Improvement of Early-Age Strength of High-Volume Siliceous Fly Ash Concrete with Nanosilica - A Review

2018 ◽  
Vol 7 (1) ◽  
pp. 20180065 ◽  
Author(s):  
Lincy Varghese ◽  
V. V. L. Kanta Rao ◽  
Lakshmy Parameswaran
Keyword(s):  
Fly Ash ◽  
High Volume ◽  
Early Age ◽  
Fly Ash Concrete

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

Nanosilica Activated High Volume Fly Ash Concrete: Effects on Selected Properties

2016 ◽  
Vol 722 ◽  
pp. 157-162 ◽  
Author(s):  
Martin Labaj ◽  
Rudolf Hela ◽  
Iveta Hájková
Keyword(s):  
Fly Ash ◽  
Raw Materials ◽  
Water Pressure ◽  
Construction Material ◽  
High Volume ◽  
Strength Development ◽  
Early Age ◽  
Fly Ash Concrete ◽  
High Volume Fly Ash ◽  
Static And Dynamic Moduli

By volume, there is no other material used as much as concrete. Its mechanical properties, durability and favorable price makes concrete the perfect construction material. In last few decades, we are seeing a growing trend of partial Portland cement’s replacement with secondary raw materials, most commonly with fly ash. So-called high volume fly ash (HVFA) concretes usually contains over 50% of it. While HVFA concrete’s long-term properties and price are improved over the classical one, its early age properties are often affected negatively. Here, a highly reactive pozzolans enters the scene. Materials like microsilica and metakaolin are known to accelerate concrete’s strength development and improve early age characteristics. In this paper, nanosilica is used for this purpose. These SiO2 nanoparticles possesses a much higher surface area and thus reactivity. Three mixtures with 0, 40 a 60% portland cement’s replacement with fly ash were prepared and tested with and without addition of small amount of nanosilica. Effects on compressive strength, static and dynamic moduli of elasticity and resistivity against water pressure were observed. Results clearly demonstrates that even with dosage in the range of tenths of percent, nanosilica can significantly improve concrete’s properties.

scholarly journals Early-age Properties of High-volume Fly Ash Concrete Mixes for Pavement: Volume 2

2021 ◽  
Author(s):  
Aniruddha Baral ◽  
◽  
Jeffery Roesler ◽  
Junryu Fu ◽  
◽  
...  
Keyword(s):  
Fly Ash ◽  
Setting Time ◽  
High Volume ◽  
Early Age ◽  
X Ray ◽  
Fly Ash Concrete ◽  
Setting Times ◽  
Chemical Admixtures ◽  
High Volume Fly Ash ◽  
Foam Index

High-volume fly ash concrete (HVFAC) is more cost-efficient, sustainable, and durable than conventional concrete. This report presents a state-of-the-art review of HVFAC properties and different fly ash characterization methods. The main challenges identified for HVFAC for pavements are its early-age properties such as air entrainment, setting time, and strength gain, which are the focus of this research. Five fly ash sources in Illinois have been repeatedly characterized through x-ray diffraction, x-ray fluorescence, and laser diffraction over time. The fly ash oxide compositions from the same source but different quarterly samples were overall consistent with most variations observed in SO3 and MgO content. The minerals present in various fly ash sources were similar over multiple quarters, with the mineral content varying. The types of carbon present in the fly ash were also characterized through x-ray photoelectron spectroscopy, loss on ignition, and foam index tests. A new computer vision–based digital foam index test was developed to automatically capture and quantify a video of the foam layer for better operator and laboratory reliability. The heat of hydration and setting times of HVFAC mixes for different cement and fly ash sources as well as chemical admixtures were investigated using an isothermal calorimeter. Class C HVFAC mixes had a higher sulfate imbalance than Class F mixes. The addition of chemical admixtures (both PCE- and lignosulfonate-based) delayed the hydration, with the delay higher for the PCE-based admixture. Both micro- and nano-limestone replacement were successful in accelerating the setting times, with nano-limestone being more effective than micro-limestone. A field test section constructed of HVFAC showed the feasibility and importance of using the noncontact ultrasound device to measure the final setting time as well as determine the saw-cutting time. Moreover, field implementation of the maturity method based on wireless thermal sensors demonstrated its viability for early opening strength, and only a few sensors with pavement depth are needed to estimate the field maturity.

scholarly journals A Review on Early Age and Long-term Compressive Strength of High-volume Fly Ash Concrete

2018 ◽  
Vol 207 ◽  
pp. 01004
Author(s):  
Mu Li
Keyword(s):  
Compressive Strength ◽  
Fly Ash ◽  
High Volume ◽  
Partial Replacement ◽  
Early Age ◽  
Fly Ash Concrete ◽  
Power Stations ◽  
High Volume Fly Ash ◽  
Curing Age

Fly ash is a by-product of the combustion of the coal-fired electric power stations, and disposal of fly ash has been one of the environmental challenges. Much of the studies have been focused on the mechanical property of fly ash concrete. It is no doubt that the use of high-volume fly ash as a partial replacement of cement is also one of the effect way to utilize fly ash. It is known that the compressive strength of fly ash concrete is lower than that of ordinary concrete at early age, especially for high-volume fly ash concrete. It is urgent for engineers to consider the compressive strength of high-volume fly ash concrete at different curing age. In this review, the compressive strength of high-volume fly ash concrete in various literature was reported and then analyzed. Furthermore, the proposal of the utilization of high-volume fly ash concrete is provided.

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