Retarders are very important during the production of cement-based materials. The delay in setting might be helpful in avoiding negative phenomena related to the long-term transport of the fresh concrete mix, unforeseen breaks in the transport, or laying of concrete. These admixtures prevent the local temperature rise of the concrete, and thus the formation of cracks and also extent the workability. Set-retarders provide a correct development of the microstructure and the undisturbed setting and hardening of cement which lead to higher strengths of cement-based materials. An investigation of the cement mortar with potassium methylsiliconate (MESI) applied as set-retarding admixture was carried out. Siliconates are a highly alkaline water solution of methylsiloxane resin in the potassium or sodium hydroxide. The study involved the cement paste and mortar with three dosages (1%, 2%, and 3% per cement mass) of organosilicon admixture. So far, the siliconates were not applied as admixtures for cement mortar or concrete. The mortar specimens were tested for compressive strength after 1, 2, 7, and 28 days and frost resistance after 25 freeze-thaw cycles. Moreover, the impact of the methylsiliconate admixture on the hydration (by isothermal calorimetry) and setting time of the ordinary Portland cement was also studied.

The purpose of this symposium and special publication is to recognize and honor Professor Amin Ghali’s outstanding long-term dedication to the concrete industry. Dr. Ghali obtained his B.Sc. and M.Sc. degrees in Civil Engineering from Cairo University, Cairo, Egypt, respectively in 1950 and 1954, his Ph.D. from Leeds University, England in 1957. He spent ten years in engineering practice before joining at the University of Calgary, AB, Canada as a professor in 1966. Dr. Ghali has developed the revolutionary, multi-patented and globally used, headed-stud shear reinforcement systems for concrete flat slabs; he has been a consultant for a number of major international structures, including offshore structures, multi-story buildings, bridges, and tanks. Dr. Ghali authored over 300 papers and eight patents. In 15 editions and 6 translations, his books include: Structural Analysis Fundamentals (2022), Structural Analysis: A Unified Classical and Matrix Approach (2017), Circular Storage Tanks and Silos (2014), and Concrete Structures: Stresses and Deformations (2012). Professor Ghali has served the industry in many ways, including his role as a voting member of ACI Committee 435, Deflection of Concrete Building Structures, 343, Concrete Bridge Design, and 421, Design of Reinforced Concrete Slabs. Jointly with associates at University of Calgary, his research on punching shear design and control of long-term deflection enables design of affordable concrete floors. Dr. Ghali served as expert, providing technical testimony, for a number of complicated engineering cases. Dr. Ghali received a number of teaching and research excellence awards over his long career, and was elected a Fellow of ACI, ASCE, CSCE, and CAE; in 2017, he received the Top 7 Over 70 Award for his outstanding continued research and engineering contributions. The papers found in this SP publication encompass a broad overview on the important issues related to punching shear resistance and sustainable serviceability of flat plates from both a theoretical and design perspectives. These papers formed the basis of presentations made at the Amin Ghali Symposium on Design of Structural Concrete Slabs for Safety Against Punching and Excessive Deflection held at the ACI Fall 2020 Virtual Convention, on October 25, 2020. Twelve presentations were made in two sessions by those who have worked closely with Dr. Ghali in his areas of interest. The SP includes nine papers on design of concrete floors for punching and for serviceability. The sessions were sponsored by ACI Committee 421, Design of Reinforced Concrete Slabs. All papers in this publication were reviewed by at least two recognized experts in accordance with ACI review procedures. Special thanks are extended to all who helped to make the two technical sessions and accompanying publication a success.

Traditionally, a time-varying mass system is viewed as the motion of moving bodies exiting or colliding with the system, such as rockets. A standing structure is not typically considered a time-varying mass system, but a silo during discharge of the infill is a subtle time-varying mass structure. Slender silos and silos with insufficiently stiffened supports are vulnerable to excessive vibration (silo quaking) and loud disruptive noises (silo honking) caused by the flow of the exiting masses. Using principles of mechanics and conservation of momentum, the equation of motion of such systems can be formulated to incorporate the discharge rate, material properties and the time-dependent characteristics of the system (mass, damping and stiffness). In this paper, the acceleration and mass flow of granular fill in a perspex tubing during discharge have been reproduced to simulate silo honking. By controlling the majority of influential factors, the replication of a small-scale silo design was possible with the repeatability of silo honking achieved in a controlled environment. A comparative study between discharge testing results of the sand fill with 0% (control), 5% and 10% moisture content shows that increasing the moisture content of the fill reduces the vibrational effect on the silo walls, and in turn reduces the magnitude of silo honking. Further, the effect of the sudden mass loss on a system of reinforced concrete columns depicting that of silo supports is investigated. The results show the exponential changes in the acceleration and velocity responses of the structure when subjected to a sudden mass loss. Finally, notes on how to consider the system of the forces in the silo structure based on the existing silo theory are provided.

This paper presents the experimental results of prestressed steel fibre reinforced concrete (SFRC) beams and it compares analytical model predictions with these results. Six beams were subjected to a force-controlled four-point bending test until failure. The three investigated parameters were the fibre dosage, the amount of prestressing force and the presence of shear reinforcement. During the test, failure mode and load, as well as deformations, displacements and cracking pattern properties were observed by means of conventional measurement devices and advanced optical techniques, including Bragg grated optical fibres and digital image correlation technique. Additionally, material properties were determined according to standardized European tests. The experimental results were compared to analytical predictions according to shear design equations in Model Code 2010. For the six beams, an average experimental-to-predicted failure load ratio of 1.43 was found with a coefficient of variation of 7.2%. Furthermore, four other analytical models for shear design of SFRC are investigated, namely DRAMIX Guideline, RILEM TC 162-TDF sigmaepsilon method, CNR-DT 204/2006 model and a model proposed by Soetens. All models underestimate the shear capacity of prestressed SFRC beams. The underestimation increases for a higher prestress level, whereas the correlation with the fibre dosage varies within the models.

The need for the assessment of structures subjected to natural and man-made hazard scenarios is steadily increasing. The analysis of a building structure with regards to potential progressive collapse as the result of a single hazardous event requires the realistic assessment of the residual capacity of structural members after the initial event. Common current building codes provide little guidance in the establishment of relevant loading scenarios and the assessment of structural members subjected to extreme loads. Using extreme loading from impact or close-in detona-tions as an example, a design path is outlined describing (1) the establishment of relevant hazard scenarios based on risk analysis, (2) the analysis of structural members subjected to high speed dynamic loading using hydrocodes, and (3) employing an efficient rigid-body spring model to analyze the entire structure subjected to potential progressive collapse. After initial member failure, the utilization of the remaining structural elements as established under regular dead and live loads is compared to the newly required capacity after the event. The degree of utilization of the remain-ing structural members after an event is amplified by additional loads redistributed from the failed member(s) and the damage caused by the initial event.