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Mix Design of Alkali Activated Concrete Having Fly Ash and Blast Furnace Slag
No full textAlkali-activated concrete (AAC) is an alternative to ordinary Portland cement concrete and has several potential benefits over normal Portland cement. This includes improved acid resistance, elevated temperature applications, resistance to weathering and reduced carbon emissions from the production of normal Portland cement. However, the field application of AAC is limited due to a lack of standard mixture proportions codes. This study focuses on developing a procedure for the mixture proportions
Leveraging the use of carbonated water for sustainable low-carbon cements
No full textThe sustainability of the construction industry has been significantly enhanced by the development and use of low-carbon cements. However, achieving net-zero emissions requires more than just reducing embodied carbon of cements; it necessitates the adoption of effective carbon sequestration methods. Although various strategies for incorporating carbon sequestration into construction materials have been explored, the use of carbonated water in low-carbon cement systems remains less-researched. This study investigates the impact of adding carbonated water to two key low-carbon cement types: Slag-based cement (80% cement replacement) and Limestone Calcined Clay Cement (LC3, 50% cement replacement). The findings show that carbonated water improves CO2 binding, increases early-age strength, and reduces setting times compared to traditional Ordinary Portland Cement (OPC) systems. These results demonstrate the potential of carbonated water to enhance the sustainability of low-carbon cements and provide a foundation for further research on its role in carbon sequestration within the construction sector
Effects of colloidal nano-silica incorporation on the durability and mechanical properties of Portland Limestone Cement (PLC) concrete
No full textPortland limestone cement (PLC) concrete is considered more environmentally friendly than ordinary Portland cement (OPC) because it contains less clicker content; however, in many cases PLC cement compromises the durability and mechanical properties of concrete. In this study, colloidal nano-silica (CNS) was used to improve the durability and mechanical properties of PLC concrete. The effects of two types of water reducers (lignin and polycarboxylate) on PLC samples were also studied. The results indicate that CNS incorporation improved the durability and mechanical properties of PLC concrete. The compressive strength of CNS samples improved by nearly 15%, the flexural strength increased by 16% with polycarboxylate, and by 4% with lignin water reducers, and the electrical resistivity increased by 40% at 28 days
Concrete Conductivity/Resistivity with Conductive Aggregate
No full textThe electrical properties of concrete (formation factor) are often used as a surrogate test method to assess fluid transport in concrete primarily because resistivity (or conductivity) can be measured rapidly and economically. While electrical properties have been measured for nearly a century, the recent rise in handheld, battery-operated testing tools coupled with the desire to quantify the transport performance of concrete has caused a sudden spike in interest in electrical property measurements as a quality control or quality acceptance tool. Standards have been developed (AASHTO T 358, AASHTO T 402, ASTM C1876) with an emphasis on the role of sample conditioning. Some users have reported that the use of certain aggregates tends to reduce the resistivity values (increase the conductivity) when compared with concrete made using the same matrix but different aggregates. This paper examines a fundamental assumption of the electrical testing, i.e., that the aggregate is resistive or non-conductive. It explores the implications if the aggregate is conductive using both an analytical and finite element approach to determining the impact of aggregate with a lower resistivity and discusses a procedure to account for aggregate conductivity
Performance of low-embodied CO2 and high early-age strength concrete full-sized slabs
No full textHigh early strength and low-embodied CO2 concretes were analyzed in full-sized slabs under California weather. Belitic calcium sulfoaluminate (BCSA), ordinary portland cement (OPC), portland limestone cement (PLC), and calcined clay (CC) were the used cementitious materials. Each material was designed to obtain a flexural strength of 2.76 MPa (400 psi) at opening time, which varied depending on the material between 4 and 10 hours. One individual slab of 4.5 x 3.6 m (15 x 12 ft) with a thickness of 23.5 cm (9.25 in) was analyzed for each material. Thermocouples and vibrating-wire strain gages (VWSG) were installed at the corner and center of the slab to monitor the slab behavior through time. The VWSGs were placed at two depths to track the differences in strains at the top and bottom of the concrete slab. Testing performed in the slabs and laboratory-prepared specimens included: corrosion, carbonation, alkali-silica reaction (ASR), albedo, flexural strength, compressive strength, and shrinkage. Low-embodied CO2 concretes with high early strength are a sustainable paving alternative concrete based on reduced carbon emissions and carbon intensities when compared to traditional concrete structures. By providing performance improvements such as higher strengths and lower shrinkage, these alternative new materials for construction and repairs will enable construction windows to be reduced, which will benefit the user and the owners. Life cycle analysis (LCA) and mechanical properties were used to determine that low-embodied CO2 concrete providing high early strengths are sustainable alternatives that can be used instead of traditional methods
Environmental and functional improvements on concrete roof shell by opening frame structure to reduce CO2 emissions
No full textDespite recent global efforts to achieve carbon neutrality, the building industry still emits large amounts of carbon dioxide, posing a major challenge in achieving a sustainable society. Concrete has been used primarily as a limited structural material in modern construction because of its structural safety, durability, and low cost. However, since the construction is based on pouring in a formwork and the members tend to be wayward and massive, it has extremely low lighting and ventilation properties if we focus on the basic characteristics related to the living environment. In this study, a concrete roof shell was created, which highlighted the darkness inside the roof due to the closed nature of concrete. Therefore, a structural analysis of the roof shape was performed to ensure sufficient openings in the concrete roof shell roof section. In addition, we evaluated the possibility of improving the environmental performance of concrete, and proved that the reduction of CO2 emissions at each concrete strength could be fulfilled, and the realization of creating a concrete shell in a frame-like structure like a wooden structure would increase the translucency of the roof interior and enable users to significantly improve the environmental performance at the stage of use. This has led to a significant improvement in environmental performance in the stage of users\u27 use
Setting Limits from Coast to Coast-US Buy Clean Policies to Decarbonize Concrete
No full textSeveral authorities have implemented Buy Clean policies with different scopes, regulatory frameworks, and incentives for implementation. These policies measure the reduction of global warming potential of eligible materials using Environmental Product Declarations. Many programs also require agencies to implement a “limit” to the carbon dioxide emissions of industrial materials. By assessing the different programs with established emission limits and quantifying the reductions against the industry benchmarks, we can evaluate their impacts to a diverse group of stakeholders, not just those who manufacture concrete. Policy makers, manufacturers, architects and engineers must become aware of the limitations of the reporting tools to ensure the mandatory building requirements are still met. A clear understanding of how the policies are implemented offers insights to how the industry value chain can meet functional performance goals while maximizing the chances of successful carbon reduction of the built environment
Modeling the fresh properties of cement-based materials for 3D concrete printing
No full textA major challenge of 3-D printable concrete lies in the design of fresh material properties. Ideally, a fresh concrete needs to be fluid-like for pumping and extrusion but solid-like during placement to support the printed structure. In practice, achieving this balance is challenging. This research addresses these challenges by leveraging machine learning and numerical simulation to model the fresh behavior of cement-based materials for 3-D printing. It begins with rheological characterization to understand how mixture design factors influence rheological properties, laying the foundation for subsequent studies. A multilayer perception (MLP) model is developed to predict the yield stress of cement-based materials, achieving a desired overall accuracy while demonstrating performance variations on some subsets of data. Additionally, both Discrete Element Method (DEM) and Smoothed Particle Hydrodynamics (SPH) are utilized to model the flow behavior of cement-based materials in common flow scenarios. These 3-D printing simulations help us understand real-life issues such as jamming and plastic collapse. Vibration of the material in the printer nozzle was shown to be effective for improving extrusion and consistency during deposition. Machine learning and numerical simulation provided insights into design of 3-D printing materials and construction processes
Graphene reinforced cement-based triboelectric nanogenerator for efficient energy harvesting
No full textThis study investigated a graphene reinforced cement-based triboelectric nanogenerator (TENG) aimed at harvesting mechanical energies in infrastructure. The triboelectric layers of the cement-based TENG consisted of a fully cured graphene modified cement-based plate and a polytetrafluoroethylene (PTFE) film, which were tested under a contact-separation mode. Microstructural analysis indicated that the graphene was well-dispersed in the cementitious matrix, and the graphene-cement composites achieved excellent compressive and flexural strengths of 53.0 and 3.5 MPa, respectively. The electrical characteristics of the graphene-cement composites, specifically their resistivity and impedance, showed that they did not reach the percolation threshold, making them ideal dielectric materials with a dielectric constant of 100 at 1 kHz. The performance of the cement-based triboelectric nanogenerator (TENG) varied depending on the amplitude and frequency of the contact-separation cycle. At a frequency of 10 Hz and under a force of 100 N, the short-circuit current and open-circuit voltage peaked at 3.62 µA and 279.4 V, respectively, achieving a maximum power density of 95 mW/m2 with a 100 MΩ resistor. In practical applications, this TENG charged a 10 μF capacitor to 3.1 V within one minute and to 57.2 V in one hour. Additionally, manual operation of the TENG enabled the lighting of 29 LEDs with one minute of hand pressure. By utilizing triboelectric effects, the results provide the feasibility of self-powering concrete structures and pavements for future smart cities
Thermochemical pre-treatments on corn stover ash to boost its reactivity
No full textWhen treated properly, corn stover ash (CSA) is known to be an effective source of supplementary cementitious materials (SCM) for use in concrete. The influence of thermochemical pre-treatments on the reactivity of CSA was studied in this project. The result shows that acid pre-treatment was effective and necessary in the removal of organic and inorganic compounds from the corn stover. The pre-treatment conditions including type and concentration of acid used, temperature, pre-treatment duration, and the acid/ash (A/A) ratio are important factors that affect the reactivity of the final product. This study shows that a proper pre-treatment condition will lead to a CSA with high amorphous silica content, high surface area and low loss on ignition (LOI)