Shrinkage Compensating Concrete for Use in Underground Concrete Structures
Matt Jabbari
Civil Engineer
CTS Cement Manufact...
mat concrete foundation was constructed using Shrinkage Compensating Concrete. Forty-five
years later this mat foundation ...
overloading during use can also cause cracking in concrete. Thus, the first challenge to anyone
trying to sort out the cau...
Shrinkage Compensating Concrete
Shrinkage Compensating concrete made with Type-K cement, is an effective way to minimize
t...
placements, absence of shrinkage cracks, and greatly reduced permeability (Valentine et al.
2000).
A tunneling design engi...
33 29 15 21 2
CONCRETECOMPONENTS, % BY VOLUME Rock
Sand
Cement
Water
Air
33 29 36 2
Shrinkage Compensating Concrete hydrat...
traffic, the finish of the Shrinkage Compensating Concrete is still crisp and looking new, due to
the materials superior a...
Type K concrete monolithic roof placements.
Edward K Rice; PE, F.ASCE, F.ACI; one of the original developers of Shrinkage ...
References
Thornton, Keith; Chusid, Michael 2009, Waterproofing Without Membrane, PTI Journal August 2009
Sullivan C.C. an...
Nat paper final version matt jabbari-011414
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Nat paper final version matt jabbari-011414

Published on: Mar 3, 2016
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Transcripts - Nat paper final version matt jabbari-011414

  • 1. Shrinkage Compensating Concrete for Use in Underground Concrete Structures Matt Jabbari Civil Engineer CTS Cement Manufacturing Corp., Cypress, California Ken Vallens Vice President Product Development CTS Cement Manufacturing Corp., Cypress, California Abstract: Tunnels and underground structures are regularly specified with 100-year design lifetime concrete. In order to achieve this we must eliminate cracking in the concrete. Cracks are pathways for the migration of water, chemicals and associated ions that can corrode structural steel, and eventually affect the integrity of the structure. The most common type of cracking is drying shrinkage cracking. The use of Shrinkage-Compensating Concrete is an effective way to minimize the cracking caused by drying shrinkage. By designing & producing controlled compressive stresses in the concrete, Shrinkage Compensating Concrete reduces shrinkage and the associated detrimental tensile forces which lead to shrinkage cracking. Shrinkage Compensating Concrete is popular in wastewater and water treatment infrastructure design, where liquid or chemical penetration/escape is strictly prohibited. Shrinkage Compensating Concrete is also widely used in industrial floors where the reduction of joints and elimination of cracking is highly desirable. Shrinkage Compensating Concrete has lower permeability, higher durability & abrasion resistance, higher freeze-thaw resistance, and higher resistance to sulfate attack than ordinary portland cement concrete. Introduction: While Shrinkage Compensating Concrete has been used in various structures since the 1960's, this type of concrete is generally not in the curriculum of the colleges and universities that teach engineering. Normally, an engineering graduate is not familiar with this type of concrete. However, the specification and use of Shrinkage Compensating Concrete is growing rapidly, and more and more infrastructures are being built with this type of concrete. Shrinkage Compensating Concrete has been used in numerous underground applications going back to the 1960s. 500 First Street NW in Washington D.C. is an eight story building with two basement levels. Similar to many sites in the Washington D.C. area, there were significant groundwater issues to contend with in constructing the foundation. In 1967, a post-tensioned
  • 2. mat concrete foundation was constructed using Shrinkage Compensating Concrete. Forty-five years later this mat foundation is still solid and watertight (Thornton, Chusid, Miller et.al. 2009). Shrinkage Compensating Concrete was used for the waffle ceilings in many of Washington D.C.’s yellow and green metro line subterranean stations. (Sullivan, Horwitz-Bennett et. al. 2013). (Figure 1) The State of Nevada used Shrinkage Compensating Concrete in the construction of the River Mountain Tunnel #2 in Henderson, NV. Shrinkage Compensating Concrete can be used in tunneling and underground construction, including but not limited to cut and cover tunnels, tunnel inverts, pre-cast concrete segmental liners, and cast-in place tunnel lining. Crack & Shrinkage Overview Why does concrete crack? Concrete cracks can occur because of shrinkage, external effects, and detrimental internal expansion. Shrinkage cracking can be either a result of plastic or drying shrinkage. The most common type of cracks are drying shrinkage cracks. External effects causing cracking can be in the form of thermal stresses, differential settlement, differential movement, or damage due to freezing and thawing. Internal expansion can result from corrosion of reinforcement or chemical reaction between the components of the concrete, such as Alkali-Silica Reaction (ASR) or Delayed Ettringite Formation (DEF). On top of all of these factors, errors in design and detailing, poor construction practices (including construction overloads, excessive water addition during mixing or finishing, and inadequate curing), or
  • 3. overloading during use can also cause cracking in concrete. Thus, the first challenge to anyone trying to sort out the cause(s) of concrete cracking is to attempt to determine the source of cracks (Coleman et al. 2013). The end use of the concrete application will determine the extent to which cracking is acceptable or unacceptable. For instance, cracks are not acceptable in tunneling construction, where they might be acceptable in a slab on grade (SOG) application. The measures used to control cracking depend, to a large extent, on the economics of the situation and the seriousness of cracking if not controlled. Cracks are objectionable where their size and spacing compromise the strength, stability, serviceability, function, or appearance of the structure (Coleman et al. 2013). A concrete tunnel liner placed below the water table may be subject to attack from sulfate bearing groundwater. In conventional portland cements, hydrated calcium aluminate (C3A) will react with sulfate ions to form detrimental expansive compounds. The consequence of this reaction is that the newly formed substance takes up a larger volume than the reactants causing expansion and cracking. Long-term exposure causes continual expansion leading to extensive deterioration. One of the contributing factors to cracking is high water content in the concrete’s cement paste. Portland cement needs a W/C ratio of 0.25 to hydrate (25 pounds of water is needed to hydrate 100 pounds of portland cement). At this W/C ratio, the concrete is very stiff and not workable (you cannot even get this concrete out of a ready mix truck). Higher W/C ratios are used to make the concrete workable. The extra water added is "water of convenience", which will end up on the concrete surface as bleed water. Excessive water is one of the culprits in shrinkage cracking. The bleed water escapes to the surface through small capillaries. These capillaries reduce the durability of the concrete. Also, bleed water on the surface of concrete causes the W/C ratio to change. The W/C ratio on the surface (present as bleed water), is higher than the W/C ratio in the bulk of the concrete, contributing to lower durability, lower abrasion resistance and higher shrinkage. Engineers constantly struggle to reduce the drying shrinkage, and cracking associated with drying shrinkage in portland cement concrete. In this effort, they try to lower the W/C ratio, use gap-graded aggregates, and even reduce the amount of cement in the mix (lowering the paste content). There are drawbacks associated with any of these measures, such as: lack of workability, material availability, and strength loss, to name a few. However, by replacing a small portion of portland cement with a mineral expansive additive (Komponent), one can convert a high shrinkage mix to a Shrinkage Compensating mix (Type-K) conforming to ASTM C 845; and consequently reduce shrinkage cracking. All of this can be done while using local portland cement and aggregates without major changes the mix design. The added cost is very minimal when you look at the overall benefits associated with the project.
  • 4. Shrinkage Compensating Concrete Shrinkage Compensating concrete made with Type-K cement, is an effective way to minimize the cracking caused by drying shrinkage. Shrinkage Compensating Concrete expands during the first part of curing process (7 days of wet curing). Expansion will induce tension in the reinforcement and compression in the concrete. Shrinkage cracks are eliminated if the Shrinkage Compensating Concrete's expansion is greater than its anticipated shrinkage. (Figure 2). (Figure 2) By designing and producing controlled compressive stresses in the concrete, Shrinkage Compensating Concrete reduces the detrimental tensile forces which lead to shrinkage cracking. The concrete mass will remain in compression as long as the compressive stresses are more than the tensile stresses. As known in the industry, concrete is about 10 times stronger in compression than it is in tension. As long as the concrete mass is in compression, it won't crack! There are no added compressive stresses in structural members, and the designer need not make any design adjustments. All other design parameters are unchanged and should be in accordance with good engineering practices, standards, and code requirements. There are three characteristics of Shrinkage Compensating Concrete that make it the product of choice for tunneling & underground construction: ability to design and construct large monolithic
  • 5. placements, absence of shrinkage cracks, and greatly reduced permeability (Valentine et al. 2000). A tunneling design engineer looks for durable, water tight, low permeability, 100-year life concrete for the underground structures he/she designs. Shrinkage Compensating Concrete has lower permeability, higher durability & abrasion resistance, higher freeze-thaw resistance, and higher resistance to sulfates than ordinary portland cement concrete. Comparing Shrinkage Compensating Concrete to Ordinary Portland Cement Concrete Shrinkage Compensating Cement consumes more water to hydrate, therefore less water "bleeding" occurs with this type of concrete (Figure 3). Comparison of hydrated portland cement concrete to hydrated shrinkage-compensating concrete by mass and volume.
  • 6. 33 29 15 21 2 CONCRETECOMPONENTS, % BY VOLUME Rock Sand Cement Water Air 33 29 36 2 Shrinkage Compensating Concrete hydrates up to 0.45 w/c Leaving no water for evaporation Rock Sand Cement Paste Air 33 29 27 9 2 Portland Cement Hydrates up to 0.25 w/c Leaving 9 % of volume for evaporation Rock Sand Cement Paste Water Air (Figure 3) Anti-ASR and ACR Calcium Sulfoaluminate cement, which one of the main ingredients in Type-K cement, is relatively inactive to Alkali-Silica Reaction (ASR) and Alkali-Carbonate Reaction (ACR) in comparison with portland cement. This is due likely to: 1) The ettringite (3CaO.Al2O3.3CaSO4.32H2O) hydration product of Calcium Sulfoaluminate cement, with 32 crystalline water molecules, decreases the porosity of hardened Calcium Sulfoaluminate cement dramatically, and 2) Lower PH-values in the liquid phase of hydration products of Calcium Sulfoaluminate cement in comparison with portland cement (Valentine et al. 1994, Yanjun, Yongmo, Chunlei, et al. 2012). Case Studies: Type K cement has been available since the 1960's and has exhibited an excellent track record. In the early 1990's at Orange County California’s John Wayne airport, portland cement concrete was used on level one of the parking structure resulting in approximately one mile of cracks. The engineer switched to Shrinkage Compensating Concrete for the placement of level 2 of the same parking structure which resulted in no cracks. As a matter of fact, after 14 years of heavy
  • 7. traffic, the finish of the Shrinkage Compensating Concrete is still crisp and looking new, due to the materials superior abrasion resistance (Chusid et al. 2007). See figure # 4. Other construction industries have used Shrinkage Compensating Concrete successfully. Shrinkage Compensating Concrete is popular in wastewater and water treatment infrastructure design, where liquid or chemical penetration/escape is strictly prohibited. Shrinkage Compensating Concrete is also popular in rock anchoring, soil nailing, and roof bolting operations, as well as grouting of post-tensioned structures. It is used due to its expansive characteristics and its ability to compensate for shrinkage. In warehouses and distribution centers, Shrinkage Compensating Concrete is used to reduce the number of joints, typically placing floors in excess of 50,000 square feet with no joints. The Turnpike Authorities of Michigan, Ohio, New Jersey, and Pennsylvania use Shrinkage Compensating Concrete toppings in their bridge rehabilitation operations to eliminate decking cracks, therefore preventing the bridge's steel reinforcement from exposure to chloride ions. Recently a monolithic roof (64 feet X 40 feet) of a custom residence in the Eastern Mountains of San Diego (Julian, CA), using Shrinkage Compensating Concrete was placed with no roofing membrane. This residence is located 4000 feet above sea level. The area is known to have a quite high accumulated snow fall in the winter. No leakage was reported by the owner. As a matter of fact Shrinkage Compensating Concrete was used to construct the entire house, including the subterranean garage and the tunnel connecting the garage to the observation tower. Please see figure 5, 6, and 7. John Wayne Airport with Portland and Post-Tensioning Same Design, Contractor, and Ready-Mix Company. The only difference is the Type-K Cement. (Figure 4)
  • 8. Type K concrete monolithic roof placements. Edward K Rice; PE, F.ASCE, F.ACI; one of the original developers of Shrinkage Compensating Concrete built his house in 1963 using Type K concrete. To this day, he lives in the same house and its exposed concrete roof has not leaked (Chusid et al. 2006). Conclusion: Shrinkage Compensating Concrete technology is ideal for, and should be adopted extensively in tunnels and underground structures. While the cost of Shrinkage Compensating Concrete can be slightly more than conventional portland cement concrete, the cost reduction associated with lesser joints and larger pours makes using Shrinkage Compensating Concrete a cost benefit. Also, savings resulting from extended life, reduced shrinkage cracking, reduced leakage, and reduced need for repairs make the overall life cycle cost significantly lower than conventional portland cement concrete construction. The true benefit is derived from having a leak-proof, structurally sound and environmentally safe underground structure. (Figure 5) (Figure 6) (Figure 7)
  • 9. References Thornton, Keith; Chusid, Michael 2009, Waterproofing Without Membrane, PTI Journal August 2009 Sullivan C.C. and Horwitz-Bennett, Barbara 2013, Building with Concrete-Design and Construction Techniques, Concrete Construction AIA Journal 2013 Chusid Michael, RA, FCSI, is principle and founder of Chusid Associates, a consultant to building product manufacturer, based in Tarzana, CA Coleman, Jeffery 2013. Cracking...Defect or Normal? When is concrete cracking a construction defect? Concrete International Sept. 2013. Valentine, Lawrence 2000. Containment Structures in the Chemical Industry Concrete International January 2000. ACI Committee 223, Standard Practice for the Use of Shrinkage-Compensating Concrete (ACI 223-98)," Chapter 1.4, American Concrete Institute, Farmington Hills, MI, Dec 1998. Valentine, Lawrence 1994. Environmental Containment Structures, Concrete International July 1994. Yanjun, Yongmo, Chunlei 2012. Sulfoaluminate Cement: An Alternative to Portland Cement. Advanced Materials Research Vols. 368-373 (2012) pp 478-484 Trans Tech Publications, Switzerland. Jindingbeilu, Shijingshan District, Beijing-100041, P.R.China Sanlihelu, Haidian District, Beijing-100083, P.R.China Chusid, Michael, RA FCSI 2007. A Perfect Match. Post Tensioning and Shrinkage Compensating Concrete Form a Durable Union at John Wayne Airport. PTI Journal July 2007. Bondy Kenneth, SE, FACI, President of the Post-Tensioned Institute (PTI) and was, in 2005, inducted into the PTI Hall of Fame Chusid, Michael 2006 All-Concrete House Turns 40 Years Old. Concrete International March 2006.

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