română NASTASIA SACA , MARIA GEORGESCU
Abstract
The behaviour of the blended cements, containing limestone filler in corrosive environments is an important aspect for assesing the durability of concrete prepared with such cements having a diminished „clinker factor”. Such cements are of great interest from economic and environmental point of view. The present paper provides information regarding the behaviour of blended cements, with 10-40% limestone filler (Blaine specific surface area of 4600 cm2/g and 7000 cm2/g respectively), immersed into 5% MgSO4 solution, from 28 to 580 days.
X-ray diffraction (XRD) and scanning electron microscopy (SEM+EDAX) data allow the formulation of some possible interactions that occur between the binding matrix and sulphate solution. As a result of such reactions some hydrates as gypsum, ettringite, brucite are formed. Corrosive processes are carried out progressively from the surface towards the inside of the samples, which involve compositional and structural differences between the two areas. The corrosive effect of MgSO4 solution is highlighted by the decreasing in mechanical strength of the mortar samples for long period of exposure, up to 580 days.
The behavior of mortars in magnesium sulfate solution seems to be positively influenced by using finer limestone filler (Blaine specific surface area of 7000 cm2/g), due to a higher compactness for samples.
Keywords
limestone filler, sulfate corrosion, mechanical strength, X-ray diffraction, scanning electron microscopy SEM
MARIA GHEORGHE, NASTASIA SACA, LIDIA RADU, RACHILA IEREMIE
Abstract
This paper reports on the results of a research about utilization of inorganic sludge (IS) produced by paper industry as cement and fine sand substitute secondary raw material in concrete. The inorganic sludge IS valorization as cement partial substitute into concrete has been supported by experimental data concerning the pozzolanic potential evaluated by Al and Si content of IS waste compounds solubility into leachant of pH=12 and by the compressive strengths time evolution. The concrete samples with the addition of inorganic sludge from paper industry have been characterized by overtime variation of the following characteristics: water absorption, dimensional changes, compressive and flexural strengths. There have also been determined leaching properties by monolithic leaching test. The evolution of the physical and mechanical characteristics suggest the inorganic sludge can be used as a substitute for fine sand in concrete in an amount up 50%, and / or substitution of up to 20% cement. The heavy metal leaching properties measured by the concrete monolithic samples leaching test with the highest content of IS, showed a heavy metal Pb, Cr and Cu release trend diminishing during time, after a logarithmic plot.
Keywords
Inorganic sludge from paper industry, pozzolana, concrete, leaching, mechanical properties
MARIN AMĂREANU
Abstract
The investigations suggested by the objective of this work are focused on the calculation of the confinement pressure, for concrete structural elements with circular section, and of the effective lateral compression stress at the ultimate limit state (ULS) due to the confinement of these elements with carbon fiber fabric. The paper also refers to the execution and consolidation of concrete structural elements by confinement with carbon fiber fabric, so that following the concrete structural elements tests for obtaining the mechanical strength values, these would be comparable with the ones obtained from the calculation.
Keywords
confined concrete, mechanical strength, design calculation
WENZHONG ZHENG, BAIFU LUO, SHUANG LU
Abstract
This paper presents the effect of temperature on mechanical properties of reactive powder concrete (RPC) at elevated temperatures. The influences of temperatures, polypropylene (PP) fibre and steel fibre content, hold time, dimension of specimens and explosive spalling were investigated. The microstructure of RPC was identified by scanning electron microscope (SEM). The experimental results show that adding 2% steel fibres and 0.2% PP fibres can prevent explosive spalling and significantly increase compressive and tensile strengths of RPC. PP fibre and steel fibre content played an important role in failures modes, explosive spalling, compressive strength and tensile strength. Cube compressive strength decreases at 100°C, increases between 200 and 500°C, and decreases beyond 600°C. Tensile strength decreases at 200°C, increases from 200 to 300°C, and decreases beyond 300°C. Pores and small channels created are beneficial for mitigating the explosive spalling at elevated temperatures.
Keywords
elevated temperature, reactive powder concrete, mechanical properties, explosive spalling, hold time
KSENIJA JANKOVIC, ANDJELIJA ILIC, MARKO STOJANOVIC
Abstract
The investigation of posibilities of concrete structure modification by silica fume to improve concrete properties was presented in this report. Percentage of silica fume in regard to cement varied between 0% and 20%. Concrete was cured as follows: in water, steam – curing regime at +60oC and +90oC. The results of the compressive and tensile strength, freeze / thaw resistance with de-icing salts, and depth of penetration of water under pressure.
Keywords
silica fume, steam – curing regime, concrete durability
TIBERIU PASCU, DAN GEORGESCU
Abstract
Determination of performance of materials for repairing of concrete must be based on experimental research. It should, on the one hand, individual testing of the properties of the various materials for repairing of concrete and, on the other hand, testing the properties of concrete repair systems, made up of individual materials previously tested, especially in the case of specific applications. This paper presents in particular the test methods and results of experimental researches carried out.
Keywords
concrete, repair systems, test methods
Formation of alpha-C2S hydrate in the mixtures with CaO/SiO2=1.75 by hydrothermal treatment at 2000C
KESTUTIS BALTAKYS, TADAS DAMBRAUSKAS, RAIMUNDAS SIAUCIUNAS, ANATOLIJUS EISNAS
Abstract
The parameters of α-C2SH hydrothermal synthesis from a non-stoichiometric composition of CaO and SiO2·nH2O mixtures (the molar ratio CaO/SiO2 = 1.75) in unstirred suspensions were determined and a sequence of intermediary compounds formation was examined and explained. It was evidenced that α-C2SH is formed already after 4 h of hydrothermal treatment at 2000C. However, together with this compound a fair amount of some intermediary compounds (C-S-H(I) and C-S-H(II)) are formed. It was determined that after 24 h of hydrothermal treatment, α-C2SH starts to recrystallized into kilchoanite which dominates in the products after extending the duration (48-72 h) of synthesis.
Keywords
α-C2S hydrate; calcium silicate hydrate (C-S-H); hydrothermal synthesis; kilchoanite
RADU CONSTANTIN VOINIŢCHI, VIOREL CRĂCIUN, CONSTANTIN DORINEL VOINIŢCHI, ALINA BĂDĂNOIU, GEORGETA VOICU
Abstract
In order to improve the properties of recycled aggregate resulted by the crushing of concrete from construction and demolition waste stream, a thermo-mechanical treatment was applied. This treatment, performed in a muffle furnace and a Los Angeles machine, simulates the conditions specific for a rotary kiln. Recycled concrete aggregate (RCA) was obtained by the crushing of a concrete C20/25 class. The crushed concrete aggregate (RCA), the one resulted after the thermo-mechanic treatment of RCA and the initial natural aggregate where compared from the point of view of physical properties (apparent and bulk densities). A good efficiency of thermo-mechanic treatment was appreciated based on these results.
New concretes were prepared using the recycled concrete aggregates (before and after thermo-mechanic treatment) in order to determine the density and compressive strength. Thus, the compressive strength values, determined on concrete prepared with recycled concrete aggregates subjected to thermo-mechanical treatment, are similar with those prepared with natural aggregate.
The thermo-mechanic process applied for the removal of cement paste/mortar adhered to natural aggregate grains is a possible solution for the improvement of recycled aggregates quality.
Keywords
recycled aggregate, thermo-mechanic treatment, concrete
ANJA TERZIĆ, LJUBIŠA ANDRIĆ, MILAN PETROV, ZAGORKA RADOJEVIĆ, LJILJANA MILIČIĆ
Abstract
Four types of refractory concretes were studied at various temperatures ranging from ambient to adopted maximal 1400°C. The concretes had same matrix composition: K concretes were based on corundum aggregate; B concretes were based on bauxite aggregate and chamotte filler; while K2 and B2 concretes had 30 % of fly ash replacement in bonding agent. Fly ash was mechanically activated by means of planetary ball mill. Samples were dried at 110°C during 24 hours to create standard specimens. Afterwards, the samples were preburned at 1100°C and subsequently subjected to compressive uniaxial creep test conducted at various temperatures (1200, 1300 and 1400°C). Thermal behavior was also investigated by dilatometry analysis starting from room temperature up to 1400°C. The evolution of the refractory concretes behavior from quasi-brittle to visco-plastic was investigated and correlated to their microstructure evolution induced by sintering process. The influence of the burning temperature and procedure duration on the concretes behavior is also discussed. Creep test and dilatometry analysis helped in defining of the sintering mechanism and its parameters, and additionally explained deformation nature of the refractory concretes.
Keywords
sintering, thermal treatment, composites, thermal properties, environment
ALEXANDRINA CUIBUŞ, ZOLTAN KISS, MARIA GOREA
Abstract
This study presents the physical-mechanical characteristics of the concretes (7 compositions) accomplished with 10% fly ash (FA), 10% metakaolin (MK), 10%FA+10%MK, 10% silica fume (SF), 10% SF+10%FA, 10%SF+10%MK additions by substitution of 10% respectively 20% cement. According to the analysis performed on the fresh concrete - density, slump, flow and entrapped air volume, this concrete is of normal volume mass concretes type. The compressive strengths of the concretes with additions of fly ash, silica fume and metakaolin to 28 days are closely to those of the reference concrete i.e. 55.01 MPa, or even higher. The flexural tensile strengths are higher after longer hardening periods of time, except the 10% FA + 10% MK concrete composition (S-4). The elasticity modulus, for all the studied compositions, has higher values than the minimum allowed value for C35/45 concrete class. The experimental studies showed that the reduction of the cement quantity in the concretes, without altering the properties, is possible by using of some industrial byproducts or wastes (fly ash or silica fume) and fired clay(metakaolin).
Keywords
concrete, fly ash, metakaolin, silica fume, pozzolan
BAO-MIN WANG, YUAN JIA, TING – TING ZHANG
Abstract
The ability to resist at chloride ion penetration and compressive strength of ocean high performance concrete (HPC) with nano-SiO2 (NS) addition was studied. The 6 hours direct current coulometry method (6-hours DC Method) in ASTM C1202-97 was adopted. The experimental results show that the ability to resist at chloride ion penetration of HPC including NS is heightened effectively, the charge through high-performance concrete with 3%, and 5% NS is reduced with 5% and 15% respectively, and the ability to resist at chloride ion penetration can be heightened gradually with of the age; the charge through high-performance concrete with NS decreases with reducing of W/B of concrete.
Keywords
nano-SiO2(NS), ocean engineering, high performance concrete(HPC), chloride ion penetration, compressive strength
NICOLAE ŢĂRANU, PAUL CIOBANU, SERGIU POPOAEI, PETRU MIHAI, MIHAI BUDESCU, VLAD LUPĂŞTEANU
Abstract
În această lucrare se analizează din punct de vedere teoretic, experimental şi prin modelare numerică, răspunsul structural al unor grinzi din beton armat consolidate cu fâşii înguste din compozite polimerice armate cu fibre din carbon (CPAFC), montate în zona din imediata apropiere a feţei întinse (NSM). Probele consolidate au fost testate la încovoiere sub încărcare monoton crescătoare până la cedare. Inserţia fâşiilor înguste din CPAFC a condus la o creştere semnificativă a capacităţii portante la încovoiere, de până la 220% şi la o reducere a deplasărilor transversale maxime de până la 49%, în comparaţie cu grinzile de control, neconsolidate. Validitatea rezultatelor experimentale a fost verificată analitic şi prin modelare numerică, utilizând programul pe bază de element finit ANSYS.
Keywords
reinforced concrete beams, carbon fibre reinforced polymer composites, strengthening with composite strips, structural response, numerical modeling
P.VALDEZ, R.X.MAGALLANES-RIVERA, A. DURÁN-HERRERA, C.A. JUÁREZ, G.FAJARDO
Abstract
Results of interrelated tests for physical-chemical and microstructural properties of four synthetic pozzolanas evaluating the hydration rate in blends with calcium hydroxide are presented. The pozzolanic activity of silica fume, classified fly ash, raw fly ash and commercial metakaolin was estimated. Results showed a clear relationship between the calcium hydroxide consumption and the reactive phase content, specific surface area and porosity of the pozzolans. The calcium hydroxide-silica fume blend consumed 98% of portlandite after 21 days, whereas the system with metakaolin also presented an effective pozzolanic activity with 94% depletion. The fly ashes were the less effective pozzolans of the study.
Keywords
D. Pozzolans; D. Mortar; C. Mechanical properties; B. X-ray methods; B. Porosity
ALIREZA FIROOZFAR, SEYED MAHDI SAJJADI, MOHD ZULKIFLI BIN MOHD YUNUS, SEYED AMIR HOSSEIN BEHESHTI, TAHA MEHMANNAVAZ
Abstract
Research on ways to increase the resistance of weak soils to build structures on it has been increased in recent years. The present article provide the effects of different mixtures containing microsilica, cement, polypropylene waste fiber and dune sand on mechanical parameters such as, compressibility, compressive strength, bending strength and durability characteristic. In this study also is investigated evaluation the effect of road subgrade based on proposed material. The used dune sand in this research was obtained from Kashan city where is located in central desert of Iran. The obtained results show that the microsilica and cement could play a major role in reducing the cost and required time for building roads and also building foundation on these types of soils.
Keywords
dune sand, fiber, cement, microsilica, stabilization
Y.A. SORVACHEVA, T.M. PETROVA, A.V. POLETAEV, E.Y. CHISTIAKOV
Abstract
Accelerated tests were conducted to evaluate the potential reactivity of one of the potentially dangerous aggregates from the point of view of combination with high alkaline cement with the measurement of linear expansion deformations in order to study the impact of nano-silica on the process of alkaline corrosion of the concrete and formation of cement matrix. It was revealed by using electron microscopy that the addition of nano-silica in concrete mixture promotes the formation of alkali-silica gel in the cement matrix, but not in the pores of the sample, which contributes to slowing, but not prevention of an alkaline corrosion of concrete.
Keywords
Alkali-aggregate reaction, nano-silica, reactivity aggregates, durability
OANA STĂNILĂ, DORINA ISOPESCU, NICOLAE ŢĂRANU
Abstract
Fibre reinforced polymeric (FRP) composites have been successfully utilized for strengthening elements made of traditional materials, such as wood. A research program carried out at The Faculty of Civil Engineering and Building Services of Iaşi tested the structural response of wood beams strengthening using carbon fibre reinforced polymeric composites, in different solutions.
The need for realistic analysis of structural behaviour of strengthened timber beams pushed researchers to find analytical and numerical evaluation methods that can correctly replace experimental programs, thus lowering the costs imposed by laboratory tests. The paper presents analytical computations and numerical modelling studies, involving three strengthening methods of timber beams using FRP composites.
Keywords
wood beams, reinforcing, FRP composites, numerical modelling, analytical computation