International Concrete Abstracts Portal

This paper presents a novel framework of analysis to assess the resistance of existing reinforced concrete (RC) members experiencing spatial variability of crack patterns and spatial variability of concrete mechanical properties. The spatial variabilities are considered by using digital image processing (DIP) to map crack patterns onto three-dimensional (3-D) nonlinear finite element (NFE) models, where the concrete mechanical properties (compressive strength, tensile strength, damage, and modulus of elasticity) are spatially varied using random fields (RFs) to form random NFE (RNFE) models. The framework was developed and applied to assess a corroded RC beam (to determine the distribution of the resistance) and column (to determine the reliability of the column at the ultimate limit state [ULS]). Research findings indicate improved accuracy in assessing the resistance of the corroded members up to 20%, and the adaptivity of the developed framework for performing reliability analysis of existing RC structures.

This study introduces a new anchorage strategy using ultra-high-performance concrete (UHPC) to attach unbonded post- tensioning (PT) strands to existing foundations. This solution complements a seismic retrofit scheme investigated by the authors, which transforms nonductile cast-in-place reinforced concrete (RC) shear walls into unbonded PT rocking shear walls following concepts of selective weakening and self-centering. In the proposed PT anchorage scheme, mild steel reinforcements are inserted through the shear wall thickness and into the foundation. Subsequently, UHPC is cast around the wall base, forming a vertical extension connected to the foundation, which is used to anchor the unbonded PT strands. The feasibility and performance of the anchorage scheme was investigated through a combination of laboratory testing and numerical simulations. Pullout testing on four scaled-down anchorage specimens was conducted in the laboratory. Hairline cracks were observed in the UHPC during testing. Additionally, three-dimensional (3-D) finite element (FE) models were created, validated, and used to study the performance of the proposed anchorage scheme under lateral loading. The simulation results support the effectiveness of the proposed anchorage strategy.

Additive construction augments the laborious construction of structural concrete; however, its implementation remains mostly limited to building envelopes. Culvert construction benefits from alternative methods due to the high demand for transportation infrastructure. In this study, extrusion-based 3-D concrete printing (3DCP) is developed for the first time for culvert construction. Large-scale unreinforced concrete pipes were printed, and the early-stage (e.g., buildability), mechanical, and durability properties of two commercially available 3DCP materials were determined. Additionally, the specimens were tested structurally and exceeded the expected structural performance (by about an average of 32%) under the three-edge bearing test. However, the desired durability was not met due to the porosity of the specimens. The mix design with microfibers exhibited marginally higher compressive and tensile strength, but did not meet durability criteria similar to non-fiber material. Results indicated the 3DCP feasibility for pipe culvert construction and mapped further direction for widespread implementation and addressing concrete pipe durability issues.

Biochar properties—in particular, its fineness and ability to absorbwater—can be exploited to modify the rheological behavior ofcementitious conglomerates and improve the hydration of cementpaste under adverse curing conditions, such as those related tothree-dimensional (3-D) concrete printing. Regarding the freshstateproperties, the study of rheological properties, conductedon cementitious pastes for different biochar additions (by weightof cement: 0, 1.5, 2, and 3%), highlights that the biochar inducesan increase in yield stress and plastic viscosity. The investigationof mechanical properties—in particular, flexural and compressivestrength—performed on mortars evidences the internal curingeffect promoted by biochar additions (by weight of cement: 0, 3,and 7.7%). In fact, compared to the corresponding specimens curedfor the first 48 hours in the formwork, specimens with biochar addition cured directly in air are characterized by a drastically lowerreduction in compressive strength than the reference specimens—that is, approximately 36% and 48%, respectively. This interestingresult can also be exploited in traditional construction techniqueswhere faster demolding is needed.

focused on the impacts of geometric design parameters on the structural performance of drilled shaft footings. Large-scale tests were conducted on specimens subjected to uniform column compression and constructed with different geometric conditions permitting the examination of varied strut inclination, shaft diameter, and footing depth. The experimental results obtained confirmed that footing strength was highly dependent on strut inclination while shaft diameter affected the ultimate damage pattern. Strength calculations based on three-dimensional (3-D) strut-and-tie modeling guidelines recently developed by the authors provided less conservative results as compared to previous recommendations and resulted in levels of accuracy consistent with those of other shear design procedures adopted in code provisions.