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Planned substantial road infrastructure investments emphasize the need for alternative materials that can reduce economic and environmental costs. Alkali-activated materials are one such alternative. These inorganic binders can be produced with fewer CO₂ emissions than asphalt and concrete binders while offering comparable mechanical properties. Alkali-activated materials also develop strength more rapidly, facilitating rapid construction and large-scale repair and maintenance operations.Existing studies suggest that alkali-activated materials would produce fewer CO₂ emissions than conventional cement. However, work to date has not considered availability of the precursors needed to produce alkali-activated materials. Limited availability of raw materials could result in significant additional emissions from transporting materials long distances to market. Researchers at the Georgia Institute of Technology analyzed published life cycle assessment literature to understand whether alkali-activated materials can achieve the same mechanical performance as Portland cement with lower CO₂ emissions, considering the local availability of raw materials. This policy brief summarizes the findings from that analysis and provides policy implications.View the NCST Project Webpage

The capital investment in the U.S. for construction and maintenance of the infrastructure road network is on the order of $100 billion/year. On average, investments in Organization for Economic Cooperation and Development (OECD) countries are likely to stabilize, while China will face an exponential growth of investments for new infrastructures driven by the development of metropolitan cities. Continued “business-as-usual” practice for portland and asphalt cement concrete pavement construction ignores the increasing warning calls for the identification of more sustainable and less energy intensive paving materials. It is therefore important to explore alternative pavement materials, which may have benefits in terms of environmental impact and durability performance over the current technology. Alkali activated materials concrete (AAM) exhibit these beneficial characteristics. AAM compositions have been studied with growing interest during the last three decades, and showing promising results in terms of mechanical performance, while also having a global warming potential impact 30-80% less than that of portland cement concrete. The global warming potential of these material is closely dependent on: 1) the alkali activating solution used to activate the raw material 2) the origin of the raw material. Specifically, the impact of the transport for both of these components has an impact quantifiable around 10% of its global warming potential. Hence, to increase the adoption of AAM for civil applications such as pavements, it is fundamental to analyze the existing literature to clarify the link between environmental and mechanical performance, identifying opportunities for applications that are tailored to the local availability of raw material, reducing transport environmental costs.View the NCST Project Webpage

Since hydration heat generated during construction has been the cause of cracking and deformations in mass concrete structures, selecting appropriate thermal control plans is crucial in mass concrete construction. However, developing numerical models to predict the heat of hydration in mass concrete involves complex processes that demand extensive knowledge in thermodynamics and related fields, which can result in increased costs and extended timelines for construction methods and material selection. To address this problem, this research aims to develop a simple decision-making framework to select a cost-effective thermal control method using nomograms for materials and construction engineers. Several nomograms, including temperature and cost nomograms, were used to provide the most cost-effective thermal control plans while satisfying the maximum temperature limits of mass concrete. A case study of an actual construction project was used to validate and demonstrate the proposed framework. The effectiveness of this framework was demonstrated through a case study on a real construction project, which validated the approach and confirmed its potential to reduce the time required for developing thermal control plans in mass concrete construction projects. The findings from this study highlight the proposed framework's capability to streamline the thermal control method selection process, thereby facilitating a more intuitive understanding of thermal control options and markedly reducing both costs and time in mass concrete construction projects. [ABSTRACT FROM AUTHOR]

This research demonstrates the feasibility of using a non-collinear wave mixing technique to image internal microscale damage throughout the interior volume of a relatively large (28 cm thick) concrete component. By exploiting the underlying mechanics of nonlinear wave mixing, it is possible to mix two incident waves with frequencies low enough to propagate without being scattered by the inherently heterogenous, concrete microstructure, while still being sensitive to damage features with length scales well below these incident wavelengths. For this study, scanning and imaging is accomplished by manually adjusting the locations of the two incident waves, while a knowledge of the wave speeds in concrete plus synchronization identifies the location of the mixing zone—the specific volume of concrete being imaged. The viability of the proposed technique is demonstrated by examining a concrete prism specimen with known, embedded internal microscale damage. [ABSTRACT FROM AUTHOR]

Many California soils are rich in sulfates, which can have deleterious effects on the cements used in rigid pavements. Field experience has demonstrated that sulfate attack usually manifests itself in the form of loss of adhesion and strength. In order to assess the sulfate susceptibility of cements submitted to the Caltrans Long Life Pavement Rehabilitation Strategy (LLPRS) program, an accelerated test program was undertaken. In the accelerated test method employed, changes in cement paste strength after periods of sulfate exposure relative to the strength after seven days hydration served to indicate the sulfate resistance of the cement in question. Five cements submitted to Caltrans by four different manufacturers, and four portland cement mixes prepared in the laboratory were tested by an accelerated test method in which pH and sulfate concentration remained constant. Conditions provided in this accelerated test method are similar to field conditions, and results should be indicative of field performance.

Caltrans specifications for the construction of rigid pavements require rapid setting, high early strength, superior workability concrete with a desired 30 year plus service life. These strict specifications provide the motivation for the investigation of advanced cementitious materials for pavement construction. The cementitious materials under consideration by Caltrans may be classified into four categories: Portland cements and blends, calcium aluminate cements and blends, calcium sulfoaluminate cements, and fly ash-based cements. To achieve the desired 30+ year design life, it is essential to select materials that are expected to exhibit long-term durability. Because most of the cementitious materials under consideration have not been extensively used for pavement construction in the United States, it is essential to characterize the long-term durability of each material. This report provides general information concerning the deleterious reactions that may damage concrete pavements in California. The reactions addressed in this report are sulfate attack, aggregate reactions, corrosion of reinforcing steel, and freeze-thaw action. Specifically, the expected performance of Portland cements and blends, calcium aluminate cements and blends, calcium sulfoaluminate cements, and fly ash-based cements are examined with regard to each of the deleterious reactions listed. Additional consideration is given to any deterioration mechanism that is particular to any of these cement types. Finally, the recommended test program to for assessing potential long-term durability with respect to sulfate attack is described.