Ju-Hyun Mun

Although accurately estimating the early age compressive strength of concrete is essential for the timely removal of formwork and the advancement of construction processes, it is challenging to estimate it in cool, cold, hot, or unmanaged conditions. Various nondestructive testing methods, including recent IoT-based techniques, have been proposed to determine the compressive strength of concrete. This study evaluates the maturity method using the wireless thermocouple sensor in assessing the early age compressive strength of concrete slabs, particularly those not subjected to watering and protection in a cool environment below 20 °C. For this purpose, wire and wireless thermocouple sensors were installed in reinforced concrete (RC) slabs, whereas wire thermocouple sensors were installed in concrete cylinders. In addition, the compressive strengths of standard-cured cylinders, field-cured cylinders, and core samples extracted from the RC slab were measured. On day 7, the maturity index (M) values for the field-cured cylinders were 7% lower than those of the standard-cured cylinders, and the M values for the RC slabs with wire and wireless sensors were 6% lower. The compressive strengths of the field-cured cylinders and core samples extracted from the RC slabs were 19% and 14% lower than those of the standard-cured cylinders, respectively. Thus, while the difference in M values was 6–7%, the difference in compressive strength was significantly higher, at 14–19%. In a cool environment without watering or protection, the difference in strength can be even greater. Consequently, a commercial IoT-based thermocouple sensor can replace conventional wire sensors and adopt to estimate early age compressive strength of concrete in unmanaged curing condition.

The effect of a recently developed socket-type shear connector (SSC) on the flexural behaviour of a composite basement wall (CBW) was examined in this work. To this end, 12 CBWs composed of cast-in-place (CIP) piles fabricated with H-shaped steel beams or reinforcing steel plates were prepared by varying the arrangement and amount of SSCs. Two-point loading was applied to simply supported CBW specimens. The CBW specimens with more SSCs had a higher effective stiffness in the elastic state and higher moment capacity in the ultimate state, irrespective of the cross-sectional details of the CIP piles. These trends were particularly prominent when a reinforcing steel plate was used in the SSCs. The post-peak behaviour of the CBW specimens subjected to a simulated load with a negative external moment tended to be more ductile. Consequently, a higher degree of composite action was fully exerted on the CBWs with greater numbers of SSCs. Using established equations for the sectional details of CBWs with SSCs, the nominal partially composite to full composite flexural capacity ratios of the CBW specimens subjected to simulated loads with positive and negative external moments were calculated to be, respectively, 0.83 and 0.91 for 0.5η sc and 0.79 and 0.90 for 0.75η sc , where η sc is the normalised shear connector capacity specified in ANSI/AISC 360-16.