Index
- Adsorbing polymers and viscosity of cement pastes;
- Obtaining rheological parameters from flow test — Analytical, computational and lab test approach;
- The influence of different drying techniques on
the water sorption properties of cement-based materials;
- Investigation of concrete exposed to dual sulfate
attack;
- Effect of superabsorbent polymers (SAPs) on rheological properties of fresh
cement-based mortars — Development of yield stress and plastic viscosity over
time;
- Study on the hydration and microstructure of Portland
cement containing diethanol-isopropanolamine;
-
Degradation modeling of
concrete submitted to biogenic acid attack;
-
Numerical modelling of
moisture transfers with hysteresis within cementitious materials: Verification
and investigation of the effects of repeated wetting–drying boundary conditions.
Julie Hot, Hela Bessaies-Bey, Coralie Brumaud, Myriam Duc, Charlène Castella, Nicolas Roussel,
Cement and Concrete Research; Volume 63, September
2014, Pages 12–19
Abstract
In this
paper, we study the physical mechanisms at the origin of a decrease in
viscosity of concentrated cement pastes containing adsorbing polymers. We
suggest from our results, similar to other authors, that plasticizers are able
to decrease viscous dissipation by modifying the flocculation state of the
system, which, in turn, impacts the way shear localizes. Our experimental
results suggest that shear concentrates in fluid layers, the thickness of which
scales with the surface-to-surface separating distance between cement grains
imposed by the adsorbed polymer conformation. These effects being identical for
all polymers, we suggest that the residual difference between polymers in the
final macroscopic viscosity comes from the more or less pronounced increase in
the local viscosity of the interstitial fluid between neighboring particles.
This increase could either be correlated to the concentration of non-adsorbed
coils in the interstitial fluid or to the local concentration of adsorbed coil
side chains.
Keywords: Admixture, Adsorption, Rheology, Dispersion, Viscosity
Corresponding
author at: IFSTTAR, 14/20 Bd Newton, Cité Descartes, Champs-sur-Marne, 77447
Marne-la-Vallée cedex 2, France.
Copyright ©
2014 Elsevier Ltd. All rights reserved.
Annika Gram,
Johan Silfwerbrand, Björn Lagerblad
Cement and Concrete Research; Volume 63, September
2014, Pages 29–34
Abstract
In the mix
design process of cementitious suspensions, an adequate rheology of the cement
paste is crucial. A novel rheological field test device for cementitious fluids
is presented here and investigated theoretically, by computer simulation and by
lab tests. A simple flow stoppage test with a timed spread passage point
provides accurate rheological parameters according to the Bingham material
model. Values for yield stress and plastic viscosity are obtained for a test specimen
of no more than 19.75 · 10− 6 m3 of fluid. This volume is equivalent to
19.75 g of water at room temperature. Such a small volume allows reliable
tests even for small amounts of fillers. Promising results show that both yield
stress and plastic viscosity can be determined by this simple test. This novel
rheological test method also enables the correlation of different rheological
equipment used by different laboratories.
Keywords: Simulation; Cement paste; Workability Bingham material model; Rheology; Modeling, Mortar
Corresponding author at: Annika Gram Swedish Cement
and Concrete Research Institute (CBI), Drottning Kristinas väg 26, SE-100 44
Stockholm, Sweden
Copyright ©
2014 Elsevier Ltd. All rights reserved.
D. Snoeck, L.F. Velasco, A. Mignon, S. Van Vlierberghe, P. Dubruel, P. Lodewyckx, N. De Belie
Cement and Concrete Research, Volume 64, October 2014, Pages 54–62
Abstract
Dynamic water vapor sorption (DVS) may be used to
characterize the pore structure of cementitious materials, but the technique is
difficult to interpret as the microstructure is very sensitive to drying and
rehydration due to humidity exposure. The removal of interlayer water or
chemically bound water can cause microstructural shrinkage. As all drying
techniques more or less dehydrate C–S–H and ettringite, they cause a restructuration
of the C-S-H.
In the present paper, DVS measurements were performed
to characterize the changes induced by different drying techniques in the
textural and sorption properties of the material, while thermogravimetric
analysis was used to elucidate carbonation.
The ideal drying technique, which can preserve the
microstructure and can remove only the non-bound water, does unfortunately not
exist. All drying techniques separately affect the microstructure to some
extent. However, these changes are minimized when using vacuum-drying and the
solvent-exchange-method with isopropanol as drying techniques.
Keywords: Drying, Calcium–Silicate–Hydrate (C–S–H), Microstructure,
Adsorption (water sorption), Carbonation.
M.L. Nehdi, A.R. Suleiman, A.M. Soliman
Cement and Concrete Research, Volume 64, October 2014, Pages 42–53
Abstract
Durability of concrete exposed to sulfates has
primarily been studied on specimens fully-submerged in sulfate solutions.
However, field experience shows that concrete exposed to sulfates can suffer
from surface scaling above ground level due to physical attack. This damage has
often been ignored and even confused with chemical sulfate attack. In this
study, concrete partially-immersed in sulfate solutions and exposed to cyclic
temperature and relative humidity was explored. Results show that concrete can
experience dual sulfate attack. The lower immersed portion can suffer from
chemical sulfate attack, while the upper portion can be vulnerable to physical
attack. Lowering the water-to-binder ratio and moist-curing reduced surface
scaling above the solution level, since the volume of pores was decreased.
Although partial replacement of cement with pozzolans also decreased the pore
volume, surface scaling increased due to increased proportion of small diameter
pores and associated growth of capillary suction and surface area for
evaporation.
Keywords: Sulfate attack; Pore size distribution; Curing; Pozzolan; Mechanical properties
Viktor
Mechtcherine, , Egor Secrieru, Christof Schröfl
Cement and Concrete Research, Volume 67, January
2015, Pages 52–65
Abstract
Superabsorbent
polymers (SAPs) are a new, promising, multipurpose chemical admixture for
concrete. This article addresses the rheological behaviour of fresh,
cement-based mortars modified with SAP. Two types of SAP with differing water
absorption and desorption kinetics were used. Additionally, for one the grading
was varied. Three reference mortars were investigated. The rheological
properties of these fresh mortars were tested for 90 min by continuous flow
rheometry. It was found that the distinct kinetics of water uptake inherent in
the SAP samples, as governed by their particular chemical structures, is the
major factor that governs the rheological properties of fresh mortar.
Furthermore, the grading of SAP distinctly affects the development of yield
stress and plastic viscosity over time. The particular effects of specific SAP
addition on the rheological characteristics of a mortar depend on the water-to-binder
ratio, the dosage of superplasticizer, and the dosage of silica fume, if
present.
Keywords: Fresh
concrete; Rheology; Admixture; Polymer; Mortar
Suhua Ma,
Weifeng Li, Shenbiao Zhang, Yueyang Hu, Xiaodong Shen
Cement and Concrete Research, Volume
67, January 2015, Pages 122–130
Abstract
Diethanol-isopropanolamine (DEIPA) is a tertiary alkanolamine used in the
formulation of cement grinding-aid additives and concrete early-strength
agents. In this research, isothermal calorimetry was used to study the
hydration kinetics of Portland cement with DEIPA. A combination of X-ray powder
diffraction (XRPD), scanning electron microscopy (SEM), differential scanning
calorimetry (DSC)–thermogravimetric (TG) analysis and micro-Raman spectroscopy
was used to investigate the phase development in the process of hydration.
Mercury intrusion porosimetry was used to study the pore size distribution and
porosity. The results indicate that DEIPA promotes the formation of ettringite
(AFt) and enhances the second hydration rate of the aluminate and ferrite
phases, the transformation of AFt into monosulfoaluminate (AFm) and the
formation of microcrystalline portlandite (CH) at early stages. At later
stages, DEIPA accelerates the hydration of alite and reduces the pore size and
porosity.
Keywords: DEIPA;
Hydration kinetics; Microstructure; Portland cement
Degradation modeling of
concrete submitted to biogenic acid attack
Haifeng Yuana, Patrick Danglaa, Patrice Chatellierc,
Thierry Chaussadentc
Cement and Concrete Research, Volume 70, April 2015, Pages 29–38
Abstract
Biodeterioration
of concrete, which is very common in sewer system, results in significant
structure degradation. The process can be described by the 3 following steps:
Concrete surface neutralization providing appropriate environment for sulfur
oxidizing bacteria (SOB) to grow, sulfuric acid (H2SO4) production by SOB on
concrete surface and chemical reaction between H2SO4 and cement hydration
products. A reactive transport model is proposed to simulate the whole
biodeterioration processes of concrete in contact with H2S gas and SOB. This
model aims at solving simultaneously transport and biochemistry/chemistry in
biofilm and concrete by a global coupled approach. To simulate the
neutralization process, the absorption of H2S gas, the dissolution of
portlandite (CH), the decalcification of calcium silicate hydrates (C–S–H) and
the precipitation of calcium sulfide (CaS) are considered. To obtain the amount
of biogenic acid, the production rate of H2SO4 by SOB is calculated via a set
of simplified models governed by pH. Coupling with the modeling of H2SO4
degradation process, the biodeterioration depth and the solid composition
evolution could be predicted. A laboratory experiment reported in literature is
simulated and the simulation results are compared with experimental results.
Keywords: Sewer pipe; Concrete (E); Organic acids (D); Corrosion
(C); Modeling (E)
Numerical modelling of
moisture transfers with hysteresis within cementitious materials: Verification
and investigation of the effects of repeated wetting–drying boundary conditions
Zhidong
Zhanga, Mickaël Thieryb, Véronique Baroghel-Bouny
Cement and Concrete Research, Volume 68, February 2015, Pages
10–23
Abstract
In natural
environment, the cover layer of reinforced concrete structures is affected by
periodic variations of external relative humidity (RH). However, most moisture
transport models in the literature only focus on drying of materials. In this
study, a method coupling a moisture transport model with any kind of hysteresis
modelling is presented. Two hysteresis models (conceptual and empirical) have
been implemented and compared. The scope of the study is limited to cyclic
variations of RH with no direct contact with liquid water during the wetting
steps. Experimental data verifications show that the conceptual approach yields
better results than the empirical one. Comparisons of non-hysteresis and
hysteresis modellings have been carried out for different cycle durations, RH
amplitudes and initial moisture states. All comparisons and investigations
enhance the necessity of considering hysteresis to quantify moisture transport
under repeated drying–wetting boundary conditions.
Keywords: Cementitious materials (E); Moisture transport (C);
Hysteresis (C); Drying–wetting cycles (A); Moisture penetration depth (B)
|
|
