DURABILITY AND POZZOLANIC REACTION OF FLY ASH CONCRETE EXPOSED TO VARIOUS OUTSIDE ENVIRONMENTS

2018 ◽  
Vol 5 (2) ◽  
Author(s):  
Yoshitaka Ishikawa
Keyword(s):  
Fly Ash ◽  
Pore Structure ◽  
Pozzolanic Reaction ◽  
Fly Ash Concrete ◽  
Exposure Testing ◽  
Exposure Conditions

In this study, outside exposure tests of fly ash concrete were started in 2009 at various places in Japan in order to assess the effect of the differences of the exposure environment on the variation of long term durability of fly ash concrete and the degree of pozzolanic reaction of fly ash. This paper shows the results of durability monitoring over seven years from the start of exposure testing and the degree of pozzolanic reaction after seven years. The durability of fly ash concrete is improved due to pore structure complicated by the pozzolanic reaction. The degree of pozzolanic reaction of fly ash in concrete exposed under any conditions ends up being the same when enough time has elapsed, such as seven years, regardless of differences in exposure conditions.

Development of the HVFAC Modulus of Elasticity

2019 ◽  
Vol 296 ◽  
pp. 155-160
Author(s):  
Martin Ťažký ◽  
Lucia Osuská ◽  
Rudolf Hela
Keyword(s):  
Fly Ash ◽  
High Volume ◽  
Pozzolanic Reaction ◽  
Strength Parameters ◽  
Fly Ash Concrete ◽  
Static Modulus ◽  
High Volume Fly Ash ◽  
Active Admixture ◽  
Term Monitoring

Concretes with high fly ash content are within a unified world nomenclature often referred to as HVFAC, resp. high volume fly ash concrete. These concretes are characterized by the percentage of fly ash as an active admixture relative to a cement dose of at least in a ratio of 1:1. The use of these concretes falls into the field of construction with the necessary reduction in the development of hydration heat. In the experiment, long-term monitoring of the development of important mechanical parameters, namely the static modulus of compressive elasticity and compressive strength, was performed. Both monitored parameters play a very important role in the design of buildings, for which construction is HVFAC often used. These parameters were monitored within the carried out research until the time of 360 days. The results of the experiment give an overview of the pozzolanic reaction progress over the in the long-term time horizon and its impact on the concrete parameters monitored. The results clearly show that even after 360 days the development of the strength parameters of these concretes is not stopped.

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.

Long term mechanical performance of nano-engineered high volume fly ash concrete

2021 ◽  
pp. 103168
Author(s):  
Charith Herath ◽  
Chamila Gunasekara ◽  
David W. Law ◽  
Sujeeva Setunge
Keyword(s):  
Fly Ash ◽  
Mechanical Performance ◽  
High Volume ◽  
Fly Ash Concrete ◽  
High Volume Fly Ash

scholarly journals Effect of Nanosilica on Impermeability of Cement-Fly Ash System

2020 ◽  
Vol 2020 ◽  
pp. 1-13 ◽  
Author(s):  
Huaqing Liu ◽  
Yan Zhang ◽  
Ruiming Tong ◽  
Zhaoqing Zhu ◽  
Yang Lv
Keyword(s):  
Fractal Dimension ◽  
Fly Ash ◽  
Bond Strength ◽  
Pore Structure ◽  
Calcium Hydroxide ◽  
Cement Hydration ◽  
Pozzolanic Reaction ◽  
Surface Protection ◽  
Durability Of Concrete

Surface protection has been accepted as an effective way to improve the durability of concrete. In this study, nanosilica (NS) was used to improve the impermeability of cement-fly ash system and this kind of material was expected to be applied as surface protection material (SPM) for concrete. Binders composed of 70% cement and 30% fly ash (FA) were designed and nanosilica (NS, 0–4% of the binder) was added. Pore structure of the paste samples was evaluated by MIP and the fractal dimension of the pore structure was also discussed. Hydrates were investigated by XRD, SEM, and TG; the microstructure of hydrates was analyzed with SEM-EDS. The results showed that in the C-FA-NS system, NS accelerated the whole hydration of the cement-FA system. Cement hydration was accelerated by adding NS, and probably, the pozzolanic reaction of FA was slightly hastened because NS not only consumed calcium hydroxide by the pozzolanic reaction to induce the cement hydration but also acted as nucleation seed to induce the formation of C-S-H gel. NS obviously refined the pore structure, increased the complexity of the pore structure, and improved the microstructure, thereby significantly improving the impermeability of the cement-FA system. This kind of materials would be expected to be used as SPM; the interface performance between SPM and matrix, such as shrinkage and bond strength, and how to cast it onto the surface of matrix should be carefully considered.

Fly-Ash Concretes of 50% of the Replacement Ratio to Reduce the Cracking in Concrete Structures

2013 ◽  
Vol 405-408 ◽  
pp. 2665-2670 ◽  
Author(s):  
Ming Jie Mao ◽  
Qiu Ning Yang ◽  
Wen Bo Zhang ◽  
Isamu Yoshitake
Keyword(s):  
Fly Ash ◽  
Concrete Structures ◽  
High Volume ◽  
Pozzolanic Reaction ◽  
Strength Development ◽  
Early Age ◽  
Replacement Ratio ◽  
Fly Ash Concrete ◽  
Massive Concrete ◽  
Normal Strength

Fly-ash concrete used in massive concrete structure has superior advantages to reduce hydration heat. On the other hand, the fly-ash concrete has negative property of low strength development at early age because pozzolanic reaction of fly-ash activates at mature age, such as after 28 days. To investigate these characteristics of fly-ash used in concrete, the present study discusses thermal cracking possibility of fly-ash concrete by using FE analysis software. The present study employs prediction formulae proposed by Zhang and Japanese design code in the simulations. The objects in this study are normal strength concrete mixed of fly-ash up to 50% of replacement ratio to cement. The comparative investigations show that temperature effect is more significant than strength development at early age. Based on the analytical study, high volume fly-ash concretes of 30-50% of the replacement ratio can be concluded as effective and useful materials to reduce the cracking possibility in massive concrete structures. Keywords-Fly-ash concrete; Early Age, Prediction Formulae for Strength; Thermal Stress Analysis

Research on Some Properties of Fly Ash Concrete with Nano-CaCO3 Middle Slurry

2009 ◽  
Vol 405-406 ◽  
pp. 186-190 ◽  
Author(s):  
Kuang Liang Qian ◽  
Tao Meng ◽  
Xiao Qian Qian ◽  
Shu Lin Zhan
Keyword(s):  
Fly Ash ◽  
Chloride Ion ◽  
Test Results ◽  
Hydration Degree ◽  
Fly Ash Concrete

Some long-term properties such as anti-carbonation properties, shrinkage, penetrability of chloride ion of fly ash concrete with nano-CaCO3 middle slurry were studied. Test results showed that the properties of anti-carbonation and impenetrability for chloride of fly ash concrete increased by adding nano-CaCO3 middle slurry because the tiny hole was filled by nano-CaCO3 and the density of concrete increased. But at the same time, the shrinkage of fly ash concrete with and without nano-CaCO3 was the same. Results of SEM also implied the hydration degree of fly ash could be increased by nano-CaCO3.

scholarly journals Effects of Mixing and Curing Temperature on the Strength Development and Pore Structure of Fly Ash Blended Mass Concrete

2017 ◽  
Vol 2017 ◽  
pp. 1-11 ◽  
Author(s):  
Ki-Bong Park ◽  
Takafumi Noguchi
Keyword(s):  
Fly Ash ◽  
Portland Cement ◽  
Pore Structure ◽  
Weather Conditions ◽  
Strength Loss ◽  
Curing Temperature ◽  
Strength Development ◽  
Mass Concrete ◽  
Term Strength

The aim of this work is to know clearly the effects of temperature in response to curing condition, hydration heat, and outside weather conditions on the strength development of high-performance concrete. The concrete walls were designed using three different sizes and three different types of concrete. The experiments were conducted under typical summer and winter weather conditions. Temperature histories at different locations in the walls were recorded and the strength developments of concrete at those locations were measured. The main factors investigated that influence the strength developments of the obtained samples were the bound water contents, the hydration products, and the pore structure. Testing results indicated that the elevated summer temperatures did not affect the early-age strength gain of concrete made using ordinary Portland cement. Strength development was significantly increased at early ages in concrete made using belite-rich Portland cement or with the addition of fly ash. The elevated temperatures resulted in a long-term strength loss in both belite-rich and fly ash containing concrete. The long-term strength loss was caused by a reduction in the degree of hydration and an increase in the total porosity and amount of smaller pores in the material.

scholarly journals Long-term Durability Characteristics of Fly ash Concrete Containing Lightly Burnt MgO Powder

2013 ◽  
Vol 33 (3) ◽  
pp. 909-916
Author(s):  
Bong-Seok Jang ◽  
Seul-Woo Choi ◽  
Kwang-Myong Lee
Keyword(s):  
Fly Ash ◽  
Fly Ash Concrete
Sign in / Sign up

Export Citation Format

Share Document