Tyre rubber additive effect on concrete mixture strength

This article describes the observed and examined effect of crumb rubber on the strength (compressive, bending and splitting tensile) of concrete. The tests have shown that the change in the strength of concrete with crumb rubber waste additives can be forecasted from exponential equations. These relationships enable to foresee the regularities of strength properties when a certain amount of crumb rubber of a certain size fraction is added to concrete. The obtained exponential equations show that concrete compressive, flexural and splitting tensile strengths decrease with increasing crumbed rubber additive amount. The testing has also shown that the addition of a small amount of crumbed rubber slightly increases (7%) the tensile splitting strength. The reason is better adhesion of the cement stone with rubber particles compared to the adhesion of sand, which was replaced by crumbed rubber. With higher content of crumbed rubber additive in the concrete, the tensile splitting strength decreases due to the significant increase of entrained air content and lower density

Fracture of concrete containing crumb rubber

Every year, colossal amounts of used and non-biodegradable rubber tyres are accumulated in the world. Experience shows that the most efficient way to increase the concrete fracture energy G F (N/m) is to use metal or polypropylene fibres. The optimal content of fibre increases concrete resistance to stress (especially tensile stress under bending force). Concrete fracture is not brittle; concrete continues deforming after maximum stresses and is able to resist certain stresses, there is no abrupt decrease in loading. The research has proved that crumb rubber can be used in concretes as an alternative to metal and polypropylene fibres. The investigation has found that rubber waste additives, through their specific properties can partly take up tensile stresses in concrete and make the concrete fracture more plastic; besides, such concrete requires a significantly higher fracture energy and concrete samples can withstand much higher residual strength at 500 µm crack mouth opening displacement (CMOD) and deflection

PURIFIED WASTE FCC CATALYST AS A CEMENT REPLACEMENT MATERIAL

Zeolites are commonly used in the fluid catalytic cracking process. Zeolite polluted with oil products and became waste after some time used. The quantity of this waste inevitably rises by expanding rapidly oil industry. The composition of these catalysts depends on the manufacturer and on the process that is going to be used. The main factors retarding hydration process of cement systems and modifying them strength are organic compounds impurities in the waste FCC catalyst. The present paper shows the results of using purified waste FCC catalyst (pFCC) from Lithuania oil refinery, as Portland cement replacement material. For this purpose, the purification of waste FCC catalyst (FCC) samples was treated with hydrogen peroxide. Hydrogen peroxide (H2O2) is one of the most powerful oxidizers known. By acting of waste with H2O2 it can eliminate the aforementioned waste deficiency, and the obtained product becomes one of the most promising ingredients, in new advanced building materials. Hardened cement paste samples with FCC or pFCC were formed. It was observed that the pFCC blended cements developed higher strength, after 28 days, compared to the samples with FCC or reference samples. Typical content of Portland cement substituting does not exceed 30 % of mass of Portland cement in samples. Reducing the consumption of Portland cement with utilizing waste materials is preferred for reasons of environmental protection

Effect of milled electrical cable waste on mechanical properties of concrete

The article focuses on investigation of mechanical and fracture properties of concrete containing electrical cable waste as well as some microstructural features of such concrete. Added to concrete, electrical cable waste reduces the overall concrete bulk density. Compressive, flexural, tensile splitting strengths and elastic modulus decreased when electrical cable waste was admixed to conventional and polymer modified concretes. The best mechanical properties of concrete samples containing electrical cable waste were identified in polymer modified concrete containing 5% of electrical cable waste. Electrical cable waste particles increase the deformability of polymer modified concretes and have almost no influence on normal concrete. Consequently, the optimal amount of electrical cable waste particles can provide concrete with desirable strength that is required for different applications

Chest Imaging in Granulomatous Lung Diseases

The aim of this study was to evaluate radiologic features of granulomatous lung diseases. Features include size, shape, distribution pattern, margins, cavitation, calcification and necrosis

The strength of concrete with an elastic additive of tires rubber waste under cyclic loading

Concrete strength under cyclic loads is much lower compared to short-term loading strength because cyclic loads stimulate the growth of microcracks in the cement matrix, reduce the adherence of cement stone and aggregates and cause higher creep deformations. The paper presents the deformations of samples with or without a rubber waste additive subjected to cyclic loads and determined by the methods developed during research. The obtained results show that relative plastic strains under cyclic load and relative residual strains after the removal of the load depend on the rubber additive. Relative strains in the rubberized concrete samples loaded at 70% prism compressive strength are 63% higher and residual strains after the removal of the load are 234% higher. When the samples are loaded at 80% of prism compressive strength, relative strains and residual strains after the removal of the load in concrete with the rubber additive are respectively 56% and even 360% higher if compared to the samples without the rubber additive. When the samples are loaded at 90% of prism compressive strength, the obtained respective relative strains are 63% and 219% higher compared to the samples without rubber additives. An increase in relative plastic and residual strains shows the influence of the rubber additive on the stress-strain behaviour of concrete subjected to cyclic loads. The conducted investigation has revealed that concrete with rubber waste additive under cyclic loads changes ultimate strains. We can see a significant difference in the yield deformations leading to the ultimate failure of concrete with or without the rubber additive. When the samples of rubberized concrete are loaded at 70% of prism compressive strength, the longitudinal ultimate strains are 36% higher; loading at 80% results in 47% higher strains and that at 90% results in 42% higher strains compared to the non-rubberized concrete samples. The analysis of changes in deformation conducted by the created method does not give a precise forecast as to the number of cycles that one or another type of concrete will resist under a certain load. Nevertheless, the obtained changes in deformations enable to make rather precise decisions with regard to the ability of concrete to absorb cyclic stresses with the higher strains of the concrete matrix. A detailed analysis of the test results has revealed the following tendencies: concrete with rubber additives has better deformation abilities under cyclic loads because of bigger plastic (residual) strains and bigger ultimate strains. This leads to the presumption that rubber additives present in the concrete matrix are able to absorb cyclic-load-stimulated internal stresses driving the concrete fragmentation process. Betono su elastingu priedu iš gumos atliekų atsparumas ciklinių apkrovų poveikiui Santrauka Nagrinėjama betono su elastingu priedu iš mechaniškai smulkintų naudotų padangų gumos atliekų priedo įtaka ciklinių apkrovų poveikiui. Skirtingos frakcijos ir skirtingas gumos atliekų priedo kiekis buvo naudojamas betonuose. Atlikti eksperimentai parodė, kad gumos atliekų priedas turi įtakos ciklinių apkrovų poveikiui. Gauta, kad to paties gniuždomojo stiprio betonuose su mechaniškai smulkintomis gumos atliekomis deformacijos po 20 ciklų 56–63 % didesnės, o liekamosios deformacijos nukrovus yra 219–360 % didesnės nei bandiniuose, kuriuose nebuvo naudojamas gumos atliekų priedas. Pastebėta, kad po ciklinių apkrovų poveikio bandiniai, kuriuose buvo naudojamos gumos atliekos, kur kas labiau deformavosi, susidarė daug didesnės ribinės deformacijos nei bandiniuose, kuriuose nebuvo naudojamas dempferuojantis gumos atliekų priedas. Iš atliktų eksperimentų matyti, kad gumos atliekas tikslinga naudoti betono konstrukcijose, veikiamose daugkartinėmis nuolat pasikartojančiomis apkrovomis. First Published Online: 16 May 2013 Reikšminiai žodžiai: betonas, gumos atliekų priedas, ciklinės apkrovos, liekamosios deformacijos, ribinės Deformacijo

Agile Project Estimation

Kvik hugbúnaðargerð er ítrunarferli sem snýst um fólk og síbreytilegt umhverfi og tekur tillit til þeirrar staðreyndar að þarfir breytast. Uppbygging og umfangsmat kvikrar hugbúnaðargerðar er talvert ólík þeirri sem tíðkast í hefðbundnari aðferðum. Hins vegar hafa mun færri rannsóknir verið gerðar á umfangsmati í kvikri hugbúnaðargerð. Ítrunarferlið í kvikri hugbúnaðargerð er öflug aðferð til að þróa hágæða hugbúnað sem afhentur er á réttum tíma. Þeir þættir sem hafa áhrif á hugúnaðargerðina þurfa að vera endurmetnir reglulega til að tryggja gæði hugbúnaðarins. Þessi ritgerð fjallar ítarlega um notendasögur og hvernig þörfum notenda er lýst sem sögum á réttu formi. Áhætta og ávinningur þarfa er kynntur og breytanleiki notendasaga er skilgreindur og notaður til umfangsmats. Breytanleiki notendasagna auðveldar að gera nákvæmara umfangsmat sem byggir á líkum þess að notendasaga taki breytingum. Helstu þæættir breytanleika eru áhætta og ávinnungur notendasögu og beiting INVEST líkansins á notendasögu. Lykilorð: Kvik hugbúnaðargerð, Scrum – aðferðafræði, kvikt umfangsmat, umfangsmat notendasagna, áætlunarpóker, breytanleiki.Agile software development is an iterative development method. Its basic concept is people – centered and as such, it acknowledges that requirements can change. Estimation and structure of agile methodologies are very different from those in traditional ones. However, research involving estimation in agile methodologies is considerably less advanced. The iterative based software development methods in agile methodologies are powerful ways to deliver high quality software on time. To ensure the quality, the impact of factors affecting the development cycle should be evaluated constantly. This thesis introduces a detailed view of user stories and how user requirements are transformed into the right format as user stories. The risk and value of given requirements is discussed and how changeability of a user story is defined and applied to the estimation process. Changeability rate of the user story helps to define estimation more accurately using probability of the possible change of the user story. Main indicators of the changeability rate are the risk and value of the user story and evaluation of the INVEST model of the user story. Keywords: Agile methodologies, Scrum development methodology, agile estimation, user story estimation, planning poker, changeability rate

Finely ground quartz sand and plasticizing admixtures influence on rheological properties of portland cement paste

The effect of finely ground quartz sand and plasticizing admixtures on yield stress, viscosity and dilatancy of cement pastes was investigated experimentally. The studies revealed that the addition of quartz sand up to 5 % of the cement without plasticizing admixtures reduces the yield stress of such cement paste, whereas higher content of quartz sand in the cement does not cause a further change in the yield stress of the cement paste. With the increase of plasticizing admixtures from 0.2 % to 1.0 % in the cement paste with quartz sand additive the yield stress of the paste decreases. When 5 % of the cement is replaced by quartz sand the viscosity of the cement paste without plasticizing admixtures slightly reduces, whereas the raising of quartz sand content up to 20 % does not have a further effect on the viscosity both at high and low shear rate. The quartz sand content up to 5 % slightly increases the cement paste dilatancy, whereas the replacement for 20 % cement does not change the dilatancy of the paste. The dilatancy of the cement paste increases with more quartz sand and different chemical composition plasticizing admixtures. The studies have proved that rheological parameters of the cement paste are affected by the percentage by weight of finely ground quartz in the cement paste and the particles shape of this additive

Investigation of Concrete Shrinkage Reducing Additives

This paper analyzes the efficiency of shrinkage reducing additives for the shrinkage deformations of ordinary Portland cement (OPC) concrete and its mechanical properties. OPC concrete was modified with an organic compound-based shrinkage reducing additive (SRA), quicklime, polypropylene fiber, and hemp fiber. It was found that a combination of 2.5% quicklime and 1.5% SRA led to the highest reduction in shrinkage deformations in concrete, and the values of shrinkage reached up to 40.0%. On the contrary, compositions with 1.5% SRA were found to have a significant reduction in compressive strength after 100 freeze-thaw cycles. Hemp fiber did not show a significant shrinkage reduction, but it is an environmentally friendly additive, which can improve OPC concrete flexural strength. Polypropylene fiber can be used in conjunction with shrinkage reducing additives to improve other mechanical properties of concrete. It was observed that 3.0 kg/m3 of polypropylene fiber in concrete could increase flexural strength by 11.7%. Moreover, before degradation, concrete with polypropylene fiber shows high fracture energy and decent residual strength of 1.9 MPa when a 3.5 mm crack appears. The tests showed a compressive strength decrease in all compositions with shrinkage reducing additives and its combinations after 28 days of hardening

The sulfate resistance of various cementitious binders according to different performance indicators at Nordic countries conditions

The sulfate resistance of moderate C3A Portland and Portland limestone cements (respectively PC and PLC) and their mixes with fly ash (FA) was monitored according to five performance indicators: changes in length, in mass, in strength, in ultrasonic pulse velocity and in appearance. Mortar samples (40 × 40 × 160 mm) were immersed in sodium sulfate solution (16 g/l of SO42−) for up to 12 months at ambient +20 °C conditions and more common for Nordic countries +7 °C conditions. The water/binder ratio in mortars was 0.6, pre-curing period before immersion of mortar samples in sodium sulfate solution was 28 days in water at +20 °C. Research results demonstrated that rating of sulfate resistance using different indicators is not simple and depends on the binder type and exposure temperature. The deterioration of mortar samples in sulfate environment can occur without noticeable expansion. Firstly surface degradation begins and then deterioration throughout the sample volume (loss in strength, decrease of UPV) occurs. The signs of deterioration occur quicker at +7 °C. Research results have showed that a significant positive effect of partial replacement of cement by FA for both PC and PLC was observed only at 20 °C. At +7 °C this effect is much weaker for normal hardening PC and there is almost no effect for rapid hardening PLC