Pore Structure Development in Portland/Fly Ash Blends

1986 ◽  
Vol 85 ◽  
Author(s):  
David J. Cook ◽  
Huu T. Cao ◽  
Everett P. Coan
Keyword(s):  
Fly Ash ◽  
Pore Structure ◽  
Mercury Porosimetry ◽  
Chemical Properties ◽  
Blended Cement ◽  
Total Porosity ◽  
Structure Development ◽  
Cement Pastes ◽  
Diffusion Parameters ◽  
One Year

ABSTRACTPore structure development in portland/fly ash blends was investigated using mercury porosimetry and methanol exchange techniques. The progress of hydration was monitored using compressive strength tests. The specimens were made using four water-cement ratios and were hydrated over a one-year period in lime-saturated water. Mercury porosimetry results indicated that the blended cement pastes generally had higher total porosity than plain cement pastes. The major contribution to this increase in porosity was in the form of smaller pore sizes. With reactive fly ash at 20% replacement, the pore structure of mature paste consists mainly of pores nominally smaller than 0.05 μm in diameter. Diffusion parameters obtained from the methanol exchange results were found to be inversely related to the volume of large pores (nominally <0.05 μm) and also to the volume of small pores (nominally <0.05 μm). The effects of the physical and chemical properties of cements and fly ashes on pore structure development are discussed.

Pore Structure Development in Portland Cement/Fly Ash Blends

1986 ◽  
Vol 86 ◽  
Author(s):  
David J. Cook ◽  
Huu T. Cao ◽  
Everett P. Coan
Keyword(s):  
Fly Ash ◽  
Portland Cement ◽  
Pore Structure ◽  
Mercury Porosimetry ◽  
Chemical Properties ◽  
Blended Cement ◽  
Total Porosity ◽  
Structure Development ◽  
Cement Pastes ◽  
Diffusion Parameters

ABSTRACTPore structure development in portland cement/fly ash blends was investigated using mercury porosimetry and methanol exchange techniques. The progress of hydration was monitored using compressive strength tests. The specimens were made using four water-cement ratios and were hydrated over a one-year period in lime-saturated water. Mercury porosimetry results indicated that the blended cement pastes generally had higher total porosity than plain cement pastes. The major contribution to this increase in porosity was in the form of smaller pore sizes. With reactive fly ash at 20% replacement, the pore structure of mature paste consists mainly of pores nominally smaller than 0.05 μm in diameter. Diffusion parameters obtained from the methanol exchange results were found to be inversely related to the volume of large pores (nominally >0.05 μm) and also to the volume of small pores (nominally <0.05 μm). The effects of the physical and chemical properties of cements and fly ashes on pore structure development are discussed.

Some Difficulties in the Assessment of Pore-Structure of High Performance Blended Cement Pastes

1984 ◽  
Vol 42 ◽  
Author(s):  
Bryan K. Marsh ◽  
Robert L. Day
Keyword(s):  
Pore Structure ◽  
High Performance ◽  
Mercury Porosimetry ◽  
Blended Cement ◽  
High Strength ◽  
Pozzolanic Reaction ◽  
Partial Replacement ◽  
Microstructural Characteristics ◽  
Cement Pastes ◽  
Correct Analysis

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.

Relationships Between Permeability, Porosity, Diffusion And Microstructure Of Cement Pastes, Mortar, And Concrete At Different Temperatures

1988 ◽  
Vol 137 ◽  
Author(s):  
Della M. Roy
Keyword(s):  
Pore Structure ◽  
Elevated Temperatures ◽  
Mercury Porosimetry ◽  
Blended Cement ◽  
Ionic Species ◽  
Chloride Diffusion ◽  
Concrete Durability ◽  
Chloride Permeability ◽  
Cement Pastes ◽  
Blended Cements

AbstractPermeabilities to water and diffusion of ionic species in cementitious grouts, pastes and mortars are important keys to concrete durability. Investigations have been made of numerous materials containing portland and blended cements, and those with fine-grained filler, at room temperature and after prolonged curing at several elevated temperatures up to 90°C. These constitute part of studies of fundamental material relationships performed in order to address the question of long-term durability. In general, the permeabilities of the materials have been found to be low [many <10−8 Darcy (10−13 m·s−1)] after curing for 28 days or longer at temperatures up to 60°C. The results obtained at 90°C are somewhat more complex. In some sets of studies of blended cement pastes with w/c varying from 0.30 to 0.60 and cured at temperatures up to 90°C the more open-pore structure (at the elevated temperature and higher w/c) as evident from SEM microstructural studies as well as mercury porosimetry are generally correlated also with a higher permeability to liquid. The degree of bonding and permeability evident in paste or mortar/rock interfacial studies present somewhat more conflicting results. The bond strength (tensile mode) has been shown to be improved in some materials with increased temperature. The results of permeability studies of paste/rock couples show examples with similar low permeabilities, and some with increased permeability with temperature.Ionic diffusion studies also bring important bearing to understanding the effect of pore structure. The best interrelationships between chloride diffusion and pore structure appear to relate diffusion rate to median pore size. Similar results were found with “chloride permeability” test.

Pore structure characterization of cement pastes blended with high-volume fly-ash

2012 ◽  
Vol 42 (1) ◽  
pp. 194-204 ◽  
Author(s):  
Qiang Zeng ◽  
Kefei Li ◽  
Teddy Fen-chong ◽  
Patrick Dangla
Keyword(s):  
Fly Ash ◽  
Pore Structure ◽  
High Volume ◽  
Structure Characterization ◽  
Cement Pastes ◽  
High Volume Fly Ash

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

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.

Mechanical Properties of Mortars Prepared by Alkali Activated Fly Ash Coming from Different Production Batches

2015 ◽  
Vol 244 ◽  
pp. 140-145 ◽  
Author(s):  
Matej Špak ◽  
Pavel Raschman
Keyword(s):  
Mechanical Properties ◽  
Fly Ash ◽  
Construction Materials ◽  
Chemical Properties ◽  
Raw Material ◽  
Fly Ashes ◽  
Coal Burning ◽  
Alkali Solutions ◽  
One Year ◽  
Alkali Activated

Fly ash is a well utilizable secondary raw material for the production of alkali activated construction materials. It is a significant alumina-silicates source suitable for the chemical reaction resulting in hardened composites. Physical and chemical properties of fly ashes as a co-product of coal burning mainly depend on characteristics of coal, burning temperature and combustion conditions. High variability of the properties of fly ash causes an uncertainty in the properties of alkali activated mortars. Time behaviour of the composition of the fly ash produced in a heating plant located in Košice, Slovakia as well as leaching behaviour of both alumina and silica from particular batches during one-year period was documented. Leaching tests were carried out using the distilled water and alkali solutions with three different concentrations. Both compressive and tensile strengths of alkali activated mortars were measured, and the correlation between the mechanical properties of hardened mortars and the chemical composition of fly ashes as well as their leaching characteristics was investigated.

Sign in / Sign up

Export Citation Format

Share Document