Browsing by Author "Kahn, LF"

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    Creep and shrinkage of high-performance lightweight concrete
    (AMER CONCRETE INST, 2004) Lopez, M; Kahn, LF; Kurtis, KE
    Two high-performance lightweight concrete (HPLC) mixtures with average compressive strengths of 68.5 and 75.4 MPa (9950 and 10,950 psi) were developed. Their air-dry unit weights were 1875 and 1905 kg/m(3) (117 and 119 lb/ft(3)), respectively. Twenty-six creep specimens were loaded at 16 or 24 h to 40 or 60% of their initial strength. This preliminary investigation showed that expanded slate HPLC experienced less creep, but slightly more shrinkage than normalweight high-performance concrete of similar paste content, mixture proportions, and strength.
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    Prestress losses in high performance lightweight concrete pretensioned bridge girders
    (PRECAST/PRESTRESSED CONCRETE INST, 2005) Kahn, LF; Lopez, M
    The purpose of this research was to determine the time-dependent behavior of high performance lightweight concrete and to examine how long-term behavior affects the prestress losses in high strength precast, prestressed concrete bridge girders made using expanded slate lightweight aggregate. Two different high performance lightweight concretes (HPLC) with strengths of 8000 and 10,000 psi (55 and 69 MPa) were developed. They had air-dry unit weights of 116 and 118 lb/ft(3) (1855 and 1890 kg/m(3)), respectively. Creep, shrinkage, and other prestress loss parameters were investigated on 36 cylinder specimens and four AASHTO Type II girders. Generally, prestress losses determined from the AASHTO Type II girders made with HPLC were less than those predicted using AASHTO, PCI, and ACI 209 methods. Based on the experimental data, the total final prestress losses were estimated to be 20 and 15 percent of the initial prestressing force for the 8000 and 10,000 psi (55 and 69 MPa) HPLC, respectively.