Ultra-high-performance concrete (UHPC) continues to attract more researchers, engineers, architects, students and experts across disciplines due to its fascinating material properties.
Over the last decades novelties have been shared in material design, mixing technology, material characterization and application, structural performance and design. While more innovations and novelties have been shared and exciting application examples are being presented, more knowledge gaps, research needs and questions have been raised.
This session will invite national and international research groups, material suppliers and contractors to share new insights in UHPC technology, structural design and applications.
(1) Investigate the carbon footprint of UHPC;
(2) Recognize its potential of environmental impact;
(3) Discuss new insights in the long-term behavior of UHPC;
(4) Identify opportunities about cost-efficiency.
Multi-Objective Density Diagrams Developed with Machine Learning Models to Optimize Sustainability and Cost-Efficiency of UHPC Mix Design
Presented By: Cesario Tavares
Affiliation: Texas A&M University - College Station
Description: The emergence of ultra-high-performance concrete (UHPC) as an attractive solution for precast and prestressed applications has coincided with global efforts towards sustainable construction. The increasing need for tools capable of intuitively demonstrating the effect of concrete mixture composition on mechanical performance, cost and eco-efficiency concurrently has motivated this work in an effort to promote design of more sustainable solutions to help meet environmental goals. Such tools are needed to effectively evaluate the environmental impact of UHPC given the outstanding mechanical properties of the material coupled with high volumetric embodied CO2. Meanwhile, artificial intelligence (AI) techniques have emerged as a great opportunity for game-changing tools capable of effectively modeling the synergistic relationships between mix proportions and material performance. This work couples machine learning models with orthogonal arrays to generate machine-learning-based tools to evaluate the tradeoffs between emissions, cost and mechanical performance concurrently. Predicted strengths are coupled with volumetric environmental factors and unit costs to generate eco- and cost-efficiency density diagrams. The makeup of these tools facilitates the evaluation of rather complicated trends associated with mix proportions and multi-objective outcomes, allowing AI-based tools to be of easy use by industry personnel on a daily basis, while serving as decision-making aids during mix design stages and provide proof of mixture optimization that could be introduced in Environmental Product Declarations. The tools developed herein enabled the design of a mix with compressive strength of 155 MPa, while keeping the aggregate-to-cementitious ratio above unit. Other mixtures were developed from these models and compared to several different concretes from the literature.
Utilization of High Carbon Waste Materials for Low Carbon UHPC
Presented By: Weina Meng
Affiliation: Stevens Institute of Technology
Description: Ultra-high-performance concrete (UHPC) is one of the most promising materials for civil infrastructure because it has superior mechanical properties and durability. However, UHPC has high CO2 emissions because UHPC contains a high content of cement. Aiming to reduce the carbon footprint of UHPC, high carbon-embedded waste materials have been utilized to replace the cement, including off-specification fly ash (OSFA) and used biochar.
The OSFA is a type of fly ash that contains more than 60% of carbon content. The production of OSFA is increasing yearly, causing some environmental issues associated with the landfills. Biochar is a by-product of pyrolysis of biomass, which is a family of renewable organic materials with carbon content of 80%. Fresh biochar is often used to purify water and soil by removing and fixing heavy metals, and it is landfilled after being used, resulting in secondary pollution to the environment. Utilizing these waste materials in UHPC can reduce the cost and carbon footprint of UHPC and partially address the enviornmental issues associated with the disposal of the wastes.
New Insights into the Sustainability of Ultra High-Performance Concrete (UHPC) and its Eco-Profile Improvement Through the Use of Recycled Aggregates (R-UHPC)
Presented By: Davide Summa
Description: Nowadays, the use of Ultra High-Performance Concrete (UHPC) is starting to be more and more widespread in the construction market. Nevertheless, due to its initial cost and to the high cement content, usually associated to huge environmental impacts, it is used to be considered as less performing in terms of environmental and economic sustainability in comparison to more traditional solutions such as Ordinary Reinforced Concrete (ORC). In view of this, this paper investigates, through the use of Life Cycle Assessment (LCA) and Life Cycle Cost (LCC) methodologies, the holistic sustainability of UHPC assessing also the potential advantages resulting from the use of recycled aggregates instead of virgin ones. In this regard, the self-healing properties of UHPC containing 0 – 2 mm recycled aggregates (R-UHPC) have been prior investigated by means of capillary water absorption tests and microscopic crack healing at predetermined time points following pre-cracking. Then, after having observed that R-UHPC showed better self-healing capabilities in comparison to UHPC, a large-scale case study has been assessed, namely a water basin structure exposed to extremely aggressive environment (chlorides attack). To better address the potential advantages deriving from the structural performances of UHPC, a Durability Assessed Design (DAD) has been performed. This allowed to design a structure with a wall thickness of 0.40 m as for the reference ORC solution, reduced up to 0.15 m and 0.10 m as or the UHPC one, depending on whether a uniform wall or a slab supported by buttresses has been designed. With regard to the use of recycled aggregates, it has been supposed the replacement of 30% of the aggregates for the reference structure while 100% has been accounted for the UHPC solution. The comparison of UHPC structure to the ORC one already outlined interesting results such as more than 50% of reduction for the Terrestrial Ecotoxicity impact indicator.
Low Shrinkage UHPC - The Why, How, and Where?
Presented By: Vic Perry
Affiliation: ceEntek North America
Description: There is a general misconception that Ultra-High-Performance Concretes (UHPC) have high shrinkage. In fact, UHPCs are a family of products with a wide range of properties, including shrinkage. In many applications of UHPC shrinkage is an important consideration, particularly where restraint during curing occurs. The tensile capacity of a given structural element can be partially consumed by shrinkage in the UHPC material as it cures, especially in restrained applications. It is therefore important that the shrinkage properties be considered to understand the associated reduction in tensile capacity. Additionally, during the curing phase, UHPCs typically have low tensile strengths and the impact of early restrained shrinkage needs to be evaluated to ensure early shrinkage cracking does not occur. In those applications such as precast elements, overlays, jacketing and other rehabilitations restrained shrinkage is an important factor to consider.
This presentation will cover the unique properties of a UHPC, specifically shrinkage vs residual tensile strength and the impact on the performance of the intended application (i.e., bridge overlays and others).
UHPC Creep and Shrinkage: Test Data and Predictive Models
Presented By: Alireza Mohebbi
Affiliation: Genex Systems
Description: This study investigated the creep and shrinkage behaviors of a suite of commercially available UHPC-class materials, with the goal being to characterize the behaviors then propose predictive models. The objectives of this research were as follows: a) quantify the compressive creep behavior of different UHPC-class materials; b) assess the effects of strength, maturity, and loading age on UHPC creep; c) develop data-driven models to predict ultimate creep coefficients and shrinkage strains of UHPC-class materials for different service conditions; d) compare the predictive models with measured data, AASHTO LRFD Bridge Design Specifications equations, and existing European recommendations for UHPC-class materials; e) examine the applicability of the proposed models by incorporating the material models into a prestress loss model then comparing the predictions to the behaviors of seven full-scale pretensioned UHPC girders. The creep and shrinkage data for different materials were observed to vary somewhat independently from the variables commonly engaged in predictive models, leading to model predictions that were generally indicative of the material response.