Performance of Concrete Containing Water-hyacinth Ash (WHA) as a Cement
Presented By: Ahmed Omran
Affiliation: University of Sherbrooke
Description: Considerable effort worldwide for utilizing local and waste materials in concrete. One of these materials is water-hyacinth plants. Under certain burning and sufficient grinding, the ash produced from the water-hyacinth plants (named water-hyacinth ash, WHA) can be used as a cement replacement material, given it has amorphous and pozzolanic nature. Thus, concrete containing WHA is expected to exhibit higher long-term strengths and better durability. The current research focuses on evaluating the possibility of using the WHA as an alternative supplementary cementitious material (ASCM) using paste, mortar, and concrete mixtures. Two burning conditions (in open air for 60 min and in closed oven at 600 oC for 30 min) and different replacement ratios (5%, 10%, 15%) of the WHA as well the three coarse aggregate types were considered as parameters in the research. The results illustrate that the WHA is a pozzolanic material contributing to strength gain over time. The concrete containing WHA showed better performance relative to the control mixture with only portland cement and comparable behavior to the mixture with 10% silica fume replacement. The 10% WHA replacement ratio could be considered as an optimal replacement ratio. The two WHA types obtained from the two different burning methods yielded slight difference in the performance. The type of the coarse aggregates affected significantly strength results.
Lightweight Rubberized Concrete Pavement Slabs Using Tire-Derived and Expanded Clay Aggregates – Life Cycle Cost Analysis
Presented By: Maryam Nazari
Affiliation: California State University, Fresno
Description: In this study, the application of Tire-Derived Aggregates (TDA) in combination with expanded clay (EC) aggregates will be investigated in concrete slabs used in road pavements and bridge decks serving non-auto traffic, such as bicycle routes, through a set of experimental testing and life-cycle cost analysis. To this end, TDA, which is obtained from recycled tires, and EC, produced in rotary kilns, substitutes coarse aggregates in conventional concrete. The final product, also known as lightweight rubberized concrete, is durable and economically-efficient. It also enhances the sustainability of transportation infrastructure by mitigating the necessary maintenance and rehabilitation needs of these slabs. In this paper, an experimental study, funded by California State University (CSU) Transportation Consortium and Fresno State Transportation Institute, has been undertaken to first estimate mechanical properties of lightweight rubberized concrete using 100% EC, 100% TDA and 20% EC with 80% TDA replacements by the volume of the coarse aggregates. Next, a series of half-cyclic static and impact-fatigue dynamic tests were performed on simply-supported beam specimens and slab assemblies, respectively, to measure their modulus of rupture and durability when subjected to the applied loads. The cyclic testing results confirmed lower flexural strength of the specimens using rubberized concrete; however, they sustained larger plastic deformations up to their failure. Using the results of impact-fatigue tests, a life-cycle cost analysis is also performed, which confirmed long-term benefits of constructing green and durable infrastructure, using TDA and EC, on transportation investments.
Effects of Rest Time and Curing Regime on the Long-Term Strength of Class C Fly Ash-Based Geopolymer Mortars
Presented By: Mohamed ElGawady
Affiliation: Missouri University of Science and Technology
Description: Fly ash (FA) sourced from two different power plants located in Missouri were used to synthesize four different mortar mixtures. The mixtures had different ratios of sodium silicate to sodium hydroxide. The effects of different rest times up to 36 hours on the compressive strength of geopolymer concrete was investigated. Different curing regimes were investigated as well. Two group of the specimens were subjected to oven, or steam-curing at either 55 °C (131 °F) or 80 °C (176 °F). A third group was subjected to ambient curing. The compressive strengths of the investigated specimens were examined at different ages up to 90 days. Results demonstrated that a rest time of 12 hours resulted in an approximately 45% increase in the compressive strength compared to two hours rest time. Furthermore, up to 300% increase in the compressive strength was observed up to 90 days for thermal and ambient curing regimes.
Mesoscopic Fracture Modeling of Recycled Concrete Aggregate Systems Generated Through Random Aggregates and Pores
Presented By: Matthew Adams
Affiliation: New Jersey Institute of Technology
Description: Mesoscopic numerical modeling has been used in broader extents to examine the nonlinear behavior and damage progression of concrete-like composite materials with a minimum of computational costs. As a common multiphase composite material, recycled concrete aggregate (RCA) systems are composed of randomly distributed recycled coarse aggregates with adhered mortar attached to the natural aggregate, cement mortar matrix, and a wide spread of interfacial transition zones at material boundaries. The mesoscopic mechanical behavior of RCA systems is nonlinear due to the existence of material heterogeneity and thus, exhibits stochastic characteristics. An efficient aggregate generation for RCA systems is proposed in this paper, through a convex hull algorithm followed by an extensive image analysis procedure to build two-dimensional finite element simulations for crushed and rounded RCA systems. The pore structure in the RCA system is dispersed within the concrete boundary comprised of circular pores ranging from 2 mm to 4 mm in sizes providing a 2% void content in the RCA system. Uniaxial tension tests are carried out for 50 mm × 50 mm RCA systems to investigate the effects of fracture patterns and load carrying capacities. Stress-strain relationships are established based on the numerical simulations using material properties, loading criteria, and material model inputs to examine the fracture initiation and propagation due to the geometric parameters of recycled concrete aggregates such as shape, adhered mortar content, and aggregate ratio.
Exploring Sustainable Preplaced Recycled Aggregate Concrete under Impact Loading
Presented By: Moncef Nehdi
Affiliation: Western University
Description: This study pioneers sustainable highly eco-efficient preplaced aggregate concrete mixtures having superior tensile characteristics and impact resistance for application in pavements and other transportation infrastructure. In addition to its very high recycled content and exceptional sustainability features, this material offers unique time and cost savings for pavement construction. Only a grout is mixed and injected in a preplaced granular skeleton. Typical problems of highwater absorption and rapid loss of workability due to recycled aggregates and segregation of tire rubber granules in normal concrete mixtures are avoided since aggregates are preplaced in the form. The much higher granular content and its denser skeleton reduce the cementitious dosage substantially and provide high volume stability against shrinkage and thermal strains. The behavior of this sustainable preplaced recycled aggregate concrete incorporating randomly dispersed steel wire fibers retrieved from scrap tires and scrap tire rubber granules was investigated under impact loading using a drop weight impact test. Results show that recycled tire steel wire fibers significantly enhanced the tensile and impact properties of the preplaced recycled aggregate concrete. A two-parameter Weibull distribution provided accurate prediction of the impact failure strength of the preplaced recycled aggregate concrete mixtures, allowing to avert additional costly laboratory experiments.
Investigating the Application of Tire-Derived Aggregate Concrete in Buckling-Restrained
Presented By: Nasreen Pathan
Affiliation: Department of Civil and Geomatics Engineering, Cal
Description: This paper investigates the application of tire-derived aggregate (TDA) concrete in buckling restrained braced frames (BRBF). Application of TDA reduces environmental footprints of infrastructure through diversion of waste from landfill, and preservation of natural resources. Existing literature confirms that the substitution of mineral aggregates with TDA generally reduces mechanical strengths of concrete materials. However, literature has also shown that TDA concrete may have higher values of ductility, toughness, and damping. Such enhancement has potentials to improve the performance of buckling-restrained members. Improved post-peak behavior of plain TDA concrete allows enhanced energy absorption by BRBF members experiencing flexural buckling due to applied compression, as well as better performance within the steel-concrete interface of members subjected to tension. The methodology of this paper consists of a series of experimental investigations of composite steel and concrete members, with and without TDA. These experimental works aim to determine tensile, compressive, and flexural behavior of BRBF members to simulate the response of the system to axial loadings, as well as induced flexural buckling. Results include backbone curves and core strains of the BRBF members, which are essential inputs to provide recommendations for practical design of BRBF with TDA concrete.