Adam S. Lubell

Drop-Weight Impact Response of Glass-Fiber Reinforced Ceramic Concrete

This paper reports on the static and impact response of a lightweight concrete fabricated using a chemically-bonded phosphate ceramic binder and expanded clay aggregates. The concrete has a density of 1700 kg/m3 and exhibits rapid strength gain. Chopped glass fibers having a length of 13 mm were included in the matrix at 0 to 2.0 % mass-fraction of the ceramic concrete. The tests were conducted on notched flexural specimens using configurations of quasi-static four-point bending and drop-weight impact three-point bending. Companion tests were performed to establish reference compressive behavior. The results show that both flexural and compressive strength increased significantly with an increase in the mass-fraction of fibers under quasi-static loading. Under impact, the flexural strength was uniformly higher compared to quasi-static loading, regardless of fiber content. However, as seen from the post-peak flexural toughness, the fiber efficiency was better under the quasi-static condition.

Behavior of Deep Beams Containing High-Strength Longitudinal Reinforcement

Steel reinforcing bars conforming to ASTM A1035 have enhanced corrosion resistance and significantly higher tensile strength compared to conventional reinforcing steel grades. However, the impact of the unique stress-strain characteristics of this steel on the failure modes and strength prediction models is not yet fully understood. This paper reports on the laboratory testing to failure of eight large-scale specimens having small shear span to effective depth ratios and containing or omitting web reinforcement. All specimens were longitudinally reinforced with deformed A1035 steel bars with measured stresses at the peak load from 695 to 988 MPa (100 to 143 ksi)—significantly higher than the design stress limits defined in current codes of practice. Members without web reinforcement failed in a brittle manner after the formation of diagonal cracks joining the loads and supports. For members containing web reinforcement, the shear span to effective depth ratio and the longitudinal reinforcement ratio were both found to influence the failure mode and post-peak ductility. It was possible to develop designs that could exploit the high reinforcement strength while exhibiting acceptable serviceability characteristics and adequate ductility at failure. The safety of capacity predictions using ACI ITG-6R-10 provisions is presented.

Properties of Phosphate-based Cements with High Fly Ash Content

Compared to the hydration process of traditional Portland cements, phosphate-based cements rely on an acid/base reaction process to quickly achieve strong, lightweight and durable binders with lower embodied energy. Since the binding action relies on the chemical composition of the initial components, the rheological and mechanical properties of the resulting ceramic concretes can also be influenced by other mix components including fly ash, fillers and aggregates. This paper reports on an ongoing study examining properties of concretes produced with magnesium potassium phosphate cement binders that incorporate fly ash contents of up to 80% of the total binder mass. Highly flowable mixes were developed with setting times that could be controlled through use of commonly available admixtures. The highest compressive strength of the binders and mortars were achieved when the fly ash content was 50% of the total binder mass. The produced binders and sand mortars had densities of 1800 kg/m(3) [3034 lb/yd(3)] and 2100 kg/m(3) [3540 lb/yd(3)] and compressive strengths of 35 MPa [5.0 ksi] and 60 MPa [8.7 ksi] after 28 days of simple ambient curing. Decreases in both strength and density were observed as the fly ash content was increased further, but remained within practical ranges for common construction applications with high fly ash contents.