Effect of Environmental Exposure on the Pore Structure and Transport Properties of Carbon Nanotube-Modified Mortars

Τhe present study investigates the pore structure and transport properties of carbon nanotube-modified cementitious mortars after exposure to freeze-thaw cycles and immersion to sulfate ion solution (sulfate attack) and compares them to those of un-exposed mortars. The effect of parameters related to carbon nanotube content (within the range of 0.2–0.8 wt.%) and type of dispersant (superplasticizer/surfactant) are investigated. It is found that carbon nanotube inclusion results, overall, in a significant drop of the total porosity before exposure. Results demonstrate that environmental exposure leads to a reduction of the fraction of small diameter pores and a respective increase in capillary porosity for both dispersive agents compared to un-exposed specimens. Diffusion coefficients of nano-modified specimens are lower compared to those of un-modified mortars, both before exposure and after sulfate attack. In the case of freeze-thaw cycling, the diffusion coefficients were found to be higher in carbon nanotube-modified mortars when surfactants were used as dispersants, although with improved gas permeability values.

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The influence of type of cement on the degradation of microstructure and transport properties of cement mortars exposed to frost induced damage

MATEC Web of Conferences ◽

10.1051/matecconf/201817401014 ◽

2018 ◽

Vol 174 ◽

pp. 01014

Author(s):

Alicja Wieczorek ◽

Marcin Koniorczyk

Keyword(s):

Absorption Coefficient ◽

Pore Structure ◽

Water Absorption ◽

Transport Properties ◽

Cement Mortar ◽

Gas Permeability ◽

Water Absorption Coefficient ◽

Freeze Thaw ◽

Cement Mortars ◽

Small Pore

The purpose of the study is to understand how the cyclic water freezing (0, 25, 50, 75, 100 and 150 freeze-thaw cycles) impacts microstructure and transport properties of cement-based materials. Tests were conducted on cement mortars with different water/cement ratios (w/c=0.45 and 0.40) and on two types of cement (CEM I and CEM III) without air-entraining admixtures. The changes of pore size distribution and open porosity were investigated by means of mercury intrusion porosimetry. Additionally, the relationship between intrinsic permeability and the water absorption coefficient of cement mortar samples was analysed. The water absorption coefficient and gas permeability were determined using capillary absorption test and the modified RILEMCembureau method. The evolution of transport coefficients with growing number of freeze-thaw cycles were determined on the same sample. It was also established that change of pore structure (a decrease of small pore volume <100nm and increase of larger pores >100nm) induces an increase of water transport parameters such as permeability and water absorption coefficient. The higher gas permeability corresponds to the higher internal damage. In particular, it is associated with the change of cement mortar microstructure, which indicates damage of narrow channels in the pore structure of cement mortars.

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The transport properties of cement mortars subjected to freeze-thaw cycles

E3S Web of Conferences ◽

10.1051/e3sconf/20184900128 ◽

2018 ◽

Vol 49 ◽

pp. 00128

Author(s):

Alicja Wieczorek ◽

Marcin Koniorczyk ◽

Dalia Bednarska ◽

Kalina Grabowska

Keyword(s):

Absorption Coefficient ◽

Water Absorption ◽

Transport Properties ◽

Positive Impact ◽

Gas Permeability ◽

Cement Matrix ◽

Capillary Absorption ◽

Water Absorption Coefficient ◽

Freeze Thaw ◽

Cement Mortars

The parameters characterizing the microstructure of cementbased materials, such as porosity or permeability, determine not only durability, but also risk of degradation of the cement matrix due to an aggressive environment. The report presents results of a research on transport properties of cement mortars subjected to cyclic water freezing. Mortars prepared on the basis of two different cements were the object of the research: Portland cement CEM I 42.5R and Portland blast-furnace slag cement CEM III/A 42.5N LH/HSR/NA, with two water-cement ratio (w/c=0.45 and 0.40). The experimental study was carried out in order to determine the relationship between intrinsic permeability and the water absorption coefficient in relation to the number of freeze-thaw cycles. The evolution of transport coefficients was determined using a capillary absorption test and the modified RILEM-Cembureau method. It was established that the degradation processes induced an increase of transport properties. Moreover, the microcracks had a more significant influence on permeability and lesser influence on the water absorption coefficient. The gas permeability of damaged mortar changed very significantly, an increase with several orders of magnitude could be noticed. Moreover, the positive impact of CEM III on ice-induced degradation was also visible.

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Transport properties of porous γ-alumina from diffusion in liquids and gases

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19881217 ◽

1988 ◽

Vol 53 (6) ◽

pp. 1217-1228

Author(s):

Petr Uchytil ◽

Petr Schneider

Keyword(s):

Liquid Phase ◽

Pore Structure ◽

Transport Properties ◽

Gas Diffusion ◽

Diffusion In Liquids

Transport characteristics of four porous samples with bidisperse or broad monodisperse pore structure were determined by combination of diffusion and permeation measurements with simple gases and compared with results obtained from diffusion of toluene or α,α,α-trifluorotoluene in cyclohexane in liquid phase. From comparison of both types of results it followed that all pores are decisive for the rate of diffusional transport in liquids, whereas only the wide transport pores are significant in gas diffusion.

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Freeze–Thaw Resistance and Air-Void Analysis of Concrete with Recycled Glass–Pozzolan Using X-ray Micro-Tomography

Materials ◽

10.3390/ma14010154 ◽

2020 ◽

Vol 14 (1) ◽

pp. 154

Author(s):

Marija Krstic ◽

Julio F. Davalos ◽

Emanuele Rossi ◽

Stefan C. Figueiredo ◽

Oguzhan Copuroglu

Keyword(s):

Fly Ash ◽

Pore Structure ◽

The United States ◽

Adsorption Method ◽

X Ray ◽

Freeze Thaw ◽

Void System ◽

Spatial Parameters ◽

Micro Tomography ◽

Air Void

Recent studies have shown promising potential for using Glass Pozzolan (GP) as an alternative supplementary cementitious material (SCM) due to the scarcity of fly ash and slag in the United States. However, comprehensive studies on the freeze–thaw (FT) resistance and air void system of mixtures containing GP are lacking. Therefore, this study aimed to evaluate GP’s effect on FT resistance and characterize mixtures with different GP contents, both macro- and microscopically. In this study, six concrete mixes were considered: Three mixes with 20%, 30% and 40% GP as cement replacements and two other comparable mixes with 30% fly ash and 40% slag, as well as a mix with 100% Ordinary Portland cement (OPC) as a reference. Concrete samples were prepared, cured and tested according to the ASTM standards for accelerated FT resistance for 1000 cycles and corresponding dynamic modulus of elasticity (Ed). All the samples showed minimal deterioration and scaling and high F/T resistance with a durability factor of over 90%. The relationships among FT resistance parameters, air-pressured method measurements of fresh concretes and air void analysis parameters of hardened concretes were examined in this study. X-ray micro-tomography (micro-CT scan) was used to evaluate micro-cracks development after 1000 freeze–thaw cycles and to determine spatial parameters of air voids in the concretes. Pore structure properties obtained from mercury intrusion porosimetry (MIP) and N2 adsorption method showed refined pore structure for higher cement replacement with GP, indicating more gel formation (C-S-H) which was verified by thermogravimetric analysis (TGA).

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