RILM (EBSCOhost)

Demand for plasticisers used in concrete industry is growing in Lithuania and other countries. The paper examines a plasticising admixture based on carboxylate and the influence of temperature on the properties of concrete mixtures. Two types of Portland cement – limestone CEM II/A – LL 42.5R and slag CEM II/A – S 42.5N – have been investigated. To determine the effect of plasticising admixtures on the rheological properties of a concrete mixture, the slump, spread and density of the mixture, along with the depth of cone penetration, were examined. Then, with reference to the obtained data, yield stress was calculated. The research results illustrate the effects specific to certain combinations of plasticising admixtures with different types of cement. A plasticised concrete mixture with limestone Portland cement retains its slump better and remains almost unchanged for 90 min. The slump of the plasticised concrete mixture with slug Portland cement, however, is decreasing gradually for the full period of two hours, from the moment the mixture is ready. At higher temperatures, plastification effect manifests itself in a less intensive manner. Concrete mixtures with slug Portland cement have a higher slump, spread and the depth of cone penetration. A 5 °C increase in temperature (from +15 °C to +20 °C) makes the slump decrease by 32–33% both in concrete mixtures with limestone Portland cement and in concrete mixtures with slug Portland cement.

Atliekant eksperimentinius tyrimus nustatytas natrio silikato tirpalo (NST) ir plastiklių poveikis betono mišinio tekėjimo vamzdžiu greičiui, našumui, transportuojant mišinius dviejų stūmoklių su S tipo vožtuvu betono siurbliu. Tyrimo metu matuotas 0,406 m3 tūrio pamatų blokų formų užpildymo betono mišiniu laikas, esant skirtingam betono siurblio mišinio tiekimo slėgiui – 25,5 ir 68,0 bar. Nustatyta, kad įmaišius į mišinį NST priedą 0,5% cemento masės kartu su superplastikliu polikarboksilo eterių pagrindu, pasiektas didesnis mišinio tekėjimo greitis vamzdynu ir gautas didesnis našumas esant mažesniam betono siurblio mišinio tiekimo slėgiui. Įmaišius į mišinį NST priedą 0,5% cemento masės kartu su plastikliu lignosulfonatų pagrindu ir sumažinus cemento kiekį mišinyje, betono mišinys blogai teka vamzdynu, kai betono siurblio mišinio tiekimo slėgis yra mažas – 25,5 bar. Įmaišius į mišinį NST priedą 0,5% cemento masės kartu su plastikliu lignosulfonatų pagrindu ir smulkiuoju užpildu naudojant tik 0/4 frakcijos smėlį, betono mišinys iš viso neteka mišinio transportavimo vamzdynu, esant mažam betono siurblio mišinio tiekimo slėgiui (25,5 bar). Padidinus siurblio mišinio tiekimo slėgį iki 68 bar, mišinys vėl pradeda tekėti mišinio transportavimo vamzdynu. Tyrimai parodė, kad natrio silikato tirpalo priedo sąveika su skirtingos cheminės sudėties plastikliu turi įtakos mišinio tekamumui.

The experiment was coducted using synthetic zeolite (modification A) obtained in the laboratory of Kaunas University of Technology by means of low-temperature synthesis (below 105 °C). Aluminium fluoride (AIF3) production waste as well as sodium hydroxide NaOH and aluminium hydroxide Al(OH)3were used to obtain a complex zeolite admixture. SEM analysis revealed that synthetic zeolite admixture was made of modification A zeolite and gypsite. SEM analysis results were confirmed by X-ray analysis. Three batches of specimens were made to determine the effect of synthetic zeolite admixture on the durability of hardened cement paste. The first batch was without synthetic zeolite admixture, the second batch and the third batch contained 5 wt% and 10 wt% of synthetic zeolite admixture, respectively. Synthetic zeolite admixture was found to have a significant effect on the durability of the hardened cement paste. The weight loss in the hardened cement paste containing 5 wt% of the admixture was three times lower, whereas the weight loss in the hardened cement paste containing 10 wt% of the admixture decreased up to 100 times.