Abstracts

Index

  1. Adsorbing polymers and viscosity of cement pastes;
  2. Obtaining rheological parameters from flow test — Analytical, computational and lab test approach;
  3. The influence of different drying techniques on the water sorption properties of cement-based materials;
  4. Investigation of concrete exposed to dual sulfate attack;
  5. Effect of superabsorbent polymers (SAPs) on rheological properties of fresh cement-based mortars — Development of yield stress and plastic viscosity over time;
  6. Study on the hydration and microstructure of Portland cement containing diethanol-isopropanolamine;
  7. Degradation modeling of concrete submitted to biogenic acid attack;

  8. Numerical modelling of moisture transfers with hysteresis within cementitious materials: Verification and investigation of the effects of repeated wetting–drying boundary conditions.



Adsorbing polymers and viscosity of cement pastes

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.



Obtaining rheological parameters from flow test — Analytical, computational and lab test approach

 

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.



The influence of different drying techniques on the water sorption properties of cement-based materials


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. 



Investigation of concrete exposed to dual sulfate attack

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




Effect of superabsorbent polymers (SAPs) on rheological properties of fresh cement-based mortars — Development of yield stress and plastic viscosity over time

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 




Study on the hydration and microstructure of Portland cement containing diethanol-isopropanolamine

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)