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

Joints are placed in concrete pavement to accommodate slab movement and to prevent natural cracking. The theory is that cracking will follow along the joints if they are correctly positioned.

The first concrete pavement slabs had no real design and no crack control joints or dowels and no steel reinforcement.

In the first part of the 1900s Joint Reinforced Concrete Pavement appeared containing steel reinforcement mesh to hold cracking tightly. Then followed Jointed Plain Concrete Pavement using contraction joints to control cracking with no reinforcement steel and dowel bars were introduced to transverse joints to assist in load transfer in 1917. In 1923 Continuous Reinforced Concrete Pavement was introduced whereby transverse cracks are allowed to form but are held tightly together with continuous reinforcing steel.

Joint Spacing

Joint spacing is very important in crack control as cracks can form naturally during the curing process without suitable control joints in place.

The formula for maximum joint spacing is the relationship between:

• The radius of relative stiffness (mm),
• the modulus of elasticity of concrete (Mpa)
• the slab thickness (mm),
• the modulus of subgrade reaction (Mpa/m),
• Poisson’s ratio for concrete, usually 0.15.

Saw Cutting

There is a short window of opportunity for saw-cutting joints in slabs. Too early and you get ravelling of the joint and the faces are torn and damaged. Too late and the internal stresses causing cracking have already started randomly in the slab.

The saw cut depth and timing is critical for joint formation.

Types of Joints

There are several types of joints which can be transverse or longitudinal in direction:

• Contraction Joints
• Construction Joints
• Isolation Joints
• Expansion Joints

All are designed to induce or control cracking.

Joint Sealants

Joint Sealants are used to minimise infiltration of surface water and incompressible material into the joint. Unsealed joints can allow sub-soil washout and voids to form and uneven subsidence of slabs resulting in differing RLs and rough transitions across joints.

Dowel Bars

Dowel Bars are used to control the joints and their alignment and spacing is critical. If dowels are misaligned and both ends of the dowels are locked in the slab concrete failure and cracking will result. The absence of dowels may cause the transitions across joints to become uneven when the adjoining slab moves out of level or concrete curling occurs.

Dowel racks are an excellent innovation as they ensure that the dowels are aligned correctly and held in place during the concrete pour.

Sub-base

The sub-base material must be compactible and pumping of water through the sub-base through un-doweled joints needs to be eliminated.

Curing

Proper curing practices delay the development of these internal stresses, controls internal temperature, delays moisture evaporation, and fosters the development of increased strength.

Curing therefore controls the evaporation of moisture during the concrete setting process and helps to prevent premature drying of the surface which can prevent or delay the evaporation of the remaining moisture below resulting in an uneven set and issues with strength and surface dusting.

Steel Reinforcement

The correct placement of steel reinforcement bars and mesh is critical to provide strength, reduce width and frequency of cracking and hold slabs together whilst setting and under load.

Typical Jointing Problems

• Concrete sawing too early causing ravelling or spalling
• Concrete sawing too late causing early-age cracking
• Concrete cracking due to insufficient joint depth
• Concrete cracking due to excessive joint spacing
• Concrete cracking due to excessive unrestrained warping
• Concrete cracking due to too much edge restraint
• Concrete cracking due to excessive slab to sub-base bonding
• Concrete cracking due to misalignment of dowel bars
• Concrete cracking due to lack of consideration of weather conditions
• Sealant not adhering to joint faces
• Sealant pulls out during operation
• Sealant gelling
• Sealant cracking or debonding
• Voids of bubbles in sealant
• Water pumping into sub-base
• Sub-base washout
• Concrete slab moving out of level

The Solution

FCS Concrete Repairs are fully resourced to Inspect, Test, Diagnose and make informed recommendations on the best permanent and cost effective methods to rectify any concrete cracking and maintenance issues. Joint repair and reinstatement is our forte!

Ref: All About Concrete Pavement Joint Design & Construction
September 19, 2013, Eric Ferrebee, EITTechnical Services Engineer, ACPA

Geopolymer Institute: 10 Apr 2006

https://www.geopolymer.org/archaeology/pyramids/are-pyramids-made-out-of-concrete-1/

The website reveals how Ancient Egyptians built the pyramids using man-made stones, which look exactly like natural rocks. The limestone blocks were cast in situ, employing an advanced technology that was later lost, leaving a puzzle hidden for thousands of years inside the pyramid stones. This theory undoubtedly shed an amazing new light on what really happened in Egypt in that remote era.

The Pyramids at Giza have more than 5 million blocks of limestone, until now believed to be CARVED stones, new evidences shows they were CAST with agglomerated limestone concrete.

The scientific background, including analysis, formula, stone making, are disclosed in the recently updated book by Prof. Joseph Davidovits Geopolymer Chemistry & Applications, in several chapters, i.e. Chapters 5, 11, 13, 17 and 20.

Geopolymer Institute: 18 Jan 2013

https://www.geopolymer.org/archaeology/pyramids/paleomagnetism-study-supports-pyramid-geopolymer-stone-2/

A recent scientific study published in the renown “Europhysics News“, The Magazine of the European Physical Society, (2012), Vol. 43, number 6, described how paleomagnetism study on several pyramid stones demonstrates the validity of Davidovits’ theory on the artificial nature of Egyptian pyramid stones.
Two scientists, Dr. Igor Túnyi from Geophysical Institute SAS – Bratislava (Slovak Republic) and Ibrahim A. El-hemaly from National Research Institute of Astronomy and Geophysics – Cairo, Egypt, made the following assumption (quote from their scientific paper):

Our paleomagnetic investigation of the two great Egyptian pyramids, Kufu and Khafre, is based on the assumption that if the blocks were made in situ by the geopolymer concrete technique described above, then their magnetic moments would all have been parallel, oriented approximately in the north-south direction. However, if the pyramids were constructed from blocks transported from the nearby quarries, having been rotated randomly during transport and construction, then the directions of their magnetic moments would be oriented randomly

Conclusion:

The aim of paleomagnetic investigation of the rock material of the great Egyptian pyramids, Khufu and Khafre, was to find out the directions of the magnetic polarization vectors of their building blocks. This is one of the possible ways to verify the hypothesis according to which the blocks were produced in situ by a concrete technique. The analysis of a limited set of paleomagnetic samples provided the following results. The paleodirections of three sampling locations (2 from Khafre and 1 from Khufu pyramid) exhibit the common north-south orientation, suggesting that they may have been produced in situ by a concrete technique. The block from one sampling location of the Khafre pyramid is of natural limestone and evidently comes from the adjacent quarry. It is likely that the block from one sampling position of the Khufu pyramid comes also from the same quarry. Finally, we conclude that even if the geopolymer concrete technique was used, the pyramids were constructed from a mixture of natural and artificial limestone blocks.

See: Igor Túnyi and Ibrahim A. El-hemaly, (2012), Paleomagnetic investigation of the great egyptian pyramids, Europhysics News43/6, 28-31.

In his book “Why the Pharaohs built the Pyramids with Fake Stones“, Professor Davidovits has clearly shown the location of the natural limestone blocks and terraces (see essentially the Circuit of the Pyramid Plateau at Giza, Egypt, pages 233-262). For example, we know that in the pyramid of Khafre, more than a quarter of the volume of the pyramid is natural stone, namely the terraces carved in the inclined limestone plateau and which constitute the first 5 layers of the pyramid. The book is available at the Geopolymer SHOP and www.amazon.com

FCS Concrete Repairs Pty Ltd has been accepted for Corporate Membership of the Industry Association, the Australasian Concrete Repair Association Ltd.

The Australasian Concrete Repair Association (ACRA) was formed in 1991 with the aim of providing a forum to promote discussion and an exchange of views in the concrete repair industry to advance the technology and practice of concrete repair and associated activities.

The Association’s members are at the forefront of concrete repair technology worldwide and include companies and individuals with an interest in repairing and protecting concrete, including:

• Specialist consultants and engineers
• Specialist repair contractors
• Specialist materials suppliers
• Asset owners

for small scale spray-cretingin shotcreting and spray applied concrete repair applications.

The Bunker Grout Pump will be used to apply such products as

Fosroc Guncrete E: Spray Applied Repair Mortar

FCS Concrete Repairsstaff are trained and equippedto carryout small scale concrete repair with spray applied repair mortar using the Gunite type process.

Fosroc Construction Chemicals use Sprayset Chemical,a chloride free liquid based on a blend of inorganic powders, which is added to a sprayed concrete mix to impart properties of high build and low rebound. Its pH level is neutral.

Fosroc Guncrete E product is a high strength, low shrinkage, high build cementitious spray applied mortar supplied as a ready to use powder for use with standard dry spray or shotcrete equipment.

The advantages of using the Gunite system with Guncrete E are:

• High build material
• High early strength
• Low drying shrinkage
• Low rebound
• Chloride free

Guncrete E has many applications in the concrete repair industry. Examples where Guncrete E can be spray applied for concrete repair:

• Bridge Repairs: Concrete cancer type repairs to bridge support columns. Concrete can be reinstated using sprayed mortar such as Guncrete E.
• Concrete ceilings/soffits. Quality repairs can be achieved using sprayed mortar in small patched areas using the Gunite process.
• Large area concrete repairs. Concrete repair can be carried out cost effectively on a large scale using spray applied repair mortar.
• Sea Wall Repair. High build spray applied mortar can be applied to repair deteriorated sea walls because of its quick setting characteristics.
• Pool Repairs. Ageing concrete pools can be effectively repaired by recoating using the Gunite technology.
• Concrete Walls. Repair spalling concrete caused by the penetration of water into the concrete can be repaired using the spray applied mortar after removing concrete using torbo-blasting methods.
• “Drummy” Concrete. Where concrete render has delaminated large areas can be repaired using spray applied mortar.
• Deteriorating foundations can be repaired effectively using spray applied mortar.
• Expansion Joint. Overhead repair of spalled expansion joint in a carpark can be repaired effectively using Guncrete.
• Concrete Beams. Structural concrete beams in suspended decks can be repaired effectively using small scale spray applied mortar methods.

Before dry-spraying the repair mortar it is necessary prepare the areas before the application of the mortar. This may be achieved by the various preparation methods such as wet grit blasting, torbo-blasting,cleaning and corrosion treatment or replacement of steel reinforcement.

Steel reinforcement primer may be used with NitoprimeZincrich, a single component zinc-rich epoxy resin specified by Fosroc.

Guncrete E spray mortar may be used for decks, slabs, horizontal and vertical concrete surfaces to be repaired in one or more layers, each layer 10-150 mm thick where compressive strength >45 MPa compressive strength in 28 days and a low level of drying shrinkage measured to ASTM modified 23°C/50%RH shall not be greater than 500 microstrains at 7 days and 700 microstrains at 28 days is required. The minimum depth for repair shall be 10 mm.

After applying the sprayed repair mortar the area is finished by striking off with a straight edge and trowelled or floated to achieve a level flush with or slightly proud of the surrounding surface.

Spray applied repair mortar is cost effective in repairing small scale areas of concrete where hand repairs may be more labour intensive and costly.