Gintautas Skripkiūnas

The effect of cement modification on the rheological properties of cement paste

AbstractExperimental tests have determined the effect of slag, opoka (silica-calcite sedimentary rock), silica fume (SiO2) suspension, dolomite dust and sodium silicate solution (NaSS) together with the polycarboxylatether based plasticizing admixture on the yield stress and viscosity of Portland cement paste the rheological properties of which have been defined applying a rotational viscometer with co-axial cylinders. The tests have revealed that slag, opoka, silica fume suspension and dolomite dust added to cement paste by replacing 10% of Portland cement (by weight) have an effect on the yield stress and viscosity of the paste subject to the form and fineness of additive particles. When 10wt% of Portland cement is replaced with slag cement, the yield stress of Portland cement paste reduces by about 25.9%, and viscosity increases by about 3.5 times compared with the yield stress and viscosity of reference cement paste. The yield stress of Portland cement paste with 0.5% NaSS admixture increases insignif...

Experimental research into leaching of metals from immobilized CIS solar module waste

AbstractThe aim of this research is to determine metal leaching from concrete specimens containing different quantities of waste recovered from copper indium selenide (CIS) solar module by replacing a certain share of sand aggregate. During the first stage of research the CIS solar module was shredded and leaching tests were performed on recovered waste by analysing six metals – Na, Mg, Fe, Cd, Cu and Zn. It has been determined that out of all metals analysed, the highest leaching was observed for sodium, while the highest leaching out of the heavy metals was found for zinc. In Phase II of the study concrete specimens with shredded CIS module waste were made and the physical properties of these specimens as well as the leaching of the same metals was determined. The results have shown that three metals, namely Fe, Cd, Zn, were successfully immobilised and did not leach from the specimens.

The influence of calcium nitrate on the plasticizing effect of cement paste

AbstractThe rheological properties of the cement pastes have been determined using a rotational viscometer under a special testing routine by increasing and retaining a steady rotation speed of the viscometer cylinder up to certain values and for a certain time. These tests, using rotational viscometer, have been conducted by making the assessment of cement paste flow curves, using Bingham rheological model. Rheological properties of cement pastes were tested at different times after pastes mixing: 0 min, 30 min, 60 min, 90 min, 120 min and 180 min. Cement pastes with same W/C ratio equal to 0.35 were tested. The content of admixture was used 0%, 0.5%, 1%, 2%, 3% and 5%. The admixture of Ca(NO3)2 can be used in cement pastes and concretes without a reduction in consistency during 120 min in the dosage of up to 2%. Dosages of Ca(NO3)2 from 3% are not recommended for cement pastes and concrete, they significantly increase the viscosity of mixtures immediately after mixing The admixture of calcium nitrate ch...

POSSIBILITIES TO USE TEXTILE CORD WASTE FROM USED TIRES FOR CONCRETE

AbstractThe goal of the study was to determine the effect of waste tire cord yarn with attached rubber particles on the properties of concrete made of different types of cement (Portland cement without additives – CEM I, Portland cement with limestone additive – CEM II). The filament waste (added at 0%, 2%, 4%, 6%, 8%, and 10% of the amount of fine aggregate) is water absorbing textile fibre additive with rubber particles, therefore a bigger amount of water is required to prepare the concrete mixture. With waste additive, the density and compressive strength of concrete reduces, but water absorption increases. The forecasted freeze-thaw resistance of concrete with cement type CEM I and recycled tire cord increases and slightly reduces when cement type CEM II is used, however retains similar resistance in about 1000 freeze-thaw cycles. The coefficient of thermal conductivity decreases approx. 35%, when 10% of recycled tire textile cord is added to concrete mixture.

Variation Of Characteristics Of Vibropressed Concrete Pavement Blocks

Abstract Concrete pavement blocks were formed and the following properties were investigated after 7 days of curing: density, tensile splitting strength, freezing-thawing resistance, using de-icing salts in one-sided way, and abrasion resistance. The scattering of the values of density and tensile splitting strength of the concrete pavement blocks in the pallet during the process of manufacture was examined. It was determined that the values of density and splitting tensile strength were similar in the diagonals of the pallet. Bigger changes were seen on the edges of the tray. The variation coefficients of the examined properties ranged from 0.5 % to 15.6 %. The biggest scattering of research results was noted in strength.

The Combined Effect of the Plasticizer and Multi-Walled Carbon Nanotubes on the Cement Hydration Products

There are many research devoted to the influence of carbon nanotubes (CNT) on the structure and properties of cement systems. In the course of this research, the combined influence of of multi-walled carbon nanotubes (MWCNT) and polycarboxylate (PCE) plasticizer on the products of hydration and the properties of hardened cement paste was investigated. The strength characteristics of nanomodified hardened cement paste and the hydration products were determined by the usage of modern methods of physico-mechanical and physico-chemical analyses. Based on the physico-chemical investigations, it was concluded the necessity of additional experiments, associated primary with questions of uniform distribution of the nanostructures and their chemical interactions with another components of admixture and cement system.

The Influence of Concentrations of Cement Particles on Rheological Behavior and Thixotropy of Portland Cement Paste

The influence of concentration of cement particles φc on rheological behavior (flow behavior, dynamic yield stress, plastic viscosity) and thixotropy of the Portland cement CEM I 42.5 R paste was investigated in this research. Also, thixotropy was evaluated by index of reversible structure of Portland cement paste. Concentration of cement particles φc ranged from 0.434 to 0.518. Investigation was carried out using rotational rheometer Rheotest RN4.1 with coaxial cylinders. The tests revealed that as φc decreases from 0.518 to 0.434, rheological behavior of Portland cement paste is improved: yield stress decreases from 12.7 Pa to 7.1 Pa as well as plastic viscosity – from 4.3 Pa·s to 0.88 Pa·s. The exponential correlation between φc and index of reversible structure of Portland cement paste was found. As φc decreases from 0.518 to 0.434, index of reversible structure of Portland cement paste, which describes a thixotropy, decreases from 5291 Pa·min to 977 Pa·min.

The Influence of Superplasticizers Based on Modified Acrylic Polymer and Polycarboxylate Ester on the Plasticizing Effect of Cement Paste

The article aims to present a research into the impact of the dosage and effectiveness of superplasticizers based on modified acrylic polymer and polycarboxylate ester (from 0 to 1.2 %) on rheological properties of the cement pastes (yield stresses and plastic viscosities), of different testing times after mixing (from 0 to 90 min). Materials used in the study: Portland cement CEM I 42.5 R, superplasticizers SP1 (modified acrylic polymer based), SP2 (polycarboxylate ester based), and water. Investigation was carried out using rotational rheometer Rheotest RN4.1 with coaxial cylinders. The tests revealed that superplasticizer SP2 is more effective than SP1 – cement paste (W/C = 0.30) exhibits better flowability and improved rheological qualities. Superplasticizers SP1 and SP2 exhibit different levels of plasticizing effectiveness and ability to retain the effect’s duration. Due to the increase in the dosage of superplasticizers SP1 and SP2 from 0 to 1.2 %, plasticizing effect increases. It is also observed that larger dosage of SP1 (0.6-1.2 %) results in slower increase in plasticizing effects until the 90 min margin. In conclusion, from the start of mixing until the 90 min margin, the best plasticizing effect and its retention achieved by superplasticizer SP2. Recommended SP2 dosage – from 0.6 to 0.8 %.

The influence of calcium nitrate on setting and hardening rate of Portland cement concrete at different temperatures

Calcium nitrate in mortars and concrete is used as a multifunctional additive: as set accelerator, plasticizer, long term strength enhancer and as antifreeze admixture. Used binding material and the amount of calcium nitrate, affect the characteristics of the concrete mixture and strength of hardened concrete. The setting time of the initial and the final binding at different temperatures of hardening (+ 20 °C and + 5 °C) of the pastes made of different cements (Portland cement CEM I 42.5 R and Portland limestone cement CEM II/A-LL 42.5 R) and various amounts of calcium nitrate from 1 % until 3 % were investigated. The effect of calcium nitrate on technological characteristics of concrete mixture (the consistency of the mixture, the density, and the amount of air in the mixture), on early concrete strength after 2 and 7 days, as well as on standard concrete strength after 28 days at different temperatures (at + 20 °C and + 5 °C) were analysed.

Cement Type Influence on Alkali-Silica Reaction in Concrete with Crushed Gravel Aggregate

Alkali-silica reaction is one of the chemical reactions which have a significant influence for durability of concrete. During alkali and silica reaction, silicon located in aggregates of the concrete, reacts with high alkali content. This way in the micropores of concrete is forming hygroscopic gel, which at wet environment, expanding and slowly but strongly destroying concrete structures. The goal of this paper- to determine the influence of cement type on alkali-silica reaction of mortars with crushed gravel. In the study crushed gravel with fraction 4/16 mm was used and four types of cements tested: CEM I 42.5 R; CEM I 42.5 SR; CEM II/A-S 42.5; CEM II/A-V 52.5. This study showed that crushed gravel is low contaminated on reactive particles containing of amorphous silica dioxide. The expansion after 14 days exceed 0.054 %, by RILEM AAR-2 research methodology (testing specimen dimension 40×40×160 mm). Continuing the investigation to 56 days for all specimens occurred alkaline corrosion features: microcracking and the surface plaque of gel. The results showed that the best resistance to alkaline corrosion after 14 days was obtained with cement CEM I 42.5 SR containing ash additive, and after 56 days with cement CEM II/A-V 52.5 containing low alkali content. The highest expansion after 14 and 56 days was obtained with cement CEM I 42.5 R without active mineral additives.