An Investigation of the Mechanical and Physical Characteristics of Cement Paste Incorporating Different Air Entraining Agents using X-ray Micro-Computed Tomography

Improving the thermal insulation properties of cement-based materials is the key to reducing energy loss and consumption in buildings. Lightweight cement-based composites can be used efficiently for this purpose, as a structural material with load bearing ability or as a non-structural one for thermal insulation. In this research, lightweight cement pastes containing fly ash and cement were prepared and tested. In these mixes, three different techniques for producing air voids inside the cement paste were used through the incorporation of aluminum powder (AL), air entraining agent (AA), and hollow microspheres (AS). Several experiments were carried out in order to examine the structural and physical characteristics of the cement composites, including dry density, compressive strength, porosity and absorption. A Hot Disk device was used to evaluate the thermal conductivity of different cement composites. In addition, X-ray micro-computed tomography (micro-CT) was adopted to investigate the microstructure of the air-entrained cement pastes and the spatial distribution of the voids inside pastes without destroying the specimens. The experimental results obtained showed that AS specimens with admixture of hollow microspheres can improve the compressive strength of cement composites compared to other air entraining admixtures at the same density level. It was also confirmed that the incorporation of aluminum powder creates large voids, which have a negative effect on specimens’ strength and absorption.EC/H2020/841592/EU/Ultra-Lightweight Concrete for 3D printing technologies/Ultra-LightCon-3

Effect of glass-fiber rods on the ductile behaviour of reinforced concrete beams

Ductility can be defined as the “ability of material to undergo large deformations without rupture before failure”. The use of Glass-fiber reinforced polymer (GFRP) bars instead of steel in reinforcing concrete structures is currently encouraged by many structural engineers, especially for their lightness and non-corrosive properties. The study compared the ductile behaviour of beams reinforced with glass-fiber to beams reinforced with steel reinforcement. A total of eighteen beams divided into six groups, each group consists of three identical beams were experimentally tested to investigate their ductile behaviour. Another objective for this study is to evaluate the existing methods utilized to estimate ductility of glass-fiber reinforced beams.Diana finite element program was used before the experimental work to investigate the theoretical behaviour of the beams such as the moment-curvature relationship and distribution of stress and strain along the beam cross-section. The study concluded that, the conventional definitions of ductility are inappropriate for evaluation of the ductility of glass-fiber reinforced (GFR) concrete beams because the GFR have no yield point. Thus, there is a need for both quantitative and qualitative evaluations of ductility when using GFR in reinforced concrete members. The deformability factor and the performance factor for steel reinforced beams have the same trend as conventional ductility, especially the deformability factor. Thus, the deformability factor may be used as a comparison index for both steel reinforced beams and GFR beams. The deformability factor showed that, the ductile behaviour of GFR beams enhanced by increasing the GFR ratio. This may be referring to the increasing in the deformation capacity before failure for the beams that reinforced with high GFR ratio. Keywords: Ductility, Bond behaviour, Deformability, Glass-fiber reinforcement bars, RC beam

Developed Mathematical Model for Indeterminate Elements with Variable Inertia and Curved Elements with Constant Cross-Section

Issues such as analysis of indeterminate structural elements that have variable inertia as well as a curved shape still have no closed form solution and are considered one of the major problems faced by design engineers. One method to cope with these issues is by using suitable the finite element (FE) software for analyzing these types of elements. Although it saves time, utilization of FE programs still needs professional users and not all engineers are familiar with it. This paper has two main objectives; first, to develop simple mathematical models for analyzing indeterminate structural elements with variable inertia and that have a curved shape with constant cross section, this model is much easier to be used by engineers compared to the FE model. For simplicity and saving time, a MATLAB program is developed based on investigated mathematical models. The force method combined with numerical integration technique is used to develop these models. The developed mathematical models are verified using the suitable FE software; good agreement was observed between the mathematical and the FE model. The second objective is to introduce a mathematical formula to determine the accurate number of divisions that would be used in the mathematical models. The study proves that the accuracy of analysis depends on the number of divisions used in the numerical integration. The optimum number of divisions is obtained by comparing the output results for both FE and developed mathematical models. The developed mathematical models show a good agreement with FE results with faster processing time and easier usage

Seismic Analysis of RC High-Rise Buildings Rested on Cellular Raft

This paper includes the investigation of the soil–structure interaction (SSI) effect on the seismic response of 20 and 30-story reinforced concrete moment resisting frames (MRFs) rested on a piled raft foundation using the direct approach. After that, a study is conducted to show the impact of using a cellular raft instead of the designed solid raft on the dynamic response of the building. A study is introduced to select the best gap size for the cellular raft. The soil model is assumed as a single layer of sandy clay. Time history analysis by the direct integration method is performed under seven earthquake records (El-Centro, Northridge, Kobe, Chichi, Friuli, Kocaeli, and Loma), which are scaled to the Egyptian Code for Loads (ECP-201) response spectrum using a full 3D model by a finite element software named (Midas GTS NX). It is concluded that considering SSI significantly affects the dynamic response of high-rise buildings, and using cellular rafts generally leads to a decrease in their dynamic response

Seismic Analysis of RC High-Rise Buildings Rested on Cellular Raft

This paper includes the investigation of the soil–structure interaction (SSI) effect on the seismic response of 20 and 30-story reinforced concrete moment resisting frames (MRFs) rested on a piled raft foundation using the direct approach. After that, a study is conducted to show the impact of using a cellular raft instead of the designed solid raft on the dynamic response of the building. A study is introduced to select the best gap size for the cellular raft. The soil model is assumed as a single layer of sandy clay. Time history analysis by the direct integration method is performed under seven earthquake records (El-Centro, Northridge, Kobe, Chichi, Friuli, Kocaeli, and Loma), which are scaled to the Egyptian Code for Loads (ECP-201) response spectrum using a full 3D model by a finite element software named (Midas GTS NX). It is concluded that considering SSI significantly affects the dynamic response of high-rise buildings, and using cellular rafts generally leads to a decrease in their dynamic response

Effect of different expanded aggregates on durability-related characteristics of lightweight aggregate concrete

Lightweight aggregate concrete (LWAC) has relatively larger porosity than conventional concrete, mainly due to the incorporation of porous lightweight aggregates. The types of used lightweight aggregates are critical in determining the physical properties of LWAC, and it is therefore important to examine their effects on the durable characteristics of the material. To perform comparative analysis, the concrete mixture designs with two theoretical density classes were developed. The mixture composition for each class was constant and the only variable parameter was the type of the used lightweight aggregates-expanded glass (Liaver®), expanded clay (Liapor®), and foam glass (Ecoglas®). Accordingly, their pore characteristics and durability-related properties, such as sorptivity, open water porosity, and water penetration depth, were examined. To understand these phenomena, the permeable characteristic, tortuosity, was also calculated using a numerical approach incorporating X-ray micro-computed tomography. The examined results confirm that the durability characteristics of LWAC are strongly affected by the used aggregate types and are highly correlated with their pore structures. In terms of permeable characteristics, expanded glass is the most beneficial material among the used particles, and the systematic approach in this study can be used to examine the durability characteristic of LWAC.EC/H2020/841592/EU/Ultra-Lightweight Concrete for 3D printing technologies/Ultra-LightCon-3

Preparation and Characterization of Ultra-Lightweight Foamed Concrete Incorporating Lightweight Aggregates

Increasing interest is nowadays being paid to improving the thermal insulation of buildings in order to save energy and reduce ecological problems. Foamed concrete has unique characteristics and considerable potential as a promising material in construction applications. It is produced with a wide range of dry densities, between 600 and 1600 kg/m3. However, at a low density below 500 kg/m3, it tends to be unstable in its fresh state while exhibiting high drying shrinkage in its hardened state. In this study, lightweight aggregate-foamed concrete mixtures were prepared by the addition of preformed foam to a cement paste and aggregate. The focus of the research is the influence of fly ash, as well as fine lightweight aggregate addition, on the properties of foamed concrete with a density lower than 500 kg/m3. Concrete properties, including stability and consistency in the fresh state as well as thermal conductivity and mechanical properties in the hardened state, were evaluated in this study. Scanning electron microscopy (SEM) was used to study the microstructure of the foamed concrete. Several mixes with the same density were prepared and tested. The experimental results showed that under the same bulk density, incorporation of fine lightweight aggregate has a significant role on compressive strength development, depending on the characteristics of the lightweight aggregate. However, thermal conductivity is primarily related to the dry density of foamed concrete and only secondarily related to the aggregate content. In addition, the use of fine lightweight aggregate significantly reduces the drying shrinkage of foamed concrete. The results achieved in this work indicate the important role of lightweight aggregate on the stability of low-density foamed concrete, in both fresh and hardened states