This article investigates the development of the following material properties of concrete with time: compressive strength, tensile strength, modulus of elasticity, and fracture energy. These properties were determined at seven different hydration ages (18 h, 30 h, 48 h, 72 h, 7 days, 14 days, 28 days) for four pure cement concrete mixes totaling 336 specimens tested throughout the study. Experimental data obtained were used to assess the relationship of the above properties with the concrete compressive strength and how these relationships are affected with age. Further, this study investigates prediction models available in literature and recommendations are made for models that are found suitable for application to early age concrete. Results obtained indicate that the relationship between the splitting tensile strength and concrete compressive strength can be approximated with a power function between 0.7 and 0.8, and this correlation is not affected by age. Fracture energy of the concrete and modulus of elasticity values obtained in this study correlate well with the square root of the compressive strength and it was found that this relationship holds true for all hydration ages investigated in this paper. Inverse analysis on the wedge-splitting test was conducted to determine the direct tensile strength. Values of tensile strength obtained from the inverse analysis have been validated numerically by carrying out finite element analysis on the wedge split, and anchor pull-out tests. The ratio of the tensile strength obtained from the inverse analysis to the splitting tensile strength was found to be in the range of 0.5–0.9 and 0.7 on average.

In this paper, the cyclic behavior of groups of double-headed anchored blind bolts (DHABBs), which are anchored within concrete-filled square hollow sections (CFSHSs), is investigated. The DHABB used in this study consists of a conventional headed anchored blind bolt (HABB) with one additional head, between the existing end head in the embedded region and head next to the tube wall. A series of full-scale experiments were conducted on the pull-out behavior of groups of DHABBs under cyclic loading. The specimens consisted of groups of two DHABBs, four DHABBs, and four DHABBs with one through bolt (TB). The effects of load distribution between individual bolts and of internal concrete cones overlapping from individual blind bolts are also investigated. The failure mode and sequence, cracking pattern, and the strain distribution for each test are explained in detail. A comprehensive three-dimensional (3D) finite element model was developed and the results were shown to compare well with the experimental results. The finite element (FE) model was then used in parametric studies to ascertain the influence of various parameters on the behavior of blind bolted connections. The effect of tube thickness, flange and web thickness of T-stub, sizes and configurations of DHABBs, and TB and the concrete compressive strength were investigated. Among them, the flange thickness of the T-stub was found to be the parameter that has the largest effect on the tensile behavior of blind bolted connections.