Influence of Meta-kaolin and Crumbed Rubber on Properties of 3-D Printable Cementitious Mixture for Application in Additive Manufacturing
Presented By: Haripriya Nekkanti
Affiliation: Clemson University
Description: There is a growing interest in investigating additive manufacturing processes using cement-based materials in the construction industry. However, the approach to developing a viable cementitious mixture for 3D printing has been empirical in nature and relies heavily on repeated trials, until suitable mixtureproportions are determined for a given set of materials. The focus of the present study is to examine the behavior of cementitious mixtures prepared with Portland cement in combination with meta-kaolin (MK), crumbed rubber and chemical admixtures such as super plasticizer, viscosity modifying agent and additives such as polypropylene fibers. In this parametric study, the influence of meta-kaolin on the rheological and mechanical behavior of mortars was investigated and the results showed that the addition of meta-kaolin enhances the mixture viscosity, aids in shape retention and reduces bleeding in the mixtures, however setting time was shortened. The combination of using
crumbed rubber with MK was found to have very good effect on the setting and flow behavior of the mix. Rheological properties of mortars (i.e. yield stress and plastic viscosity) of these mixtures were measured and correlated with the performance measures such as extrudability, buildability, thixotropic open time and shape retention. The results from this investigation showed that combination of MK and crumbed rubber can beneficially be used to provide a good 3D printable mix, and the proportions of the materials in mixture can be tailored to meet desired rheological and performance measures for viable 3D print operations.
Development of a New Test Method to Evaluate the Impact of Curing on the Near-surface Chloride Penetration Resistance of Concrete
Presented By: Majed Karam
Affiliation: University of Toronto
Description: The fluid penetration resistance (permeability) of concrete in the near-surface curing-affected zone is variable due to the differential early-age hydration kinetics. The temperature and moisture gradients near the surfaces of elements cause the concrete cover to have higher permeability than in the core concrete. In terms of concrete structures exposed to chlorides, the permeability of the cover zone is one of the main parameters controlling the structure’s durability performance. Thus, it is essential to quantify the near-surface concrete
permeability and relate it to durability performance. Due to a lack of existing quality assurance test methods for assessing near-surface permeability, curing specifications are generally prescriptive. Their prescriptive nature hinders the adoption of potentially more efficient curing techniques, such as accelerated heat curing common in the precast concrete industry. The present work utilizes a new test method for assessing the depth-dependant effect of curing in the cover zone by measuring capillary absorption at different depths. Cores from different depths in the concrete cover and characterized as a function of the
initial rate of absorption of a sodium chloride solution. In addition, the results are correlated to the depth of chloride penetration after 6 hours, by the total charge passed as determined by ASTM C1202, and by bulk electrical resistivity. A range of curing regimes of varying quality is used to experimentally validate the sensitivity and accuracy of the test method.
Nonlinear Modeling Parameters and Acceptance Criteria for Reinforced Concrete Coupling Beams
Presented By: Christopher Motter
Affiliation: Washington State University
Description: Reinforced concrete coupled walls are often used in buildings to resist lateral demands from
earthquakes and wind. The response of coupled walls subjected to lateral demands is highly
dependent on the behavior of the coupling beams. Existing recommendations for nonlinear
modeling parameters and acceptance criteria for reinforced concrete coupling beams were
developed based upon a limited dataset that did not account for the influence of axial restraint on
coupling beam behavior. The objective of this research is to formulate revised recommendations that consider new test data and the influence of axial restraint. A database of reinforced concrete coupling beam tests was developed, and a simplified coupling beam model to estimate deformation capacity was developed and validated with existing data. The model was comprised of an elastic beam element with plastic rotation hinges and bond-slip rotation hinges at each end of the beam. The model included separate strain-based limits for the onset of reinforcement buckling and confined concrete crushing. The model was used to aid in the determination of key parameters expected to influence deformation capacity, and new recommendations were developed for behavior categories for nonlinear modeling parameters and acceptance criteria. The database was used to formulate revised recommendations for the values of the nonlinear modeling parameters and acceptance criteria within each of the new behavior categories. Due to the limited number of tests on coupling beams with axial restraint, a laboratory testing program is being conducted on
diagonally-reinforced concrete coupling beams subjected to varying levels of axial restraint,
ranging from full axial restraint to no axial restraint. It is anticipated that preliminary test results will be available at the time of presentation. A finite element model (FEM) was formulated and used to guide the design of the test specimens.
Freeze-Thaw Durability of the Bond Zone Between Cementitious Rapid Repair Materials and Concrete Substrate
Presented By: Noah Thibodeaux
Affiliation: New Jersey Institute of Technology
Description: Rapid repair cements are important for extending the longevity of critical infrastructure while minimizing delays. There are many types of rapid repair systems which can vary significantly in system chemistries and performance potential, however, they are often used interchangeably by the end client. This can result in poor durability and extended maintenance needs. Understanding how each system performs and the environments each system is suited for will improve the durability and cost effectiveness of infrastructure repairs. Of paramount importance is a good quality bond to the existing concrete, especially
in adverse environments where freeze-thaw may be a significant factor in concrete deterioration. The goal of this work was to understand the rate and magnitude of freeze-thaw deterioration at the bond zone between ordinary portland cement concrete and repairs made with alternative cement systems. Three rapid repair systems were examined: a proprietary ternary blend, a calcium sulfoaluminate cement system, and a blended system comprised of calcium aluminate cement, calcium sulfate, and ordinary portland cement.
Concrete prisms were cast, and then scarified before being overlaid with the various rapid repair systems. The specimens were subjected to freeze-thaw testing according to ASTM C666. Pull off tests were performed in accordance with ASTM C1583 after various numbers of freeze-thaw cycles. Results of this testing are presented indicating how each type of system performed in freezethaw compared to a monolithically cast ordinary portland cement concrete
system. In addition, the effect of freeze-thaw cycling on the pull-off strength of the repair overlay are also presented.
The Effect of Chemical Composition of Superabsorbent Hydrogels on Their Influence on Cementitious Materials
Presented By: Ali Ghahremaninezhad
Affiliation: University of Miami
Description: Autogenous shrinkage cracking is considered a critical durability issue in high performance cementitious materials. Due to the low water/binder ratio used in the formulation of these materials, reduced relative humidity and self-desiccation result in the generation of capillary forces and development of tensile stresses in cementitious materials. Cracks are formed when the tensile stresses exceed the fracture strength of the material. Crack formation increases the transport rate of deleterious species into the material speeding up other degradation processes including reinforcing steel corrosion. This presentation reports the use of superabsorbent hydrogels as a reservoir of water for the internal curing applications. Superabsorbent hydrogels with different chemical compositions were synthesized to allow us
to establish a link between the chemical composition of hydrogels and their interaction with cementitious materials and, consequently, their effect on the properties of cementitious materials. The absorption and desorption of hydrogels in cementitious materials were investigated. Fourier transform infrared spectroscopy was used to investigate changes in the chemical characteristics of hydrogels. The effect of superabsorbent hydrogels on autogenous shrinkage was evaluated and discussed.
Use of Splay Anchors in Flexural Strengthening of RC Bridge Girders with CFRP Sheets
Presented By: Hayder Rasheed
Affiliation: Kansas State University
Description: This study investigates the effectiveness of CFRP splay anchors when used to secure CFRP sheets for flexural strength enhancement of reinforced concrete bridge-scale girders. Six full scale T-beams are designed, built, and tested under four-point bending until failure. One beam is tested as a control specimen. A single layer of unidirectional CFRP sheet is applied to the beam soffit for each of the remaining beams. CFRP splay anchors are installed to anchor the CFRP sheet and to transfer stresses from the sheet to the concrete core when the
CFRP sheet tends to debond at a later stage of loading. Variables are the number and spacing of the CFRP splay anchors along the shear span of the girders. Comparison between the test results and nonlinear numerical analysis are made. A simplified design model is proposed to account for sizing the CFRP splay anchors to achieve a certain design objective.
Assessing the Comparability of Concrete Environmental Product Declarations (EPDs) Through a Probabilistic Analysis
Presented By: Hessam AzariJafari
Affiliation: Massachusetts Institute of Technology
Description: The industry-average environmental product declarations (EPDs) have been used as a set of benchmarks to represent the environmental impacts of concrete mixtures across a range of producers and product types. Data quality assessments of background life cycle inventory data are reported in EPDs but are not used in a quantitative way to assess its impact on results. Analyzing the uncertainty related to this data quality can provide a comprehensive perspective on the transparency, reliability, comparability, and clarity of the scoring. Funded
majorly by ACI Foundation, in this project, we propose a method to enable comparability of EPDs with each other and industry-average benchmark results using a probabilistic method that incorporates uncertainty and variability sources. To do so, we consider a case study of the industry-average concrete EPDs and analyze their results through a meta-analysis for different functional classes. Considering the requirements for comparability in the ISO 14025, the probabilistic analysis enables ones to assess the statistical significance of the
difference between the benchmark and EPD results. Hence a threshold value is implemented to show this significance. The ultimate goal of EPDs is to enable comparisons of the performance of different building products. However, in their current form, they cannot be compared because they do not satisfy the ISO requirements for comparability. Until EPDs are created specifically for comparison, this approach is critical for identifying the key factors that need to be harmonized to enable comparability for the purposes of LEED and supporting
Development of Ecological Nano-engineered Strain-hardening Cementitious Composites with High-volume Ground Glass Pozzolans
Presented By: Hisseine Ousmane Ahmat
Affiliation: Universite de Sherbrooke
Description: This study shows how nanoscale cellulose filaments (CF) can be used as a novel tool for tailoring the properties of strain-hardening cementitious composites (SHCC) incorporating high-volume ground-glass pozzolans (HVGP) towards improved strength and ductility. CF was introduced (at dosages of 0, 0.03, 0.05 and 0.10% by weight of cement) into SHCC incorporating ground-glass pozzolans (GP) in replacement of fly ash (FA) at 0, 40, and 100%.
Micromechanical guidelines were adopted for tailoring the formulations. The performance of resulting formulations was then validated by uniaxial-tensile and flexural tests. Results indicate that CF allows nanoengineering matrix and interface properties by increasing matrix elastic modulus and imparting a significant slip hardening effect. Consequently, higher complementary energy and lower crack tip toughness were obtained, thereby leading to enhanced ductility. Thus, while an increase in uniaxial post-peak strength of up to 23% can
be achieved with CF, the most significant effect of CF was on the ultimate tensile strain capacity (eu) particularly in the mixtures with 40 and 100%GP. Thus, improvements in eu of up to 26, 37, and 258% were achieved for the three respective GP contents (0, 40, and 100%). Consequently, the energy absorption capacity was enhanced with CF by up to 52, 83, and 238%, respectively. Thus, with the incorporation of CF, it was possible to produce SHCC with up to 100%GP replacement of FA exhibiting higher strength and ductility, while
contributing to promoting ecoefficiency.