International Concrete Abstracts Portal

Although the issue of progressive collapse has been significantly studied within the broader field of structural engineering, the literature on the analysis and design of connections in precast concrete cross-wall buildings is rather limited. This study aims to investigate the progressive collapse behaviour of a typical precast floor-to-floor system, considering the pull-out failure mode of the deformed bar into grouted keyways of slabs at the joints. To do so, the pull-out behaviour of deformed bars in grouted keyways of the connections was first experimentally studied. Subsequently, by integrating the pull-out force-displacement data with findings from full-scale floor-to-floor experiments, an approximate analytical approach was formulated and validated to estimate the resistance to progressive collapse. The findings reveal that the floor-to-floor system, when subjected to the pull-out failure mode following the removal of a wall support, demonstrates a secondary peak strength and considerable ductility in contrast to the bar fracture failure mode.

This study focuses on enhancing the durability of two-component grouting materials by incorporating ground granulated blast furnace slag (GGBFS) and replacing cement with industrial waste to reduce environmental pollution. A ternary cementitious system was developed using 30% GGBFS and 10% carbide slag (CS) as partial cement replacements. The research investigates the effects of different water-bentonite ratios, water-binder ratios, and AB component volume ratios on the physical and mechanical properties of the grout, including density, fluidity, bleeding rate, setting time, and strength performance. The microstructural evolution and hydration products were analyzed using scanning electron microscopy (SEM), X-ray diffraction (XRD), mercury intrusion porosimetry (MIP), and thermogravimetric analysis (TGA). The findings provide insights for optimizing the mix design of grouting materials in shield tunneling applications, with a focus on improving performance and sustainability.

This study used finite element analysis to examine how tendon configuration affects the temperature behavior of post-tensioned concrete structures during fire exposure. The thermal behavior of various tendon configurations was modeled, showing good agreement with experimental data. Parametric studies found that unbonded single-strand tendons (S) and prestressing (pretensioned) strands (R) had lower thermal resistance than bonded post-tensioned tendons (B), unbonded post-tensioned tendons (U), and grouted extruded-strand tendons (G). The S and R specimens stayed at or below the critical temperature for one-way slabs, validating current safety codes. The B, U, and G specimens remained well below critical temperatures, indicating that a thinner concrete cover might suffice. These findings highlight the need to consider tendon configuration in structural fire-resistance evaluation and incorporate heat resistance assessment to ensure the safety and efficiency of prestressed concrete structures during fires.

This paper presents research focused on the development of a test method that can be used to gauge the susceptibility of a post-tensioning (PT) grout to form soft grout. Depending on the grout formulation, soft grout may have a lower pH, retain excessive moisture, and be corrosive to the tendon. While relatively rare, it has been documented in bridge construction in the U.S. and abroad and in some cases has prompted the replacement of PT tendons.

One of the causes of the soft grout is thought to be the result of the use of low reactivity fillers such as ground limestone. When tendons are deviated significantly, these fillers can segregate and then accumulate into a mass of material that does not harden. The modified inclined tube test (MITT) was developed based on the Euronorm inclined tube test. None of the commercially available PT grouts produced soft grout when the grout was mixed and injected in accordance with the manufacturer’s recommendations and tested well before their expiration date. Additional mix water or residual water in the tube, however, produced soft grout consistently in one of the PT grouts.

Corrosion of prestressing steel can threaten the durability of prestressed concrete. To ensure the durability of unbonded post-tensioning (PT) systems, it is crucial to investigate the effects of construction defects such as grease leakage and high-density polyethylene (HDPE) sheath damage. This study quantified the thickness of grease coating (PT-coating) and HDPE sheath damage as experimental variables. An accelerated corrosion test was conducted in two environments: 1) chloride ions only (Cl-) and 2) both chloride ions and dissolved oxygen (Cl- + DO). The corrosion current density and weight loss of prestressing strands and the suspended concentration density of corrosion cell solution were measured to quantify the corrosion performance. Increasing the grease coating thickness over 0.3 mm (0.012 in.) did not significantly enhance corrosion resistance. Realistic levels of HDPE sheath damage had no significant detrimental effects on durability; however, excessive HDPE sheath area loss must be avoided for long-term durability. It was examined to quantify the interrelationship between three data: electrochemical measurement, weight loss, and suspended concentration density as quantitative corrosion data. The findings of this study can serve as a basis for developing durability-related provisions, as well as controlling the construction defects of unbonded PT systems in field applications.