english KOLIMI SHAIKSHA VALI, S. BALA MURUGAN
Rezumat
Increased construction activities, leads in deficiency of conventional building materials. To overcome the problem now a day’s different techniques have been used to benefit industrial by-products which are available in large quantities. Manufacturing of artificial lightweight aggregates by pelletization method is one important technique to substitute natural aggregates in concrete. The present study examines the manufacturing of twenty one (21) different types of artificial aggregates from industrial by-products with the addition of glass fibers at a fixed 17min pelletization time, along with 28% of water content. Manufactured fresh pellets were air-dried for 24 hours and later hardening of aggregates through cold-bonding technique (Water Curing) at room temperature for 28 days and tested with different aggregate properties. The study results that the highest individual aggregate compressive strength of 48.1MPa was observed for 12mm F21 aggregate. The lowest impact strength of 13.3% for F16 aggregate. Similarly, the lowest water absorption of 16.3% was noticed for F14 aggregate. The impact of binders with fibers in the manufacturing of aggregates was noted to be an essential factor for attaining high strength artificial aggregates.
Cuvinte cheie
metode de peletizare, agregate artificiale ușoare, fibre de sticlă alcalii rezistente, proprietăți fizice și mecanice, SEM
B KARTHIKEYAN , A SUBIN , T MUTHULAKSHMI
Rezumat
This paper reports the experimental investigation of strength and durability characteristics of fiber reinforced concretes made with silica fume (SF) and ultra-fine TiO2 (UFTiO2) as partial substitution for cement and basalt fibers added to it. The size of the ultra-fine TiO2 used was obtained using zeta analyzer. M50 grade of concrete was used and the specimens were cast using cement blended with silica fume in a uniform proportion of 10% and ultra-fine TiO2 added in 1%, 2%, 3% and 4%, by weight of cement. Basalt fibers were added in different levels at 0.5% and 1% by volume of concrete. The specimens were subjected to various mechanical tests such as compression, split tensile strength, test for modulus of rupture and impact strength. In addition, durability parameters such as deterioration, sorptivity, porosity and corrosion of rebar using half-cell potential were also performed and the results are reported. By comparing the results it was observed that the mechanical properties showed improvement with addition of basalt fibers and for an optimum use of UFTiO2 up to 2% after which there was reduction in strength. Also, it was noted that, all the specimens with UFTiO2 and basalt fiber added to them, possessed better strength characteristics.
Cuvinte cheie
TiO2 ultrafin, fibre de bazalt, deteriorare, porozitate, sorpție
ABIDENG HAWA, WORAPHOT PRACHASAREE
Rezumat
This study focused on the mechanical properties of fly ash geopolymer mortars with short heat curing and incorporating some field Para rubber latex (FPRL). The geopolymer mortar mixtures were prepared with fly ash to FPRL ratios 1:0.01, 1:0.025 and 1:0.05 by weight, and with varied heat curing times ranging from 0.5 to 4 h. The microstructure is investigated with scanning electron microscopy (SEM), but X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) analysis are used to obtain information about phase composition. The compressive strength and drying shrinkage were determined. The FPRL content of 1% and heat curing for 4 h gave the maximal compressive strengths after demolding and at 28 days, namely 47 and 61 MPa, respectively. SEM analysis indicated that the 1% FPRL geopolymer sample has a dense compact matrix with the low proportion of unreacted fly ash, which is likely associated with the high compressive strength.
Cuvinte cheie
geopolimeri, latex de cauciuc, microstructură, contracție la uscare
PAVEL REITERMAN , VENDULA DAVIDOVÁ, JIŘÍ PAZDERKA, WOJCIECH KUBISSA
Rezumat
Maintenance of the present concrete infrastructure is of great concern, because a great many concrete structures are approaching the end of their service lives. Considerable attention in contemporary research is focused on advanced technologies, such as self-healing processes. One the oldest is the use of crystallizing treatments, which improve the impermeability of the concrete and contribute to prolonged durability. This work deals with the reduction of concrete surface permeability properties by using a repair mortar with a crystallizing admixture for penetrating the concrete. The evaluation was based on the chloride migration test, water penetration test and initial surface absorption test (ISAT). The mortar was polished prior to testing to eliminate the barrier effect of the applied mortar and assess the quality of the penetration. The performed experiments confirmed significant improvement of the surface concrete layer based on all the permeability procedures over time. After a year of the program, the permeability of the treated concrete surface was decreased by approximately by 40 %, but the greatest sealing effect was recorded during the first two weeks.
Cuvinte cheie
adaosuri pentru cristalizare, permeabilitatea suprafeței, încercare de migrare a clorurii, permeabilitatea la apă
SAKTHIESWARAN N., DHANARAJ. R., SURESH P.
Rezumat
This study aims at utilizing industrial wastes and hybridized fibres to improve the strength and stability of concrete to obtain an eco-friendly healthy concrete. Steel, basalt and alkali reactive glass fibres were hybridized in various ratios to obtain modified concrete mixes containing 7% silica fume as cement replacement. This study also focuses on the effective ways of utilizing copper slag as fine aggregate replacement thereby reducing the pollution as well as meets the increasing demand of river sand for concrete. This experimental investigation includes the mechanical strength characterization such as compressive strength, flexural strength and split tensile strength at various ages and durability properties such as water absorption, porosity and resistance towards acid attack. The results obtained showed that the hybridization of fibres in combination with copper slag replacement can be incorporated in concrete to improve their mechanical strength and durability.The results also show that such fibre hybridization is indeed a promising concept that can significantly enhance the strength of the industrial waste incorporated concrete.
Cuvinte cheie
silice ultra fina, zgură de cupru, fibre hibridizate, rezistență mecanică, durabilitate
LEONID DVORKIN, YURI STEPASYUK, VADIM ZHITKOVSKY, YURI RIBAKOV, SVETLANA LAPOVSKAYA
Rezumat
The paper presents effective ways to increase activity of slag Portland cement with a clinker content of 5-19%. The influence of complex sulfate-fluoride and sulfate-fluoride-alkaline activation is studied. The results obtained at the first stage of the research are used for investigating properties of concrete produced using the above mentioned low clinker slag Portland cement with a clinker content of less than 20%. The influence of different plasticizing additives and heat treatment on the strength characteristics of concrete has been determined. A method for design of concrete compositions using low clinker slag Portland cement is proposed.
Cuvinte cheie
aditivi de activare, clincher de ciment, tehnologie de economisire a energiei, fosfogips, ciment portland cu zgură
CHUN LIU, DENG CHEN
Rezumat
The internal structure has an important role in determining the properties of cementitious materials. Shrinkage reducing admixture (SRA) is often applied in concrete for reducing shrinkage, but there is little systematic work on the internal structure especially form the nano-scale. The internal structure characterizations of hardened cement paste containing SRA have experimental been investigated by the combined use of nanoindentation and SEM techniques. The results indicate that the utilization of SRA increases the volume fractions of porosity and unhydrated particles of hardened cement paste, but reduces the volume fractions of hydration products at 3 days, and however, with the increase of curing age to 28 days, the effect of SRA is reversed, and importantly, the utilization of SRA also increases the ratio of HD C-S-H to LD C-S-H. In addition, the internal microstructure is also improved due to the utilization of SRA.
Cuvinte cheie
adaosuri pentru reducerea contracției, structură internă, pastă de ciment întărită, nanoindentare, SEM, C-S-H
ZHENSHAN WANG, YONGJIAN FENG, JUNLONG LU, HONGCHAO GUO, JIANBO TIAN
Rezumat
An experimental investigation was conducted to study the axial compression behavior of thin-walled concrete-filled steel tubular (TWCFST) column with spiral stiffeners. In order to explore the impact of spiral stiffener on the engineering properties of TWCFST column, the columns without and with 3 types of stiffening form tests were carried out. The mechanical properties and failure mechanism of 4 types of columns were observed and analyzed, and the stress-strain curves and load-displacement curves were obtained. Test results showed that, compared with the ordinary TWCFST column, the TWCFST column with spiral stiffeners could effectively improve the bearing capacity. Meanwhile, the spiral stiffener could effectively combine with the internal concrete, which would improve the stability of the steel pipe wall, delay the local buckling, and limit the penetration cracks caused by the internal filling concrete. The spiral ribbed concrete column had better integrity and significantly improved deformation capacity. Based on the experimental research, the parameters of the diameter-thickness ratio of the round steel tube, the width-thickness ratio of the spiral stiffener and the pitch were analyzed, and the design suggestions were put forward. This paper proposed a new type of restrained steel tubular concrete member. The research results would provide some technical support for the engineering application of the composite column.
Cuvinte cheie
beton umplut cu tuburi de oțel (TWCFST), conductă de rigidizare, încercare la compresiune axială, modul de rupere, simulare elemente finite
ANDREI GIRBOVEANU , MOUAD JEBLI , FRÉDÉRIC JAMIN, VINCENT HUON, MOULAY SAÏD EL YOUSSOUFI, DAN PAUL GEORGESCU
Rezumat
Studiul durabilității betonului supus levigării necesită cunoașterea mecanismelor de degradare chimică a pastei de ciment și a legăturii pasta/agregat. Zona de tranziție inter facială (ITZ), porțiunea de pastă de ciment aflată în contact cu agregatele, este o zonă vulnerabilă în contextul degradării chimice datorită gradului ridicat de solubilitate și difuzivitate. Pentru a evalua cinetica de levigare, precum și amploarea disoluției chimice a pastei de ciment propriu zise și a ITZ, s-au produs eșantioane paralelipipedice din pastă de ciment și compozite paste / agregate de ciment. Ulterior, acestea au fost supuse levigării accelerate. Măsurarea grosimii degradate a fost efectuată ca urmare a analizei imaginii secțiunilor transversale ale pastei de ciment și ale interfeței. Cinetica de degradare a pastei de ciment propriu zise este proporțională cu rădăcina pătrată a timpului. Pe de altă parte, cea a ITZ urmează inițial aceeași tendință, dar se accelerează ușor după un prag critic. Analizele chimice au fost efectuate prin spectroscopie energetică dispersivă (EDS) pentru a măsura raporturile molare Ca / Si la nivelul ITZ și al pastei de ciment pentru o singură perioadă de degradare. Scăderea mai mare a raportului Ca / Si la nivelul ITZ indică o amploare a disoluției a portlanditei semnificativ mai mare decât la nivelul pastei de ciment propriu-zise.
Cuvinte cheie
beton ITZ, levigare, cinetici de levigare, dizolvare
A.MELINESCU, G.IONIȚĂ, R.TRUȘCĂ, M.PREDA
Rezumat
În această lucrare, s-au studiat sinteza și caracterizarea fizico-chimică a unor materiale ceramice poroase folosind ruta de procesare geopolimerică. S-au sintetizat probe care să conțină teoretic drept component mineralogic mulitul. Pentru sinteză s-a folosit metacaolinul și o soluție de NaOH. Probele au fost tratate termic la temperaturi cuprinse între 1100 și 12000C. A rezultat că, în acest interval de temperatură se obțin materiale cu densitate mică, aceasta scăzând odată cu creșterea temperaturii, iar la 12000C densitatea este sub 1 g/cm3. Compoziția mineralogică a probelor s-a examinat prin difracție de raze X, constatându-se prezența mulitului, cordieritului, α-cuartului și a nefelinului ca faze cristaline. De asemenea, s-a observat prezența fazei vitroase, care crește odată cu creșterea temperaturii de tratament termic. Prin studii de microscopie electronică de baleiaj s-a observat că, probele conțin pori de diferite forme și dimensiuni, închiși și necomunicanți, ceea ce explică densitatea mică a probelor.
Cuvinte cheie
rută de procesare geopolimerică, metacaolin, soluție alcalină, XRD, SEM
SARUMATHI K., ELAVENIL S.
Rezumat
A simple concrete - based structure model is proposed by developing it from nano to macro structure. In this model, the structure is divided into four levels and each level is represented by a parametric model. The parameters of the four based structures are identified, in terms of elastic modulus (EM) and poisson’s ratio at any time period (t) at Calcium silicate hydrates (CSH), cement paste, mortar and concrete levels. Then, by integrating the proposed model with Bazant – Baweja (B3) model, the compressive strength (CS) and EM of concrete at different curing periods is estimated. Further, it is analyzed and validated by other international models such as B3 model alone, Comite Euro – International Du Beton (CEB) model and Indian standards (IS) method. Few tests were done to investigate the CS of concrete with the inclusion of 25% fly ash (fa) and varying ratios of waste foundry sand (WFS) – 0, 25, 50, 75 and 100%. The results are compared with the obtained values by other models and validated with the experimental results. It is found that the proposed model (PM) i.e., Multiscale modeling (MS) can be used reliably integrated with the other models and builds the interaction between the various matrix to estimate and study the strength parameters of the concrete. MS is a new technique which is based on the mathematical formulation, it doesn’t require any earlier data about the mechanical properties of the concrete except the intrinsic values of the cement-based materials and mix details to evaluate the strength of the concrete.
Cuvinte cheie
beton, modele internaționale, parametrii de rezistență, modul de elasticitate, raport poisson, model parametric
HUAWANG SHI, ZHIYANG AN, RUIZHEN GAO
Rezumat
The purpose of this paper is to simulate and investigate the relationship of shell structural characteristics and ultimate bearing capacity (UBC) on glass fiber reinforced mortar (GRP) mortar pipes. In this paper, numerical simulation technology is used to analyze the ultimate strength which is very concerned about the scheme design of GRP mortar pipe. Combined with the static load experiment, the developed finite element numerical model of GRP mortar pipe is validated. The variations of UBC versus ply scheme are investigated for the optimum shell structure as [0/30/90/-30]s. The influence of three main parameters as laying layer, fiber volume ratio and volume ratio of spiral wound are investigated. It is observed that UBC of pipeline increase with increasing the fiber volume ratio and volume ratio of spiral wound layer; however the UBC increases with the pipe layers when the shell structure is within 6 plies and decreases when it is larger than 6 plies.
Cuvinte cheie
conducte din mortar armat cu fibre de sticlă, proiectare optimă, ANSYS, capacitate portantă ultimă
TAHA H. ABOOD AL-SAADI, ABDULRAHMAN SALEH IBRAHIM, HAZIM FALEH
Rezumat
Foaming geopolymers (light-weight porous inorganic materials) were successfully synthesized by alkali activator of mixed color waste glass powder without/with pure graphite powder (0.1 wt%) and dry intercalated graphite powder(0.1 wt%) as foaming agents; the specimens were thermally treated at 500,600,700 and 800ºC for 1hour. An important volume increase was recorded (-11.8-240.68%), (68.25-146.64%) and (43.79-968.54%) for MG-N5, MGG-N5 and MGIG-N5 respectively after thermal treatment. A sharp increase in volume (important swelling) and shape deformation was recorded for the specimens with intercalated graphite (MGIG-N5 pastes) at temperature 600ºC. The microstructure and mechanical properties of these materials were also studied. The foaming geopolymers containing glass and graphite powder (G or IG) which were obtained from this work are strong candidates mostly for the applications demanding thermal insulation with favorable combination of light weight, porosity, mechanical strength and performance to produce construction materials.
Cuvinte cheie
deșeu de sticlă, grafit, spumă de polimeri, tratament termic
ANDREI GÎRBOVEANU, MOUAD JEBLI, FRÉDÉRIC JAMIN, VINCENT HUON, LAURENT BONNET, MOULAY SAÏD EL YOUSSOUFI, DAN PAUL GEORGESCU
Rezumat
Legătura dintre pasta de ciment și agregat influențează durabilitatea betonului supus levigării, din cauza existenței unei anumite zone mai vulnerabile în pasta de ciment, adiacentă agregatelor - Zona de Tranziție Inter facială (ITZ). Pentru a evalua comportamentul mecanic al betonului la scara locală a legăturii pastă de ciment/agregat, s-au efectuat încercări de întindere pe eșantioane din pastă de ciment și compozite pastă/agregat. Relația dintre degradarea chimică și proprietățile mecanice (modulul lui Young și rezistența la întindere) a fost exprimată prin noțiunea de degradare chimică. Alte aspecte discutate, cum ar fi cinetica de levigare, dizolvarea chimică și fisurarea au fost evocate pentru a evidenția originea pierderii proprietăților mecanice ale pastei de ciment și a legăturii pastă / ciment. În ceea ce privește legătura pastă/agregat, după o dizolvare importantă în cadrul ITZ, se produce treptat o pierdere totală de aderență între pasta de ciment și agregat. În ceea ce privește pasta de ciment, aceasta suferă o scădere mai mică a modulului lui Young și a rezistenței la întindere în comparație cu compozitele, fiind de asemenea mai puțin afectată de fisurare. În general, acest studiu evidențiază mecanismul prin care comportamentele mecanice ale pastei de ciment și ale legăturii de pastă de ciment / agregate sunt afectate de levigare.
Cuvinte cheie
beton, levigare, incercări la întindere, scară locală
PEERZADA DANISH, MOHAN GANESH G
Rezumat
Gainful utilization of mineral admixtures like Metakaolin (MK), Fly Ash (FA) and filler material like Waste Marble Powder (WMP) in various construction practices has become a new topic of interest in research area. This paper presents the studies regarding the use of MK and FA as cement substitution (partial) and WMP as fine aggregate replacement (partial) in Self-Compacting +Concrete (SCC). The pozzolanic nature of the MK and FA due to their high silica and alumina content enables them to be the most valuable Supplementary Cementing Materials (SCM’s) for utilization in the production of SCC. The MK was used as partial replacement of cement in seven different proportions of 5, 7.5, 10, 12.5, 15, 17.5 and 20% while as the FA replacement level (by weight of cement) was kept fixed at 15%. The fine aggregate was partially replaced by 20% WMP. To evaluate the influence of FA, the control mix with 15% FA substitution of cement was also designed. Thus, a total of nine mixes including the reference mix without fly ash were designed. The different tests to evaluate the workability were performed, which are presented in this paper. The specimens were tested in the hardened state at different ages for assessing the mechanical properties of SCC. The use of ternary binding blends consists of OPC+FA+MK and addition of WMP as fine aggregate replacement have shown a positive impact on fresh and mechanical characteristics of SCC. A significant correlation has also been observed between fresh properties and hardened properties of SCC.
Cuvinte cheie
beton autocompactant (SCC), puzzolane, adaosuri, cenușă zburătoare (FA), metacaolin (MK), deșeu din pudră de marmură (WMP)
ILHAMI DEMIR, OZER SEVIM, GOKHAN OZEL, ORHAN DOGAN
Rezumat
Cement is one of the essential constituent for the production of concrete. However, large amounts of carbon dioxide (CO2), green house gases etc are emitted during the calcinations of limestone; for the production of one tonne of cement, the raw materials of about 2 tonnes is required and it releases approximately 1 tonne of CO2. Since, the production of cement involves excessive emission of greenhouse gases that leads to damaging of ozone layer and many environmental problems, a substitute or alternative material to cement for a sustainable construction was required. Research works are being carried out for finding out the alternate cementing material which will replace cement partially or fully due to its ill effects on the environment. The present paper reports an attempt in this direction by experimental examination on the hardened properties of concrete by replacing cement with combination of Fly ash (FA), Alccofine (AL) and Colloidal Nano Silica (CNS) in order to form a blended concrete (BC). From the experimental results, it was clearly observed that the combination of FA, AL and CNS had shown a high early age strength gaining property. Incorporation of a combination of these admixtures enhanced the mechanical and water absorption properties of the concrete. BC mix with a combination of 25% FA, 10% AL and 1% CNS with a total of 36% replacement of cement has achieved higher mechanical and water absorption properties as compared with all other mixes. The relationship between compressive strength and splitting tensile strength as well as between compressive strength and percentage water absorption is also investigated.
Cuvinte cheie
beton autoclavizat (AAC), cenușă zburătoare, rezistență la compresiune, densitate în stare uscată, conținut de umiditate, conductivitate termică
JIANMIN WANG, CHENGFENG ZHU, BO CHENG, JUNZHE LIU
Rezumat
The elastic modulus of ceramsite lightweight aggregate concrete (LWAC) after elevated temperatures is studied and modeled in this work. The degeneration for the effective stiffness contribution by ceramsite aggregates to LWAC together with the phase transformations of hardened cement paste are considered. Five levels, room temperature (20°C), 200°C, 400°C, 600°C and 800°C, are selected to conduct the elevated temperature experiment. For the phase-change analysis at the cement paste level, the mass loss of test blocks after drying at 120°C is obtained to further validate the initial volume fraction of the remaining water, the capillary voids and the water in gels in the cement paste. The experimental damage characteristics of ceramsite LWAC after elevated temperatures indicate a reduction in the effective stiffness contribution of ceramsite aggregates to LWAC. The effective elastic modulus E′a of ceramsite aggregates in LWAC and the nominal elastic modulus Ea of the ceramsite particle are utilized to formulate the degradation model for the stiffness contribution of ceramsite aggregates to LWAC after elevated temperatures. The proposed polyline reduction model effectively characterizes the variation trend of the elastic modulus of LWAC after elevated temperatures.
Cuvinte cheie
beton cu agregate usoare, modul de elasticitate, ceramsit, temperatură ridicată, model
K.S. ELANGO, V. REVATHI
Rezumat
This study deals with the evaluation of mechanical and durability studies on pervious concrete produced with Ordinary Portland Cement (OPC), Portland Pozzolana Cement (PPC) and FaL-G (Fly ash, Lime & Gypsum) as binder. This study was conducted at constant aggregate to binder ratio as 3.3 and water to binder ratio as 0.35 with aggregate size ranging from 6.3 mm to 12.5 mm. As a result of this, the mechanical properties of PPC binder pervious concrete results rate was reduced slightly from the conventional control mix OPC. Durability studies such as chemical resistance test and impact resistance test has been evaluated and it was found that significant improvement in chemical resistance was observed in PPC mix, whereas for impact resistance it is vice versa. As a final, this paper demonstrates an adequate mechanical and durability of pervious concrete with OPC, PPC binder and FaL-G binder for low traffic applications.
Cuvinte cheie
beton permeabil, lianți, capacitate de umectare, rezistență la impact, durabilitate
DING XIANGQUN, ZHANG YICHAO, WANG FENGCHI, ZHOU JINGHAI
Rezumat
The fractal dimension of pore distribution of concrete is calculated based on the test of mercury intrusion porosimetry. In addition, the fractal dimension of pore distribution is used to measure and analyze the thinning effect of internal factors (such as mineral admixtures) and external factors (such as different salt ions) on pores of concrete. Results showed that the fractal dimension of pore distribution is between 1 and 2, which is greater than its topology dimension and the correlation coefficient could reach 0.98. Mineral admixtures have various extent influence of thinning effect on pores of concrete. The total porosity increases with the increasing of the fractal dimension of pore size distribution. Furthermore, the erosion experimental results and fractal analysis indicate that different kinds of compound ions solutions have different thinning effects on pores of concrete with different water-binder ratios.
Cuvinte cheie
teorie fractală, distribuție pori, dimensiune frontală, efect de mișorare
BAIFU LUO, YI LUO
Rezumat
With the purpose of further researching the fire-resistant performance of reactive powder concrete (RPC), the significant influence of hold times on the compressive stress versus strain relationship for RPC with 2% steel fibers (in volume) at elevated temperatures was investigated in this paper. Pursuing this objective, the experiment was performed at temperatures of 20 ℃, 200 ℃, 400 ℃, 600 ℃, and 800 ℃. In addition, axial compressive strength, elastic modulus, peak strain and energy absorption capacity (toughness) of RPC were evaluated at elevated temperatures. Furthermore, the compressive stress-strain constitutive equation was developed based on regression analysis. Results from the tests demonstrate that, with the increase of hold time, axial compressive strength of the RPC increases below 400 ℃, approximately decreases ranging from 400 ℃ to 600 ℃ and increases again at 800 ℃. At the temperature of 800 ℃, the elastic modulus (initial elastic modulus and peak secant modulus) and peak strain present adverse variation trends as the hold time increases. Moreover, the formula related to the initial elastic modulus and peak secant modulus was proposed.
Cuvinte cheie
influența timpului de menținere a tensiunii de compresiune, temperatură ridicată, beton cu pudră reactivă, relație efort - întindere
CHUN LIU, DENG CHEN, ZHI-QING CHENG
Rezumat
In order to promote the application of zeolite powder in concrete, the hydration and microstructure evolution of hardened cement paste containing zeolite powder at low water-binder ratio have experimentally been investigated by compressive strengths, non-evaporable water, mercury intrusion porosimetry (MIP), scanning electron microscope (SEM) and nanoindentation. The results indicate that compared with the control cement paste, the addition of zeolite powder reduces compressive strengths of hardened cement paste at early ages, but 10% zeolite powder increases the compressive strength at later ages. The variation of non-evaporable water of hardened cement paste is similar with that of the strength. Zeolite powder degrades the internal structure to increases the porosity of hardened cement paste at 28 days, but the addition of 10% zeolite powder improves the microstructure to reduce the porosity at 60 days. Zeolite powder increases the volume fractions of UHD C-S-H.
Cuvinte cheie
zeolit pudră, hidratare, microstructură, pastă de ciment întărit, raport apa - liant scăzut
DI SHI , JIAYUAN YE, WENSHENG ZHANG, WEIGUO SHEN
Rezumat
Alkali-activated materials (AAMs) were synthesized from calcium silicate slag (CSS), ground granulated blast furnace slag (GGBFS) and class F fly ash (FA). The damage behavior, including the appearance, compressive strength, phase changes and microstructure evolution, of CSS-based AAMs exposed to pre-heated temperatures up to 1000oC were investigated. The findings showed that the microstructure and the compressive strength gradually degraded with elevated temperature from 20oC to 800oC, while upgraded during 800oC to 1000oC. The cracks induced by the quick dehydration of f-H2O were the main reasons for the strength deterioration as the exposed temperature was lower than 600oC. The continuous dehydroxylation of gel products, incompatibility between shrinking gel products and expanding quartz, as well as the decomposition of calcite resulted into the severe microstructure and strength deteriorations from 600oC to 800oC. As the exposed temperature was elevated from 800oC to 1000oC, the phase transition of gel products into crystal phases e.g. β–wollastonite (CaSiO3) and gehlenite (Ca2Al2SiO7) contributed to the further deterioration of CSS-based AAMs. Furthermore, the molten phases filled into cracks and bonded the particles together. This contributed to the increasing of density and compressive strength of AAMs matrix.
Cuvinte cheie
materiale activate alcalin, zgură de silicat de calciu, temperaturi ridicate, comportare la deteriorare, microstructură
TAO LI , XIAOLONG WANG,MING LI, DEYI NAN,QIYUAN SHAN, WEIXIN CHEN
Rezumat
In cut-and-fill mining, cement slurry is piped over a long distance from the mixing plant to the filling site underground. The long-distance transport poses a challenge to the long-term rheological stability of cement slurry. If the properties are undesirable, the pipeline will be easily plugged, bringing the mining to a standstill. This paper carries out rheological experiments on four groups of cement slurries, which differ in the dosages of suspending agent (SA) and air entraining agent (AEA). The synergy between SA and AEA was verified through analysis on images captured by a scanning electron microscope (SEM) and an X-ray diffractometer (XRD). The results show that the optimal SA and AEA dosages are 0.045% and 0.009% respectively; under the synergy between SA and AEA, the rheological properties of cement slurry could be modified to achieve long-term rheological stability. The research results contribute to the long-term homogeneity and flowability of cement slurry, and improve the effects of cut-and-fill mining.
Cuvinte cheie
transport pe distanță lungă prin conducte, proprietăți reologice, agent de antrenare la aer (AEA), agent de suspensie (SA), sinergie
The effect of alkali content of cement on ASR expansion: evaluation and its mitigation using fly ash
HAMZA TARIQ , RIZWAN AZAM, ALI AHMED, WASIM ABBASS, SAFEER ABBAS
Rezumat
Alkali silica reaction (ASR) is one of the main deterioration problems faced by reinforced concrete structures. Many structures including dams and bridges are severely affected by this phenomenon. To prevent ASR in new construction, the deterioration mechanism and the factors affecting the ASR phenomenon must be investigated. Many studies have been conducted to understand the deterioration mechanism of the concrete by ASR. However, there are still a few areas which need further research. The current study was designed to investigate the effect of alkali content of cement on expansion by ASR. In addition, effectiveness of fly ash to mitigate ASR expansion was evaluated. Moreover, the effect of ASR on mechanical properties of the mortars was investigated. For this purpose, a total of 27 mortar bar specimens and 54 cubes and prisms were cast, conditioned and tested as per guidelines of ASTM C 227 and ASTM C1260. The test variables included the alkali content of cement (0.58%, 0.53% and 0.43%) and Fly ash proportions (25%, 30% and 35% by cement weight). Test results indicated that ASR expansion is significantly affected by the alkali content of cement to such extend that alkali content of cement should be considered as one of the parameters while evaluating the alkali silica reactivity of the aggregates. It was also observed that minimum 30% fly ash was needed to mitigate the expansion by ASR in highly reactive aggregates. Due to ASR, the compressive and flexural strengths of specimens were reduced by 15% and 31%, respectively.
Cuvinte cheie
reacții alcalii - silice, dilatare mortar, cenușă zburătoare, conținutul de alcalii al cimentului
PEERZADA DANISH, MOHAN GANESH G.
Rezumat
This investigation was carried out to find the effect of various admixtures on the durability properties of Self-Compacting Concrete (SCC) with ternary blends of powders. In this investigation SCC was prepared with Metakaolin (MK), Fly Ash (FA) as partial replacement of cement and Waste Marble Powder (WMP) as a filler material (replacing partial the sand). The MK and FA contains higher concentrations of Silica and Alumina and are therefore considered as congenial Supplementary Cementing Materials (SCM’s). Seven different proportions of MK were used in this investigation. The partial replacement of 15% FA with cement was kept constant for all the mixes (M1- M7) except control mix (M0). The efficiency of FA was evaluated by designing a control mix with 15% FA substitution (M8) of cement. The fine aggregate was replaced partially by 20% WMP. A total of nine mixes were designed. The specimens were tested in the hardened state at different ages for assessing the durability characteristics of SCC such as water absorption and porosity, sorptivity and resistance to acid attack. The results of this investigation revealed that the influence of above admixtures used was quite effective in production SCC with improved durability properties.
Cuvinte cheie
beton autocompactant (SCC), adaosuri, cenușă zburătoare, metacaolin, deșeu din pudră de marmură, durabilitate
BAO-LIN GUO , BAO-MIN WANG, YU HAN, RUISHUANG JIANG
Rezumat
Controlled permeability formwork (CPF) has been used inner the steel and wood formwork to investigate the effect on surface properties improvement. The water-retaining ability of CPF under different lateral pressure, water requirement of cement paste and mortar in curing process, and surface hardness at different ages were measured, and the mechanism of surface concrete properties improved by CPF was researched. The results showed that lasting moisture curing of concrete can be realized with impounding type CPF. The carbonation resistance and chloride penetration resistance were also researched, and the results showed that CPF can significantly improve the surface concrete appearance quality, carbonation resistance, chloride penetration resistance. The morphological structure, porosity and pore size distribution of the composites were measured using mercury intrusion porosimetry and field emission scanning electron microscopy, and the results indicated that concrete using CPF had lower porosity and a more uniform pore size distribution.
Cuvinte cheie
cofraj cu permeabilitate controlată, capacitate de reținere apă, duritatea suprafeței, proprietăți de rezistență la carbonatare, clorură
SAKTHIESWARAN N. , RENISHA M.
Rezumat
Reactive Powder Concrete (RPC) is one of the advancements in concrete well known for its dense, compact structure and its superior performance at elevated temperatures. The momentous fact behind the dense matrix of Reactive powder concrete is exclusion of coarse aggregates, inclusion of fine materials possessing pozzolanic properties, steel fibers and super-plasticizers at proper proportions. The main objective of this research is to investigate the performance of RPC produced by partial replacement of cement by alccofine and quartz sand by coal bottom ash (CBA) and Recycled Aggregate Fines (RAF). CBA and RAF used were crushed and grinded to attain the particle size to effectively fill the voids and to reduce the porosity. The experimental investigation to determine the mechanical properties such as compressive strength, split-tensile strength and flexural strength and durability characteristics such as water absorption, sorptivity and acid attack tests were performed. The results showed that the fineness and particle size range of the CBA and RAF increase the potential to develop ultra-high strength in Reactive Powder Concrete. The RPC composed of 10% of CBA and 10% of RAF as partial replacement of Quartz Sand performed well in all mechanical strength characteristics and also within permissible limits in durability terms. The replacement of 40% Quartz sand by equal proportions of CBA and RAF proved to be satisfactory compared with that of control RPC specimens.
Cuvinte cheie
pudră de beton reactivă, cenușă de furnal, agregate fine reciclate, rezistență mecanică, durabilitate
SELÇUK MEMİŞ , ALİ ALSHAAB RAMROOM
Rezumat
Ultra high performance concrete (UHPC) generally has low workability due to the fact that it is a material with low water/cement (w/c) ratio and contains fiber in it. Therefore, adding a superplasticizer (SP) in its production may be a solution, so that it can self-compress, but there may be an overdosing problem. This research, conducted in two stages to determine ideal UPHC mixture, consisted of the first stage involving the determination of the sand/binder (s/b) ratio and the two stages, which included the determination of the ideal steel fiber ratio. To achieve ultra-high performance, the w/c ratio was reduced to 0.2 and the steel fiber was increased to a maximum of 2%. The fresh and hardened properties of UPHC were examined, for better workability their flow diameters and also compressive strengths, flexural strengths, densities, water absorption rates, total voids were determined in UPHC mixtures. It has been determined that the maximum strength can reach about 110 MPa without steel fiber reinforcement, but 130- 140 MPa strengths can be achieved if up to 2% steel fiber is added to the mixtures. It has been found that the strength of the UHPC is related to the s/b ratio and the fiber volume used and that the UHPCs can be obtained when the ideal ratios are taken into account.
Cuvinte cheie
beton ultraperformant, ciment, fibre de oțel, superplastifiant bazat pe eterpolicarboxilat
Cuvinte cheie
lucrabilitate, rezistență înaltă cu fibre de oțel, VeBe timp, factor de compactare, modele de regresie
ALEKSANDAR MILKOV RADOEVSKI , RAZMIK-ROGER GHANBARI, ANDREAS KOLBITSCH
Rezumat
The maintenance of a building is an important requirement to guarantee its functionality. An essential part of this maintenance is the restoration of cracks, which can represent both aesthetic and technical faults. In interiors, a long-term and inexpensive solution to these problems can be found in the use of elastic coating systems that can successfully bridge static noncritical cracks. In this study, the crack-bridging ability (CBA) of selected coating systems is evaluated and compared with the crack formation in an actual building. For the evaluation of the CBA an innovative strain measurement test and an optical deformation analysis are used. The crack formation in the building was initiated by artificial dehydration and was recorded for nearly 2.5 years of continuous monitoring. On the basis of the obtained data from the monitoring and the test results, the application of elastic coating systems as a remediation method for crack-afflicted buildings is reviewed and discussed.
Cuvinte cheie
capacitate de fisurare (CBA), efort, sistem de acoperire, interior, încercare de măsurare a efortului prin îndoirea grinzii, monitorizare clădire
HAJAR KADDOURI , TOUFIK CHERRADI, IBTISSAM KOURDOU, ANCUȚA ROTARU, NICOLAE ȚĂRANU, PETRU MIHAI
Rezumat
Structurile din zidărie simplă/ nearmată (URM) reprezintă o componentă importantă a actualului fond construit din întreaga lume. În ultima vreme, îmbunătățirea performanțelor structurale ale acestora a fost facilitată de dezvoltarea mortarelor compozite armate cu fibre textile (TRM). Lucrarea consideră aplicarea TRM pe exteriorul panoului de zidărie ca o alternativă la folosirea polimerilor armați cu fibre (FRP). Eficacitatea cămășuirii cu TRM este evaluată în comparație cu cea dată de cămășuirea cu FRP. Programul experimental constă în încercări de compresiune pe diagonală pe un număr de cinci pereți de cărămidă plină din argilă arsă. Un perete a fost considerat referință, doi pereți au fost armați pe exterior cu plasă din fibră de sticlă rezistentă la mediul alcalin (FRCM) pe una sau ambele fețe, iar alți doi pereți au fost cămășuiți cu polimeri armați cu fibre de carbon sau sticlă pe o singură față. Parametrii analizați au inclus materialul matricei (mortar și rășină), tipul de fibră și dispunerea simetrică sau nesimetrică a armăturilor. Rezultatele experimentale demonstrează eficiența consolidării FRCM în ceea ce privește îmbunătățirea rezistenței la forfecare a peretelui din zidărie.
Cuvinte cheie
perete de zidărie nearmat, FRCM, TRM, compresie pe diagonală
P.JAISHANKAR, S. KANCHIDURAI, K. SARAVANA RAJA MOHAN
Rezumat
When extra water in concrete evaporates, it leaves voids in the concrete element developing capillaries, which might be directly related to the porosity and permeability of concrete. By proper selection of components, and mix proportioning and following right construction practices, an almost impervious concrete can be obtained. The pores in cement paste consist of gel pores and capillary pores. The pores in concrete, because of incomplete compaction, are voids of large size which provide a honeycomb shape leading to concrete of low strength. In order to reduce the porosity, cement is partially substituted with nano silica in percent by weight and strive is made to examine durability homes of concrete composite. Since the water absorption test measures the response of concrete to pressure, which is rarely the driving force of fluids entering concrete, there is a need for another type of test. This test should measure the rate of absorption of water by capillary suction, and sorptivity of unsaturated concrete. By use of 0 to 4 % addition of nano silica, there is a considerable reduction in capillary absorption and there is an increase in the compression strength and modulus of elasticity of the concrete. Micro analysis was carried out by Scanning Electron Microscope (SEM) and Energy Dispersive Spectroscopy (EDS), and the studies indicate that nano silica is uniformly distributed by improving microstructure of concrete.
Cuvinte cheie
nanosilice, TEM, SEM, EDS
YASEMIN AKGÜN, ÖMER FATIH YAZICIOĞLU
Rezumat
In the future, depending on the increasing demand of cement, the additives in the market may not be able to meet the demand or there may be a need to use high amounts of additives. So, there is a need to new alternative additive materials. The aim of this study is to evaluate the potential of analcime which may be alternative to clinoptilolite. Therefore, it was performed some tests on mortars/concretes containing analcime and clinoptilolite. The amounts of natural zeolites (analcime, clinoptilolite) which were used for blended cements were 0, 10, 30 and 50% of Portland cement weight. In the study, i) physical, chemical, mineralogical, pozzolanic properties of natural zeolites, ii) strength, abrasion resistance and capillarity on samples containing analcime and clinoptilolite blended cements, iii) the energy evaluations for cements/concretes used in the study were investigated. According to the results, analcime has been showed similar properties to clinoptilolite. In some cases, due to these similar properties, it has been concluded that analcime may be an alternative pozzolan to clinoptilolite which is widely used in blended cement industry.
Cuvinte cheie
zeolit natural, analcim, clinoptilolit, puzzolană, beton
CRISTINA ANDREEA VÎJAN, ALINA BĂDĂNOIU, ADRIAN IONUȚ NICOARĂ, IULIA BARCAN
Rezumat
Lucrarea prezintă influența exercitată de natura componentului oxidic (magnezită calcinată sau dolomită calcinată) asupra timpului de priză și a rezistențelor la compresiune ale cimenturilor fostatice în care s-a folosit ca precursor fosfatic NaH2PO4. Aceste cimenturi au fost folosite pentru imobilizarea a două compoziții simulate de deșeuri cu conținut de Ni sau Pb. Prezența Ni sau Pb în aceste sisteme liante determină o scădere a rezistenței la compresiune la perioade scurte de întărire (o zi). Testul de levigare (SR EN 12457-4), realizat pe cimenturi cu conținut de deșeuri întărite timp de 28 zile, a arătat că se realizează o imobilizare a acestor metale grele în cele două tipuri de cimenturi fosfatice studiate; cu toate acestea, în cazul cimentului fosfatic pe bază de dolomită calcinată (cu/fără deșeu cu Ni sau Pb) se constată o scădere importantă a rezistenței la compresiune la perioade mai lungi de întărire ( 28 zile, 1 an) datorată foarte probabil hidratării întârziate a CaO cu creștere de volum. Analiza de difracție de raze X s-a utilizat pentru a identifica compușii cristalini formați în cimenturile hidratate și microscopia electronică de baleiaj cuplată cu spectroscopia cu raze X pentru a evalua microstructura și a realiza o analiză elementală a fazelor identificate.
Cuvinte cheie
magnezie, dolomit calcinat, fosfat de sodiu, nichel, plumb, deșeu
YAHYA RAHBAR, S. YASIN MOUSAVI, HEYDAR DASHTI NASSERABADI
Rezumat
In recent years, binary and ternary use of supplementary cementitious materials (SCMs) has received special attention by researchers throughout the world. This can combine the benefits of each SCM and minimize its adverse effects on the properties of concrete. The main purpose of this study was to investigate the performance of high-strength concrete (HSC) produced by the combined use of 0%, 5%, 10% and 15% natural zeolite (NZ) and different nano-particles including 2%-4% nano-SiO2 and 0.5%-1.5% nano-CaCO3 in aggressive environment. In this respect, different samples of HSC were made and besides slump and compressive strength; they are tested for chloride ion penetration depth and chemical resistance. The chemical resistance of HSCs were measured by evaluation the variations in the mass and crushing load of concretes after 28, 56 and 84 days of exposure to 5% sulfuric acid solution (H2SO4). Results showed that all HSC samples had a 28-day compressive strength greater than 81.36 MPa which passed the minimum strength value (≥ 60 MPa) considered in this study for HSC. Also, compared to using only NZ, by substituting the optimum level of nano-particles and NZ as SCM in HSC, lower depth of chloride ion penetration can be obtained. The results also revealed that the highest percentages of mass loss and crushing load loss were obtained for plain HSC which could decrease by the ternary incorporation of Portland cement, nano-particles and NZ.
Cuvinte cheie
beton de înaltă rezistență, nano-SiO2, nano-CaCO3, zeolit natural, durabilitate
T.R. DANYA, N.SAKTHIESWARAN
Rezumat
This research examined the workability, mechanical properties and durability properties of self-compacting concrete (SCC) with fly ash and glass fibers. Glass fiber was added to the concrete at a rate of 0.25% by the weight of binder, fly ash and metakaolin was replaced at the rate of 5%, 10%, 15%, 20%, 25% and 30% respectively to the cement. The workability of fresh concrete samples was assessed using slump flow, slump flow T50 and J-ring. The overall strength of hardened concrete was investigated by using compressive, tensile strength and flexural strength tests for a fixed water/binder ratio of 0.35with grade of M30 at 28, 56 and 180 days. The mechanical properties of SCC show an enhanced performance compared to the control mix and satisfy the fresh concrete properties such as filling ability and passing ability. SCC shows better resistance to the external environment. Thus, it shows a successful use of waste products in the SCC leads to the sustainable nature.
Cuvinte cheie
beton autocompactant, cenușă de termocentrală, metacaolin, fibre de sticlă
ALI SABERI VARZANEH, MAHMOOD NADERI
Rezumat
In this paper, the flexural and compressive strength of polymer-modified mortars (PMM), using the "Twist-off" and "Pull-off" semi-destructive tests has been evaluated. The shear and tensile bond strengths between the PMM and the concrete substrate have also been investigated. The SBR Latex has been used in mortars with 10, 15, and 20% ratios of cementitious materials. The correlation between the results obtained from experimental tests and semi-destructive tests at different ages using linear and power regression analysis was determined, and the calibration curves were presented. Calibration curves can be used to convert the results of the "Twist-off" and "Pull-off" tests to the compressive and flexural strength of PMM. In the following, the effect of polymer content on shrinkage and bond strength of repair mortars with the concrete substrate was investigated. Furthermore, to investigate the obtained stress results during semi-destructive tests, the "Twist-off" and "Pull-off" tests were analyzed by utilizing the ABAQUS finite element analysis software. The results showed a high correlation between the mechanical properties of polymer-modified mortars and the resulted data of semi-destructive tests, and high compatibility with the numerical analysis was observed. Moreover, due to the high correlation between shear and tensile bond strength resulting from "Twist-off" and "Pull-off" tests, it is possible to use a simple and inexpensive "Twist-off" machine instead of using an expensive "Pull-off" machine
Cuvinte cheie
teste 'Twist - off', 'Pull-off', metoda elementului finit, mortar modificat cu polimeri, rezistență
LILIANA MARIA NICULA, OFELIA CORBU, MIHAI ILIESCU, DELIA GEORGETA DUMITRAȘ
Rezumat
Lucrarea curentă își propune să analizeze caracteristicile zgurii de furnal granulată și negranulată utilizată la prepararea betoanelor rutiere, respectiv influența acestora asupra celor mai importante caracteristici ale betonului cum ar fi consistența, densitatea aparentă, volumul de aer oclus, rezistențele mecanice, la uzură și la îngheț-dezgheț. S-au preparat trei amestecuri de betoane rutiere cu materiale convenționale (ciment Portland și agregate naturale) și cu diferite proporții de materiale artificiale de proveniență locală, din zgură de furnal granulată și măcinată utilizată ca liant și zgură negranulată și concasată utilizată ca substituție a agregatului natural sort 0/4 mm. Caracteristicile geometrice, fizice și chimice ale zgurii de furnal analizate confirmă că are proprietăți adecvate pentru realizarea unor amestecuri de betoane rutiere durabile. Conținutul elementelor toxice testate la zgura de furnal nu depășesc valorile limită admise în normele europene. Rezistențele la întindere prin încovoiere obținute la 28 de zile au înregistrat valori care au permis încadrarea amestecurilor în clase de beton rutier BcR 4.5 și BcR 5.0. Rezistențele la îngheț-dezgheț și la uzură a betoanelor rutiere cu zgură au fost mai mari decăt rezistențele betoanelor rutiere de referință.
Cuvinte cheie
zgură de furnal, rezistențe mecanice, îngheț-dezgheț, beton rutier
XIAOZHEN LI, JUNZHE LIU, HUI WANG, XIANGWEI XING
Rezumat
This paper aimed to present the morphology features and elements’ distribution at the interface between steel and concrete in the presence of chloride and carbonation by means of electron probe (EPMA) and X-ray energy spectrum analysis (EDX-SEM). The results showed that the corrosion products of steel bars at the interface of steel and cement paste in chlorinated reinforced concrete diffusing into concrete through the steel-concrete interface. According to the penetration depth of corrosion products, the corrosion degree of the steel bars in the concrete can be determined. The chloride ions produced by the decomposition of Friedel salt in the cement paste migrated to the surface of steel bar in non-carbonated zone. As a result, the concentration of chloride ions accumulated on the surface of steel bars reached the critical concentration of corrosion, which increased the probability of steel corrosion. When concrete was mixed with nitrite, NO2-AFm, which was evenly distributed originally in the cement paste, decomposed into nitrite ions under carbonation and diffuses to non-carbonized zone. This increased the NO2-/Cl- molar ratio around the steel bar and effectively prevented corrosion of steel bars.
Cuvinte cheie
interfață beton - oțel, carbonatare, cloruri, EPMA, distribuția elementelor