scholarly journals Phosphate Cements Based on Calcined Dolomite: Influence of Calcination Temperature and Silica Addition

Materials ◽  
2021 ◽  
Vol 14 (14) ◽  
pp. 3838
Author(s):  
Cristina Andreea Vijan ◽  
Alina Badanoiu ◽  
Georgeta Voicu ◽  
Adrian Ionut Nicoara
Keyword(s):  
Compressive Strength ◽  
Calcination Temperature ◽  
Rapid Expansion ◽  
Partial Substitution ◽  
Hardened Cement ◽  
X Ray Diffraction ◽  
High Increase ◽  
Cement Pastes ◽  
System Temperature ◽  
Hardened Cement Pastes

The aim of this study is to assess the possibility of obtaining phosphate cements based on dolomite calcined at various temperatures with/without quartz sand addition. A lower calcination temperature of dolomite (1200 °C) determines a high increase in the system temperature when calcined dolomite is mixed with KH2PO4 (MKP) solution and also a rapid expansion of the paste. The increase in calcination temperature up to 1400 °C reduces the oxides reactivity; however, for lower dosages of MKP, the expansion phenomenon is still recorded. The increase in MKP dosage increases the compressive strength due to the formation of K-struvite. The mixing of dolomite with sand, followed by thermal treatment at 1200 °C, modifies its composition and reactivity; the compressive strength of phosphate cements obtained by mixing this solid precursor with MKP increases up to 28 days of curing. We assessed the nature of hydrates formed in the phosphate systems studied by X-ray diffraction in order to explain the hardening processes and the mechanical properties of these systems. The microstructure and elemental composition of hardened cement pastes were assessed by scanning electronic microscopy with energy-dispersive spectroscopy. The phosphate cements based on calcined magnesite or dolomite were used to immobilize an industrial hazardous waste with high chromium content. The partial substitution of calcined magnesite/dolomite with this waste determines an important decrease in compressive strengths. Nevertheless, the leaching tests confirm an adequate immobilization of chromium in some of the matrices studied (for a waste dosage corresponding to 0.5 wt % Cr).

OPTIMAL CRITERIA OF ALGERIAN BLENDED CEMENT USING LIMESTONE FINES/ALŽYRIETIŠKAS MIŠRUSIS CEMENTAS SU MALTU KALKAKMENIU

2008 ◽  
Vol 14 (4) ◽  
pp. 269-275 ◽  
Author(s):  
Z’hor Guemmadi ◽  
Musa Resheidat ◽  
Hacéne Houari ◽  
Belkacem Toumi
Keyword(s):  
Compressive Strength ◽  
Portland Cement ◽  
Blended Cement ◽  
Total Porosity ◽  
Hardened Cement ◽  
Compact Structure ◽  
Limestone Filler ◽  
Cement Pastes ◽  
Limestone Fines ◽  
Hardened Cement Pastes

The effect of substitution of Portland cement by limestone up to 40% as well as its fineness on the physico‐mechanical properties of fresh and hardened cement pastes is studied. The binder was prepared by substitution of cement by limestone filler. Fillers were chosen of various particle sizes and with percentages from 5 to 40. Test results revealed that the replacement of Portland cement by the finest filler of limestone slightly decreases the consistency and the setting times (initial and final). The total porosity decreases and accordingly the compressive strength is improved with the content and fines of limestone. Although limestone has a little accelerating effect on the hydration process of Portland cement, but acts only as a filler reducing the porosity due to its compact structure, in which the compressive strength of the hardened cement paste is enhanced. The XRD and DTA analyses of samples cured up to 28 days showed that this amelioration is due to formation of new hydrated compounds. It is concluded that an addition of finely ground limestone filler only up to 15% gives a better strength. Santrauka Tirtos šviežios ir sukietėjusios cementinės tešlos, kurioje iki 40 % cemento pakeista įvairaus smulkumo maltu kalkakmeniu, savybės. Rišiklis buvo paruoštas dalį cemento pakeitus maltu kalkakmenio užpildu. Užpildo dalelės buvo įvairaus dydžio, o jų kiekis buvo keičiamas nuo 5 % iki 40 %. Tyrimai parodė, kad priedas leidžia sumažinti vandens kiekį, reikalingą tos pačios konsistencijos mišiniui gauti, taip pat cemento rišimosi pradžiai ir pabaigai paankstinti. Sumažėja cementinio akmens suminis poringumas ir atitinkamai padidėja stipris gniuždant cementinio akmens, kuriame yra kalkakmenio priedų. Nors kalkakmenio priedas nedaug pagreitina portlandcemenčio hidratacijos procesą, tačiau veikia kaip užpildas, sutankinantis struktūrą, dėl to labai padidėja sukietėjusio cementinio akmens stipris gniuždant. Bandinių, išlaikytų 28 dienas, rentgenostruktūrinė ir diferencinė terminė analizė parodė, kad pagerėjimas yra dėl susidariusių naujadarų. Apibendrinant galima teigti, kad 15 % malto kalkakmenio priedas turi didžiausią įtaką stiprumo rezultatams.

Compressive strength of radiation-induced polymer impregnated hardened cement pastes

1981 ◽  
Vol 17 (1) ◽  
pp. 35-40 ◽  
Author(s):  
A.A. El Miligy ◽  
M.R. Ziadan ◽  
S.A.S. El-Hemaly ◽  
S.A. Abo-El-Enein
Keyword(s):  
Compressive Strength ◽  
Hardened Cement ◽  
Cement Pastes ◽  
Radiation Induced ◽  
Hardened Cement Pastes

scholarly journals Studying physico-mechanical properties of cement pastes in presences of blend polymer as chemical admixtures

2015 ◽  
Vol 4 (3) ◽  
pp. 297 ◽  
Author(s):  
Elsayed Negim ◽  
G. Yeligbayeva ◽  
Rimma Niyazbekova ◽  
R. Rakhmetullayeva ◽  
A.A Mamutova ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Compressive Strength ◽  
Setting Time ◽  
Hardened Cement ◽  
Sem Images ◽  
Cement Pastes ◽  
Setting Times ◽  
Blend Ratios ◽  
Hardened Cement Pastes ◽  
Blend Polymer

<p>Physico-mechanical properties of cement pastes were studied by setting time, combined water, compressive strength, SEM as well as porosity in presence of blend polymers. Blend polymers were used based on polyvinyl alcohol and carbamide with blend ratios 20/80, 40/60 and 80/20 respectively. The addition of blend polymers to cement pastes affected the physico-mechanical properties of cement pastes. As the content of carbamide in the polymer blends decreased, the water of consistency decreased, whereas the setting times (initial &amp; final) were elongated. The combined water content and compressive strength of the hardened cement pastes were increased at all ages of hydration. The SEM images showed that the addition of these polymers to cement material improves the dispensability and workability of cement pastes.</p>

scholarly journals Effect of Mineral Composition and w/c Ratios to the Growth of AFt during Cement Hydration by In-Situ Powder X-ray Diffraction Analysis

Materials ◽  
2020 ◽  
Vol 13 (21) ◽  
pp. 4963
Author(s):  
Bo Chen ◽  
Yongming Zhang ◽  
Qing Chen ◽  
Fei Yang ◽  
Xianping Liu ◽  
...  
Keyword(s):  
Portland Cement ◽  
Cement Hydration ◽  
Hardened Cement ◽  
X Ray Diffraction ◽  
Cement Pastes ◽  
X Ray ◽  
Hardened Cement Pastes ◽  
Maximum Content ◽  
Very High

AFt is one of the major products at the early stage of cement hydration. It is an important product that influences the performance of the fresh and hardened cement pastes such as the setting time. However, there is a lack of detailed investigation on the growth of AFt in the cement pastes with a long-time scale. In this work, we reported a detailed analysis by using in-situ powder X-ray diffraction (XRD) on the growth of AFt in the cement pastes during hydration. Samples of the hydrated ordinary Portland cement (OPC) and another locally produced Portland cement with very high tricalcium silicate (C3S) content with different water–cement (w/c) ratios were investigated continually till they were hydrated for about 270 days by powder XRD. The work shows that during Portland cement hydration, the AFt reaches its maximum content with very high speed within about 24 h, which is influenced by the content of C3S in the raw cement samples and the w/c ratios of the cement pastes. Once the maximum content of AFt was reached, it decreases very fast within the following couple of days, and then decreases slowly and finally reaches a stable level at the late stage of hydration. The results also present that a lower w/c ratio is beneficial to the formation of AFt and the conversion of AFt to AFm as well. While higher w/c ratios are favorable for the AFt to remain stable in the hardened cement pastes.

Hydration Modification of Cement in the Presence of Diethanol-Isopropanolamine

2021 ◽  
Vol 1036 ◽  
pp. 230-239
Author(s):  
Xia Ling Liao ◽  
Hong Huang ◽  
Fu Qiang He ◽  
Chang Hui Yang
Keyword(s):  
Intermediate Phase ◽  
Early Stage ◽  
Strength Development ◽  
Hardened Cement ◽  
Chemical Compositions ◽  
X Ray Diffraction ◽  
Cement Pastes ◽  
Strength Enhancement ◽  
Formation Of Hydrates ◽  
Hardened Cement Pastes

In this investigation, calorimetry, quantitative X-ray diffraction analysis and the scanning electron microscopy were applied to explore the mechanism of hydration modification of cement with diethanol-isopropanolamine (DEIPA). It showed that the addition of DEIPA favoured the strength development on 3 and 28 days, but was undesirable for the 1d strength. The reason for this was that the dissolution of intermediate phase being promoted by DEIPA participated in the aluminate reaction interrupting the normal hydration of C3S. Appropriate adjustment on SO3 content in the cement was able to slow down the rate of aluminate reaction allowing C3S to react in a right fashion, which gave an optimum strength enhancement at early ages. The addition of DEIPA also impacted the formation of hydrates. Significant differences can be recognized in quantities, chemical compositions and the morphologies of hydrates in blank sample and the DEIPA-dosing ones. With the help of SO3 adjustment in cement with DEIPA, a great number of hydro-sulfoaluminates precipitated at the early stage of hydration to decrease the porosity of hardened cement pastes, which contributed to the strength gain of cement.

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