Yes / Recycled aggregate concrete filled stainless steel tube (RAC-FSST) is a new type of composite member combining the advantage of stainless steel and RAC. In this paper, a total of twenty-four RAC-FSST stub columns were tested under axial load, considering the influences of coarse recycled aggregate (CRA) content, steel ratios and compressive strengths of RAC. The obtained results, including the failure patterns, responses of axial load vs. deformation, stress states of external stainless steel tube and inner RAC and confinement effects, were systematically analyzed. Results indicated that all specimens presented good ductility and high residual strengths after reaching the maximum axial load. The elastic stiffness of RAC-FSSTs obviously declined with the increasing CRA content, while the strain at the ultimate load was larger. The inclusion of CRA could advance the occurrence of the confinement and lead to lower confining stress. Based on the experimental results, an analytical model with consideration of confinement action was developed to predict the axial response of RAC-FSST stub columns. Besides, the current design provisions for the normal CFST and RAC-FST members were employed to evaluate their applicability to RAC-FSSTs. In general, the design rules EN 1994-1-1:2004, GB 50936-2014 and T/CECS 625-2019 gave a conservative and relatively accurate prediction on ultimate strength of RAC-FSST stub columns. / This work was supported by the National Natural Science Foundation.

No description available.

The rapidly growing demand for carbon fiber reinforced plastics in high-tech industries, such as aerospace, defense, automotive, wind turbine engineering, building and sports, resulted in a high amount of waste in the form of dry waste (e.g., production off-cuts), wet waste (e.g., out-of-date prepreg) and end-of-life components waste (e.g., aircraft components). Furthermore, the production of carbon fibers is cost and energy-intensive. Therefore, technological developments for the gentle processing of recycled carbon fiber and its integration into high-performance composites with promising tensile properties have gained considerable attention. Consequently, injection molding, nonwovens and hybrid yarn technologies were developed in recent years to integrate recycled carbon fiber into the high-performance thermoplastic composite. It is unfortunate that these technologies develop composites with a lack of unidirectional fiber orientation; therefore, the potential of recycled carbon fiber in high-performance composites is not thoroughly exhausted. This thesis primarily addresses the development of an innovative structure with a unidirectional fiber orientation termed “unidirectional recycled carbon fiber tape structure” for high-performance thermoplastics composites. The technological concept of the unidirectional structure comprises fiber opening, carding, drawing and a novel tape-forming process. In this concept, fiber opening, carding, and drawing processes were utilized to develop homogeneous, uniform, and highly oriented hybrid slivers. In the next step, these hybrid slivers were converted into a unidirectional recycled carbon fiber tape structure through a novel tape-forming process. To implement this concept, technological developments (investigations, modifications, optimization and further developments), were carried out in fiber opening, carding and drawing processes to develop a hybrid sliver with improved uniformity, homogeneity and unidirectional orientation. In the second phase, conception, design, technological developments, construction and prototype development were implemented to develop a novel tape-forming process. The result confirms that tape development technology comprising fiber opening, carding, drawing and prototype tape forming processes is an innovative, eco-friendly and sustainable technology compared to existing technologies. Furthermore, the consolidation process transformed the unidirectional tape structure into high-performance thermoplastic composites. Subsequently, technology-structure-property relationships were established to develop composites with tailor-made properties. The analysis reveals that selecting optimum technological, consolidation and structural parameters develop tape and composite structures with unidirectional fiber orientation. As a result, experimental results of a high-performance composite developed from a unidirectional recycled carbon fiber tape structure show a very high tensile strength of 1350 ± 28 MPa and an E-module of 84.7 ± 2.3 GPa. This analysis confirms that unidirectional fibers configuration in composites brings a revolution toward developing cost-efficient, high-performance composites for load-bearing structural applications. Finally, theoretical and finite element modeling of tensile properties of high-performance composites reveals that modified models show good agreement with composite tensile properties.

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No description available.

State highway agencies are searching for more cost-effective methods of rehabilitating roads. One sustainable solution is full-depth reclamation (FDR), a pavement rehabilitation technique that involves pulverizing and reusing materials from existing distressed pavements in place. There is, however, limited information on the long-term properties of these recycled materials. One important property, the elastic modulus, indicates the structural capacity of pavement materials and is highly recommended for design purposes by the Mechanistic Empirical Pavements Design Guide (MEPDG). The elastic modulus directly impacts selection of the overall pavement thickness, and an accurate estimation of the modulus is therefore key to a cost-effective pavement design. This thesis researched the modulus trends and functional properties of three in-service pavements rehabilitated with the FDR technique during the 2008 Virginia Department of Transportation (VDOT) construction season. Foamed asphalt (2.7% with 1% cement), asphalt emulsion (3.5%), and Portland cement (5%) were used as stabilizing agents for the FDR layers. Several deflection tests and distress surveys were conducted for the pavement sections before and after construction. An automated road analyzer (ARAN) was used to collect distress data over a period of 7 years. Deterioration models were developed to predict the durability of differently stabilized FDR pavements and compared to reference sections rehabilitated with traditional asphalt concrete (AC) overlays. The results of the moduli measured for the recycled base materials varied significantly over time. These changes were attributed to curing after construction, seasonal effects, and subgrade moisture. The structural capacity of the pavements improved irrespective of the stabilizing agent used. Rutting was higher for the foamed asphalt and emulsion sections. The International Roughness Index (IRI) was better for the cement stabilized sections compared asphalt stabilized sections. The Critical Condition Index (CCI) was similar for all treatments at the end of the evaluation period. The durability of the sections was comparable, with the cement stabilized FDR sections slightly outperforming the asphalt stabilized sections. / Master of Science / Replacing all roads in bad condition with new reconstruction or with traditional rehabilitation alternatives such as the mill and overlay will cost state highway agencies (SHAs) huge sums of funds. State departments of transportation are therefore seeking cost-effective ways to rehabilitate roads under their jurisdiction. An innovative technique being used by several SHAs today is full depth reclamation (FDR) which involves breaking down an existing roadway and immediately reusing the materials to construct a strengthened base layer for a new road. Despite the increasing use of FDR in recent years, several questions remain unanswered regarding the behavior of the strengthened base materials and their performance in the long-term under traffic loads. The elastic modulus is one material property that indicates the strength or structural capacity of pavement materials and usually impacts the selection of the overall thickness of the roadway. This thesis researched the modulus trends and functional properties of three in-service roadways rehabilitated with the FDR technique in 2008 by the Virginia Department of Transportation. Foamed asphalt (2.7% with 1% cement), asphalt emulsion (3.5%), and Portland cement (5%) were used to strengthen the FDR base layers. Several deflection tests and distress surveys were conducted for the pavement sections before and after construction. The moduli measured for the recycled base materials varied significantly over time. These changes were attributed to curing after construction, seasonal effects, and subgrade moisture. Long term performance monitoring of the projects showed that rutting was higher for the foamed asphalt and emulsion sections. The International Roughness Index (IRI), which gives an indication of the overall ride quality i.e. how smooth the pavement surface is, was better for the cement stabilized FDR sections compared to the asphalt stabilized counterparts. The structural capacity of the pavements improved irrespective of the stabilizing treatment used. The Critical Condition Index (CCI) was similar for all treatments at the end of the evaluation period. The durability of the sections was comparable, with the cement stabilized sections projected to last slightly longer than asphalt sections.

State highway agencies are searching for more cost-effective methods of rehabilitating roads. One sustainable solution is full-depth reclamation (FDR), a pavement rehabilitation technique that involves pulverizing and reusing materials from existing distressed pavements in place. There is, however, limited information on the long-term properties of these recycled materials. One important property, the elastic modulus, indicates the structural capacity of pavement materials and is highly recommended for design purposes by the Mechanistic Empirical Pavements Design Guide (MEPDG). The elastic modulus directly impacts selection of the overall pavement thickness, and an accurate estimation of the modulus is therefore key to a cost-effective pavement design. This thesis researched the modulus trends and functional properties of three in-service pavements rehabilitated with the FDR technique during the 2008 Virginia Department of Transportation (VDOT) construction season. Foamed asphalt (2.7% with 1% cement), asphalt emulsion (3.5%), and Portland cement (5%) were used as stabilizing agents for the FDR layers. Several deflection tests and distress surveys were conducted for the pavement sections before and after construction. An automated road analyzer (ARAN) was used to collect distress data over a period of 7 years. Deterioration models were developed to predict the durability of differently stabilized FDR pavements and compared to reference sections rehabilitated with traditional asphalt concrete (AC) overlays. The results of the moduli measured for the recycled base materials varied significantly over time. These changes were attributed to curing after construction, seasonal effects, and subgrade moisture. The structural capacity of the pavements improved irrespective of the stabilizing agent used. Rutting was higher for the foamed asphalt and emulsion sections. The International Roughness Index (IRI) was better for the cement stabilized sections compared asphalt stabilized sections. The Critical Condition Index (CCI) was similar for all treatments at the end of the evaluation period. The durability of the sections was comparable, with the cement stabilized FDR sections slightly outperforming the asphalt stabilized sections. / Master of Science

<p dir="ltr">The construction industry is one of the largest contributors to carbon emissions, abiotic depletion of natural resources, and waste generation due to the vast quantity of concrete produced. Concrete’s main components have a significant environmental impact. The manufacturing of cement is responsible for 8% of global carbon emissions. In 2019, over 45 billion tons of aggregates were produced. Furthermore, the production of concrete generated over 600,000 tons of concrete waste in 2018.</p><p dir="ltr">Conversely, vegetation consumes 30% of the global carbon dioxide emissions. Recent studies indicated that cryptogamic species, and in particular moss, present a CO₂ uptake of 6.43 billion metric tons more than bare soil. Cryptogamic covers, such as moss and other CO₂ sequestering organisms, are key for the global cycles of carbon and nitrogen. By promoting the growth of living cryptogamic organisms in concrete building facades and roofs, the carbon footprint of concrete can greatly decrease, potentially achieving sub-zero carbon footprint. To attain this solution, cementitious composites must be designed to have an improved bio-receptivity, defined as a material's ability to be colonized by living organisms, or as a substrate to grow living organisms.</p><p dir="ltr">Previous studies show that the bio-receptivity of cementitious composites depends on a material’s acidity and ability to capture and retain water. Yet, the inter-relationship between these properties and bio-receptivity is currently not well understood. Additionally, existing methods to achieve enhanced bio-receptivity in cementitious composites in terms of are often either expensive or counterproductive in terms of sustainability.</p><p dir="ltr">This thesis aims to investigate and develop new methods to create ultra-sustainable composites with enhanced bio-receptivity and low abiotic depletion of natural resources. Additionally, this thesis aims to understand the importance, inter-relationship, and influence of the acidity and water storage properties of cementitious composites on their bio-receptivity.</p><p dir="ltr">The first portion of this thesis is focused on proposing a new method to enhance bio-receptivity of precast cementitious composites elements through accelerated CO₂ exposure treatment and elucidating the function of recycled concrete aggregate use to create ultra-sustainable composites with enhanced bio-receptivity and low abiotic depletion of natural resources. Thus, this study simultaneously tackles the reduction of waste generation and abiotic depletion of natural resources, as well as the promotion of bio-receptivity while reducing the net carbon footprint of the cementitious composites. Results suggested that the proposed accelerated CO₂ exposure treatment enhanced the bio-receptivity of mortars, especially in mortars with RCFA. The combined effect of the RCFA’s high porosity plus the effect of accelerated CO₂ exposures decrease on pH drastically enhanced the ability of promoting moss growth on mortars, enabling the production of low carbon bio-receptive cementitious material with a sub-zero abiotic depletion of natural resources.</p><p dir="ltr">The purpose of the second portion of this thesis was focused on understanding of the inter-related role of the mortar’s porosity, water absorption, and surface pH on the bio-receptivity of cementitious composites. This portion of this thesis also focused on creating a predictive model of bio-receptivity of mortars as a function of water storage properties and surface pH. By conducting this study, the extent of importance of the water storage properties and surface pH on bio-receptivity can be determined. Results suggested that w/c ratio heavily influences the bio-receptivity of mortar, in which a higher w/c ratio increases bulk porosity, water absorption, and decreases the average surface pH. The use of accelerated CO₂ exposure improved bio-receptivity due to and decrease in average surface pH. Additionally, the combined effects of high w/c ratio and accelerated exposure CO₂ exhibited even greater improvements in bio-receptivity. Furthermore, the increase in w/c ratio resulted in the mitigation of accelerated CO₂ exposure adverse effects on bulk porosity and absorption. The developed bio-receptive predictive model successfully predicts the bio-receptivity of mortars as a function of the average surface pH and water absorption. This bio-receptivity prediction model provides us with an instrument to assist in engineering concretes with a target bio-receptivity. The results of this study also show that, while previous literature indicated a maximum pH of 5.0-5.5 to produce a bio-receptive cementitious composite, the pH threshold to obtain a bio-receptive cementitious composite depends on other factors such as porosity of the material, and it is possible to create bio-receptive concretes with a surface pH of 6.2-8.3.</p><p dir="ltr">This research will contribute to creating target-by-design living-engineered concrete facades that can capture CO₂ while reducing the consumption of natural resources.</p>

No description available.

Yes / Limited information related to the application of nano silica in recycled aggregate concretes has been available in the literature. However, investigations on the effect of nano silica on the bond performance of reinforcement embedment length in recycled aggregate concrete have not been conducted yet. Therefore, the present study aimed at investigating the bond strength for recycled aggregate concretes incorporating nano silica under different levels of corrosive environments. The experimental work consisted of testing 180 pull-out specimens prepared from different mixtures. The main parameters studied were the amount of recycled aggregate (i.e. 0%, 25%, 50% and 100%), nano silica (1.5% and 3%), embedment length (5 and 13Ø) as well as reinforcement diameter (12 and 20mm). Different levels of corrosion were electrochemically induced by applying impressed voltage technique for 2, 5, 10 and 15 days. Finally, the experimental results were compared with the existing models. Experimental results showed that the bond performance between un-corroded steel and RCA concrete slightly reduced, while a significant degradation was observed after being exposed to corrosive conditions, in comparison to normal concrete. On the other hand, the use of a small quantity of NS (1.5%) showed between 8 and 21% bond enhancement with both normal and RCA concretes under normal conditions. However, much better influence was observed with the increase of corrosion periods, reflecting the improvement in corrosion resistance. NS particles showed a more effective role with RCA concretes rather than conventional concretes in terms of enhancing bond and corrosion resistance. Therefore, it was superbly effective in recovering the poor performance in bond for RCA concretes. By doubling the content of NS (3%), the bond resistance slightly enhanced for non-corroded samples, while its influence becomes more pronounced with increasing RCA content as well as exposure time to corrosion.