Web viewCrystalline Technology: Concrete Waterproofing and Protection. for Longer Lasting Bridges. Every country in the world faces transportation infrastructure challenges,

Xypex -- Bridges whitepaperTarget Pubs: VariedDRAFT DEC 10, 2012

Crystalline Technology: Concrete Waterproofing and Protectionfor Longer Lasting Bridges

Every country in the world faces transportation infrastructure challenges, particularly those with well-developed highway systems. Structures built in the 1950s and 1960s are reaching the end of their service life and most transportation organizations are hard pressed to replace or rehabilitate them. In the United States, there are over 150,000 structurally deficient or functionally obsolete bridges on the U.S. National Highway System and many more thousands of locally owned bridges are in just as bad or even worse shape. The rest of the world faces similar infrastructure woes.

Reinforced concrete bridges are constantly under attack by the destructive effects of moisture and chloride-induced corrosion. Without proper protection, the structural integrity of a bridge is soon compromised, leading to expensive remediation efforts and a shortened life span. Once the moisture and chlorides have reached the reinforcing steel, an expansive oxidation process begins to take place. This causes the formation of cracks and spalling in the concrete. When cracking takes place and is combined with weathering effects such as freeze/thaw damage or accelerated corrosion in hot weather climates, this deterioration takes place at a faster pace.

To minimize the potential for water seepage and corrosion of reinforcing steel in concrete structures, engineers use thicker concrete covers, specialized rebar coatings and surface sealers and, more recently, high performance concrete. All of these options help improve the durability of concrete structures; they also have inherent disadvantages such as high cost and limited effectiveness over the lifecycle of a structure.

Recent studies and tests by leading independent scientific laboratories and regulatory bodies have found that crystalline waterproofing technology—installed during concrete batching or applied after construction—is just as effective as conventional solutions for providing impermeability and longer lifecycle advantages but at a lower cost and without the typical installation challenges and skilled labor requirements of other solutions.

Crystalline technology has also proven its effectiveness in the field by improving the durability of new bridge components such as pier caps, foundations, bridge decks and towers as well as extending the service life of existing bridge structures around the world.

The following paper outlines the challenges associated with waterproofing complex bridge structures and then compares crystalline waterproofing technology to conventional waterproofing systems.

Waterproofing alternatives

More than 70% of bridges are constructed of concrete. The challenge for every concrete bridge structure is how to waterproof and protect the concrete from chemical attack, which by extension, protects the reinforcing steel from corrosion.

Specialized concrete materials can help. The most common approach is to use durable, low maintenance high-performance concrete (HPC). HPC mixes generally have high cement content and a low water-cement ratio and often include Supplementary Cementitious Materials (SCMs) such as fly-ash, silica fume or calcined clay. This combination aims to provide a high strength, high density concrete with reduced permeability and increased resistance to attack by chlorides, carbonation and sulfates thus slowing down the time to initiation of corrosion of the reinforcing steel.

One example of HPC application is the 8.1-mile (13 km) Confederation Bridge that connects Prince Edward Island to New Brunswick in Canada. Built to last 100 years, the bridge is constructed of high performance concrete with a mix design that includes a low 0.30 water/cement ratio and fly ash. Contractors also added water reducing agents and plasticisers. However, the initial cost of HPC can be 50%-100% more than standard concrete. In addition, HPC mix designs have a far greater tendency to produce shrinkage and thermally induced cracks at the site despite the use of admixtures such as super plasticisers. The risk of shrinkage can be mitigated with strict supervision of placement and curing practices.

Another measure to reduce or prevent corrosion is to increase the thickness of the concrete cover over the steel reinforcement. Unfortunately, thick concrete covers can increase the likelihood of larger cracks developing in the reinforced concrete members thus opening the door for moisture and chemicals that attack the concrete and, in time, the reinforcing steel. The additional concrete also increases the dead load on the structure and results in increased costs.

Corrosion-inhibiting admixtures added to the concrete at the time of batching form a protective layer on steel reinforcement. This raises the chloride ion threshold needed to initiate corrosion from 0.5% to 1.5% or 2.0%. These inhibiting admixtures are based on calcium nitrite or amino alcohol. While there is good evidence that corrosion inhibiting admixtures are effective at inhibiting the corrosion of reinforcing steel, they do not reduce the permeability of the concrete or help cracks to “self-heal,” which means that large amounts of chlorides can still reach the level of the steel in specific areas and possibly initiate corrosion.

Epoxy coated rebar, which provides similar chemical protection as epoxy coatings, is another alternative. While it’s 30% more expensive than uncoated black steel, the consensus among experts is that epoxy coated rebar can extend time to initiation of corrosion by 14 years. However, it’s not a foolproof solution. The coating can have defects right from the steel plant, it might be damaged at construction site and absorption of moisture leading to swelling and de-bonding of the coating. Once corrosion is initiated, the rate of corrosion is much the same as uncoated black steel.

Another alternative is stainless steel rebar. It’s highly effective and recommended for use with concrete designed for a 75-120 year life cycle. However, stainless steel rebar is five times more expensive than standard steel, has limited availability and there’s always a risk of contamination from other metallic products. Other options include galvanized steel rebar and non-metallic rebar.

Surface protection systems include polymer coatings that bond to the outer surface of the concrete, forming a film, and clear liquid sealers which also act at the surface. While most offer impermeability and chloride resistance if properly installed, they often suffer from errors during installation and can be easily punctured in service and have deteriorating performance over time. Many also have a high carbon footprint and require extensive surface prep.

In comparison, crystalline technology provides comparable or better waterproofing without many of the disadvantages outlined above.

Integral waterproofing

Concrete is chemical in nature. Although the aggregate base of a concrete mix is formed by rock and sand, it is the cement and water paste that binds the aggregates together. The mix water causes the cement particles to hydrate and this reaction forms calcium silicate hydrates, which cause the mixture to harden into a solid, rock like mass. This reaction also generates soluble calcium hydroxide and other chemical by-products, which lay dormant in the concrete.

Crystalline waterproofing products react with the calcium hydroxide and other by-products of cement hydration such as carbonates and sulfates of sodium, potassium and calcium found within the cement matrix to form

mineral-based “dendritic crystalline structures” that are insoluble in water. The formation of the crystals in the concrete pores, cracks and other voids is a gradual process, requiring several days to a couple of weeks for the crystals to reach maturity. As the crystals grow across the diameter of the concrete’s pores, they form a microscopic, mesh-like barrier that blocks the flow of liquids, even under extreme hydrostatic pressure.

When used in conjunction with proper building practices, such as those outlined in ACI 318 and ISO 19338, crystalline waterproofing improves the durability and performance of concrete structures,

lowers maintenance costs and extends the lifespan of the structure by protecting against the effects of water ingress and aggressive chemicals. The crystals become a permanent, integral part of the concrete matrix, never needing to be repaired or maintained.

Crystalline waterproofing products are produced as a coating material, admixture and dry shake which provide the designer and contractor with flexibility to choose the most suitable application method depending on the structure and conditions.

Crystalline waterproofing has been used on all types of bridges including beam (girder), arch, suspension, cable-stayed and truss bridges to protect the concrete members of their substructure, typically piers or columns, pier caps, abutments and foundations (pile footings, drilled piles, pedestal piers, driven piles and spread footings) as well as for the superstructure’s bridge deck, primary load carrying beams, cables anchors, towers and parapets. Bridge decks are typically concrete with a wearing surface that is either asphalt or concrete overlay.

As an example of crystalline technology’s performance when compared to conventional solutions, consider the construction of the beam bridges and parapets on the Highway 51 bridge parapet wall in Wisconsin where crystalline waterproofing admix (Xypex Admix C-2000) was used at a dosage of 2% of the Portland cement weight significantly reducing the problem of cracking. One parapet wall was placed using the crystalline admix (Xypex Admix) and the second without the Admix. The crystalline treated (Xypex) concrete had 50% fewer cracks compared to the reference parapet wall.

In La Crosse, Wisconsin, the Wisconsin Dept. of Transportation used Xypex products to repair a bridge deck on the heavily traveled truck route between Minneapolis and Chicago. Repairs included the routing out and dry packing of 92 meters (300 lin. ft.) of crack, and a one-coat application of crystalline waterproofing coating (Xypex Concentrate) over the entire surface. Even though much of the original coat of crystalline waterproofing (Xypex Concentrate) has since worn off, inspections of the underside of the bridge confirm no evidence of any water seepage.

In another case, contractors used approximately 1,500,000 lbs (680,400 kg) of crystalline waterproofing admixture (Xypex Admix) on 150 miles (240 km) of precast barriers and 5 miles (8 km) of retaining walls on a portion of the Pennsylvania Turnpike to protect from freeze-thaw deterioration and chloride ion attack. The addition of crystalline admix was used to extend the life of the concrete median barriers and retaining walls.

Remedial work was carried out on the bridge decks on the new Koeberg Interchange in Cape Town, South Africa, where crystalline waterproofing (Xypex Concentrate) was applied to 10 miles (17 km) of existing joints and new joints on all the old and new fly-over sections. The concrete on the existing sections of the ‘fly-over’ was topped with asphalt. When crews removed the asphalt, they found that the concrete was of poor quality in places, particularly at the joints. With the goal of enhancing durability of the parent concrete in the joint zone, crews applied a slurry coat of Xypex Concentrate at 1kg/m² in a band approximately 180 mm (7 inch) wide along the entire length of each joint line.

These are just a few of the examples of crystalline waterproofing to preserve and protect bridge structures. A number of other bridges from around the world are outlined below.

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Bridge Case Studies

Markham Valley Highway, Papua, New GuineaThe bridge deck concrete soffit on the Markham Valley Highway showed signs of fine cracking and increased porosity caused by leaching and water permeation. Contractors formed a two-coat application of Xypex Concentrate cured with Xypex Gamma Cure (due to hot conditions) to fully waterproof and restore the bridge deck. An added advantage of the crystalline waterproofing was that the bridge remained in service throughout

the rehabilitation work. Also, because Xypex requires saturated concrete surfaces to allow the diffusion of its crystalline technology, it could be applied during the rainy season.

Badaling Expressway Overpass, Beijing, China The Badaling Expressway, located outside of Beijing on the road to the Great Wall, includes four arched overpasses. A crystalline enhanced hydraulic cement compound (Xypex Patch 'n Plug) was used to repair defects in the concrete structures. Following the repairs crystalline waterproofing was applied as a coating (Xypex Concentrate) over the entire surface.

Noble Street Foot/Cycle Bridge, AustraliaContractors building the 51-m (167 ft) Noble Street Foot/Cycle Bridge needed to restore the profile of two deteriorated concrete columns. The columns narrowed at the pour joint and skewed off to one side. A crystalline enhanced repair mortar (Xypex Megamix II) was used to bring the columns back to their original contour after which the surfaces were coated with a cementitious skim coat (Xypex Megamix I) to help improve the aesthetics of the repair.

Pentele Bridge, HungaryFor concrete waterproofing and protection, Xypex Concentrate (2,000 kg/907 kg) was applied to concrete base rings of the 1,682-m (5,518 ft) Pentele Bridge pillars prior to being submerged in the Danube River. Patch ‘n Plug (600lb/275 kg) was utilized to repair defects in the pillars and seal joints between the rings.

Bethanga Bridge, AustraliaThe Xypex coating system was specified and applied to the concrete abutments on the Bethanga Bridge, located on the Victorian and New South Wales border. Both abutments were treated with the Xypex coating system, which incorporates the unique Xypex crystalline technology. The treatment was specified to address concrete deterioration caused in part by fluctuating water levels and the impact of wave action. A flexible sealant was used on cracks greater than 0.4 mm (0.016 inches), while Xypex crystalline technology was used on cracks less than 0.4mm (0.016 inches) and surrounding substrates to achieve long term durability.

Hsin Shen North Viaduct, TaiwanThis 36 year-old Hsin Shen North Viaduct is the main artery for the city of Taipei, connecting the Northern urban communities to the city center. The viaduct showed significant deterioration in the deck slab and the girder beams as well as heavy leaking and deemed “dangerous” and unsuitable for the heavy traffic in Taipei. The City Government agreed to the consulting engineering firm’s proposal to rehabilitate the viaduct with environmentally friendly products. Crystalline waterproofing coatings (Xypex Concentrate) were used to coat a total area of 170,000 m2 (1,830,000 sq.ft), including the girders, beams and abutments. Initial replacement costs were estimated at more than US$140 million. However, with crystalline waterproofing, the total cost was about US$56 million.

Orinoquia Bridge, VenezuelaCompleted in 2006, the Orinoquia Bridge cable stay bridge over the Orinoco River is one of the most important recent transportation infrastructure projects in Latin America. It includes four lanes for automobile traffic and a rail line in the center. Located in the western part of Bolívar state, its construction was instrumental for the economic development in the city of Ciudad Guyana and provided a much-needed link to the whole of Guyana. It also provided a link for Venezuela’s East and Southeastern regions with Roraima state in Brazil as well as with the Caribbean and the Atlantic Ocean coasts. More than 66,000 lbs (30,000 kg) of crystalline waterproofing coating (Xypex Concentrate) was used for the protection of concrete and reinforcement steel before placement of stone ballast for the railway line down the center of the bridge. Crystalline waterproofing was chosen to

protect the reinforced concrete slab that forms the foundation of the railway section of the bridge because it would not be damaged by the placement of the stone ballast. Over 160,000 sq. ft. (15,000 m2) was treated with crystalline waterproofing. Prior to the application, water was leaking through the bridge deck and falling into the river, posing environmental concerns for the river water.

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Research Directives

Leading independent scientific laboratories and regulatory bodies have conducted a number of studies to evaluate crystalline waterproofing technology and compare it to conventional solutions.

The new ACI 212.3R – 10 Report on Chemical Admixtures for Concrete guide published in November 2010 has a substantially improved chapter on waterproofing admixtures or Permeability Reducing Admixtures (PRAs). Chapter 15 specifically concluded that crystalline technology should be classified as a “PRAH” or Permeability Reducing Admixtures where hydrostatic pressure is present as opposed to “PRAN” or Permeability Reducing Admixtures where hydrostatic pressure is not present. Hydrophobic and mineral fillers were classified as PRAN and therefore not suitable for use where hydrostatic pressure is present. The report concludes that due to the crystalline deposits becoming integrally bound with the cement paste and their ability to resist water penetration against hydrostatic pressure, PRAH’s are “appropriate for water containment structures, below grade structures, tunnels and subways, bridges and dams and recreational facilities such as aquatic centers.”

Mahaffey associates of Australia designed a test to assess the performance of Xypex Admix in a tidal marine environment. To simulate construction practices, one of the trial concrete mixes was cured for just 7 days. To simulate the tidal action the samples were submitted to wetting and drying cycles in a sodium chlorate solution for 90 days. The chloride diffusion coefficient for the Xypex Admix sample compared to the untreated control sample and a sample treated with a conventional pore blocking admix was 35% and 27% lower respectively. An uncured sample was also tested and showed a 42% lower diffusion.

The U.S. Corps of Engineers CRD C48 and DIN 1048 evaluates the appropriate testing procedures for Xypex treatment to prevent water flow through a structure. Each of these tests measurement focuses on either the amount of water “output” or “depth of penetration” using incremental variations in hydrostatic pressure. In the testing, Xypex Admix treated samples and six untreated concrete samples were tested for water permeability. Increasing pressure was applied in increments over seven days and then maintained at 7 bars (224 ft./68 m head of water) for 10 days. Five of the six reference samples showed water flowing through on the sixth day and increasing throughout the test period. The results of the test, completed in Singapore, showed zero flow of pressurized water through the concrete sample treated with Xypex, in comparison to significant flows through 5 of the control samples. DIN 1048 measures the penetration depth of pressurized water in the concrete sample.

Kleinfelder’s laboratory in California evaluated the compressive strength on concrete containing the Xypex Admix. Samples were procured from a parking deck in Los Gatos. At 28 days, the compressive strength of the Xypex sample measured 7160 psi (49 MPa) as compared to the control sample of 6460 psi (44 MPa). At 56 days the compressive strength of the Xypex sample measured 8340 psi (57 MPa) as compared to the control sample of 7430 psi (51 MPa) this translates to a 12% strength increase.