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Volume 14, Number 1, July 2022

Due to the physical-chemical characteristics of some bottom ash (BA), there are technical, economic and environmental limitations to find a destination that will add value to it. In Brazil, this residue is eventually used for filling coal extraction pits or remains in sedimentation ponds, creating a susceptible panorama to environmental issues. The geopolymers binders are one of the alternatives to the proper use high amounts of these materials. In this work, geopolymeric binder pastes were produced with BA mixed to activators with different alkali contents (expressed as %Na2O), as well as the incorporation of soluble silicates (Ms content). The production of binary geopolymeric pastes based on the use of two industrial wastes: fluid catalytic cracking (FCC) and aluminum anodizing sludge (AAS), was also assessed. The content in mass of BA/FCC and BA/AAS ranged from 100/0, 90/10; 80/20 and 70/30. Systems with soluble silicates as activator in a molar ratio SiO2/Na2O of 1.0 (Ms = 1.0) and Na2O content of 15%, showed the best results of mechanical strength (42 MPa at day 28th). The improvement is up to 5X when compared to NaOH based systems. For systems with partial replacement of BA of 10% of AAS and 20% of FCC (80/20), the presence of soluble silicates was also effective to increase compressive strength.

Key Words
bottom ash; geopolymers; valorization of wastes

(1) Muriel S. Froener, Márlon A. Longhi, Fabiana de Souza, Ana Paula Kirchheim:
Building Innovation Research Unit, Universidade Federal do Rio Grande do Sul (NORIE/UFRGS), Av. Osvaldo Aranha, 99. 3o andar, Porto Alegre, Brazil;
(2) Muriel S. Froener:
Caxias do Sul University (UCS), Rua Francisco Getúlio Vargas 1130, Caxias do Sul, CEP 95070-560, Brazil;
(3) Erich D. Rodríguez:
Department of Structures and Civil Construction, Technology Centre, Universidade Federal de Santa Maria (UFSM), Santa Maria, Av. Roraima 1000, Prédio 10A, RS, Brazil.

The use of waste rubber in concrete can reduce natural aggregate consumption and improve some technical properties of concrete. Although there are several equations for estimating the mechanical properties of concrete containing waste rubber, limited numbers of machine learning-based models have been proposed to predict the mechanical properties of rubbercrete. In this study, an extensive database of the mechanical properties of rubbercrete was gathered from a comprehensive survey of the literature. To model the mechanical properties of rubbercrete, M5P tree and linear gene expression programming (LGEP) methods as two machine learning techniques were employed to achieve reliable mathematical equations. Two procedures of input variable selection were considered in this study. The crucial component ratios of rubbercrete and concrete age were assumed as the input variables in the first procedure. In contrast, the volumes of the coarse and fine waste rubber and the compressive strength of concrete without waste rubber were considered the second procedure of the input variables. The results show that the models obtained by LGEP are more accurate than those achieved by the M5P model tree and existing traditional equations. Besides, the volumes of the coarse and fine waste rubber and the compressive strength of concrete without waste rubber are better predictors of the mechanical properties of rubbercrete compared to the first procedure of input variable selection.

Key Words
linear gene expression programming; M5P model tree; machine learning; mechanical properties; rubbercrete

(1) Kaveh Miladirad, Majid Safehian, Alireza Sarkar:
Department of Civil Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran;
(2) Emadaldin Mohammadi Golafshani:
Department of Civil Engineering, Monash University, Melbourne, Australia.

Based on novel Galerkin's technique, the theoretical study gives a prediction to estimate the vibrations of FG rotating cylindrical shell. Terms of ring supports have been introduced by a polynomial function. Three different laws of volume fraction are utilized for the vibration of cylindrical shells. Variation frequencies with the locations of ring supports have been analyzed and these ring supports are placed round the circumferential direction. The base of this approach is an approximate estimation of eigenvalues of proper functions which are the results of solutions of vibrating equation. Each longitudinal wave number corresponds to a particular boundary condition. The results are given in tabular and graphical forms. By increasing different value of height-to-radius ratio, the resulting backward and forward frequencies increase and frequencies decrease on increasing length-to-radius ratio. There is a new form of frequencies is obtained for different positions of ring supports, which is bell shaped. Moreover, on increasing the rotating speed, the backward frequencies increases and forward frequencies decreases.

Key Words
backward and forward; cylindrical shell; location of ring; simply supported

Department of Mathematics, Govt. College University Faisalabad, 38000, Faisalabad, Pakistan.

In this article, the flexural and shear capacity of ultra-high-performance fiber-reinforced concrete beams (UHPFRC) using two kinds of rebars, including GFRP and steel rebars, are experimentally investigated. For this purpose, six UHPFRC beams (250 × 300 × 1650 mm) with three reinforcement ratios (ρ) of 0.64, 1.05, and 1.45 were constructed using 2% steel fibers by volume. Half of the specimens were made of UHPFRC reinforced with GFRP rebars, while the other half were reinforced with conventional steel rebars. All specimens were tested to failure in four-point bending. Both the load-deformation at mid-span and the failure pattern were studied. The results showed that utilizing GFRP bars increases the flexural strength of UHPFRC beams in comparison to those made of steel bars, but at the same time, it reduces the post-cracking strain hardening. Furthermore, by increasing the percentage of longitudinal bars, both the post-cracking strain hardening and load-bearing capacity increase. Comparing the experiment results with some of the available equations and provisions cited in the valid design codes reveals that some of the equations to predict the flexural strength of UHPFRC beams reinforced with conventional steel and GFRP bars are reasonably conservative, while Khalil and Tayfur model is un-conservative. This issue makes it essential to modify the presented equations in this research for predicting the flexural strength of UHPFRC beams using GFRP bars.

Key Words
flexural behavior; GFRP bar; steel rebar; Ultra-high-performance fiber-reinforced concrete (UHPFRC)

(1) Yousef Abbasi Parvin, Taleb Moradi Shaghaghi, Seyyed Saeed Mirrezaei, Yousef Zandi:
Department of Civil Engineering, Tabriz Branch, Islamic Azad University, Tabriz, Iran;
(2) Masoud Pourbaba:
Department of Civil Engineering, Maragheh Branch, Islamic Azad University, Maragheh, Iran.

The spiral case concrete (SCC) used in the underground powerhouse of large hydropower stations is complex, difficult to pour, and has high requirements for temperature control and crack prevention. In this study, based on the closed-loop control theory of "multi-source sensing, real analysis, and intelligent control", a new intelligent cooling control system (ICCS) suitable for the SCC is developed and is further applied to the Wudongde large-scale underground powerhouse. By employing the site monitoring data, numerical simulation, and field investigation, the temperature control quality of the SCC is evaluated. The results show that the target temperature control curve can be accurately tracked, and the temperature control indicators such as the maximum temperature can meet the design requirements by adopting the ICCS. Moreover, the numerical results and site investigation indicate that a safety factor of the spiral case structure was sure, and no cracking was found in the concrete blocks, by which the effectiveness of the system for improving the quality of temperature control of the SCC is verified. Finally, an intelligent cooling control procedure suitable for the SCC is proposed, which can provide a reference for improving the design and construction level for similar projects.

Key Words
intelligent cooling control; mass concrete; pipe cooling; spiral case structure; Wudongde hydropower station

(1) Zeyu Ning, Peng Lin, Jianshu Ouyang:
Department of Hydraulic Engineering, Tsinghua University, Beijing, China;
(2) Zongli Yang, Mingwu He:
China Three Gorges Projects Development Co., Ltd., Chengdu, China;
(3) Fangping Ma:
Guodian Dadu River Hydropower Development Co., Ltd., Chengdu, China.

Creep phenomenon affects the stability and integrity of concrete structures. An inaccurate prediction of these strains may lead to the appearance of cracks and excessive deflections which may cause in some cases the demolition of structures. In fact, the measured values of these uncontrolled strains appear often to be clearly different and larger than the expected ones. Therefore, an accurate prediction of concrete deformations is a necessity. As a matter of fact, the codified descriptions of this phenomenon are unreliable and don't consider the effect of admixtures. The physical nature of creep is not well understood and almost all creep models are mainly of empirical nature. To overcome this issue, a study of the correlation between different parameters affecting concrete creep is performed and a new model for predicting creep of concrete is elaborated. This new model considers the effect of admixtures, specifically the silica fume, in predicting concrete creep and allows an accurate prediction of this phenomenon. The proposed model is based on the observation of physical behavior of creep phenomenon. It targets at expressing creep compliance in terms of structural and environmental parameters. In fact, the experimental observations show that creep curves follow two kinetic regimes leading to a model called Phenomenological Creep Model. By adequate regressions and substitutions, and according to this model, we can express creep compliance in terms of structural, environmental parameters and admixture types and percentage. The proposed new Phenomenological Creep Model Silica Fume (PCM19SF) calculates accurately creep of concrete by considering the effect of silica fume.

Key Words
admixtures; concrete; creep; phenomenological creep model; silica fume

(1) Elise Zgheib, Rodolph Sawma, Judith El Khoury, Wassim Raphael:
Ecole Supérieure d'Ingénieurs de Beyrouth (ESIB), Saint-Joseph University, CST Mkalles Mar Roukoz, Po Box 11-514 Riad El Solh Beirut, 1107 2050, Lebanon;
(2) Elise Zgheib:
Le CNAM Institut Supérieur des Sciences Appliquées et Economiques, Beirut, Lebanon.

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