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2 Archives of Civil and Mechanical Engineering

2 2017

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Thermal and mechanical properties of sustainable lightweight strain hardening geopolymer composites

Nematollahi B., Ranade R., Sanjayan J., Ramakrishnan S.

Archives of Civil and Mechanical Engineering

2017

Vol. 17, no. 1

55--64

The thermal and mechanical properties of sustainable lightweight engineered geopolymer composites (EGCs), exhibiting strain-hardening behavior under uniaxial tension, are reported in this study. Fly ash-based geopolymer was used as complete replacement of cement binder to significantly increase the environmental sustainability of the composite compared to the engineered cementitious composite (ECC). Additionally, three types of lightweight aggregates including expanded perlite, microscopic hollow ceramic spheres and expanded recycled glass were used as complete replacement of micro-silica sand to reduce density and thermal conductivity of the composite. The influences of the type of aggregates on the fresh and hardened properties of the composite including matrix workability, density, compressive strength, thermal conductivity and uniaxial tensile performance were experimentally evaluated. The results indicated that the density and compressive strength of all EGCs developed in this study, even the EGC containing normal weight micro-silica sand, were less than 1833 kg/m3 and more than 43.4 MPa, respectively, meeting the density and compressive strength requirements for structural lightweight concrete. Replacing normal weight micro-silica sand with lightweight aggregates reduced the compressive and tensile strengths of the EGCs by a maximum of 24% and 32%, respectively. However, the tensile ductility of the EGCs containing lightweight aggregates was comparable to that of the EGC containing micro-silica sand. In addition, the thermal conductivity of the EGCs containing lightweight aggregates were significantly (38–49%) lower than that of the EGC containing normal weight micro-silica sand, resulting in an end-product that is greener, lighter, and provides better thermal insulation than ECC.

High ductile behavior of a polyethylene fiber-reinforced one-part geopolymer composite: A micromechanics-based investigation

Nematollahi B., Sanjayan J., Qiu J., Yang E. H.

Archives of Civil and Mechanical Engineering

2017

Vol. 17, no. 3

555--563

This study investigates the tensile performance a one-part strain hardening geopolymer composite (SHGC) reinforced by ultra-high-molecular-weight polyethylene (PE) fibers. The developed composite as a “dry mix” uses a small amount of solid activator rather than large quantities of commonly used alkaline solutions and eliminates the necessity for heat curing. The quantitative influences of curing condition (heat and ambient temperature curing) and type of fiber (poly vinyl alcohol (PVA) and PE fibers) on the macroscale properties of the matrix and composite including workability, density, compressive strength, and uniaxial tensile performance were evaluated. A micromechanics-based investigation was performed to explain the experimentally observed macroscopic high tensile ductility of the developed one-part PE-SHGCs. The investigation involved determination of the matrix fracture properties and the fiber–matrix interface properties using fracture toughness tests and single-fiber pullout tests, respectively. The fiber-bridging constitutive law of the composites was computed via a micromechanics-based model to link the material microstructures to macroscopic composite tensile performance. The results indicated that the ambient temperature curing increased the compressive and tensile strengths, but reduced the tensile ductility of the one-part PE-SHGCs. The one-part PE-SHGCs exhibited lower compressive and tensile strengths, but higher tensile ductility compared to the one-part PVA-SHGC.