Sustainability Indices to Foster the Development of a Forward-Looking Market for UHPC Materials and Structures
Presented By: Davide di Summa
Affiliation: Ghent University
Description: In response to the ever-evolving demands of end-users within the construction sector, also due to the heightened global awareness regarding the pivotal role of the construction industry in sustainability ramifications, it has become imperative to wield strategic tools to steer the market toward farsighted choices. A notable example of this paradigm shift lies within innovative cementitious materials, which are progressively captivating market interest due to their potential for enhanced overall sustainability performance. Henceforth, a crucial role is played not only by sustainability evaluation tools like Life Cycle Assessments (LCA) and Life Cycle Costing (LCC) analyses but also by the integration of the latter into a more comprehensive approach able to promptly gauge the ecological and economic performance of the intended structural application. Some investigations have started exploring this opportunity, positing novel approaches that proffer immediate evaluations. These methods center around a range of indices that pivot upon ecological implications, along with structural performance indicators In light of this, the current study introduces a series of “decision making” indices with a more inclusive purview, encompassing not only environmental considerations but also costs, structural and durability performance. One index, aimed at evaluating the viability of using different types of binders includes the aforementioned parameters on a cubic meter scale. In pursuit of this objective, part of the investigation is focused on the comparison between the mix design of Ordinary Portland Cement Concrete (OPCC) and the one of Ultra High Performance Concrete (UHPC), with CEM I or CEM III alternatively. The outcomes revealed the limits of this first approach as it does not include some essential parameters, with OPCC that performs better than UHPC in general. On the opposite, a complementary index has also been proposed, seeking to optimize the optimal mix design to be us
System-Wide Sustainability by Design with UHPC
Presented By: Anthony Ragosta
Affiliation: ceEntek Inc.
Description: It is understood that UHPC is more carbon intensive on a per-unit basis than traditional concrete or some other building materials. The current strategy discussed is to look at the volume savings in an actual element (e.g. a 0.5cy panel of UHPC versus a 1.0 cy panel of NWC). Life cycle has also been included in some of these analysis but there is a third major contributor which is often neglected – system optimization. Using UHPC to replace NWC can benefit a structure “downstream,” for example, extending the span of a bridge or building framing system with UHPC can remove rows of columns and foundations, which use significantly less materials. UHPC in retrofit applications can facilitate the prolonging of reconstruction, saving carbon on construction materials and traffic. Use of UHPC waffle decks can reduce the load on the overall superstructure making the beams more efficient and/or reducing the loads on the footings. This can drastically reduce the amount of mass concrete required in the substructure of a bridge.
UHPC is a highly optimized product and should be combined with all of the analytical tools and capabilities we have. By combining the potential to use less material per element, extending the life cycle, and by optimizing the structure as a whole, UHPC can have significant impacts on the carbon footprint of a structure. Many people are concerned about the lack of clarity or number of assumptions required to model the service life extensions gained using UHPC but through sensitivity analysis, you will see that the benefits are significant enough that the “break-even” service life is often a small fraction of the expected service life.
Low Cement Content UHPCs - Performance and Life Cycle Impacts
Presented By: Narayanan Neithalath
Affiliation: Arizona State University
Description: UHPCs rely on high cement content to attain early strength development, which negatively impact their sustainability metrics. We proportion UHPCs with 30-50% replacement of cement (by mass) with a variety of commonly available cement replacement materials, guided by considerations of particle packing and rheology, harnessing the filler effect of fine particles at early ages and their reactivity at later ages. Mixtures with and without steel fibers are designed, attaining compressive strengths in excess of 150 MPa at 28 days. Detailed cradle-to-gate life cycle analysis (LCA) is carried out using openLCA to determine the environmental impacts of the designed UHPCs and develop comparisons with conventional UHPCs. The CO2 and energy impacts of the UHPC mixtures are compared using normalized indices such as CO2-eq per MPa of strength to arrive at environmental metrics that are coupled with performance. We also evaluate the sustainability impacts while considering the construction aspects – where the use of a closure pour between precast structural elements in a bridge deck is used as a case study.
Sustainability Measures of UHPC through Increased Efficiency by Serviceability Based Design
Presented By: Barzin Mobasher
Affiliation: Arizona State University
Description: The directive for sustainable design through a serviceability-based performance approach of structures is the driver for development of new materials and design methods. A paradigm shift is proposed for the design of sustainable structures using UHPC. Using a combination of new low carbon footprint materials formulations, and hybrid reinforcing methods, one is able to develop a new class of materials with optimal properties. Three main stages of sustainable product development will be addressed using the material properties of UHPC as well as the development of composite from materials and structural shapes, the mechanical properties measured by means of structural testing under tension and flexural modes, and finally, analytical closed form solutions are presented for design and analysis of reinforced concrete systems applicable to beams, slabs, retaining walls, and buried structures. Structural design using fiber reinforced concrete (FRC), and Ultra-high-performance concrete, (UHPC) as breakthroughs in industry due to their mechanical performance and enhanced durability compared to conventional concrete. The enhanced tensile behavior in the post-cracking stage in a reinforced UHPC flexural member is defined among the efficiency metrics that are primarily due to the residual tensile strength of distributed fiber systems and defined in terms of mechanical anchorage and bond characteristics of the fiber phase. This efficiency prolongs the extent of stress transfer to the rebar, and thus improves the efficiency and the ductility of the matrix. The significant extension in the rate of stiffness loss and damage localization allows for deflection hardening responses that increase the rate of energy dissipation significantly and provide ductility. Such quantitative measures can be documented using the closed form solutions derived specifically for a variety of input materials and structural parameters.
Rapid Setting Low Embodied Carbon UHPC
Presented By: Fabian Paniagua
Affiliation: Rapid Set - CTS Cement
Description: A rapid setting low embodied carbon UHPC was developed using BCSA cement which has a 30 percent reduction in carbon emissions compared to portland cement. Rapid Set UHPC mortar was prepared following its recommended use, which means that the water content was 12.3 percent by weight of UHPC mortar. Additionally, steel fibers with a diameter of 0.2 mm (1/16 in) and a length of 13.0 mm (0.51 in) were used at the recommended dosage of 1.70 kg per 22.68 kg bag (3.75 lbs per 50 lbs bag) of UHPC Mortar. The test methods followed were ASTM C1609/C1609M-12: Standard Test Method for Flexural Performance of Fiber-Reinforced Concrete (Using Beam With Third-Point Loading), ASTM C39/C39M-21: Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens, ASTM C1583-04: Standard Test Method for Tensile Strength of Concrete Surfaces and the Bond Strength or Tensile Strength of Concrete Repair and Overlay Materials by Direct Tension (Pull-off Method). Additionally, the shrinkage of UHPC prismatic specimens was estimated using an embedded vibrating wire strain gage and keeping the specimens in a temperature and moisture-controlled room. The tests were performed at ages ranging between 4 hours and 56 days. It was found that the rapid setting UHPC can reach a compressive strength of 12,000 psi in 4 hours, provide a ductile behavior with an average equivalent flexural strength ratio over 75%, and have a shrinkage of 100 µe after 75 days of analysis. This early strength UHPC also comes at a significant reduction in Global Warming Potential compared to portland-based UHPC.