International Concrete Abstracts Portal

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.

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.

Noncorrosive fiber-reinforced polymer (FRP) reinforcement presents an attractive alternative to conventional steel reinforcement, which is prone to corrosion, especially in harsh environments exposed to deicing salt or seawater. However, FRP reinforcing bars’ lower axial stiffness leads to greater crack widths when FRP reinforcing bars elongate, resulting in significantly lower flexural stiffness for FRP bar-reinforced concrete members. The deeper cracks and larger crack widths also reduce the depth of the compression zone. Consequently, both the aggregate interlock and the compression zone for shear resistance are significantly reduced. Additionally, due to their limited tensile ductility, FRP reinforcing bars can rupture before the concrete crushes, potentially resulting in sudden and catastrophic member failure. Therefore, ACI Committee 440 states that through a compression-controlled design, FRP reinforced concrete members can be intentionally designed to fail by allowing the concrete to crush before the FRP reinforcing bars rupture. However, this design approach does not yield an equivalent ductile behavior when compared to steel-reinforced concrete members, resulting in a lower strength reduction, ϕ, value of 0.65. In this regard, using FRP-reinforced ultra-high-performance concrete (UHPC) members offer a novel solution, providing high strength, stiffness, ductility, and corrosion-resistant characteristics. UHPC has a very low water-cementitious materials ratio (0.18 to 0.25), which results in dense particle packing. This very dense microstructure and low water ratio not only improves compressive strength but delays liquid ingress. UHPC can be tailored to achieve exceptional compressive ductility, with a maximum usable compressive strain greater than 0.015. Unlike conventional designs where ductility is provided by steel reinforcing bars, UHPC can be used to achieve the required ductility for a flexural member, allowing FRP reinforcing bars to be designed to stay elastic. The high member ductility also justifies the use of a higher strength reduction factor, ϕ, of 0.9. This research, validated through large-scale experiments, explores this design concept by leveraging UHPC’s high compressive ductility, cracking resistance, and shear strength, along with a high quantity of noncorrosive FRP reinforcing bars. The increased amount of longitudinal reinforcement helps maintain the flexural stiffness (controlling deflection under service loads), bond strength, and shear strength of the members. Furthermore, the damage resistant capability of UHPC and the elasticity of FRP reinforcing bars provide a structural member with a restoring force, leading to reduced residual deflection and enhanced resilience.

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.

To use alternative cements such as belitic calcium sulfoaluminate (BCSA) cement for structural concrete, perhaps the most important consideration is ensuring that the rectangular stress block parameters used in flexural strength design are still applicable. This article describes a complex experimental study consisting of flexural-compression specimens loaded to replicate the compression side of the stress distribution in a reinforced concrete beam. From these coupled compression-flexural tests, the shape of the stress distribution in a BCSA cement concrete specimen can be derived and used to develop equivalent rectangular stress distribution parameters. BCSA cement concrete and portland cement concrete (PCC) unreinforced flexural compression specimens with various water-cement ratios (w/c) were fabricated and tested at varying ages. The results from the BCSA cement concrete flexural compression specimens were compared with PCC tests, extensive historical PCC data, and design code values. The current code equations approximating the rectangular stress block were found to be equivalent or conservative for BCSA cement concrete flexural members within the strength range of 54 to 85 MPa (7.8 to 12.4 ksi). This should give designers confidence in using this cement for structural concrete.