english GANESH BABU O., DANYA TR., SAKTHIESWARAN N, SURESH P., MUTHURAMASAN U.
Rezumat
Development of sustainable and energy efficient construction material has been the viewpoint of research efforts worldwide in recent years. Although the use of Portland cement is unavoidable, many efforts are being made to minimize the use of Portland cement in concrete to a greater extent in infrastructure applications. It is time to utilize new technology materials like geopolymers that offer waste utilization and emissions reduction with enormous ability. An alternate binding material to the OPC has been found out known as geopolymer concrete (GPC). In this study, GPC will be made of fly ash incorporating alccofine in various percentages of 5%, 10%,15% and 20% as partial replacement to fly ash. Zeolite was partially added to fine aggregate at 10%, 20%, 30% and 40%. Rubber fibers were added at 2% by the weight of binder. Alkaline activator for geopolymerisation was prepared by mixing Sodium hydroxide solution at 10M with Sodium silicate solutions are used. Control mix is casted for M30 grade concrete. The samples are proposed to be cured by hot-curing for 24 hours thus mechanical and durability properties were examined. Addition of zeolite at 30% and alccofine at 15% is found to be an optimal content in geopolymer content and when the concentration of zeolite in geopolymer concrete is increased the slump value decreases. The rubber fiber contents kept constant at 2%, only lesser voids are generated due to improper bonding between rubber fiber particles, which does not contribute more in compressive strength. Geopolymer presents denser microstructure, lower total pore volume and optimized pore structure compared to OPC paste and therefore geopolymer concrete is much more durable in an aggressive environment.
Cuvinte cheie
beton cu polimeri, cenușă de termocentrală, alccofine, zeolit, fibre de cauciuc
P. MARIA ANTONY SEBASTIN VIMALAN , G. LAVANYA
Rezumat
The influence of glass powder as fine aggregate when used in combination with calcined zeolite for the betterment of the workability and strength improvement of self compacting concrete was analyzed in the study. Initially the fresh state properties such as the passing ability, flowing ability and the filling capacity of the SCC were examined. Then the mechanical strength of the zeolite- glass powder containing self compacting concrete was investigated using compression, flexural and split tensile tests. The durability of the SCC was assessed by the water absorption, porosity, chloride permeability and sorptivity tests. The durability and strength results were validated with microstructure analysis such as XRD and scanning electron microscopy studies. Furthermore the Alkali – silica reactivity of the concrete was characterized to analyze the reactivity of the glass aggregates. The results show that the SCC with 30% of glass powder as fine aggregate replacement and 20% of cement replacement by zeolite showed overall better performance. Thus the use of calcined zeolite can reduce the expansiveness in concrete caused by reactive glass powder aggregates and is also an eco-friendly option to minimize the cement utilization thereby reducing the global warming.
Cuvinte cheie
durabilitate, pudră de sticlă, rezistență mecanică, microstructură, zeolit natural, beton autocompactant
MOBIN GHAVIDEL SHAHRBABAKI, ALI DELNAVAZ, MAJID GHASEMI, MOHAMMAD DELNAVAZ
Rezumat
The present study investigates the effect of aggregate type on the amount of chloride ion penetration in normal weight concrete (NWC) and lightweight concrete (LWC) samples under the influence of sulfate ion. To examine the effect of W/C ratio, all mixes are made with three different W/C ratios of 0.4, 0.45 and 0.5 in this research. Also, the amount of silica fume (SF) in three values of 0, 7% and 10% were substituted for cement to consider the effect of pozzolanic materials on the level of penetration of chloride and sulfate ions. Compressive strength tests, Capillary water absorption, electrical resistivity, Rapid chloride migration test (RCMT) and accelerated corrosion test were done on concrete samples with light-weight and normal aggregates. The results of these two concrete specimens were compared. The results showed that the corrosion rate of steel bar was higher with increasing ratio of W/C. Also, the mechanical and durability properties of concrete was improved by adding SF to the concrete mix design , resulting in the lowest corrosion rate in the two, chloride solution and combined magnesium sulfate - chloride solution. In addition, concrete samples in the chloride solution became more corrosive than the combined chloride - magnesium sulfate solution. Finally, a neural network model was developed to determine the chloride ion permeation coefficient and the corrosion rate of steel in normal and lightweight aggregates.
Cuvinte cheie
penerare ioni de Cl, sulfat de magneziu, silice ultrafină, coroziunea barelor de oțel pentru armătură, silice ultrafină
A.VISHNU, V. PONMALAR
Rezumat
This research mainly focuses on the durability of self-compacting concrete replaced with cement and Nano-metakaolin (NMK). NMK was prepared by heating kaolin at (760-780) oC sustaining for 2 hrs. NMK was used in this study by replacing cement by weight with 1, 2, 3, 4, 5 and 6 % individually. The optimal proportion of replacement of river sand by manufactured sand is 45 %. The consistency, initial and final setting of NMK were predicted and compared with ordinary Portland cement (OPC). Fresh concrete tests like slump flow, T50 cm, U Box, V-funnel, and hardened concrete tests like compressive tests were conducted at 7, 28, 60 and 90 days. Water absorption, Porosity test (Absorbency), Acid Attack, sulphate Attack, Indicator of Concrete’s Capability to Attack Chloride Ion Penetration (RCPT) tests were conducted to observe the durability of Self-compacting concrete (SCC). From the analysis it is clear shown that addition of NMK increases with 7, 28, 60, 90 and 180 days compressive strength and the optimum level was found to be 4 %. The fissure width had diminished by the incorporation of Nanometakaolin while reducing the calcium hydroxide (CH) and mediating calcium silicates to calcium silicate hydrate (C-S-H). The final consequences of compressive strength, durability and flow property shows that 4 % of Nanometakaolin by weight of cement increases the workability, strength and compromises the durable properties.
Cuvinte cheie
nanometacaolin, beton autocompactant, încercare rapidă de penetrare clorură (RCPT), lucrabilitate absorbantă
GOKHAN CALIS, MUHAMMET ENES AKPINAR SADIK ALPER YILDIZEL, MUSTAFA TOLGA ÇÖĞÜRCÜ
Rezumat
Due to high consumption of natural sources in the production of cement, scholars have been studying alternative materials that can replace cement in the concrete. Metakaolin and fly ash are used by scholars for their chemical properties and filler effect as pozzolanic material. In this study effect of PVA fiber, metakaolin and fly ash in concrete samples are investigated. The number of experiments to be carried out was reduced to 25 with the Taguchi optimization method, in this research. In addition, the recommended mixing ratios were obtained by this preliminary optimization study. Taguchi optimization were applied according to the experimental test results. F-value comparison of each ingredients were analyzed via ANOVA to list the most effective factors on the strengths based on the Taguchi optimization results. Later Response Surface Design was applied to the output parameters of the ANOVA and Taguchi methods to obtain better and detailed clarifications of relations between the input parameters and the strengths.
Cuvinte cheie
fibre PVA, beton armat cu fibră, optimizare
OZER SEVIM, MEHMET BARAN, ŞÜKRÜ DEMIR
Rezumat
Fly ash (FA) and granulated blast furnace slag (GBFS) produced as waste materials from coal power plants and iron/steel sector are commonly used in the concrete industry for partial substitution of cement. As the production of cement releases a substantial amount of carbon dioxide, its replacement with FA or GBFS reduces carbon dioxide emissions. This study explores the effects of FA and GBFS fineness determined by particle size distribution (PSD) on the hydration rate and compactness of cementitious materials. Firstly, FA and GBFS were classified to have three different fineness ranges with the help of PSDs without any grinding process: FA and GBFS without PSD, FA and GBFS with 0-25 µm PSD and FA and GBFS with 0-63 µm PSD. Then, flexural strength, compressive strength, and water absorption properties of cementitious composites containing FA and GBFS with four different replacement levels up to 20% wt. of cement and with three different fineness were investigated at curing ages of 7, 28, and 90 days. Results revealed that cementitious composites that contain FA and GBFS with lower PSD yield better mechanical and physical properties.
Cuvinte cheie
compozite pe bază de ciment analiză granulometrică, finețe, cenușă de termocentrală, zgură de furnal granulată
WEICHAO YING, GE ZHANG, YINGZI YANG
Rezumat
In winter construction, it is of crucial importance to predict the temperature field of concrete, to avoid frost damage, control the temperature gradient, and ensure the construction quality of concrete. In this study, a modified finite element model (FEM) considering the characteristics of winter construction was proposed to predict the temperature field of concrete. The freezing process of free water and the heat release of hydration varied with concrete temperature was involved in this model. Then, the temperature histories of two types of concrete placed at different subzero temperatures were monitored experimentally and simulated by using the modified FEM. Good agreement of these results confirms the validity and reliability of this model. Finally, some numerical experiments were performed to explore the effects of engineering parameters on the temperature field of early age concrete by using the validated finite element model. The results show the law of influence of concrete placing temperature and geometry, ambient temperature, and the thickness and thermal conductivity of insulation material on the concrete temperature field.
Cuvinte cheie
analiza elementului finit, construcție supusă la frig, domenii de temperatură, termoizolație
HUSSEIN HAKIM HASAN, RADU PASCU, DAN PAUL GEORGESCU
Rezumat
Sistemul cu plase de armare din fibre de carbon înglobate într-o matrice de mortar bicomponent pe bază de ciment (FRCM) reprezintă o metodă relativ nouă de consolidare care este utilizat în scopul îmbunătățirii rezistenței și ductilității structurilor din beton. Articolul prezintă un studiu comparativ al performanțelor unor stâlpi confinați cu FRCM rezultate atât prin efectuarea unor cercetări experimentale cât și prin aplicarea unor relații de calcul analitice și a metodei elementelor finite (FEM). S-au încercat 6 stâlpi, 2 stâlpi de referința neconsolidați, 2 stâlpi la care s-a aplicat un strat de FRCM și 2 stâlpi la care s-au aplicat 2 straturi de FRCM. Pentru analiza comportării stâlpilor s-a dezvoltat un model neliniar tridimensional FEM cu ajutorul programului Abaqus pentru fiecare din stâlpii încercați experimental. De asemenea comportarea stâlpilor sub solicitări a fost analizata în conformitate cu Eurocode 2 în scopul obținerii curbelor efort unitar - deformație specifică ale stâlpilor supuși la compresiune axială. Modelul de beton cu plasticitate deteriorată a fost atribuit componentelor din beton. Performanțele stâlpilor au fost evaluate în termeni de forța ultimă la compresiune și în deformații axiale și deformații specifice. Datele obținute experimental au fost comparate de asemenea cu cele rezultate prin aplicarea unor relații de calcul propuse de diverși cercetători.
Cuvinte cheie
stâlpi din beton, matrice pe bază de ciment armată cu fibră (FRCM), confinare, matodă element finit (FEM), model de deformare plastică a betonului (CDPM), model analitic
LEONID DVORKIN, VADIM ZHITKOVSKY, YURI RIBAKOV
Rezumat
The paper shows the use of activators for the hardening of cement-ash concrete, incl. passing when heating concrete. Such an activator is a composition of sodium fluorosilicate and naphthalene-formaldehyde superplasticizer. The addition of sodium fluorosilicate makes it possible to increase the early strength of the cement-ash binder, enhance the kinetics of pozzolanic reaction and reduce the drop in the strength of the cement-ash stone when it is heated to 800°C. Experimental dependences of concrete mixture water demand and concrete strength on the cement and aggregates consumption for different workability mixtures have been obtained. These dependences take into account the influence of complex admixtures of superplasticizer and sodium fluorosilicate that enabled to propose a method for design of ash and slag concrete compositions. The positive role of the proposed complex activating admixture on the change in strength and shrinkage of ash and slag concrete after drying and subsequent heating has been experimentally confirmed. A complex of experimental-statistical models of ash and slag concrete properties has been obtained, taking into account the influence of activation admixture, superplasticizer and sodium silicon fluoride consumption, cement-water ratio, temperature and the number of heating and cooling cycles.
Cuvinte cheie
beton rezistent la temperatură, cenușă de termocentrală, amestec cenușă - zgură, superplastifiant, fluorosilicat de sodiu
DENG CHEN, ZHI-HAI HE, AI-GUO WANG, TAO YANG
Rezumat
Shrinkage of cement-based materials may cause cracking in concrete structure under restrained conditions. In this study, light-burnt dolomite (LBD) as a mixture of periclase and calcite obtained by calcinations of dolomite at 750-850 °C was incorporated in Portland cement to compensate shrinkage of cement-based materials at early age. The results show that the water requirement for normal consistency of blended cement is increased with the increase of dosage, calcination temperature and holding time of LBD. The addition of 10% LBD calcined at 800 °C for 2.0 h can effectively enhance the compressive strengths of blended cement at all ages. This is due to that 10% LBD can improve the microstructure attributed to the filler effect and hydration reactivity of LBD. Furthermore, the hydration of periclase in LBD leads to the expansion of blended cement at early age, and increases the expansion value with the increase of dosage, calcination temperature and holding time of LBD.
Cuvinte cheie
dolomit ușor ars, rezistență, deformare, ciment aditivat
P. AMSAYAZHI, K. SARAVANA RAJA MOHAN
Rezumat
The study of High strength concrete with fibers had become the most popular topic as the demand for height and load carrying capacity of every infrastructure is increasing. The addition of fibers in concrete increases durability, tensile strength, toughness, energy absorption, high impact resistance, in terms of both static and dynamic loading. In this paper, the strength properties of glass fiber reinforced concrete as a structural element was investigated. Different ratios of GFRC mixes were designed, cast, tested, and compared with the results of compressive strength, tensile strength, flexural strength, and also impact strength.M50 grade of concrete was used in this study with five proportions (0, 0.5%, 1%, 1.5%, 2%) of Glass fibers. The impact strength test was analyzed using Weibull analysis to compare with the experimental data. The main objective of this study is to show how the increase in fibre percentage increased the strength of concrete.
Cuvinte cheie
fibră de sticlă, beton cu rezistență înaltă, rezistență la impact, metodă de rezistență Weibull, analiza numerică, proprietăți
B. SUGUMARAN, G. LAVANYA
Rezumat
Insufficient and ineffective curing may decrease the strength of self compacting concrete forming high shrinkage cracks and voids. The shrinkage due to evaporation is the main reason for the deterioration of concrete structures. The use of internal curing agents in combination with expansive agents can solve the problems of shrinkage and self desiccation caused due to self curing and has the potential for achieving predefined properties. The present research works aims at the production of self compacting concrete with higher strength and durability by utilizing GGBS, alccofine and nano metakaolin as cement admixture along with copper slag as partial substitute for fine aggregate. Several investigations were carried out to analyze the influence of using MgO based compounds as expansive agents in the concrete on the mechanical, fresh state and durability tests. The results show that addition of expansive agent provided desirable strength values and durability properties in the self compacting concretes. The use of highly free flowing concrete that are self compacting in nature with high strength and dimensional stability is also achieved due to the synergistic effect of expansive agents and mineral admixtures in the concrete.
Cuvinte cheie
beton autocompactant, nano metacaolin, alccofine, zgură de cupru, agent expansiune, agent de autoîntărire, rezistență, durabilitate
ALI SADRMOMTAZI, NEGAR GHASEMI KHAMENEH, REZA KOHANI KHOSHKBIJARI, MORTEZA AMOOIE
Rezumat
As a novel solution, to reduce or even eliminate the dependence on the ordinary Portland cement (OPC) which as an energy-intensive and highly polluting production, and simultaneously, for effectively using waste materials, Geopolymer concrete (GPC) has emerged. GPC is manufactured by using alkali-activated binders instead of OPC. In this study, the differences and impacts of the partial replacement of the Slag by the most common pozzolans such as Rice Husk Ash (RHA), Fly Ash (FA), Metakaolin (MK), Silica Fume (SF), and Zeolite on the durability of the Slag-based GPC are investigated. To evaluate the durability performance of the specimens, a series of tests including compressive strength (7, 28 and 90-days), Rapid Chloride Permeability Test (RCPT), Rapid Chloride Migration Test (RCMT) and Accelerated Corrosion Test (ACT) were performed. Also, the samples were exposed to Sulfuric acid solution in order to investigate the effect of this corrosive environment on the weight reduction and compressive strength changes of the mix designs. The results indicated that using up to 10% replacement of Slag in GPC with FA, SF and MK can improve the durability in RCPT, RCMT, and ACT and also can cause significant improvements in durability against Sulfuric acid in all replacement ratios.
Cuvinte cheie
beton geopolimeric, zgură, durabilitate, înlocuitori de lianți solizi
LINCHUN ZHANG, AILIAN ZHANG, QIAN WANG, YAN HAN
Rezumat
This study aimed to investigate the preparation of cement foamed mortar mixed with coal gangue power. Moreover, the following rheological parameters and compressive strength were determined. Additionally, a scanning electron microscope (SEM) was used to reveal its compressive strength`s inner mechanism. Results indicated that slump flow of fresh coal gangue power foamed mortar increased first and then kept stable with water-reducing agent. The increasing content of coal gangue power could descend the compressive strength of foamed cement mortar. Compressive strength of foamed cement mortar decreased linearly with foam content and ascended in the exponential or linear functions with volume density. The scanning electron microscope (SEM) images showed that many shapes of hydration products existed in the specimens. Moreover, the microstructure of specimens became denser with decreasing cement-sand ratios.
Cuvinte cheie
Mortar spumat, pulbere din gangă de cărbune, parametrii reologici, rezistență la compresiune, SEM
A. SIČÁKOVÁ, E. FIGMIGOVÁ
Rezumat
One of the progressive and currently rapidly developing methods for improving the properties of concrete with recycled aggregates is internal curing, which means the supply of curing water directly from the inside of the concrete. This article introduces two variants of internal curing of concrete with recycled brick aggregate (RBA) by pre-soaking process as a part of specific mixing course. The presented variants differ in the dosage of aggregates and water in the soaking process. Results of consistency, compressive strength, total water absorption capacity and capillary moisture content are analysed in terms of their change due to pre-soaking process, as well as due to time of processing the fresh concrete (90 minutes). The process of pre-soaking of RBA is beneficial for the consistency of concrete when evaluated immediately after mixing. For both the compressive strength and total water absorption capacity, the variant of pre-soaking is determining. Pre-soaking of only coarse RBA by amount of water derived of its absorbability (variant 1) gives better results than pre-soaking of all amount of aggregate by ½ of total mixing water (variant 2). The processing time 90 minutes does not adversely affect the compressive strength of concretes either with pre-soaked RBA or non pre-soaked RBA, even the strength increases slightly with processing time.
Cuvinte cheie
Beton, întărire internă, agregate din cărămidă reciclată, cenușă zburătoare, curs de amestecare, timp de amestecare
ALI SABERI VARZANEH, MAHMOOD NADERI
Rezumat
Today, it is significantly important to perform non-destructive tests to evaluate the quality of cement materials. However, in such tests, some parameters are typically measured indirectly to estimate the strength of the material by specific relations. Thus, the present study evaluates the compressive and flexural strengths of cement mortars reinforced with polypropylene fibers at different ages by using the slight-destruction twist-off and pull-off tests. For this purpose, using the linear and power regression analyses, the relationships between the results of the mentioned in-situ tests and the strengths of fiber-reinforced mortars were identified. Then, calibration diagrams were provided to translate the twist-off and pull-off results into the compressive and flexural strengths of the fiber-reinforced mortars. Also, given that the proper connection between cement materials and steel is one of the crucial issues in civil engineering, in this paper, has investigated the effect of polypropylene fibers on the shear and tensile bond strength between cement mortar and steel plates, using “Push-out”, “Twist-off” and “pull-off” tests. At the end, using the finite element method (FEM), the fiber-reinforced and non-fiber reinforced samples were modeled, analyzing the effects of fibers on the tests. The results indicated a high correlation coefficient between the experimental results and semi-destructive tests. Moreover, the addition of fibers improved the behavior of cement mortars subjected to compression. The modeling results of the in-situ tests revealed the delayed cracks and increased strengths of the fiber-reinforced mortars. Also, the obtained results revealed the marked effect of fibers in increasing the bond strength between the mortar and steel.
Cuvinte cheie
încercări semidistructive, metoda elementului finit, legătură, mortar, oțel
PAVLA BAUEROVÁ, PAVEL REITERMAN, VENDULA DAVIDOVÁ, EVA VEJMELKOVÁ, MAGDALENA KRACÍK ŠTORKÁNOVÁ, MARTIN KEPPERT
Rezumat
Linseed oil has been used as mortars admixture in times before the modern synthetic admixtures were introduced. The present study deals with influence of linseed oil on the engineering properties of air lime mortar. The composition of mortar was inspired by a mortar used for fixing of 1890´ mosaic in Krásná Lípa (Czech Republic). The knowledge of complex influence of the oil on mortar’s performance is important for the preparation of renovation mortars but also for possible application of the oil as sustainable mortar admixture, replacing the nowadays synthetic ones. The oil is reducing the yield stress of the fresh mortar (i.e. acts as plasticizer) and is increasing its air entrapment. The water-repealing effect is the most important impact of the oil admixing on the harden mortar; it was evaluated by measurement of water absorption coefficient. The higher air entrainment and water-repellence are resulting to the improved frost resistance of the mortar containing the oil.
Cuvinte cheie
mozaic, mortar, ulei de in, durabilitate
AHMET ONUR PEHLİVAN
Rezumat
Concrete is a brittle material that should be enhanced with better tensile strength and toughness capacity. Concrete matrix is generally reinforced with fibers which are extremely helpful inhibiting the crack propagation and supplying the ability of strain accumulation into concrete matrix. In this study, an environment friendly type of fiber was introduced into concrete for the investigation of mechanical properties and fracture characteristics by size independent double-K fracture parameters asserted in the literature. Effect of basalt fibers with different lengths and contents were investigated under notched three-point bending tests and relevant parameters obtained and calculated, were compared for two distinct parameters: fiber length (6, 12, 24 mm) and content (0, 0.1%,0.3%, 0.5%, 1%). Shorter fibers confronted dispersion problems when used in higher content whereas 12 mm fiber specimens performed more stable results. Fracture energy dissipation was found to be linearly increasing with increasing fiber content and also longer fibers were found to be more efficient. Double-K fracture parameters were found to be resourceful when considering toughness and ductility of the material besides these parameters indicated useful information regarding the pre-cracking and post-cracking behavior of concrete. SEM investigations were also conducted to monitor the bonding between basalt fibers and concrete matrix.
Cuvinte cheie
parametrii de rupere, fibră de bazalt, CMOD, energie de rupere, lungime fibră
A.SUMATHI, D. ELAVARASI, K. SARAVANA RAJA MOHAN
Rezumat
In this research, the flexural and impact resistance of steel fibre reinforced concrete (SFRC) under static and impact loadings was experimentally investigated. High-strength reinforced concrete steel fibre containing 1% by volume fibre content with a constant w/c 0.39. Hooked steel end fibers were used with a circular cross section of 1 mm in diameter and an aspect ratio of 30. Flexural behaviour of SFRC was carried out on a beam specimen of size 1200 x 100 x 200 mm subjected to two-point bending test as per ASTM C78 standard specification. Impact resistance was performed on a thin SFRC slab specimen of size 600 x 600 x 50 mm subjected to low velocity drop weight impact test as per the prescribed ACI 944-89. For comparison purpose, the conventional RCC specimens were also cast and tested. The test results found that the flexural strength and toughness of SFRC specimen remarkably increased by 35% and 50% respectively compared to RCC specimen. The addition of steel fibers to concrete increases the stiffness and ductility characteristics. The first crack and ultimate energy absorption potential of SFRC slab specimens were increased by 173.5 and 3.72 times, respectively, compared with RCC slab specimens. From the test results concluded that the flexural and impact resistance was significantly improved with addition of steel fibres in concrete.
Cuvinte cheie
HSFRC, duritate, ductilitate, energie de absorbție, raport rezistență reziduală la impact
EYUBHAN AVCI
Rezumat
In this experimental study, the effects of different curing temperatures and curing conditions on the unconfined compressive strength of microfine cement injected sand samples were investigated. The experiments started with determination of the rheological properties of the microfine cement suspensions prepared in different Water/Cement (W/C) ratios. With the increase in the W/C ratio, setting times and bleeding percentage decreased and viscosity values increased. After determination of rheological properties, injection experiments were carried out microfine cement suspensions with W/C ratios of 1.5, 2.0, 2.5, 3.0. While the injectability was increased with the increase of W/C ratio, it also decreased with the increase of the fine sand content. The samples that were successful in injection were kept in different curing temperatures and conditions. Then, the unconfined compressive strength tests were carried out on the 3rd, 7th, 14th, 28th, 56th and 120th days. The unconfined compressive strengths of the grouted sand samples were increased with time and the rate of increase started to slow down after a certain value. Due to the increase of temperature, the grouted sand samples were gained faster strength. The unconfined compressive strength values of the injected samples increased with increasing temperature. The unconfined compressive strength of the sand samples that were grouted and kept in the air-dried environment was higher than the unconfined compressive strength of the sand samples that were injected and kept in the wet-curing conditions.
Cuvinte cheie
Condiții de întărire, temperatură de întărire, ciment microfin, rezistență la compresiune neconfinată
SUHANG YANG, ZHIFENG XU, ZHENGNING BIAN
Rezumat
Shear strength is the essential mechanical property of structural concrete, especially for complex stress analysis and finite element analysis. Laboratory core double shear testing (LDST) is considered time-consuming and expensive testing for the measurement of the in-situ shear strength of concrete. The object of this paper is to introduce an innovative in-situ shear test (IST) method for the measurement of the shear strength of partial concrete cores. According to the principle of the clamping mechanism, the time required for field testing was reduced to less than 30 minutes. The core samples in different diameters and lengths were compared by IST and LDST. Student’s t-tests of shear strength results obtained by using LDST and IST showed an evident difference between the two methods. The shear strength of the core increases with the decrease of the core length and increases with the core diameter. The standard deviation of the results was considered as an increase with a reduction of core diameter for both LDST and IST. Since no extraction of core specimen is needed, and the core length is less than that of tested using LDST, and the specimens can be easily carried and quickly performed in-situ with less damage to the structure. The shear strength of concrete measured by IST is inferior to that of obtained by the LDST method, and correction efficiency must be adopted to adjust IST test results to that LDST. A good correlation between concrete IST strength and cube compressive strength is proposed in the paper.
Cuvinte cheie
beton, rezistență la compresiune, rezistență la forfecare, LDST, IST, rezistență la compresiune
İSMAİL HOCAOĞLU
Rezumat
Today, materials are produced with nanotechnology, which are new products as a result of the development of technology. For cement-based composites, porosity is very important in terms of the strength and durability of the material after the material hardens. Today, with the innovations in technology, new materials are produced in the construction sector. New generation materials are produced on nano-meter scale using nanotechnology. These materials are used in cement-based composites to reduce porosity and improve durability properties. This research is aimed to reduce the porosity of the mortars by adding the nanomaterial graphene oxide (GO) to cement-based mortars whose sizes are 4cm x 4cm x 16cm. To investigate the effect of graphene oxide on porosity, series were produced as water/cement ratios are 0.55, 0.70, 0.90, and 1.00, by substituting 0.025 % GO in the mortars instead of cement. Besides, to investigate the effect of DC stress intensity on porosity, 25 V DC current is applied to all series. Mortar internal temperatures were measured from the beginning of hydration reactions in fresh mortars. Various comparisons have been made by calculating the maturity values of the mortars. Hardened mortars were cured for 7 and 28 days, then current passes on the mortars were measured by using an ampere meter. It has been investigated whether a relationship can be established between flow transfer and porosity. As a result of this study, the porosity of mortars can be reduced and maturity values can be increased by adding GO to cement-based mortars and applying DC current. In addition, porosity of cement-based materials can be estimated by using electrical methods.
Cuvinte cheie
nanomaterial, oxid de grafen, DC curent, porozitate, măsurare electrică
AZHAR BADAOUI , M’HAMMED BADAOUI
Rezumat
The industry poses many problems to the disposal of waste materials; the impact on the environment and space occupied by storage sites. It is necessary to find a way to valorize and re-use this waste to protect the environment.
The research aims to apply a probabilistic approach to the simple leaching of mortars based on mineral fines of industrial by-products such as marble powder by pure or low mineralized water to maximize its recycling in the formulation of cementitious matrix building materials and to solve ecological and economic problems. The leaching phenomenon is studied using a probabilistic approach in this article. The statistics of the dissolving front in the material are investigated using a parametric approach that takes into account the variation of the mortar’s calcium diffusion coefficient porosity. A lognormal probability distribution is used in Monte Carlo simulations. In comparison to solely deterministic studies, the study found that probabilistic approaches are effective tools coupled with adequate deterministic models, providing extra information. As a result, concrete buildings may be better tailored for specific service life and environmental conditions.
Cuvinte cheie
lixiviere, coeficient de variație, simulare, mortar, deșeuri de marmură
DENG CHEN , TAO YANG, KAI-WEI LIU, AI-GUO WANG
Rezumat
The effects of dolomite powder (DM) with different fineness on the hydration of Portland cement (PC) are investigated by using a multi-method approach. Results show that the addition of DM decreases the hydration heat and compressive strength of PC. However, at the same replacement of PC by DM, the hydration heat and compressive strength can increase with increasing the fineness of DM. When cured at 20 °C, an increase in the fineness and amount of DM can promote the formation of carboaluminate due to the improvement of the reaction degree of DM. When cured at 60 °C, hydrotalcite (Ht) is observed in the samples containing DM, and Ht may be formed in the surface layer of DM particles. With the increase of the DM fineness and amount, the Ht strongly increases.
Cuvinte cheie
praf de dolomită, finețe, produși de hidratare, temperatură de întărire
R. TUĞRUL ERDEM , MURAT BERBEROĞLU
Rezumat
Grout mortars are non-permeable, non-shrink and flowing cement based construction materials. Due to reaching high strength values in a short time, grout mortars are used in construction works. However, behavior of cement mortars under sudden impact loading is complex. Because, loading duration is very short in impact scenarios, effect of strain rates is much higher than static loading. So, dynamic responses and failure modes of the materials are different. In this study, it is aimed to investigate the dynamic behavior of slabs that are produced by cement based grout mortars under impact loading. A drop test setup is developed for this purpose and several measurement devices utilized in the impact experiments. Acceleration, displacement and impact load values are obtained as well as drop durations and drop numbers. After completing the experimental part of the study, artificial neural networks (ANN) analysis which is used to model different physical dynamic processes depending on the experimental variables is performed to predict the impact results. So, ANN analysis is used in the verification of experimental study. Due to the comparison of experimental and analysis results, it is considered that proposed ANN model can be used for the evaluation of the dynamic responses of test specimens.
Cuvinte cheie
ANN, test picătură, chituri, impact, dale
S.S.VIVEK
Rezumat
In the present research, ternary blended Self Compacting Concrete (SCC) was prepared to evaluate the performance by replacing cement with the Silica Fume (SF) from 5% to 20% and ground granulated blast furnace slag (GGBS) from 20% to 60% in the total percentage of the weight of the cement. An attempt was made to study the performance of fresh concrete by slump flow test, T-500, U-box and L-box test, and the hardened properties of concrete by cube compression and cylinder split tensile test. The superplasticizer and stabilizer were added in optimum dosages to prevent the segregation and bleeding of fresh concrete. More powder content, say 60% GGBS and varying SF from 5% to 20%, as cement replacement for ternary blended SCC has obtained better fresh property behaviour. But lower content of GGBS, say 20% blended with SF 10% and SF 15% obtained higher split tensile and compressive strength, respectively.
Cuvinte cheie
beton autocompactant, silice ultra fină, GGBS, EFNARC, rezistență la compresiune
ALI NAJM ABED ALMAGSOOSI, DAN PAUL GEORGESCU, ION RADU PASCU
Rezumat
In the past years, it has commonly seen the use of Carbon Fibers Reinforced Polymer (CFRP) externally bonded as an active technique for strengthening and repairing of deficient existing concrete columns. Accurate design models for FRP – confined concrete are required to help engineers to design suitable FRP jacket and manage the cost-effective solutions for strengthening or repairing. In this paper the evaluating of the ultimate load carrying capacities of confined square concrete columns obtained from design models are presented. Five theoretical design models, provided in codes and researchers including: ACI 440.2R-2017; FIB Bulletin-90-2019; CNR-DT 200 R1-2013; Lam and Teng model (2003) and Ouyang and Liu model (2007) have been evaluated. A comparison was made between the load carrying capacities obtained from the experimental test data and the capacities obtained from the theoretical predictions results by the mentioned codes and researchers. All three models presented by Codes showed a good agreement with experimental values except for FIB Bulletin-90-2019 that showed conservative values in two confinement cases, while Lam and Teng model showed good agreement with experimental values and Ouyang and Liu model showed conservative values with respect to the experimental values.
Cuvinte cheie
FRP, coloană de beton, sectiune pătrată, închidere, capacitate de încărcare
P. AMSAYAZHI , K. SARAVANA RAJA MOHAN
Rezumat
The strength, toughness and ductility of the High strength fiber reinforced concrete (HSFRC) is presented in this paper. the glass and polypropylene fibers are used in this study. The fiber volume fraction differs from 0.25 to 1.5. Single fibers and combined fibers in the concrete is added. From this entire study it can be understood that the hybrid fibers showed more strength, ductility and toughness when compared to the single fiber concrete. There was an increase of 67% in terms of ductility and 20% in terms of toughness in high strength hybrid fiber reinforced concrete (HSHFRC). Regression analysis is used to predict the strength, toughness and ductility of HSHFRC and HSFRC. The experimental and predicted results show a close agreement.
Cuvinte cheie
rezistență la compresiune, rezistență la tracțiune, beton armat cu fibre hibride, beton cu rezistență înaltă, duritate, alungire, ductilitate
L. J. SANJEEV KUMAR, P. BHUVANESHWARI
Rezumat
The study concentrated on the resistance of lightweight concrete slabs against impact load using a low-velocity drop hammer impact test device. Coconut procured from nearby processing units has been observed to have high impact resistance on initial testing. The lesser density was achieved by replacing 30% of natural coarse aggregate with waste coconut shells (CS 30). In order to compensate for degradation in characteristic strength, cement was partially replaced with ultrafine Ground Granulated Blast Furnace Slag – GGBFS (Alccofine) in increasing percentage of 6% (CS 30 6A); 8% (CS 30 8A); 10% (CS 30 10A); 12% (CS 30 12A). Both strength tests (compressive strength, tensile strength, flexure strength, Impact strength) and durability tests (Water absorption, Porosity, Sorptivity, Acid resistance) were carried out for the combinations. Comparing the results, the optimum mix was fixed as CS 30 8A. Square slabs of 600 mm with 60 mm thickness were cast using the predesigned mix of M40 grade (slab-CC). Slab-CS 30 8A were cast using the optimum mix for the same dimensions. Low-velocity impact tests were performed on the slabs up to failure. Parametric analysis was carried out for crack pattern, energy absorption, crack resistance, ductility indices, crack resistance ratio for the slabs. Comparison of results shows that the coconut shell-based lightweight concrete slabs performed well under impact loading.
Cuvinte cheie
coji de nucă de cocos, GGBFS ultarafin, beton ușor, rezistență, durabilitate, impact, analiza parametrilor
ABHIJIT WARUDKAR , S ELAVENIL
Rezumat
Since the exploration of natural aggregate for construction is leading to environmental concerns, the development of sustainable construction materials, such as steel slag, is being promoted. Ecology gets threatened by the disposal issue of steel slag, as million tonnes of steel slags are produced as a by-product in steel industry. This investigation, analyze the potential of steel slag as a partial and complete replacement for coarse aggregates in cement concrete. It is seen that the inclusion of steel slag improves the abrasion resistance property of cement concrete. This study is strengthened by Scanning Electron Microscopy and Energy Dispersive X-ray Spectroscopy analysis which is carried out on the basis experimental fallouts. It is concluded that, the use of steel slag improved compressive strength and the abrasion resistance property of cement concrete, that is applicable in flooring, pavements or in places where concrete surface being in contact with external forces and environment.
Cuvinte cheie
rezistență la abraziune, standard indian 9284, rezistența la compresiune, beton cu zgură de la oțelării
SANAA EL MALYH , AZZEDDINE BOUYAHYAOUI, TOUFIK CHERRADI, ANCUȚA ROTARU
Rezumat
The externally bonded fiber-reinforced polymer is an innovative technique for enhancing the strength of masonry structures, however the link between fiber reinforced polymer (FRP) and the masonry presents the fragile zone. To improve the bond performance and to determine the influence of the unidirectional reinforcement bonded geometry on the local bond-slip behavior, this paper investigates the shear bond behavior of carbon fiber reinforced polymer (CFRP) laminate externally bonded to masonry prisms, to ameliorate their structural applications and to assess their effectiveness on the stress distribution and also on the load capacity along the bonded zone. The single-lap shear tests was performed on five unidirectional carbon fiber reinforced polymer laminate externally bonded on masonry prisms via epoxy adhesive. The failure modes and the displacement behavior analysis show that the strengthening system is most effective when enhancing the bonded surface, as it reduce the stress concentration along the bonded length and it increase the load bearing capacity .
Cuvinte cheie
legătură CFRP, zidărie, polimer armat cu fibre, comportare legături, întărire, rezistență la forfecare (încercarea adezivității mortarului la suport)
J. SHANMUGA PRIYA , K. CHINNARAJU , V.JAGANATHAN
Rezumat
This research studies self compacting concrete mixes with 0, 30, 40 and 50% fly ash as replacement which are internally cured with super absorbent polymer and lightweight expanded clay aggregates against Self Compacting Concrete which are conventionally cured by submerging in water for a specific period. The optimum dose of the Internal curing agent was determined based on the chemical shrinkage of cement paste and it was presoaked in the mixing water and incorporated at the time of mixing. Fresh properties like slump cone, V funnel and L box tests were made and the effect of fly ash and internal curing agent was reported. Properties like compressive strength and durability factors such as rate of water absorption and resistance to chloride penetration were studied. Also the relationship between compressive strength and chloride penetration was established. It was found that the addition of fly ash seems to be beneficial for self curing concrete specimens up to 40% in terms of strength and durability. Concrete internally cured with super absorbent polymer showed better performance when compared with concrete cured with clay aggregates.
Cuvinte cheie
întărire internă, beton autocompactant, ductibilitate, polimer superabsorbant, agregate ușoare din argilă expandate, cenușă zburătoare, întărire
HAJAR KADDOURI, TOUFIK CHERRADI, IBTISSAM KOURDOU, ANCUȚA ROTARU, NICOLAE ȚĂRANU, MARINELA BĂRBUȚĂ
Rezumat
Sistemele compozite realizate din materiale textile cu rezistență mecanică ridicată și încorporate într-o matrice de mortar (cunoscute și sub denumirea de matrice cementoase armate cu plasă de fibre - FRCM) se bucură de o atenție deosebită dat fiind faptul că utilizarea acestui material la consolidarea clădirilor de patrimoniu este promițătoare. Caracterizarea mecanică a sistemelor FRCM are o importanță deosebita în definirea corectă a parametrilor folosiți la proiectarea lucrărilor de consolidare. Cu toate acestea, este necesară evaluarea corectă a comportamentului la tracțiune a FRCM și influența acestuia asupra performanței structurale. Scopul acestei lucrări este de a analiza comportamentul mecanic al probelor FRCM supuse la tracțiune. În acest scop, lucrarea studiază efectul suprapunerii fibrelor în contextul general al sistemului. Încercările de tracțiune s-au efectuat pe cupoane din FRCM cu lungimi de suprapunere a fibrelor ce variază între 100 și 200 mm. Obiectivul este determinarea lungimii minime necesare de suprapunere a fibrelor astfel încât continuitatea fibrei să fie menținută și să fie păstrată rezistența la tracțiune în a probelor de FRCM.
Cuvinte cheie
materiale compozite, FRCM, suprapunere, încercare la întindere, întărire
IAKOV ISKHAKOV, YURI RIBAKOV
Rezumat
Creep is a well-known property of concrete elements, which cannot be avoided. It is defined as an increase in deformations over time due to constant stresses at uniaxial compression. In general, linear and non-linear creep of concrete elements are considered. However, there are no strong dependences that govern these two types of creep. It is still not clear when linear creep becomes non-linear, how creep changes the concrete modulus of elasticity, which energy is dissipated by the concrete section at linear and non-linear creep, etc. Predicted creep values are important for accurate design of concrete elements at service and ultimate limit states. The present study analyzes linear and non-linear creep and proposes a creep effect algorithm. The methodology is based on Structural Phenomenon and new theoretical concepts, using just one empirical coefficient related to non-linear creep. It can be used by engineers in order to perform more accurate and rather simple design of concrete elements considering creep.
Cuvinte cheie
infiltrare beton, infiltrare liniară și neliniară, potențialul elastic și elastico - plastic al unui sistem RC la infiltrare, fenomen structural
K. SARUMATHI , S. ELAVENIL, M. SATISH REDDY
Rezumat
When the sand can no longer be reused in the foundry, it is removed from the foundry and this high quality silica sand in large volumes is used in making concrete as partial replacement of fine aggregate. In this paper investigations were carried out on the mechanical properties and durability studies of concrete by adopting silica sand and fly ash during the formation of concrete where, fly ash is used as a partial replacement material of cement. Silica sand (SS) or foundry sand (FS) is incorporated (0%, 25% and 50%) along with fly ash (FA) in different proportions (0% and 25%) with water – cement ratio (w/c) as 0.5. The outcomes indicated that the inclusion of FA and SS improved the compressive as well as tensile strength of material. The study reveals the feasibility of using spent foundry sand as a partial replacement of M-sand and also that full factorial design method is a reliable tool to arrive the conclusion that the FA and SS can be replaced with 25% effectively. The statistical software was used with full factorial design to predict the values and to validate the results with true values.
Cuvinte cheie
nisip de siliciu, cenușă zburătoare, proprietăți mecanice, proiectare factorială
ARATHI KRISHNA , SARAVANA RAJA MOHAN KALIYAPERUMAL
Rezumat
Reinforced concrete structures exposed to high temperatures may significantly reduce the characteristics of concrete in terms of strength, plastic deformation of reinforced steel bar and most precisely, the bond between the concrete and the reinforcing steel. Since there are only limited literature available in the field of concrete reinforced with hybrid fibres, which contain natural fibres subjected to elevated temperature, a thorough investigation needs to be done in this area. Hence, this investigation was carried out to evaluate the strength properties of concrete after adding different types of fibres under normal and elevated temperature conditions (27oC, 200oC, 400oC and 800oC). Micro steel, polypropylene and sisal fibres were used monolithically and in hybrid form with a volume fraction of 1%. The fresh property of the mixes was evaluated by conducting slump cone test, and the hardened properties were evaluated by density, compressive strength and split tensile strength tests. In addition, the bond between the concrete and the reinforcing bar was evaluated, and the residual properties were compared with the control mix. The results reveal that in elevated temperature conditions, the inclusion of micro steel fibres has a significant role in enhancing concrete strength and bond characteristics. The addition of polypropylene and sisal fibres mainly helps prevent spalling and has a slight effect on the bond characteristics of concrete compared to that of the control specimen subjected to elevated temperature.
Cuvinte cheie
fibre, fibre hibride micro oțel, polipropilenă, sisal, proprietăți de întărire, liant, extragere, temperaturi ridicate
BEKİR ÇOMAK , ALPER BİDECİ, BATUHAN AYKANAT, ÖZLEM SALLİ BİDECİ
Rezumat
With the development of computer technologies in recent years, the usage of image processing techniques in different areas have significantly increased. Image processing is the computer study for altering the measured or saved digital image data in a manner to fit for a purpose in an electronical media. In this study, by adding red iron oxide pigment (RIOP) into cement mortars in 2%, 4%, 6% and 8% ratios, physical and mechanical characteristics of the mortars were analysed, and color homogenization of them were determined by image processing method. On the manufactured samples, consistency, density, water absorption, porosity, compressive strength, flexural strength tests and image processing analysis by open source coded ImageJ programme were performed. Also, SEM-EDS analyses were performed in order to determine the inner structure characteristics of the samples. As a result of this study, changes in physical and mechanical characteristics of the mortars have been observed in different ratios. When it is desired to obtain a red colored mortar, it is determined by image processing analysis that 6% of red iron oxide pigment (RIOP) addition to the mortar mixture would give the optimum result.
Cuvinte cheie
beton colorat, procesare imagine, microstructuri, SEM-EDS
V. JAGANATHAN , K. CHINNARAJU
Rezumat
This study aims at simplifying the process of mix design of Self Compacting Concrete (SCC) which is generally done through trial and error. Concrete being a heterogeneous material, the desired qualities are attributed to several factors, in addition SCC has the requirement of better workability, which leads to the complexity in the design process. In this paper, the various factors affecting the strength and workability of SCC such as Total Cementitious Material (TCM) content, water-cementitious material ratio, percentage of fly ash replacement, coarse aggregate content and fine aggregate content were analyzed with four different values for each factor. Based on the Taguchi optimization method, an orthogonal array with sixteen experiments was designed to obtain the best factors for the SCC mix. The performance parameters selected were slump flow value for flowing ability, T5min of V funnel test for segregation resistance, L Box ratio for passing ability and compressive strength test for strength aspect. The results indicated that the TCM content and water-cementitious material ratio plays an important role in the workability of SCC, whereas TCM content and coarse aggregate content are predominant in the compressive strength of SCC.
Cuvinte cheie
beton autocompactant, șir ortogonal Taguchi, cenușă zburătoare, lucrabilitate
P.KAVIMUHIL, A.BALAJI, R.SOORAJ, V.VADHUL KRISHNAN, B.KARTHIKEYAN
Rezumat
This paper discusses heavy density (HDC) concrete performance by partially replacing the fine and coarse aggregate in concrete with magnetite in its fine and coarser form. Three series of mixes, namely HDC-I, HDC-II and HDC-III, were developed for the research. HDC-I series contained 10% magnetite powder (MP) and 10% quartz powder (QP) as fine aggregates, whereas the HDC-II series had 15% magnetite power MP and 5% QP. The replacement level of magnetite aggregate as coarse aggregate was maintained constant by 30%, 40% and 50% for both the series. HDC-III series mix was made by replacing coarse aggregate with a significant content of 50%, 60% and 70% of magnetite aggregate by weight. Only 20% of magnetite powder was used for replacing the fine aggregate in HDC-III. Silica fume and nano-silica were also used in a constant replacement proportion in cement by 10% and 1%. Various tests related to the mechanical and durability characteristics of the concrete were performed. Compared with conventional concrete mix, the results revealed that increasing the proportion of magnetite aggregate leads to a considerable increase in unit weight and other mechanical properties. Also, it was observed that quartz powder and magnetite did not fetch any significant benefit in the mechanical properties.
Cuvinte cheie
beton de densitate mare, particule de magnetită, agregat magnetită, particule de cuarț, nano-silice, mediu agresiv, test la impact
ASIF HAMEED, MOHSIN USMAN QURESHI, ALI MURTAZA RASOOL, JAVAID KHALID, ASADULLAH QAZI, MUHAMMAD USMAN RASHID, ZAFAR MAHMOOD
Rezumat
Self-compacting concrete (SCC) can compact itself under its weight without any external effort and has characteristics of flowability, passing-ability, viscosity, inhibiting segregation and filling narrow architectural sections, etc. SCC requires a larger quantitative proportion of fines e.g. pozzolans like fly ash, blast furnace slag, silica fume, metakaolin, rice husk, or non-pozzolanic materials like limestone and sandstone. However, a higher quantity of pozzolanas with lower water content may cause autogenous shrinkage. The objective of this research is to find the best mix design of SCC to reach the highest compressive and flexural strength while maintaining flowability, passing ability, and segregation resistance. For this purpose, first twenty-eight (28) mix designs were prepared and tested in a fresh state for assessing flowability, passing-ability, and segregation resistance properties. The results of these tests were found compatible with previous studies without any significant variations. Then, hardened concrete was tested by casting 448 cylinders for determining the compressive strength at 7, 14, 28, 56, and 90 days and 168 prisms were tested to determine the flexural strength at 28, 56, and 90 days. It was observed that two combinations i.e. 30%FA, 17.5%SF, and 25%FA, 7.5%SF replacement are the most favorable mineral fine admixtures in producing good quality SCC.
Cuvinte cheie
beton autocompactant, cenușă zburătoare, silice ultrafină, puzzolane, coeficient de variație