scholarly journals Difference between Internal and External Hydration of Hardened Cement Paste under Microwave Curing

2021 ◽  
Vol 2021 ◽  
pp. 1-9
Author(s):  
Guoshun Yan ◽  
Jiazheng Li ◽  
Yuqiang Lin ◽  
Xia Chen
Keyword(s):  
Cement Paste ◽  
Outer Part ◽  
Total Porosity ◽  
Fracture Morphology ◽  
Hardened Cement ◽  
Hydration Products ◽  
Hardened Cement Paste ◽  
Hydration Degree ◽  
Microwave Curing ◽  
The Difference

In order to investigate the difference between internal and external hydration of hardened cement paste under microwave curing, a comparative study on the hydration products, hydration degree, fracture morphology, and pore structure between the inner part and outer part of hardened cement paste (Φ120 mm × 120 mm) under microwave curing was carried out by XRD-Rietveld refinement, TG-DSC, SEM, and MIP methods. The results show that the total hydration degree of the inner part is lower at early ages, but with the hydration, there is little difference in the hydration degree between inner and outer parts at later ages. Apart from granular AFt crystal formed in the inner part of hardened cement paste, there is little difference in the fracture morphology between internal and external hydration. The total porosity of the outer part is lower than that of the inner part.

The Influence of Pore-Strucrure on the Campressive Strength of Hardened Cement Paste

1984 ◽  
Vol 42 ◽  
Author(s):  
Huang Yiun-Yuan ◽  
Ding Wei ◽  
Lu Ping
Keyword(s):  
Mechanical Properties ◽  
Compressive Strength ◽  
Pore Structure ◽  
Cement Paste ◽  
Total Porosity ◽  
Hardened Cement ◽  
Hardened Cement Paste ◽  
New Information ◽  
The Relationship ◽  
Empirical Constants

AbstractThe pore-structure strongly influences the carpressive strength of hardened cement paste (hcp) and other porous materials, as well as other mechanical properties. The simplest but most currently used expression representing the relationship between the pore-structure and compressive strength is fram Balshin: σ = σ0 (l-P)A, in which only the total porosity P is involved as a single parameter and σ0 and A are empirical constants. The influence of pore size distribution and pore shapes etc. are not considered.The authors introduce second parameter w - the factor of relative specific surface area of the pores other than the total porosity P into consideration and a new expression is proposed:σc=K11-p/1+2p(K2(1-p))K3w+K4 all the constants K1 - K4 can be determined experimentally. By using of this expression the new information relating the influence of pore-structure on the caopressive strength of hcp can be predicted.

Thermodynamic Interpretation of Carbonation Process of Portland Cement Hydration Products

2013 ◽  
Vol 753-755 ◽  
pp. 543-557
Author(s):  
Yan Jun Liu ◽  
Bo Tian Chen ◽  
Yong Chao Zheng
Keyword(s):  
Carbon Dioxide ◽  
Free Energy ◽  
Gibbs Free Energy ◽  
Cement Paste ◽  
Cement Hydration ◽  
Hardened Cement ◽  
Hydration Products ◽  
Hardened Cement Paste ◽  
Equilibrium Pressure ◽  
Carbonation Process

Cement hydration products carbonation is not only blamed for the carbonation-induced hardened cement paste or concrete cracking, also attributed to the pore water PH-value decrease, which causes the reinforcement corrosion under the existence of water and oxygen due to removal of oxide film passivating rebar surface, in hardened cement paste and concrete. Based on chemical thermodynamics, this paper presents the susceptibility of different cement hydration products to carbonation through calculating their Standard Gibbs Free Energy respectively, Gibbs free energy under temperature variation and the minimum equilibrium pressure of carbon dioxide triggering the carbonation process. The calculated results show that, under standard state (25°C, 100kpa), the minimum equilibrium pressure of carbon dioxide triggering carbonation process is significantly variable for different types of cement hydration products. For example, mono-sulfate sulfoferrite hydrates (3CaOFe2O3CaSO412H2O) is the most susceptible to carbonation, followed by mono-sulfate aluminate hydrates (3CaOAl2O3CaSO412H2O), while multi-sulfate sulfoaluminate hydrates (3CaOAl2O33CaSO432H2O) is the least vulnerable to carbonation, followed by silicate hydrates (5CaO6SiO25.5H2O). The findings in this paper are significant in understanding thermodynamic mechanism of cement hydrates carbonation and seeking the solution to prevent cement hydrates from carbonation-induced deterioration.

scholarly journals Effect of Ultrafine Additives on the Morphology of Cement Hydration Products

Crystals ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 1002
Author(s):  
Grigory Yakovlev ◽  
Rostislav Drochytka ◽  
Gintautas Skripkiunas ◽  
Larisa Urkhanova ◽  
Irina Polyanskikh ◽  
...  
Keyword(s):  
Silica Fume ◽  
Cement Paste ◽  
Cement Hydration ◽  
Chemical Reactivity ◽  
Xrd Analysis ◽  
Hardened Cement ◽  
Hydration Products ◽  
Hardened Cement Paste ◽  
X Ray ◽  
Strong Adhesion

The present research is focused on the investigation of the influence of ultrafine additives on the structure formation of hardened cement paste and the establishment of the mechanisms of the morphological transformations, which determine the properties of hydrated products. In the course of the research, the modification of ordinary Portland cement was performed by the suspension of multi-walled carbon nanotubes (MWCNTs), carbon black (CB) paste, and silica fume (SF). Scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) microanalysis, X-ray diffraction (XRD) analysis, thermal analysis, and Fourier-transform infrared (FTIR) spectroscopy were used to study cement hydration products. The morphology of hardened cement paste depends on the chemical reactivity of additives, their geometry, and their genesis. The action mechanism of the inert carbon-based additives and pozzolanic silica fume were considered. The cement hydration products formed in the process of modification by both types of ultrafine additives are described. In the case of the modification of cement paste by inert MWCNTs and CB paste, the formation of cement hydration products on their surface without strong adhesion was observed, whereas in the case of the addition of SF separately and together with MWCNTs, the strong adhesion of additives and cement hydration products was noted.

scholarly journals HYDRATION AND MICROSTRUCTURAL PROPERTIES OF CEMENT PASTE CONTAINING NANO AND MICROSILICA

2014 ◽  
Vol 1 (1) ◽  
Author(s):  
P. L. Chow ◽  
Salim Barbhuiya
Keyword(s):  
Cement Paste ◽  
Ordinary Portland Cement ◽  
Setting Time ◽  
Xrd Analysis ◽  
Hardened Cement ◽  
Microstructural Properties ◽  
Hydration Products ◽  
Hardened Cement Paste ◽  
Final Setting Time ◽  
Binder Ratio

The influence of nano-and microsilica addition on ordinary Portland cement (OPC) pastes has been studied in terms of hydration and microstructural properties. Three different combinations of nano-and microsilica mixes were used. A constant water-binder ratio of 0.35 was maintained throughout the experiment. All samples were tested for initial and final setting time and compressive strengths were determined at the age of 3, 7, 28, and 90 days of hydration. The hydration products were examined by SDT and XRD analysis at various curing ages. The inclusion of nano-and microsilica reduced the initial and final setting time significantly, increased the compressive strength of hardened cement paste after 7 days of hydration, and reduced the amount of calcium hydroxide in the hardened paste compared to mixes without these nanoparticles.

Effects of Polycarboxylate Superplasticizers on Hydration and Microstructure of Hardened Cement Paste

2012 ◽  
Vol 487 ◽  
pp. 692-696
Author(s):  
Rui Jun Gao ◽  
Sheng Hua Lv ◽  
Qiang Cao
Keyword(s):  
Calcium Carbonate ◽  
Cement Paste ◽  
Hydration Product ◽  
Ammonium Persulfate ◽  
Radical Copolymerization ◽  
Nucleation And Growth ◽  
Hardened Cement ◽  
Hydration Products ◽  
Hardened Cement Paste ◽  
Early Hydration

Polycarboxylate (PC) superplasticizer was synthesized by radical copolymerization using ammonium persulfate (APS) as initiator at 90 °C for 5 h. The effect of PC on the hydration process and microstructure of hardened cement at different hydration ages (4 h, 1 d and 7 d) was investigated. Hydration of cement paste results show that the nucleation and growth of hydration product of ettringite (Aft) was inhibited by PC at the early hydration ages, and the generation of the hydration products of calcium hydroxide (CH) and calcium carbonate (CaCO3) was promoted at late hydration ages. SEM result indicates that PC can make the structure of hardened cement more homogeneous and more density.

scholarly journals DISTRIBUTION OF HYDRATION PRODUCTS IN THE MICROSTRUCTURE OF CEMENT PASTES

2020 ◽  
Vol 27 ◽  
pp. 84-89
Author(s):  
Michal Hlobil
Keyword(s):  
Compressive Strength ◽  
Cement Paste ◽  
Numerical Study ◽  
Hardened Cement ◽  
Spatial Gradient ◽  
Hydration Products ◽  
Hardened Cement Paste ◽  
Cement Pastes ◽  
Hydration Model

This case study focuses on the quantification of the amorphous hydrate distribution in the microstructure of hardened cement paste. Microtomographic scans of the hardenend cement paste were thresholded based on histogram image analysis combined with microstructural composition obtained from CEMHYD3D hydration model, to separate unhydrated cement grains, crystalline and amorphous hydrates, and capillary pores. The observed spatial distribution of the amorphous hydrate exhibited a strong spatial gradient as the amorphous gel tended to concentrate around dissolving cement grains rather than precipitate uniformly in the available space. A comparative numerical study was carried out to highlight the effect of the spatially (non)uniform hydrate distribution on the compressive strength of the hardened cement paste.

Study on Resistance to Sulphate Attack of Polymer Modified Sulphoaluminate Cement

2009 ◽  
Vol 79-82 ◽  
pp. 961-964
Author(s):  
Ling Chao Lu ◽  
Yun Chao Li ◽  
Shou De Wang ◽  
Xiang Yang Guo
Keyword(s):  
Flexural Strength ◽  
Cement Paste ◽  
Total Porosity ◽  
Sulfate Attack ◽  
Hardened Cement ◽  
Sulphate Attack ◽  
Polymer Particles ◽  
Hardened Cement Paste ◽  
Acrylic Emulsion ◽  
Sulphoaluminate Cement

Styrene-acrylic emulsion was synthesized by pre-emulsification and semi-continuous emulsion polymerization, with styrene and butyl acrylate as monomers. The effects of initiator dosage and ratio of polymer to cement on durability of polymeric sulphoaluminate cement were investigated. SEM, pore structure and resistance to sulfate attack were also studied. The results show that the total porosity of the polymer sulphoaluminate hardened cement paste is lowest when P/C is 7.5%. Innocuous pores of the hardened paste are the least when P/C is 5.0%. It shows that polymer particles can spread around the cement paste, and polymer particles, aggregates, hydration products and pores come into being a compact mass. Flexural strength is higher when initiator dosage is 5‰ than that is 4‰. Flexural strength is the highest when initiator dosage is 5‰ and P/C is 7.5%, in other words, the performance of resistance to sulfate attack is best when initiator dosage is 5‰ and P/C is 7.5%.

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

2018 ◽  
Vol 276 ◽  
pp. 21-26
Author(s):  
Gintautas Skripkiūnas ◽  
Grigory Ivanovich Yakovlev ◽  
Ekaterina Karpova ◽  
Anastasiia Gordina ◽  
Arina Shaybadullina
Keyword(s):  
Carbon Nanotubes ◽  
Cement Paste ◽  
Cement Hydration ◽  
Hardened Cement ◽  
Hydration Products ◽  
Hardened Cement Paste ◽  
Physico Chemical ◽  
Cement System ◽  
Multi Walled Carbon Nanotubes ◽  
Walled Carbon Nanotubes

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.

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