When the energy performance of concrete is substantially higher than that of normal type concrete, such concrete is regarded as energy efficient concrete (WBSCSD 2009). An experimental study was conducted to investigate mechanical properties of energy efficient concrete with binary, ternary and quaternary admixture at different curing ages. Slump test for workability and air content test were performed on fresh concretes. Compressive strength, splitting tensile strength were made on hardened concrete specimens. The mechanical properties of concrete were compared with predicted values by ACI 363R-84 Code, NZS 3101-95 Code, CSA A23.3-94 Code, CEB-FIP Model, EN 1991, EC 2-02, AIJ Code, JSCE Code, and KCI Code. The use of silica fume increased the compressive strengths, splitting tensile strengths, modulus of elasticities and Poisson’s ratios. On the other hand, the compressive strength and splitting tensile strength decreased with increasing fly ash.

This paper provides experimental results to investigate the mechanical properties of sustainable strain-hardening cement composite (2SHCC) for infrastructures after freeze-thaw actions. To improve the sustainability of SHCC materials in this study, high energy-consumptive components—silica sand, cement, and polyvinyl alcohol (PVA) fibers—in the conventional SHCC materials are partially replaced with recycled materials such as recycled sand, fly ash, and polyethylene terephthalate (PET) fibers, respectively. To investigate the mechanical properties of green SHCC that contains recycled materials, the cement, PVA fiber and silica sand were replaced with 10% fly ash, 25% PET fiber, and 10% recycled aggregate based on preliminary experimental results for the development of 2SHCC material, respectively. The dynamic modulus of elasticity and weight for 2SHCC material were measured at every 30 cycles of freeze-thaw. The effects of freeze-thaw cycles on the mechanical properties of sustainable SHCC are evaluated by conducting compressive tests, four-point flexural tests, direct tensile tests and prism splitting tests after 90, 180, and 300 cycles of rapid freeze-thaw. Freeze-thaw testing was conducted according to ASTM C 666 Procedure A. Test results show that after 300 cycles of freezing and thawing actions, the dynamic modulus of elasticity and mass loss of damaged 2SHCC were similar to those of virgin 2SHCC, while the freeze-thaw cycles influence mechanical properties of the 2SHCC material except for compressive behavior.

In order to assess the bond behavior of deformed steel rebars in recycled-aggregate concrete (RAC) incorporating both fine and coarse recycled aggregate, pull-out tests were carried out in this study on 16-mm diameter deformed steel rebars embedded concentrically in RAC. The concrete was designed using equivalently mixed proportions of both recycled coarse aggregate and recycled fine aggregate. The tests employed five types of recycled aggregate replacement combinations and three types of rebar placement orientation (i.e., vertical bars and two-tiered and three-tiered horizontal bars). Based on the pull-out test results, the maximum bond strength tended to decrease and the slip at the maximum bond strength increased as the average water absorption of the aggregate increased, irrespective of the rebar orientation or placement location within the concrete member. The pull-out test results for the horizontal steel rebars embedded in RAC indicate that the casting position effect could be determined from the mid-depth of the concrete member, irrespective of the member’s height. The normalized bond versus slip relationship between the deformed rebar and the RAC could be predicted using an empirical model based on regression analysis of the experimental data.

The present study intended to find a way to use TiO₂, one of the most widely used photocatalysts, as a construction material. To that end, nano-SiO₂/Al₂O₃-TiO₂ powder (NTCP) was synthesized by coating SiO₂ and Al₂O₃ support materials with TiO₂. The NTCP was anatase phase spherical particles, specific surface areas were 319 m²/g and 267 m²/g for the SiO₂-TiO₂ powder and Al₂O₃-TiO₂ powder. UV absorption test results showed the developed NTCP had a light absorption peak at wavelengths of 380 nm or below, and its absorbance was much larger than that of commercial TiO₂. The NTCP formed smaller pores on the surface than commercial TiO₂. As a result, the flow of the mortar decreased as the adsorption strength increased and combined a large number of water molecules. In addition, the Pozzolanic reaction by SiO₂ and Al₂O₃ used as support materials produced many calcium silicate hydrate (C-S-H) and calcium aluminate hydrate (C-A-H). This has shown an increased strength of mortar mixed with the NTCP by promoting a nucleation effect and reducing the filling effect and the number of harmful holes in the mortar.

This study investigated the effects of shrinkage compensation on the tensile and cracking responses of strain-hardening cement composite (SHCC) by adding calcium sulfoaluminate (CSA)-based expansive additive (EXA) to the mixture. Such responses are closely related to the durability of concrete structures, of dumbbell-shaped SHCC specimens, and reinforced SHCC ties. For this study, two SHCC mixtures and a conventional concrete mixture with a specific compressive strength value of 30 MPa were prepared and measured in terms of shrinkage history, compressive strength, flexural strength, and direct tensile strength. The test results show that the mechanical properties of shrinkage-compensated SHCC with 10% CSA-based EXA are superior to those of conventional SHCC and concrete mixtures. Also, reinforced tension ties with shrinkage-compensated SHCC exhibited the best multiple cracking and tension-stiffening behavior among the three types of tension ties tested. The results show that shrinkage compensation using CSA-based EXA in SHCC with rich mixture is effective for resisting crack damage. Shrinkage-compensated SHCC may be used for civil infrastructure facilities that require high levels of durability and are exposed to extreme environments.

This research examines the influence of an embedded steel reinforcing bar and micro steel fibers on the tensile and electrical properties of polyethylene (PE) fibers reinforced cement composite dumbbell-shaped specimens with multi-walled carbon nanotubes (MWCNTs) in direct tension. The cement composites are reinforced with 0.75 vol.% PE fibers to achieve a strain-hardening performance in direct tension and 1.0 wt % MWCNTs are incorporated to give the electrical conductivity into the cement composites. To investigate the steel bar and steel fibers effect on the electrical behavior of synthetic PE fiber reinforced strain-hardening cement composites (PE-SHCCs), a round bar with a diameter of 4 or 7 mm is placed at the center of specimen’s cross-section. Additionally, steel fibers’ content of 0, 0.5 and 1.0 vol.% are added into the PE-SHCC mixtures. The test result indicates that the addition of steel fibers improves the tensile strength and electrical behavior of synthetic PE fiber reinforced SHCC. The self-sensing ability of PE-SHCC with 1.0% steel fibers is improved by the presence of the embedded steel bar before an initial crack while the reinforced PE-SHCC specimens were less sensitive as the tensile strain increased after the initial crack. The optimal linear regressions between fractional changes in resistivity (FCR) and tensile strain were achieved for PE-SHCC containing 1.0% steel fibers.