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Fiber Reinforced Concrete Composites - Seminal Contributions of Surendra Shah
No full textThe authors review the scholarly contributions of Surendra P. Shah during a prolific six-decade academic career in fiber reinforced concrete composites. This compilation includes discussions on often cited seminal publications encompassing experimental mechanics, analytical modeling, the development of test standards, materials characterization and innovations in the science of fiber reinforced concrete (FRC) materials. Collectively, these contributions have greatly improved our insights on how the nano- and micro-mechanics of such composites and processing techniques affect the macroscopic performance of creatively engineered reinforced cement composites. Starting with his Ph.D. the first contribution to understanding the inelastic behavior and fracture of concrete, the early fracture mechanics applications to FRC, his push to introduce energy dissipation and toughness via ACI 544 (new concepts at the time), his seminal theoretical and experimental contributions in the specialty during the last six decades, including macro fibers, hybrid fibers and the more recent nanofiber reinforced systems
Autoclave Curing of Cement Pastes with Sugarcane Bagasse Ash
No full textThis study proposes an alternative way of using sugar cane bagasse ash (SCBA) in cementitious materials by investigating the influence of autoclave curing on the microstructure of cement paste. Samples were prepared with 0%, 10%, 20%, 30%, 40%, and 50% SCBA as a replacement for cement. Two curing methods were used for the pastes: room temperature curing and autoclave curing. The results showed that the samples cured at room temperature showed similar microstructure development, while distinct hydration products formed under autoclave curing. Tobermorite and traces of xonotlite were detected in samples with high SCBA content, and traces of α-C2SH were present in samples with low SCBA content. These findings demonstrate the potential of autoclave curing to optimize the use of SCBA in cementitious materials
“If I Ruled the World”: Deploying Spatial Imaginaries for Examining Anti-Blackness and Space in Precollege Engineering Education
No full textEngineering’s systemic exclusion of Black people has been a decades-long inquiry. While critical race theory and community cultural wealth have been utilized to examine anti-Blackness in precollege engineering education, critical geographies have been underutilized. This essay contends that the deployment of a spatial imaginaries lens could be used to expand understandings of the spatial imaginary of anti-Blackness in the discipline. Using historical and contemporary data from an engineering high school as well as nonpositivist ways of knowing, the essay contends that examining spatial realities and underpinnings are opportune provocations for redefining purposes, assumptions, and values in precollege engineering education
Performance Optimisation and Field Application Research of Emergency Repair Mortar in High-cold and High-altitude Areas
No full textQinghai Province is located in a high-cold and high-altitude area, with low average annual temperature, large daily temperature difference, strong ultraviolet irradiation, and arid climate with little rain in some places, which greatly exacerbates the deterioration of the material and structural performance, especially the frequent occurrence of earthquakes, mudslides, landslides, and other geologic hazards have also resulted in structural damage. However, common emergency repair materials have decreased strength at low temperatures and require complex maintenance conditions to harden, which increases the difficulty of repair. Based on the characteristics of high-cold and high-altitude areas, this study systematically investigated the working performance, mechanical properties, and durability of repair mortar in low-temperature environments using magnesium phosphate cement as a cementitious material. The practicality and applicability of engineering were verified through field applications. The research was applied in practice on the Gongyu Heka section of the Xili Expressway in Gonghe County, Hainan Tibetan Autonomous Prefecture, Qinghai Province. Two winter maintenance rapid repair demonstration projects were completed, with road repairs completed, and traffic reopened in less than three hours. This confirmed that the research results are of great significance for emergency rescue and rapid repair of damaged infrastructure, as well as the daily maintenance of infrastructure in the high-cold and high-altitude environment of Qinghai Province
Ultra High Performance Concrete (UHPC) Bridge Deck Overlays as a Corrosion Mitigation Strategy
No full textCorrosion of steel reinforcement is one of the primary contributing factors to bridge deck deterioration. To extend the service life of a bridge deck, different corrosion mitigation strategies can be employed including overlays and corrosion mitigation chemicals. Traditionally, deteriorated bridge decks were repaired using localized patches or thin bonded overlays composed of conventional concrete materials. However, UHPC overlays gained traction from the bridge owners in recent years, in part due to their superior mechanical and durability properties. On the other hand, corrosion mitigation chemicals are added to the concrete surface to reduce ingress of deleterious ions and thereby reducing corrosion propensity. This study evaluates the effect of different corrosion mitigation strategies on the bond between UHPC overlay and the substrate concrete. The corrosion mitigation strategies include use of sealers, corrosion inhibitors and overlays by themselves or in conjunction with sealers, corrosion inhibitors or both. Corrosion activity was monitored using half-cell potential and cyclic polarization using standardized test protocols. Furthermore, the effect of corrosion mitigation measures on the bond performance was assessed using direct tension bond testing. UHPC overlays were found to be effective in reducing corrosion rates by more than 50 percent. Sealers and corrosion inhibitors applied to the concrete substrate in combination with an UHPC overlay reduced the corrosion rates even further. However, sealers and corrosion inhibitors appeared to negatively affect bond strength, potentially increasing the likelihood of overlay delamination, and thereby affecting the service life of the bridge deck
ACI Standards for Concrete Proportions, Qualification Testing and In-Process Testing during Construction
No full textThis paper provides a summary of the American Concrete Institute (ACI) design standards concrete mixture proportions for various exposure conditions in USA. As defined by ACI 318, for each class of concrete and exposure condition, minimum water to cementitious ratio and compressive strength, are prescribed. The responsibility of selecting the concrete mixture proportions design rest with a Professional Engineer, licensed in the State where the construction is carried out. Trial batches of concrete are performed in accredited laboratory, in accordance with ACI 211.1, with adequate lead time to ensure that the test results are available, prior to construction. Attention is given to selection of aggregate, cement type, supplementary cementitious materials (including fly ash and slag), air-entrainment, and the need for chemical admixtures for workability and durability requirements. A case study for a recent project, constructed in the USA, is discussed to provide guidance for appropriate selection of the concrete materials, mixture proportions consistent with the site and exposure conditions, including qualification tests. During construction, the fresh concrete properties were verified by testing slump. air content, unit weight, before placement. The variations in the delivered concrete properties (slump, air content, unit weight, etc.) from the specified requirements were dealt with through non-conformance reports for evaluation and resolution by a Professional Engineer
Strength and Non-Steady-State Chloride Migration of Concrete Incorporating Fly Ash-Based Artificial Aggregate
No full textThis study explores the mechanical performance and chloride resistance of concrete incorporating artificial aggregate (AA) synthesized from low-calcium fly ash using an environmentally friendly process. The AA was produced by combining fly ash with a small amount of Portland cement and a low concentration of sodium hydroxide, followed by mild heat curing. The hardened material was crushed and used as coarse aggregate in artificial aggregate concrete (AAC). Concrete mixes were prepared with two water-to-cement (W/C) ratios (0.49 and 0.67), and their performance was compared with that of natural aggregate concrete (NAC). Compressive strength tests at 28 days showed that AAC had significantly lower strength than NAC, attributed to the higher porosity and lower strength of the AA. However, AAC with a W/C of 0.49 still met the minimum structural requirements, suggesting potential for practical application. To assess durability, non-steady-state chloride migration tests were conducted at curing ages of 60 and 120 days. The results demonstrated that AAC exhibited better resistance to chloride ion ingress than NAC, particularly at later ages. This improvement is likely due to pozzolanic reactions between unreacted fly ash in the AA and the surrounding cement paste, leading to progressive densification of the interfacial transition zone (ITZ). These findings highlight the potential of fly ash-based AAC for use in chloride-laden environments and suggest promising durability performance despite its lower mechanical strength
Evaluating Cover Crop Performance: A Spatial Approach to Biomass and Nutrient Prediction with UAS Imagery
No full textFarmers and agronomists need accurate, efficient methods for evaluating cover crop (CC) biomass and nutrient content to optimize fertilization strategies and improve soil health. Traditional biomass assessments are labor-intensive and time-consuming, often delaying timely data-driven management decisions. While multispectral cameras, including near-infrared (NIR) and RedEdge sensors, provide high-accuracy data for this purpose, their high cost limits accessibility for many farmers. This study explores the potential of using regular RGB cameras on unmanned aerial vehicles (UAVs) as an affordable alternative to multispectral sensors for estimating CC biomass and key nutrients such as nitrogen (N) and sulfur (S).
Data was collected from cereal rye fields at Purdue University’s Agronomy Center for Research and Education (ACRE) using two UAVs equipped with different cameras: a MicaSense RedEdge-MX multispectral camera and a DJI Mavic 3M RGB camera. Flights were conducted on three separate dates: April 3, 12, and 18. Biomass samples were collected at each drone sampling point using a 50 cm x 50 cm square frame, and laboratory analysis was conducted to measure biomass and nutrient content. Images captured by the UAVs were processed with Pix4D Mapper to generate georeferenced maps, and vegetation indices such as NDVI, NDRE, GLI, and MGRVI were calculated from the imagery to assess plant health and growth.
Strong correlations (R² \u3e 0.90) were observed between spectral indices and biomass, particularly in the final sampling date. NDVI and NDRE demonstrated the highest correlations, proving to be reliable indicators of crop health and nutrient status. RGB-derived indices such as GLI and MGRVI also showed promising results, indicating that standard RGB cameras may serve as a viable, cost-effective alternative for early and mid-growth stages. The research supports the development of variable rate maps, enabling precise nutrient application, reducing fertilizer waste, and improving sustainability in agricultural practices