Effects of Replacement Ratio and Fineness of GGBFS on the Hydration and Pozzolanic Reaction of High-Strength High-Volume GGBFS Blended Cement Pastes

AbstractPartial replacement of cement by fly-ash allows the production of concretes with high strength and low permeability. The correct analysis and prediction of engineering behaviour requires a knowledge of the development of pore-structure of these materials. However, a study of the relationships between engineering and microstructural characteristics has revealed problems in the accurate assessment of pore-structure.Porosities of plain and blended pastes were analysed by both helium pycnometry and mercury porosimetry. Pastes showing pozzolanic reaction gave values of helium porosity whidh were different from the mercury porosity (measured on the same sample); pastes showing no pozzolanic reaction gave equal values for mercury and helium porosity. Also, significant differences in porosity and pore-size distribution were found for identical specimens when prepared by different techniques, namely direct oven-drying and solventreplacement; these differences occurred whether there was pozzolanic reaction or not.It is suggested that as well as experimental difficulties, there may be fundamental differences in the way pore-structure develops in plain and blended cement pastes.

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High Volume Slag and Slag-Fly Ash Blended Cement Pastes Containing Nano Silica

Materials Science Forum ◽

10.4028/www.scientific.net/msf.967.205 ◽

2019 ◽

Vol 967 ◽

pp. 205-213

Author(s):

Faiz U.A. Shaikh ◽

Anwar Hosan

Keyword(s):

Compressive Strength ◽

Fly Ash ◽

Cement Paste ◽

Ordinary Portland Cement ◽

Blended Cement ◽

High Volume ◽

Ash Content ◽

Partial Replacement ◽

Nano Silica ◽

Cement Pastes

This paper presents the effect of nanosilica (NS) on compressive strength and microstructure of cement paste containing high volume slag and high volume slag-fly ash blend as partial replacement of ordinary Portland cement (OPC). Results show that high volume slag (HVS) cement paste containing 60% slag exhibited about 4% higher compressive strength than control cement paste, while the HVS cement paste containing 70% slag maintained the similar compressive strength to control cement paste. However, about 9% and 37% reduction in compressive strength in HVS cement pastes is observed due to use of 80% and 90% slag, respectively. The high volume slag-fly ash (HVSFA) cement pastes containing total slag and fly ash content of 60% exhibited about 5%-16% higher compressive strength than control cement paste. However, significant reduction in compressive strength is observed in higher slag-fly ash blends with increasing in fly ash contents. Results also show that the addition of 1-4% NS improves the compressive strength of HVS cement paste containing 70% slag by about 9-24%. However, at higher slag contents of 80% and 90% this improvement is even higher e.g. 11-29% and 17-41%, respectively. The NS addition also improves the compressive strength by about 1-59% and 5-21% in high volume slag-fly ash cement pastes containing 21% fly ash+49%slag and 24% fly ash+56%slag, respectively. The thermogravimetric analysis (TGA) results confirm the reduction of calcium hydroxide (CH) in HVS/HVSFA pastes containing NS indicating the formation of additional calcium silicate hydrate (CSH) gels in the system. By combining slag, fly ash and NS in high volumes e.g. 70-80%, the carbon footprint of cement paste is reduced by 66-76% while maintains the similar compressive strength of control cement paste. Keywords: high volume slag, nanosilica, compressive strength, TGA, high volume slag-fly ash blend, CO2 emission.

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

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.405-408.2665 ◽

2013 ◽

Vol 405-408 ◽

pp. 2665-2670 ◽

Cited By ~ 1

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

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Effects of flue gas desulphurization sludge on the pozzolanic reaction of reject-fly-ash-blended cement pastes

Cement and Concrete Research ◽

10.1016/j.cemconres.2004.02.027 ◽

2004 ◽

Vol 34 (10) ◽

pp. 1907-1918 ◽

Cited By ~ 37

Author(s):

C.S. Poon ◽

X.C. Qiao ◽

Z.S. Lin

Keyword(s):

Fly Ash ◽

Flue Gas ◽

Blended Cement ◽

Pozzolanic Reaction ◽

Cement Pastes ◽

Flue Gas Desulphurization

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Fire Resistance of Sewage Sludge Ash Blended Cement Pastes

Journal of Engineering ◽

10.1155/2013/361582 ◽

2013 ◽

Vol 2013 ◽

pp. 1-7 ◽

Cited By ~ 5

Author(s):

M. A. Tantawy ◽

A. M. El-Roudi ◽

Elham M. Abdalla ◽

M. A. Abdelzaher

Keyword(s):

Sewage Sludge ◽

Fire Resistance ◽

Calcium Silicate ◽

Blended Cement ◽

Total Porosity ◽

Pozzolanic Reaction ◽

Cement Matrix ◽

Cement Pastes ◽

Sewage Sludge Ash ◽

Sludge Ash

The aim of the present study is to investigate the hydration characteristics and the fire resistance of sewage sludge ash blended cement pastes by the determination of compressive strength, bulk density, and total porosity in addition to XRD and SEM techniques. Sewage sludge ash modifies the hydration of cement because of its pozzolanic reaction with portlandite favoring the formation of crosslinked fibrous calcium silicate of low Ca/Si ratio. Hence, it was concluded that thermal damage of cement pastes after the exposure to high treatment temperatures (i.e., crack formation and loss of mechanical properties) was effectively reduced with sewage sludge as content up to 20 wt% because of that the presence of crosslinked fibrous calcium silicate strengthens the cement matrix.

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Enhanced Metakaolin Reactivity in Blended Cement with Additional Calcium Hydroxide

Materials ◽

10.3390/ma15010367 ◽

2022 ◽

Vol 15 (1) ◽

pp. 367

Author(s):

Kira Weise ◽

Neven Ukrainczyk ◽

Aaron Duncan ◽

Eduardus Koenders

Keyword(s):

Calcium Hydroxide ◽

Blended Cement ◽

Initial Mixture ◽

Pozzolanic Reaction ◽

Replacement Ratio ◽

Pozzolanic Reactivity ◽

Thermogravimetric Data ◽

Binder Ratio ◽

Water To Binder Ratio ◽

Mass Balance Approach

This study aims to increase the pozzolanic reactivity of metakaolin (MK) in Portland cement (PC) blends by adding additional calcium hydroxide (CH_add) to the initial mixture. Cement paste samples were prepared with PC, MK and water with a water-to-binder ratio of 0.6. Cement replacement ratios were chosen from 5 to 40 wt.% MK. For higher replacement ratios, i.e., 20, 30 and 40 wt.% MK, CH_add was included in the mixture. CH_add-to-MK ratios of 0.1, 0.25 and 0.5 were investigated. Thermogravimetric analysis (TGA) was carried out to study the pozzolanic reactivity after 1, 7, 28 and 56 days of hydration. A modified mass balance approach was used to normalize thermogravimetric data and to calculate the calcium hydroxide (CH) consumption of samples with CH_add. Results showed that, without CH_add, a replacement ratio of 30 wt.% or higher results in the complete consumption of CH after 28 days at the latest. In these samples, the pozzolanic reaction of MK turned out to be restricted by the amount of CH available from the cement hydration. The increased amount of CH in the samples with CH_add resulted in an enhanced pozzolanic reaction of MK as confirmed by CH consumption measurements from TGA.

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Study on the pozzolanic reaction of clay brick powder in blended cement pastes

Construction and Building Materials ◽

10.1016/j.conbuildmat.2019.03.307 ◽

2019 ◽

Vol 213 ◽

pp. 209-215 ◽

Cited By ~ 12

Author(s):

Jiahu Shao ◽

Jianming Gao ◽

Yasong Zhao ◽

Xuemei Chen

Keyword(s):

Blended Cement ◽

Pozzolanic Reaction ◽

Clay Brick ◽

Cement Pastes ◽

Brick Powder

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Hydration and strength evolution of air-cured zeolite-rich tuffs and siltstone blended cement pastes at low water-to-binder ratio

Clay Minerals ◽

10.1180/claymin.2015.050.1.12 ◽

2015 ◽

Vol 50 (1) ◽

pp. 133-152 ◽

Cited By ~ 3

Author(s):

M.H. Cornejo ◽

J. Elsen ◽

C. Paredes ◽

H. Baykara

Keyword(s):

Compressive Strength ◽

Blended Cement ◽

Cementitious Materials ◽

Pozzolanic Reaction ◽

Supplementary Cementitious Materials ◽

Experimental Conditions ◽

Cement Pastes ◽

Carbonation Reaction ◽

Curing Conditions ◽

Strength Evolution

AbstractThis contribution is the second part of an in-depth study on the hydration and strength evolution of blended cement pastes at a water to binder (W/B) ratio of 0.3, cured by two different methods. The blended cement pastes showed significant hydration up to 7 days, when almost all of the hydration products had already formed; thereafter, carbonation played an important role up to, and possibly beyond, 91 days. Likewise, the hydration of alite (tricalcium silicate, Ca3SiO5, C3S) proceeded up to 14 days and then started to slow down. However, the hydration of belite (dicalcium silicate, Ca2SiO4, C2S) was affected most strongly, as it nearly ceased, under the air-curing conditions. During hydration, some of the blended cement pastes had a larger calcium hydroxide (CH) content than the unblended (plain) ones. The accelerating effects of the addition of supplementary cementitious materials (SCMs), the air-curing conditions and the low W/B ratio may explain these unusual results. Under these experimental conditions, the water incorporated into hydrates was about 50% of the total amount of water used during full hydration of the cement pastes. The pozzolanic reaction predominated during the early ages, but disappeared as time passed. In contrast, the carbonation reaction increased by consuming ∼45% of the total amount of CH produced after aging for 91 days. Only one blended cement paste reached the compressive strength of the plain cements. The blended cement pastes containing 5% of the zeolitic tuffs, Zeo1 or Zeo2, or 10% of the calcareous siltstone, Limo, developed the greatest compressive strength under the experimental conditions used in this study.

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