patches. A layer of corrosion inhibitor must also be applied for the repair to last.

Unprotected concrete elements

Some bridges were built using bare concrete elements with black steel. Others used reinforced steel without epoxy or galvanized coating or a polymer concrete overlay. Others were made with a low slump dense concrete that results in low permeability concrete and allows chloride ions to do corrode the structure.

REPAIRS

Deck patching: for temporary partial depth repairs, bitumous concrete, quick-set hydraulic concrete, polymer mortar can be used. For full-depth patch repairs, Portland cement is the choice material.

Deck overlays:
In this method, repairs are done without removal of the chloride contaminated concrete.
Material used for these temporary repair methods are: latex-modified concrete (LMC), low slump dense concrete (LSDC) and hot mix asphaltic concrete with a preformed membrane.

Patching with Cast-in-Place PCC for Superstructure and Substructure:
This method requires the removal of loose concrete identified by sounding with a hammer. Formwork may be needed, which excludes the application of bonding agents but requires keeping forms cool by providing a cover during the curing phase.

shotcrete pump

Reed B50 Shotcrete pump

SchwingBPA500

Schwing BPA 500 Shotcrete Pump

Patching with shotcrete:
Removal of lose concrete is required. Repairs on superstructure and substructures tend to use dry-mix mortar. No bonding agent should be used. A single layer of shotcrete should be applied to avoid cold layers. A bottom up application technique should be followed to fill vertical cavities. Overhead surface may require multiple layers, 1 to 2 in. thick so that sagging doesn’t occur. Moist curing for 7 days should be provided using a cover or sprinkling system.

Encasement and Jacketing:
When column and piers have greatly deteriorated over time, concrete can be place to fill cavities, providing a new encasement for the element. In worse cases, a concrete jacket can be added after the damaged concrete has been removed.

EXPERIMENTAL  METHODS
For deck, some of the techniques involve Microsilica concrete overlays, corrosion inhibitor overlays, polymer impregnation and more.

For Superstructure and substructure elements, patching with Corrosion inhibitors is mostly used.

PREVENTION

Anything that will prevent chloride ions from entering and diffusing into concrete will work. It needs to be breathable so that water vapor can pass but not liquid water.

Deck sealers are a good option, they are either solvent or water based. Penetrating sealers are the only via options for the job (a combination of silanes and siloxanes). However, they should not be used on structure with active corrosion or high chloride contaminated concrete.

In general, large scale bridges in urban areas should be repaired first since the demand on them is higher than in rural areas. So if you are looking for a good shotcrete machine at a competitive price, give us a call at: 503-283-2105.

Further Reading:

Infrastructure Report Card (2013)

Concrete Bridge Protection Repair & Rehabilitation Plan from the Strategic Highway Research Program

 

 

 

 

Share
Jan 30

United Equipment Sales Expands Its Operations!

Moving into a new home is considered to be a life event, but when you move 40 years of business, a warehouse and its entire inventory, it takes a move to an entire new level! So when we decided to move to a new and larger facility, we knew that it would temporarily disrupt our business so we chose a quieter period. We ended up not only expanding our working space, but also upgrading some of our office equipment, software that was in serious need of upgrade. More space means more machines, more business, more custom repair which have kept us busy, busy, busy!  And that’s a good thing!

So, we have put together a short video tour of our new 13,000 sq ft facility. You’ll get to meet Dick Hibbard, a.k.a. Mr. Concrete Pump! See our certified mechanics take concrete pumps in dire need of TLC and bring them back to life!

Our PARTS SHOP has everything you need!

Parts Shop

Clamps, couplings, reducers, gaskets, nozzles, elbows, adapters, welded groove ends, hoses of all sizes and much more…

 

Rich runs the repair Shop

 

 

 

 

 

Talk to Rich in our Repair Services if your pumps or hoses need to be repaired or have some custom work done.

Our staff is here to serve you and your business.

Meet The Team!

Our company mascot and official greeter couldn’t make it for the group photo, so here she is in her command post:

Snowbella

 If you are in the area, come by and visit us, we would love to see you!
Or call us at: (503)283-2105

 

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.