Wyniki wyszukiwania - Biblioteka Nauki

1

CHITOSAN APPLIED FOR GYPSUM MODIFICATION

100%

Mucha M. , Mróz P. , Wrona D.

Progress on Chemistry and Application of Chitin and its Derivatives

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2017

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tom 22

166 - 175

EN

In order to improve the properties of gypsum materials, including workability, mechanical strength and ability to retain water, various admixtures (also polymers), known as plasticisers, have been applied. These polymers can be soluble in water, such as cellulose and starch ethers, or unsoluble applied in a form of dispersion up to 5% of weight fraction. The admixtures are added into initial water and mixed with hemihydrate calcium sulphate in a proper ratio. In the hydration process of the hemihydrate into dehydrate, a crystallisation process leading to gypsum setting occurs. In the present work, a chitosan sample of DD=85% in two forms was applied: dissolved in 1% acetic acid and as a water dispersion in the weight fraction up to 1% of the gypsum matrix. The water to gypsum ratios of 0.6 or 0.74 was applied. The influence of chitosan on the rate of setting and kinetics of crystallisation of gypsum was investigated and discussed. The morphological structure of the resulting gypsum sample was examined using SEM microscopy. In the presented results, chitosan in the form of a 1% dispersion was a setting retardant and it changed the morphological structure of gypsum. However, mechanical tests showed a decrease of bending strength. When chitosan was applied as a biomaterial, the chitosan content in the composite was equal to 10%, and thus a compressing strength increased. The presence of PVA (polyvinyl alcohol) in the gypsum matrix caused a small effect on gypsum setting in contrast to PVAc (polyvinyl acetate), which is a good admixture for both cement and gypsum [2,3].

2

Dry building mixtures on the basis of gypsum-free portland cement

72%

Shcturmay M. , Sobol K. , Drymalyk A. , Terlyga V.

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2009

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tom z. 53 [265]

131-135

EN

Theoretical principles for obtaining gypsum-free Portland cement (GFPC) modified by organic-mineral additives were investigated. Gypsum-free Portland cement was improved by rational selection of the chemical additives which act as hardening accelerators, plasticizers and setting retarders. The hydration and structure formation processes as well as building-technical properties and running ability were established. The influence of alkaline metals carbonates as hardening accelerators on pH of a liquid phase, hydration degree in the alkaline systems as well as features of plasticizers action in constitution complex chemical additives were investigated. The possibility of speed regulation of GFPC early structure formation by introduction setting retarders which are replacing the effects of gypsum was determined. There were investigated the characteristics of the phase structure and microstructure of the artificial cement stone on the basis of gypsum-free Portland cement modified by the complex chemical additives and fine-dyspersated lime stone. Early structure formation is characterized by hydroaluminate hardening type with formation of metastable carbonate replaced by AF-phase followed by structurally active hexagonal AFm-phase C4A.C02-11H20.

3

Wpływ jonów fosforanowych PO3-/4 na proces hydratacji cementu

58%

Tkaczewska E. , Kłosek-Wawrzyn E.

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2012

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tom R. 17/79, nr 6

401-408

PL

W artykule omówiono badania wpływu jonów fosforanowych, dodawanych w formie fosforanu sodu, na właściwości zaczynu i zaprawy z cementu portlandzkiego. Dodatek fosforanu spowodował opóźnienie, lub przyspieszenie, procesu wiązania i zmniejszenie wytrzymałości na ściskanie. Wpływ ten zaznaczył się szczególnie wyraźnie w przypadku dodatku fosforanu, wyrażonego jako P2O5, wynoszącego 2,5 i 12,5 g/kg cementu. Badania rentgenograficzne próbek wykazały obecność Ca3(PO4)2, co prawdopodobnie było przyczyną tego niekorzystnego wpływu.

EN

Paper presents experiments concerning the influence of phosphate ions, added as sodium phosphate, on the properties of Portland cement paste and mortar. Addition of this phosphate caused setting retardation, or acceleration, and compressive strength reduction. This effect is particularly intensive when the content of phosphate, expressed as P2O5, is 2.5 and 12.5 g/kg of cement. XRD examination of the samples has shown the formation of Ca3(PO4)2, which probably caused this negative influence.

4

Metakaolin jako dodatek pucolanowy modyfikujący właściwości zapraw

58%

Mansour M. S. , Abadlia M. T. , Jauberthie R. , Messaoudene I.

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2012

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tom R. 17/79, nr 2

102-108

PL

Przygotowano zaprawy cementowe, w których 10% cementu portlandzkiego zastąpiono metakaolinem. Zbadano właściwości fizyczne zapraw, a mianowicie skurcz i wytrzymałość mechaniczną. Wyniki badań pokazują, że metakaolin zmniejsza szybkość hydratacji cementu, zmniejsza przewodnictwo i pH zawiesiny cementowej i spowalnia wiązanie zaczynu. Te zmiany powodują zmniejszenie lepkości plastycznej, a poprawiają urabialność mieszanki betonu. Wytrzymałość na ściskanie zaprawy z dodatkiem metakaolinu osiąga wartości zbliżone do zaprawy kontrolnej po 28 dniach, jednak wczesna wytrzymałość jest mniejsza. Ponadto dodatek metakaolinitu zwiększa skurcz w porównaniu do zaprawy kontrolnej.

EN

Cement mortars were produced in which 10% of Portland cement was replaced by metakaolin. The physical properties i.e. shrinkage and mechanical strength of the mortar were studied. The results show that the metakaolin slows cement hydration, decreases the conductivity and the pH of cement suspensions and increases the setting time of cement paste. Due to these changes the plastic viscosity and workability of mix concrete are enhanced. The compressive strength of mortar with metakaolin addition is close to the strength of reference mortar after 28 days, but early strength is lower. Moreover, the metakaolin addition is increasing shrinkage in relation to the reference mortar.