The strength of Ultra-High Performance Concrete (UHPC) can be sensitively affected by the curing method used. However, in contrast to the precast plant production of UHPC where a standard high-temperature steam curing is available, an optimum curing condition is rarely realized with cast-in-place UHPC. Therefore, the trend of the compressive strength development of UHPC was experimentally investigated in this study, with a focus on early-age strength by assuming the various curing conditions anticipated on site. Concrete specimens were cured under different conditions with variables including curing temperature, delay time before the initiation of curing, duration of curing, and moisture condition. Several conditions for curing are proposed that are required when the cast-in-place UHPC should gain a specified strength at an early age. It is expected that the practical use of UHPC on construction sites can be expedited through this study.

Prestressed Concrete Wire and Strand (PC) strands are the most used materials to introduce prestress in a Pre-Stressed Concrete (PSC) structure. However, it is difficult to evaluate the final prestress force of the PC strand after prestressing or its residual prestress force after completion of the structure on site. This impossibility to assess eventual loss of prestress of the PC strand has resulted in a number of serious accidents and even in the collapse of several structures. This situation stresses the necessity to maintain the prestress force residual or after prestressing for the evaluation of the health of the concrete structure throughout its lifespan. Recently, several researchers have studied methods enabling one to verify the prestress force by inserting an optical fiber sensor inside the strand but failed to provide simple techniques for the fabrication of these devices to fulfill measurement performance from the design prestress to failure. Moreover, these methods require the additional installation of electrical resistance strain gages, displacement sensors and load cells on the outer surface of the structure for long-term precise measurement. This paper proposes a method enabling one to evaluate precisely and effectively the prestress force of the PC strand and intends to verify the applicability of the proposed method on actual concrete structures. To that end, an innovative PC strand is developed by embedding a Fiber Bragg Grating (FBG) sensor in the core wire of the PC strand so as to enable short term as well as long term monitoring. The measurement performance of the developed strand is then evaluated experimentally and the reliability of the monitoring data is assessed.

In this study, a series of pull-out tests on fibre-reinforced polymer (FRP) perfobond rib shear connectors were conducted to investigate their shear behavior. The test specimens were designed to examine only the effects of the resistance by rib holes. The test variables were the size and number of rib holes. In the tests, the resistance by concrete dowel action was practically linearly proportional to the area of the rib hole. However, the resistance appeared to be nonlinearly proportional to the number of rib holes with a slight loss for a larger number of the rib holes, due to the sequential failure of the rib holes. The constitutive equation of the discrete spring model representing the concrete dowel including post-failure frictional effects, adopting the diameter of the rib hole as parameter, was derived through regression analysis of the load – relative displacement curve obtained for specimens with a single rib hole. The proposed discrete spring model resulted in good correlation with the experimental results for specimens with a larger number of rib holes. It is expected that the derived constitutive equation would be useful for the analysis and design of structures using FRP perfobond rib shear connectors.

This study examined the effect of aggregate size and density on the shear and tensile bond characteristics of the coarse sand coated interface between stay-in-place fibre-reinforced polymer (FRP) formwork and concrete. Shear and tension tests were performed for five test variables according to aggregate size and density. Based on the test results, the appropriate size and distribution density of the aggregates is examined. In addition, based on the shear test results, the local shear bond stress-slip model for each of the test variables was derived through an optimization process.

Prestressed concrete (PSC) is one of the most reliable, durable and widely used construction materials, which overcomes the weakness of concrete in tension by the introduction of a prestress force. Smart strands enabling measurement of the prestress force have recently been developed to maintain PSC structures throughout their lifetime. However, the smart strand cannot give a representative indication of the whole prestress force when used in multi-strand systems since each strand sustains a different prestress force. In this paper, the actual distribution of the prestress force in a multi-strand system is examined using elastomagnetic (EM) sensors to develop a method for tracking representative indicators of the prestress force using smart strands.