Scielo RSS <![CDATA[Revista de la construcción]]> vol. 20 num. 2 lang. es <![CDATA[SciELO Logo]]> <![CDATA[Strength and durability of roller compacted concrete with different types and addition rates of polypropylene fibers]]> Abstract Roller compacted concrete (RCC) is a relatively new alternative construction material that can be used in road and dam constructions by allowing rapid use after production and the use of conventional building materials in production. RCC, which can be produced with low water/cement ratio, is one of the rigid road pavement types and shows similarity to flexible road pavements with the production technique. Different types of fibers such as steel and polypropylene (PP) are used in concrete roads with the aim of preventing cracks, reducing the pavement thickness and increasing the permissible joint gap. In this study, flexural strength, compressive strength, unit weight, water absorption, ultrasonic pulse velocity, modulus of elasticity and freeze-thaw resistance were determined in roller compacted concretes produced by using two different polypropylene-based fibers. In RCC design, fiber addition was insufficient to improve concrete properties in terms of strength and durability. It has been observed that there was a 14.4% reduction in compressive strength with 0.20% fiber inclusion, and a 46.8% reduction in compressive strength with 0.50% fiber inclusion. Polypropylene fiber inclusion increased the water absorption percentages and decreased the specific weights of fiber reinforced roller compacted concretes. However, roller compacted concretes produced with PP-fiber exhibited a good performance under freeze-thaw attack. <![CDATA[Enhanced quadratic approximation integrated with butterfly optimization: a new search algorithm tested on structural and mathematical problems]]> Abstract The Butterfly Optimization Algorithm (BOA) is a swarm-based technique, inspired by mating and food searching process of butterflies, developed last year. Experiments indicate that the BOA provides substantial exploration capability on conventional unconstrained benchmark problems, however for the cases with more complex and noisy domains the algorithm can easily be trapped into local minima due to its restricted exploitation behavior. To tackle this issue, the current study deals with introducing an alternative search strategy to explore the region of the search domain with high certainty. Such that, firstly a weighted agent is defined and then a quadratic search is performed in the vicinity of this pre-defined agent. This alternative search strategy is named Enhanced Quadratic Approximation (EQA) and it is combined with the BOA method to improve its exploitation behavior and provide an efficient search algorithm. Thus, obtained new method is named as Enhanced Quadratic Approximation Integrated with Butterfly Optimization (EQB) algorithm. Different properties of the proposed EQB are tested on mathematical and structural benchmark problems. Acquired results show that the introduced algorithm, in comparison with its parent method and some other well- established reported algorithms in the literature, provides a competitive performance in terms of stability, accuracy and convergence rate. <![CDATA[Mechanical properties of recycled aggregate concrete treated by variation in mixing approaches]]> Abstract Increased demand for natural aggregates (NA) due to infrastructural development has necessitated the use of alternative aggregates in the field of construction. One such option is the utilization of construction and demolition wastes, preferably named as recycled coarse aggregates (RCA) to produce a sustainable recycled aggregate concrete (RAC). Perhaps, the quality of RCA is usually poor due to the presence of adhered mortar on its surface affecting the strength and durability properties of RAC. Consequently, it is essential to improve the behavior of recycled aggregate concrete. In order to improve the recycled concrete aggregate, four different processing techniques such as two-stage mixing approach (TSMA), mortar mixing approach (MMA), sand enveloped mixing approach (SEMA) and double mixing approach (DMA) were used to improve the quality of RAC. This paper aims at providing a comparative study on the suitability of different mixing approaches and their influence over the fresh and hardened properties of recycled aggregate concrete. The performance behaviour of RAC was evaluated at 7, 14, 28 and 90 days with various percentage replacements of RCA at w/c ratios of 0.45 and 0.5. Experimental results indicate that the strength of concrete made of 100% RCA was equivalent to the target strength at 90 days. Also, among the various mixing processing techniques, MMA shows better fresh and hardened properties of concrete at different curing ages. Micro-structural investigations through SEM were performed to investigate the modification in the ITZ of the RAC through MMA approach. <![CDATA[Properties of concrete having treated recycled coarse aggregate and slag]]> Abstract The possibility of using substitute materials for aggregates and cement in concrete were studied and reported in this paper. Concrete mixtures with untreated recycled coarse aggregates (URCA) and treated recycled coarse aggregates (TRCA) were used to prepare two mix groups of without slag (Mix I) and with slag (Mix II). The recycled aggregates were treated with hydrochloric acid (HCl) having different molarities (0.1M, 0.3M and 0.5M) before used as a substitute material for virgin aggregate in concrete. The concrete mechanical, durability properties and morphology of concrete were examined through standard experiments and analysed. In both mix groups considerable improvement in all characteristics were identified in TRCA mixes than URCA mixes. Among the two mix groups the concrete mix with slag (Mix II) showed better durability characteristics than mix without slag (Mix I). The combination of TRCA and slag in concrete substantially increases the characteristics of concrete in all means. <![CDATA[Classification and resolution procedure for disputes in public construction projects]]> Abstract Construction sector, which is associated with approximately two hundred sub-sectors in terms of employment area, plays the role of locomotive sector in economic development of countries. This feature of the sector affects economy directly and indirectly. Despite this positive contribution of the sector, disputes are inevitable between parties -administration and contractor- in a bid, contract and implementation processes, which are parameters of the construction process. Formal judicial process applied for the purpose of resolving disputes encountered in construction projects that the public assumes the role of employer, takes a long time. Therefore, while contractor is exposed to financial losses, administration cannot conclude public investment. In the study; disputes in public construction projects are classified, and proposals preventing disputes are presented. In this scope, firstly, 174 of 10591 disputes submitted to Court of Cassation, and 84 of 102 disputes submitted to Directorate of High Technics Board are selected regarding public construction projects. In the second stage, parameters causing disputes are classified under six main items. Thirdly, reasons of the disputes for each classification are detailed, and then proposals are presented for prevention of the disputes based on FIDIC (International Federation of Consulting Engineers) contract forms. Finally, a resolution procedure is developed for the processes including bid, contract and implementation phases based on FIDIC. By the presented proposals for GCCW (General conditions of construction works) official resolution paths can be reduced to a minimum, and the processes result positively for administration and contractors. It is concluded that the developed procedure is suitable as a practical tool for resolution process of the disputes in the public construction projects. <![CDATA[Mechanical properties of roller compacted concrete containing recycled concrete aggregate]]> Abstract The compressive strength, splitting tensile strength, pulse velocity and drop weight impact resistance of roller compacted concrete (RCC) mixtures containing recycled concrete aggregate (RCA) were investigated. The cement contents of the RCC mixtures were chosen as 150, 200 and 250 kg/m3. In addition to the control mixtures containing no RCA, 25, 50, 75 and 100 wt% of the crushed limestone aggregate was replaced with RCA. In this way, 15 RCC mixtures were prepared. The water content of RCC mixtures was determined by the maximum density method. The results showed that increasing the amount of recycled aggregate decreased the mechanical properties of the concrete. However, up to 25% replacement level, recycled aggregate had not a significant detrimental effect on the properties of RCC. Besides, the detrimental effect of RCA substitution was more pronounced in leaner mixtures and reduced by increasing the cement content of the RCC. <![CDATA[Long-term sulfuric and hydrochloric acid resistance of silica fume and colemanite waste reinforced metakaolin-based geopolymers]]> Abstract For this paper, silica fume (SF), slag (S), and colemanite waste (C) were added to metakaolin (MK)-based geopolymer composites and exposed to 10% (by volume) hydrochloric acid (HCl) and sulfuric acid (H2SO4) solutions for up to 12 months. Geopolymer composites were examined in terms of weight loss, compressive strength, and flexural strength at 3, 6, and 12 months in solutions. Furthermore, Scanning Electron Microscopy (SEM), Micro-computed Tomography (micro-CT), Fourier Transform Infrared Spectroscopy (FTIR), and X-ray Diffraction (XRD) analyses were carried out to examine the microstructure before and after acid attacks. An important decrease in flexural and compressive strengths was seen when geopolymer mortars were subjected to sulfuric and hydrochloric acid attacks. The main cause of this situation is the deterioration of the oxy-aluminum bridge (-Al-Si-O) when exposed to sulfuric and hydrochloric acid. The oxy-aluminum bridge (-Al-Si-O), the primary factor in the geopolymer matrix, plays a significant role in consolidating the gel and enhancing the bond formed between the matrix components. Despite this, geopolymer mortar samples maintain the aluminosilicate structure. Compared to hydrochloric acid, sulfuric acid is a stronger solution, resulting in a greater loss of compressive and flexural strengths. <![CDATA[An investigation of concrete stress-strain behavior by the image analysis method]]> Abstract Concrete is a composite load-bearing building material. The deformation behavior of load-bearing materials under load is vital for the building system. Investigation of these brittle and quasi-brittle behavior patterns at various load levels provides an advantage in the evaluation of mechanical properties. In this study, the deformations occurring within the concrete samples in different stress-strain regions were investigated using an image analysis technique. The experimental samples experienced elastic-limit loading for two hours to clearly monitor the deformations at elastic, plastic, and breaking points. For the microstructure studies, the samples were prepared with epoxy for image analysis. Thin-sections were taken from each series of epoxy-impregnated concrete test samples, examined under a microscope, and photographed. Deformation studies on the digital photographs were carried out by the image analysis method. The results show that crack formation and crack types change because of increased stress and deformations. Crack formations within the concrete are parallel to the loading direction and occurred mainly in the aggregate-cement-paste interface. At 85% of the ultimate stress, crack length was measured as 0.665-29.505 mm and crack width 0.180-4.128 mm, while the crack length was 0.305-32.688 mm and crack width were 0.106-2.906 mm at fracture stress. <![CDATA[Comparative analysis of stress distributions and displacements in rigid and flexible pavements via finite element method]]> Abstract In many countries of the world, rigid and flexible pavements are widely used. Some of the external factors such as stresses and displacements play major role in the design of pavement layers such as coating, base and sub-base. Although empirical formulas and methods were used in the calculation and design of the pavement layers, complexity of today's transportation engineering demands effectiveness of the empirical formulas were diminished. Nowadays complex problems can be easily simulated and solved thanks to the higher analysis capabilities of the computer-aided softwares. In this study, the stress distributions and displacements were examined under traffic loads in rigid and flexible pavements with different coating layer thicknesses (30 mm, 50mm, 70mm, 100 mm, and 150 mm) by using finite element method. As a result, the vertical displacement in the flexible pavements were obtained as 5% higher than the vertical displacement in the rigid pavements. Based on the stress distribution results, the stress values of flexible pavements were 60% lower than the stress values of the rigid pavements. Moreover, It was determined that the stresses in the rigid pavements remain in the coating layer, while the stresses in the flexible pavements reach the base and sub-base. In addition, regression models have been developed to predict stress and displacements by using layer thicknesses. High correlation and determination coefficient values (&gt; 0.90) were achieved based on the regression analysis both in flexible and rigid pavements. <![CDATA[Frictional properties between geocells filled with granular material]]> Abstract The parameters concerning the interaction between geocell and granular materials is required for the design of many geotechnical structures. With this in mind, a series of experiments using simple direct shear tests are conducted in order to understand the frictional properties between geocells filled with granular materials. The 54 test samples are prepared by filling the geocell with granular materials having three different gradations. These samples are tested at three different relative densities under three different normal stress levels. As a result, it was observed that interface resistance between the geocells filled with granular material is found to be generally greater than in the samples without geocells. Additionally, these samples with geocells are found to be stiffer; this is due to the fact that the samples with geocell gained more cohesion because geocells confined the grains within a restricted volume. <![CDATA[Dynamic responses of reinforced concrete slabs under sudden impact loading]]> Abstract Reinforced concrete (RC) slabs may be subjected to low-velocity impact effect in their service lives. In this study, it is aimed to investigate dynamic responses of two-way rc slabs. So, a total of 6 slabs with 500x500, 550x550 and 600x600 mm side lengths and having same thickness are both experimentally and numerically investigated under low velocity impact loading. Two different reinforcement configurations are used in the production of each slab. A drop test setup is designed for the experimental study. Besides, measurement devices such as accelerometer, lvdt, dynamic load cell, data logger and optic photocells are used in the experimental program. Experiments on the specimens are carried out for the same level of impact energy. Acceleration, displacement and impact load values of slabs are presented by time dependent graphs. In addition, cracks and deformations are observed during tests. In the numerical part of this study, a detailed finite element procedure where explicit dynamic analysis is performed by Abaqus finite elements software is established. The simulations are performed for each test specimen under impact effect and analysis results are used in the verification of experimental results. The relationship between experimental and numerical studies is comparatively examined in terms of crack patterns and average ratios of accelerations, displacements, impact loads. Finally, it is considered that the proposed numerical model could be used in the evaluation of experimental results under impact loading. <![CDATA[Mechanical and durability properties of the concrete with copper slag]]> Abstract Increased Development in the field of construction with the use of sand, stones etc. depletes the natural resources and thus resulted in the scarcity of construction materials. Furthermore, generation of waste from several industries such as steel slag, copper slag, blast furnace slag etc. are being dumped in the nearby landfills leading to disposal problems. The scarcity of construction materials necessitated the utilization of suitable alternative materials with equivalent physical and chemical characteristics. This paper investigates the suitability of copper slag (CS) as a substitute to natural fine aggregate (NFA) in the concrete. The concrete mixes are prepared with 0%, 10%, 30%, 50%, 70% and 100% of copper slag at 0.45 w/c ratio. The behaviour of CS in the concrete was assessed by hardened properties such as compression, tension and flexure at 7, 14, 28 and 90 days and durability properties such as water absorption, porosity and chloride ion penetration at 56 days. Results indicate that the replacement of CS beyond 50% affects properties of the concrete; however increased curing improved the properties of the concrete at higher replacement levels. Characterization studies such as XRD and SEM was performed to examine the effect of CS on the properties of the concrete. <![CDATA[Effects of mortar compressive strength on out of plane response of unreinforced masonry walls]]> Abstract In this study, the out-of-plane response of infill walls that are widely used in Turkey and the surrounding regions were experimentally investigated. Several out-of-plane wall tests were performed in the laboratory, with the walls specimens produced with lateral hollow clay bricks (LHCB) and different mortar qualities. The walls were tested in their out-of-plane (OOP) direction under static load conditions and evaluated based on the load-bearing and energy dissipation capacities, crack propagations, mortar strengths, and initial stiffnesses. These walls are experimentally investigated to understand the effects of the mortar strength on the infill wall structural behaviors and to assess the effectiveness of the out-of-plane strength formulations. It was found that when the mortar strength is low, the first major crack occurs at the mortar, however, because of the arch mechanism efficiency in this situation the OOP load-carrying and energy dissipation capacities of unreinforced walls can be significantly increased. When the first major crack in the wall occurs in the brick itself, the arc mechanism is provided with delicate sections in the brick, which leads to strength decreasing in the walls. In this case, excessive deviations occur in the out-of-plane strength formulations estimates. This study shows that the arc mechanism, the damage start region and progress can change significantly unreinforced masonry (URM) infill walls behaviors. <![CDATA[Selection of insulation materials with PSI-CRITIC based CoCoSo method]]> Abstract The performance effect of construction on energy conservation substantially depends upon application of correct materials and energy saving methodologies. A sizable financial impact is accomplished through insulated walls. The criteria explaining the present wall insulating material options may have different values. Furthermore, they may alter in different aspects, i.e. higher values of certain criteria show a preferable status, while for others they denote an inferior status. In this framework, a variant of compromise is needed, which can be situated through multi-criteria assessment methodologies. To diminish the effect of different methodologies on computational results, few diverse techniques can be considered, with descriptions of the mean predicted values. Thus, drawbacks of certain multi-criteria assessment techniques could be compensated through others. A hybrid methodology through the combination of individual techniques will be accurate if there is a relationship between the values determined through diverse methodologies. In this study, the most efficient insulation material used at external walls is selected by using PSI-CRITIC based CoCoSo Method. The analytical results are important both from financial and engineering point of views as the applied methodology is commercially viable and practically implementable. Precise and up-to-date material properties are derived from the leading companies in the sector. <![CDATA[Influences of high temperature on mechanical properties of fly ash based geopolymer mortars reinforced with PVA fiber]]> Abstract In this study, a geopolymer composite containing PVA fiber was produced to recycle waste fly ash and obtain an eco-friendly binder. Mechanical properties of geopolymer mortars, produced by using F class fly ash which was activated with NaOH (sodium hydroxide), and reinforced by PVA (polyvinyl alcohol) fiber were investigated after high temperature effect. Geopolymer mortar samples produced by mixing with fly ash, sand, water and NaOH were placed in standard molds of 40×40×160 mm3. PVA fibers were used at percentages of 0.5%, 1% and 1.5% by volume in the experiment. Tests were performed on mortars exposed to high temperatures of 200°C, 400°C, 600°C and 800°C for physical and mechanical properties. For the specimens not subjected to high temperatures, an increase in the compressive strength of mortars containing PVA fibers was observed in comparison to mortar without PVA fiber. On the other hand, it was concluded that losses in compressive strength were less for mortar without PVA fiber when compared with the mortars containing PVA fibers. As a result of the modeling, the PVA ratio, which gives the optimum flexural and compressive strength, was determined as 1.47%. As a result of melting of PVA fibers under the effect of high temperature, 83.58% loss of compressive strength was determined in samples containing 1.5% PVA after 800ºC temperature.