A unique bridge that resides about 15 miles south of Lincoln has given Tuan reason to feel confident. In 2002, Tuan and the Nebraska Department of Roads made the 150-foot Roca Spur Bridge the world’s first to incorporate conductive concrete. Inlaid with 52 conductive slabs that successfully de-iced its surface during a five-year trial run, the bridge exemplifies the sort of targeted site that Tuan envisions for the technology.

The concrete mix’s designer, UNL professor of civil engineering Chris Tuan, has added a pinch of steel shavings and a dash of carbon particles to a recipe that has literally been set in concrete for centuries. Though the newest ingredients constitute just 20 percent of Tuan’s otherwise standard concrete mixture, they conduct enough electricity to melt ice and snow in the worst winter storms while remaining safe to the touch.

By replacing the limestone and sand typically used in concrete with a mineral called magnetite, Tuan has shown that the mixture can also shield against electromagnetic waves. Cell phones are unable to receive service for example and the conductive concrete may be useful in shielding against espionage.

University of Nebraska-Lincoln
Nebraska Today
By Scott Schrage
University Communication

For morinformation visit news.unl.edu

There are four types of concrete!

Concrete that can crack!

Concrete that has cracked!

Concrete that can leak!

Concrete that has leaked!

Truism: This observation is obviously true and says nothing new or even interesting about concrete but if you have a problem and need a solution then:

TALK TO THE DIRECTORS AT FCS CONCRETE REPAIRS.

They are ready to help you!

Shrinkage cracks may occur when water evaporates from the concrete soon after it is layed during the drying process. (that is, the curing process) Hot weather can cause rapid evaporation if curing compound is not properly used to slow the evaporation and cold weather can slow the evaporation process. Fine cracks give the opportunity for water to penetrate the concrete and cause the steel reinforcement to rust and concrete degradation.

Structural cracks when the concrete structure is over-loaded or subject to design flaws will allow water to penetrate the concrete and cause the steel reinforcement to rust leading to concrete degradation.

Concrete cancer cracking when water penetrates into the concrete and causes the internal steel reinforcement to corrode, expand and cracks form from within allowing water to leak through the concrete element.

Concrete cracking when the sub-base is inadequate or a washout occurs allowing water to flow under and through the concrete element.

Soil movement below the sub-base due to natural movement or the expansion and contraction of the underlying clay earth in times of heavy rain or drought allowing water to flow below and washout the concrete element.

Cracking due to freezing conditions followed by thawing which may also cause expansion and contraction and allow water to leak through and below the concrete element.

Hot summers can cause cracking due to expansion of the concrete and allow the ingress of water.

Washouts behind retaining walls may also result in structural cracking and gushing leaks.

HEADLINE NEWS!

Fortunately, experienced Concrete Repair Contractors like, FCS Concrete Repairs, have the solutions. Experienced tradesmen, high-tech equipment and repair materials, and technical knowledge can combine to provide near permanent solutions to concrete cracking and leaking. Early intervention is also critical in enabling effective repair and cost effective solutions.

What can be done?

Badly damaged concrete can be replaced BUT this can be costly and involves:

• Investigation
• Demolition
• Removal
• Replacement

Modern crack injection methods can provide a cost effective alternative solution:

• Polyurethane injection

Single component hydrophobic foam can be injected to stop water infiltration and to stop high pressure flowing water and to fill voids behind the structure or joints or cracking in concrete.

Two component hydrophobic rapid setting foam can be injected. This foam is highly reactive, high strength and expands up to ten times when in contact with ground water.

• Polyurea Silicate

Two component low density foam to fill cavities provides structural strength and flexibility to stabilise strata.

• Acrylic

One component water based acrylic joint sealant and gap filler which has low adhesive and compressive strength, but high tear strength.

• Cementitious Grout

A combination of cement and water, plus admixes or additives to alter their properties. There are three main types – pure cement mixes (PCMs) composed of cement and water, admixed cement mixes (ACMs) composed of PCM and admixtures, and additive cement mixes (ADCMs) composed of ACM and additives.

• Epoxy injection

Two component, low viscosity, solvent free, moisture insensitive, structural epoxy injection resin used to seal cracks and cavities and forms an effective barrier against the infiltration of water and bonds concrete to restore structural integrity. Doesn’t bond as well to wet surfaces.

FCS Concrete Repairs has the expertise to investigate, test, diagnose and recommend on the most appropriate and cost effective solution to your concrete cracking and leaking problem.

Prime Flex 900 XLV polyurethane resin is a low viscosity, hydrophilic resin that reacts with water and expands to form a closed cell, watertight foam. It is typically injected under pressure to seal actively leaking joints and cracks in concrete structures, including hairline cracks. This product is independently tested and proven to meet NSF/ANSI Standard 61.5 for contact with potable water.
Recommended Uses include injecting hairline cracks, expansion joints, wide cracks, pipe joints, or pipe penetrations, or sealing active leaks in above-grade or below-grade concrete structures.

This can be used for water treatment tanks, dams, below-grade concrete walls, tunnels, manholes and elevator service pits.

Prime Flex 900XLV is compliant for contact with potable water, can expand and contract parallel to the crack in varying temperatures, can expand up to 600% unconfined and has a low viscosity to allow it to penetrate tight hairline cracks deep into the structure.

When the material contacts water, it reacts to form a white, flexible gel-like foam that acts as a barrier, sealing the cracks that allowed water to leak. As the foam reacts, it expands to fill the space and bond to the concrete to hold it in place, creating a closed cell mass that does not allow water to pass through or around it. The foam’s flexibility allows it to expand and contract along with the structure it has sealed, so it remains water tight despite temperature fluctuations.

FCS Concrete Repairs are experts in leak repair and are available to help with your concrete repair requirements. FCS Concrete Repairs are approved applicators for this product in Australia.

Problem: Sinkholes had developed around storm drainage manholes in grassy areas of a military housing subdivision in Richmond, Virginia.

Identifying the source: To pinpoint the sources of the problem, the contractor’s crew flooded the existing sinkholes and monitored the dry manhole to see where the infiltration entered.

Solution: With on-site technical support from Prime Resins, the contractor injected Prime Flex 920 through the manhole wall to fill the voids and create a watertight curtain around the manhole. Prime Flex 920 is an expansive, hydrophobic polyurethane resin that reacts to form a rock-hard watertight mass. The grouting was done from inside the manhole because the repair locations were so deep, as much as 20 feet from the surface. Probe grouting from the surface outside the manhole can be done if the manhole is too narrow to work within.

They installed four injection ports per pipe and injected each leak location starting at the lowest point and working up. This revealed a leaking injection hole from the previous repair attempt. Some 920 seeped out this hole and sealed it as well. The technicians repaired wide gaps around the main connection plus spalls and chips inside the collar using the activated oakum technique. They soaked oil-free oakum with Prime Flex 900 XLV and pushed it into the gaps where the reacted resin sealed the openings. The 900 XLV is a very low viscosity polyurethane and is hydrophilic, so it creates a tenacious bond with the wet concrete.

Outcome: The crew tested their repair by flooding the sinkhole again. No water drained into the manhole: their repairs stopped the infiltration. Finally, they removed the ports and plugged the holes with hydraulic cement.

Read the complete case study here.

FCS Concrete Repairs are experts in leak repair and are available to help with your concrete repair requirements. FCS Concrete Repairs are approved applicators for Prime Resins in Australia.

Request a quote here.

Will the Roman 2000 year product guarantee stand up for today’s concrete mix designs?

Ancient concrete mixes have stood the test of time and withstood all of the environmental attacks known to mankind for over 2000 years. Today’s concrete, however, is susceptible to environmental damage and often needs protection or repair or, in the extreme, reinstatement within thirty (30) years.

What is the secret to 2000 year old concrete?

Roman concrete mix designs were simple. No admixtures. No risk from sulphates. No issues with the penetration of water. No steel reinforcement to rust. No concrete cancer.

Ancient concrete consisted of just three elements:

• The paste – limestone (crushed and burnt)
• The “sand” – volcanic ash
• The aggregate – large lumps of rock

The burnt volcanic ash has an amorphous silica structure with many holes in the molecular network which fill with calcium hydroxide upon mixing with wet lime and becomes the paste which binds the rocks together. Sand in modern concrete however is crystalline and does not have holes in the molecular structure to accommodate the cement paste.

Ancient Romans mixed their concrete product by hand and tamped the mortar into place thus minimising the water content and therefore created a low slump and highly durable mix.

They also discovered that the volcanic ash developed hydraulic properties when mixed with lime and then realised the advantages of hydraulic lime, i.e. cement that hardens underwater.

Modern Fly Ash Mix Designs.

Some modern concrete mixes use fly ash as a supplementary cementitious material which delivers improved workability and, like the Ancients, later age strength and high durability.

Modern Concrete Mixes.

But unlike those majestic Roman structures, today’s cities are plagued by crumbling concrete tower blocks and decaying bridges and expressways.

Today’s concrete is made using Portland cement, coarse and fine aggregates of stone and sand, and water steel reinforcement.

Admixtures are chemicals added to the concrete mix to control its setting properties and are used primarily when placing concrete during environmental extremes, such as high or low temperatures and windy conditions.

Although steel reinforced concrete is one of the most widely used construction materials around the world, it can suffer degradation over time due to the embedded steel corroding, causing the concrete to crack and “spall”.

In extreme situations, the integrity of the structure may be lost, resulting in the need for partial or complete demolition. Corrosion affects all reinforced concrete buildings and structures to some extent, with an estimated annual cost of billions of dollars to national economies. In addition, loose damaged pieces of spalled concrete falling from buildings and structures is a real safety risk.

When chlorides, carbon dioxide gas and other aggressive agents penetrate concrete, they initiate corrosion of reinforcement that typically results in cracking, spalling and weakening of the concrete infrastructure. As reinforcing bars rust, the volume of the rust products can increase to many times that of the original steel, increasing pressure on the surrounding material which cracks the concrete. The cracks can then propagate to delamination and eventually spalling of the concrete.

Usually, the most exposed elements deteriorate first but because the active corrosion may take five to 15 years to initiate cracks in the concrete, much of the actual corroded reinforcement is not visible. Such corrosion is often called “concrete cancer”, because it appears as if the structure was being eaten away from the inside.

We have now realised these issues with modern concrete, for example:

• Thousands of passengers have been travelling over Hawkesbury River Rail Bridge connecting Sydney to the Central Coast every day, despite a crucial supporting pylon being riddled with “concrete cancer”. With cracks up to two metres long, the pylon is so severely deteriorated it crumbles away like powder.

• Edgewater Towers in St Kilda’s Marine Parade is a notorious example of how costly concrete cancer can be. The modernist block of 100 apartments sprang up in 1961 but by the 90s spalling was ravaging its balconies. Issues were still being remediated as recently as 2011.

• Gold Coast’s Ageing High-Rises. Bodies corporate of these ageing buildings are now faced with the prospect of either having to spend hundreds of thousands of dollars, if not millions of dollars, rectifying concrete cancer and other building defects, or they look to cash out and sell to developers.

• It was recently revealed that one building — the landmark Focus Apartment tower — needed $2.7 million in repairs to prevent “extremely dangerous” deterioration from concrete cancer or spalling.

• The 20-storey Iluka Surfers Paradise high-rise was demolished after concrete cancer destroyed its structural integrity.

• Dozens of 40-year-old Gold Coast high rise apartment towers built in the 1970s face million-dollar concrete cancer repair jobs similar to the $215 million in repairs needed by Brisbane’s City Hall.

• When it was finished in 1978, the 67-storey MLC Centre in Martin Place, Sydney, was not only Australia’s tallest office building, but also the biggest reinforced concrete structure in the world. Thirty-three years later in 2011, the Harry Seidler-designed structure is showing its age. Its concrete facade is breaking up and the owners have agreed to spend $100 million repairing it in an operation that will go 24 hours a day, seven days a week for four years.

• The Sydney Opera House might be one of the world’s most iconic buildings but it faces potentially significant conservation challenges, a US philanthropic organisation says. The Getty Foundation has awarded the Sydney Opera House Trust $US200,000 ($A224,000) for a study of the concrete elements of the building and to develop long-term conservation strategies should it become necessary in the future.

Concrete Repair Methodology

Concrete repair methods need to provide a permanent solution in order to avoid a recurrence. FCS Concrete Repairs will Investigate, Diagnose, Test and Recommend the appropriate solution which will depend on the extent of damage and the feasibility of the repair or if necessary reinstatement of the concrete element affected.

The nature and type of repair will be determined by:

• Extent of corrosion of reinforcement
• Extent of loss of strength of reinforcement
• Extend of loss of the bond between the reinforcement and the concrete
• Extent of deficiency in concrete cover over reinforcement
• Extent of deflection due to cracking in the tensioned areas.
• Extent of honeycombing in concrete
• Extent of porosity of concrete
• Extent of damage and loss of strength due to sulphate attack.
• Extent and width of cracking