Rüstem Gül

The effects of expanded perlite aggregate, silica fume and fly ash on the thermal conductivity of lightweight concrete

Thermal conductivity coefficients of concretes made of mixtures of expanded perlite and pumice aggregates (PA) were measured. To determine the effect of silica fume (SF) and class C fly ash (FA) on the thermal conductivity of lightweight aggregate concrete (LWAC), SF and FA were added as replacement for cement by decreasing the cement weights in the ratios of 10%, 20%, and 30% by weight. The highest thermal conductivity of 0.3178 W/mK was observed with the samples containing only PA and plain cement. It decreased with the increase of SF and FA as replacement for cement. The lowest value of thermal conductivity, which is 0.1472 W/mK, was obtained with the samples prepared with expanded perlite aggregate (EPA) replacement of PA and 70% cement + 30% FA replacement of cement. Both SF and FA had a decreasing effect on thermal conductivity. EPA (used in place of PA) also induced a decrease of 43.5% in thermal conductivity of concrete.

Effects of expanded perlite aggregate and mineral admixtures on the compressive strength of low-density concretes

Abstract This article investigates the compressive strength of concretes made up of mixtures of expanded perlite (EPA) and pumice aggregates (PA). To determine the effects of silica fume (SF) and class C fly ash (FA) on the compressive strength of these lightweight aggregate concrete (LWAC), SF and FA were added as replacement for cement by decreasing the cement weights in the ratios of 10%, 20%, and 30% by weight. The binder dosage was kept constant at 200 kg/m 3 throughout this study. Superplasticizer was used 1.5% by weight of Portland cement (PC) to reduce w/c ratios. The obtained results showed that: Unit weights of all groups decreased from 1154 to 735 kg/m 3 with the increase of EPA in the mixtures. Both SF and FA decreased unit weight of samples. The compressive strengths increased by 52%, 85%, 55% for 7-day samples, and 80%, 84%, 108% for 28-day samples due to 20%, 40%, and 60% of EPA (used in place of PA) added into the mixtures, respectively. In general, FA decreased 7- and 28-day compressive strength of all groups for all percentage of FA replacement for PC. SF decreased 7-day compressive strength with increasing expanded perlite ratio in the mixtures. With the increasing curing period, the reductions in compressive strength due to SF and FA decreased drastically.

THE EFFECTS OF DIFFERENT CEMENT DOSAGES, SLUMPS AND PUMICE AGGREGATE RATIOS ON THE COMPRESSIVE STRENGTH AND DENSITIES OF CONCRETE

Abstract Compressive strengths of concretes made up of mixtures of pumice aggregate (PA) and normal aggregate were measured. To determine the effect of PA ratio, different cement dosage and slumps on the compressive strength of concrete, (1) 25%, 50%, 75% and 100% pumice ratios were used instead of normal aggregate by volume, (2) 200, 250, 350, 400 and 500 kg/m 3 cement dosages were used and (3) 3±1, 5±1 and 7±1 cm slumps were also used in this study. The analysis of the test results leads to the conclusion that PA decreased the density of concretes up to 41.5% and reductions occurred due to the increase of the PA ratio in the mixes. With the increase of cement dosage in the mixes, both density and compressive strength of concretes increased up to 3.2% and 265%, respectively, when compared to the control sample that contain 200 kg/m 3 cement dosage. The effect of the slump on the density and compressive strength was varied. Elasticity moduli were decreased with an increase of PA ratio and increased with an increase of cement dosage. Water absorption improved with an increase of cement content.

Determination by the taguchi method of optimum conditions for mechanical properties of high strength concrete with admixtures of silica fume and blast furnace slag

The deterioration of concrete structures is a major problem in many countries throughout the world. This has prompted the search for methods of predicting the service life of both existing and new structure. The present work submits results of experiments evaluating the mechanical properties of portland cement (PC), silica fume (SF) and blast furnace slag (BFS) concrete mixes. In this paper, the Taguchi method has been used to determine optimum conditions for some properties of concretes prepared with SF and BFS by weight of cement under different curing regimes. At first, all the concrete specimens were cured up to 14 days in lime saturated water at 23±2 °C. Afterwards, the concrete specimens were subjected to prepared cure regimes up to experimental days. Chosen experimental parameters were mineral admixture, water-binder ratio, cure regime and cure time. The optimum conditions were found to be mineral admixture 5%SF+10%BFS, water-binder 0.30, best cure regime lime saturated water, and cure time 28-days.

Influence of mineral admixtures on the mechanical properties and corrosion of steel embedded in high strength concrete

The corrosion rate of steel material in concrete is extremely low when the metal is in passive state at normal conditions. This situation is completely different in the regions where corrosive ions are available. Chlorine ions around steel, at the passive state, destroy the reinforced concrete. To improve the mechanical properties of concrete and to increase the corrosion resistance of steel embedded in concrete, silica fume (SF) and blast furnace slag (BFS) were used at different ratio instead of Portland cement (PC). The dry-unit weight, the compressive strength and the ultrasonic pulse velocity (UPV) of the samples without steel reinforcement were determined. The corrosion current densities of the samples with steel reinforcement in 5% NaCl solution were measured by the linear polarization technique on the 28th, 75th, 150th and 250th days. Finally, it was observed that the samples with 10% SF+20% BFS had the highest compressive strength, and that the concrete samples with 10% SF+40% BFS and 0.35 water-binder ratios had the lowest corrosion current density. As a result, it can be concluded that the mineral admixtures improved the compressive strength, UPV and corrosion current density.

Taze Beton Özelliklerinin Optimizasyonu / Optimization of Fresh Concrete Properties

OZET : Bu calismada; su-cimento orani, cimento dozaji ve hava surukleyici katki maddesinden olusan parametrelerin betonun taze haldeki ozellikleri uzerindeki etkileri incelenmistir. Deney tasarimi asamasinda ve sonuclarin istatistiksel analizinde Taguchi Yontemi kullanilarak optimizasyon yapilmistir. Optimizasyon sonucunda betonun islenebilirligi icin cimento dozaji; birim agirlik ve hava icerigi icin ise hava surukleyici katki maddesi en onemli parametre olarak bulunmustur. Genellikle betonun donmacozulmeye karsi direncini artirmasi icin kullanilan hava surukleyici katki maddesi, taze betonun akiskanligini da artirmistir. Deneylerde kullanilan Taguchi Yontemi; deney sayisini azaltmis, her uc deney icin gecerli olacak sekilde parametrelerin optimum seviyelerinin belirlenmesini saglamis ve yapilmayan deneylerin sonuclarinin kestirimini mumkun kilmistir. Anahtar kelimler: Taze beton, cokme, dozaj, birim agirlik, hava icerigi, Taguchi Metodu ABSTRACT : In this study, the influence of water-cement ratio, cement dosage and air-entrainment admixture (AEA) on the properties of fresh concrete was investigated using Taguchi Method. The Method was used for both experimental design and statistical analysis of the results to optimize the parameters mentioned. The optimisation results showed that the most important parameter is cement dosage for the workability, is AEA for the unit weight and for the air content. AEA which is generally used to improve the resistance of concrete exposed to freezing and thawing increased the workability of fresh concrete. Taguchi Method decreased the number of experiments, enabled to determine the optimum levels of the parameters for all the three experiments and to estimate the results of not conducted experiments. Keywords: fresh concrete, slump, dosage, unit weight, air content, Taguchi Method