english VAN-HUONG NGUYEN, NORDINE LEKLOU, PIERRE MOUNANGA
Rezumat
Delayed ettringite formation (DEF) is a type of internal sulphate attack caused by heat-induced decomposition and/or prevention of normal ettringite formed during the initial hydration of cement at elevated temperature (above about 70°C) and its re-crystallization in the hardened matrix. DEF is a physico-chemical phenomenon inducing an expansion of the cement paste that could lead to cracking of concrete. In this paper, the effect of metakaolin on DEF of the heat-cured mortars was investigated. To fulfil the aim of this study, a portion of cement was replaced by metakaolin, with three different dosages (10, 20 and 30%). The mortars were heat-cured at early-age, and the tests of expansion, strength, dynamic elastic modulus and thermogravimetric analysis were carried on these mortars a period of 650 days. Additionally, scanning electron microscopy (SEM) observations were realized. The test results obtained highlighted the mitigation effects of metakaolin on DEF.
Cuvinte cheie
metacaolin, formare întârziată etringit (DEF), mortar întărit termic, dilatare, beton
G. SKRIPKIUNAS, G. YAKOVLEV, E. KARPOVA, P.L. NG
Rezumat
The application of accelerating admixtures is required in construction work where fast-setting is required or in an environment of low temperature. This type of admixtures allows to regulate the setting and hardening time of cement composites and could influence on their strength and performance. The accelerating admixtures are exemplified by chloride, nitrate and other salts. Some investigations demonstrated the application of different types of nano- and complex additives as a method to accelerate the hydration processes of cement composites.
The present study focuses on the investigation of the combined action of multi-walled carbon nanotubes (MWCNT) dispersion and various types of accelerating admixtures such as calcium chloride, calcium nitrate and magnesium chloride. The amount of accelerating admixtures ranged from 1% to 3% by weight of cement, the amount of MWCNT for all compositions remained equal to 0.005% by weight of cement. The setting time of cement pastes modified by different types of accelerating admixtures and MWCNT dispersion was determined. The combined effects of MWCNT dispersion and accelerating admixtures on compressive and flexural strength, water absorption and porosity of cement mortar modified by calcium chloride and MWCNT were studied. Besides, the cement hydration products were evaluated by FT-IR spectroscopy and XRD analysis. The individual and combined effects of accelerating admixtures and MWCNT addition are reported in the article.
Cuvinte cheie
ciment, adaosuri acceleratoare, timp de priză, clorură de calciu, nanotuburi de carbon, multistrat
NORDINE LEKLOU, PIERRE MOUNANGA
Rezumat
This article presents a study on the microstructural evolution of the cementitious matrix at early stages of hydration. The main objective was to follow the development of the interfacial zone between cement paste and granular inclusions during the hardening process. For this purpose, the “simple replica” method was used. This technique consists in observing a facsimile of the polished sample surface. This prevents drying and cracking of the sample during observation under vacuum with a scanning electron microscope (SEM). The study was conducted on Portland cement mortars containing glass beads with diameters of 3 and 8 mm. The effects of inclusion size and temperature were analysed at different time of observation, between 8 and 120 hours of hydration. The results showed a progressive separation between cement paste and glass beads, and the presence of microcracks in the matrix kept at 40°C.
Cuvinte cheie
matrice cimentoidă, granule sticlă, microstructură, metoda replică, microfisuri endogene
YUE LI, ZHONGZHENG GUAN, ZIGENG WANG, PENG WANG, GUOSHENG ZHANG, QINGJUN DING
Rezumat
This paper presents an integrated investigation of deterioration process of corroded concrete by experiments and theoretical model. First of all, the porosities of concrete samples with different corrosion periods were measured by the mercury intrusion porosimetry (MIP). Then the distribution of sulfate ions in the concrete was measured by the spectrophotometric method. Afterwards, the compressive strength were measured. The results indicated that the porosity and the compressive strength of concrete in water firstly increased and then progressively stabilized at a constant value due to the hydration of cement. However, those values of concrete soaked in 5wt.% Na2SO4 solution increased and then decreased, resulted from the combination of cement hydration and the corrosion of sulfate ions. Moreover, a Stratified-Theoretical calculation model was established with the input parameters of corrosion depth of sulfate ion, length of concrete specimen, strength of concrete immersed in water and in sulfate solution. At last, the corrosion resistance coefficient of corrosion layer was firstly put forward to evaluate the deterioration process of concrete with high effectiveness.
Cuvinte cheie
beton, atac sulfatic, dispersie, rezistență la compresiune
DAMIR ZENUNOVIC , NESIB RESIDBEGOVIC, RADOMIR FOLIC
Rezumat
The experimental tests were carried out with the aim to develop a rapid procedure for predicting chloride penetration into concrete, without stimulating the migration of chloride ions with electricity. Pressure Penetration Test (PPT) results were compared with the results obtained using the standardized Bulk Diffusion Test (BDT). The testing was carried out on 15x15 cm concrete cubes. Chloride penetration into concrete samples was modeled by analyzing previous studies and selecting suitable mathematical models. The two models were modified by introducing chloride penetration coefficients, experimentally determined by comparing PPT and BDT chloride profiles. The study confirmed the possibility of applying the PPT procedure for the rapid prediction of chloride penetration into concrete.
Cuvinte cheie
beton, clorură, difuzie, penetrare, modelare, comparații
YANG LI, ZHENDI WANG, LING WANG
Rezumat
Air entraining admixture is often used to improve fluidity and freeze-thaw resistance of concrete through introducing dispersed micro bubbles. Driven by the Great Western Development Strategy and the Belt and Road Initiative of China, a large amount of concrete are used for the construction at high altitude areas of western China. But it was found that the fluidity and freeze-thaw resistance of concrete decreased a lot due to low atmospheric pressure at high altitude. To explore the influence of low atmospheric pressure on the performance of cementitious material, flow-through time of cement paste and pore size of hardened cement paste were tested. The flow-through time at 20 kPa was increased by 27.6% to 135.0% compared to normal atmospheric pressure (100 kPa). As the atmospheric pressure decreased from 100 kPa to 40 kPa, the average pore diameter of the high W/C hardened cement paste decreased to 75.3% to 71.3%, whereas the average pore size of the low W/C hardened cement paste increased by 39.0%. This reflects that the fluidity and the freeze-thaw resistance of cementitious material will decrease more or less at lower atmospheric pressure. The changes of fluidity and freeze-thaw resistance durability may be explained by the increased diameter of bubbles in fresh cement paste at lower pressure.
Cuvinte cheie
presiune atmosferică scăzută, pori, bule, amestec de aer de antrenare
LINGJIE WU, LINZHU SUN, FANG YANG, DONGYAN WU, JUNLIANG ZHAO
Rezumat
Based on the fiber dispersion and concrete compressive strength tests, the effects of mixing method, mixing time and fiber content on the dispersion performance of ternary copolymer fibers in concrete were studied. The experimental results show that a modified dry mixing method benefits the dispersion of the fibers in concrete and obtains a desirable mechanical performance as compared with wet mixing and ordinary dry mixing methods. With an increase in mixing time, the fiber dispersion coefficient and the compressive strength of concrete increased at initial stage and then decreased. In addition, the fiber dispersion coefficient and the compressive strength of concrete decreased with the increase of fiber content. Taking both the strength properties of the concrete and economic factors into consideration, the modified dry mixing method was considered the most desirable mixing method, with an optimum mixing time of 6 minutes and an ideal fiber content of 0.14%.
Cuvinte cheie
beton, fibre copolimer ternare, dispersie, rezistență la compresiune
RĂZVAN LISNIC, CRISTINA BUSUIOC , GEORGETA VOICU, SORIN-ION JINGA
Rezumat
Două tipuri de ghips natural prelevate din regiuni diferite ale României şi două tipuri de ghips sintetic provenite din instalaţiile industriale de desulfurare a gazelor de ardere au fost caracterizate din punct de vedere compoziţional, structural şi morfologic prin analiză termică, difracţie de raze X, microscopie electronică cu baleiaj cuplată cu spectroscopie de raze X cu dispersie după energie şi granulometrie laser. Mortarele obţinute pe bază de ciment portland şi diferite proporţii de ghips au fost, de asemenea, investigate din punctul de vedere al timpului de priză şi al proprietăţilor mecanice (rezistenţă la încovoiere şi rezistenţă la compresiune), în corelare cu evidenţierea produşilor de hidratare prin microscopie electronică cu baleiaj. Rezultatele au fost corelate cu puritatea şi omogenitatea specimenelor de ghips analizate.
Cuvinte cheie
ciment portland, gips natural, gips FGD, timp de priză, rezistență la flexibilitate, rezistență la compresiune
AGNE SMIGELSKYTE, RAIMUNDAS SIAUCIUNAS, MATTHIAS WAGNER, LIUDVIKAS URBONAS
Rezumat
Rankinite binder material was synthesised from the mixture (C/S = 1.5) of locally (Lithuania) available materials – opoka and limestone – at 1250 °C for 45 min. Its suitability as a non-hydraulic binder for carbonation curing has been assessed.
Mortar samples prepared of binder and sand mixture (15:85 wt%, w/c = 0.35) were pressed and cured in a pressure reactor using gaseous (5 and 50 bar at 20 and 50 °C) and supercritical CO2 (150 bar at 50 °C) for 4 and 24 h. It was determined that with increasing pressure, exposure time and/or temperature the carbonation process is intensified, sample compressive strength is highly increased. Hardening samples at the highest conditions led to full carbonation and the highest strength. For the first time it was shown, that at the supercritical CO2 conditions the compressive strength of the rankinite binder samples was higher than the OPC ones. The study showed that rankinite as a binder material is suitable for carbonation curing and could be used to produce carbonated construction materials.
Cuvinte cheie
rankinit, liant nehidraulic, CO2, var, Ca-Si roci naturale
KAMILE TOSUN FELEKOĞLU, EREN GÖDEK
Rezumat
In this study, the matrix rheology, mechanical performances and thermal insulation properties of high tenacity polypropylene fiber (HTP) incorporated lightweight engineered cementitious composites were investigated. Matrices were prepared by using air entraining admixture 2, 4 and 8% of cement weight and HTP fibers added to matrices by 2% of total matrix volume. Before fiber addition, rheological properties of matrices were investigated by using a ball type rheometer. After fiber addition, the air entrainment percentages of composites were determined through theoretical calculations, aerometer test, and image processing methodology for comparison purpose. Specimens were cast into: 25x60x300 mm prismatic molds for flexural strength and thermal tests; dog-bone molds for tension tests; 50x50x50 mm cubes for compression tests. Crack numbers and crack widths of specimens were measured additionally to the mechanical test by using a portable hand microscope at unloaded state in order to investigate crack properties after flexural and tensile test. Thermal properties of composites were also investigated by thermal conductivity and thermal permeability measurements. The thermal conductivity values of composites were achieved by using prismatic specimens before flexural tests. Correlations between air-dry densities and thermal conductivities were calculated. Additionally, thermal permeability of composites were obtained by using a novel thermal camera integrated test setup, which simulates actual site conditions, and related with the thermal conductivity test results. In conclusion, composites were lightweightened by 19-35%. The accuracy of the aerometer test was confirmed by image processing technique. Yield stress and viscosity of matrices were decreased by increasing air entraining admixture dosage and 8% of air entraining admixture dosage was found much preferable in terms of consistency preservation. First crack (in both flexural and tensile tests) flexural, tensile and compressive strengths of composites were decreased by increasing air entrainment percentage. By taking air entrained composites into account, deflection and strain capacity of HTP-LECCs were increased by increased admixture dosage. Also, crack numbers were increased and crack widths were decreased by increasing admixture dosage within air entrained composites. Thermal permeability of composites were investigated by novel thermal camera test setup. Strong correlation (R=0.96) was found between thermal conductivity and thermal permeability tests.
Cuvinte cheie
compozite ușoare pe bază de ciment (ECC), antrenare aer, proprietăți reologice, mecanice, termice, HTP
ANCUŢA ROTARU, VASILE BOBOC, NICOLAE ȚĂRANU , MONTHER ABDELHADI, ANDREI BOBOC, OANA-MIHAELA BANU
Rezumat
Lucrarea analizează comportarea la compresiune a agregatelor stabilizate cu cenușă de termocentrală din România, investigând posibilitatea de a utiliza reziduurile de cenușă zburătoare rezultate din arderea lignitului ca pe un substituent al cimentului în lucrările de drumuri. Încercarea experimentală a unor amestecuri de agregate cu adaosuri de cenușă zburătoare colectată de la termocentralele din Iași și Vaslui de 20%, 25%, respectiv 30%, raportat la masa totală a amestecurilor, indică faptul că doar în cazul amestecului de agregat stabilizat cu 30% cenușă zburătoare sunt îndeplinite condițiile de acceptabilitate pentru utilizarea ca strat de bază în lucrările de drumuri. Amestecurile stabilizate cu procente de 20% și 25% cenușă zburătoare ar putea fi utilizate, în schimb, ca straturi de fundare.
Cuvinte cheie
rezistență mecanică, cenușă zburătoare de termocentrală, agregate, material substituent al cimentului, lucrari de drumuri
DAN GEORGESCU, LAURENȚIU RECE, ANCA IONESCU, ADELINA APOSTU
Rezumat
Utilizarea adaosurilor la prepararea cimentului și betonului reprezintă deja o soluție larg raspândită pe plan național și european. Se pune deseori problema promovării unor compoziții noi având diverse procente și tipuri de adaosuri pentru anumite aplicații și medii de expunere, principala problemă fiind cea legată de asigurarea unei bune comportări în timp și asigurarea unei durate de viață corespunzătoare. Articolul prezintă aplicații ale unor metode asociate performanțelor utilizate pe plan european pentru verificarea posibilității utilizării unor compoziții noi în anumite medii de expunere. Aceste metode reprezintă instrumente utile, în completarea metodei raportului apă ciment echivalent, presupus a asigura comportări în timp similare cu ale unei compoziții de referință. În articol se prezintă aplicarea unor metode asociate performanței betonului în ceea ce privește rezistența la carbonatare și la îngheț-dezgheț a betonului pe baza rezultatelor unor cercetări experimentale efectuate de autori.
Cuvinte cheie
beton, ciment, adaosuri minerale, rezistența la compresiune a betonului, concept k-value, metode de performanță
PENG ZHAO, QIN LEI, XIUZHI ZHANG, WENJUAN HUAN, HAIJIAN MA
Rezumat
This experiment takes the mass loss rate and relative dynamic elastic modulus as indicators to study the damage degradation process of black bricks in freezing-thawing environment and sulfate corrosion environment under pressure load, it compares and analyzes the characteristics of freezing-thawing damage and mutual influence of various failure factors. This paper also performs experimental research and theoretical analysis of the process of damage degradation of black bricks under action of freezing-thawing cycles. The study finds that under the action of only freezing-thawing factor, the relative dynamic elastic modulus of the black brick test piece decreases to about 0.60 after 80 cycles of freezing-thawing, reaching the failure criteria of the test piece. The coupling effect of the load and sodium sulfate accelerates the decline of the relative dynamic elastic modulus of the test piece under the action of freezing-thawing. Finally, this paper combines with the freezing-thawing fatigue damage equation model, through the number of indoor freezing-thawing cycles of the black brick, uses the Geographic Information System (GIS) software TopMap7 to draw various freezing-thawing life distribution maps of the black bricks under water freezing, load and salt freezing environment.
Cuvinte cheie
cărămizi negre, durabilitate, îngheț - dezgheț, prognozarea duratei de viață, model
S. JANANI, A.S. SANTHI
Rezumat
Concrete, being one of the most commonly used building materials in construction industries, has, cement as its principle component. Cement paste is responsible for bonding and strength gain in concrete. The production of cement releases an equal amount of CO2 to the atmosphere causing environmental pollution. This Study identifies the property enhancement of concrete due to the partial replacement of cement with pozzolanic materials such as fly ash and silica fume at 40% and 7% respectively. Tests were conducted to identify mechanical properties – compression, split tension, flexure; and Impact resistance. Steel fibres were also incorporated at 0.75%, 1.15% and 1.55% to the mix. Addition of steel fibre to blended concrete showed an increase of 33-77% on mechanical properties and 186% on impact resistance of concrete at 28 days. A Multiple linear regression model was formulated using SPSS, and consequently, equations were derived to predict the mechanical properties and impact resistance of concrete. The equations were found to be in a good agreement with the experimental results obtained by various other researches with significance level lesser than 0.05 in ANOVA.
Cuvinte cheie
cenușă zburătoare de termocentrală, silice ultrafină, fibre de oțel, proprietăți mecanice, rezistență la impact, regresie
AVUTHU NARENDER REDDY, T. MEENA
Rezumat
Cement is one of the essential constituent for the production of concrete. However, large amounts of carbon dioxide (CO2), green house gases etc are emitted during the calcinations of limestone; for the production of one tonne of cement, the raw materials of about 2 tonnes is required and it releases approximately 1 tonne of CO2. Since, the production of cement involves excessive emission of greenhouse gases that leads to damaging of ozone layer and many environmental problems, a substitute or alternative material to cement for a sustainable construction was required. Research works are being carried out for finding out the alternate cementing material which will replace cement partially or fully due to its ill effects on the environment. The present paper reports an attempt in this direction by experimental examination on the hardened properties of concrete by replacing cement with combination of Fly ash (FA), Alccofine (AL) and Colloidal Nano Silica (CNS) in order to form a blended concrete (BC). From the experimental results, it was clearly observed that the combination of FA, AL and CNS had shown a high early age strength gaining property. Incorporation of a combination of these admixtures enhanced the mechanical and water absorption properties of the concrete. BC mix with a combination of 25% FA, 10% AL and 1% CNS with a total of 36% replacement of cement has achieved higher mechanical and water absorption properties as compared with all other mixes. The relationship between compressive strength and splitting tensile strength as well as between compressive strength and percentage water absorption is also investigated.
Cuvinte cheie
silice nano-coloidală, cenușă zburătoare de termocentrală, alccofine, beton, rezistență la compresiune, rezistență la flexibilitate, absorbție de apa
GIDEON BAMIGBOYE , ADEOLA ADEDEJI, DAVID OLUKANNI, KAYODE JOLAYEMI, OLALEKE FASANYA
Rezumat
This study focus on durability to saline environments of self-compacting concrete (SCC) made of granite-gravel combination as coarse aggregates in concrete production. In this study fine aggregates, water, superplasticizer and cement were kept constant. The percentages replacement of gravel in place of granite aggregates were 10, 20, 30, 40, and 50, while 100% granite serves as control. A total of 162 cubes of 100 x 100 x 100 mm concrete specimens were immersed over the initial curing in a water container and further cured in 5% sodium chloride (NaCl) and sodium carbonate (Na2CO3) solutions for 28, 56 and 91 days in line with ASTM C39 (2003). The tests results indicate that concrete cured in five percent (5%) of NaCl solution have compressive strength accelerating properties at early age that could not be sustained for long. While those cured in 5% of Na2CO3 solution reduced significantly the compressive strength of concrete.
Cuvinte cheie
beton autocompactant, durabilitate, clorură de sodiu, ciment, carbonat de sodiu, rezistență la compresiune
ODAY M. ALBUTHBAHAK , ASHRAF A. M. R. HISWA
Rezumat
As a non-destructive technique for concrete compressive strength assessment for existing concrete structures, Ultrasonic Pulse Velocity (UPV) test method has been widely used. Since the UPV affected by many factors, it is not easy to accurately assess the concrete compressive strength. Effect of some factors which are coarse aggregate grading type, slump, the water-cement ratio (w/c), sand volume ratio, coarse aggregate volume ratio, testing age, concrete density, and pressure of steam curing, were analyzed on the relationship between ultrasonic pulse velocity and concrete strength. 436 records of data, extracted from published research work, were used to build seven supervised machine learning regression models which are; Artificial Neural Network (ANN), Support Vector Machine (SVM), Chi-squared Automatic Interaction Detector (CHAID) decision tree, Classification and Regression Trees (CART) decision tree, non-linear regression, linear regression, and stepwise linear regression models. Also, the independent variable importance for each predictor was analyzed and for each model. With an adequate tuning of parameters, ANN models have produced the highest accuracy in prediction, followed in sequent with SVM, CHAID, CART, non-linear regression. Linear and stepwise linear regression models have present low values of predictive accuracy. w/c was observed to be the highest importance factor in prediction of concrete strength, and the forecasting of the concrete strength was efficient when using w/c and UPV only as predictors in any of the used predictive models.
Cuvinte cheie
rezistență la compresiune beton, viteză pulsată ultrasonică, modele, rețea neurală artificială - ANN, regresie
RIMVYDAS KAMINSKAS, IRMANTAS BARAUSKAS
Rezumat
The study aims at investigating the possibility of using Autoclaved Aerated Concrete Waste (AACW) as an additive (replacement) for Portland cement. 5%, 10% and 15% (by weight) of Portland cement were replaced with this additive. The specimens of cement paste were hardened for 28 days under normal conditions in water. It was estimated that recycling of AACW as the micro-filler required one and a half less energy than a natural additive of limestone and four times less energy than conventional construction and demolition wastes i.e. cement mortar. Under normal conditions, Autoclaved Aerated Concrete Waste additive accelerates the initial hydration of ordinary Portland cement (OPC), promotes the formation of additional calcium silicate hydrates, and increases the density of cement stone. It was estimated that up to 10 % wt. of the OPC can be replaced by AACW additive without impairing the strength properties of cement paste samples.
Cuvinte cheie
ciment portland, deșeu de beton celular autoclavizat, aditivi, consum de energie
QUAN WAN , MINLI ZHENG, SHUCAI YANG, WEIWEI LIU
Rezumat
Micro-texturing can greatly improve the cutting performance of tools. Thus, this paper attempts to disclose the effects of laser machining on the morphology and surface performance of micro-textured tools. Firstly, the 2D and 3D morphologies of micro-textures were explored and the effects of different laser machining parameters were analyzed. After that, the author examined the microstructure and the composition of the heat affected zone (HAZ) around each micro-texture. Furthermore, the micro-hardness and nano-hardness in different areas of HAZ were subjected to comparative analysis. The results show that laser parameters directly affect the micro-texture morphology and surface material properties. With the same total energy, high power density and the number of scans can reduce the deposition of sputtering materials, improve the size accuracy of micro-texture, and increase the performance of micro-texture surface materials. The research findings lay the basis for the fabrication of micro-textured cemented carbide cutting tools.
Cuvinte cheie
prelucrare cu laser, suprafață microtexturată, zonă afectată de căldură (HAZ), instrument din carbid cementat
S PRAVEENKUMAR , G SANKARASUBRAMANIAN
Rezumat
In this study, the experimental investigation on the flexural test of bagasse ash blended high performance concrete (HPC) and influence of steel fibre (STF) and polypropylene fibre (PPF) are carried out. The flexural test was done for beam size of 150 mm x 200mm x 1800mm with two point loading system. The concrete was considered for M60 grade (P series) as recommended by P.C.Aitcin. The blend mix included both free STF (Q series) and PPF (R series), and furthermore the hybridization of STF and PPF (S series) at a total volume fraction of 1.0% by volume of concrete with 10% bagasse ash as a substitution of cement. Structural behavior of eleven bagasse ash blended high performance concrete beams reinforced with steel, polypropylene and hybrid fibres were examined. The behavior of each beam was assessed with respect to initial crack, ultimate load, ultimate deflection, flexural strength, ductility and toughness. The inclusion of fibres increased the failure load and ensured the ductile behavior of the beams. The results demonstrated that adding hybrid fibres enhanced the mechanical properties as well as the structural behavior of beams
Cuvinte cheie
cenușă de bagasă, beton de înaltă performanță, fibră de oțel, fibre de polipropilenă
LIVIA INGRID DIACONU, DIANA PLIAN, NICOLAE ȚĂRANU , OANA MIHAELA BANU, ADRIAN CONSTANTIN DIACONU, DĂNUȚ TRAIAN BABOR
Rezumat
Scopul acestei lucrări a fost prezentarea unei metode utilizate pentru evaluarea modificării unor caracteristici ale betoanelor realizate cu adaos de cenușă de termocentrală, supuse unui proces de coroziune accelerată utilizând apă caldă dedurizată. În elementele de construcție care vin în contact cu apa, fenomenul de coroziune se manifestă prin dizolvarea şi levigarea hidroxidului de calciu din piatra de ciment, cu implicații asupra caracteristicilor de durabilitate. În vederea supunerii probelor de beton la acest tip de atac coroziv, s-a proiectat și executat o instalație specială care permite accelerarea proceselor care au loc în structura betonului atunci când este expus acţiunii apei calde dedurizate. În urma supunerii epruvetelor din beton la acțiunea apei calde dedurizate, au fost efectuate câteva încercări fizice și mecanice care au vizat determinarea densităţii, a absorbției de apă, a permeabilității și a rezistenței la compresiune. Un număr total de 117 probe cubice au fost testate pe parcursul a 36 luni, pentru a caracteriza comportarea betoanelor realizate cu cenușă de termocentrală la acțiunea corozivă a apei calde dedurizate.
Cuvinte cheie
beton, adaos de cenușă, coroziune, dizolvare - levigare
LIANA IUREŞ, CORNELIU BOB, REMUS CHENDES, CĂTĂLIN BADEA, RADU POPA
Rezumat
Betonul este livrat pe şantier având două caracteristici principale: se va întări şi va prezenta fisuri de uscare. Crăpăturile datorate întăririi betonului vor duce la reclamaţii din partea beneficiarului şi la reducerea durabilităţii structurii de beton. Contracţia datorată uscării influenţează sensibil integritatea structurilor de rezistenţă. S-a constatat că pentru elementele care au contracții împiedicate, este posibil să apară fisuri. Lucrarea de faţă propune introducerea a doi noi coeficienţi: - contracţie caracteristică şi - indice de fisurare, utili pentru o caracterizare facilă a eficienţei unui amestec utilizat în beton, asupra reducerii efectelor contracţiei şi a tendinţei de crăpare.
Cuvinte cheie
beton, durabilitate, contracție, adaosuri
RUI-XI DAI, HUA CHENG, GUO-XIN ZHENG, JUN-RU REN, CHAO-SHAN YANG, XIN-HAO ZHENG
Rezumat
In this study, a new type of concrete brick, which is suitable for island environment and non-autoclaved, is developed, and the mechanical properties of the bricks are tested. The results show that the compressive strength, flexural strength and compression ratio of the concrete brick can reach 28 MPa, 4.58 MPa and 0.16 respectively after 28 days. The study also discusses the binder which can be used in the brick material, and puts forward the design idea of the special binder. These experimental and theoretical results can be applied to the construction of new masonry structure in island environment, and have certain guiding significance and application prospect for island engineering.
Cuvinte cheie
cărămizi din beton ne-autoclavizat, polimeri superabsorbanți, liant special
LEONID DVORKIN, VADIM ZHITKOVSKY , YURI RIBAKOV, OLEH BORDIUZHENKO , ANTON STEPANUK
Rezumat
The paper deals with the features of obtaining a composite binder containing cement kilns dust, blast furnace slag and Portland cement, in which increased complex activation of blast-furnace granulated slag is achieved, due to the increased content of alkalis in cement dust, as well as the effects of hydroxide and calcium sulphate, contained in the cement. The influence of composition, fineness of grinding and content of chemical additives on the hydration degree and strength of low water demand binders was studied. The optimal relationships between the binder composition and the required fineness of the grinding are established, which ensure the strength characteristics and the hardening speed. The influence of superplasticizers naphthalene formaldehyde and polycarboxylate types, which provide low water demand of binder and high fineness of its grinding, is studied. Using the method of the experiment mathematical planning, equations for the regression of compressive and flexural strengths in different compensations were obtained, which allow predicting strength, taking into account the composition and features of the technology for obtaining the binder.
Cuvinte cheie
liant, praf, cuptor, măcinare, grad de hidratare, rezistență
R. GOPI , V. REVATHI
Rezumat
This paper presents the finding of an experimental study on strength and durability performances of self compacting concrete (SCC) with pre-saturated light expanded clay aggregate (LECA) and fly ash aggregate (FAA). The fine aggregate was replaced in the mixes in the range of 0% to 25% with 5% interval on volume basis. Also, the blend of LECA and FAA was used to make Self Compacting Self Curing Concrete (SCSCC) mixes. The influence of LECA and FAA on the fresh properties, strength, acid resistance (HCl) and sulphate resistance (MgSO4) on SCC and SCSCC were studied. From the results it was observed that replacement of fine aggregate by presaturated LECA and FAA as self curing agent to SCC mixes gives cost-effective and technical benefits.
Cuvinte cheie
beton autocompactant, întărire, rezistență, microstructură, durabilitate
KADIR GÜÇLÜER , İSMAIL DEMIR
Rezumat
This study aimed to use metakaolin and blast furnace slag as main raw materials in the production of autoclaved aerated concrete (AAC). AAC is a light building material obtained by bringing of silica sand, cement, gypsum, lime and pore-forming agent together and hardening it in autoclave. In this study, instead of silica sand, samples of AAC were produced using metakaolin and blast furnace slag (BFS). Experimental measurements were carried out to determine the physical, mechanical and thermal properties of the AAC samples. The micro structural investigations were carried out using SEM and XRD technique.
Cuvinte cheie
beton autoclavizat, metacaolin, zgură de furnal, microstructură, proprietăți mecanice
KARTHIK PRABHU.T, SUBRAMANIAN.K , JAGADESH.P , NAGARAJAN.V
Rezumat
Experimental programme is conducted on steel slag blended concrete, by partially replacing offline aggregate by steel slag up to 50%. The mechanical properties were determined by conducting cylinder compressive strength (CRCS), modulus of elasticity (MSE) and modulus of rupture (MSR).Comparison was done with conventional concrete and steel slag blended concrete in terms of strength and economy. Further modeling of relationships between the mechanical properties as CRCS, MSE and MSR of the concretes with fine aggregate replacement was done and validated with NZS:3101 (New Zealand Standard code 3101), AS: 3600 (Australian Standard code 3600) and ACI: 318 (American Concrete Institute code 318)
Cuvinte cheie
zgură de la oțelării, rezistență la compresiune, model de rupere, modul de elasticitate
LIU LIN , HAIXIA ZHANG, KAI GUO
Rezumat
In terms of curing method for buried heat-source concrete in winter, internal temperature field of concrete shows characteristic opposite to temperature field in the traditional concrete curing period during the curing process, with surface temperature higher than internal temperature. Therefore, based on porous structure characteristics of concrete, concrete moisture movement control equation is established according to the mechanism of moist heat transfer. The effects of ambient temperature, heat source temperature and heat source heating time on moisture transfer of buried heat-source concrete columns during the curing period in winter are analyzed by numerical simulation. Studies have shown that before the end of hydration, for the influencing factors, the higher the concrete-casting temperature and ambient temperature is, the lower the relative humidity is. After the end of hydration, the lower the ambient temperature is, the lower the relative humidity is, while the effect of surface exothermic coefficient on humidity is exactly opposite. The effect of heat source heating time on relative humidity is shown after the end of hydration. That is, for a longer heating time, vapor pressure in the pores increases due to the temperature field, and the relative humidity increases. The heat source temperature rises in the hydration stage accelerates hydration, and shortens the time for relative humidity to reach the reduction inflection point.
Cuvinte cheie
proces de cuplare hidraulică și termală, întreținerea construcțiilor iarna, transfer de umiditate
ANITA JESSIE. J., SANTHI A. S
Rezumat
Steel Fibre Reinforced Concrete (SFRC) has been very widely used in the structures such as thermal power plants due to its bonding effect, ductility, durability and stability of the structures at high temperatures. The concrete structure when exposed to high temperatures, shows the numerous chemical changes in the concrete which leads to deterioration of the structure. The flexural behaviour of the concrete prism with steel fibre volume fraction of 1.35% and without steel fibre, at room temperature (28ºC) and when exposed to elevated temperatures of 150ºC, 350ºC, 550ºC and 750ºC for the time period of 1 hour were observed. The Finite Element Analysis was done for the prism, to find the deflection on the plain concrete and steel fibre reinforced concrete when subjected to the same temperatures as mentioned above. The main objective of this study was to decrease the structural element failure when exposed to elevated temperature, which in turn increases the evacuation period of the occupants during fire accidents.
Cuvinte cheie
SFRC, temperatură ridicată, rezistență la flexibilitate, FEA, ABAQUS
R.MANJU
Rezumat
The structural integrity of concrete is known to improve by the incorporation of fibres in recent days. A 10% of Ground Granulated Blast furnace Slag (GGBS) and 10% of Silica Fume (SF) were used as replacements for cement binder along with 1.5% of fibre content dispersed in the mixture. This research discusses the influence of steel fibres, polypropylene fibres and supplementary cementitious materials in attaining High Strength Fibre Reinforced Concrete (HSFRC). Manufactured sand (M-sand) is employed as fine aggregate now that river sand has a commercial ban due to its scarce availability. A superplasticizer (SP) commercially marketed as Conplast SP430 is proportioned to 1.5% by weight of cement to improve the workability of the mixture. The study investigates the flexural behavior of three HSFRC beam specimens casted for a design characteristic compressive strength of 60MPa (M60 grade) under normal water curing conditions. The specimens were supported by a two-point loading setup and tested as per the Indian standards. It was evident from the results that the flexural strength of beams increased notably with the use of fibres in comparison with normal plain reinforced concrete beams and the same was validated through an analytical study using ANSYS software. The formation and width of cracks was much reduced in HSFRC beams compared to the conventional concrete beams. Reduction in cracks are an advantage in building up the durability of the specimens.
Cuvinte cheie
HSFRC, GGBS, SF, fibre polipropilenă, fimbre de oțel, nisip - M
XIAOGANG WU, SHUREN WANG, JIANHUI YANG, SEN ZHU
Rezumat
In view of the significant influence of fibre type and dosage on the mechanical properties of lightweight concrete, an experimental study was undertaken to analyze the mechanical performance characteristics, including compressive strength, splitting tensile strength, energy absorption, high temperature deterioration performance, fracture toughness and dynamic mechanical properties of steel fibre reinforced all lightweight concrete (SFRALWC), polypropylene fibre reinforced all lightweight concrete (PFRALWC), and basalt fibre reinforced all lightweight concrete (BFRALWC). Results showed that the specific strength, energy absorption index and dynamic peak stress of shale ALWC/FRALWC improved with the increase of the compressive strength, and the relation exhibites strong correlation characteristics, which ccould be expressed by quadratic polynomial. SFRALWC with optimal fibre dosage had the highest splitting tensile strength, specific strength, compressive strength and fracture toughness values. Steel fibre (SF) could significantly increase the plasticity, high temperature resistance to deterioration and dynamic impact resistance of all lightweight concrete (ALWC). Polypropylene fibre (PPF) could improve the plasticity and inhibited the high temperature bursting performance of ALWC. BFRALWC was most sensitive to the strain rate of dynamic impact. The conclusions obtained in the study can provide the reference to the similar engineering.
Cuvinte cheie
beton ușor, fibre, ceramsit, impact dinamic, performanță la deteriorare la temperatură ridicată
İLKNUR BEKEM KARA
Rezumat
This study investigates the effects of nano silica admixture on the behavior of cement mortars containing micro silica exposed to elevated temperatures. The cement mortars were incorporated with an optimized ratio of 5 wt% micro silica and 0,1,2,3wt % of nano silica admixtures. The specimens were exposed to elevated temperatures of 300 and 600 °C. After cooling, the mass loss, ultrasonic pulse velocity and compressive strengths of the specimens were determined. The investigations undertaken in this study were supported by scanning electron microscopic images. As a result, there is an optimum nano silica content which can be beneficial for improving the thermal resistance of cement mortars. Nano silica (2 wt%) improved the resistance of cement mortars containing 5 wt% micro silica at elevated temperatures.
Cuvinte cheie
mortar de ciment, nanosilice, microsilice, temperatură ridicată
K.SRINIVASREDDY , S.BALAMURUGAN
Rezumat
Using the geopolymer concrete/mortar in the construction industry can reduce CO2 emissions by consuming low embodied energy and fewer natural resources than the Ordinary Portland Cement (OPC). Most of the previous works on geopolymer concrete/mortar were cured in elevated temperature to attain the strength. This is considered to be a limitation in using the geopolymer technology in the construction industry. The present study investigated the effect of alccofine 1203 in the ternary blended geopolymer mortar and concrete with msand as fine aggregate and geopolymer specimens cured at ambient temperature. The results showed that with increasing the percentage of alccofine 1203 content in the ternary blended binder has significantly influenced the consistency, setting times and the compressive strength than the mix without alccofine 1203. Using fly ash, GGBFS and alccofine 1203 with msand can replace the use of OPC completely. The study also includes the effect of setting times and the SiO2 to Al2O3 ratio on the compressive strength of geopolymer specimens.
Cuvinte cheie
cenușă zburătoare, GGBFS, alccofine 1203, soluție alcalină, rezistență la compresiune
ALIREZA AFSHAR , AMIRHOSSEIN NOBAKHTI, ALI SHOKRGOZAR, AMIRHOSSEIN AFSHAR
Rezumat
In this research, we simulate the corrosive behavior of steel reinforcements on 5 different mixtures to investigate the effect of two powerful protective methods, including pozzolanic additives and corrosion inhibitor on concrete, by artificial neural networks (ANNs).
Related to this model, fly ash (FA), micro silica (MS), and slag were used as pozzolanic materials at an optimum 25%, 10%, and 25% of cement weight, respectively. Moreover, Ferrogard 901 as an inhibitor was also utilized. The producer recommends using12 kg/m3 to get the best possible results. The non-linear corrosion of concrete into a marine solution (3.5% NaCl) was simulated by the feed forward back propagation (FFBP) algorithm. Data acquisition happened over a period of 180 days, and according to the ASTM C876 standard for simulating harsh conditions, a period of 10 years was selected as the simulation period. The simulated results all align with collected data. The mixture with 10% of MS has the lowest corrosion current density and corrosion rate at the end of 3600 days, which are 0.38 µA/cm2 and 0.20 mpy, respectively. It provides the best protection against reinforcement corrosion.
Cuvinte cheie
beton puzzolanic, inhibitor, coroziune, simulare, rețele neurale artificiale
SADIK ALPER YILDIZEL , GOKHAN CALIS
Rezumat
In this study, physical, mechanical and durability properties of basalt fiber reinforced lightweight pumice concrete including water absorption, bulk density, strength and sulfate attack resistance were investigated. Taguchi method was proposed to optimize compressive strength, flexural strength and sulfate resistance properties. Ground Calcium Carbonate (GCC), Basalt Fiber (BF), and Pumice Aggregate (PA) ratio were used as three factors in the L16 Taguchi array. GCC was partially replaced with cement at the rates of 0 %, 5%, 10% and 15 % by weight. BFs (6mm) were added in four contents of 0.25 %, 0.50 %, 0.75 % and 1 % by volume of the mixtures. PA to aggregate content ratio were considered as 25 %, 30 %, 34 % and 38 %. 16 series of laboratory tests were performed on the prepared samples. The contribution of each factor was also evaluated with analysis of variance (ANOVA) method to determine the optimum levels. Experimental tests were also conducted in order to validate Taguchi optimization and ANOVA results.
Cuvinte cheie
beton ușor, fibre bazaltice, optimizare, metoda Taguchi, GCC
MURAT MOLLAMAHMUTOĞLU , EYUBHAN AVCI
Rezumat
The effect of superplasticizer on the grouting performance of superfine cement and the engineering properties of grouted sand were investigated. At first, the bleeding, setting time, and viscosity tests were conducted to determine the rheological characteristics of superfine cement grouts with or without superplasticizer at different water-cement ratios. Thereafter, the groutability of superfine cement grouts into various graded sand specimens with or without superplasticizer were tested. Those specimens grouted successfully were then subjected to unconfined compression tests at different time intervals. The addition of superplasticizer to superfine cement grouts increased their bleeding, initial and final setting times but decreased their viscosities. As the unconfined compressive strength (UCS) of superfine cement grouted sand specimens increased with the addition of superplasticizer. It was shown that the engineering properties of superfine cement grouted sand specimens were better improved with the addition of superplasticizer.
Cuvinte cheie
superplastifiant, ciment superfin, rezistență la compresiune, permeabilitate
JIANGANG NIU, JIAN LIANG, JINGJUN LI , XIAOPENG WANG
Rezumat
In this work, to decrease the chloride ion penetration of high-performance polypropylene fiber reinforced lightweight aggregate concrete (HPPLWAC), mineral admixtures were added into concrete mixtures in two forms. One was added in powder form and the other was using the mineral admixture paste to prewet the lightweight aggregates. The mineral admixtures including fly ash, slag, silica fume added in the separate or composite mixed forms. The scanning electron microscope (SEM) was used to observe the microstructures of concrete to reveal the improvement mechanism of permeability. The results showed that the separate mineral admixtures could decrease the chloride ion penetration of HPPLWAC. When 10% silica fume was added, the chloride ion diffusion coefficient of HPPLWAC decreased by 71.1% compared to the reference group and obtained the best resistance to chloride ion penetration compared to other groups. Composite mixed mineral admixtures could effectively improve the resistance to chloride ion penetration of HPPLWAC. The optimal resistance to chloride ion penetration was obtained when adding 20% slag and 10% silica fume into the reference group and its chloride ion diffusion coefficient decreases by 73.2% compared to the reference group. The lightweight aggregates prewetted by using mineral admixture paste could improve the chloride ion penetration of HPPLWAC, and the slag paste had the best effect. Using DPS to prewet lightweight aggregates had more significantly effect on improving the resistance to chloride ion permeability of HPPLWAC than lightweight aggregates prewetted by using mineral admixture.
Cuvinte cheie
fibre de polipropilenă de înaltă performanță, penetrarea ionului de clorură
NENAD RISTIĆ, ZORAN GRDIĆ, GORDANA TOPLIČIĆ ĆURČIĆ, DUŠAN GRDIĆ, DEJAN KRSTIĆ
Rezumat
Rapid technological and industrial development in the recent decades caused considerable environmental problems, and one of the most significant is, undoubtedly, disposal and recycling of waste materials and by-products of industrial production. Since concrete is a composite material, waste materials can suitably be used in its composition. In this paper, the research of effects of milled recycled glass from cathode tubes, flotation tailings from a copper mine, red mud and fly ash as mineral admixtures on properties of fresh and hardened self compacting concrete was presented. The test results indicated that the addition of such materials does not cause a decline in physico-mechanical characteristics and properties of durability of self-compacting concretes (SCC), and they even improve some aspects of concrete performance in comparison with SCC made with limestone filler as mineral admixture. Waste materials such as fly ash and recycled glass of cathode tubes (CRT) exhibit a puzzolanic activity, so the performances of the concretes with these admixtures proved to be better after ageing than the concretes with other admixtures.
Cuvinte cheie
beton autocompactant, CRT reciclare, nămol roșu, cenușă zburătoare, filer de calcar, proprietăți în stare proaspătă și întărită, durabilitate
MONTHER ABDELHADI, ANCUŢA ROTARU, NAFETH ABDEL HADI, NICOLAE ȚĂRANU, ANDREI BOBOC, OANA-MIHAELA BANU
Rezumat
Vestul orașului Amman, capitala Iordaniei, prezintă o stratificație de 4 până la 5 metri în adâncime de argilă brună care este considerată un teren dificil de fundare datorită variațiilor mari de plasticitate și de umflare-contracție, precum și a tasărilor diferențiate, având o capacitate portantă scăzută. Pe de altă parte, sudul Iordaniei dispune de depozite impresionante de șisturi bituminoase care se extind până la adâncimi considerabile. Guvernul iordanian a dat startul utilizării șisturilor bituminoase pentru producerea curentului electric și a petrolului rezultând cantități importante de cenușă. În această lucrare de cercetare se analizează efectul cenușii provenite din şisturi bituminoase, cenuşă bogată în var, asupra comportării argilei brune prăfos-nisipoase care ocupă zone întinse în centrul și nordul Iordaniei. Cenușa provenită din șisturile bituminoase a fost amestecată cu argilă brună, în diferite procente, analizându-se parametrii geotehnici ai amestecurilor obținute. Rezultatele arată efectul semnificativ de reducere a indicelui de plasticitate și a greutății specifice pe care cenușa provenită din șisturile bituminoase îl are asupra amestecului, precum și creșterea rezistenței la compresiune și a permeabilității până la un anumit procent de adaos. În ceea ce privește compresibilitatea, amestecul are un efect pozitiv în reducerea indicelui de compresiune (Cc) și al celui de umflare (Cs) ale argilei brune nisipos-prăfoase.
Cuvinte cheie
cenușă din șisturi bituminoase, argile brune nisipos prăfoase, indice de plasticitate, rezistență la compresiune
ADRIAN VOLCEANOV, ENIKÖ VOLCEANOV, COSMIN MĂRCULESCU
Rezumat
Scopul prezentei lucrări este de a investiga influenţa cenuşii provenind din arderea completă a lemnului de plop şi respectiv a lemnului de salcie. În acest scop, s-au preparat mortare de tencuială cu adaos de cenuşă în pondere de 2 şi 5% raportat la masa unui mortar de referinţă comercial. Elementele majore din cenuşa lemnoasă investigată sunt calciul, magneziul, potasiul şi carbonul. Sulful, fosforul şi manganul sunt prezente în pondere de aproximativ 1%. Siliciul, sodiul, fierul, aluminiul, cuprul, zincul şi borul sunt prezente în cantităţi relativ mai mici. In ambele cenuşi, au fost evidenţiate interferenţe puternice de difracţie cu raze X corespunzătoare Ca(CO3)2. Cenuşa de salcie conţine cantităţi relativ mai mari de potasiu în comparaţie cu cenuşa de plop şi prezintă interferenţe puternice corespunzător K2Ca(CO3)2. Cenuşa de salcie fiind mai bogată în sulf şi potasiu are în compoziţia mineralogică K2Ca(SO4). În mod similar, plopul, fiind mai bogat în sodiu, prezintă interferenţe foarte slabe, care corespund probabil compusului Na2Ca(SiO2)3. Adăugarea de cenuşă, indiferent de natura sa (plop sau salcie) sau de cantitatea sa nu a contribuit semnificativ la creşterea rezistenţei la compresiune a mortarului de referinţă comercial după 3 zile, 7 zile sau 28 de zile de întărire. Rolul lor a fost în principal de umplutură împreună cu agregatele de silice preexistente din mortarul comercial. În cele din urmă, rezistenţele la compresiune determinate experimental după 28 de zile de întărire plasează aceste mortare cu adaosuri de cenuşă sub valorile acceptate de clasa mortarului de referinţă. Cu toate acestea, utilizarea acestor cenuşi de plop sau de salcie generată după calcinarea lemnului la 650oC ca adaosuri pentru materialele liante din mortare pare să fie eficientă pentru reciclarea lor la tencuieli .
Cuvinte cheie
cenușă de plop, cenușă de salcie, mortare de tencuială, reciclare deșeuri
ERGANG XIONG , KUN ZU, TUANJIE FAN, LINBO LIU , LIANGYING SONG , QIAN ZHANG
Rezumat
This paper attempts to disclose the shear behavior of reinforced concrete (RC) beams designed by compressive force path (CFP) method. For this purpose, three beams were designed by the CFP method and another three by GB 50010-2010. For each type of beams, the three beams were prepared with different shear span ratios, respectively 2.0, 1.5 and 1.0. Then, a monotonic loading test was performed on all the beams. To identify the effect of shear span ratio on shear behavior, the author compared the CFP beams with GB beams in terms of ultimate load, failure process and failure mode. In addition, the load-deflection curve and load-strain curves of concrete, reinforcement and stirrups were analyzed in details. The results show that the shear capacity of RC beams is mainly affected by the stress transmitted along the CFP; Compared with the GB method, the CFP method, despite using fewer number of stirrups, effectively guaranteed the shear capacity of the beams with any of the three shear span ratios, and did not significantly change the ultimate load; the amount of stirrups saved by the CFP is negatively correlated with the shear span ratio of the beam. To sum up, the CFP method was proved as a feasible and rational way to design RC beams.
Cuvinte cheie
metoda prin compresiune Force Path (CFP), capacitatea de forfecare, proprietăți mecanice, beton armat