Hardened slag-cement pastes of various porosities I. Compressive strength, degree of hydration and total porosity

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.

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Hardened alite pastes of various porosities. I. Degree of hydration, compressive strength and total porosity

Journal of Applied Chemistry and Biotechnology ◽

10.1002/jctb.5020270155 ◽

2007 ◽

Vol 27 (1) ◽

pp. 375-381 ◽

Cited By ~ 3

Author(s):

Salah A. Abo-El-Enein ◽

Seishi Goto ◽

Renichi Kondo ◽

Raouf Sh. Mikhail

Keyword(s):

Compressive Strength ◽

Total Porosity ◽

Degree Of Hydration

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Influence of Ultrasonication of Functionalized Carbon Nanotubes on the Rheology, Hydration, and Compressive Strength of Portland Cement Pastes

Materials ◽

10.3390/ma14185248 ◽

2021 ◽

Vol 14 (18) ◽

pp. 5248

Author(s):

Laura Silvestro ◽

Artur Ruviaro ◽

Geannina Lima ◽

Paulo de Matos ◽

Afonso R. G. de Azevedo ◽

...

Keyword(s):

Carbon Nanotubes ◽

Compressive Strength ◽

Portland Cement ◽

Mechanical Performance ◽

Isothermal Calorimetry ◽

Hydration Kinetics ◽

Cement Pastes ◽

Degree Of Hydration ◽

Vis Spectroscopy ◽

Localized Defects

The functionalization process usually increases the localized defects of carbon nanotubes (CNT). Thus, the ultrasonication parameters used for dispersing non-functionalized CNT should be carefully evaluated to verify if they are adequate in dispersing functionalized CNT. Although ultrasonication is widely used for non-functionalized CNT, the effect of this dispersing process of functionalized CNT has not been thoroughly investigated. Thus, this work investigated the effect of ultrasonication on functionalized CNT + superplasticizer (SP) aqueous dispersions by ultraviolet-visible (UV-Vis) spectroscopy, dynamic light scattering (DLS), and Fourier transform infrared spectroscopy (FTIR). Furthermore, Portland cement pastes with additions of 0.05% and 0.1% CNT by cement weight and ultrasonication amplitudes of 0%, 50% and 80% were evaluated through rheometry, isothermal calorimetry, compressive strength at 1, 7 and 28 days, X-ray diffraction (XRD), and thermogravimetric analysis (TGA). FTIR results from CNT + SP dispersions indicated that ultrasonication may negatively affect SP molecules and CNT graphene structure. The increase in CNT content and amplitude of ultrasonication gradually increased the static and dynamic yield stress of paste but did not significantly affect its hydration kinetics. Compressive strength results indicated that the optimum CNT content was 0.05% by cement weight, which increased the strength of composite by up to 15.8% compared with the plain paste. CNT ultrasonication neither increases the degree of hydration of cement nor the mechanical performance of composite when compared with mixes containing unsonicated CNT. Overall, ultrasonication of functionalized CNT is not efficient in improving the fresh and hardened performance of cementitious composites.

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Hardened alite pastes of various porosities. I. Degree of hydration, compressive strength and total porosity

Journal of Biochemical Toxicology ◽

10.1002/jbt.2570270155 ◽

1977 ◽

Vol 27 (1) ◽

pp. 375-381

Author(s):

Salah A. Abo-El-Enein ◽

Seishi Goto ◽

Renichi Kondo ◽

Raouf Sh. Mikhail

Keyword(s):

Compressive Strength ◽

Total Porosity ◽

Degree Of Hydration

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Hardened portland cement pastes of low porosity III. Degree of hydration. Expansion of paste. Total porosity

Cement and Concrete Research ◽

10.1016/0008-8846(72)90060-9 ◽

1972 ◽

Vol 2 (4) ◽

pp. 463-480 ◽

Cited By ~ 28

Author(s):

Ivan Odler ◽

Marvin Yudenfreund ◽

Jan Skalny ◽

Stephen Brunauer

Keyword(s):

Portland Cement ◽

Total Porosity ◽

Cement Pastes ◽

Degree Of Hydration ◽

Low Porosity

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Extraction of lignin from wastes of sugarcane bagasse and its utilization as an admixture for Portland cement

NanoNEXT ◽

10.34256/nnxt2113 ◽

2021 ◽

pp. 13-27

Author(s):

Darweesh H.H.M

Keyword(s):

Compressive Strength ◽

Image Analysis ◽

Sugarcane Bagasse ◽

Lignin Content ◽

Total Porosity ◽

Heat Of Hydration ◽

Gradual Reduction ◽

Cement Pastes ◽

Free Lime ◽

Setting Times

The influence of the prepared carboxy-methylated lignin extracted from sugarcane bagasse was investigated. Results showed that the w/c ratio and also setting times of the blank (L0) were reduced with the lignin content. The heat of hydration, combined water content, bulk density and compressive strength of the blank (L0) slightly increased with increasing of lignin content, but only up to 0.3 % lignin (L5) and then decreased. The free lime content decreased with the lignin content nearly at all hydration times up to 90 days due to the gradual reduction of the cement portion. The total porosity of the blank (L0) reduced gradually with lignin content up to 0.3 % lignin, and then increased with further increase of lignin. The FTIR spectra illustrated that the rate of hydration increased with lignin content. The SEM-EDAX image analysis showed the improved microstructure of cement pastes in presence of carboxy-methylated lignin when compared with that of the blank.

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Hydration and Early Age Properties of Cement Pastes Modified with Cellulose Nanofibrils

Transportation Research Record Journal of the Transportation Research Board ◽

10.1177/0361198120945993 ◽

2020 ◽

pp. 036119812094599

Author(s):

Hosain Haddad Kolour ◽

Warda Ashraf ◽

Eric N. Landis

Keyword(s):

Compressive Strength ◽

Flexural Strength ◽

Cement Paste ◽

Isothermal Calorimetry ◽

Cellulose Nanofibrils ◽

Autogenous Shrinkage ◽

Early Age ◽

Hydration Reaction ◽

Cement Pastes ◽

Degree Of Hydration

In this work, the effects of cellulose nanofibrils (CNFs) on workability, hydration reaction, microstructure, early age shrinkage, fracture properties, flexural strength, and compressive strength of cement paste were investigated. Six batches with variable CNF concentrations with the same water-to-cement (w/c) ratio (0.35) were tested. Flow table test showed a reduction in the workability as CNF dosage increased. Isothermal calorimetry (IC) tests showed that after 3 days, degree of hydration (DOH) improved up to 8% because of the addition of CNFs. Thermogravimetric analysis (TGA) tests at 7 and 28 days showed no significant changes in DOH for all pastes. After 7 days, mixture with 0.15% CNF resulted in up to 31% improvement in compressive strength. For 0.09% CNF addition, cement paste showed 26% increase in compressive strength after 28 days. Tests revealed that adding a small quantity of CNF (0.06%) along with entraining 0.05 extra water reduces autogenous shrinkage by 49% at a cement paste with w/c = 0.30. For interpreting the results, a tunnels, reservoirs, and bridges (TR&B) model is proposed. This model suggests that, as proposed by others, CNFs can modify microstructure by providing tunnels for transporting water to unhydrated cement grain. Because of their hydrophilicity, CNFs retain water and work as reservoirs (internal curing), which explains the improvement in properties at low w/c ratios. Significant increases in fracture energy (up to 60%) and flexural strength (up to 116%) suggest that CNFs are an effective toughening mechanism, acting as bridges that increase the energy required for crack propagation.

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Effect of Calcium Nitrate on the Properties of Portland–Limestone Cement-Based Concrete Cured at Low Temperature

Materials ◽

10.3390/ma14071611 ◽

2021 ◽

Vol 14 (7) ◽

pp. 1611

Author(s):

Gintautas Skripkiūnas ◽

Asta Kičaitė ◽

Harald Justnes ◽

Ina Pundienė

Keyword(s):

Compressive Strength ◽

Cement Paste ◽

Setting Time ◽

Calcium Nitrate ◽

Curing Temperature ◽

Hardened Concrete ◽

Cement Pastes ◽

Initial Setting Time ◽

Initial Setting ◽

Early Strength

The effect of calcium nitrate (CN) dosages from 0 to 3% (of cement mass) on the properties of fresh cement paste rheology and hardening processes and on the strength of hardened concrete with two types of limestone-blended composite cements (CEM II A-LL 42.5 R and 42.5 N) at different initial (two-day) curing temperatures (−10 °C to +20 °C) is presented. The rheology results showed that a CN dosage up to 1.5% works as a plasticizing admixture, while higher amounts demonstrate the effect of increasing viscosity. At higher CN content, the viscosity growth in normal early strength (N type) cement pastes is much slower than in high early strength (R type) cement pastes. For both cement-type pastes, shortening the initial and final setting times is more effective when using 3% at +5 °C and 0 °C. At these temperatures, the use of 3% CN reduces the initial setting time for high early strength paste by 7.4 and 5.4 times and for normal early strength cement paste by 3.5 and 3.4 times when compared to a CN-free cement paste. The most efficient use of CN is achieved at −5 °C for compressive strength enlargement; a 1% CN dosage ensures the compressive strength of samples at a −5 °C initial curing temperature, with high early strength cement exceeding 3.5 MPa but being less than the required 3.5 MPa in samples with normal early strength cement.

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Carbonization Durability of Two Generations of Recycled Coarse Aggregate Concrete with Effect of Chloride Ion Corrosion

Sustainability ◽

10.3390/su122410544 ◽

2020 ◽

Vol 12 (24) ◽

pp. 10544

Author(s):

Chunhong Chen ◽

Ronggui Liu ◽

Pinghua Zhu ◽

Hui Liu ◽

Xinjie Wang

Keyword(s):

Compressive Strength ◽

Coarse Aggregate ◽

Chloride Ion ◽

Total Porosity ◽

Recycled Concrete ◽

Carbonation Depth ◽

Aggregate Concrete ◽

Recycled Coarse Aggregate ◽

Carbonation Resistance ◽

Two Generations

Carbonation durability is an important subject for recycled coarse aggregate concrete (RAC) applied to structural concrete. Extensive studies were carried out on the carbonation resistance of RAC under general environmental conditions, but limited researches investigated carbonation resistance when exposed to chloride ion corrosion, which is an essential aspect for reinforced concrete materials to be adopted in real-world applications. This paper presents a study on the carbonation durability of two generations of 100% RAC with the effect of chloride ion corrosion. The quality evolution of recycled concrete coarse aggregate (RCA) with the increasing recycling cycles was analyzed, and carbonation depth, compressive strength and the porosity of RAC were measured before and after chloride ion corrosion. The results show that the effect of chloride ion corrosion negatively affected the carbonation resistance of RAC, and the negative effect was more severe with the increasing recycling cycles of RCA. Chloride ion corrosion led to a decrease in compressive strength, while an increase in carbonation depth and the porosity of RAC. The equation of concrete total porosity and carbonation depth was established, which could effectively judge the deterioration of carbonation resistance of RAC.

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