Ramazan Demirboga

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.

Thermo-mechanical properties of sand and high volume mineral admixtures

Abstract The effects of sand, high volume class C fly ash, blast furnace slag and both fly ash+blast furnace slag on the thermal conductivity were studied. In addition, influence of these mineral admixtures on density, water absorption, and compressive strength at different curing periods were studied. Fifty and 70% fly ash and blast furnace slag replaced for cement for both cement paste and mortar. Thermal conductivity decreased with the increase of fly ash and blast furnace slag as replacement for cement. The reductions in the thermal conductivity due to fly ash and blast furnace slag were respectively up to 54 and 21% for mortar, and 60 and 31% for cement paste. Both fly ash and blast furnace slag had a decreasing effect on thermal conductivity. Sand increased thermal conductivity of cement paste up to 83%. Fly ash and blast furnace slag decreased compressive strength, and increased water absorption as a function of replacement percent. Reduction in compressive strength decreased with increasing curing period and blast furnace slag increased compressive strength 6% at 120-day curing period.

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.

Development of Nanotechnology in High Performance Concrete

Concrete is the most widely used building material all around the world which has been undergoing many changes aligned with technological advancement. The most recent available type of concrete is high performance concrete which is produced employing different admixtures both chemical and mineral to enhance mechanical and durability qualities. As sustainability emerged as an indispensable factor in concrete industry, many researchers targeted micro sized mineral admixtures such as silica fume, fly ash, rice husk ash, slag and so on in order to replace Portland cement which is known to be responsible for almost 7% of carbon dioxide emission into atmosphere.Recently, technology has made it easy for scientist to study nanoscale admixtures and their effect on structure of concrete. This paper reviews nanomaterials in cement composites and how they can improve different properties of concrete.

Application of adaptive neuro-fuzzy technique and regression models to predict the compressive strength of geopolymer composites

This article introduces an adaptive network-based fuzzy inference system (ANFIS) model and two linear and nonlinear regression models to predict the compressive strength of geopolymer composites. Geopolymers are highly complex materials which involve many variables which make modeling its properties very difficult. There is no systematic approach in the mix design for geopolymers. The amounts of silica modulus, Na2O content, w/b ratios, and curing time have a great influence on the compressive strength. In this study, by developing and comparing parametric linear and nonlinear regressions and ANFIS models, we dealt with predicting the compressive strength of geopolymer composites for possible use in mix-design framework considering the mentioned complexities. ANFIS model developed by generalized bell-shaped membership function was recognized the best approach, and the prediction results of linear and nonlinear regression models as empirical methods showed the weakness of these models comparing ANFIS model.

HSC with Expanded Perlite Aggregate at Wet and Dry Curing Conditions

High-strength concrete (HSC) has undergone many developments based on the studies of influence of cement type and cement dosages, type and proportions of mineral admixtures, type of superplasticizer, and the mineralogical composition of coarse aggregates. Most studies were carried out using natural sand. In practice, lightweight aggregates from various sources are frequently used in concrete. In the study, concrete mixtures with varying expanded perlite aggregate (EPA) ratios were subjected to dry and wet curing conditions. The variables for the mixtures were 0, 7.5, 15, 22.5, and 30% EPA ratios, in replacement of fine aggregate, in dry and wet curing conditions. The 28-day compressive strengths varied from 40 to 57 and 54 to 81 MPa for dry and wet curing conditions, respectively. The research results show that both EPA ratios and dry curing condition induced the reductions in compressive strength. The reductions due to the dry curing condition were 30, 33, 35, 40, and 26% for 0, 7.5, 15, 22.5, and 30% EPA ratios, respectively. EPA ratios of 0, 7.5, 15, 22.5, and 30% also reduced compressive strengths of 11, 12, 17, and 33% for wet cured samples. The results also show for the mixtures developed in the study that up to a total EPA content of 30% is able to provide HSC for wet curing condition and only 7.5% EPA is also adequate to achieve the HSC threshold, 50 MPa, in dry curing condition. In addition, ultrasound pulse velocity (UPV), thermal conductivity, and oven dry density of samples at both wet and dry curing conditions were determined, and relationship between thermal conductivity and oven dry density, compressive strength, and UPV were exponential for both wet and dry curing conditions.

Behavior of high-strength concrete cylinders repaired with CFRP sheets

This study aims to investigate the behavior of damaged high-strength concrete cylinders repaired using carbon fiber reinforced polymer (CFRP) sheet. The experimental work on CFRP-wrapped concrete cylinders with various predamage levels indicated that CFRP can precisely resist the axial aggravated deformation of cylinders caused by damaging under uniaxial loading. The findings also revealed that the energy absorption of the damaged specimens confined with CFRP was restored approximately three times more than that of the undamaged specimens without confinement. Therefore, an empirical relationship exists between the pre-damage levels and the uniaxial compressive strength reduction of the concrete cylinders.

Effect of heat treatment temperature on ground pumice activation in geopolymer composites

Abstract In emerging countries, the driving elements for sustainable development are greenhouse and global warming concerns and the need for the development of low-CO2 cements as replacement for Portland cement. Pumice is an aluminosilicate-type material that can be condensed with NaOH and Na2SiO3 solution and can be used for green building with reduction in CO2 footprint. The present paper highlights the effect of curing temperature on Hasankale pumice activation. Four curing temperatures have been investigated in this paper, 25°C, 45°C, 65°C, and 85°C, and 65°C has been confirmed as the best temperature for ground pumice activation. Furthermore, the aging effect has been studied at different curing temperatures. The aging of the samples before 28 days has a remarkable effect on compressive strength gain, but after 28 days this effect is inconsiderable for all heat treatment temperatures.

Prediction of compressive strength of geopolymer composites using an artificial neural network

Geopolymers are highly complex materials which involve many variables and make for which modelling the properties is very difficult. There is no systematic approach in mix design for geopolymers. Since the amounts of silica modulus, Na2O content, w/b ratios and curing time have a great influence on the compressive strength, an ANN (artificial neural network) method has been established for predicting compressive strength of ground pumice based Geopolymers and the possibilities of adapting ANN and artificial intelligence system for predicting the compressive strength have been studied. Consequently, a multilayer ANN by using back propagation architecture can be developed for geopolymer compressive strength prediction. In this study, the coefficient of determination (R2) has been used for investigating the proposed model accuracy. As a result, proposed ANN model can predict the compressive strength of geopolymer with R2 = 0.958.