DAN GEORGESCU, ADELINA APOSTU, RADU GAVRILESCU, TUDOR SEBA
The environmental actions can cause deteriorations of concrete having as consequence an intensified reduction of the elements/construction structures’ performance. The design of the service life of certain structures is performed considering methods with different complexities which must consider a rigorous selection of materials as well as important execution, execution inspection, maintenance factors and status assessment during service life. No matter the complexity of the method used, the design process of the service life must be based on the results obtained from certain experimental researches, necessary for the assessment of the evolution of materials’ characteristics, depending on different environmental conditions.
The freeze/thaw attack with /and without de-icing agents represents one of the actions with frequent occurrence, causing important deteriorations of concrete.
In the first part was presented an analysis of the main experimental methods related to the freeze/thaw action. In this part will be presented the results of certain experimental researches performed by authors in order to determine the freeze/thaw resistance of concretes manufactured with different types of cement produced by CARPATCEMENT HOLDING S.A. – HEIDELBERGCEMENT GROUP.
concrete, cements, experimental methods, freeze/thaw attack
IOANA PAPAYIANNI, ELEFTHERIOS ANASTASIOU
The use of concrete road pavements in Greece is very limited while there are many benefits from their use, especially in road parts of high inclination and heavy track circulation. The development of low-cost concrete, tailor-made for pavements will contribute to this alternative road construction. The design and properties of this type of concrete, which could be applied by using conventional equipment, are presented in this paper. The technical characteristics of the concrete which includes local fly ash as hydraulic binder and steel slag as aggregate are well described, including long-term performance observation.
durability, mechanical properties, special concretes
DRAGAN BOJOVIĆ, DRAGICA JEVTIĆ, MILOŠ KNEŽEVIĆ
This paper presents the optimization of concrete mixtures composition related to a physical property and the process of production of trial mix design by using the multi-layered feed-forward neural networks. This optimization was conducted because there is no clear method of designing concrete mixture composition and for the purpose of shortening procedure of the trial mix design of concrete. Mix design depend on many variables and deterministic models cannot give good results. The goal of the research was to make a model of a neural network, on the set of available data from 288 trial mix, which would, with highest accuracy, predict the compressive strength of concrete at the age of 28 days. In order to attain as high accuracy of obtained results as possible, three levels of input data to the neural networks were considered. On each of the applied groups of input data, the neural networks with 1 and 2 hidden layers were formed. On the basis of the adopted neural network, an algorithm for usage of the network in actual situations was made, applied on an actual model.
concrete strength, neural networks, prognostic model
LAVINIA ELENA MUNTEAN, DANIELA LUCIA MANEA, CONSTANTIN COSMA
This article presents the results related to the concentration of radionuclides and radioactivity index in the case of various mixing formulae of dry mortars.
The determinations have been carried out for 10 mixing formulae of plastering mortar (cement-lime and cement), where the Portland cement CEM I 42.5R, calcium hydrated lime EN 459/1 CL80-S and river aggregates originating from various areas of the Alba county are used.
The results reached indicate the influence of the origin of the river aggregates, differences between the concentrations of radionuclides being noticed in the case of mortars under test.
plastering mortars, radioactivity, gamma spectrometry, radioactivity index
ANDREEA MONCEA, MARIA GEORGESCU, ANA-MARIA PANAIT, CARMEN MUNTEANU
High Aluminate Cement is known almost exclusively like a refractory binder. The researches achieved in the last decades, especially in the Kerneos company (the inventor of cement Fondue, in 1908 – known under Lafarge name), have lead at interesting results, concerning the use of this binder, associated with Portland cement and calcium sulfate in complex binders, constituents of the „dry mortars”, for construction works.
In such complex binders, Calcium Aluminate Cement, himself, or by interactions with others components, give specific properties like: setting time and rapid hardening, size variation control, aesthetical qualities (non efflorescence, color stability), good resistance of corrosion, good mechanical strength, including abrasion resistance, reduction of pollution ("eco-friendly"). These properties meet the requirements imposed by applications in areas: leveling masses, ceramic tiles and natural stone adhesive, composites masses for external thermal insulations with decorative characteristics, mortars and concretes for repairs, with rapid setting, mortars with water resistance.
Considering these information, some systematic researches concerning achievement and characterization of ternary binders, in Portland cement (PC) – Calcium Aluminate Cement (CAC) – calcium sulphate (CSHx) system, were initiated at the S.I.M.O.Na department in POLITEHNICA University from Bucharest. Complex binder masses with ranging: 10 – 80% Portland cement, 10 – 60% Calcium Aluminate Cement, 5 – 30% calcium sulphate (hemihydrates or anhydrite III) was realized. This work brings data concerning setting time and mechanical strength, of the ternary binders from Portland cement (PC) – Calcium Aluminate Cement (CAC) – calcium sulphate (CSHx) ternary system, as information regarding size variations, during hardening.
Calcium aluminate cement, Portland cement, compressive strength, ternary binders
ION ROBU, IONELA PETRE, NASTASIA SACA
This paper contains information regarding durability of mortars/concrete with cement with 0%, 10% and 20% metakaolin addition (MK). Durability was assessed by determinations on the mortar such as water absorption, freeze-thaw resistance, shrinkage and behavior in sulfate solution (MgSO4, K2SO4) and on concrete: workability, volume of entrapped and entrained air, mechanical strength and permeability tests.
The results indicate that MK is a pozzolanic addition, which can be used in the production of composite cements with good physical, mechanical and chemical properties. Studies have revealed MK’s favorable effect on the properties over time of mortars and concretes.
The mortars based on cement with MK additions exposed to sulfate solutions have a good behavior up to one year exposure. The sulfates resistance of MK cements has to be correlated with the decrease in C3A content by partially replacing clinker with MK.
metakaolin, pozzolana, mortar, concrete
CARMEN MUNTEANU, MARIA GEORGESCU
The polycarboxylate type superplasticizers are substances with dispersing and fluidizing effect on cement pastes, allowing a very important reduction of the water/cement ratio, with favorable influences on mechanical strengths that the binding materials are developing. Depending on their nature, cement nature and dosage, the polycarboxylate superplasticizers cause certain changes in the kinetics of hydration processes and hydrates formation.
This paper brings information regarding the influence of polycarboxylate type superplasticizers on hydration processes and on the hardening structure formation for binding systems containing cements with different mineralogical compositions, synthesized in laboratory. The considered superplasticizer additive was CHRYSO Fluid Premia 180 type, used as a solution, containing the active substance in the proportion of 21.5 % ± 1.0%.Their dosage was in proportion of 0.3 % and 0.9%, related to the cement (these values were chosen based on literature data).
The influence of this additive on cements hydration processes was investigated by X-ray diffraction analysis on the binding pastes, after hardening till 28 days.
Information regarding the influence of the polycarboxylate additive on the binding properties were assessed by mechanical strength measurements on micro samples prepared from plastic mortars without/with addition of 0.9 % superplasticizer, after hardening periods of time 2-28 days. The proportion of 0.9% superplasticizers was selected considering the results obtained on the cement pastes prepared from an ordinary Portland cement CEM I 52.5 R with the same superplasticizer additive, varying the proportion between 0.3% and 1.3%.
metakaolin, pozzolana, mortar, concrete
GORDANA TOPLIČIĆ-ĆURČIĆ , ZORAN GRDIĆ, NENAD RISTIĆ, IVA DESPOTOVIĆ, DRAGAN ĐORĐEVIĆ, MILOŠ ĐORĐEVIĆ
Permeability of concrete to water depends on a number of factors. The actual micro-structure of cement paste, and consequently also the number and size of pores in the paste have a major impact on it. Aggregate type used in concrete making also affects the depth of pressurized water penetration into the concrete. The influence of various types of crushed mineral aggregates (basalt, limestone, diabase and andesite) on the concrete pressurized water absorption in comparison to the benchmark concrete produced with river aggregate was studied. The porosity of hardened concrete cement matrix has been examined by the Krüss optical stereo-zoom microscope and adequate software. The share of the pores smaller than ≤1μm in the hardened cement paste decreases with the increase of water-cement factor. On the other hand, the share of the pores larger than ≥10μm increases with the increase of water/cement factor.
hardened cement structure, concrete, porosity, optical microscopy, aggregates
ANJA TERZIĆ , LJUBICA PAVLOVIĆ, ZAGORKA RADOJEVIĆ, LJILJANA MILIČIĆ
Concrete undergoing thermal treatment before and during life-service can be applied as building material for thermal insulation in high-temperature plants. When such concretes are designed with secondary raw materials they show satisfying performances. Sintering and microstructural changes occur within concrete with increasing temperature. Change progression can be monitored by measuring compressive strength and porosity with destructive and non-destructive tests (ultrasonic pulse velocity technique, image analysis). Experiment has been performed on standard, corundum concrete and recycled, bauxite concrete. Samples were thermally treated from 110 to 1500ºC. Destructive tests were used in compressive strength and porosity investigation. Non-destructive tests were performed in order to compare results. Creep testing was conducted to prove sintering process. Results showed that recycled concrete has equal properties as standard concrete.
ultrasonic pulse velocity, sintering, high-temperature concrete, image analysis, recycling
ANA MARIA MONCEA, MARIA GEORGESCU, ALINA BĂDĂNOIU, ECATERINA MATEI
Portland cement and derived blended cements, represent binding matrices adequate for the immobilization of hazardous waste. The high pH of the intergranular pore solution in the cement stone along with the presence of calcium silicates hydrates with high specific surface area, as main hydrates, are key elements in the immobilization capacity of noxious elements in these matrices. Portland clinker free binding systems such as alkali activated slag have also a good immobilization capacity of toxic elements such as heavy metals.
The present study brings information regarding the immobilization of a glass waste with high Pb content (> 15%), derived from cathode ray tube glass (CRT) recycling, in three types of matrices: ordinary Portland cement (CEM I), slag cement (CEM III A) and alkali – activated slag binder. All binders showed a good immobilization capacity of the Pb waste (over 99%).
The mechanical strengths developed by the ordinary Portland cement were not adversely affected by the presence of CRT waste (dosed in amounts corresponding to 0.18-10% Pb content).
The compressive strength recorded for the slag cement with a high amount of waste (corresponding to 10% Pb) decreased with 25% and for alkali activated slag with 15% (with reference to the binder without waste).
Portland cement, alkali – activated slag, waste, Pb immobilization, compressive strengths
C.Y.HEAH, H.KAMARUDIN, A.M.MUSTAFA AL BAKRI, M.BNHUSSAIN, M.LUQMAN, I.KHAIRUL NIZAR, Y.M.LIEW
Alkali concentration is the most significant factor in geopolymerization process that must be taken into consideration during the synthesis of kaolin geopolymers. The kaolin geopolymers were prepared by mixing kaolin and alkali activator solution. The alkali activator solution used was mixture of sodium hydroxide (NaOH) and sodium silicate (Na2SiO3). This study aims to analyze the effect of NaOH concentration (6-14M) on mechanical properties of kaolin geopolymers. Compressive strength results showed that the optimum NaOH concentration is 8M. SEM, XRD and FTIR analysis were performed to study the transformation taken place during the geopolymer synthesis.
kaolin, geopolymers, alkali concentration, mechanical properties
DANIELA AURELIA PÎRVU, BOGDAN MIHAI GĂLBINAŞU, ION PĂTRAŞCU, CRISTINA FLORENTINA PÎRVU, DAN NIŢOI
Self- adhesive cements are the lmost recent class of cements based on resin composites designed to secure the prosthetic restorations to dental tissues. Comparatively to classic cements based on resins, they are more attractive to dentists because there is no requirement for a preconditioning of the substrates. Nevertheless, their adhesive performance has been less evaluated.
The purpose of this study is to evaluate and compare the shear bond strength of the three resin self- adhesive cements: MaxcemElite (Kerr)- ME, Biscem (Bisco)- BC, Rely XU100 (3MEspe)- RU and a classic version of resin cement - Variolink II ( Ivoclar)- VL to ceramic substrates: glass matrix and zirconia.
The results evaluated by one-way ANOVA test indicated no statistically significant differences among the four cements in terms of adhesion to glass ceramics – the means of the values were: 14.33 MPa (SD+4.16)- ME, 17.55 MPa (SD+6.45)- BC, 21.45 MPa (SD+5.46)- RU and 21.40 MPa (SD+4.38)- VL. There are differences among the means of the values of the four groups analyzed (probability p <0.0001), the adhesion to zirconia: 4.9 MPa (SD+0.61)- ME, 10.84 MPa (SD+0.25)- BC, 8.2 MPa (SD+0.24)- RU and 15.65 MPa (SD+1.07)- VL.
composite cements, glass ceramics, zirconia, shear bond strenght
Cement industry has to prepare its future in the context of European Union’s stringent need for a long term vision. If the vision is missing, serious consequences may occur, as for example, the European Commission’s failure in reaching a consensus with countries as Brazil, China, India, USA and many others, regarding reduction of global warming carbon emissions.
Major challenges which Cement industry from Europe must meet on future are mainly refer to:
Climate changes, that includes CO2 allocation for the period 2013-2020, revision of list for vulnerable sectors at carbon leakage, roadmap for a low carbon economy by 2050, tax of CO2 for energetic products, adaptation at climate changes, etc.
Energy Efficiency Directive
Implementation of Industrial Emissions Directive and of BATs (Best Available Technics)
Implementation of Agreement regarding crystalline silica
Sources efficiency and the access at raw materials and durable using of resources
Biodiversity and Nature 2000
Waste Framework Directive and also wastes management from constructions and demolishes
REACH and CLP (classification, labeling and packing)
Revision of the Directive SEVESO II
Implementation of Regulation for construction products
Revision of cement and concretes standard
Environment Product Declaration
Gamma radiations from building materials
cement, durability, environment, concrete
ECATERINA ANDRONESCU, DORU VLADIMIR PUŞCAŞU
This paper aims at providing more recent information concerning dioxins and furans emissions in cement plants. The evaluated results were obtained from thousands of monitoring tests carried out worldwide and in Romania, after 2006. The measurements cover most of the production technologies and a great variety of waste based alternative fuels.
Due to the conditions inherent to clinker production: high temperatures, approx. 2000 °C for gases and long residence times of flue gases in the kiln (about 10 seconds at temperatures higher than 1100 – 1200 °C and 5 – 6 second at temperatures over 1800°C), the release of dioxins and furans from clinker kilns is very low, no matter the fuels, even when alternative fuels based on hazardous waste are used.
As a result of the existing conditions, a DRE (destruction and removal factor) of 99.9999% can be reached in the clinker kilns for POPs (Persistent Organic Pollutants), like dioxins and furans. The measurements carried out worldwide and in Romania confirm the very low level of dioxin and furan emissions of clinker kilns.
dioxins, furans, alternative fuels
DOREL RADU, ANDREEA DAVID
Considering that cement industry is more often and more serious confronted with crises of fossil fuels, therefore with the necessity of reducing specific heat consumptions, the use of alternative fuels may be an efficient solution.
Although in the past few years the research in this domain has increased, at present there is little information regarding how the use of alternative fuels may influence the values of the main thermo-technological indicators of combustion process and rotary kilns: temperature and enthalpy of hot gases, absolute productivity and specific heat consumption.
This paper aims to present some data regarding the influence of partial/total substitution of a reference fuel with an alternative one on specific heat consumption of rotary kilns.
alternative fuels, oxygen enriched air, enthalpy of hot gases, specific heat consumption
ZHITAO CHEN, YINGZI YANG, YAN YAO, YANGCAN WU
Quasi-static compressive strength and dynamic impact compressive response of PVA fiber reinforced cement-based composite (PVA-FRCC) with different water binder ratio were studied. The quasi-static compressive strength decreased with increasing water binder ratio. The split Hopkinson pressure bar (SHPB) was used to obtain the dynamic impact compressive response of PVA-FRCC. The results showed that the stress-strain relationship of PVA-FRCC with different water binder ratio performed obvious strain rate effect. The deformation capacity of PVA-FRCC under dynamic load was improved with the increase of water binder ratio. The energy absorption capacity also performed rate dependency; as water binder ratio increase, the energy absorption capacity of PVA-FRCC was weakened.
water binder ratio; PVA-FRCC; dynamic mechanical properties; SHPB
INÉS GARCÍA-LODEIRO, OLGA MALTSEVA, ÁNGEL PALOMO, ANA FERNÁNDEZ-JIMÉNEZ
Concerns around the CO2 emitted in Portland cement manufacture have driven the scientific community to seek alternative materials with the same features as Portland cement but which can be sustainably manufactured. One such category of materials includes the blended or hybrid cements.
These cements form when blends containing low proportions of cement and high proportions (60-70 %) of mineral additions (slag, fly ash or metakaolin) are alkali activated. This article reviews the fundamental chemistry governing these new reactive systems. It also analyses the nature of the reaction products formed and their compatibility under different reaction conditions.
hybrid cement, alkaline activation, N-A-S-H gel, geopolymer
The harmonization of Romanian regulations with the European ones has led to significant changes regarding the rules for concrete production, for design and execution of the elements and structures. The enforcement, in Romania staring with 2002 year of the European standards continuing to require significant changes regarding minimum strength classes and concrete works’ execution conditions.
The national infrastructure development program has become a priority in Romania. This aspect together with the additional strength and durability requirements make it necessary to use specialized high-strength cements.
The article shows the main features of cement CEM I 52,5R as well as the results of some studies carried out on concrete prepared with this type of cement.
performance, specialized, resistance, durability, concrete
ANDREEA MONCEA, MARIA GEORGESCU
Considering some previous data concerning binding properties of silicate–aluminate–sulfate composites, the present paper brings complementary data regarding the influence of environmental factors (temperature, humidity), on the behavior of such kind of binders. Composite materials based on ternary binders with Portland cement, high aluminate cement and calcium sulfate (as hemihydrates or anhydrite III) content were investigated.
For selected compositions, taking into account their good binding properties in normal conditions, the influence of high temperatures and freezing–thawing effects on the mechanical strengths of such binders were investigated.
X–ray diffraction and thermal analysis were carried out for deeper research of involved processes in this complex masses behavior.
High aluminate cement, Portland cement, thermal properties, ternary binders
CARMEN MUNTEANU, MARIA GEORGESCU, ANDREEA MONCEA
The paper provides information regarding the influence of fly ash additions - alone or associated with a polycarboxylate type superplasticizer – on the main physical and mechanical properties of pastes and mortars containing Portland cement CEM I 52.5 R.
Fly-ash, from Govora plant, was used as addition in blended cements, in quantities of 10% up to 50%. The superplasticizer was of polycarboxylate type - CHRYSO Fluid Premia 180 (solution containing 21.5±1.0% active substance). The superplasticizer was dosed at a ratio of 0.9% (with reference to cement).
Information of the influence of the fly ash addition, associated with superplasticizer, on the physical properties of cement pastes were obtained by the assesment of water for normal consistency and setting time. The hardening processes of cement mixed with different amounts of fly ash associated with polycarboxylate type superplasticizer, were evaluated by the assessment of mechanical strength, on the mortar specimens with binder/sand = 1/3 and water to binder ratios in order to ensure a similar workability for mortars without and with superplasticizer.
The increase of fly-ash addition determines a continous increase of water for standard consistency (32.2%-37.6%). Polycarboxylate superplasticizer addition (0.9%) significantly reduced the values of the water for standard consistency, at levels between 22% and 28%, for cement containing 10 - 50% fly ash. The increase of fly ash amount increases the setting time, but for the pastes with 0.9% polycarboxylate additive this retarding effect is dimished.
Mechanical strengths of the mortars based on cements with fly ash decreased, while the content of fly ash increased. The decrease of mechanical strengths was less important for the cements containing fly ash and 0.9% polycarboxylate superplasticizer, in correlation with the smaller water/binder ratio. Thus, for the binder with 30% fly ash and 0.9% superplasticizer, the compressive strengths were higher as compared with the ordinary Portland cement.
fly ash, polycarboxilate superplasticizer, physical and mechanical properties
ANA MARIA MONCEA, MARIA GEORGESCU, ALINA MELINESCU, ŞTEFANIA STOLERIU, ANDREEA MONCEA
Beside traditionali binders – Portland cement and blended cements, the binders of type alkali activated slag (AAS) and geopolymer can represent efficient matrices for immobilization of noxious substances.
The present paper brings informations regarding the phisical and chemical processes at the hardening of alkali-activated slag and geopolymer, in which a waste with Pb content was immobilised. Geopolymer binder was prepared using a fly ash and as activator – a mixture of Na2O.nSiO2 and NaOH with silica modulus of 1.12. Alkali activated slag binders,were prepared with the same alkali-activator.
This type of binders have a good immobilization capacity of the glass waste resulted from discarded cathode ray tube (CRT) with Pb content, added in amounts corresponding to 0.18-10% Pb. The inclusion of Pb2+ ions into the binding systems determines a certain retarding influence on the hardening processes, the effect being more intense for shorter periods of hardening and for higher amounts of Pb. The X-ray difraction data sugests the formation of a complex aluminosilicate with Pb content.
Alkali-activated slag, geopolymer, CRT waste, reaction products, hardening processes
CORNELIU BOB, TAMAS DENCSAK, CRISTIAN TANASIE, IONEL BALCU
Concrete is the most frequently used man-made construction material. Although it is considered non-ecological due to the great amount of CO2 emissions at cement production, concrete can reabsorb a part of the released CO2.
This paper encompasses theoretical work and laboratory determinations regarding the ability of concrete to absorb atmospheric CO2 by carbonation. The presentation contains an original model for the calculation of carbonation depth, followed by a short overview of existing studies in the field of CO2 uptake. The second part of the paper unveils an experimental program that uses an original and unconventional procedure that is also combined with traditional methods. The main aims are to determine the CO2 uptake using a direct procedure and to obtain an adequate coefficient for the carbonation capacity of the initial calcium oxide with a tribute to the existing theoretical considerations. The experimental results were in good correlation with the theoretical models and an appropriate coefficient has been obtained.
concrete, carbonation, CO2 uptake, drying, X-ray method
GUANGBIN QU, AILIAN ZHANG
Cement mortar prisms were made with three different cementitious materials (with or without mineral admixture) plus 30% mass of limestone filler. After 28 days of curing in water at room temperature, these samples were submerged in 2% magnesium sulfate solution at different temperatures (50C, 200C and alternate temperature between 5℃ and 20℃) for a year. The strength development was measured on these immersed prisms at intervals, and samples selected from the surface of prisms were examined by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The results show that the influence of temperature on the resistance to sulfate attack of mortar is related to the binder compositions. A higher temperature leads to a quicker strength loss of the mortar without mineral admixture. For blended cements, a higher temperature is favorable for the pozzolanic reaction of mineral admixture and the overall deterioration of mortar is reduced. After 1 year of exposure to magnesium sulfate solutions, the formation of thaumasite was checked in the OPC mortars at both 5℃ and 20℃. It is concluded that the thaumasite formation is not limited to structures at low temperature (less than 15℃).
cement, mineral admixture, sulfate attack, temperature, thaumasite
GABRIEL OPRIŞAN, NICOLAE ŢĂRANU, MIHAI BUDESCU, IOANA ENTUC
Fibre reinforced polymer (FRP) composites are currently successfully implemented to strengthening of reinforced concrete (RC) beams improving their structural response to frequent loading conditions. The most utilized techniques are based on prefabricated composite plates bonded to the tension side with adhesives or by bonding quasi-unidirectional fabrics made of carbon fibre reinforced polymer (CFRP) composites or glass fibres fabrics impregnated with polymeric resins.
An experimental program has been carried out at The Faculty of Civil Engineering and Building Services Iaşi, to verify a number of strengthening solutions and reveal the working conditions, failure types and the structural efficiency of the proposed systems. The structural response has been evaluated through testing the RC beams under four points loading scheme. The difference in structural behaviour of unstrengthened and strengthened beams has been revealed on both loading bearing capacity and stiffness. The experimental results have been compared to those obtained by numerical modeling.
plate bonding, failure modes, carbon fibres, numerical modeling, structural response
LU SHUANG, WANG ZHENG
On-site corrosion sensor was developed to monitor the adverse effects in the chloride – contaminated concrete structures. Galvano-static Pulse Technique(GPT) was applied to measure the polarization resistance of the anodes and the electrical resistance of the surrounded concrete using the sensor. This paper presents the analysis of GPT measurements performed in the chloride-contaminated concrete for the laboratory tests. The relationship between the corrosion rate of steel electrodes and surrounded concrete resistance measured by corrosion sensor confirms the reliability of developed corrosion sensor. The results further show that the concrete resistance is also an indicative parameter which is related to the corrosion state of concrete structures.
corrosion monitoring, concrete structures, GPT, polarization resistance