Concrete Products

MAR 2019

Concrete Products covers the issues that attract producers of ready mixed and manufactured concrete focusing on equipment and material technology, market development and management topics.

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Page 52 of 67 March 2019 • 51 foaming agent, glass fleece, and kaolin in a tunnel kiln. Prior to cooling, the FGA is produced as a single continuous sheet of approximately 2 in. thickness. During sub- sequent rapid cooling, a series of random cracking occurs that generates random- ly-shaped particles with nominal maximum diameters approaching 3 in. For this effort, the FGA particle size was further reduced by manual pulverization to produce an aggregate meeting the gradation requirements of AASHTO M43 #67 with a nominal maximum diameter of 0.75 in. The manufacturing process utilized for the par- ticular FGA utilized in this study produces a closed cell FGA incorporating a variety of non-interconnected air voids. Both beam specimens exhibited predict- able transitions between expected ranges of behavior, and achieved equal ultimate flexural capacities that well exceeded design predic- tions. Within the anticipated service range (cracked linear elastic behavior), the FGA con- crete beam exhibited a reduction in flexural stiffness of approximately 30 percent as com - pared to the conventional concrete specimen. The FGA specimen exhibited increased ductility compared to the control specimen as demonstrated by its ability to undergo an additional 1.10 in. of midspan deflection while sustaining peak load, whereas the con- trol specimen failed immediately upon peak loading. The authors concluded: • The use of closed-cell FGA is viable to produce sound concrete with sufficient workability and mechanical properties for potential use in reinforced concrete structural applications; • The hardened properties of FGA concrete (and corresponding observed FGA particle failure mechanisms) seem closely related to mixture composition, including the relative volumes of coarse aggregate to concrete paste, the gradation of coarse aggregate used, and FGA replacement rate; • The 50 percent coarse aggregate replace- ment FGA concrete mixture developed in this study exhibited a 20 percent reduction in unit weight and a 30 percent reduction in compressive strength when compared to a conventional control mixture with an identi- cal water-cementitious materials ratio; • The FGA concrete mixture composition explored in this study differed from pre- vious work by others by the inclusion of multiple sizes of coarse aggregate (#8 and #67), which may have helped minimize the expected compressive strength and elastic stiffness reductions previously observed by others; and, Foamed glass aggregate as produced (left) and after pulverization. IMAGES: Nicholas, Shoemaker and Mante Reinforced concrete beam specimens with control mixture (left) and FGA mixture (right) after loading to failure. • Failure of FGA concrete in compression was characterized by the progressive partial or complete powdering of FGA particles in areas of maximum compressive stresses. • Specific conclusions regarding full-scale load testing of reinforced concrete specimens incorporating FGA concrete mixture include: • The reinforced concrete FGA and conventional concrete specimens exhibited relatively predictable transitions from uncracked to cracked linear elastic behavior and ultimate flexural capacities; • Within the cracked linear elastic behavior region (service range), the FGA concrete specimen exhibited a flexural stiffness approximately 31 percent less than the conventional specimen. This observed reduction in flexural stiffness was no more than expected by the differences in concrete density and compressive strength of the FGA as compared to the conventional mixture; • The flexural capacity of the FGA concrete specimen included in this study approached 97 percent of the flexural capacity of the con- ventional concrete control specimen; • After first reaching ultimate capacity, the FGA concrete specimen experienced an addi- tional 1.10 in. of residual deflection while sustaining peak load, whereas the conven- tional control beam experienced immediate failure upon peak loading; and, • The FGA concrete specimen exhibited sig- nificantly increased ductility as compared to the conventional concrete beam, suggesting that FGA concrete may have a tendency to redistribute internal stresses either through or around local areas of progressively failing FGA particles. TECHNICAL TALK TRB 2019 MEETING

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