română ALINA BĂDĂNOIU, ELENA IORDACHE, RUXANDRA IONESCU, GEORGETA VOICU, ECATERINA MATEI
Abstract
In this study was assessed the possibility of geopolymers synthesis by alkaline activation of cathode ray tube (CRT) glass waste with/without fly ash addition. The nature of solid component and alkali activator (sodium or potassium hydroxide solution) combined with the curing conditions (initial curing at 60oC for different times – 1 up to 7 days) exert an important influence on the fresh mortars workability, microstructure and consequently on mechanical properties. The higher values of the compressive strength were obtained for geopolymers based on CRT glass waste activated with KOH solution cured the first 4 days at 60oC. The substitution of CRT glass waste with fly ash decreases the workability of fresh mortars and consequently the compressive strength values. The durability of this type of geopolymer is affected by water conservation but the substitution of CRT glass waste with 25% fly ash improves to a certain extent this property.
Keywords
Geopolymer, Cathode ray tube glass waste, Fly ash, Properties, Water stability
P.VALDEZ, G. FAJARDO, C.A. JUAREZ, A.DURAN-HERRERA, J.A.DEL REAL
Abstract
Mixtures were designed to produce hollow masonry units (blocks) conform to Mexican specification; these blocks were subjected to a 60°C temperature a 90% relative humidity steam curing in an atmosphere of 20% CO2 concentration. Thermo-gravimetric methods were used to evaluate the water vapor effect and carbonation in replicate pastes of the concrete blocks to determine portlandite, carbonates and CO2 concentration in the block. Results illustrate that the application of CO2 curing in activated fly ash-Portland cement masonry units can lead to 30% savings in cement consumption, to an average CO2 fixation of 7% without modification of the compressive strength.
Keywords
D. Concrete, B. Thermal analysis, D. Pozzolans, D. Lime, D. Portland cements
ADRIANA MOANŢĂ, VIOREL FUGARU, ROXANA TRUŞCĂ, MARIA GHEORGHE, MARIANA COARNĂ, IONELA PETRE
Abstract
The paper presents the results of laboratory researches regarding the possibility of using, as addition in the raw mix for cement of barite – alternative raw material with high specific weight. The raw mixes with barite constitute the base for prepare of the clinkers designated to obtaining the cements with capacity of attenuation of gamma radiations. Technological behavior of the raw mixes with addition of barite was investigated in comparison with those of a raw mix obtained from current raw materials, considered as reference sample.
It was investigated the influence of barite on clinkers characteristics, from chemical, mineralogical and structural point of view, using X-ray diffraction, scanning electron microscopy (SEM analyses) .
From obtained clinkers, cements type CEM I in accordance with SR EN 197-1were performed. These cements were characterized both regarding to usual physical-mechanical properties and of the capacity for attenuation of gamma radiations. In order to evaluate the capacity of gamma radiations attenuation it was determined the dose rate equivalent for different radioactive source (Ir-192, Cs-137, Co-60). The presence of barite, in raw mixes composition for the clinkers, determined the increase of the value for linear coefficient of attenuation and an increased capacity of gamma radiations attenuation, respectively.
Keywords
Clinker, Barite, Cement, Linear coefficient of attenuation
LIU HUI, WANG BAOMIN, HAN YU, QU JUN, GUO ZHIQIANG
Abstract
The influence of multi-walled carbon nanotubes (MWCNTs) mixed with silica fume (SF) on the mechanical property of cement-based composites was investigated. Results indicate that SF particles have a favorable dispersion effect on MWCNTs and MWCNTs can be dispersed uniformly in cement matrix when mixed with SF particles. MWCNTs mixed with SF can decrease the sample porosity and the amount of harmful pores and delay the formation process of micro cracks in the cement paste, improving the strength of specimens effectively. The compressive strength of the sample filled with 10% SF reaches maximum when the MWCNT addition is 0.15% and the flexural strength of the sample filled with 0.08% MWCNTs and 10% SF reaches maximum, the increase percent of flexural strength and compressive strength is both above 35%, displaying well reinforcement effect of MWCNTs mixed with SF particles on the mechanical properties of cement-based composites.
Keywords
Multi-walled carbon nanotubes; Silica fume; Cement-based composites; Mechanical properties
MARIA STEFANIDOU, VASILIKI PACHTA
Abstract
Coatings, such as plasters and renders have been continuously used for dwellings’ protection even from the Neolithic period. Diachronically, they present similar technological characteristics forming unwritten normes of manufacture. This paper focuses on the analysis and characterization of coatings from four monuments of Greece, dated through the 4th C BC. The physico-mechanical and chemical properties of samples were determined, leading to the characterization of their consistency and structure. Their stratigraphy showed that they consisted of two to four well compacted layers, the width of which decreased from the inner to the surface layer. The main binding system used was hydrated lime in combination with natural pozzolan, while the aggregates gradation as well the binder/aggregates ratio varied according to the coating’s stratigraphy.
Based on the results, it can be concluded that even from the 4th C BC the functional role of renders and plasters was clear and their technology definite. A carefully selected binding system was used, while additional parameters were taken into account in order to achieve the optimum performance and efficasy of the final material.
Keywords
Historic mortars, Renders, Plasters, Masonry, Stratigraphy, Technology
MIHAI BUDESCU, PETRU MIHAI, NICOLAE ŢĂRANU, IRINA LUNGU, OANA-MIHAELA BANU, IONUŢ-OVIDIU TOMA
Abstract
The paper presents a study on the concrete compression behaviour in the post-peak range, utilising an innovative system, conceived and patented at the Faculty of Civil Engineering and Building Services from Iasi. The designed mechanical system is attached to the universal testing machine and controls the deformation rate after reaching the peak stress. The theoretical bases related to this additional system are presented, along with its design and utilisation to the concrete testing aiming to determine the complete characteristic curve. The paper is finalised with a presentation of an extended experimental study related to the complete characteristic curve, determined by testing a series of concrete cylindrical specimens. A particular value of the stress relevant to the evaluation of the energy dissipation capacity is finally recommended.
Keywords
loading rate, specimen stiffness, displacement control, post-peak range
DAN GEORGESCU, RADU PASCU, RADU GAVRILESCU, TIBERIU PASCU
Abstract
The shrinkage deformations may lead to concrete cracking with adverse effects on structural reliability, durability and aspect of the reinforced concrete elements and structures. For preventing and mitigation of shrinkage effects measures must be taken in structural design in determining the composition and in concreting. The paper presents theoretical, practical and experimental aspects related to shrinkage strains calculation, pointing out the differences between the values computed using the provisions of SR EN 1992-1-1 -„Design of concrete structures” and measured values. Due to these differences we consider that a new approach for computing the shrinkage deformations is needed. This need is emphasized by the large number of cases in our country of cracked structural elements short time after the concrete was cast.
Keywords
Concrete, Shrinkage, Test methods
N.R. RAKHIMOVA
Abstract
The effects of ground used sand (GUS), ground fly ash (GFA) (class F), and microsilica (MS) on water requirement, setting time, and compressive and bending strength development of alkali-activated slag-blended cements (AASBC) were studied. Siliceous blending materials were found to be able to replace up to 50% of ground granulated blast furnace slag (GGBFS) and contributed to up to 90% improvement of strength of AASBCs, The granulation for GUS, granulation, curing conditions, and basicity of GGBFS for GFA, and curing conditions for MS have effects on the development of the properties of the AASBCs.
Keywords
Blast furnace slag, alkalis, activators, binding composite materials, setting time, mechanical properties
M.P.PEREIRA, J.B. AGUIAR, A. CAMÕES, P.LOURENÇO
Abstract
This study deals with the characterization of masonry mortars produced with different binders and sands. Several properties of the mortars were determined, like consistence, compressive and flexural strengths, shrinkage and fracture energy. By varying the type of binder (Portland cement, hydrated lime and hydraulic lime) and the type of sand (natural or artificial), it was possible to draw some conclusions about the influence of the composition on mortars properties. The results showed that the use of Portland cement makes the achievement of high strength classes easier. This was due to the slower hardening of lime compared with cement. The results of fracture energy tests showed much higher values for artificial sand mortars when compared with natural sand ones. This is due to the higher roughness of artificial sand particles which provided better adhesion between sand and binder.
Keywords
Masonry, composition, D.a. mortar, D.a. Portland cement, D.a. lime, D.d. sandstone
HAKAN BOLAT, OSMAN ŞIMŞEK
Abstract
This study aims to determine the energy absorption of concrete slabs (60×60×10cm) using polyester, polypropylene and steel fiber reinforced (SFRC, PYFRC, PPFRC) according to EN 14488-5. Significant differences in the energy absorption were observed between the concrete slabs strengthened with different fibers. The highest gain in energy absorption was observed in SFRC. Furthermore, concrete slabs strengthened with PPFRC and PYFRC showed 23.4% and 14.8% less energy to SFRC. Although the SFRC showed the highest energy absorption under directly negative conditions, it is important to evaluate the durability issues associated with SFRC, such negative conditions.
Keywords
Fiber reinforced concrete, steel fiber, synthetic fiber, energy absorption, slab test
CARMEN (GHEORGHE) OPROIU, GEORGETA VOICU
Abstract
The use of alternative fuels in the manufacturing of cement can influence the thermo-chemical processes in the kiln as well as the quality of the obtained clinker. Also, the use of alternative fuels has impact both from economic and environmental point of views.
In the present study are assessed the composition and microstructure of clinkers manufactured with conventional fuel i.e. coal-coke mixture, and alternative fuels - solid residual (SRF). The substitution rate of conventional combustible was 30%.
No significant differences were identify, in terms of composition (oxide and mineralogical) and microstructure for clinkers obtained using alternative (SRF) and conventional (coal-coke mixture) fuels.
Keywords
solid residual fuels (SRF), clinker quality,composition and microstructure, Riedveld method, scanning electron microscopy
Effect of alkaline activator on the main properties of geopolymers based on cullet glass and red mud
TAHA H. ABOOD AL-SAADI, ALINA BĂDĂNOIU, ŞTEFANIA STOLERIU, GEORGETA VOICU
Abstract
In this paper are presented results regarding the synthesis and properties of geopolymers based on glass powder, with/without red mud (solid part), activated with the solution resulted in the filtration process of red mud slurry (RF). The compressive strengths achieved by these materials are below 20 MPa, smaller as compared with those assessed on the geopolymers based on the same solid components but activated with NaOH 5M solution (up to 40MPa); these results can be explained by the lower alkalinity of RF. Nevertheless, for the materials activated with RF, the substitution of glass powder with 25% red mud powder (resulted by the drying of solid part separated from red mud slurry - R), determines an increase of compressive strength values - 15-100% with reference to the one assessed on the geopolymer based only on glass powder. This increase can be explained by the ability of red mud powder (R) to continuously release alkaline ions in RF solution.
Keywords
geopolymer, cullet glass, red mud, compressive strength, microstructure, hydrolytic stability
CONSTANTIN DORINEL VOINIŢCHI, RADU CONSTANTIN VOINIŢCHI
Abstract
This paper presents experimental work made in order to asses the influence of correction coefficients considered by a Romanian norm proposal for evaluating in situ compressive strength of concrete. It has been evaluated coefficients linked by influence of degraded end layer, the influence of nature of capping layer, cores humidity and presence of the reinforcement bars in the tested cores. Results show the luck of influence or contrary influences to that considered in Romanian norm proposal, generally in accordance with europen and american standards.
Keywords
concrete testing, in situ compressive strength, cores
KESTUTIS BALTAKYS, ANATOLIJUS EISINAS, JOLANTA DONELIENE, DEIMANTE MONSTVILAITE, AGNE BANKAUSKAITE, AURIMAS URBUTIS
Abstract
In this work the influence of Al2O3 on the formation of calcium aluminium silicate hydrates under hydrothermal conditions and the effect of this additive on the early hydration of Ordinary Portland cement (OPC) were investigated. The primary mixtures with molar ratios CaO/(SiO2+Al2O3) of 0.55 and Al2O3/(SiO2+Al2O3) of 0.05, 0.1 and 0.15 were mixed with water to obtain the water/solid ratio of the suspension equal to 10.0. Meanwhile, the hydrothermal synthesis of C-A-S-H has been carried out in air atmosphere at 130 °C temperature for 4–72 hours. It was determined that not only the amount of Al2O3 additive, but also the duration of hydrothermal synthesis strongly affect the formation of mentioned compounds. The largest amount of calcium aluminium silicate hydrates was obtained after 8 h of hydrothermal treatment, in the mixtures with a higher amount of Al2O3 (A/(S+A) = 0.15). Meanwhile, the formation of mentioned compounds is inhibited, when the duration of isothermal curing is extended from 16 to 72 h. It was determined that calcium aluminium silicate hydrates affect the early hydration of OPC. These compounds effectively shorten the induction period and accelerate the dissolution of C3S, C3A and the formation of ettringite.
Keywords
Calcium aluminium silicate hydrates, Hydrothermal synthesis, Portland cement hydration, Additives
SANJEEV KUMAR VERMA, SUDHIR SINGH BBHADAURIA, SALEEM AKHTAR
Abstract
In the last few decades, failure of concrete structures awakened researchers to focus on durability influencing parameters along with compressive strength. Factors like environmental or exposure conditions are found to be governing the service life of reinforced concrete (RC) structures significantly. One of the major processes influencing condition of steel bars is carbonation of concrete surrounding steel bars in RC structures. Hence, considerable researches on the carbonation of concrete in laboratory and field are carried out around the world. Present article reviewed several previous carbonation studies conducted by researchers and by utilizing the results of a field survey determines coefficient of carbonation ‘K’ for concrete structures located in the City of Bhopal, India and for other semitropical regions.
Keywords
concrete, carbonation, model, reinforcement, corrosion
XIAOJIAN GAO, HUI WANG, SHUANGXIN LI, LIANG LU, YILUNG MO
Abstract
The addition of well-dispersed carbon nanofiber (CNF) can improve the mechanical and electrical property of concrete and the produced concrete (CNFC) shows a good piezoresistive effect, which is very useful for structural health monitoring. In order to confirm the feasibility of long-term application in real structures, the piezoresistive effects of CNFC samples were measured before and after different environment exposure test including freezing and thawing cycles, chloride penetration and drying under different relative humidity conditions. The results show that the electrical property of CNFC did not change obviously after 200 cycles of freezing and thawing, the resistivity of CNFC was increased by the addition of chloride during the mixing process possibly due to the accelerated cement hydration, and the resistivity of CNFC was increased and the polarization time was decreased with the decreasing relative humidity of exposure surroundings. However, the same or similar piezoresistive effects were found for all the concrete samples before and after different exposure treatment. Therefore, it is suggested that such CNFC can be used for the long-term monitoring of real structures.
Keywords
carbon nanofiber, piezoresistive effect, structural health monitoring, different environment exposure
ZINA VULUGA, JENICA PACEAGIU , MICHAELA IORGA, MARIANA COARNĂ
Abstract
In the present work, polypropylene (PP) based composites filled with natural aluminosilicate materials were prepared. The volcanic tuff and kaolinite clay are used as filler in different proportions up to 15% by mass. PP composites filled with aluminosilicate materials were prepared using extrusion compounding and injection molding by dynamical melt processing.
The effects of filler content on the elasticity modulus and thermal conductivity of the composites were studied. Also, the morphology of the composites was evaluated by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS).
The results showed that the elasticity modulus of composites improved with increasing the filler content. A better behavior is noticed in case of volcanic tuff using.
Keywords
polypropylene, volcanic tuff, clay, elasticity modulus, thermal conductivity
DOREL RADU, ZENO GHIZDĂVEŢ
Abstract
A comprehensive characterization of the particle size of polygranular powders can be done by:
- selecting the parameters to be used in the design, optimization and process control of various technological processes;
- establishing correlations between the properties of the mixtures and their particle size features.
One of the parameters to characterize powder mixtures is the particle size uniformity degree. For its evaluation, this paper gives two new indicators calculated by some factors coming from information theory: Shannon entropy - H - and Onicescu’s informational energy – E. Particle size uniformity calculated by these indicators (that are applicable to any granular materials) controls the specific surface area of the powder mixtures.
As applications, a series of quantitative relationships between the specific surface area of some Portland cements and their particle size uniformity were extracted. The results are characterized by a very good correlation for both several foreign cements as well as a set of local cements.
Keywords
informational energy, informational entropy, degree of uniformity, cement specific surface
IONUŢ-OVIDIU TOMA, NICOLAE ŢĂRANU , OANA-MIHAELA BANU, MIHAI BUDESCU, PETRU MIHAI, RAREŞ-GEORGE ŢĂRAN
Abstract
The growing amount of waste rubber produced from used tires has resulted in an environmental problem needed to be addressed. The paper investigates the effect of fine aggregate replacement by waste tyre rubber crumbs on the mechanical properties of concrete at different curing ages. The aim is to assess the suitability of the newly obtained material to load bearing elements in civil engineering.
The results presented in the paper are part of a larger research project related to the innovative use of all tyre components in concrete. The percentages considered were 40%, 60% and 80% by volume of fine aggregate. The general trend is a decreasing one in terms of mechanical properties. Even in such cases, the obtained values are above the minimum requirements, prescribed by norms, in terms of strength for some structural elements. The complete stress-strain curves determined at the age of 28 days show a softer descending trend for rubberized concrete compared to the reference mix. The embedded strain energy is larger in the post-peak region.
Keywords
rubberized concrete, modulus of elasticity, compressive strength, complete stress-strain curve
CARLOS CALADO , AIRES CAMÕES, TIBÉRIO ANDRADE, JOÃO RIBEIRO, BÉDA BARKOKÉBAS
Abstract
This study addressed the application, strength and durability of self-compacting concrete (SCC) in a large-scale construction site, comparing its performance with vibrated conventional concrete (CC) with similar characteristics, assessing its economic feasibility.
The studies were undertaken in the Arena Pernambuco project and involved the concreting during May, June and July 2012, for data collection, accompanying the routine concrete control tests and performing specific strength and durability tests.
The SCC compressive strength was on average 4% higher than the CC one, and its formwork reinforced to withstand greater lateral pressure of the fresh concrete. The durability indicators results were in favour of SCC, which cost was 13% higher than CC.
Keywords
self-compacting concrete (SCC), durability and applicability on a jobsite
SANJEEV KUMAR VERMA , SUDHIR SINGH BHADAURIA, SALEEM AKHTAR
Abstract
Premature deterioration and failure of reinforced structures in last 4 -5 decades deviated focus of researchers from compressive strength to durability and service life of structures. Several structures constructed before invention of modern cement and other advanced building materials are in service condition, whereas new structures were deteriorating faster than those old structures. Therefore, determination of remaining service life of concrete structures is significant. This article presents a service life model suitable for semitropical regions of India, developed using MATLAB for estimating residual service life of deteriorating structures and for predicting corrosion initiation time for new structures.
Keywords
concrete, carbonation, model, reinforcement, corrosion, deterioration, service life