Topology optimization of double-curved double-layer grids

A topology optimization procedure for double layer grids which have square-on-square configuration and top and/or bottom layers are curved in one or two directions is presented. The number of nodes is treated as design variables during optimization process; as a result, the number of members varies. The configuration of grid structures is generated using the graph product operations. The coordinates of nodes and the cross sections of members are taken as continuous and discrete design variables, respectively. As an optimizer, a new swarm based optimization algorithm called Artificial Bee Colony algorithm is used. A design example is included to show the applicability of the presented procedure for optimization of double-curved double-layer grids

Mechanical and Physical Properties of Autoclaved Aerated Concrete Reinforced Using Carbon Fibre of Different Lengths

In this study, series of tests have been conducted to indicate the mechanical and physical properties (compressive strength, flexural strength, dry density, thermal conductivity and shrinkage) of autoclaved aerated concrete (AAC) reinforced with carbon fibres of different lengths. AG2/350 AAC block specimens without carbon fibre were prepared as a control specimen. The mixtures were prepared by replacing 0.5% weight of cement in the AAC with 4 mm, 6 mm, 12 mm length carbon fibres and these mixtures were poured into moulds and subjected to 58 °C for 4 hours to expand until reaching workable hardness. After preliminary curing, the produced AAC specimens were subjected to 180 °C and pressure of 11 bar for 6 hours in a steam cure until required hardness. The mechanical and physical properties of the reference and the fibre reinforced AAC specimens were determined and compared to each other. As a result, the use of 12 mm fibre reinforcement in AAC gave the best performance in comparison to the other fibre reinforcements of different lengths by increasing compressive strength for 10.63%, flexural strength of 31.48% and thermal conductivity up to 4.23% while reducing the shrinkage ratio to 51.47%. Herein for the specimen using 0.5% replacement of the AAC in weight with 12 mm carbon fibre is recommended

Investigating of Mechanical Properties of Mortars Based on Fly Ash and Blast Furnace Slag Activated with Alkali

Alkali activated mortars obtained from granulated blast furnace slag and fly ash were used instead of Portland cement by activating with alkali. Sodium silicate and sodium hydroxide were activated blast furnace slag and fly ash. Mortar samples were prepared 40x40x160 mm as prismatic samples according to TS EN 196-1 and they were cured at room temperature. Compressive and flexural strength of the mortar samples including blast furnace slag and fly ash were investigated by experimenting

An Atomic Force Microscope with Dual Actuation Capability for Biomolecular Experiments

We report a modular atomic force microscope (AFM) design for biomolecular experiments. The AFM head uses readily available components and incorporates deflection-based optics and a piezotube-based cantilever actuator. Jetted-polymers have been used in the mechanical assembly, which allows rapid manufacturing. In addition, a FeCo-tipped electromagnet provides high-force cantilever actuation with vertical magnetic fields up to 0.55 T. Magnetic field calibration has been performed with a micro-hall sensor, which corresponds well with results from finite element magnetostatics simulations. An integrated force resolution of 1.82 and 2.98 pN, in air and in DI water, respectively was achieved in 1 kHz bandwidth with commercially available cantilevers made of Silicon Nitride. The controller and user interface are implemented on modular hardware to ensure scalability. The AFM can be operated in different modes, such as molecular pulling or force-clamp, by actuating the cantilever with the available actuators. The electromagnetic and piezoelectric actuation capabilities have been demonstrated in unbinding experiments of the biotin-streptavidin complex

Nanomechanics on FGF-2 and Heparin Reveal Slip Bond Characteristics with pH Dependency

Fibroblast growth factor 2 (FGF-2), an important paracrine growth factor, binds electrostatically with low micromolar affinity to heparan sulfates present on extracellular matrix proteins. A single molecular analysis served as a basis to decipher the nanomechanical mechanism of the interaction between FGF-2 and the heparan sulfate surrogate, heparin, with a modular atomic force microscope (AFM) design combining magnetic actuators with force measurements at the low force regime (1 × 101 to 1 × 104 pN/s). Unbinding events between FGF-2–heparin complexes were specific and short-lived. Binding between FGF-2 and heparin had strong slip bond characteristics as demonstrated by a decrease of lifetime with tensile force on the complex. Unbinding forces between FGF-2 and heparin were further detailed at different pH as relevant for (patho-) physiological conditions. An acidic pH environment (5.5) modulated FGF-2–heparin binding as demonstrated by enhanced rupture forces needed to release FGF-2 from the heparin-FGF-2 complex as compared to physiological conditions. This study provides a mechanistic and hypothesis driven model on how molecular forces may impact FGF-2 release and storage during tissue remodeling and repair

Fresh and Hardened Properties of Cementitious Composites Incorporating Firebrick Powder from Construction and Demolition Waste

Firebricks are generally used in furnace basins where glass, ceramics, and cement are produced. Firebricks have an important place in construction and demolition waste (CDW). However, there is a limited understanding of the effects on fresh and hardened state properties of cementitious composites. This study investigates the mechanical, physical, and microstructural properties of cementitious composites incorporating firebrick powder (FBP) from CDW. In this regard, the FBP was used at 5, 10, 15, 20, and 25% replacement ratio by weight of cement to produce cementitious composites. The consistency, setting characteristics, and 3, 7, and 28 days compressive and flexural strength tests of produced cementitious composites were performed. In addition, ultrasonic pulse velocity, water absorption, porosity, unit weight, and microstructure analysis of cementitious composites were conducted. As a result, the 28-day compressive strength of the cementitious composite mortars containing up to 10% firebrick powder remained above 42.5 MPa. The flow diameters increased significantly with the increase of the FBP. Therefore, it has been determined that the FBP can be used up to 10% in cementitious composites that require load-bearing properties. However, FBP might be used up to 25% in some cases. Using waste FBP instead of cement would reduce the amount of cement used and lower the cost of producing cementitious composites

Physical and permeability properties of cementitious mortars having fly ash with optimized particle size distribution

Sevim, Ozer/0000-0001-8535-2344; Demir, Ilhami/0000-0002-8230-4053WOS: 000457506100025Gradation of powder materials is often avoided in pozzolanic materials, such as fly ash and slag. Without good gradation, powder materials result in high void ratios similar to the case of aggregates and the products obtained after hydration would still have voids. It is therefore necessary to optimize the particle size distributions (PSDs) of pozzolanic materials for improved compactness. This study calculated the PSDs of fly ash using a vacuum sieve in accordance with the Dinger-Funk PSD modulus. The optimal PSD was defined, and the compressive strength of fly ash-blended cement mortars at 7, 28 and 90 days was explored. Properties including water absorption capacity, dry density, rapid chloride permeability and consistency of mortars having optimized fly ash compositions were analysed by varying the replacement levels. Results reveal that the water absorption capacity of the optimized fly ash-blended cement mortar was lower than that of the blended cement mortar having non-optimized fly ash. Moreover, at 90 days, the chloride permeability of the cement mortar blended with optimized fly-ash improved up to 39.1% when compared to that of blended cement mortar having non-optimized fly ash. The results showed that it is possible to use 20% optimized fly ash instead of 10% non-optimized fly ash by simply changing the PSD of fly ash used. Findings of this study clearly show that even slight modifications in the PSDs of pozzolanic materials can make marked contributions to the certain properties of mortars.Scientific and Technical Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [215M081]The authors gratefully acknowledge the financial assistance of the Scientific and Technical Research Council of Turkey (TUBITAK) provided under Project: 215M081

Optimization of fly ash particle size distribution for cementitious systems with high compactness

Sevim, Ozer/0000-0001-8535-2344; Demir, Ilhami/0000-0002-8230-4053WOS: 000457659600010Compactness is of special importance for aggregates in concrete; however, the particle-size distribution (gradation) of powdery ingredients is commonly disregarded especially for pozzolanic materials such as fly ash. Without good gradation, powdery materials will result in higher void ratios, as in the case of aggregates, and the products obtained after hydration will still have some voids. Using a vacuum sieve, this study found the particle-size-distribution of fly ash in accordance with the Dinger-Funk particle-size distribution modulus, q, and explored the effects of various fly ash particle-size distributions on the compressive and flexural strengths of 7-, 28- and 90-day-old fly ash-blended cement mortars. After defining the optimal size distribution, the mechanical properties of cement mortars were assessed for several fly ash replacement levels. Results reveal that q of 0.4 yields the best mechanical property results. Further, the cement mortar with a 20% fly ash replacement level and a previously optimized particle-size distribution offered improved mechanical properties and high-compactness results over the control cement mortar after 90 days. Experimental results clearly indicate that only by properly adjusting the particle size distribution of fly ash used in the mixtures, better mechanical properties than the control mixtures without any fly ash addition can be achieved at a fly ash replacement ratio of 20%. The findings of current study are believed to greatly contribute to new lines of research on more effective replacement techniques for different pozzolanic materials without risking basic properties expected from cement-based materials. (C) 2018 Elsevier Ltd. All rights reserved.Scientific and Technical Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [215M081]The authors gratefully acknowledge the financial assistance of the Scientific and Technical Research Council of Turkey (TUBITAK) provided under Project: 215M081

Effect of sulfate on cement mortars containing Li2SO4, LiNO3, Li2CO3 and LiBr

Sevim, Ozer/0000-0001-8535-2344WOS: 000413879400005The purpose of this study is to explore the influence of sulfate on the fresh and hardened mortars containing lithium additives added with the aim to prevent alkali-silica reaction (ASR). Four different types of lithium additives (Li2SO4, LiNO3, Li2CO3 and LiBr) were added to the cement at the ratios of 0.5%, 1%, 1.5%, and 2% by mass in order to produce mortar specimens. Influence of sulfate on the specimens was then investigated. Used in order to keep the expansion under control, expansion characteristics and mechanical properties of Li2SO4, LiNO3, Li2CO3 and LiBr were defined. Initial setting and final setting tests were conducted on the cement pastes as per the provisions of TS EN 196-3 standard. Flexure and compressive tests were conducted in accordance with TS 196-1 in order to identify the mechanical properties of cement mortars. Prisms of 25 x 25 x 285 mm in dimension were produced as per ASTM C 1012-95 in order to measure the length change of the cement bars and results were analyzed. The results showed that Li2CO3 among the other lithium additives was effective in shortening the initial setting and final setting times, while LiNO3 and LiBr additives gave the best results in terms of strength and length change when tested for 1% additive ratio by mass. The highest length change was observed for the specimens with Li2CO3 cured both in water and sulfate solution. The lowest length change was observed for the specimens with LiNO3 cured both in water and sulfate solution. 1% LiNO3 additive gave the best results under sulfate effect for all test days. The length change of cement mortar with 1% LiNO3 additive was decreased by 53%, 25%, and 41% under sulfate effect for the 90th, 180th, and 360th day, respectively. It is believed that the use of LiNO3 and LiBr additives at the ratio of 1% by mass will reduce the unfavorable influence of sulfate. Li2CO3 and LiSO4 should not be used because they have negative effects on mechanical properties and length changes. (C) 2017 Elsevier Ltd. All rights reserved

Effects of sulfate on cement mortar with hybrid pozzolan substitution

Sevim, Ozer/0000-0001-8535-2344; Demir, Ilhami/0000-0002-8230-4053WOS: 000433239500001Sulfate is one of the most important chemical risks which affect the durability of concrete and reinforced concrete structures. Therefore, this study investigates the effects of sulfate on blended cement mortars. In this paper, cement mortar specimens were prepared with the substitution of CEM I 42.5 R cement with Fly ash + Bottom ash + Blast-furnace Slag at the ratios of 5%, 10%, 15%, and 20% along with a control specimen without additives. These prepared cement mortar specimens were then cured for 2, 7, 28, 90, 180, and 360 days either in potable water or 10% sodium sulfate (Na2SO4) solution. Cement paste specimens were subjected to the initial setting, final setting, and volumetric expansion tests in accordance with the TS EN 196-3 standard. Cured for 2, 7, 28, 90, 180, and 360 days, cement mortars were subjected to compressive strength tests as per the TS EN 196-1 standard while length change tests were conducted as per the ASTM C 1012 standard. It was found that the compressive strength of cement mortars blended with 5% Fly ash + Bottom ash + Blast-furnace Slag cured in sodium sulfate for 360 days was approximately 2% higher than that of the cement mortar without additives. The length change of specimens obtained from cured in sodium sulfate solution shows best results in higher additive ratio. These all length changes ratio are greater than 0.087% ratio which is maximum length change expansion in potable water. This study suggests that 15% and 20% additive ratios are effective in reducing unfavorable effects of sulfate. (C) 2018 Karabuk University. Publishing services by Elsevier B.V