This Week's Featured Presentation
Blast Resistance of Precast Concrete (ACI Fall 2018 Convention, Las Vegas, NV)
This paper presents and discusses results from arena blast tests and shock tube tests on non-load bearing precast concrete wall panels and compares observed dynamic response and damage against single-degree-of-freedom (SDOF) analysis results. The tests include single-span panels and two-span continuous panels with conventional and prestressed reinforcement, and include both solid and insulated (“sandwich”) precast panels. The measured dynamic deflections and reactions are compared to the corresponding values calculated with SDOF analysis method commonly used for blast resistant design. Also, the observed panel damage levels at measured levels of response are compared to current response criteria for reinforced concrete panels. These comparisons are used to evaluate the accuracy and adequacy of the simplified SDOF methodology and the degree of conservatism in the current response limits for blast design of precast concrete wall panels. The current and proposed methodology for modeling the rebound response of concrete walls panels and the amount of composite action for sandwich panels in SDOF analysis are evaluated. The results from this study can be used to evaluate and update current guidelines for blast-resistant design of precast concrete wall panels.
July 29 – August 4
Microstructural Packing, Rheology, and Ram Extrusion Characteristics of 3-D-Printable Cementitious Binders
by Sooraj Nair, Arizona State University; Aashay Arora, Arizona State University; Hussam Alghamdi, Arizona State University; and Narayanan Neithalath, Arizona State University
Materials Science Aspects Related to Digital Manufacturing (3-D Printing) of Cementitious Materials (ACI Fall 2018 Convention, Las Vegas, NV)
Cementitious binders amenable to extrusion and layered 3D printing are formulated by ensuring appropriate particle size distributions using fine limestone powder or a combination of limestone powder and microsilica or metakaolin. Mixtures were proportioned with and without a superplasticizer to enable different particle packings at similar printability levels. A microstructural packing coefficient, based on simulated fresh paste microstructure is defined, which is well-related to rotational and extensional rheological parameters of the pastes. This parameter is shown to be useful in selecting preliminary material combinations for layer-wise printable pastes. Extrusion rheology experiments, where the ram extruder is moved at different velocities and the corresponding extrusion force recorded, are used in conjunction with a phenomenological model to better understand extrusion printing of cementitious materials. The extensional yield stress and die wall slip shear stress extracted from the model, critical in extrusion-based 3D printing, show good correlation with microstructural packing.