Effect of Pore Structure and Ion Concentration of Solution on the Formation of Ettringite in Composite Cement Paste

2020 ◽  
Vol 993 ◽  
pp. 1382-1387
Author(s):  
Yan Zheng ◽  
Su Ping Cui
Keyword(s):  
Pore Structure ◽  
Cement Paste ◽  
Pore Solution ◽  
Formation Rate ◽  
Ion Concentration ◽  
Hydration Reaction ◽  
Composite Cement ◽  
Ettringite Formation ◽  
Effective Expansion ◽  
Cement System

Under the background of shrinkage cracking of cement and concrete, ettringite is regarded as the most effective expansion source because of its outstanding expansion characteristics. In order to study the expansion mechanism of ettringite, the growth process and formation conditions of ettringite in composite cement system were studied by means of SEM, MIP and ICP. The effects of pore structure and ion concentration of pore solution on the morphology and expansion properties of ettringite were also analysed in this paper. The results show that the pore structure of cement paste directly affects the expansion properties of ettringite. It is verified that there is no obvious linear relationship between the expansion rate of ettringite and its quantity. The concentration of SO42- and Al(OH)4- in pore solution is the determinant of ettringite formation rate and quantity in composite cement system at the initial stage of hydration reaction. The change of crystallinity of ettringite will be directly caused by pH.

scholarly journals Alkali Ion Concentration Estimations in Cement Paste Pore Solutions

2019 ◽  
Vol 9 (5) ◽  
pp. 992 ◽  
Author(s):  
Miguel Sanjuán ◽  
Esteban Estévez ◽  
Cristina Argiz
Keyword(s):  
Composite Materials ◽  
Cement Paste ◽  
Amorphous Silica ◽  
Reliable Method ◽  
Pore Solution ◽  
Ion Concentration ◽  
Alkali Silica Reaction ◽  
Distribution Method ◽  
Structural Problems ◽  
Over Time

The alkalinity of the pore solution is of great interest for evaluating the rising of the alkali–silica reaction (ASR) when reactive amorphous silica is found in some aggregates in some cement-based composites. This reaction is not desirable because it generates swelling gel materials around the aggregates, which produce an expansive pressure inside concrete over time, and can cause the cracking of concrete, leading to serious structural problems. The purpose of this study is to develop a quick, easy and reliable method to estimate the available alkali concentrations in the pore solution of cement-based composites. The bound alkalis were initially calculated based on Taylor’s alkali distribution method. The proposed procedure to estimate the available alkalis content is a reliable method for use in construction and building composite materials.

Influence of Perlite Admixture on Pore Structure of Cement Paste

2010 ◽  
Vol 97-101 ◽  
pp. 552-555 ◽  
Author(s):  
Le Hua Yu ◽  
Hui Ou ◽  
S.X. Zhou
Keyword(s):  
Pore Structure ◽  
Cement Paste ◽  
Pore Diameter ◽  
Total Pore Volume ◽  
Hydration Reaction ◽  
Curing Time ◽  
Cement Pastes ◽  
Mercury Intrusion ◽  
Pore Surface Area ◽  
Strength And Durability

The parameters on pore structure of Portland cement pastes blended respectively with 0, 10, 20, 30 and 40% perlite admixture at 3，28，60 curing day were determined by Mercury Intrusion Porosimetre and presented in the paper to investigate affection on performance of cement-based material due to mix the admixture. The research results indicated that since the second hydration reaction had gone on with curing time, perlite admixture could diminish porosity, decrease pore diameter and reduce pore surface area in cement paste. Pores were gradually evolved from original small pores to later smaller pores, moreover fully filled with hydration products and disappeared during hydration reaction. So that the total pore volume in the paste was descended, and the proportion of harmless pores (gel pores and micropores) to whole pores was increased but that of harmful pores (macropores) subtracted. It is concluded that perlite admixture should help to increase the mechanical strength and durability of cement-based materials.

scholarly journals Inhibition of the Alkali-Carbonate Reaction Using Fly Ash and the Underlying Mechanism

Crystals ◽  
2020 ◽  
Vol 10 (6) ◽  
pp. 484 ◽  
Author(s):  
Xin Ren ◽  
Wei Li ◽  
Zhongyang Mao ◽  
Min Deng
Keyword(s):  
Fly Ash ◽  
Pore Structure ◽  
Cement Paste ◽  
Migration Rate ◽  
Pore Solution ◽  
Ph Value ◽  
Underlying Mechanism ◽  
Microscope Analysis ◽  
Alkali Carbonate ◽  
Carbonate Reaction

In this paper, fly ash is used to inhibit the alkali-carbonate reaction (ACR). The experimental results suggest that when the alkali equivalent (equivalent Na2Oeq) of the cement is 1.0%, the adding of 30% fly ash can significantly inhibit the expansion in low-reactivity aggregates. For moderately reactive aggregates, the expansion rate can also be reduced by adding 30% of fly ash. According to a polarizing microscope analysis, the cracks are expansion cracks mainly due to the ACR. The main mechanisms of fly ash inhibiting the ACR are that it refines the pore structure of the cement paste, and that the alkali migration rate in the curing solution to the interior of the concrete microbars is reduced. As the content of fly ash increases, the concentrations of K+ and Na+ and the pH value in the pore solution gradually decrease. This makes the ACR in the rocks slower, such that the cracks are reduced, and the expansion due to the ACR is inhibited.

Using of Untreated Carbon Nanotubes in Cement Compositions

2016 ◽  
Vol 865 ◽  
pp. 6-11 ◽  
Author(s):  
Kateryna Pushkarova ◽  
Maryna Sukhanevych ◽  
Artur Martsikh
Keyword(s):  
Carbon Nanotubes ◽  
Cement Paste ◽  
Cementitious Materials ◽  
Positive Influence ◽  
Mechanical Tests ◽  
Strength Characteristics ◽  
Concrete Durability ◽  
Cement Mortars ◽  
Optimum Decision ◽  
Cement System

One of the most important problem of concrete durability is increasing of waterproofing. Researches are devoted studying of cement mortars modified by carbon nanotubes, dispersed in plasticizers solutions. Were investigated physico-mechanical properties of cement paste, cement-sand mortar into which structure entered untreated carbon nanotubes (production of plant TM "Spetsmash" Kyiv, Ukraine) in various quantity. Were used as plasticizers in cement compositions additives substances of the various chemical nature – naphtaleneformaldehyde, melamineformaldehyde and polycarboxylate. Quantity of untreated nanotubes varied from 0,5%; 1,0% and to 1,5%. Concentration of additives was accepted taking into account recommendations of producers and made about 1% from the weight of cement. Were studied some technological processes of introduction untreated carbon nanotubes in cement system and is shown that the way of introduction of nanomodifiers has essential impact on strength characteristics of cementitious materials. Optimum decision introduction of untreated carbon nanotubes is using its in dispersion plasticizer of the working concentration prepared in an ultrasonic dispergator is established. Results of physico-mechanical tests of cement paste and cement-sand mortar showed positive influence at introduction of untreated carbon nanotubes as cement modifiers on strength characteristics of samples. Resalts is shown that the nanomodifier, used quantity about 1% in solution of lignosulfonate with polycarboxylate and melamineformaldehyde plasticizer has great impact on strength characteristics.

Fractal Analysis on Pore Structure and Hydration of Magnesium Oxysulfate Cements by First Principle, Thermodynamic and Microstructure-Based Methods

2021 ◽  
Vol 5 (4) ◽  
pp. 164
Author(s):  
Jiasheng Huang ◽  
Wenwei Li ◽  
Desheng Huang ◽  
Lei Wang ◽  
E Chen ◽  
...  
Keyword(s):  
Pore Structure ◽  
Fractal Analysis ◽  
Equilibrium Phase ◽  
Molar Ratio ◽  
Hydration Status ◽  
First Principle ◽  
First Principle Calculation ◽  
Cement System ◽  
Magnesium Oxysulfate ◽  
Modeling Strategy

Magnesium oxysulfate (MOS) cement is a typical eco-friendly cementitious material, which presents excellent performances. In this work, a novel multiscale modeling strategy is proposed to simulate the hydration and pore structure of MOS cement system. This work collected and evaluated the Gibbs free energy of formation for main hydrates and equilibrium constant of main reactions in MOS cement system based on a first principle calculation using Material Studio. Followingly, the equilibrium phase compositions of MOS cement system were simulated through PHREEQC to investigate the molar ratio dependence of equilibrium phase compositions. Results showed that large M (MgO/MgSO4) was beneficial for the formation of 5Mg(OH)2·MgSO4·7H2O (Phase 517) and large H (H2O/MgSO4) tended to decompose MOS cement paste and cause leaching. The microstructure-based method visualized the hydration status of MOS cement systems at initial and ultimate stages via MATLAB and the results showed that large M was significant to reduce porosity, and similar results for the case of small H. Fractal analysis confirms that fractal dimension of pore structure (Df) was significantly decreased after the hydration of MOS and was positively correlated to the porosity of the paste. In addition, it can be referred that large M and small H were beneficial for modifying the microstructure of MOS paste by decreasing the value of Df.

Influence of Lightweight Aggregate on Durability of High Performance Concrete

2009 ◽  
Vol 405-406 ◽  
pp. 197-203
Author(s):  
Bao Sheng Zhang ◽  
Li Juan Kong ◽  
Yong Ge
Keyword(s):  
Pore Structure ◽  
Cement Paste ◽  
Frost Resistance ◽  
High Performance ◽  
High Performance Concrete ◽  
Bound Water ◽  
Lightweight Aggregate ◽  
Normal Weight ◽  
Lightweight Aggregate Concrete ◽  
Aggregate Concrete

High performance concrete (HPC) with a water/cement ratio (w/c) of 0.32 and different lightweight aggregate (LWA) contents (0%, 25%, 50%, 75%, 100%) were prepared, and the influence of LWA on concrete frost-resistance and impermeability at different ages were studied, as well as the hydration degree, hydrated product, pattern and pore structure of the paste around aggregate. The results show that, by replacing normal weight aggregate (NWA) with 50% and 100% volume contents of pre-wetted LWA respectively, the chemical bound water of the cement paste surrounding aggregate are increased 12.1% and 22.7% as compared to concrete mixed without LWA. And at 28 days, lightweight aggregate concrete has the highest Ca(OH)2 content, whereas the 90-day Ca(OH)2 content of normal weight concrete is the highest. This proves that, with the increase of LWA content in concrete, both of the internal curing effect of pre-wetted LWA and secondary hydration effect of fly ash (FA) are strengthened, this can also be verified by the SEM study. Furthermore, the pore structure of the cement paste around aggregate can be improved consequently. The performance of frost-resistance of HPC can be improved by mixing LWA, the 90 day-frost-resistance of lightweight aggregate concrete is about 2.5 times of that of concrete mixed without LWA. The influence of LWA on the impermeability of HPC is different from normal concrete. When LWA content is more than 50%, the HPC impermeability decreased obviously, however at later age the difference between them becomes minor.

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