International Concrete Abstracts Portal

This study investigates the impact of air-entraining admixtures (AEA) on mortar performance, focusing on fresh-state and hardened-state properties critical to durability and engineering applications. Ten distinct mortar mixtures were analyzed, following guidelines established by EFNARC (European Federation of National Associations Representing Producers and Applicators of Specialist Building Products for Concrete). AEAs were introduced at varying proportions (0.01–0.5% of cement weight) to evaluate their effects on intrinsic properties (density, void ratio, water absorption), rheological parameters (plastic viscosity, yield stress), and mechanical characteristics (compressive strength, ultrasonic velocity, modulus of elasticity).

Regression models were developed, yielding high predictive accuracy with R² values exceeding 0.98. Notably, ultrasonic velocity and modulus of elasticity demonstrated strong correlations with intrinsic properties across all curing ages. Similarly, compressive strength showed significant associations with rheological parameters, highlighting the influence of air content and flow behavior on structural performance. These findings offer precise quantitative models for predicting mortar behavior and optimizing formulations for enhanced performance.

The modulus of elasticity of concrete is typically estimated usingnumerical models that consider factors such as the compressivestrength of the concrete, aggregate properties, unit weightof concrete, and water-cement ratio. The most-used equationdepends on the relationship between the compressive strength ofthe concrete and its modulus of elasticity. However, this simplifiedformula may provide an inaccurate estimate of the modulusof elasticity of concrete containing different types of aggregatesunder varying loading conditions. More sophisticated models canbe used to accurately estimate the modulus of elasticity for specificapplications, such as expressions involving the unit weight ofconcrete. This study presents a probabilistic update to the expressions used for estimating the modulus of elasticity of concretebased on an extensive database of over 2600 experimental testsfrom 20 different studies. Bayesian inference was used to updatethe currently proposed models, allowing for the determination ofthe expressions representing the trends of the current databasealong with their associated uncertainties. The updated expressionswere formulated considering either the compressive strength ofconcrete or both the compressive strength and the unit weight asinput parameters. Expressions for estimating the modulus of elasticity, considering the aggregate’s origin, were also updated. Thiscomprehensive approach enhances the accuracy and reliability ofpredicting the modulus of elasticity, providing valuable insightsand tools for concrete structures’ design and structural reliabilityanalysis.

Pourbacks and overlays are commonly used in bridge elements and repairs, as it is crucial to corrosion protection that the bond between grout and concrete in these regions is carefully constructed. The integrity of the bond is crucial to ensure a barrier against water, chloride ions, moisture, and contaminants; bond failure can compromise the durability of concrete structures’ long-term performance. This study examines the influence of surface preparation methods on the bond durability and chloride permeability between concrete substrate and grouts, including both non-shrink cementitious and epoxy grouts. A microstructural analysis of scanning electron microscopic (SEM) images was conducted to characterize the porosity of specimen interfaces. Pulloff testing was performed to quantify tensile strength. Results show that a water-blasted surface preparation technique improved the tensile bond strength for cementitious grout interfaces and reduced porosity at the interface. In contrast, epoxy grout interfaces were less affected by surface preparation. The study establishes a relationship between chloride ion permeability, porosity, and bond strength. The findings highlight the importance of surface preparation in ensuring the durability of concrete-grout interfaces.

With a well-thought-out packing theory for sand, fine aggregates, cement, a water-cement ratio lower than 0.2, and steel fibers, ultra-high-performance concrete (UHPC) achieves remarkable mechanical properties. Despite UHPC’s superior mechanical properties compared to conventional concrete, its use remains limited, especially in structural applications, due to factors such as high cost, lack of design standards and guidelines, and inadequate correlation between material properties and structural behavior. By compiling and synthesizing the behavior of 70 structural- or full-scale axial UHPC columns, this research provides a new set of generalized design and detailing guidelines for axial UHPC columns. The study first uses the assembled database to assess and revisit the current ACI 318 axial strength design factors for applicability for UHPC. Next, the behavior trends are carefully analyzed to provide detailed recommendations for proper transverse reinforcement (ρt volume), spacing-to-longitudinal reinforcing bar diameter ratio (s/db, where s represents the centerline-to-centerline spacing between transverse reinforcement), and UHPC steel fiber ratio for best use of confinement.

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 rebars’ lower axial stiffness leads to greater crack widths when FRP reinforcing bars elongate, resulting in significantly lower flexural stiffness for FRP-reinforcing 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-reinforcing bar-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-reinforcing bar-reinforced concrete members, resulting in a lower strength reduction, ϕ, value of 0.65. In this regard, using FRP-reinforcing bar-reinforced ultra-high-performance concrete (UHPC) members offers a novel solution, providing high strength, stiffness, ductility, and corrosion-resistant characteristics. UHPC has a very low water-to-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 also 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.