Microstructural examination of the effect of elevated temperature on the concrete containing clinoptilolite

WOS: 000345723500036In this study, the effect of elevated temperature on the properties of concrete containing clinoptilolite was investigated by microscopic analyses. For this purpose, seven different mixtures were prepared (the control mixture and six mixtures including 5%, 10%, 15%, 20%, 30% and 40% clinoptilolite by weight). The water binder (w/b) ratio used in the mixtures was 0.475. The dry unit weights, water absorption ratios, porosity ratios, compressive strengths and thermal conductivity coefficients of the mixtures were measured. In addition the specimens exposed to elevated temperatures of 250, 500,750 and 1000 degrees C. Two different cooling methods were used (slow cooling and fast cooling). The residual compressive strengths of the specimens which were exposed to elevated temperatures were measured. In addition the mineral and texture changes of the specimens were examined by using plane polarized microscope. Test results indicated that, clinoptilolite substitution decreased the compressive strength of the specimens in early days, but increased at later days. The positive effects were observed about clinoptilolite substitution on the residual compressive strength of the specimens. It was observed from microscopic analyses that, as the amount of clinoptilolite increased in the mixtures, aggregates were less affected from elevated temperatures. Fast cooling (FC) method resulted in strength losses when compared to slow cooling (SC) method. Additionally, clinoptilolite substitution decreased the thermal conductivity coefficient of the concrete. (C) 2014 Elsevier Ltd. All rights reserved.Nigde University Scientific Research and Projects Unit [FEB2013/24]The authors would like thank Nigde University Scientific Research and Projects Unit that supported the present work (Project number: FEB2013/24)

Microstructural examination of concrete exposed to elevated temperature by using plane polarized transmitted light method

WOS: 000327561200093In this study, the influence of elevated temperature on the residual compressive strength and ultrasonic wave velocity of the concrete specimens has been investigated. In addition, the effect of elevated temperature on the aggregate-cement paste interface and aggregate microstructure of the concrete specimens was also has been examined by plane polarized transmitted light (PPTL) method. Investigation was carried out by using one concrete mixture which was produced by normal Portland cement (PC), quartzitic natural sand and crushed basaltic coarse aggregate. The water-cement (w/c) ratio used in the mixtures was 0.50. The produced concrete specimens were exposed to 200, 400, 600, 800 and 1000 C. Test results indicated that the residual compressive strength and ultrasonic wave velocity values of the concrete specimens decreased depending on increase in elevated temperature. In addition PPTL examinations showed that, increasing temperature caused weakening of the adherence of aggregate and cement matrix. Film layers and discontinuities observed in the aggregate-cement matrix depend on increasing temperature. Fast cooling (FC) method resulted in strength losses when compared to slow cooling (SC) method

Thermal conductivity, compressive strength and ultrasonic wave velocity of cementitious composite containing waste PET lightweight aggregate (WPLA)

WOS: 000314193200076In this study, the influence of waste PET as lightweight aggregate (WPLA) replacement with conventional aggregate, on thermal conductivity, unit weight and compressive strength properties of concrete composite was investigated. For this purpose, five different mixtures were prepared (the control mixtures and four WPLA mixtures including 30%, 40%, 50%, and 60% waste PET aggregate by volume). Thermal conductivity (TC) coefficients of the specimens were measured with guarded hot plate apparatus according to TS ISO 8302 [1]. The thermal conductivity coefficient, unit weight and compressive strength of specimens decreased as the amount of WPLA increased in concrete. The minimum thermal conductivity value was 0.3924 W/m K, observed at 60% WPLA replacement. From this result, it was concluded that waste PET aggregates replacement with conventional aggregate in the mixture showed better insulation properties (i.e. lower thermal coefficient). Due to the low unit weight and thermal conductivity values of WPLA composites, there is a potential of using WPLA composites in construction applications. (c) 2012 Elsevier Ltd. All rights reserved.Nigde University Scientific Research and Projects Unit [2009/16]The authors would like to thank Nigde University Scientific Research and Projects Unit that supported the present work (Project Number: FEB 2009/16)

Recycling of waste PET granules as aggregate in alkali-activated blast furnace slag/metakaolin blends

WOS: 000335103300005In this study the utilization of waste PET aggregate in alkali-activated slag and slag/metakaolin blended mortar was investigated. Sodium hydroxide (NaOH) pellets and liquid sodium silicate were used as activators. Eighteen different mortar mixtures were prepared for the laboratory tests. In the reference mixture, unground slag (max Size of 4 mm) was used as aggregate. In PET aggregate mixtures, slag aggregate was replaced with waste PET aggregate, in amount of 20%, 40%, 60%, 80% and 100% by volume. The water-binder (w/b) ratio and aggregate-binder ratio used in the mixtures were 0.50 and 2.75, respectively. The unit weight, compressive strength, flexural tensile strength, ultrasonic wave velocity and water absorption and porosity ratios of the mixtures were measured. The test results showed that, using PET aggregate contributed to decrease of unit weight of alkali-activated mortars due to the low density of PET aggregate. Although the strength values of the specimens decreased depending on increasing waste PET aggregate amount, the compressive strength values of the alkali-activated slag mortars containing waste PET aggregate were satisfactory. In addition, alkali-activated slag mixtures containing 60% and 80% waste PET aggregate were drop into structural lightweight concrete category in terms of unit weight and strength properties. However, the compressive strengths of alkali-activated slag/metakaolin blended mixtures were lower than alkali-activated slag mixtures at the same cure condition. It is concluded from the test results that there is a potential for the use of waste PET as aggregate in the production of alkali-activated slag mortar. Because of using waste materials as binder and aggregate for mortar production in this study, alkali-activated slag mortar with PET aggregate is thought to be a good alternative for recycling of waste materials. (C) 2014 Elsevier Ltd. All rights reserved.Nigde University Scientific Research Projects Unit [FEB 2012/31]The authors would like thank Nigde University Scientific Research Projects Unit that supported the present work (Project Number: FEB 2012/31)

The use of a non-standard high calcium fly ash in concrete and its response to accelerated curing [Utilización de una ceniza volante de alto contenido en cal en el hormigón y su comportamiento frente a curados acelerados]

An experimental work was carried out to investigate the use of a non-standard high calcium fly ash in concrete. The response of the same fly ash to the accelerated curing was also explored. With three different cementitious material contents, a total of 48 concretes were produced. The water/cement ratios were varied from 0.40 to 0.87. Compressive strengths of the moist cured cube specimens cast from the concrete mixtures made with 0%, 15%, 30% and 45% replacement of normal Portland cement with fly ash were measured at 28 days and 3 months. Accelerated compressive strengths were also measured using warm-water method and boiling-water method in accordance with the relevant ASTM and Turkish Standards. Despite the fact that the fly ash used was a non-standard, the laboratory test results showed that it could be utilized in concrete production at a replacement level between 15% and 30% by weight basis because fly ash concrete developed comparable or higher compressive strength than that of corresponding normal Portland cement concrete. The laboratory test results also indicated that the accelerated curing could be used to predict the compressive strength of fly ash concrete with 85% correlation coefficient. The amount of fly ash was found to be immaterial in the strength prediction. The relation between warm-water method and boiling-water method was of linear form with 93% correlation coefficient

Examination of mechanical properties and microstructure of alkali activated slag and slag-metakaolin blends exposed to high temperatures

This paper reports an experimental study of the influence of elevated temperature on alkali activated slag (AAS) and slag-metakaolin (MK) systems. The residual compressive and flexural tensile strengths, ultrasonic pulse velocity (UPV) and porosity and water absorption ratios of AAS and AAS-MK composites after subjected to elevated temperatures of 200, 400, 600, 800, and 1000 degrees C were investigated. Two different procedures were applied for cooling the specimens. The changes in the microstructure of the composites after subjected to high temperature were examined with scanning electron microscope and X-ray diffraction. Test results reveal that depending on the increasing temperature, the residual compressive strength, flexural tensile strength, and UPV values of the specimens decreased, and porosity and water absorption ratios increased. The minimum strength results of AAS and AAS-MK specimens were observed at 800 and 600 degrees C, respectively. In particular, there have been significant changes in the internal structure of AAS and AAS-MK specimens exposed to 1000 degrees C and new reaction products were observed. Test results have shown that AAS specimens are a new alternative that can be developed for use in environments exposed to high temperatures. Since this new composite contains only slag binder and slag aggregate, it can be an economical product that use fully recycled material and these properties can increase the application areas of environmentally friendly material

The use of a non-standard high calcium fly ash in concrete and its response to accelerated curing

WOS: 000178265000002An experimental work was carried out to investigate the use of a non-standard high calcium fly ash in concrete. The response of the same fly ash to the accelerated curing was also explored. With three different cementitious material contents, a total of 48 concretes were produced. The water/cement ratios were varied from 0.40 to 0.87. Compressive strengths of the moist cured cube specimens cast from the concrete mixtures made with 0%, 15%, 30% and 45% replacement of normal Portland cement with fly ash were measured at 28 days and 3 months. Accelerated compressive strengths were also measured using warm water method and boiling-water method in accordance with the relevant ASTM and Turkish Standards. Despite the fact that the fly ash used was a non-standard, the laboratory test results showed that it could be utilized in concrete production at a replacement level between 15% and 30% by weight basis because fly, ash concrete developed comparable or higher compressive strength than that of corresponding normal Portland cement concrete. The laboratory test results also indicated that the accelerated curing could be used to predict the compressive strength of fly ash concrete with 85% correlation coefficient. The amount of fly ash was found to be immaterial in the strength prediction. The relation between warm-water method and boiling-water method was of linear form with 93% correlation coefficient