română VAN-HUONG NGUYEN, NORDINE LEKLOU, PIERRE MOUNANGA
Abstract
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.
Keywords
Metakaolin, Delayed ettringite formation (DEF), heat-cured mortar, expansion, concrete
G. SKRIPKIUNAS, G. YAKOVLEV, E. KARPOVA, P.L. NG
Abstract
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.
Keywords
Cement, Accelerating admixtures, Setting time, Calcium chloride, Multi-walled carbon nanotubes
NORDINE LEKLOU, PIERRE MOUNANGA
Abstract
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.
Keywords
Cementitious matrix, glass beads, microstructure, replica method, endogenous microcracking
YUE LI, ZHONGZHENG GUAN, ZIGENG WANG, PENG WANG, GUOSHENG ZHANG, QINGJUN DING
Abstract
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.
Keywords
concrete; ternary copolymer fibers; dispersion; compressive strength
DAMIR ZENUNOVIC , NESIB RESIDBEGOVIC, RADOMIR FOLIC
Abstract
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.
Keywords
concrete, chloride, diffusion, penetration, modeling, comparison
YANG LI, ZHENDI WANG, LING WANG
Abstract
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.
Keywords
Low atmospheric pressure; Pore; Bubble; Air entraining admixture
LINGJIE WU, LINZHU SUN, FANG YANG, DONGYAN WU, JUNLIANG ZHAO
Abstract
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%.
Keywords
concrete; ternary copolymer fibers; dispersion; compressive strength
RĂZVAN LISNIC, CRISTINA BUSUIOC , GEORGETA VOICU, SORIN-ION JINGA
Abstract
Two types of natural gypsum from different regions of Romania and two types of synthetic gypsum resulted in the flue gas desulfurization (FGD) industrial installation where characterized from compositional, structural and morphological point of view by thermal analysis, X-ray diffraction, scanning electron microscopy coupled with energy dispersive X-ray spectroscopy and laser granulometry. The mortars developed based on portland cement and different proportions of gypsum were also investigated in terms of setting time and mechanical properties (flexural strength and compression strength), in correlation with the visualization of the hydration products through scanning electron microscopy. The results were correlated with the purity and homogeneity of the analysed gypsum specimens.
Keywords
Portland cement; Natural gypsum; FGD gypsum; Setting time; Flexural strength; Compression strength
AGNE SMIGELSKYTE, RAIMUNDAS SIAUCIUNAS, MATTHIAS WAGNER, LIUDVIKAS URBONAS
Abstract
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.
Keywords
Rankinite, non-hydraulic binder, carbonation curing, CO2, opoka, limestone
KAMILE TOSUN FELEKOĞLU, EREN GÖDEK
Abstract
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.
Keywords
Lightweight ECC, air entrainment, rheological, mechanical, thermal, HTP
The compressive behaviour of aggregates cemented with fly ash collected from coal-fired power plants
ANCUŢA ROTARU, VASILE BOBOC, NICOLAE ȚĂRANU , MONTHER ABDELHADI, ANDREI BOBOC, OANA-MIHAELA BANU
Abstract
The paper analyses the compressive behaviour of aggregates stabilized with fly ash in Romania, investigating the possibility to use the fly ash residue obtained from the combustion of lignite type coal as a cement substitute material for road construction works. The experimental testing of some proposed mixes embedding 20%, 25%, and 30% of fly ash by weight of total mixture, collected from Iaşi and Vaslui coal-fired power plants, reveals that only the mixtures of aggregates stabilized with 30% of fly ash fulfill the acceptability conditions to be used as a base layer in road construction works. Instead, the mixtures stabilized with 20% and 25% of fly ash could be used as sub-base layers.
Keywords
compressive strength, fly ash, aggregates, cement-like material, road building work.
DAN GEORGESCU, LAURENȚIU RECE, ANCA IONESCU, ADELINA APOSTU
Abstract
The use of admixtures in the preparation of cement and concrete is already a widespread solution at national and European level. There is often the issue of promoting new compositions with varying percentages and types of additions for certain applications and exposure environments, the main issue being to ensure good behavior over time and to ensure a proper working life. The article presents the applications of performance-related methods used at European level to check the possibility of using new compositions in certain exposure environments. These methods stand for useful tools in completing the water/cement equivalent ratio method,expected to provide similar time behaviors to a reference composition. The article presents the 1frost-thawing resistance of concrete based on the results of experimental research carried out by the authors.
Keywords
concrete, cement with mineral admixture, compressive strength of concrete, k-value concept, performance methods.
PENG ZHAO, QIN LEI, XIUZHI ZHANG, WENJUAN HUAN, HAIJIAN MA
Abstract
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.
Keywords
Black Brick; Durability; Freezing-Thawing; Life Prediction; Model
S. JANANI, A.S. SANTHI
Abstract
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.
Keywords
fly ash; silica fume; steel fibres; mechanical properties; impact resistance; regression
AVUTHU NARENDER REDDY, T. MEENA
Abstract
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.
Keywords
Colloidal Nano Silica; Fly Ash; Alccofine; Blended Concrete; Compressive Strength; Split Tensile Strength; Flexural Strength and Water Absorption
GIDEON BAMIGBOYE , ADEOLA ADEDEJI, DAVID OLUKANNI, KAYODE JOLAYEMI, OLALEKE FASANYA
Abstract
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.
Keywords
Self-compacting concrete, concrete, durability, sodium chloride, cement, sodium carbonate, compressive strength
ODAY M. ALBUTHBAHAK , ASHRAF A. M. R. HISWA
Abstract
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.
Keywords
Concrete Compressive Strength, Ultrasonic Pulse Velocity, Machine Learning Models, Artificial Neural Network ANN, Support Vector Machine, Decision tree, Regression.
RIMVYDAS KAMINSKAS, IRMANTAS BARAUSKAS
Abstract
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.
Keywords
Portland cement, Autoclaved Aerated Concrete Waste, additives, energy consumption
QUAN WAN , MINLI ZHENG, SHUCAI YANG, WEIWEI LIU
Abstract
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.
Keywords
Cemented Carbide Tool; Micro-Textured Surface; Laser Machining; Heat Affected Zone (HAZ)
S PRAVEENKUMAR , G SANKARASUBRAMANIAN
Abstract
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
Keywords
bagasse ash, high Performance concrete, steel fibres, polypropylene fibres
LIVIA INGRID DIACONU, DIANA PLIAN, NICOLAE ȚĂRANU , OANA MIHAELA BANU, ADRIAN CONSTANTIN DIACONU, DĂNUȚ TRAIAN BABOR
Abstract
The aim of this paper is to present an assessment method for the modification of some essential characteristics of the concrete mixes embedding fly ash subjected to an accelerated corrosion process using softened warm water. In the construction elements exposed to water, the dissolving – levigation corrosion phenomenon occurs by washing the calcium hydroxide from the cement stone, affecting the durability characteristics. A special equipment that enables the acceleration of the processes developed in concrete structure when exposed to softened warm water was designed and constructed to subject the concrete samples to this type of corrosive attack. After subjecting the concrete specimens to softened warm water, several physical and mechanical tests were performed to determine the unit weight, the water absorption, the permeability and the compression strength. A total number of 117 cubic samples were tested for a period of 36 months to observe the behaviour of fly ash concrete mixes subjected to the corrosive attack of softened warm water.
Keywords
concrete, ash admixture, corrosion, dissolving – levigation
LIANA IUREŞ, CORNELIU BOB, REMUS CHENDES, CĂTĂLIN BADEA, RADU POPA
Abstract
The concrete it is delivered on the construction site having two main characteristics: it will harden and it will present drying cracks. The cracks due to hardening of the concrete will lead to complains of the beneficiary and to shortening of the durability of the concrete structure. The drying shrinkage sensibly influences the resistance structures’ integrity. It was noticed that for the elements that have the free shrinkage constrained, it is possible to appear cracks. The present paper propose the introduction of two new coefficients: - characteristic shrinkage and - cracking indices, that are for a facile characterisation of the efficiency of an admixture used in concrete, on the reduction of the shrinkage effects and cracking tendency.
Keywords
concrete, durability, shrinkage, admixtures
RUI-XI DAI, HUA CHENG, GUO-XIN ZHENG, JUN-RU REN, CHAO-SHAN YANG, XIN-HAO ZHENG
Abstract
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.
Keywords
non-autoclaved; concrete brick; superabsorbent polymer; special binder; island environment
LEONID DVORKIN, VADIM ZHITKOVSKY , YURI RIBAKOV, OLEH BORDIUZHENKO , ANTON STEPANUK
Abstract
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.
Keywords
binder, dust, kiln, grinding, hydration degree, strength
R. GOPI , V. REVATHI
Abstract
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.
Keywords
Self compacting concrete, Curing, Strength, Micro structure, Durability
KADIR GÜÇLÜER , İSMAIL DEMIR
Abstract
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.
Keywords
Autoclaved aerated concrete, Metakaolin, Blast Furnace Slag, Microstructure, Mechanical Properties
KARTHIK PRABHU.T, SUBRAMANIAN.K , JAGADESH.P , NAGARAJAN.V
Abstract
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)
Keywords
Steel Slag, Cylinder Compressive Strength, Modulus of rupture, Modulus of Elasticity
LIU LIN , HAIXIA ZHANG, KAI GUO
Abstract
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.
Keywords
heat and moisture coupling; winter construction maintenance; moisture movement
ANITA JESSIE. J., SANTHI A. S
Abstract
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.
Keywords
SFRC, High temperature, Flexural strength, FEA, Deflection, ABAQUS
R.MANJU
Abstract
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.
Keywords
High Strength Fibre Reinforced Concrete (HSFRC), Ground Granulated Blast Furnace Slag (GGBS), Silica Fume (SF), Polypropylene fibre, Steel fibre and M-sand
XIAOGANG WU, SHUREN WANG, JIANHUI YANG, SEN ZHU
Abstract
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.
Keywords
Lightweight concrete, Fibre, Shale ceramsite, Dynamic impact, High temperature deterioration performance
İLKNUR BEKEM KARA
Abstract
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.
Keywords
Cement mortar, nano silica, micro silica, elevated temperature
K.SRINIVASREDDY , S.BALAMURUGAN
Abstract
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.
Keywords
fly ash, GGBFS, alccofine 1203, alkaline solution, and compressive strength
ALIREZA AFSHAR , AMIRHOSSEIN NOBAKHTI, ALI SHOKRGOZAR, AMIRHOSSEIN AFSHAR
Abstract
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.
Keywords
pozzolanic concrete, inhibitor, corrosion, simulation, artificial neural networks
SADIK ALPER YILDIZEL , GOKHAN CALIS
Abstract
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.
Keywords
Lightweight concrete, basalt fiber, pumice concrete, optimization, Taguchi method, GCC
MURAT MOLLAMAHMUTOĞLU , EYUBHAN AVCI
Abstract
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.
Keywords
Superplasticizer; Superfine cement; Groutability; Unconfined compressive strength; Permeability
JIANGANG NIU, JIAN LIANG, JINGJUN LI , XIAOPENG WANG
Abstract
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.
Keywords
high-performance polypropylene fiber; lightweight aggregate; chloride ion penetration; prewetting; microstructure
NENAD RISTIĆ, ZORAN GRDIĆ, GORDANA TOPLIČIĆ ĆURČIĆ, DUŠAN GRDIĆ, DEJAN KRSTIĆ
Abstract
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.
Keywords
self compacting concrete, recycled CRT, flotation tailings, red mud, fly ash, limestone filler, fresh and hardened properties, durability
MONTHER ABDELHADI, ANCUŢA ROTARU, NAFETH ABDEL HADI, NICOLAE ȚĂRANU, ANDREI BOBOC, OANA-MIHAELA BANU
Abstract
The western part of Amman, the capital of Jordan, holds a layer of 4 to 5 meters depth of problematic brown clay that exhibits a wide range of plasticity, swelling, settlements and low shear resistance. On the other hand, south Jordan holds large deposits of bituminous oil shale that extend to considerable depths. The government of Jordan has decided to start using the bituminous oil shale for power generation and oil production resulting large amounts of ash. This research work studies the effect of bituminous oil shale ash, rich in lime, on the characteristics of the silty-sandy brown clay that spreads on large areas in the middle and northern areas of Jordan. The oil shale ash has been mixed with brown clay in different percentages and some geotechnical parameters of the resulted mixtures have been measured and analysed. The outcomes of this work show that there is a significant effect of the bituminous oil shale ash on reducing the plasticity index of the mixture, on decreasing its dry unit weight, as well as on increasing its compressive strength and permeability to a certain percentage of added ash. In addition, the mixture has a positive effect on reducing the compression index (Cc) and the swelling index (Cs) of brown silty-sandy clays.
Keywords
bituminous oil shale ash, silty-sandy brown clay, plasticity index, compressive strength
ADRIAN VOLCEANOV, ENIKÖ VOLCEANOV, COSMIN MĂRCULESCU
Abstract
The purpose of the present paper is to investigate the influence of ash coming from the complete burning of poplar wood and willow wood, respectively. For this purpose, plaster mortar with ash with 2 and 5% admixtures to a commercial reference mortar was prepared. The major elements in the investigated wood ash are calcium, magnesium, potassium and carbon. Sulfur, phosphorus and manganese are present at around 1%. Silicon, sodium, iron, aluminum, copper, zinc, and boron are present in relatively smaller amounts. Strong peaks corresponding to Ca(CO3)2 were identified in both ash. The willow ash contains relatively higher amounts of potassium compared to poplar ash and show strong peaks corresponding to K2Ca(CO3)2. Willow ash being richer in sulphur and potassium has K2Ca(SO4). Similarly, poplar, being richer in sodium, displays very weak peaks corresponding probably to Na2Ca(SiO2)3 compound. The addition of ash, regardless of its nature (poplar or willow) or its amount did not contribute to the increase of the resistance of the commercial reference mortar after 3 days, 7 days or 28 days of hardening. Their role was mainly of filler together with pre-existing silica aggregates from the commercial mortar. Finally, the compressive strengths determined experimentally after 28 days of hardening place these mortars with ash admixtures below the values accepted by the starting reference mortar class. However, the use of poplar or willow ash generated after calcinations at 650oC as admixtures for binder materials in mortar seems to be effective for their recycling in plastering mortars.
Keywords
Ash, Willow, Poplar, Wood, Mortar, Waste Recycling
ERGANG XIONG , KUN ZU, TUANJIE FAN, LINBO LIU , LIANGYING SONG , QIAN ZHANG
Abstract
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.
Keywords
Compressive Force Path Method; Shear Capacity; Shear Span Ratio; Mechanical Properties; Stirrup