Improving the Freeze-and-Thaw Resistance of High-volume Fly Ash Concrete Using Ground Recycled Rubber
Presented By: Mohamed ElGawady
Affiliation: Missouri University of Science and Technology
Description: Fly ash has been used in concrete to improve both the sustainability and performance. However, concrete incorporating a high volume of fly ash has counters an issue with incompatibility between fly ash and performance-enhancing admixtures, such as air entraining admixture (AEA). This study investigates using ground recycled rubber (GRR) as an eco-friendly alternative to AEA to improve the freeze-thaw performance of mortar mixtures incorporating two different types and ratios of fly ash. Two different sizes and ratios of GRR were used in this study. The results were compared with mixtures having two different types and dosages of AEA as well as a reference mortar mixture having neither GRR nor AEA. Foam index was investigated for both types of fly ash and compared with cement. The compressive strength retention values of mortar cubes after exposing them to 36 freeze-thaw cycles was determined and related to the air content of each mixture. This study revealed that the GRR outperformed the AEA in terms of the freeze-thaw durability where some of the mixtures exceeded 100% compressive strength retention due to the crystallization of the rubber particles under low temperature.
The Use of Rubber and Plastic Waste in Cementitious Mortars
Presented By: Alessandro Fantilli
Affiliation: Politecnico di Torino
Description: Cement-based mortars, containing polypropylene or rubber waste particles as aggregates, are investigated herein. Specifically, their mechanical and ecological performances are compared with the traditional mortars made by stone sands, plain or fiber-reinforced. The substitution rate of the stone aggregates with polymeric particles varied from 30% to 80% in weight. From the environmental point of view, the substitution strategy is a good practice in the zones where row materials are scarce. On the other hand, considering the mechanical properties, the mortars manufactured with polymeric aggregates are generally lightweight and show a greater ductility, allowing a reduction of the building mass and a better capacity to dissipate energy.
Investigating the Impact of Foundry Waste on the Mechanical Performance of Self Consolidating Concrete
Presented By: Anthony Torres
Affiliation: Texas State University
Description: The United States produces approximately 6–10 million tons of from the ferrous and non-ferrous foundry industry and estimates have shown that only 15% of the waste produced is being recycled. The increasing scarcity of landfill space and disposal cost has fashioned a need for an alternative disposal method of this waste. This type of waste can consist of many products, such as spent foundry sand, slag, ash, refractory, coagulant, baghouse dust, pattern shop waste, and debris. Past researchers have demonstrated an alternative disposal method by using spent sand and slag as constituents in concrete with positive results. This study generalizes the foundry waste for use in Self Consolidated Concrete (SCC) in order to increase the recycling percentage, by reducing processing time/cost and using all the waste produced by the foundry industry. This was done by partially replacing both fine aggregate and coarse aggregate of an SCC mixture with lightly processed foundry waste. Since foundry waste contains both fine and coarse materials, as-received foundry waste was lightly processed and sieved to match the natural concrete mixtures coarse and fine aggregate distribution. Both virgin coarse and fine aggregates were replaced by mass at 10%, 20%, and 30%. Two mixture groups replaced individual constituents separately (coarse and fine), and one mixture group replaced both coarse and fine in the same mixture. The compressive strength, splitting-tensile strength, flexural strength, and modulus of elasticity were measured for all groups at 7, 14, and 28 days. The results indicated that general foundry waste as either coarse, fine, or combined by mass replacement of natural aggregate has no impact on the mechanical performance of SCC up to 20% for individual replacement or 10% combined. This result not only demonstrates a possible avenue to increase the amount of foundry waste recycled annually, but it also reduces the demand for virgin aggregates for SCC.
Fresh, Mechanical, Durability and Corrosion Properties of Basalt Fiber Reinforced Concrete
Presented By: Kevin Ramirez
Affiliation: University of Idaho
Description: Addition of fibers to concrete improves its mechanical properties such as compressive strength, flexural strength and toughness. Fibers made from steel, polypropylene, and glass are currently the most common fiber types used to produce fiber reinforced concrete (FRC). A relatively new type of fiber that has been suggested for use in FRC is the basalt fibers. Basalt fibers consist of bundles of filaments which are produced by processing naturally occurring basalt. Basalt has excellent characteristics such as high tensile strength, high heat resistance, and relatively low cost, which make it a potential alternative to common FRC fiber types. The main goal of this study is to investigate the mechanical and corrosive properties of basalt fiber reinforced concrete (BFRC). This study is conducted with varying basalt fiber volumes of 0%, 0.15%, 0.30%, 0.45% and 0.50%; utilizing two different water/cement ratios (0.35, 0.40). The BFRC properties will be compared to conventional concrete samples as well as steel fiber reinforced concrete samples. The experimental testing consisted of producing 14 different concrete mixtures, while those mixtures will be developed using conventional Portland cement with a target compressive strength of 4,000 psi at 28 days. Various fresh, mechanical, and durability testing will be considered such as flexural strength, compressive strength, unrestraint shrinkage, splitting tensile strength, Macrocell corrosion, and surface resistivity have been. The mechanical properties will be evaluated by following American Society for Testing and Materials (ASTM) standards while corrosion properties will be evaluated by utilizing a Rapid Mini Macrocell Accelerated Test Guide.
Optimization of the Equivalent Volume (EV) Method through Particle Packing Models (PPM) to Mix-Proportion Fine Recycled Concrete Aggregates (FRCA) Mixtures
Presented By: Hian Macedo
Affiliation: University of Ottawa
Description: In the past decades, a number of studies have focused on mix-proportioning sustainable concrete mixtures through the use of coarse recycled concrete aggregates (CRCA). Most of the results obtained in the literature so far show that CRCA mixtures present an inferior performance when compared to companion conventional concrete. The latter was found due to the presence of residual mortar (RM) adhered to the aggregate particles which brings multiple interfacial transition zones (ITZ) to the system. Ever since, numerous mix-design techniques that account for the RM in the RCA concrete were developed. Among those, the Equivalent Volume (EV) method showed to be very promising and recycled mixtures presenting similar hardened state behaviour than conventional concrete are obtained through this technique, especially when it is optimized through the use of particle packing models (PPMs). Yet, the EV method has never been used to mix-design recycled mixtures made of fine aggregates, the so-called FRCA. This work presents the use of EV and continuous PPM to mix-proportion 35 MPa FRCA mixtures containing 100% replacement. Non-destructive (electrical resistivity), fresh (i.e. consistency and rheological behaviour) and hardened state (i.e. compressive strength and modulus of elasticity) properties are conducted. Discussion and comparisons among the different recycled and conventional mixes are then performed.
Prediction of Mechanical Properties of Concrete Made with Recycled Concrete Aggregates Using Statistical Analysis of Data Available in Literature
Presented By: Anuruddha Jayasuriya
Affiliation: New Jersey Institute of Technology
Description: The concrete design and construction industry has been eagerly adopting sustainability initiatives over the last 20 years to help reduce its carbon footprint, improve economic sustainability, and ensure the important natural resources that support the industry remain available for years to come. Despite these advances, recycled concrete aggregates (RCA) have been significantly underutilized even though they are becoming an increasingly available sustainable resource that can be used to reduce the amount of natural aggregates used in concrete. Use of RCA has been limited, in part, because of a lack of standardized guidance on creating mixture designs and how aggregates may impact concrete properties. Presented in this paper are the results of a statistical analysis of data from over 80 peer reviewed articles that can be used to predict performance in mixtures containing RCA. A large database consisting of 850 compressive strength, 682 elastic modulus, 197 flexural strength, and 462 splitting tensile strength results was created from this literature review with data ranging from 1988 to 2018. Non-linear regression analyses determined that the empirical trends related to compressive strength, elastic modulus, flexural strength, and splitting tensile strength had a linear relationship with the RCA replacement levels depending on absorption capacity, RCA replacement level, effective water-to-cement ratio, maximum aggregate size, and strength of the RCA’s parent concrete. Overall, the RCA replacement ratio and the water-to- cement ratio had significant impacts on concrete mechanical strengths, while other factors such as mix proportioning parameters and aggregate properties had minor effects on the mechanical properties of RCA systems over the large dataset. Additionally, significant reductions in strength were not observed until replacement levels of RCA increased above 20%.