International Concrete Abstracts Portal

Maintaining workability can be a challenge when the total cement content of a concrete mixture is minimized in order to lower the carbon footprint. This is especially the case in everyday concrete where Portland cement content is mostly optimized for a targeted strength. Unlike high-performance or self-consolidating concretes (SCC) which commonly have high cement or cementitious materials contents, a minimum paste volume is generally required in normal strength concrete (NSC) mixtures to ensure adequate workability for the application and to be acceptable in the field. In this study, a new generation of rheology-modifying water-reducing admixture that improves concrete rheology is used to further reduce cement content and provide favorable workability for concrete applications. Comparisons to reference concrete are presented for their fresh and hardened properties, including plastic viscosity, dynamic yield stress, finishability, pumpability, and targeted strength. By combining concrete technology and this new rheology modifying water-reducing admixture, an economical, workable low-carbon concrete can be achieved.

This study investigates the potential of machine learning (ML) models to predict the rheological properties of self-consolidating concrete (SCC), with a focus on yield stress and viscosity. The significance of this research arises from the environmental impact of cement production and the pressing need to explore low-carbon alternatives. Supplementary cementitious materials (SCM), such as slag and fly ash, offer promise for reducing carbon emissions in the cement industry. However, their incorporation can alter the rheological properties of concrete, impacting its mechanical and durability characteristics. Predicting these properties is complex due to the multifaceted interplay of various factors. To address this challenge, ML models were employed, including Random Forest (RF) and Gradient Boosting (GB). A comprehensive database comprising 12 input parameters, such as mixture proportions, aggregate characteristics, and rheological attributes, was meticulously compiled from existing literature. Training and testing these ML models revealed GB as a standout performer for predicting yield stress, while RF excelled in forecasting viscosity. Furthermore, a comprehensive SHapley Additive exPlanations (SHAP) analysis was conducted to unravel the most influential parameters impacting yield stress and viscosity. These findings can contribute in advancing our understanding of SCC behavior and the development of sustainable construction materials that align with environmental objectives.

Earthen construction techniques in sustainable building can offer numerous advantages. However, it comes with certain limitations, with the most notable one being the labor-intensive and time-consuming nature of the construction process. To address this challenge, self-consolidating earth concrete (SCEC) emerges as a promising solution, particularly when dealing with the presence of fine clay and silt particles, as it can help attain the desired rheological properties more efficiently. In this study, supplementary cementitious materials (SCMs) such as cement, metakaolin, and limestone filler have been used as stabilizers to evaluate their impact on the workability and rheology of earth-based mixtures. A high-range water-reducing polycarboxylate ether (PCE), either with or without the initial incorporation of sodium hexametaphosphate, was applied to various clay compositions. The presence of finer clay particles required a higher dosage of admixture to achieve the desired workability, resulting in elevated yield stress and plastic viscosity values.

Sixty percent of the nation's highly toxic and radioactive mixed wastes are stored at Hanford in 177 deteriorating underground storage tanks. To close or remove these storage tanks from service and place them in a condition that is protective of human health and the environment, the tanks must be physically stabilized to prevent subsidence once wastes have been retrieved. Remaining residual liquid waste in the tanks that cannot be removed must be solidified and the solid wastes encapsulated to meet the Nuclear Regulatory Commission, Department of Energy, Environmental Protection Agency, and the State of Washington requirements. The Department of Energy has developed cementitious flowable concretes to restrict access and provide chemical stabilization for radionuclides. Formulation, laboratory, and field testing for application at Hanford began with flowable, self-leveling structural and non-structural fills. A slump flow equal to or greater than 610 mm, 0% bleed water, and 0.1% (by volume) shrinkage measurements were key parameters guiding reformulation efforts that resulted in highly flowable, self-consolidating concretes that met Hanford 241-C Tank closure short- and long-term regulatory and engineering performance requirements.

This research investigates the High Performance Concrete (HPC) jacketing method to strengthen reinforced circular concrete piers/columns. Four different types of HPC jackets such as Self-Consolidating Concrete (SCC), Engineered Cementitious Composites (ECC) and two types of Ultra-High Performance Concrete (UHPC) with three jacket thicknesses of 25 mm, 38 mm and 51 mm, with same reinforcement configuration were used to strengthen reinforced SCC core piers and analyze behavior. Thirteen pier specimens were tested to failure under concentric axial load applied through the SCC core. Test results indicated performance enhancement of piers strengthened with UHPC and ECC jackets, which not only prevented brittle failure but also improved the ductility and energy absorbing capacity by achieving a superior ultimate axial load capacity increase by more than 90% with a jacket thickness of 33% of the core diameter. Existing Code and analytical equations with reduction factors can be used for predicting axial load capacity of the strengthened piers/columns but choice of equations should be based on types of jacket concrete to ensure safe design.