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Tag: Ultra-High Performance Concrete
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  • Suggested Updates for the Inclusion of Guidance on Ultra-High Performance Concrete to USACE Engineering Manual 1110-2-2000, Standard Practice for Concrete for Civil Works Structures

    Abstract: Ultra-high performance concrete (UHPC) is a relatively modern class of concrete with properties that include very high compressive strengths, increased tensile strengths, very low permeability, and superior durability compared to conventional, normal-strength concrete. As research of this material continues to progress, its applications under both military and civil works categories expand. However, mixture and structural design guidance using UHPC is limited, particularly in the United States. This special report provides an overview of UHPC as initial guidance for the US Army Corps of Engineers (USACE) so that the material may be more easily utilized in civil works infrastructure. The information contained in this report is based on years of experience researching and developing UHPC at the US Army Engineer Research and Development Center (ERDC) and is intended to be a basis for the incorporation of this material class into USACE Engineer Manual (EM) 1110-2-2000, Standard Practice for Concrete for Civil Works Structures, when it is next updated.
  • Probabilistic Neural Networks that Predict Compressive Strength of High Strength Concrete in Mass Placements using Thermal History

    Abstract: This study explored the use of artificial neural networks to predict UHPC compressive strengths given thermal history and key mix components. The model developed herein employs Bayesian variational inference using Monte Carlo dropout to convey prediction uncertainty using 735 datapoints on seven UHPC mixtures collected using a variety of techniques. Datapoints contained a measured compressive strength along with three curing inputs (specimen maturity, maximum temperature experienced during curing, time of maximum temperature) and five mixture inputs to distinguish each UHPC mixture (ce-ment type, silicon dioxide content, mix type, water to cementitious material ratio, and admixture dosage rate). Input analysis concluded that predictions were more sensitive to curing inputs than mixture inputs. On average, 8.2% of experimental results in the final model fell outside of the predicted range with 67.9%of these cases conservatively underpredicting. The results support that this model methodology is able to make sufficient probabilistic predictions within the scope of the provided dataset but is not for extrapo-lating beyond the training data. In addition, the model was vetted using various datasets obtained from literature to assess its versatility. Overall this model is a promising advancement towards predicting mechanical properties of high strength concrete with known uncertainties.
  • On Enhancing the Mechanical Behavior of Ultra-High Performance Concrete Through Multi-Scale Fiber Reinforcement

    Abstract: Steel fibers are typically used in ultra-high performance concretes (UHPC) to impart flexural ductility and increase fracture toughness. However, the mechanical properties of the steel fibers are underutilized in UHPC, as evidenced by the fact that most of the steel fibers pull out of a UHPC matrix largely undamaged during tensile or flexural tests. This research aims to improve the bond between steel fibers and a UHPC matrix by using steel wool. The underlying mechanism for fiber-matrix bond improvement is the reinforcement of the matrix tunnel, surrounding the steel fibers, by steel wool. Single fiber pullout tests were performed to quantify the effect of steel wool content in UHPC on the fiber-matrix bond. Microscopic observations of pulled-out fibers were used to investigate the fiber-matrix interface. Compared to the control UHPC mixture with no steel wool, significant improvement in the flexural behavior was observed in the UHPC mixtures with steel wool. Thus, the addition of steel wool in steel fiber-reinforced UHPC provides multi-scale reinforcement that leads to significant improvement in fiber-matrix bond and mechanical properties of UHPC.
  • Development of CORPS-STIF 1.0 with Application to Ultra-High Performance Concrete (UHPC)

    Abstract: This report introduces the first release of CORPS-STIF (Concrete Observations Repository and Predictive Software – Structural and Thermodynamical Integrated Framework). CORPS-STIF is envisioned to be used as a tool to optimize material constituents and geometries of mass concrete placements specifically for ultra-high performance concretes (UHPCs). An observations repository (OR) containing results of 649 mechanical property tests and 10 thermodynamical tests were recorded to be used as inputs for current and future releases. A thermodynamical integrated framework (TIF) was developed where the heat transfer coefficient was a function of temperature and determined at each time step. A structural integrated framework (SIF) modeled strength development in cylinders that underwent isothermal curing. CORPS-STIF represents a step toward understanding and predicting strength gain of UHPC for full-scale structures and specifically in mass concrete.