Oparty na cemencie sensor naprezen: krok w kierunku inteligentnego betonu

According to a report published in USA, 30% of the bridges in USA were found to be structurally de cient while concrete infrastructures have a state of material deterioration before the design life is reached (1). Earthquakes, material degradations and other environmental effects decrease the performance of the structures. The assessment of structures by structural health monitoring is very important to protect the lives of people. The best decision about a damaged structure after an earthquake can be made by use of structural tests and structural health monitoring. Structural tests and structural health monitoring are important steps in the decision making of asset management for maintenance and repair of infrastructures. The classical sensors (strain gauges, piezo-electric sensors) have low durability, low sensitivity and high cost. The low durability of classical sensors disables long term measurement while their high cost limits the amount of sensors that can be used (2). The addition of carbon ber to cement based material decreases the electrical resistance of the material. By application of load, the electrical resistance of the material changes (3-5).Scientific and Technological Research Council of Turkey (TUBITAK) 110M22

Time-dependent rheological characteristics of self-consolidating concrete containing various mineral admixtures

The study herein was intended to evaluate the influence of elapsing time on rheological properties and thixotropy of self-consolidating concrete (SCC) mixtures containing various mineral admixtures. For this purpose, variation of T50 flow time, torque plastic viscosity, apparent yield stress and thixotropy were investigated as a function of time in a standstill condition. Various amounts of silica fume (SF), metakaolin (MK), Class F fly ash (FAF), Class C fly ash (FAC) and granulated blast-furnace slag (BFS) were utilized in binary, ternary and quaternary cementitious blends in 17 different SCC mixtures having a constant slump flow value. The results showed that SCC mixtures containing various mineral admixtures were highly stable or moderately stable (VSI between 0 and 1) at 0 min according to ASTM C 1611. However, mixtures containing FAC, FAF and BFS exhibited some bleeding and segregation at 50 min. In a standstill condition, apparent yield stress and thixotropy increased significantly with time while torque plastic viscosity values changed only in a limited range. In addition, with elapsing time, MK and FAC were found to have more influence on torque plastic viscosity and yield stress values in comparison with the other admixtures. However, increase in the yield values were more pronounced in comparison with the torque plastic viscosity values. Increase in thixotropy with time for the SF and MK blended mixtures were higher when compared to the control mixtures and mixtures containing the other mineral admixtures

Use of spent foundry sand and fly ash for the development of green self-consolidating concrete

In the United States alone, the foundry industry discards up to 10 million tons of sand each year, offering up a plentiful potential resource to replace sand in concrete products. However, because the use of spent foundry sand (SFS) is currently very limited in the concrete industry, this study investigates whether SFS can successfully be used as a sand replacement material in cost-effective, green, self-consolidating concrete (SCC). In the study, SCC mixtures were developed to be even more inexpensive and environmentally friendly by incorporating Portland cement with fly ash (FA). Tests done on SCC mixtures to determine fresh properties (slump flow diameter, slump flow time, V-funnel flow time, yield stress, and relative viscosity), compressive strength, drying shrinkage and transport properties (rapid chloride permeability and volume of permeable pores) show that replacing up to 100% of sand with SFS and up to 70% Portland cement with FA enables the manufacture of green, lower cost SCC mixtures with proper fresh, mechanical and durability properties. The beneficial effects of FA compensate for some possible detrimental effects of SFS.Natural Sciences and Engineering Research Council (NSERC) of Canada, and the Canada Research Chair Progra

Doświadczalne badania i modelowanie wytrzymałości BWW, wytwarzanego z dwuskładnikowych i trójskładnikowych spoiw

Silica fume (SF), fl y ash (FA) and ground granulated blastfurnace slag (S) are among the most widely utilized mineral additions for normal strength concrete (NSC) and high strength concrete (HSC). High Reactivity Metakaolin (HRMK) is a relatively new mineral addition, produced by calcination of highly pure kaolin. The replacement of cement with HRMK increases the strength, especially at early ages, and improves durability of concrete. (1-3). Pumice (P) is a porous volcanic glass containing 60-75 SiO2% and 13-17% Al2O3. When fi nely ground, it shows pozzolanic characteristics but it is generally used as a lightweight aggregate in the concrete industry (4, 5). HRMK and P have white color and, therefore, are useful for production of white concrete when applied with white Portland cement (WPC)ÇimSA Cement Production and Trading Co

Specimen size effect on the residual properties of engineered cementitious composites subjected to high temperatures

In this study, size effect on the residual properties of Engineered Cementitious Composites (ECC) was investigated on the specimens exposed to high temperatures up to 800 C. Cylindrical specimens having different sizes were produced with a standard ECC mixture. Changes in pore structure, residual compressive strength and stress-strain curves due to high temperatures were determined after air cooling. Experimental results indicate that despite the increase of specimen size, no explosive spalling occurred in any of the specimens during the high temperature exposure. Increasing the specimen size and exposure temperature decreased the compressive strength and stiffness. Percent reduction in compressive strength and stiffness due to high temperature was similar for all specimen sizes

Katkılı çimento üretiminde kullanımı için perlitin puzolanik özelliğinin araştırılması

Perlite is a glassy volcanic rock that contains approximately 70-75% silica and 12-18% alumina. There are very large perlite reserves in the world (~6700 million tons) and approximately two thirds of these is in Turkey. Due to its high amounts of silica and alumina, at the beginning of such a study, it seemed that it would be worth first to find out whether perlite possesses sufficient pozzolanic property when it is a finely divided form and then to investigate whether it could be used as a pozzolanic addition in producing blended cements. In this study, perlites from two different regions (Izmir and Erzincan) were tested for their pozzolanic properties. After obtaining satisfactory results, grindability properties of the clinker, perlites and their different combinations were investigated. Several blended cements with different fineness values and different perlite amounts were produced by either intergrinding or separate grinding methods. The tests performed on the cement pastes and mortars containing the blended cements produced were as follows: Water requirement, normal consistency, setting time, soundness, compressive strength, rapid chloride permeability, resistance to sulfate attack and resistance to alkali-silica reactions. The results showed that Turkish perlites possess sufficient pozzolanic characteristics to be used in cement and concrete industry. Moreover, the properties tested in this study satisfied the requirements stated in the standards for blended cements. The durability of the mortars was found to be improved by 20% or more perlite incorporation.Ph.D. - Doctoral Progra

Oparty na cemencie sensor naprezen: krok w kierunku inteligentnego betonu

According to a report published in USA, 30% of the bridges in USA were found to be structurally de cient while concrete infrastructures have a state of material deterioration before the design life is reached (1). Earthquakes, material degradations and other environmental effects decrease the performance of the structures. The assessment of structures by structural health monitoring is very important to protect the lives of people. The best decision about a damaged structure after an earthquake can be made by use of structural tests and structural health monitoring. Structural tests and structural health monitoring are important steps in the decision making of asset management for maintenance and repair of infrastructures. The classical sensors (strain gauges, piezo-electric sensors) have low durability, low sensitivity and high cost. The low durability of classical sensors disables long term measurement while their high cost limits the amount of sensors that can be used (2). The addition of carbon ber to cement based material decreases the electrical resistance of the material. By application of load, the electrical resistance of the material changes (3-5).Scientific and Technological Research Council of Turkey (TUBITAK) 110M22

Cement Based Strain Sensor: A Step to Smart Concrete

In this study cement based sensor (CBS) which will be used as strain sensors was investigated. Eleven mixes having steel fibers of different lengths and volume fractions were designed. Electrical resistance measurements with and without compressive load were conducted. The correlations between the electrical resistance change and strain were determined. The performance measures of gage factor, linearity and strain limit were determined. The gage factor (fractional change in electrical resistance per unit strain) of commercial metal strain gages is around 2 while much higher gage factors as high as 30 is obtained from CBS. The CBS is much more sensitive in strain sensing with respect to commercial metal strain gages. The CBS will be placed in the concrete member and act like an aggregate while working as a strain sensor. The development of CBS will be an important step for use of smart materials in the construction industry