Fresh, Mechanical and Absorption Characteristics of Self-Consolidating Concretes Including Low Volume Waste PET Granules

This study evaluates the effect of waste polyethylene terephthalate (PET) granules on the fresh, mechanical and absorption characteristics of self-consolidating concretes (SCCs). Fine aggregates were replaced with different percentages (from 0% to 8%) of PET granules obtained by crushing waste PET bottles. The fresh properties of SCC containing PET granules were determined using slump flow and V-funnel flow time tests. Mechanical properties (compressive strength and splitting tensile strength tests) and absorption properties (sorptivity and water absorption tests) were evaluated. The results indicated that utilization of waste PET granules in production of SCC could be an effective way for recycling purpose. The maximum amount of PET replacement should be limited to 5%. Exceeding 5% of PET content may result in an increase of V-funnel flow time to overpass the limiting value, decrease in compressive strength, reduction in sorptivity and increase in the water absorption. The production of high performance SCC containing 5% PET granules satisfies all the requirements for SCC with satisfactory outputs

A novel formulation of the flexural overstrength factor for steel beams

The ductile design of steel structures is directly influenced by the flexural behaviour of steel beams,which should be sufficient to allowplastic hinges to rotate until the collapsemechanismis completely developed. To guarantee the achievement of such a performance, the beam flexural overstrength must be quantified to appropriately apply capacity design principles. To this aim, analytical formulations to predict the flexural overstrength factor (s) of steel beams with a wide range of cross-section typologies (I and H sections, square and rectangular hollow sections) were developed based on gene expression programming (GEP). An experimental database was gathered from the available literature and processed to obtain the training and testing databases for the derivation of the closed-form solution through GEP. The independent variables used for the development of the prediction models were the geometric properties of the sections, the mechanical properties of the material, and the shear length of the steel beams. The predictions of the proposed GEP-based models were compared with the results obtained using the existing analytical equations proposed in the current literature. Comparative analysis revealed that the proposed formulation provides a more accurate prediction of beam overstrength

Assessment of shear capacity of adhesive anchors for structures using neural network based model

In this study, an artificial neural network (NN) based explicit formulation for predicting the edge breakout shear capacity of single adhesive anchors post-installed into concrete member was proposed. To this aim, a comprehensive experimental database of 98 specimens tested in shear was used to train and test NN model as well as to assess the accuracy of the existing equations given by American Concrete Institute and prestressed/precast concrete Institute. Moreover, the proposed NN model was compared with another existing model which had been derived from gene expression programming by the authors in a previous study. The prediction parameters utilized for derivation of the model were anchor diameter, type of anchor, edge distance, embedment depth, clear clearance of the anchor, type of chemical adhesive, method of injection of the chemical, and compressive strength of the concrete. The proposed model yielded correlation coefficients of 0.983 and 0.984 for training and testing data sets, respectively. It was found that the predictions obtained from NN agreed well with experimental observations, yielding approximately 5 % mean absolute percent error. Moreover, in comparison to the existing models, the proposed NN model had all of the predicted values in ±20 % error bands while the others estimated up to %160 error

The effect of elevated temperature on bond strength between glass fibre reinforced polymer bar and concrete

Elyaf takviyeli polimer donatının, yüksek korozyon direncine ve yüksek çekme dayanımına sahip olmasının yanında hafif bir malzeme olmasından dolayı, geleneksel çelik donatının yerine kullanılabileceği düşünülmektedir. Elyaf takviyeli polimerlerin, betonun içinde donatı olarak kullanılabilirliğindeki en kritik sorunlardan biri de aderans dayanımıdır. Donatı ile beton arasındaki aderans dayanımı beton sınıfı, donatının türü, çapı, gömülme derinliği, yüzey özellikleri gibi birçok faktöre bağlıdır. Bu çalışmada, cam elyaf takviyeli polimer (CETP) donatı çapının (18, 16, 14 ve 12 mm), beton sınıfının (C20 ve C40) ve yüksek sıcaklığın (150 ve 250 oC), CETP donatı ile beton arasındaki aderans dayanımına etkisi araştırılmıştır. Çalışmanın ilk aşamasında, C20 ve C40 sınıfında hazırlanan beton karışımlar ve dört farklı çaptaki CETP donatıları kullanılarak üretilen numunelere sıyrılma testi uygulanmış olup, donatı çapındaki ve beton sınıfındaki değişimin aderans dayanımı üzerindeki etkisi incelenmiştir. Çalışmanın ikinci aşamasında ise, C20 ve C40 sınıfındaki beton karışımlar için 12 ve 16 mm çapındaki CETP donatılar kullanılarak hazırlanan numuneler, 3 saat süre ile 150 ve 250 oC sıcaklıklara maruz bırakılmıştır. Daha sonra oda sıcaklığına kadar soğutulan numunelere sıyrılma testi uygulanarak, yüksek sıcaklığın aderans dayanımı üzerindeki etkisi incelenmiştir. Bu çalışmanın sonucunda, CETP donatı çapı arttıkça aderans dayanımının arttığı, betonun basınç dayanımındaki artışın da aderans dayanımını olumlu yönde etkilediği görülmüştür. Ayrıca, sıcaklık artışının CETP donatı ile beton arasındaki aderansı olumsuz yönde etkilediği belirlenmiştir.The utilisation of fibre reinforced polymer (FRP) bars in concrete instead of the conventional steel rebar is generally considered to be viable due to their fundamental traits such as lightweight, higher corrosion resistance and tensile strength. One of the most critical issues in this FRP application is in fact the bond strength between FRP bars and concrete which depends on many factors including the strength of concrete, FRP diameters, types, embedment depth and surface properties etc. In this study, the effects of bar diameters (18, 16, 14 and 12 mm), the strength classes of concrete (C20 and C40) and the elevated temperature (150 and 250 oC) variation on the bond strength were investigated. In the first stage of the study, the pull-out tests were applied to the samples produced by using concrete mixtures prepared as C20 and C40 class and FRP reinforcements having four different diameters. Thus, the effects of variation in FRP diameter and the strength classes of concrete on the bond strength were investigated. In the second stage of the study, the samples prepared using 12 and 16 mm diameters of FRP reinforcements for C20 and C40 concrete mixtures were exposed to the temperatures of 150 and 250 oC for 3 hours. Then, the effect of elevated temperature on the bond strength was carried out by applying the pull-out tests to the samples cooled to the room temperature. The test results reveal that the bond strength is improved with increasing FRP diameter, the compressive strength of concrete and adversely affected from the high temperature exposed

SOFT-COMPUTING MODEL FOR COMPRESSIVE STRENGTH OF MORTARS WITH BLENDED CEMENTS

The 90 experimental data samples previously validated in the current literature regarding the compressive strength of mortars have been collected and evaluated to develop the practical soft-computing model which is presented in this study for prediction of the compressive strength of mortars with blended cements. The presented model provides many economical, technical and environmental benefits to be swiftly implemented into the practice. It is formulated based on the soft-computing techniques of genetic expression programming (GEP) by considering the model factors including as specific weight and surface of cement, water/cement ratio, testing age, the amounts of clinker, limestone, pozzolana and gypsum. Paper explains the validity of the presented model with that randomly selected experimental sub datasets available in the current literature. The findings illustrate that the presented GEP model has a favorable potential for estimating the compressive strength of mortars with blended cements

Modeling Compressive Strength of Lightweight Geopolymer Mortars by Step-Wise Regression and Gene Expression Programming

This article presents a comprehensive study aimed at developing suitable mathematicalmodels for the prediction of compressive strength of lightweight geopolymer mortar(LWGM) with different types and amounts binders with different curing regimes. Lightweightpumice aggregate, alkali activated powder materials are the main components of geopolymerbinder. From the experimental study 306 data samples were obtained and these wereused to derive explicit formulas for estimation of the compressive strength of LWGMs. Twomethods are used to produce the models. The first is the simplified linear step-wise regression,while the second method is the genetic expression programming. Step-wise regressionis a statistical tool that uses the impact of each factor to evaluate its effect on the equation.This impact is calculated based on the probability effect based on the F-distribution and thenull-hypothesis. The default value of probability that refers to the significance of each factoris 0.05. Thus, the software calculates the probability of each of the independent variables andincludes only those with probability values less than 0.05. Based on the included independentvariables, simplified linear regression equation is introduced. The genetic programming onthe other hand, is much more sophisticated method that uses the principles of gene evolution.The modeling is separated for each type of binder. Thus, two sets of formulas are obtainedfrom each modeling, one for the granulated blast furnace slag -based LWGM, while thesecond is for the fly ash-based LWGM. These models revealed that genetic algorithm basedmodeling has a reliable potential for estimating the strength of LWGMs

Experimental evaluation and genetic programming based modeling of the compressive strength of concretes produced with various strength classes of cements

This study aimed to propose a prediction model for estimation of strength of concretes withvarious cements and mixture proportions. The strength of the samples produced with threedifferent types of cement at different rates of water-to-cement ratios and cement richness wereinvestigated experimentally and evaluated statistically. Three type of cement possessing 28-day strengths of 32.5, 42.5, and 52.5 MPa was used in the production of concretes. Theconcretes were produced at cement richness values of 300, 400, and 500 kg/m3 and w/c ratesat changing levels within the interval of between 0.3 and 0.6. By this way, combined influencesof cement strength, amount of cement and w/c ratio was experimentally investigated. Totally36 mixes were cast then the compressive strength values were examined after specified moistcuring periods (7 and 28 day). A statistical study were conducted on the experimental resultsand the significances of the cement strength, w/c values and amount of cement on thecompressive strength of the concretes were assessed. Another crucial focus of the current paperis to generate an explicit expression to predict the compressive strength of the concretestackled with the current study. To derive an explicit formula for estimation, a soft computingmethod called gene expression programming (GEP) was benefited. The GEP model was alsocompared with a less complicated estimation model developed by multi linear regressionmethod. The results revealed that compressive strength of the samples were significantlyinfluenced by cement type and aggregate-to-cement ratio. It was observed that there is a highcorrelation between experimental and predicted values obtained from the proposed GEPmodel

EFFECT OF GLASS FIBER ADDITION ON THE STRENGTH PROPERTIES AND PORE STRUCTURE OF FLY ASH BASED GEOPOLYMER COMPOSITES

This paper presents the results of an experimental program to determine the properties of glass fiber reinforced geopolymermortar which is a mixture of fly ash, alkaline liquids, fine aggregates, and glass fibers. The effects of inclusion of glass fiberson density, compressive strength, splitting tensile strength, absorption and sorptivity of hardened geopolymer composite (GPC)was studied. Alkaline liquid to fly ash ratio was fixed as 0.33. NaOH and NaSiO3 solutions were used as alkaline liquids foractivation of fly ash. The alkaline liquid combination ratio of 2.5:1 were used for Na2SiO3:NaOH. Glass fiber was added to themixes in 0.2%, 0.4%, 0.6%, 0.8%, 1.0% and 1.2% by volume of mortar. A curing regime of 48 hours with 60 ˚C temperaturewas applied. The experimental results indicated that inclusion of the glass fibers resulted in a decrease in the workability, yet,an improvement in compressive strength and splitting tensile strength of fly ash based GPC was obtained by increasing thefiber content. However, the inclusion of glass fiber did not indicate a remarkable change in the water absorption and sorptivityof GPCs

EFFECT OF GLASS FIBER ADDITION ON THE STRENGTH PROPERTIES AND PORE STRUCTURE OF FLY ASH BASED GEOPOLYMER COMPOSITES

This paper presents the results of an experimental program to determine the properties of glass fiber reinforced geopolymermortar which is a mixture of fly ash, alkaline liquids, fine aggregates, and glass fibers. The effects of inclusion of glass fiberson density, compressive strength, splitting tensile strength, absorption and sorptivity of hardened geopolymer composite (GPC)was studied. Alkaline liquid to fly ash ratio was fixed as 0.33. NaOH and NaSiO3 solutions were used as alkaline liquids foractivation of fly ash. The alkaline liquid combination ratio of 2.5:1 were used for Na2SiO3:NaOH. Glass fiber was added to themixes in 0.2%, 0.4%, 0.6%, 0.8%, 1.0% and 1.2% by volume of mortar. A curing regime of 48 hours with 60 ˚C temperaturewas applied. The experimental results indicated that inclusion of the glass fibers resulted in a decrease in the workability, yet,an improvement in compressive strength and splitting tensile strength of fly ash based GPC was obtained by increasing thefiber content. However, the inclusion of glass fiber did not indicate a remarkable change in the water absorption and sorptivityof GPCs

Effect of aggregate properties on the mechanical and absorption characteristics of geopolymer mortar

Even though aggregate constitutes major volume in geopolymer concrete, only limited study related to this parameter has been reported. This paper presents the summary of study carried out to understand the influence of aggregate content and grading on the mechanical and absorption characteristics of geopolymer mortar. Three types of aggregates, namely, natural river sand, crushed limestone, and combined sand-limestone were used in geopolymer mortar. Fly ash was used as source material. Effectiveness of aggregates was evaluated in terms of the workability, fresh unit weight, absorption and strength of geopolymer mortar. The alkaline activator is a mix of 12 molarity of NaOH solution with Na2SiO3 in ratio of 1:2.5. The experiments were performed on geopolymer mortar cubes under curing temperatures of 90 °C with curing period of 24 h. Test results indicate that geopolymer mortar including natural sand shows better flowability compared to other aggregates, moreover, coarse grading of sand caused higher flow. The highest compressive and splitting tensile strength was obtained in crushed limestone. The combined sand-limestone shows the lowest water absorption and sorptivity compared with other types of aggregates