International Concrete Abstracts Portal

Three-dimensional (3D) printing, also known as additive manufacturing, is a revolutionary technique, which recently has gained a growing interest in the field of civil engineering and the construction industry. Despite being in its infancy, 3D concrete printing is believed to reshape the future of the construction industry because it has the potential to significantly reduce both the cost and time of construction. For example, savings between 35 and 60% of the overall cost of construction can be achieved by using this technique due to the possibility of relinquishing the formwork. Moreover, this innovation would free up the architectural gesture by offering a wider possibility of shapes. However, key challenges should be addressed to make this technique commercially viable. The effect of mixture composition on the rheological properties of the printed concrete/mortar is vital and should be thoroughly investigated. This paper investigates the effect of using red mud, nanoclay, and natural fibers on the fresh and rheological properties of 3D-printed mortar. The rheological properties were evaluated using the penetrometer test, flow table test, and cylindrical slump test. The estimated yield stress values were then calculated based on the cylindrical slump test. Further, relationships between the tested parameters were established. The main findings of this study indicate that the use of an optimum dosage of a nanoclay was beneficial to attain the required cohesion, stability, and constructability of the printed mortar. The use of natural fibers reduced pulp flow by improving cohesion with a denser fiber network and reducing the cracks. With respect to red mud, it may be appropriate for printable mortar, but more testing is still required to optimize its use in a printable mixture. A printability box to define the suitability of mixtures for 3D printing was also established for these mixtures.

An investigation into the bonding capabilities of 0.6 in. (15.2 mm) prestressing strands cast in belitic calcium sulfoaluminate (BCSA) cement concrete beams was performed to determine if the current ACI development length requirements for prestressing strands are applicable to BCSA cement. Portland cement and BCSA cement concrete beam specimens of one mixture design were cast, with varying concrete ages at prestress release. Transfer lengths were determined for 28 days after casting using surface strain measurements and strand end slip. Prestress losses were measured using vibrating wire strain gauges and were compared to the AASHTO and PCI/Zia et al. methods. Flexural tests were performed to determine if adequate flexural bond performance was achieved with the specified development length. The BCSA prestressed concrete beams performed at least as well as the portland cement control specimens with regards to transfer length, development length, and flexural performance even when prestress release was performed at 2 hours after casting. Measured prestress losses for BCSA cement concrete beams were significantly less than predicted using the currently available methods. More work is needed to extend these findings to other mixture designs and water-cement ratios (w/c).

An increase in the fill height of buried box culverts leads to an increase in the thickness of the slab and wall, as well as in the number or size of longitudinal slab reinforcements required to resist flexure. This geometrical configuration imposes a shear behavioral mode. This study focuses on determining the shear strength of reinforced concrete (RC) box culverts with uniformly distributed load at the top slab. A framework, consisting of several subframes, was designed to convert the single displacement applied at the top of the framework to the equivalent uniformly distributed forces at the top slab of the culvert, allowing a displacement control analysis algorithm to be performed. To validate the loading mechanism, using the proposed framework, the load was applied on the top of an RC beam in the laboratory, and numerical studies were conducted. After validation, two sizes of RC box culverts were experimentally and numerically investigated. The results from the experimental program and verified numerical models differed from ACI 318-14 formulation for the shear strength of top slabs of RC box culverts.

Disc. 109-S57/From the Sept.-Oct. 2012 ACI Structural Journal, p. 655. Development Length of Unconfined Conventional and High-Strength Steel Reinforcing Bars. (Paper by Amr Hosny, Hatem M. Seliem, Sami H. Rizkalla, and Paul Zia). Discussion by Jonathan Rivera, Bismarck Luna, and Andrew Whittaker. Disc. 109-S65/From the Nov.-Dec. 2012 ACI Structural Journal, p. 755. Bond Performance in Self-Consolidating Concrete Pretensioned Bridge Girders. (Paper by Young Hoon Kim, David Trejo, and Mary Beth D. Hueste). Discussion by José R. Martí-Vargas. Disc. 109-S66/From the Nov.-Dec. 2012 ACI Structural Journal, p. 767. Determining Slipping Stress of Prestressing Strands in Confined Sections. (Paper by Mohamed K. ElBatanouny and Paul H. Ziehl). Discussion by José R. Martí-Vargas. Disc. 109-S70/From the Nov.-Dec. 2012 ACI Structural Journal, p. 805. Shear Strength of Reinforced Concrete Girders with Carbon Fiber-Reinforced Polymer: Experimental Results. (Paper by C. Higgins, G. T. Williams, M. M. Michell, M. R. Dawson, and D. Howell). Discussion by Emil de Souza Sánchez Filho, Marta de Souza Lima Velasco, Júlio. J. Holtz Silva Filho, and Dario Vaca Diez-Busch. Disc. 109-S71/From the Nov.-Dec. 2012 ACI Structural Journal, p. 815. Longitudinal Joint Details with Tight Bend Diameter U-Bars. (Paper by Zhongguo John Ma, Qi Cao, Cheryl E. Chapman, Edwin G. Burdette, and Catherine E. W. French). Discussion by Dun Wang and Xilin Lu. Disc. 109-S73/From the Nov.-Dec. 2012 ACI Structural Journal, p. 835. Toward an Improved Understanding of Shear-Friction Behavior. (Paper by Kent A. Harries, Gabriel Zeno, and Bahram Shahrooz). Discussion by Vasiliki Palieraki, Elizabeth Vintzileou, and John F. Silva. Disc. 109-S73/From the Nov.-Dec. 2012 ACI Structural Journal, p. 835. Toward an Improved Understanding of Shear-Friction Behavior. (Paper by Kent A. Harries, Gabriel Zeno, and Bahram Shahrooz) Discussion by Dun Wang and Xilin Lu. Disc. 109-S73/From the Nov.-Dec. 2012 ACI Structural Journal, p. 835. Toward an Improved Understanding of Shear-Friction Behavior. (Paper by Kent A. Harries, Gabriel Zeno, and Bahram Shahrooz). Discussion by Alan H. Mattock. Disc. 109-S74/From the Nov.-Dec. 2012 ACI Structural Journal, p. 845. Slab Effects on Response of Reinforced Concrete Substructures after Loss of Corner Column. (Paper by Kai Qian and Bing Li). Discussion by Qingfeng He and Weijian Yi. Disc. 109-S78/From the Nov.-Dec. 2012 ACI Structural Journal, p. 889. Experimental Investigation on Punching Strength and Deformation Capacity of Shear-Reinforced Slabs. (Paper by Stefan Lips, Miguel Fernández Ruiz, and Aurelio Muttoni). Discussion by Andor Windisch.

Disc. 109-S51/From the September-October 2012 ACI Structural Journal, p. 595. Effect of Load Distribution and Variable Depth on Shear Resistance of Slender Beams without Stirrups. (Paper by Alejandro Pérez Caldentey, Patricio Padilla, Aurelio Muttoni, and Miguel Fernández Ruiz). Discussion by Shiming Chen and Long Miao. Disc. 109-S54/From the September-October 2012 ACI Structural Journal, p. 625. Methodological Aspects in Measurement of Strand Transfer Length in Pretensioned Concrete. (Paper by Ho Park, Zia Ud Din, and Jae-Yeol Cho). Discussion by José R. Martí-Vargas. Disc. 109-S63/From the September-October 2012 ACI Structural Journal, p. 715. Repair of Corroded Prestressed Concrete Piles of Harbor Landing Stages. (Paper by Tseng-Cheng Lin, Chyuan-Hwan Jeng, Chung-Yue Wang, and Ting-Hung Jou). Discussion by José R. Martí-Vargas.