durability - Durability Construction Project Life Cycle...

Info icon This preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon
Durability Dr. Kimberly Kurtis School of Civil Engineering Georgia Institute of Technology Atlanta, Georgia Construction Project Life Cycle Time Concept Engineering and Design Procurement Construction Start-up Operation Decomissioning Construction Costs Other 55% Materials 45% Source: Engineering News-Record Indexes of Costs Trend, 1949-1979. Infrastructure Durability Cost of Environmental Remediation, 1987-2000: air pollution $26.7 - 44 billion radiation pollution $327 - 896 billion water pollution $34.4 - 57.5 billion Cost of Bridge Repair, 1981-2000: $102.6 billion Forms of Attack Chemical –leaching, sulfate attack, delayed ettringite formation, acid attack, carbonation, alkali-aggregate reactions Electrochemical – corrosion Physical Attack – freeze/thaw, abrasion, erosion, fire Permeability Permeability - measure of the rate of flow through a material; related to interconnectivity of pores, microcracks, and cracks Permeability of the paste Permeability and gradation of the aggregate Quality of the paste and ITZ Relative proportion of aggregate to paste
Image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Permeability Largely influenced by the structure (I.e., size and distribution of voids and cracks) and porosity of the HCP, which in turn is strongly influenced by the w/c or w/cm Permeability Related to capillary pore volume Capillary space in hydrated cement pastes increase markedly for w/c>0.42 Size of the pores is very important; water moves through capillary pores (10-50+nm), NOT gel pores (<10nm) In concrete, ITZ is also important for transport Permeability: Cement Paste Flow of water through cement paste obeys D’Arcy’s law for flow through porous media: dq/dt = v = K p (h/x) Where dq/dt or v is the rate of flow of water K p is the permeability coefficient h is the hydraulic pressure exerted by the water x is the specimen thickness K p is strongly dependent on the capillary porosity, which is related to the w/c or w/cm and the degree of hydration Typical values for K p Hardened cement paste, kept moist 0.1-120x10 -12 cm/s (for w/c 0.30-0.70) Coarse aggregate 1.7-3.5x10 -13 cm/s High strength concrete 1x10 -13 cm/s Mature, good quality concrete 1x10 -10 cm/s Why is the permeability in normal strength concrete so much larger? Permeability: Concrete Influence of curing Permeability: Concrete Influence of SCMs Silica fume reduces the number of pores < 10 µ m
Image of page 2
Chemical Transport In addition to flow of water through the concrete, we must also consider chemical interactions between the ingressing water or solution and the pore solution and solids in the concrete (I.e., adsorption, precipitation, dissolution) The moisture content of the concrete also affects the rate of ingress; D’Arcy’s Law is applicable to saturated concrete. Capillary draw is important in dry or semi-dry concrete Fick’s Second Law Often used to describe transport in near-saturated concrete where no pressure head exists dC/dt = K d ( δ 2 C/ δ x 2 ) Where C = concentration t = time K d = diffusion coefficient x = depth For semi-infinite slab, the solution to this equation is C(x,t) = C o {1-erf[x/(2 K d t)]}
Image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 4
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern