română DOREL RADU, ZENO GHIZDAVET
Abstract
Clinker minerals are of the outmost importance as they are responsible for final product’s performance, i.e. cement’s performance. Experimental are the best way to achieve accurate results as concerning the optimal clinker composition but they become expensive when exploring a large searching space. Mathematical optimization programing techniques, used here, can help to reduce the amount of experiments. An additional benefit is that such computational techniques can incorporate, as it is shown here, various technological and/or thermo-technical constraints. In this paper, raw materials’ burnability and the oxides basicity weight played a decisive role along with other, supplementary constraints.
Keywords
clinker composition, optimization, burnability
QINGWEI SUN , HAN ZHU, HAOYU LI, HAIYANG ZHU
Abstract
A series of research experiments was designed and conducted in this study using the Box–Behnken design method of response surface methodology (RSM) to solve the optimization problem of parameters effectively in fly ash geopolymer concrete preparation. First, single-factor gradient analysis was adopted to determine the reasonable level of various factors in the response surface analysis. The 28-day compressive strength development was investigated in terms of the water–binder ratio, dosage of alkali, unit water dosage, and sodium silicate modulus. Results showed that the order of the factors in terms of their influence on concrete strength was dosage of alkali, sodium silicate modulus, and water–binder ratio, and the unit water dosage exerted a minimal influence. Second, the preparation parameters were optimized to improve the 28-day compressive strength of the concrete based on the single-factor analysis using the RSM. The optimum parameters were a water–binder ratio of 0.35, an alkali dosage of 7.9%, and a sodium silicate modulus of 1.66. This study also analyzed the response surface optimization results through a validation test to prove the effectiveness of the RSM in optimizing the preparation of geopolymer concrete.
Keywords
fly ash; geopolymer concrete; strength; preparation parameters; response surface methodology
XIAONIU YU , SUN LINZHU, FANG YANG
Abstract
With a double-layer stirrup confined high-strength concrete column as study object, vertical loading experiments were conducted, and the strain field of the member during loading was measured dynamically using the digital image correlation technology. The experimental results show that, for double-layer stirrup confined high-strength concrete, the strain change differs greatly between the early and late stages of loading, being smooth in the early stage and active in the last stage. Through the analysis of the full-field strain of the member, the displacement grid diagrams and strain distribution contour plots at different stress levels were obtained. From the contour distribution was determined that, during loading, the strains in the member are different at different positions and they are also different at different time points at one position. There is a stress concentration area during loading, where a “strain rebound” phenomenon occurs after the stress reaches its peak. The strain calculation results also reveal that selecting different areas for calculation will have large influence on the calculation results regarding the overall strain of the member. In addition, the experiments also indicate that, due to its non-contact and full-field features, the digital image correlation technology is suitable for dynamic measurement of structural force, and it is a powerful means for deformation detection and health monitoring of a structure.
Keywords
digital image correlation; double-layer stirrup; concrete; bearing capacity; strain rebound
A.SUMATHI , K. GOWDHAM , K. SARAVANA RAJA MOHAN
Abstract
The study of High Strength Concrete (HSC) has become interesting as concrete structures grow taller and larger. The usage of HSC in structures has been increased worldwide and has begun to make an impact in India. Ordinary cementitious materials are weak under tensile loads and fiber reinforced cementitious composites (FRCCs) have been developed to improve this weak point. Specimens such as cubes, cylinders were cast for High Strength concrete containing Alccofine as mineral admixture and reinforced with micro steel fibers to study the mechanical and durability properties at 28 days and 56 days of curing. The concrete were designed to have compressive strength of 60 MPa. Mixtures containing 0% and 10% replacement of cement by Alccofine and with 1%, 2% and 3% of micro steel fibers by weight of concrete were prepared. Durability properties such as Sorptivity, water absorption, resistance against Sulphuric acid, Sodium sulphate and Magnesium sulphate were studied for control, Alccofine and Alccofine with steel fibers for different days of curing. Mixtures incorporating Alccofine with fibers developed marginal increase in strength and durability properties at all ages when compared to control concrete.
Keywords
HSC, Alccofine, Micro steel fibers, Fiber content, Compressive strength, Split tensile strength, Durability, Sorptivity, Acid and Sulphate resistance, Water absorption
MALHEIRO RAPHAELE, AIRES CAMÕES, GIBSON MEIRA
Abstract
To ensure the durability of concrete structures it is necessary to understand its behaviour in the presence of aggressive agents. Carbonation and chloride ingress are the two main causes of degradation in reinforced concrete. The combination of these factors can create a very harsh environment for concrete structures. Given the importance of chloride migration coefficient for areas such as service life prediction, this work intends to study the influence of carbonation on the chloride migration coefficient of ordinary Portland cement (OPC) concrete. Concrete specimens were cast with different water cement ratios: 0.4, 0.5 and 0.6. After 90 days of curing, half of samples were subjected to carbonation chamber (4% CO2, 20 ºC and 55% RH) for 6 months. The other half was protected with plastic sheet during the same period. Non-steady-state migration test was performed in specimens with and without exposure to carbon dioxide environment. The results show that, for these conditions, the carbonation has a direct influence on chloride diffusion coefficient, increasing it. The carbonated samples studied showed a chloride migration coefficient up to 130% higher than noncarbonated ones. This fact can be related to the reduce in chloride binding capacity caused by carbonation front.
Keywords
Chloride, migration test, carbonation, concrete, combined action.
YAO YAN , TANG GUANBAO, WANG LING, CUI SUPING, CAO YIN
Abstract
In this study, the effect of CO2 concentration on carbonation depth, semi-carbonated zone, pore size distribution and carbonation products in concrete were investigated. The CO2 concentration was increased from 0.035 % to 2 % and 20 % at 70 % relative humidity and 20 °C. The results show that the carbonation process of 2 % CO2 was more similar to natural carbonation than 20 % CO2, as evidenced by the better linearity fitness of carbonation depth. The length of semi-carbonated zone was 6 mm at 2 % CO2 and 8 mm at 20 % CO2 within 16 weeks, a number that cannot be ignored when predicting the service life of concrete under carbonation. CH remained in a small amount in the completely carbonated zone instead of being completely consumed, and CH consumed at 20 % CO2 is about 1.5-2.0 times that of 2 % CO2. The content of CaCO3 in the completely carbonated zone at 20 % CO2 was higher than that of 2 % CO2. CaCO3 could fill in large pores between hydration products, so the porosity, average pore size and aperture decreased with CO2 concentration.
Keywords
Concrete Carbonation; CO2 Concentration; Carbonation Depth; Semi-carbonated Zone; Carbonation Products
ILDIKÓ ANGER, ENIKÖ VOLCEANOV, GEORGIANA PLOPEANU, LEONARD ILIE, LAVINIA GABRIELA POPESCU, GEORGIANA ALEXANDRA MOISE
Abstract
The paper presents some researches on ladle furnace slag potential to be used in agriculture, as soil amendment. The ladle furnace (LF) slag results from steel secondary refinery. The main components of LF slag used in our experimental trials were: CaO, SiO2, Al2O3, MgO. The LF slag contains high quantity of CaO, which forms different compounds with SiO2 and Al2O3, as well as unreacted CaO too. This is the main reason why this slag can be considered in agriculture as soil amendment to correct the soil acidity. The soil acidity influences the soil fertility and the crop yield. Usually, the soil acidity is corrected by using limestone or dolomite, natural materials. The utilization of LF slag as soil amendment to soil acidity is a novelty in Romania.
It is presented the influence of LF slag admixture on soil remediation, namely on pH, chemical properties and heavy metal content. It is also shown the influence of ladle slag used as soil amendment on the crop yield and on the heavy metal content in the soil and cultivated plants (maize, wheat and soybean) at the experimental sites. The experimental trials indicate that the LF slag can be used for acid soil remediation, having a positive influence on soil chemical properties and increase the crop yield.
Keywords
steelmaking, ladle furnace (LF) slag, acid soil, soil amendment
RĂZVAN LISNIC, SORIN ION JINGA
Abstract
Fossil fuels used in thermal power plants contain significant amounts of sulfur. At burning, about 95% of the sulfur is converted to sulfur dioxide (SO2), which reacts with the particles of water in the atmosphere, forming acid rain under normal conditions of temperature and pressure. Sulfur dioxide, through its annual emissions, is the main gas pollutant, which is why over the last 80 years has been a concern for the development and streamlining of desulphurization processes. The flue gas desulphurization can be done both by wet or dry process. The most widespread process is wet desulphurization of limestone or lime, accounting for about 85% of all desulphurization processes. The paper presents the current state of the desulphurization technologies in the world, their advantages and disadvantages, as well as the future trends in this field.
Keywords
limestone, flue gas desulphurization, sulphur dioxide, FGD-gypsum, fly ash
SEBASTIAN MARIAN ZAHARIA, CRISTIN OLIMPIU MORARIU, MIHAI ALIN POP
Abstract
The sandwich panels are frequently used as structural elements in various industrial applications, due to their increased rigidity reported to their weight, but also due to their advantages compared to conventional metallic structures or laminated composite structures. This paper presents the behaviour under static and fatigue regime of two sandwich structures with the same type of Nomex honeycomb core, but with skins made from glass fibre reinforced polymer composites, manufactured through different methods. Likewise, the mechanical characteristics of the two types of sandwich structures were compared and analysed. In this paper the behaviour under cyclical fatigue of the two sandwich structures, subjected to 3-point bending, was tested and predicted by implementing the accelerated testing techniques. The accelerated methodology developed in this paper has determined a significant reduction of the testing time for the analysed specimens. Consequently, the testing time for the GFRP1-Nomex specimens was reduced by 6.35 times, respectively by 7.9 times for the GFRP2-Nomex specimens, which determined a significant cost reduction in the testing of composite sandwich structures. Also, the main failure modes of the sandwich structures, subjected to Charpy impact, were identified and analysed using microscopically analysis.
Keywords
glass fiber reinforced polymer, sandwich panels, bending, fatigue, accelerated testing
LINO BIANCO
Abstract
The Lower Globigerina Limestone Member, the earliest member of the Globigerina Limestone Formation, is the lithostratigraphical bed which had provided limestone for the erection of Malta’s built heritage since Neolithic times. It is massively bedded, pale yellow in colour and consists predominantly of globigerinid planktonic forminifera. Occasionally, blue coloured lenticular patches occur in this member. The first published research relating to these features was by John Murray in 1890. His results and interpretation were corroborated and refined through a recent publication by the author which noted variations from packstone to wackestone along these patches. This paper further studies their petrological characteristics. Petrographically, the limestone of these patches gradually alternates from wackestone to mudstone to bioclastic wackestone. They are composed of micrite matrix (in varying amounts), ferrugenized unbroken pelagic foraminifera, bioclasts, and terrigenous quartz. The appearance of these blue lenticular patches must be linked to another process other than limestone texture.
Keywords
Globigerina Limestone, sol, sol ikħal, blue patches, John Murray, Malta
CRISTINA DIMA (VĂDUVA), ALINA BĂDĂNOIU, ȘTEFANIA STOLERIU, CRISTIANA DANEȘ
Abstract
The valorization of industrial wastes in the manufacture of composite materials is topical in construction industry. The main objective of this study is to improve the thermal insulation properties of some gypsum plaster composites by it’s partial substitution (5 and 30%wt.) with three types of industrial wastes i.e. polyurethane, rubber and chopped electric cables; the paper present also the influence of wastes on the main properties specific for thermal insulation materials (thermal conductivity, compressive strength, short-term water absorption by partial immersion).
The use of the above mentioned industrial wastes in the composition of gypsum plaster elements determines an improvement of thermal insulation properties (thermal conductivity decrease with 17-23%) correlated with a decrease of compressive strength comprised between 68-87%.
The manufacture of this type of insulation materials can contribute to solving environment issues, decreasing the amount of natural raw material used and valorization of industrial as sustainable sources of alternative raw materials.
Keywords
thermal insulation materials, gypsum plaster, industrial waste, thermal conductivity, properties
N. KYBARTIENĖ, D. NIZEVIČIENĖ, Z. VALANČIUS, G. VAICKELIONIS
Abstract
Gypsum raw material (reagent gypsum, phosphogypsum and processed phosphogypsum) was dehydrated by dry method (i.e. in dry air environmental) and wet method (i.e. saturated water vapour environment) using microwaves. Influence of dehydration method on hemihydrate gypsum, hemihydrate phosphogypsum and processed hemihydrate phosphogypsum crystal morphology was researched. Gypsum raw material dehydration in dry air environment using microwaves does not significantly influence the morphology of hemihydrate gypsum, hemihydrate phosphogypsum or processed hemihydrate phosphogypsum crystals. Meanwhile, when raw material is dehydrated in the saturated water vapour environment using microwaves, the produced product crystals are smaller comparing to crystals of products dehydrated without microwaves. Therefore, it may be stated that using microwaves for gypsum raw material dehydration has no positive effect on the morphology of the obtained product crystals.
Keywords
gypsum, phosphogypsum, dehydration, microwaves, crystals
YAOHUI MA, DEZHI ZHAO, LIN CHI, ZHENG WANG, YAN YAO, SHUANG LU
Abstract
In this numerical study, finite element method (FEM) is employed to demonstrate temperature and stress simulations of autoclaved aerated concrete (AAC) shear walls in different seasons by using ANSYS software. Structural behavior simulation is conducted by a good combination of comprehensive material properties and reasonable models. Calculation results show that, compared with the ordinary mortar (OM), the insulation mortar (IM) can effectively reduce f temperature variation in AAC matrix layer by 1.668℃ in summer and 5.315℃ in winter, which indicates a better performance on heat insulation. In terms of thermal stress, IM layer would withstand a greater stress in all cases, but it could lower the maximum stress in AAC layer and interface stress by almost 50% in winter compared with wall structures with OM. As for temperature deformation, a 17% reduction in winter and a 30% reduction in summer are observed in AAC matrix layer coated with IM.
Keywords
FEM, AAC shear walls, thermal stress, temperature deformation
JUAN HE, JUN CAI, ZHENMAO SUN
Abstract
Hydration Characteristics of alkali–activated slag cement (AASC) are different of those of ordinary Portland cement. Effects of activator type, modulus of water glass (WG), and Na2O equivalent on setting time, compressive strength, hydration heat and hydration products were studied. The results show that with the increase of modulus in the range of 0.8-2.0, initial and final setting time of AASC extends gradually. As for hydration heat, When WG modulus increases from 0.8 to 2.0, the first combined peak of AASC grows lower and grows a bigger diffusion; accelerated hydration peak appears later; induction period prolongs and cumulative hydration heat reduces. When Na2O equivalent increases from 3% to 6%, for WG-activated slag, the first peak and accelerated hydration peak appear earlier and higher, induction period becomes shorter and setting time of paste is somewhat longer. Besides, for NaOH (NH)-activated slag, initial peak and accelerated hydration peak appear earlier and higher and setting time of paste is shorter. Cumulative hydration heat of both AASC increases with the increase of Na2O equivalent. At the same Na2O equivalent, setting time of slag activated by NaOH is longer than WG-activated slag cement, and compressive strength of the former is lower than the later. In the range of 0.5-2.2, with the increase of modulus, compressive strength of AASC first increases, then was followed by a decrease. The main hydration product is C-A-S-H gel.
Keywords
Alkali–activated slag cement, Activator, Hydration heat
NAILIA R. RAKHIMOVA, RAVIL Z. RAKHIMOV, YEVGEN S. LUTSKIN, VLADIMIR P. MOROZOV, YURI N. OSIN
Abstract
In this study, a mineral matrix based on alkali-activated slag cement (AASC) was found to be suitable for solidification of up to 35% (by volume) of borate ion-exchange resins (IERs) at pH values of 8.5 to 10.5. Experimental-statistical modelling, X-ray diffraction, and scanning electron microscopy/energy dispersive spectroscopy analyses were used to study the waste samples. According to the results of a four-factor experiment, the strengths of waste samples based on AASC-based mineral matrices and borate IERs were mostly determined by the nature of the alkali component and the pH of the borate IERs. The strengths of the waste samples could be improved by some modifications of the binder material - increasing the Na2O concentration and introducing polypropylene fibres. The main reaction products in the (GGBFS)-(sodium metasilicate, sodium hydroxide)-(borate solution) system were C-(A)-S-H, calcite (CaCO3), hydrotalcite (MgO6.667Al0.333)(OH)2(CO3)0.167(H2O)0.5, calcium silicate hydrates
Keywords
alkali-activated slag cement, modeling, ion-exchange resin waste, compressive strengths, calorimetric test, polypropylene fibre
DAN GEORGESCU, LAURENȚIU RECE, BIANCA PIRONEA, ADELINA APOSTU
Abstract
This paper presents a methodology for assessing the concrete characteristics starting from the analysis of the critical points generated by concealed works. It presents a new approach to the existing one and is exemplified by an application for assessing the strength of concrete in new constructions. The application of the method is based on the most recent proposals for revision of specific European regulations.
Keywords
concrete, strength, assessment, methodology, concealed works
CAI JUN, LI GENGYING, ZHAO XIAOHUA
Abstract
As an advanced construction material, self-consolidating concrete (SCC) is a highly flowable concrete that is able to fill the formwork under its own weight without vibration. This paper presents a study on fatigue performance of SCC under flexural load. An experimental program has been carried out to investigate the fatigue lives of SCC for various levels of the fatigue stress. The fatigue tests on SCC beam specimens (100 × 100 × 400 mm) were conducted. The fatigue test data of SCC is used for regression analysis. The results indicate that the flexural fatigue life distribution of SCC approximately follow the double-parameter Weibull distribution. The regression parameters of the fatigue equation corresponding to different survival probabilities have been obtained. The flexural fatigue strength of SCC for the desired level of survival probability can be estimated by using the fatigue equation.
Keywords
self-consolidating concrete, fatigue, flexural load, stress level.
V. KARTHIKA, P. O. AWOYERA, I. I. AKINWUMI, R. GOBINATH, R. GUNASEKARAN, N. LOKESH
Abstract
This study investigates the structural properties of lightweight self-compacting concrete produced using mineral admixtures and pumice stone as aggregate. Lightweight self-compacting concrete (LWSCC) mixes were prepared using pumice stone as replacement for natural coarse aggregate, and ground granulated blast furnace slag and rice husk ash were added as mineral admixtures. The flowability of the concrete mixtures was achieved by using gelinium B223 super plasticizer. Structural properties such as: density, compressive strength, flexural strength, and split-tensile strength of the concrete samples were determined for different mix proportions. Test results revealed that 30-40% replacement of coarse aggregate by pumice stone is considerable for improved density, compressive strength, split tensile strength and flexural strength development in LWSCC.
Keywords
self-compacting concrete, pumice stone, Lightweight concrete, mineral admixture, Super plasticizer
G. MURALI, K. KARTHIKEYAN, M.K. HARIDHARAN
Abstract
In this paper, the impact strength of four concrete mixtures namely green high performance plain concrete (GHPPC), green high performance and steel fibre reinforced concrete (GHPSFRC) subjected to drop weight test was statistically investigated. The steel was incorporated each at a dosage of 0.5%. The pre-determined green concrete mixtures were prepared with 2% of nano silica as cement replacement and 30% of copper slag as fine aggregate replacement. From each type, 40 specimens were tested using the drop weight test in accordance with procedure proposed by ACI Committee 544 and their impact strength was determined. Results showed that the distribution of impact strength of GHPPC and GHPSFRC were approximately normal. The minimum number of tests necessary for attaining the impact failure strength of, GHPPC and GHPSFRC specimens were found to be 57 and 41 respectively at 95% level of confidence with an error below 10%.
Keywords
Statistical analysis, First crack strength, Failure strength, Fibres, Steel
LING QIN , XIAOJIAN GAO, HUAN YE, TIEFENG CHEN
Abstract
This paper aims to investigate effects of anti-foaming admixture (AFA) on air content, flowability, mechanical strength and microstructure of ultra-high performance concrete (UHPC). UHPC mixtures were prepared with two water-binder ratios of 0.17, 0.2 and three AFAs (XP1, XP2, XP3) were added by 0.05-0.4% of the mass of binder. Results reveal that the air content of fresh UHPC mixture decreases whit the incorporation of AFA and XP1 behaves the best decreasing effect. The compressive strength of UHPC added with AFA is increased and XP2 presents the best effect. The decrease of water-binder ratio from 0.2 to 0.17 doesn’t lead to an increase in compressive strength due to the more air bubbles entrapped in very low water-binder ratio mixture. A good exponential relationship (f=a*x^b) can be found between compressive strength and entrapped air content. The incorporation of AFA decreases the coarse pore content (＞100nm) and air bubbles with diameter bigger than 100μm in hardened specimen, playing a positive role in optimizing pore structure and improving strength.
Keywords
Ultra-high performance concrete; Workability; Compressive strength; Pore size distribution; Anti-foaming admixture
SADIK ALPER YILDIZEL
Abstract
Fiber reinforced composites have been widely used for various building purposes. Glass fiber reinforced composite containing white cement, gypsum, silica sand and perlite were analyzed in this research. The flexural strength, shrinkage behavior and the freeze-thaw (F&T) resistance of the composites were examined. It was obtained that the use of expanded perlite and silica sand enhances the shrinkage properties of the composite. Especially, expanded perlite used as the replacement of silica sand at the rate of 15 % has significantly enhanced the mechanical properties of the gypsum added composites against the freeze and thaw (F&T) and the shrinkage effects. Researched composite type and the outcomes of the study can be used in the composite production industry for improving the durability and sustainability.
Keywords
Glass fiber, gypsum, white cement, composite, silica sand, perlite
IRINA ȘTEFAN (OANCEA), MARINELA BĂRBUȚĂ, MIHAI BUDESCU, PETRU MIHAI, ANA MIHAELA BANU, NICOLAE ȚĂRANU
Abstract
The paper presents the experimental results in terms of mechanical properties obtained for some types of innovative micro-concrete (MC) mixes. This type of concrete utilises aggregates up to 8mm and the main intended use is for non-structural elements such as insulation panels. In this respect, two concrete mixes have been prepared using fly ash (FA) as replacement for 10% of the cement dosage, and two types of waste plastic materials: polystyrene (PO) granules and recycled polyethylene terephthalate (PET) bottles aggregate. They were introduced as substitution of the fine natural aggregate (FNA) (0-4 mm), in different proportions ranging from 30% to 100%.
The values of the experimentally determined mechanical strengths (compressive strength, flexural strength, split tensile strength) for both types of micro-concrete are smaller than the ones of the reference mix. The complete stress-strain curves of these materials subjected to compression have been established to evaluate the absorption capacity of the strain energy. The values achieved for the micro-concrete mixes with PET aggregates were higher than the ones of the mixes embedding polystyrene granules. By increasing the dosage of waste materials as natural aggregates partial replacement, a lightweight concrete was obtained.
Keywords
fly ash, waste PET bottles aggregate, polystyrene granules, mechanical strengths, complete stress-strain curves.
AYDIN RUSEN
Abstract
High temperature crystal chemistry and thermal behavior of the boron minerals bear special attraction, owing to the increase in their application areas requiring elevated temperature. Colemanite 2CaO·3B2O3·5H2O) is one of the most commonly found and used compound among the boron minerals. In this study, therefore, thermal and mineralogical characterization of the colemanite was performed by X-ray Diffractometer (XRD) and Thermal Gravimetric Analysis (TG-DTA). Also, mineralogical changes in crystal structure were measured and recorded during heating from room temperature up to its melting temperature for each 50°C by using High Temperature XRD device. By this way, structural changes in the colemanite up to melting point were determined with increasing temperature for the first time. Results indicate that the thermal decomposition of colemanite has revealed a multi stage internal process; i) moisture removal, ii) dehydration- dehydroxylation, iii) amorphization of the crystal structure, iv) recrystallization of the amorphous solid (gradual reconstitutions).
Keywords
Colemanite, Thermal decomposition, HTXRD, TG-DTA
ZHANG XIAO-NAN, SHAN REN-LIANG, QI CHENG-ZHI
Abstract
Through the monitoring of the displacement of the middle accross section in concrete filled steel tube (CFST) arch with 0.26 rise-span ratio, which fixed at both ends under the condition of uniform loading, as well as the strain and the ultimate bearing capacity of outer steel pipe and inner core of concrete which combined with ABAQUS for simulation analysis of bending process. Meanwhile, based on the ABAQUS simulation software with cohesive elements as the main research method in the constitutive model of concrete was put forward. The actual simulating and experiment results shows that the local failure characteristics of core concrete of CFST arch is similar to those of uniaxial compression on concrete short columns, and there is only compressive stress exists among the middle accross section of CFST arch which causes the volume of the inflated burst when fixing at both ends. Moreover, there is no influence on the bearing capacity of the overall core concrete with and the load displacement curves, which proved the efficiency of the proposed method and the basis for the study of other components of CFST during the mine construction.
Keywords
Bending experiment of CFST arch, ABAQUS, Cohesive elements, Constitutive model, Uniaxial compression experiment
BELEBCHOUCHE CHERIF, MOUSSACEB KARIM, HAMMOUDI ABDELKADER, AMOURI CHAHINEZ
Abstract
This article focuses on the study of the release of Pb2+, stabilized/solidified by hydraulic binder (cement CEM II-42.5) for 28 days in an acid medium. Three mortars were prepared with different percent of PbO namely 0.6, 0.96 and 1.2%. Vicat needle indicated that lead retards the hydration process of mortars compared to the control sample. In the study interval [0.6%-1.2%], the increase in the percentage of PbO in mortars decreased the mechanical strength. The release of lead during TCLP test (Toxicity Characteristic Leaching Procedure) and the effectiveness of the process of Solidification/Stabilization depended on the initial concentration of the pollutant (Pb2+), and of the time of leaching. The use of X-ray diffraction allowed the identification of the new complex crystalline phases within the structure of Stabilized/Solidified samples, namely: Pb2Al4(OH)8(CO3)43H2O and Pb(OH)2. This study was completed by modeling the experimental data which revealed that the release process is much more a surface phenomenon (dissolution or precipitation). The evaluation of degradation of samples gave no sign of any major deterioration of the stabilized/solidified materials.
Keywords
Hazardous compound (PbO); TCLP test; Leaching; X-ray diffraction; Modeling; Degradation
GONZÁLEZ-LÓPEZ, R., DÍAZ-PEÑA, I, ZALDÍVAR-CADENA, A.A., HERNÁNDEZ-SANDOVAL, J., RANGEL-PERAZA, G, RODRÍGUEZ-MATA, A.E
Abstract
The addition of nano-SiO2 (NS) in the mix stage of cementitious materials (CM) based in Ordinary Portland Cement (OPC) has been demonstrated as a promising approach to lead the improvement of properties such as microstructure density, hydration kinetic and pozzolanic reaction rate, which are very important parameters concerning to the structure durability. However, in the case of hardened structures, the mechanism of how NS interacted with cement matrix is limited, because most of the involved reactions have already happened. In this work, the effect of the colloidal nano-SiO2 application in the surface of an early age hardened limestone mortar is studied and a comparison between two different methods is presented: migration (by electrical field) and capillary absorption (by wet-dry cycles). Measurements of potential difference, current intensity and electrical resistance were carried out in migration cells and electrical resistance for capillary absorption cell. Optical microscopy (OM) and scanning electron microscopy (SEM) in backscattering electrons (BE) coupled with energy dispersive x-ray spectroscopy (EDS) were used to characterize the microstructure of the cement mortar samples. It was found that the nano-SiO2 penetrate the cement mortar sample by both migration and capillary absorption from the surface to the interior and interact with the phases of the cement matrix. Ca/Si rates below the conventional values of the conventional phases were found (up to 0.5), which means that an increasing of cement matrix silicon content was promoted.
Keywords
Limestone Cement Mortar, Nano-SiO2, Surface Treatment
N. KYBARTIENE, D. NIZEVICIENE
Abstract
A full factorial design was employed to evaluate the hydration of anhydrite cement produced from flue gas desulfurization gypsum (FGD gypsum) using three activators (KAl(SO4)2·12H2O, Na2SO4, FeSO4·7H2O). The effect of three independent variables such as the calcination temperature of FGD gypsum (500-800oC), the hydration time (3-28 days) and the amount of activator (0-1%) on the hydration of anhydrite cement were studied. The experimental results and statistical analysis showed that the hydration time and the amount of activator had a positive effect on the hydration of anhydrite cement, while the temperature had a negative effect on this process. The multiple linear regression models were developed to correlate the significant variables to the chemically combined water content in hydrated anhydrite cement. The mean absolute percentage error between experimental and calculated values of the chemically combined water content in hydrated anhydrite cement was less than 2%.
Keywords
factorial design, anhydrite cement, hydration, activators
JUAN HE, YONGHUA WU, CHANGHUI YANG, QIE GAO, XIAOLIN PU
Abstract
AAS binders activated by water glass (WG) and sodium hydroxide (NaOH) solution was used to investigate its carbonation properties. Carbonation product, carbonation shrinkage, and effect of carbonation on pore structure of AAS paste were studied. Compared with noncarbonated one, when AAS paste was carbonated, specific surface area and cumulative pore volume increased, and average pore diameter and most probable pore diameter reduced. As for carbonation product, the main form of CaCO3 is calcite, and the phases as vaterite and aragonite are lesser. The amount of aragonite and vaterite increases with the increase of carbonation age. During carbonation, the shrinkage only comes from the migration of Ca2+ from C-A-S-H gel and the increase of degree of polymerization (DP) of C-A-S-H gel. Carbonation process of AAS paste doesn’t increase the dry shrinkage.
Keywords
Alkali-Activated Slag; Carbonation; Pore structure; Carbonation product; Carbonation shrinkage
F.J. VÁZQUEZ-RODRIGUEZ, J.VALADEZ-RAMOS, R. PUENTE-ORNELAS, J.E.CONTRERAS, A.ARATO, EDÉN A. RODRÍGUEZ
Abstract
An alternative solution to reduce environmental pollution using aluminum waste foundry sand (AWFS) and fly ash (FA) to produce sustainable construction materials was studied. New mortars were prepared by partially replacing ordinary Portland cement with fly ash at 5, 10 and 15 % mass. and a total replace of Ottawa sand (OS) with AWFS. The specimens were cured at 25°C with a 100% relative humidity. The mechanical behavior was evaluated by compression test at the ages of 7, 14 and 28 days. The microstructural characteristics were analyzed by scanning electron microscopy (SEM). The results indicate that the addition of milling fly ash in AWFS mortars increases the mechanical resistance, mostly at 5% mass reaching the maximum value of 10 MPa at 28 days of age. Microstructurally, it was found a porous cement matrix with some cracking caused by the reaction of portland cement with the metallic aluminum remaining in the waste sand, which is correlated to the low mechanical resistance obtained. The final mechanical characteristic makes this new product a serious candidate to be used as a sustainable building material working at low load.
Keywords
construction, mortars, Portland cement, fly ash, composite, pollution
MAHIMA GANESHAN, DR. V. SREEVIDYA, L. NIRUBANCHAKRAVARTHY, G. SINDHU
Abstract
This study extends the ongoing investigation on bond performance of embedded steel in self consolidating geopolymer concrete, when Class F fly ash is blended with Class C fly ash. 5% OPC and 10% Class C fly ash are replaced to the basic source material Low calcium Fly ash, to facilitate the external exposure curing conditions and thereby aiming for cast in situ concrete production. Synthesising solutions for source material used are combination of sodium hydroxide and sodium silicates. Normal self compacting concrete, Self compacting geopolymer concrete with added OPC and Self compacting geopolymer concrete with OPC and Class C fly ash are the types of concrete selected for experimental investigation. Pull out tests are carried out by varying diameter and bond length of embedded steel in concrete. Comparison of bond stress on 54 pull out specimens was determined using IS: 2770 (Part 1) and studies revealed that inclusion of Class C fly ash in self consolidating geopolymer improves the bond strength tremendously. Results were compared to the latest empirical models proposed by researchers and FIB model code 2010.
Keywords
Self compacting geopolymer concrete; Ordinary Portland Cement; Class C fly ash; Bond Length; Bond Strength; External exposure curing
RAYED ALYOUSEF
Abstract
Nowadays, the construction industry over the entire world is looking for more economical construction materials. In addition, the existence of self-compacting concrete is facing brittleness problems due to their high binder content and low aggregate amount. On the other hand, the fiber is widely known to enhance the properties of concrete by bridging the crack width and hence, overcoming the brittleness problem in concrete. The goal of this paper is to evaluate the effect of different fibers on the properties of self-compacting concrete such as stand chopped basalt (SCB) and polyvinyl alcohol (PVA) fibers. The experimental work conducted were fresh tests, such as slump flow, slump T50 and V-funnel, while the hardened properties were compressive, flexural and bond strength. The results gathered from the empirical work showed that the fibers had a slight effect on the fresh properties and the compressive strength. While the flexural and bond strengths increased with the addition of the fiber content.
Keywords
Self-compacting concrete, Chopped basalt, Polyvinyl alcohol, Fresh and Hardened test
NANDHINI. K, PONMALAR. V
Abstract
The main constituent of concrete is cement which has a noteworthy negative ecological issue causing colossal CO2 commitment amid the concrete creation. This cement content should be replaced with by-products like Micro-Silica (MS) in order to prevent the greenhouse effect to some extent. This study examines the penetrating response of Self-compacting concrete (SCC) made of micro-silica as partial cementitious replacement material. The utilization of micro-silica in varying percentage like 5%, 10% and 15% along with the appropriate dosage of chemical admixtures were experimentally investigated. This concrete proportion was tested for fresh properties like slump flow, J-ring test and U-Box test. The split tensile strength of SCC was determined at the age of 28 and 90 days. The water permeability properties like saturated water absorption, sorptivity, porosity were conducted on hardened concrete. The rapid chloride penetration test was conducted to evaluate the amount of charge passed in concrete. These results revealed that the replacement level of cement by optimized proportion of 10% MS improved the workability to 3.8%, the tensile strength to 22.82% and enhanced the durability properties.
Keywords
micro-silica, flowing ability, strength, water absorption, sorptivity, chloride penetration
BIN LUO, WEI HUANG
Abstract
This paper aims to disclose the bending properties of composite slab and base slab made from recycled concrete. For this purpose, our research group created haydites from underground sludge and discarded bricks, and mixed them with steel fibres into steel fibre-reinforced recycled haydite concrete (Concrete A) and steel fibre-reinforced recycled brick concrete (Concrete B). Then, each of the two recycled concretes was casted into a rectangular-finned prefabricated (RFP) base slab, which is known for its excellent rigidity, strong bearing capacity and large contact area. For comparison, another RFP base slab was made from ordinary concrete. After that, ordinary concrete was poured onto the three RFP base slabs, forming three composite slabs. Next, static load tests were performed on full-size specimens on all three RFP base slabs and three composite slabs. Based on the test results, the failure features of the specimens and the synergic effect between old and new concretes were discussed in light of the load-deflection curves, load-bar strain curves, contact area between base slab and upper-layer concrete, load-compressive strain curves and feature parameters. It is concluded that under static vertical load, the base slabs and composite slabs made from recycled concretes shared the same failure process with those made from ordinary concretes; the old and new concretes exhibited excellent bonding and synergic effects; the base plate made from Concrete B boasted the highest bearing capacity and lowest deflection among all base plates and composite plates investigated in our research. The research findings lay a solid basis for the research and application of recycled concrete composite slabs.
Keywords
Recycled aggregates; Bending properties; Rectangular-finned prefabricated (RFP) base slab
XIAO-YING LIANG, DONG-XIA YUAN, JUN LI, CHANG-LONG WANG, XIAO-RAN LIN, NING CHANG
Abstract
Based on the background that large amount of iron ore tailings (IOT) are stockpiled in China, the utilization of iron ore tailings to prepare autoclaved aerated concrete (AAC) was studied. The AAC samples were prepared on a laboratory scale with with a bulk density of 588 kg·m-3, compressive strength of 4.82 MPa, and thermal conductivity of 1.50 W/(m·K) which was in line with the requirement of A3.5, B06-class AAC products regulated by autoclaved aerated concrete building blocks (GB 11968-2006). The optimal grinding time of iron ore tailings was 25 min. The AAC samples after autoclaving were examined by using XRD (X-ray diffraction analysis), SEM (scanning electron microscope) as well as 29Si and 27Al NMR (Nuclear Magnetic Resonance). Results show that the main minerals in the AAC samples are tobermorite-11 Å, C-S-H gels, calcite, anhydrate, ferrotschermakite, quartz, with small amount of other minerals brought in by the iron ore tailings. It was also suggested that most minerals in the iron ore tailings participated in the hydration reaction, and the chemical elements in them got into the structure of acicular and platy tobermorite in the subsequent autoclaving process.
Keywords
iron ore tailings; autoclaved aerated concrete; tobermorite; reaction mechanism
HUAWANG SHI, LIANYU WEI, YANCANG LI, RHUIZHEN GAO
Abstract
In order to investigate the fatigue performance and microstructure evolution of glass fiber reinforced plastic mortar (FRPM) pipes under cyclic loading, fatigue test was carried out. In the process of fatigue test, the deflection, crack and crack width of each feature of FRPM were observed and recorded. Then, the micro-structure of original samples was scanned by electron microscope(SEM). Mechanical properties of FRPM pipe is analyzed from the view of microstructure for the specimens before and after fatigue loading. Finally, the fatigue life of FRPM pipe under cyclic loading is predicted. The results show that the residual stiffness of FRPM pipe decreases monotonically with the increase of fatigue times, therefore the stress amplitude or stress level is the main influencing factor. The FRPM pipe has a smaller residual stiffness and shorter fatigue life when being applied higher maximum cycling stress and amplitude. The crack in the FRPM tube without fatigue occurs instantaneously and obviously larger than that after fatigue.
Keywords
mechanical performances, FPRM, microstructure, fatigue properties, SEM
ANA J. MOMČILOVIĆ-PETRONIJEVIĆ, GORDANA A.TOPLIČIĆ-ĆURČIĆ,DRAGAN M. ĐORĐEVIĆ, DUŠAN Z. GRDIĆ, ZORAN J. GRDIĆ, NENAD S. RISTIĆ
Abstract
Felix Romuliana is an archeological site located in the vicinity of Zaječar, in the east part of Serbia, south of the Danube. Felix Romuliana is a monument of Roman court architecture in the period of the Tetrachy. It is the only archeological site in Serbia, which is under the UNESCO’s protection. It is a fortified palace, built at a request of the Roman Emperor Gaius Valerius Maximianus, in the honor of his mother Romula, which is why it was named Romuliana. There are two fortification systems around this palace: and older inner system, and a younger outer system which encompasses the palace, temples, military facilities, storage buildings…Mortar samples were analyzed with the goal of obtaining information about their morphological, mineralogical, chemical and basic physical properties. For an analysis of these properties, optical and scanning electron microscopy were used, as well as XRF and XRD analysis. Depending on the location of the sampled mortars, differences of the individual properties of mortar were observed. The mortar analysis determined that lime was used as a binder. The mortars prevalently consist of the river aggregate grains, crushed limestone aggregate grains and traces of crushed masonry blocks. Further research should be focused on production of repair mortars.
Keywords
Romuliana;mortars;Stereomicroscopic;XRF;XRD;SEM/EDS
CRISTINA DIMA (VĂDUVA), ALINA BĂDĂNOIU, ȘTEFANIA STOLERIU, DIANA LUCA
Abstract
The study presents one possible way for the valorization of an ash resulted by the combustion of hydrocarbon-containing residues from petroleum industry (waste A). The substitution of gypsum plaster with 5 wt.%, 20 wt.% and 30 wt.% waste A, results in the modification of tcompressive strength values, in correlation with the amount of gypsum plaster substituted; the increase of ash A amount (from 5% to 30%) determines the increase of setting time, therefore for the composition with 30% ash A, the setting time is similar with the one specified in gypsum plaster standard. The activation of ash A with sulfate salts shortens the setting time and increases the compressive strengths (with reference to plain ash A paste).
Keywords
valorization, waste ash, gypsum plaster, accelerator additions
CARMEN OPROIU, MARIUS PÂRVAN, GEORGETA VOICU, ALINA IOANA BĂDĂNOIU
Abstract
A common method used for the inertization of industrial waste is solidification / stabilization (S / S); it consists in the mixing of waste with a binder so as the final product meets the standards imposed by environmental agencies. Solidification describes the processes that transform waste into a waterproof solid with strong cohesion, i.e. good physical and mechanical properties. Stabilization is the effect of processes aiming to reduce or even eliminate the mass transfer phenomena of pollutants into water and soil. This paper presents the inertization and immobilization of a chromium-rich waste (from the potassium dichromate industry) in inorganic matrices based on hydraulic binders, namely in special structures called cement C and cement D. It presents also results regarding the influence of waste on hydration-hydrolysis processes and on the main properties of resulted mortars obtained by X-ray diffraction, complex thermal analysis, scanning electron microscopy (SEM and EDX).
Keywords
special hydraulic binders, properties, waste, solidification/stabilization processes.
MIHAI BRATU, OVIDIU DUMITRESCU, OVIDIU VASILE, LUOANA FLORENTINA PASCU, CAROL LEHR
Abstract
Pollution, in all its current views, is a permanent concern of the researchers. Therefore, making sound-absorbing materials that include waste is a very useful approach.
The paper deals with two environment related issues: noise pollution due to different sources in industry and transport, as well as waste storage, also affecting the quality of the environment.
The paper presents the researches on obtaining some oxide materials containing various solid wastes that may affect the environment. The schema of obtaining process and the actual composition of these materials are described.
Some physico-mechanical properties have been measured to characterize these oxide materials: particle size distribution of starting materials, compressive strength, apparent density and apparent porosity and sound absorbing properties.
The microscopy analyses (SEM and EDAX) have been used to study the morphology, homogeneities and existing pores could be highlighted in order to explain the obtained physico-mechanical properties, especially those of sound absorption.
The values of the measured properties allow for the determination of the best oxide materials obtained from solid wastes in terms of sound absorption.
Keywords
solid wastes, physico-mechanical and microstructural properties, sound absorption coefficient
Evaluation of strength and durability of natural fibre reinforced high strength concrete with M-sand
SHANMUGA PRIYA T, THIRUMALINI S
Abstract
The experimental investigation was carried out to study the variation in strength and durability properties of high strength concrete incorporated with sisal, banana and coir fibres. In this study, three different percentage 0.5%, 1% and 1.5% by volume of sisal , banana and coir fibres were casted and results compared with control mix. The strength properties such as compressive strength, splitting tensile strength and flexural strength and durability properties like water absorption, sorptivity and rapid chloride permeability was studied. Test results show that, the addition of sisal , banana fibre and coir fibre resulted in the enhancement of compressive strength, splitting tensile strength and flexural strength of concrete in the range of 4% to 10%. The optimum mix was arrived as 1% sisal and banana fibre and 0.5% coir fibre. The durability properties of optimum mix like water absorption, sorptivity and Rapid Chloride Penetration Test (RCPT) values have better performance compared to control mix due to its pore filling effect of natural fibres making the concrete denser.
Keywords
Natural Fibre, Strength, Durability, High Strength Concrete
HAIYAN LI, QI QIAO, BOYANG ZHANG
Abstract
Reactive powder concrete (RPC) is characterized by the ultra-high strength and excellent durability, so it has widely application prospects in the fields of oil, nuclear power, municipal works, marine engineering and military facilities. This paper will focus on the flexural properties of RPC after high temperature. To do this, 300 specimens with the size of 40×40×160mm were tested after exposure to 20~900℃. The effect of the fiber type and dosage change on the spalling of RPC is investigated through high-temperature test. By bending experiments, the degradation of RPC flexural strength with heating temperature, fiber type and fiber content are studied. The results indicate that, with the increase of steel fiber and polypropylene fiber dosage, RPC spalling probability reduces significantly. The flexural strength decreases with increasing temperature, and the incorporation of steel fibers exhibits positive impact on flexural strength, but the polypropylene fibers exhibit adverse effect. Formulas are proposed to express the decay of the flexural strength with increasing temperature, and the results are compared with normal strength concrete (NSC) and high strength concrete (HSC).
Keywords
reactive powder concrete (RPC); high temperature; flexural strength; spalling; steel fiber; polypropylene fiber
ZHIHAI HE, JINGYU CHANG, CHUANG LIU, SHIGUI DU, MAN HUANG, DENG CHEN
Abstract
The effect of rice husk ash (RHA) without processing content on compressive strengths of concrete with different strength grades was studied experimentally at 28 days. The size effect of specimen on compressive strengths was also analyzed and discussed. The results indicate that RHA without processing reduces the cubic compressive strengths of concrete, the brittleness coefficient and the size effect of strengths. With the increase of RHA content, the reduction effect is more and more obvious. There exists a good linear relationship between the brittleness coefficient and the size effect of strengths of concrete. Based on the brittleness coefficients, the size effect law is proposed, which can well predict the size effect of cubic compressive strengths of concrete. RHA without processing increases the volume fractions of porosity and high-density calcium silicate hydrates, but reduces the volume fractions of calcium hydroxide.
Keywords
concrete, rice husk ash without processing, cubic compressive strength, size effect, brittleness
MERT TERZI
Abstract
Sensitive determination of the particle size distribution is an important procedure in terms of efficiency as well as affordability in mining operations which includes many stages such as blasting and mineral processing. Digital image processing methods used in mineral processing discipline found different application areas due to providing accurate data in relatively short time. In this study, the particle size distribution analysis of the samples taken from privately owned aggregate processing plants using sieve analysis and digital image processing methods were conducted and accordingly a comparison of these methods in terms of the applicability on industrial scale were realized. In this context, a pilot setup was assembled for the laboratory and plant scale image processing analysis purposes. Particle size distribution measurements of the samples were conducted by digital image processing method using this pilot setup and conventional sieve analysis methods. As a result, d20, d50 and d80 sizes of a crushed stone plant product were determined with confidence levels of 94.75%, 88.45% and 80.00%, respectively. The obtained results showed that a system based on digital image processing method can be applied in particle size analysis with high success as alternatives to conventional methods.
Keywords
aggregate, particle size distribution, digital image processing
D. ELAVARASI, K.SARAVANA RAJA MOHAN
Abstract
Several research works have been executed to examine the performance of slurry infiltrated fibrous concrete (SIFCON) under static and impact loading. But limited works have been done on the strength and durability characteristics of SIFCON made with binary blends of supplementary cementitious materials. The experimental investigation was carried out to study the strength and durability characteristics of slurry infiltrated fibrous concrete with partial substitution by fly ash (10, 15, 20, 25 & 30% as replacement of cement. SIFCON matrix containing a constant fibres content (10%) and water/binder = 0.4 were used throughout the entire investigations. The test results revealed that the incorporation of a blended cement with fly ash in SIFCON decreases the mechanical properties and improves the durability thus indicates the sorption coefficient decreases compared to control specimen. Regression model has been developed from the experimental results for estimating the compressive strength, split tensile strength, flexural strength and water permeability of SIFCON made with the binary cementitious blend of fly ash. The predicted values were satisfied with the experimental results.
Keywords
Fly ash, SIFCON, Toughness, Ductility factor, Stiffness, Permeability, Sorption coefficient, Acid resistance