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.

Effect of Composition of Cementitious Materials on Alkalinity of Pore Solution and Strength of Cement Paste

2013 ◽  
Vol 671-674 ◽  
pp. 1732-1735
Author(s):  
Xiao Lu Yuan ◽  
Shi Hua Zhou ◽  
Dong Mei Liu
Keyword(s):  
Compressive Strength ◽  
Cement Paste ◽  
Pore Solution ◽  
Ph Value ◽  
Cement Content ◽  
Cementitious Materials ◽  
Mineral Admixtures ◽  
Aluminate Cement

Alkalinity of the surroundings is the basis to study the MICP technology. Alkalinity of pore solution and strength of cement paste made of various cementitious materials were studied. Results show that the alkalinity of pore solution of cement paste decreased with the increase of sulpho-aluminate cement content. pH value of cement paste was about less than 10 when sulpho-aluminate cement content exceeded 75%. Incorporation of sulpho-aluminate cement decreased compressive strength of paste obviously; however, compressive strength of paste was improved when the addition of sulpho-aluminate cement was more than 75%. Addition of mineral admixtures reduced the alkalinity of pore solution of cement paste and increased its compressive strength. Compressive strength of specimens was decreased when the content of mineral admixtures increased.

Effect of Internal Activation Using Porous Ceramic Aggregate on Hardness and Pore Structure of Fly Ash Cement Paste

2016 ◽  
Vol 711 ◽  
pp. 95-102 ◽  
Author(s):  
Kazuki Ootaishi ◽  
Phuong Trinh Bui ◽  
Yuko Ogawa ◽  
Kenji Kawai
Keyword(s):  
Fly Ash ◽  
Pore Structure ◽  
Cement Paste ◽  
Porous Ceramic ◽  
Pozzolanic Reaction ◽  
Experimental Program ◽  
Early Age ◽  
Fly Ash Concrete ◽  
Activating Agent ◽  
Sulfate Activation

The utilization of fly ash not only reduces the environmental impact but also improves some mechanical properties and durability of concrete. However, the early-age strength of fly ash concrete is sometimes lower than that of normal concrete due to the slow pozzolanic reaction of fly ash. In recent years, some researchers have suggested alkali or sulfate activation to accelerate the pozzolanic reaction. Some studies have used sodium hydroxide (NaOH) solution, while others have applied potassium sulfate (K2SO4) or sodium sulfate (Na2SO4) as activators which are effective in accelerating the pozzolanic reaction and increasing the strength at early age. On the other hand, the early-age strength of fly ash concrete is also improved by using porous ceramic aggregate (PCA) as an internal curing agent. Therefore, the present study aims at investigating the effect of an internal activating agent using PCA on hardness and pore structure of fly ash cement paste. In the experimental program, PCA immersed in two kinds of solution (K2SO4 and Na2SO4) was placed in the center of specimen with dimension of 21x21x20 mm. In addition, normal aggregate (NS) was used for reference. As a result, internal sulfate activation using PCA improved the hardness of interfacial transition zone (ITZ) between paste and PCA, and reduced the Ca(OH)2 content in cement paste with 40% replacement with fly ash significantly at the age of 1 day, but negligibly at the ages of 7 and 28 days when compared with reference specimen. K2SO4 was more effective in improving hardness of ITZ as an internal activating agent than Na2SO4. Although the total pore volumes of the fly ash cement pastes using PCA imbibing sulfate activators were not reduced at the age of 28 days, their pore volumes with diameters less than 0.05 µm were increased.

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.

Influence of Lime Dust on the Pore Structure and Strength of Fly Ash-Cement Paste

2011 ◽  
Vol 99-100 ◽  
pp. 739-744
Author(s):  
Xiang Hao Wu ◽  
Li Zhen Bai ◽  
Cong Kai Zhang ◽  
Pan Yuan
Keyword(s):  
Compressive Strength ◽  
Fly Ash ◽  
Pore Structure ◽  
Cement Paste ◽  
Volume Ratio ◽  
Strength Test ◽  
Dust Content ◽  
Test Results ◽  
Compressive Strength Test ◽  
Water Test

By evaporable water test and compressive strength test, this paper studies on the influence of lime dust on pore structure and compressive strength of fly ash-cement paste. The test results show that: 1) With the volume of lime dust as cement replacement increasing, porosity and big pore to total volume ratio of fly ash-cement paste are gradually raising .However, with the volume of lime dust as fly ash replacement increasing, porosity of fly ash-cement paste decreases gradually, while big pore to total volume ratio firstly increases, and then decreases. 2) Substituting lime dust for isometric cement, compressive strength of fly ash-cement paste containing over 5% lime dust reduces gradually when the proportion of lime dust replacing cement raises. Whereas, substituting lime dust for isometric fly ash, the influence of lime dust content on compressive strength of fly ash-cement paste within less than 6% lime dust is not obvious. But When lime dust content is 9%, the compression strength of fly ash-cement paste increases by 20.0% around.

Hydration Performance and Pore Structure of Fly Ash-Cement Pastes

2012 ◽  
Vol 204-208 ◽  
pp. 3867-3871 ◽  
Author(s):  
Xiang Li ◽  
Yun Dong ◽  
Hua Quan Yang
Keyword(s):  
Fly Ash ◽  
Pore Structure ◽  
Pore Solution ◽  
Ex Situ ◽  
Replacement Ratio ◽  
Cement Pastes ◽  
Binder Ratio ◽  
Very High ◽  
Reaction Degree ◽  
Curing Age

The hydration performance and pore structure of fly ash-cement (FC) pastes were investigated by means of XRD, TG, ex-situ leaching (ESL) and MIP. The results reveal that the influence of curing age to the kinds of hydration products of FC pastes is unconspicuous. As the content of fly ash increase, the Ca(OH)2 content decrease gradually. However, the content of Ca(OH)2 left in every paste is almost constant after 28d, regardless of the replacement ratio of fly ash and water-binder ratio. The decline of alkalinity of pore solution is not endless, even though the contents of fly ash in FC pastes is very high(65%).The incorporation of fly ash in proper ratios could increase the ratio of harmless pores and improve the microstructure of the FC pastes. Ca(OH)2 was not consumed heavily or exhausted when cementitious material was hydrated due to the low reaction degree of fly ash.

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