ACI Online Learning & Presentations

3D concrete printing (3DCP) has inspired a new generation of architectural and structural designs that combine research advancements in sustainable cementitious materials and material optimized structural geometries. The construction of bio-inspired structural geometry with high specific strength (strength to weight ratio) is now feasible because of the ability of 3D-printing to build intricate and mass-customizable geometries. The 3D printed structures created for this study take inspiration from nature by utilizing geometric shapes of strength and cellular aggregation techniques to create bio-inspired high-performance structures. Taking full advantage of the robotic 3D printing process, such structures can be efficiently customized to reduce material usage for specific load cases in individual structural elements. Beside the reduction of the materials used for construction, the carbon footprint of 3D-printed bio-inspired structures can be further reduced by developing a sustainable-printable concrete. In this study, Portland Limestone Cement (PLC) is used as the base cementitious material for developing the 3D-printable mix. In addition, high dosages of supplementary cementitious materials (SCMs) were used to achieve a high-performance sustainable concrete (HPSC) mixture. The experimental investigation showed that combining bio-inspired structural geometries with HPSC resulted in low-carbon footprint structures with sufficient strength for structural applications.

High carbon emissions of cementitious materials are increasingly raising concerns under the grand goal of global carbon neutrality. This presentation will introduce an approach to achieve low-carbon cementitious materials and enhance the mechanical properties while retaining the desired constructability for cast-in-place and precast applications of civil infrastructure. The proposed approach utilizes CO2 to produce a CaCO3 suspension that is uniformly dispersed and used to prepare cement pastes. The mechanical properties were tested, and the results showed that the 28-day compressive strength was increased by up to 16%. Further research was conducted to understand the effects of CaCO3 suspension on cement hydration kinetics and microstructures of cement pastes through isothermal calorimetry, thermal gravimetry analysis, mercury intrusion porosimetry, dynamic light scattering analysis, and scanning electron microscopy. The results revealed that the CaCO3 suspension promoted cement hydration and densified the microstructures because of the nucleation effect caused by the high-level dispersion of CaCO3 particles. The proposed approach provides an alternative solution for CO2 utilization in the concrete industry with minimal modification of the manufacturing facility and offers a promising avenue for achieving low-carbon infrastructure.

This presentation will demonstrate how construction productivity and sustainability could be improved using a Systems approach. Also, it will introduce a range of research and innovation in construction materials and technologies which could improve construction productivity and carbon footprint.

This presentation will discuss experiences with high SCM (low carbon) concrete mix designs and a discussion of items for consideration for all project team members when these mixes are specified and used.

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Carbon nanotube hybrids/coal ash-based concrete was prepared showing unmatched mechanical/fracture properties and sensing functionalities. The newly synthesized nanotube hybrid suspensions, prepared using ultrasonication, were found to exhibit excellent dispersibility and long-term stability for a period over 90 days. The chemical structure and functional groups of the dispersed nanotube hybrids were evaluated by FTIR and Raman Spectroscopy. A considerably increased (around 65%) electrical conductivity was observed, as compared to the plain coal ash concrete, which coupled with the enhanced modulus and toughness led to a superior electromechanical response, essential for strain sensing and progressive failure monitoring.

This presentation will review and provide examples of challenges faced by a concrete producer from perspective "low carbon" specifications, and contrasting projects where these issues have been avoided, while still providing significant carbon reduction to the project.

Building code provisions address structural stability, fire safety, adequate means of egress (exits), sanitation, and more. However, most of these provisions are to minimal standards and laggard to adopting technological advancements, growing interests in sustainability, resilience, and net-zero concepts -all of which provide significant opportunities to leverage climage solutions. Building codes have far-reaching impacts that could assist in decarbonizing the energy, transportation, and construction sectors. In addition, decisions made on codes impact building efficiency, public health, and climate goals - and the process and outcome should not be discounted or disregarded.

Finding a sustainable alternative to cement is crucial to mitigate climate change. This presentation introduces an innovative approach to investigate alkali-activated binders and monitor kinetic reaction using Raman spectroscopy. The dissolution of precursors by alkalis was continuously monitored for 24 hours immediately after mixing, which was found to be especially helpful to optimize the appropriate mixing procedure. Coupled with a new method for predicting the final products of alkali-activated materials using comprehensive phase-analysis, the cost and performances could be better controlled and optimized. Field applications of optimized AAM mixes based on fly ash, slag, or red mud could achieve 1) cement free with more than 80% reduction in carbon footprint, 2) ~25% reduction in cost, 3) cured at ambient temperature with well controlled setting time, flowability and other fresh properties, 4) similar or even superior hardened properties and durability, and 5) mass production ready.

Concrete, the most used material on earth after water, contributes a great deal to the environment and the atmosphere. Concrete’s main ingredients are cement, sand and coarse aggregates. Cement alone is responsible for emitting a considerable amount of CO2, a total of 8% of the sum of the global greenhouse gas emissions. Sand and c oarse aggregate are also using up the topsoil and need to be conserved being mother earth’s valuable resources. Replacing any of the ingredients with recycled waste material reduces the carbon footprint of a virgin concrete mix. Coal fly ash is such a material that is used in concrete as a supplementary cementitious material (SCM) for making concrete greener and more economic. However, coal industries being shut down for its pollution effect poses a new challenge in finding this most popular SCM in near future. Fly ash obtained from wood and lumber industries has a great potential for being a substitute for coal fly ash. The main challenge in using wood fly ash lies in the inconsistency of its properties for seasonal and source variations. Along with wood fly ash, wood bottom ash is a good option for being used as a replacement for sand. In this study, an experimental program was carried out to observe the fresh and mechanical properties of mortar and concrete using different percentages of wood fly ash and bottom ash as cement and sand replacement respectively. It was concluded that incorporating wood bottom ash did not have a significant effect on the properties of concrete, but a 30% replacement of cement with wood fly ash provided concrete with comparable compressive and tensile strength.

Cement is typically the largest individual contribution to the embodied global warming potential (CO2-equivalent) of a concrete mixture. The cement industry has developed roadmaps to reaching carbon neutral concrete by mid-century, both for the US and globally. This presentation will identify how cement and cementitious materials are expected to evolve in the roadmaps and discuss how effective updates to codes and standards can help to accelerate the achievement of carbon neutral concrete.

This presentation will be from the concrete contractor's perspective on lower carbon concrete and constructability, a discussion of what has worked on projects and what challenges have been encountered.