română A.UĞUR OZTURK, R. TUĞRUL ERDEM
Abstract
Compatibility of different based superplasticizers with air-entraining admixture has been investigated. Physical and mechanical properties such as flow, setting time and compressive strength of cement mortars incorporating an air-entraining admixture (HS) with naphthalene sulfonate (SPNS) and modified polymer (SPMP) based admixtures have been determined. Also, the effects of their combinations on the freeze-thaw resistance of cement mortars have been determined. All admixtures are used with three different ratios and one of them is for overdosage effect. Results indicate that cement mortars having lowest early strength values are mortars incorporating 1.5% SPMP and 2.0% SPNS by mass of cement. The most effective series for the ultimate highest strength values were series with 0.05 % HS and 0.8 % SPMP. The freeze-thaw resistances of cement mortars were investigated for 50, 100, 150 and 200 freeze-thaw cycles. Indeed, the most effective series for freeze-thaw resistance were series with 0.05 % HS and 0.8 % SPMP.
Keywords
Admixtures; superplasticizer; compatibility; compressive strength; freeze-thaw
JANNE PESONEN, JUHO YLINIEMI, TOIVO KUOKKANEN, KATJA OHENOJA, MIRJA ILLIKAINEN
Abstract
Combustion affects the physical and chemical characteristics of fly ash. Peat and biomass are typically combusted using fluidized-bed combustion (FBC) technique, which causes the fly ash to have a low chemical reactivity. Especially low-Ca FBC ashes have very weak hardening properties, which reduce their utilization potential in many applications. This study examined the effect of adding alkaline activator and Portland cement on the hardening of two peat-wood fluidized bed combustion fly ash samples—one of high-calcium fly ash (24.9 % Ca) and the other low-calcium fly ash (9.7 % Ca). The reactive components of the raw materials, the mineralogical compositions, and compressive strengths of the resulting mortars were studied. Significant improvement to strength development was achieved. The addition of Portland cement proved necessary for low-Ca ash to harden at all. The ash cannot be considered solely as a filler material, since the reactive component (Ca, Si, Al, and S) contents of the ash, especially the Ca content, affect the strength development. Strength development of the mortars can be partly explained by the Ca/(Si + Al + S) ratio and the sum of the reactive components.
Keywords
fly ash, biomass, peat, Portland cement, alkaline activation, fluidized bed combustion
BORDJIBA ABDELHAK, HACEN-CHAOUCH ABDELMADJID, GUENFOUD HAMZA, GUENFOUD MOHAMED
Abstract
The design of a safe and respectful roadway to the environment must meet the users’ requirements in the present without compromising those of future generations. Under the traffic action, always more constraint and the climatic blitzes, the pavements crumbling occurs rapidly, which leads to severe impairments that are reflected on the surface layers: rutting, cracking, substances rejection, polishing and pulling out the aggregates on surface. This situation often involves the renovation of the surface’s layers. It is, therefore urgent to appeal to a new vision of pavement design based on optimizing the use of local materials, non-renewable, and respect for the environment. The recycling of bituminous substances are one of the relevant solutions. It has the advantage of reusing building materials by mixing them with a proportion of refined ones to achieve the required performance. This assignment researches for different rates of coated aggregates, the effects of manufacturing temperature and blending time in the mixing of the constituents during production as well as the additive plastomers of polyolefins on the improvement of the recycled asphalt rutting. Rutting is one of the most encountered degradation phenomena in the Algerian roads. The formulated hypothesis used here assumes that the elastomer polyolefins additive have an influence on the mechanical performance (rutting) of the recycled asphalt and also on the rate of the used asphalt aggregates. To justify this hypothesis it is mandatory to go through the manufacture of the asphalt with different rate of asphalt aggregates. To reduce the number of experimental tests necessary for this study, we used the experimental approaches method.
Keywords
asphalt, Recycling, polymers, environment, binder, penetrability
ZHOU LINA , WANG ZHENG, LU SHUANG
Abstract
The leaching behaviour of hydraulic concrete can’t be ignored for its long-term exposure to surrounding water resulting in irreversible damage of durability, such as strength loss and porosity increase. The coupled effect of leaching and freeze-thaw cycles on the durability of hydraulic concrete in severe cold regions is a bigger challenge. For the quite slow process of natural leaching, electrochemical accelerated leaching method (EALM) was proposed to investigate the damage evolution under two test schemes (scheme one is only leaching for 50 days and scheme two is first 100 rapid freeze-thaw cycles and then leaching for 50 days) designed in this work. The electrical resistivity and calcium oxide dissolved mass were measured through electrode impedance spectroscopy (EIS) and EDTA titration method, respectively. Based on electrical resistivity measurement, the measurable damage can be discussed during above-mentioned single and coupled tests. The results indicate that compared with single leaching the coupled leaching with the freeze-thaw cycling leads to over 50% electrical resistance loss, the largest difference of both calcium oxide dissolved mass and pH in cathode room on the 21st day.
Keywords
leaching, hydraulic concrete; coupled effect; EALM; damage evolution; EIS; calcium oxide dissolved mass
ELENA DUMITRESCU, ECATERINA ANDRONESCU
Abstract
This paper presents experimental results for solid waste (with heavy metals content) inertization in chemically bonded phosphate ceramic (CBPC) matrix. This process turns hazardous waste in non-hazardous waste.
It was studied the inertization of contaminated soil with 2000 mg/kg heavy metals (Cu, Ni, Pb and Zn) in chemically bonded phosphate ceramic versus inertization in Portland cement paste. Waste load was 50%, 70% and 80%. As the CBPC is a fast setting system, it was also used a retarder (i.e. boric acid and calcium lignosulfonate) in concentration of 1% (based on the amount of magnesium oxide and potassium dihydrogen phosphate). To determine the effectiveness of inertization were performed leaching tests in water and in acid solution, and the obtained values were compared with regulated limits.
All wastes stabilized with portland cement and CBPC meet specific criteria for compressive strength for accepting waste in landfill, but stabilization in CBPC is more effective.
In terms of nickel leachability in water, stabilizing of waste in CBPC allows soil waste loading of 80% compared with those stabilized in cement that allows waste loading of 50%.
Keywords
waste inertization, contaminated soil, heavy metals, chemically bonded phosphate ceramic, portland cement, leachate.
CLAUDIU ACIU, CECILIA ROMAN, DANA - ADRIANA ILUŢIU - VARVARA, CARMEN PUIA, OANA CADAR
Abstract
This study was focused on the development of plastering mortars with good antibacterial and antifungal properties and adequate physical and mechanical characteristics regarding the mechanical strengths (CS IV), good adhesion to the substrate and low water absorption by capillarity (W2). As testing microorganisms, four bacterial (Escherichia coli, Staphylococcus aureus, Enterococcus faecalis, Pseudomonas aeruginosa) and two fungal species (Aspergillus niger and Penicillium chrysogenum) as suspensions with density 106 cells/ml were used. In order to obtain antibacterial and antifungal effect on mortar surface, concentrations of more than 5% Ag/ZnO nanopowders (0.05 wt.%) are required. As a result, the obtained plastering mortars can be used for inhibiting the growth of pathogens of environmental and hygienic concern.
Keywords
mortar, zinc oxide, silver, antibacterial and antifungal properties
BOJAN MILOŠEVIĆ, ŽARKO PETROVIĆ, MARINA MIJALKOVIĆ, SLOBODAN RANKOVIĆ
Abstract
Self-compacting concrete (SCC) is intensively used in civil engineering due to its excellent characteristics both in fresh and in hardened state. In the several recent years, there is a growing need for testing of recycled aggregate use for making of concrete, which protects the environment and solves the problem of construction rubble disposal sites. The goal of this paper is to test the potential of usage of coarse recycled aggregate, obtained by crushing of concrete elements mechanically damaged in the production process of prefabrication elements, for making of SCC. Three concrete mixes were prepared for the experiment: the mixture made with the river aggregate as a reference mixture, the mixture where the coarsest fraction of the river aggregate was replaced by the recycled aggregate and the mixture in which both coarse fractions of the river aggregate were replaced by the recycled aggregate. In making of these concrete mixes, the principle of equal consistency of mixtures was followed. The mechanical characteristics determined for all the mixtures were: compressive strength, splitting tensile strength and modulus of elasticity. The obtained results indicate that the properties of these concretes exhibit minimal differences, and the application of the recycled aggregate obtained by crushing of prefabricated elements mechanically damaged in production process is justifiable for making of SCC.
Keywords
Self compacting concrete, recycling aggregate, compressive strength, tensile splitting strength, tangent and secant elasticity modulus
ELENA DUMITRESCU, ECATERINA ANDRONESCU
Abstract
This paper presents experimental results for liquid waste inertization in chemicaly bonded phosphate ceramic (CBPC). This process turns waste hazardous in non-hazardous waste.
It was studied the inertization of liquid wastes containing heavy metals (Ba, Cd, Cu, Ni, Pb) with concentrations between 3000 mg/l and 30000 mg/l in CBPC versus inertization in portland cement paste. As the CBPC is a fast setting system, it was also used boric acid as retarder in concentration of 3% (based on the amount of magnesium oxide and potassium dihydrogen phosphate). To increase the efficiency of cadmium inertization, phosphoric acid was added. Also it was studied the influence of sodium dimetilditiocarbamate. It was determined the maximum temperature of the obtained systems, the setting time and compression strength. To determine the effectiveness of waste inertization it was performed leaching tests in water and in acid solution, and the obtained values were compared with regulated limits.
Keywords
waste inertization, heavy metals, chemically bonded phosphate ceramic, CBPC, portland cement, leachate, TCLP
VASILE RUS, HORAŢIU VERMEŞAN, ANDREEA HEGYI, ANCUŢA ELENA TIUC
Abstract
The scope of the paper is to find a model for the evolution of corrosion products formed on hot dip galvanized rebars in fresh concrete, regarding layer thickness and density. In this study, non-passivated and passivated hot dip galvanized rebars were used, with various passivation solutions. Tests were performed using Electrochemical Impedance Spectroscopy (EIS). The corrosion products layer evolution was analyzed using the equivalent circuit model, best fitted with the EIS experimental plots. The layer evolution model was built by monitoring the layer thickness variation with time, and based on polarization resistance data.
Experiment results show the formation of two corrosion products layers, one in the rebar vicinity and the other in the concrete matrix vicinity. The two layers density and resistance evolutions are different; their thickness and density variations are independent from each other. The presence and effects of hot dip galvanized rebar passivation before the embedment in fresh concrete, was also emphasized.
Keywords
Electrochemical Impedance Spectroscopy, hot dip galvanized rebar, corrosion, fresh concrete interface
QINGFENG WANG
Abstract
The calcium magnesium aluminate cement often presents a longer setting time than the conventional calcium aluminate cement containing 70wt. % Al2O3, owing to the presence of the MgAl2O4 spinel in the cement clinker. In this paper, calcium chloride was used to control the hydration rate of the cement containing MgAl2O4 spinel. The temperature development of cement pastes was employed to characterize the hydration and setting behavior of the cement. The electrical conductivity measurement was utilized to evaluate the dissolution-precipitation rate of the cement. X-ray diffraction was conducted to identify the hydrates after halting cement hydration by vacuum freeze drying at a certain curing time. And scanning electron microscopy was used to observe the microstructure development during the cement hydration. These results reveal that calcium chloride addition intensifies the hydration of the calcium magnesium aluminate cement.
Keywords
calcium chloride, calcium magnesium aluminate cement, hydration, dissolution-precipitation rate, microstructure
KSENIJA JANKOVIĆ , LJILJANA LONCAR, DRAGAN BOJOVIĆ, MARKO STOJANOVIĆ
Abstract
Adequate measures must be taken during the determination of the concrete composition for ensuring the durability of concrete exposed to an aggressive environment. The influence of the cement type on the freeze/thaw resistance with and without de-icing salt of concrete was tested. Samples were made using five types of cement. All types of concrete made according to the recommendations of the Serbian and European norms had the required frost resistance. Besides the respected recommendations, concrete made using cement with 35% mineral additions of fly ash and lime was not freeze/thaw resistant with de-icing salt.
Weathering resistance for paving units is determined according to EN 1338 and EN 1339 for freeze/thaw resistance with de-icing salt or water absorption. Taking into account previous investigations, only samples which were made in accordance with the recommendations of the Serbian Building code requirements for concrete and reinforced concrete - BAB 87 and European norms EN 206-1 were tested. Regarding water absorption, it is expected that in the case of established production all types of concrete would be integrated into class 2 according to EN.
Also, for two representative types of concrete with different air content and degree of damage done by destructive test, non-destructive test by device RapidAir 457 was done (specific surface, spacing factor, void frequency and average chord length).
Keywords
types of cement, concrete durability, freeze/thaw resistance, scaling, spacing factor, weathering resistance
IONELA PETRE, MIRELA MENICU, ILEANA MOHANU, FLORIN BERNEA, CAMELIA ȘERBAN
Abstract
In the clinkerization process a negative influence on the kiln operations and the quality of clinker has the presence of volatile compounds (alkalis, sulphur, chlorine). These are brought into the system by the raw materials and fuels. At the international level an efficient method for reducing the negative effects of volatile compounds is the bypass introduction. In this paper the results of theoretical calculations of bypass revealing the influence of bypass degree on reducing of the alkali content from clinker are presented.
Keywords
bypass, alkali volatility, clinker, clinkerization installation, cement
DAN GEORGESCU , ADELINA APOSTU
Abstract
The article presents a proposal with a view to extending the application of the equivalent durability procedure (EDP). It proposes and applies criteria for determining the freeze-thaw of concrete in the context of extending the field of application of the procedure of equivalent durability to existing buildings. The proposed method represents an extending of EDP procedure considering: reducing uncertainties related to the placing of concrete, finishing, curing of concrete and the rate of improving the performance of concrete over time. The application of standardized test methods in Europe also for assessing the freeze-thaw resistance of concrete in existing buildings represent a step forward in increasing concrete durability and prolonged working life of the buildings. The proposed method is similar to the one used in assessing concrete resistance.
Keywords
concrete, durability, assessing, performance, existing building
M. HRAITA, Y. EL RHAFFARI, G. FADILI, A. SAMAOUALI, Y. GÉRAUD, M. BOUKALOUCH
Abstract
The importance of capillary imbibition and evaporation processes in the alteration of building stones under the action of salt crystallization can be estimated by various experimental techniques. The aim of this study is to understand the direct relationships between salt weathering, petrophysical and structural properties. We chose to work on calcarenite stone which was commonly used as building material in historical monuments in Morocco. Laboratory wetting-drying cycles were tested on calcarenite specimens with sodium chloride solutions of different concentrations. Results show that the permeability and specific mass of precipitated salt depend on the material porosity and solution concentration. Moreover, variations of thermal conductivity and permeability during applied cycles are less important for samples taken parallel to the sediment bedding than for those taken perpendicularly. The material anisotropy will also be discussed.
Keywords
Calcarenite stone, Salt weathering, Moroccan historic monuments, Permeability, Thermal conductivity.
MIHAI ROHAN
Abstract
In Romania, there are several industries that already apply the concept of circular economy, amoung which the cement/concrete industry that turns waste into alternative sources of raw materials and energy and already recovers significant amounts of waste from other industries as well as sorted household waste. Waste co-processing in cement industry is a waste recovery method, recognized as being one of the best practices for an efficient use of resources. By co-processing take place simultaneously, both the recycling of waste mineral content as well as their energy recovery, which leads to the reduction of indirect CO2 emissions.
Also, the product of wide consume of this industry – cement concrete – can be 100% recycled as alternative aggregates used in building the transport infrastructure or getting a new concrete.
Thus, the cement/concrete industry contributes to the conservation of natural resources by replacing them with alternative resources from waste, and becomes an integrant part of the circular economy - European goal for an efficient use of resources and ensuring energy security.
Keywords
cement, concrete, waste, recycling, circular economy, recovery
ANGEL PALOMO, OLGA MALTSEVA, ANA FERNANDEZ-JIMENEZ
Abstract
Coal fly ash can be subject to large variations in characteristics as a function of the type of coal burned, the operation status of the coal power plant and the ash separation technology employed. Good quality fly ash is in demand in the cement industry (and in the concrete plants) due to its ability to partially substitute some Portland cement (typically between 10% and 25%). On the other hand, coal bottom ash, due to its coarser nature, is generally considered as a low value by-product that may at best be used as a partial replacement for aggregates in concretes or as geotechnical fill material. In this paper authors propose a procedure (mechanical-chemical combined procedure) by which to transform regular coal combustion products (fly ashes and/or bottom ashes) into Ultra-Reactive Ashes (URA).
URA is a product with very interesting cementitious characteristics which can become the most important component of a new family of extra-durable and cheap ecoconcretes.
Keywords
Fly ash, chemical activation, mechanical activation, geopolymer concrete
CARMEN MUNTEANU, MARIA GEORGESCU
Abstract
The paper brings information obtained by own researches regarding manufacture and characterization of some concretes in which the binder was Portland cement with variable content of fly ash. As aggregate, an old crushed concrete was used, which substituted partially or totally the conventional aggregate (of ballast-pit). A polycarboxilic type superplasticiser (dosed as 0.9% relative to the cement content) was used for all the concretes.
Based on the experimental data, some useful correlations between compositions and properties (mechanical strength, impermeability, and freeze-thaw resistance) could be established. These allow the assessment that it is possible the manufacture of some concretes by simultaneous use of the fly ash and recycled concrete, without significant change in the principal properties (mechanical strength, impermeability, freeze-thaw resistance). Such waste valorization has favorable influences on the environment.
Keywords
concrete, recycled aggregate, fly ash, properties
GORDANA TOPLIČIĆ ĆURČIĆ, DUŠAN GRDIĆ, NENAD RISTIĆ, ZORAN GRDIĆ
Abstract
The share of aggregate in concrete composition, in terms of volume is 70%-80%. The properties of fresh and hardened concrete depend on the aggregate properties, primarily on particle size distribution. The paper considered impact of particle size distribution of aggregates from two screening plants from the South Morava river on the properties of concrete. The intention was to make concrete mixtures with the aggregate which would have as identical particle size distribution, as similar consistency of fresh concrete as possible and same compressive strengths. For making of afore mentioned concrete mixes, the same sort of cement and same admixtures were used.
It was concluded that the difference in the particle size distribution of aggregate fractions had an impact on the composition of concrete mixes of the identical properties. Specifically, the quantities of cement, admixtures and water were different in the afore mentioned mixtures.
The technical specifications of the cement manufacturers include a recommended quantity of cement for specified concrete classes. It is concluded that these values are only rough guidelines. The same holds for the recommended quantities of admixtures. For that reason, every required concrete mixture must be verified in laboratory, i.e., previously tested.
Keywords
river aggregate, particle size distribution, cement, admixture, concrete
R. TUĞRUL ERDEM , A. UĞUR OZTURK, ENGIN GÜCÜYEN
Abstract
Due to several advantages of cementitious materials especially mortars, they are widely used in construction works. It is important to determine the mechanical properties of cementitious materials to understand their behavior under different effects. In this study, Artificial Neural Networks (ANN) analysis is used to predict the 7 and 28 days compression strength values of cement mortars. Physical-mechanical properties such as flow, setting time and compressive strength of cement mortars incorporating of different chemical admixtures such as air-entraining admixture (HS), naphthalene sulfonate based (SPNS) and modified polymer (SPMP) based admixtures have been determined. The aim of the usage of combinations of air-entraining admixture with two different based superplasticizers is to form different inner structure affecting on compressive strength. All admixtures are used with three different ratios by cement weight and one of them is for overdosage effect. ANN analysis has been performed to predict the compression strength values after 7 and 28 days, in correlation with experimental part of the study. According to this view, 28 sets have been prepared with different combination of admixtures. At early ages, HS015-SPNS2.0 series had the lowest strength whereas the highest compressive strength at 28 days were obtained for HS005-SPMP0.8 series. Obtained compression strength values after 7 and 28 days have also been predicted by ANN analysis. It is stated that the established ANN model indicates a great capacity to predict the compressive strength values in the end.
Keywords
ANN; admixtures; superplasticizer; compressive strength; cement mortars
Behaviour of reinforced concrete beams subjected to dynamic loading in various stages of degradation
CONSTANTIN GAVRILOAIA, NICOLAE ȚĂRANU, RALUCA ONOFREI, MIHAI BUDESCU, PETRU MIHAI, IOANA-SORINA ENȚUC
Abstract
The dynamic characteristics of a building element are represented by vibration frequency, damping coefficient and stiffness. The vibration frequency of a reinforced concrete element modified with respect to the degradation state caused by the cracking of concrete and the yielding of reinforcement is analyzed in this paper.
An experimental program, carried out at the Faculty of Civil Engineering and Building Services in Iasi, revealed a specific relation between the vibration frequency and the damage level of some reinforced concrete elements. In this experimental program four reinforced concrete beams with the same concrete class but different reinforcing ratios have been tested in bending up to various levels of degradation. The experimental results have been validated through numerical modeling using the software package LUSAS based on finite element analysis.
Keywords
reinforced concrete beams, vibration frequency, damage level, numerical modeling
MICHAL HORA, PAVEL REITERMAN
Abstract
This research is focused on concrete with rubber powder content exposed to low (freezing) temperatures. Rubber powder serves as air-entraining agent and should provide better freeze-thaw protection. On the other hand, rubber powder limits maximum compressive strength of concrete. The main purpose of this research is to find an optimal rubber powder content in order to satisfy needs for the minimal loss in strength of concrete as well as high freezing-thawing resistance. A freeze-thaw test was carried out on five concrete mixes with different contain of several rubber fractions to determine the optimal rubber grading. Specimens with rubber powder were tested on compressive strength, splitting tensile strength, tensile strength and moduli of elasticity. The specimens with rubber content were tested at laboratory temperature as well as at freezing temperatures. Influence of rubber addition was assessed on the base of original and residual values of studied properties after freeze-thaw loading. Resistance to frost damaged was determined by splitting tensile strength test and tensile strength test. Non-destructive methodology was predominantly used to monitor gradual deterioration during freeze-thaw cycling.
Keywords
freezing, thawing, rubber powder, compressive strength, air-entrainment
GENG LIN, CHANG-LONG WANG , CHUN-YU QIAO, HAN-LONG CUI, LIE CHEN, SHUO YU
Abstract
To comprehensively utilize lead-zinc tailings (LZT), it was used as main siliceous materials in autoclaved aerated concrete (ACC) in this study. The effects of fineness and content of LZT on the properties, hydration products and microstructures of AAC were investigated by the mechanical test, X-ray diffraction analysis (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric/differential scanning calorimeter (TG-DSC) and scanning electron microscope (SEM). And the composition and morphology of the hydration products in AAC at varying stages were detected. The results show that the ACC containing 62% LZT (in mass percentage) with a specific surface area of 325 m2 kg-1 can achieve a bulk density of 587 kg m-3 and compressive strength of 4.94 MPa, which qualifies the requirements of A3.5, B06 level of AAC sample regulated by the composition and morphology GB/T 11969-2008. The mobility of slurry and hydration activity both increase as the fineness of LZT decreases. However, the small size of LZT particles and the high thickness of the slurry are harmful to form a good pore structure, which would influence the properties of AAC. When the blending percentage of LTZ is too high, the unreacted LTZ particles increase and accumulate within the system, which reduces the space among them and thus influences the growth and crystallization of hydration products. The main hydration products before curing are AFt and C-S-H gels. And then AFt decomposes and some amount of C-S-H transitions to tobermorite after curing and autoclaved.
Keywords
lead-zinc tailings, autoclaved aerated concrete, fineness, content, tobermorite
FAEZEHOSSADAT KHADEMI, MAHMOOD AKBARI, SAYED MOHAMMADMEHDI JAMAL
Abstract
Ultrasonic pulse velocity (UPV) test method is used in this study for evaluating the compressive strength of concrete. A series of UPV tests were performed to evaluate the 28-day compressive strength of concrete and examine the effect of concrete mixture parameters on the UPV of concrete. It was found that concrete with higher 28-day compressive strength gives higher UPV and that an exponential relationship exists between the UPV and 28-day compressive strength of concrete. The results showed that the aggregate size has a significant effect on the strength of concrete. Concrete with larger aggregate size was found to give lower UPV and compressive strength. UPV results also indicated that the UPV and compressive strength of concrete consistently decrease with increase in water-cement ratio of concrete. The effect of using microsilica (Silica fume) in concrete is also studied. It was found that as the microsilica to cement ratio increases in concrete, the UPV and compressive strength of concrete increase. The effects of the ingredient materials on UPV were analyzed and potential mechanisms were proposed. To make the results applicable, the artificial neural network (ANN) method was used to predict the compressive strength of concrete based on the evaluated concrete mix parameters and ultrasonic pulse velocity. The ANN analysis demonstrated high reliability in predicting the compressive strength values of concrete.
Keywords
Concrete, Compressive Strength, Ultrasonic Pulse Velocity, Aggregate, Water-Cement Ratio, Microsilica, Artificial Neural Network.
AYED KADA, KERDAL DJAMEL EDDINE, SOLTANI RABAH
Abstract
The study carried out herein aims at investigating the instantaneous and deferred mechanical behaviours of self compacting concrete (SCC). The survey was carried out in three steps. In the first step, local industrial waste fines, such as limestone (L), siliceous (S) and natural pozzolanic (PZ) fillers, were used in the preparation of the self compacting concrete; in the second, a study was performed to optimize the SCC formulation by varying the volume of paste; and finally, the effect of varying the volume of paste on the mechanical strength and shrinkage of the SCC was examined in the third part. Results showed that the addition of local fillers, according to international recommendations, in the preparation of SCC mixes gives better compressive strength and shrinkage behaviour than that of vibrated concretes.
Keywords
Self compacting concrete; Limestone fillers; Siliceous fillers; Natural pozzolana; Shrinkage; Compressive strength
NALAN KALKAN, RECEP KANIT
Abstract
The importance of capillary imbibition and evaporation processes in the alteration of building stones under the action of salt crystallization can be estimated by various experimental techniques. The aim of this study is to understand the direct relationships between salt weathering, petrophysical and structural properties. We chose to work on calcarenite stone which was commonly used as building material in historical monuments in Morocco. Laboratory wetting-drying cycles were tested on calcarenite specimens with sodium chloride solutions of different concentrations. Results show that the permeability and specific mass of precipitated salt depend on the material porosity and solution concentration. Moreover, variations of thermal conductivity and permeability during applied cycles are less important for samples taken parallel to the sediment bedding than for those taken perpendicularly. The material anisotropy will also be discussed.
Keywords
Masonry Structure, Out of plane loading, Steel reinforced shotcrete.
LAVINIA GABRIELA POPESCU, ENIKÖ VOLCEANOV, ILDIKO ANGER, ALEXANDRA GEORGIANA MOISE, ADRIAN VOLCEANOV, ECATERINA MATEI
Abstract
Present paper presents a comparative assessment of environmental factors by using an industrial waste from secondary metallurgy, such as white slag. LF slag generated at two sources as powder and subsequently as pelletized form were investigated. The chemical composition of the investigated slags were analysed by x-Ray Fluorescence (XRF).
Leachability tests and the chemical analysis were carried out by various methods. Consequently, the chemical composition of the leachate for various particle size fractions of the waste LF slag was determined by using flame atomic absorption spectrometry (FAAS) and by induction coupled plasma optical emission spectrometry (ICP-OES) to determine the content of heavy metals - Ni, Cu, Pb, Zn, Cd, brought by slag.
The values of pH and electrical conductivity on leachate samples, prepared with solid / liquid ratio of 1:2 and 1:10 were also measured.
The advantage of LF slag using as pellets consist in decrease the LF slag instability, comparatively with the initial powdered slag, which leads to dispersion as dust in the environment. This is possible by processing the slag to an optimal grain size distribution in conjunction with physical and chemical characteristics to obtain a homogeneous product. Their use as acid soil amendment in agriculture is effective.
Keywords
pellets, LF slag, leachability, acid soil amendment, agriculture
RODICA-MARIANA ION, MIHAELA-LUCIA ION, ADRIAN RADU, RALUCA-IOANA ŞUICĂ-BUNGHEZ, RADU-CLAUDIU FIERĂSCU, IRINA FIERĂSCU, SOFIA TEODORESCU
Abstract
In the field of architectural restoration, ancient materials and their decay in aggressive environments are studied, through case-histories. Some properties (capillarity, porosity) are tested on different façade surfaces, in order to identify the existing materials and to select the proper materials useful for restoration. The achieved microscopy (MO, AFM) studies allow observing the presence of the main weathering signs and the previous consolidation results. The EDXRF and ICP-AES techniques offer informations about the elemental composition of sample, while GC-MS allow the identification of the previous coniferous resins from the glue used for restoration. The identification of mainly of terpenes and derivative patterns highlighted the presence of plant oils and pine resins. Also, the CIELAB color parameters are a proof of the efficacy of the conservation process. Moreover a comparison between traditional mortars (based on cement) and those based on nanomaterials (calcium hydroxide, hydroxyapatite and their controlled mixture) used in restoration are investigated in this paper.
Keywords
nanomaterials, façade preservation, analytic characterization
PAVEL KRIVENKO, OLEG PETROPAVLOVSKII, HRYHORII VOZNIUK
Abstract
At present, a tendency to substitute hazardous organic adhesives in the majority of building materials is clearly observed. This is connected with the more strict than before requirements for health safety, fire safety and durability. The most important task is substitution of organic binders, traditionally used as adhesives for gluing concrete, brick and ceramics with non-hazardous inorganic binders. To solve this problem an adhesive for concrete, brick and ceramics based on ecologically friendly alkaline aluminosilicate binder (geocement) has been developed. This binder is itself an inorganic polymer, which combines properties of inorganic substances (high strength and frost resistance) and those of organic substances (elasticity, adhesion to various materials etc.) and is analogue to alkaline aluminosilicate materials occurring in nature: zeolites, feldspathoids, etc. Bonding strength of the geocement-based adhesives to various surfaces is higher than 1 MPa. With taking into account high pH of the geocement stone a proper choice of fillera and additives is important. The purpose of the study was to reveal influence of the geocement-based adhesive composition on properties and, accordingly, on structure of the interfacial transition zones: "concrete−concrete", "concrete−ceramics", "ceramics−ceramics".
Keywords
aluminosilicate structures, geocement-based adhesives, metakaolin, mica, feldspathoid, quartz sand, zeolite formation
IOANA GOMOIU, MADALIN ENACHE, ILEANA MOHANU, ROXANA COJOC, SIMONA NEAGU, DAN MOHANU
Abstract
Microbial colonization and biodeterioration of mural paintings in historical monuments have as result structural and aesthetic damages due to degradation of organic binders, biomineralization, colored biofilms and discoloration.The original and infilling mortar from refectory of Hurezi monastic complex-Romania was analyzed from structural point of view as well as from microbiological point of view. Visual inspection performed in situ on the northern and western walls revealed: cracks, small and large pink areas on the pictorial layer, original and infilling mortar, small black areas on the infilling mortar and white and pink efflorescences appearing mostly on the infilling mortar. Microscopical observation performed both in situ and in laboratory (Optical Microscope and Scanning Electron Microscope) revealed a pink biofilm and small black colonies. Microbiological analysis confirmed the bacterial origin of the pink biofilm and fungal origin of black colonies. The characteristics of the mortars sustain adhesion of the bacteria and fungi and organic deposits favor their multiplication which is reflected in colonization of the substrate.
Keywords
microbial colonization, pink biofilm, black biopigmentation, mortar, pictorial layer
ILEANA MOHANU, DAN MOHANU, IOANA GOMOIU, ADRIANA MOANŢĂ, LILIANA RADU, CRISTINA SERENDAN
Abstract
The wooden churches painted in fresco, present exclusively in south zone of Romania, represents a limited category, very little explored and, additional, threaten with disappearance. The main problem of preservation is represented by remaking of the adherence of fresco at wood support.
This paper presents the results of the first researches regarding the obtaining of some materials which will serve in the process of consolidation of mural pictures on wood support. For this purpose were performed a series of mortars based on hydrated lime, river sand and fibers of hemp. For improvement of the adherence an acrylic additive was added. Different characteristics of mortars in hardened state were evaluated, such as: apparent density, water absorption, water vapor permeability, flexural and compressive strength, and resistance at the phenomenon of biodegradation. By using the fibers the flexural and compression strengths of the mortars were improved.
Keywords
fresco, lime mortar, fiber, mechanical strength, water vapor permeability, biodegradation
ZENO GHIZDĂVEȚ, DANIELA NĂSTAC, MIHAI EFTIMIE, B. ȘTEFAN, IONELA STANCIU, ADRIAN VOLCEANOV
Abstract
Multivariate Analysis (MVA) on a complex database has been performed, aiming to reveal correlations composition-processing conditions-microstructure for some clinkers. Database was made of cement clinker chemical analysis, information extracted from image analysis on clinker micrographs and clinkering plant process parameters. Clinkers were burned in different conditions in industry (19) or in laboratory (14 different clinkers in two groups). Image analysis of each clinker has been made by computing Shape Parameters, Fractal Dimension and a parameter derived from Shannon Entropy, called the Uniformity Degree. Also, the intermixed C3A and C4AF minerals as interstitial phase of the clinkers have been isolated and analyzed. MVA results clearly identified the influential parameters on the database. It was found that the free CaO content in clinker was influential on both composition-microstructure and process parameters. Therefore, we concluded that the free CaO can be seen as a link between laboratory and industrial parameters in understanding these complex correlations.
Keywords
Image Analysis, Multivariate Analysis, clinker, optical microscopy, Shannon entropy, Fractal Dimension, Interstitial Phase
YU HAN, BAO-MIN WANG , SHUAI LIU
Abstract
Mechanical performances of carbon nanotubes reinforced cement-based composites have been studied separately. The autogenous shrinkage of cement-based composites doped with multi-walled carbon nanotubes (MWNTs) were investigated with low MWNTs concentration of 0, 0.05%, 0.1% and 0.15% by weight(wt%) of cement in the early age in this paper. Ultrasonic processing and a commercially surfactant were utilized to achieve homogenous MWNTs suspensions. The addition of MWNTs decreased the autogenous shrinkage of cement composites compared to the reference sample. When the MWNTs dosage was 0.15 wt%, the autogenous shrinkage of specimen was the minimum, which was 28% lower than the reference sample. The water-cement ratio affects the early-age autogenous shrinkage more obviously. The results indicated that MWNTs can also have a beneficial effect on the early strain capacity, the early-age and long term durability of the cement-based composites
Keywords
Multi-walled carbon nanotubes; cement-based composites; durability; early-age autogenous shrinkage
J.S. POZO-ANTONIO, J. FEIJOO
Abstract
Concrete lime- and NHL-based mortars were prepared with river sand and a standard ASTM sand as aggregate. The mortar samples were subjected to different curing conditions for 28 days in order to achieve the acceptable mortar strength in a shorter period of time, with the aim to move the repaired artworks from the restoration departments of museums while avoiding possible contamination or damages. The results are provided under the study of the influence of the curing conditions, the binder nature, the binder/aggregate ratio relation and the aggregate nature. The test results showed that ASTM sand was a good alternative to river sand; it even improved the mechanical characteristics and drying shrinkage of the NHL-based mortars and lime cement-based mortars. NHL5, with a lower amount of aggregates, achieved higher values of flexural tensile and compressive strength and performed mortars with lower shrinkage values, being the ASTM sand the aggregate that provided better properties. Synthetically, the lime based mortar NHL5 (1:1.75) with ASTM sand under 14 days at a RH of 90 ± 5% and 14 days at a RH of 60 ± 5% seemed to be a satisfactory solution to be used as repair mortar in order to achieve good mechanical and physical properties without long periods in restoration departments.
Keywords
Portland cement, lime, mortar, aggregate, curing, Compressive strength, Modulus of Elasticity, Mechanical properties, Drying shrinkage
CAI JUN, LI GENGYING
Abstract
Self-compacting concrete (SCC), also known as self-consolidating concrete, can be classified as an advanced construction material. SCC is a highly flowable concrete that can achieve full compaction without the need of vibration. In this study, the influence of fly ash on workability, mechanical properties and drying shrinkage of SCC specimens were investigated. The amount of fly ash was varied from 0% to 60% by mass of the binder material. Workability of SCC was characterized by the slump flow and the V-funnel tests. Test results showed that the workability of fresh SCC is improved by increasing the amount of fly ash. Compressive strength, splitting tensile strength and flexural strength decrease with the increase of fly ash. Fly ash can obviously reduce the drying shrinkage of SCC.
Keywords
self-compacting concrete, mechanical properties, drying shrinkage
RADU VOINIȚCHI, CONSTANTIN DORINEL VOINIȚCHI, VIOREL CRĂCIUN, ALINA BĂDĂNOIU
Abstract
This paper presents new insight regarding the influence of aggregate particles dosage and shape on the main properties of pervious concretes. The results presented in this paper show a correlation between the permeability coefficients assessed on aggregate mixture and corresponding previous concretes with various cement contents. This suggests that is possible to design pervious concretes with a prescribed permeability value, using as imput values the results obtained in permeability test of aggregate mix and applying a correction coefficient which depends on cement matrix content.
The replacement in the coarse aggregate fraction (8/16 mm) of polyhedral particles with flat particles (length to thickness ratio higher than 3) do not exert a major influence on the values of permeability coefficient of aggregate mixtures and derived pervious concretes. Nevertheless, a significant decrease of compressive strength is observed when the polyhedral aggregate particles of the coarse aggregate fraction (8/16 mm) are replaced with flat particles.
Keywords
pervious concrete, aggregate shape, water permeability, compressive strength
G. MURALI, A.S. SANTHI , G. MOHAN GANESH
Abstract
The aim of the study is to investigate the loss of mechanical properties such as compressive and splitting tensile strength of fiber-reinforced concrete (FRC) when exposed to impact load. Two different steel fibers i.e. hooked end and crimped end having the length of 50 mm and an aspect ratio of 50 were used as reinforcing materials in 0.5%, 1.0% and 1.5% volumes with a water-binder ratio of 0.42. The American concrete institute (ACI) committee 544 drop weight test was performed on 28 days cured cylinders, in order to determine the impact failure energy. In order to identify the loss of compressive and splitting tensile strength due to the effect of impact, another set of samples were prepared from the same concrete mixtures and exposed to impact loads of 25%, 40%, and 55% of their impact failure energy. Based on the results obtained from the experimental work, multivariate linear regression (MLR) models were developed using SPSS software to predict the percentage loss of compressive and splitting tensile strength due to the effect of impact load and the validity of the proposed model were verified with the test data of an earlier research. The results showed that the loss of compressive and splitting tensile strength in FRC significantly decreased compared with concrete without fiber, when exposed to impact loads. The results of the proposed model provided good agreement with the experimental results.
Keywords
Compressive strength, Tensile strength, Fiber, Impact, loss of strength
ASLAM HUSSAIN , SALEEM AKHTAR
Abstract
Structural Health Monitoring (SHM) plays an important role in retrofitting of concrete structures. In this paper, soundness of concrete material in three domes of a structure was evaluated by the use of Schmidt Rebound Hammer test and X-ray Diffraction (XRD) test after initially investigating the whole structure visually. It has been realized that value addition in the field of NonDestructive Testing (NDT) of Civil Engineering Structures is possible only through combination of various testing techniques. By successfully combining the results of visual inspection, strength based physical test and chemical test, authors have succeeded in introducing a novel idea for further research. XRD test, which has generally not been categorized as an NDT tool for structural evaluation, gives satisfactory results when combined with a strength based NDT tool.
Keywords
Structural Health Monitoring; Soundness of Concrete Material; X-ray Diffraction; Visual Inspection; NonDestructive Testing; Combination of Testing Techniques
AREF MOHAMAD AL-SWAIDANI
Abstract
The objective of the present work is to predict the compressive strength, water permeability, chloride penetrability and porosity of concretes containing volcanic scoria as cement replacement after 2, 7, 28, 90 and 180 days curing. Concrete specimens have been produced with three different water-binder ratios of 0.5, 0.6 & 0.7 and replacement levels ranging from 10 to 35%. Test results revealed that curing time, the scoria content and the water-binder ratio had a large influence on all the examined properties of scoria-based concrete. An estimation equation has been developed by the authors to predict the studied properties depending on the water-binder ratio, the curing time and the replacement level of volcanic scoria. SEM/EDX analysis has been reported, as well.
Keywords
Blended cement, Volcanic scoria, Concrete, Prediction of properties
EMILIA MOSONYI, NICOLETA COBÂRZAN
Abstract
The paper presents an interdisciplinary study based on: site inspections, petrographical and mineralogical research (staining methods, transmission polarizing microscopy, XRD analyses) and water absorption tests performed on amples extracted from replaced masonry units (tiles, blocks), weathered and non-weathered Portland cement mortars and tuff tiles from fortifying walls of a monumental tuff-made construction. The main outlined weathering processes were: intensive cracking (drying shrinkage; alkaline-aggregate-reaction, carbonation and salt crystallization, frost attack) and leaching associated with secondary carbonation and sulphate (intrinsic and extrinsic) attack induced expansive phenomena. The chemical and physical incompatibility between tuff, brick and cement based mortar beside the high level of stagnant humidity along the zeolites- bearing tuff blocks surfaces appears to be the first cause of decay and deleterious effects.
Keywords
historical building, volcanic tuffs, petrographic microscopy, sulphate-attack, staining methods, compatibility.
FLORENTINA ALINA BURLACU, CARMEN RĂCĂNEL, ADRIAN BURLACU
Abstract
Road safety has an increasing importance, especially after UN proclaiming 2011-2020 the Decade of Action for Road Safety. As many factors contribute to producing traffic accidents, infrastructure has its own part in this. Studies related to road surface are very important, especially due to the fact that the quality of the tyre-road surface contact could influence the occurrence of road accidents. Aspects like skid-resistance, permeability, and evenness are the main properties that should be taken into consideration for a road surface. The present research paper has the aim to correlate the characteristics of materials used in the wearing layer with the risk of producing road accidents, by calculating the braking distance, as a sub-component of stopping sight distance. The results of the laboratory tests undertaken on aggregates will show that only by varying the source of materials, stopping sight distance can differ with up to 20 meters.
Keywords
road materials, road safety, laboratory tests, roughness, polishing, stopping sight distance