Sintetiniu ceolitu modifikuoto cementbetonio atsparumas šalčiui

Betono irimo procesas dėl cikliško užšaldymo ir atšildymo veikiant betoną druskų tirpalais, pagreitėja 4–5 kartus. Ledą tirpdančių druskų poveikis pasireiškia kelių betonuose, betoniniuose aplinkos tvarkymo gaminiuose, tiltų ir viadukų konstrukcijose ir kt. Mokslininkai atlieka daug tyrimų modifikuojant betonus aktyviais mineraliniais priedais kaip silicio mikrodulkės, lakieji pelenai, katalizatoriai iš katalitinio naftos krekingo reaktoriaus bei ceolitais. Pagrindinis darbo tikslas – nustatyti sintetinio ceolito priedo, gauto iš a-liuminio fluorido gamybos atliekos, poveikį, cementinio akmens, betono ir vibropresuoto betono gaminių savybėms. Disertaciją sudaro įvadas, trys skyriai, rezultatų apibendrinimas ir išvados, naudotos literatūros ir autoriaus publikacijų disertacijos tema sąrašai. Įvadiniame skyriuje aptariama tiriamoji problema, darbo aktualumas, aprašomas tyrimų objektas, formuluojamas darbo tikslas bei uždaviniai, aprašoma tyrimų metodika, darbo mokslinis naujumas, darbo rezultatų praktinė reikšmė, ginamieji teiginiai. Įvado pabaigoje pristatomos disertacijos tema autoriaus paskelbtos publikacijos ir pranešimai konferencijose bei disertacijos struktūra. Pirmajame skyriuje atlikta literatūros apžvalga. Nagrinėti moksliniai tyrimai apie ceolitą bei jo struktūrą, aprašyta sintetinių ceolitų gamyba. Šiame skyriuje aprašytas ceolitinių ir pucolaninių priedų panaudojimas cementinėse sistemose. Atlikta literatūros analizė, betono poringumo ir ilgaamžiškumo klausimais. Skyriaus pabaigoje formuluojamos išvados ir tikslinami disertacijos uždaviniai. Antrajame skyriuje aprašomos tyrimams naudojamos medžiagos, mišinių sudėtys ir tyrimų metodai. Trečiajame skyriuje analizuojamos ceolitinių priedų savybės. Nagrinėjama ceolitiniais priedais modifikuotų cementinių tešlų reologija. Aprašomi cementinio akmens, betono ir betoninių grindinio trinkelių poringumo ir ilgaamžiškumo tyrimų rezultatai. Disertacijos tema paskelbta 10 straipsnių: penki – straipsnių rinkinyje, įtrauktame į Thomson ISI sąrašą, du – konferencijų medžiagose, įtrauktose į ISI Proccedings leidinių sąrašą, du – recenzuojamuose mokslo žurnaluose; bei vienas – recenzuojamoje užsienio tarptautinės konferencijos medžiagoje. Disertacijos tema perskaityti 8 pranešimai Lietuvos bei kitų šalių konferencijose

The effect of synthetic zeolite obtained from aluminium fluoride waste production on hardened cement paste

The synthetic zeolite additive received from aluminium fluoride production waste changes the processes of cement hydration thus binding portlandite formed within hydration and making new cement hydration products such as calcium hydro aluminium C[3]AH[6] as well as increasing the content of calcium hydro-sulphate-aluminates C[4]ASH[12] in hydrated hardened cement paste

Influence of Aggregate Granulometry on Air Content in Concrete Mixture and Freezing - Thawing Resistance of Concrete

Concrete frost resistance is one of the main factors that effects its durability. This is particularly important in the harsh climate regions where the water in concrete pores gets multiple freeze-thaw cycles. Concrete frost resistance can be increased by changing the coarse aggregate content by volume in the concrete mixture, as it is changing and concrete porosity. It was found that coarse aggregate volume concentration increase has a negative effect on predicted freezing - thawing resistance of concrete. It was found the correlation between a closed porosity of concrete, coarse aggregate volumetric concentration, air content in the concrete mixture and the predicted frost resistance of concrete. After statistical processing of test results it was found significant dependencies between coarse aggregate volumetric concentration in concrete, its closed porosity and predicted concrete freezing – thawing resistance and durability of concrete.12th international conference “Modern Building Materials, Structures and Techniques” (MBMST 2016

Properties of concrete modified by amorphous alumina silicate

Concrete is the most widely used building material obtained by hardening the mix made of coarse and fine aggregates, cement as the binding material, and water. The basic properties of concrete depend on the quality and properties of cement, w/c ratio and the homogeneity of compaction. Compressive strength is one of the most important properties of concrete. Materials used: Portland cement CEM I 42.5 R, 0/4 fraction sand, 4/16 fraction gravel, amorphous alumina silicate admixture, polycarboxylate ether-based superplasticizer Muraplast FK 63.30, and tap water. Five compositions of concrete mixes containing 0%, 2.5%, 5%, 7.5% and 10% of amorphous alumina silicate admixture by mass of cement were produced. The article analyses the effect of amorphous alumina silicate on the properties of concrete depending on the admixture content. The results revealed that the compressive strength of concrete after 7 days of curing increased by 7.1%, after 28 days of curing increased by 13.3% when the amorphous aluminum oxide doped silicate content was increased to 10%. Amorphous alumina silicate admixture added in quantities of up to 10%, increased the density of hardened concrete by 0.75%, and ultrasonic pulse velocity in specimens with the admixture increased up to 2.63%. First published online: 27 Mar 201

Porous permeable high-alumina ceramic materials for macro- and microfiltration

Designed composition of ceramic mass for high-alumina porous permeable ceramic material for disperse micro hydro systems. The filler used alumina fraction 100–250 microns, as a binder system studied refractory clay Veselovskaya–medicalglass–gibbsite. Formation of material carried by dry pressing at a pressure 60 MPa, the temperature of synthesis was 1250–1350 °C, holding at the maximum temperature – 1 h. The processes occurring in the binder during sintering was investigated. The effect of the sintering temperature of the material, the amount of binder composition on the acid resistance, mechanical strength, porosity and permeability of open high-alumina permeable porous material was investigated. The structure and phase composition of the submissions received, the average pore diameter was 10 mm, it can be used for microfiltration of liquids and gases, the material is homogeneous at the macro level, the structure is represented by an extensive network of channels of pores. Phase composition is represented mainly corundum and mullite. The material has the following set of physico-chemical properties: open porosity 46.41–49.74%, acid resistance 99.24–99,65%, mechanical strength in compression 6.41–12.53 MPa, permeability 5.32·10−8 m2.

The effect of synthetic zeolite on hardened cement paste microstructure and freeze-thaw durability of concrete

Tests were done with synthetic zeolite obtained by synthesizing alumina fluoride production residue, sodium hydroxide and alumina hydroxide. The synthesis lasted for two hours at 95 C temperature. The obtained product was a mix of synthetic zeolite of modifications A and X. The binding material was cement CEM I 42.5R. The test results revealed that substitution of cement with 10% of synthetic zeolite reduces water absorption of hardened cement paste 23.8%; the addition of air entraining admixture does not change the rate of water absorption. With the increase of zeolite content in concrete with and without air entraining admixture increases the volume of closed pores from 1.6% to 2.1% and from 4.1% to 7.6% respectively. The open porosity determined by water absorption of concrete with and without air entraining admixture changes insignificantly. The average distance between pores reduces from 360 lm to 190 lm when part of concrete is replaced by zeolite addition without air entraining admixture and from 190 lm to 130 lm in the case of using air entraining admixture. The addition of 10% of synthetic zeolite results in reduced content of portlandite and development of hydro aluminate compounds C3AH6 (cubic crystals) in hardened cement paste. Rose-shaped plates of calcium hydrosulphoaluminates (mono sulphate form) were also detected. These crystals together with hydroaluminates fill in the pores of hardened cement paste and thus reduce the open porosity of concrete. Substitution of 10 wt% of cement with synthetic zeolite addition increases the freeze-thaw resistance of concrete, i.e. reduces the loss of surface mass after 28 freeze-thaw cycles more than 1.6 times without the air entraining admixture and up to 3.5 times with air entraining admixture

Lithuanian quarry aggregates concrete effects of alkaline corrosion tests / Lietuvos karjerų užpildų poveikio betono šarminei korozijai tyrimai

Aggregate alkaline corrosion of cement in concrete is going to respond in sodium and potassium hydroxide (lye) with active SiO2 found in some aggregates. During this reaction, the concrete has resulted in significant internal stresses which cause deformation of the concrete, cracking and disintegration. The reaction is slow and concrete signs of decomposition appear only after a few months or years. The study used two different aggregates quarries. Studies show that Lithuania gravel contaminated with reactive particles having amorphous silicon dioxide reacting with cement in sodium and potassium hydroxide and the resulting alkaline concrete corrosion. It was found that, according to AAR 2 large aggregates include Group II – potentially reactive because of their expansion after 14 days, higher than 0.1%. Santrauka  Užpildų šarminė korozija betone vyksta reaguojant cemente esantiems natrio ir kalio hidroksidams (šarmams) su aktyviu SiO2, esančiu kai kuriuose užpilduose. Vykstant šiai reakcijai betone susidaro didelių vidinių įtempių, kurie sukelia betono deformacijas, pleišėjimą ir suirimą. Reakcija vyksta lėtai, betono irimo požymių atsiranda tik po kelių mėnesių ar metų. Tyrimams buvo naudojami dviejų skirtingų karjerų užpildai. Atlikus tyrimus nustatyta, kad Lietuvos žvyro karjerai užteršti reaktyviomis dalelėmis, turinčiomis amorfinio silicio dioksido, reaguojančio su cemente esančiais natrio ir kalio šarmais, ir sukeliančiomis betono šarminę koroziją. Nustatyta, kad pagal AAR 2 stambieji užpildai priskiriami II grupei – galimai reaktyviems užpildams, nes jų plėtra po 14 parų viršija 0,1 %. Raktiniai žodžiai: betono šarminė korozija, užpildai, reaktyvumas, šarmai, higroskopinis gelis, plėtra

The effect of synthetic zeolite on the viscosity of cement paste / Sintetinio ceolito priedo įtaka cemento tešlos klampumui

The paper reports the effect of the synthetic zeolite admixture on the viscosity of cement paste. Materials include Portland cement CEM I 42.5 R, synthetic zeolite obtained through low-temperature synthesis under laboratory conditions, polycarboxylate ester based supeplasticizer Muraplast FK 63.30 and tap water. Three compositions of cement paste were made adding 0%, 5%, and 10 wt% of synthetic zeolite. A rotating cylinder viscometer was used for measuring the consistence of the paste; viscosity was measured employing vibrational viscometer SV–10. The consistency test on cement paste showed that spread with no addition of synthetic zeolite made 149 mm, containing 5% of synthetic zeolite the slump was 85 mm and containing 10% of synthetic zeolite spread was 70 mm. The viscosity test also indicated that for the period of 30 minutes, changes in the viscosity of cement paste were as follows: 81.11 mPa s with no addition of synthetic zeolite, 746.5 mPa s containing 5% of synthetic zeolite and 827.1 mPa s containing 10% of synthetic zeolite. Data on the viscosity of cement paste were statistically processed applying software Statistica. Dispersion diagrams demonstrate changes in the viscosity of cement paste adding from 0 to 10 wt% of synthetic zeolite. Taking into account synthetic zeolite, the following correlation coefficients were calculated: 0% – 0.938, 5% – 0.967, 10% – 0.988. The coefficients of determination made 0% – 0,880, 5% – 0,935, 10% – 0,976. Equations for a dependent variable were produced by regression analysis. Santrauka Šio darbo tikslas – nustatyti, kokią įtaką cemento tešlos klampumui turi sintetinio ceolito priedas. Naudotos šios medžiagos: portlandcementis CEM I 42,5 R, sintetinis ceolitas, gautas laboratorijoje atliekant žematemperatūrę sintezę, superplastiklis Muraplast FK 63.30 multikarboksilato esterio pagrindu ir vandentiekio vanduo. Buvo maišomos trijų sudėčių cemento tešlos dedant 0 %, 5 %, 10 % sintetinio ceolito priedo nuo cemento masės. Cemento tešlos konsistencijai nustatyti buvo naudojamas Sutardo viskozimetras, klampumui – vibroviskozimetras SV-10. Atlikus cemento tešlos konsistencijos bandymą nustatyta, kad be sintetinio ceolito priedo cemento tešlos pasklidimas – 149 mm, su 5 % sintetinio ceolito priedu – 85 mm, 10 % – 70 mm. Nustačius cemento tešlos klampumą gauta, kad be sintetinio ceolito priedo cemento tešlos klampumas per 30 minučių kinta 81,11 mPas, su 5 % priedo – 746,5 mPas, 10 % – 827,1 mPas. Cemento tešlos klampumo tyrimo duomenys buvo statistiškai apdorojami kompiuterine programa „Statistica“. Šiame darbe pateikiamos sklaidos diagramos, kuriose pavaizduota, kaip kinta cemento tešlos klampumas laiko atžvilgiu naudojant sintetinio ceolito priedą nuo 0 iki 10 %. Nustatyti korealiacijos koeficinetai: 0 % – 0,9380, 5 % – 0,9669, 10 % – 0,9881, bei determinacijos koeficientai: 0 % – 0,8798, 5 % – 0,9348, 10 % – 0,9763. Atlikus regresinę analizę buvo gautos priklausomybių lygtys. Reikšminiai žodžiai: sintetinis ceolitas, cemento tešla, klampumas, portlandcementis, rišiklis, superplastikli

The use of steel cord scrap in concrete

Materials used for the study: Portland cement CEM I 42.5 R, 4/16 gravel, 0/4 sand. The fine aggregate in four concrete mixtures was substituted with steel cord scrap added at 1.5 %, 3.0 % and 4.5 %. Water absorption and compressive strength was measured in concrete specimens after 7 and 28 days of curing. Total, closed and open porosity was measured in the modified concrete specimens. The tests of predicted freeze-thaw cycles were done. Test results showed that the substitution of fine aggregate with steel cord scrap results in lower water absorption and higher compressive strength in the modified concrete specimens. The porosity parameters have also changed: the closed porosity has increased and consequently the freeze-thaw resistance of modified concrete has improved