International Concrete Abstracts Portal

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.

Biochar properties, in particular, its fineness and its ability to absorb water, can be exploited to modify the rheological behaviour of cementitious conglomerates and to improve the hydration of the cement paste under adverse curing conditions such as those related to 3D concrete printing. Regarding the fresh state properties, the study of the rheological properties conducted on cementitious pastes for different biochar additions (by weight of cement: 0%, 1.5%, 2%, and 3%) highlights that the biochar induces an increase in yield stress and plastic viscosity. The investigation of mechanical properties, in particular flexural sand compressive strength, performed on mortars, evidences the internal curing effect promoted by biochar additions (by weight of cement: 0%, 3%, and 7.7%). In fact, compared to the corresponding specimens cured for the first 48 hours in the formwork, specimens with biochar addition cured directly in air are characterised by a drastically lower reduction in compressive strength than the reference specimens, i.e., approximately 36% and 48% respectively. This interesting result can also be exploited in traditional construction techniques, where faster demolding is needed.

This study investigates the impact of air-entraining admixtures (AEAs) 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 the European Federation of National Associations Representing Producers and Applicators of Specialist Building Products for Concrete (EFNARC). AEAs were introduced at varying proportions (0.01 to 0.5% of cement weight) to evaluate their effects on intrinsic properties (density, void ratio, and water absorption), rheological parameters (plastic viscosity and yield stress), and mechanical characteristics (compressive strength, ultrasonic velocity, and modulus of elasticity). Regression models were developed and yielded 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.