Reactions in the Setting of High Strength Cement Pastes

1984 ◽  
Vol 42 ◽  
Author(s):  
S. A. Rodger ◽  
W. Sinclair ◽  
G. W. Groves ◽  
S. A. Brooks ◽  
D. D. Double
Keyword(s):  
Isothermal Calorimetry ◽  
High Strength ◽  
Water Soluble ◽  
High Alumina ◽  
X Ray Diffraction ◽  
Water Soluble Polymer ◽  
Cement Pastes ◽  
Polymer Addition ◽  
Shear Mixing ◽  
Very High

AbstractMaterials of very high flexural strengths (> IOOMPa) can be made by high shear mixing of cement pastes with small amounts of water soluble polymer. Two such systems - high alumina cement/partially hydrolysed polyvinyl acetate and OPC/polyacrylamide - have been examined using a variety of techniques including isothermal calorimetry, infra-red spectroscopy and X-ray diffraction. In both systems the polymer addition appears to become cross-linked by ions released by the cement powder leading to an increase in stiffness of the material. In particular the reactions involved in the OPC system are analogous to those occurring in certain dental cements. The importance of removing excess water from the pastes is demonstrated.

The Microstructure of High Strength Cement Pastes

1984 ◽  
Vol 42 ◽  
Author(s):  
W. Sinclair ◽  
G. W. Groves
Keyword(s):  
High Strength ◽  
Water Soluble ◽  
Organic Polymer ◽  
High Alumina ◽  
Cement Pastes ◽  
Alumina Cement ◽  
High Alumina Cement ◽  
Transmission Electron ◽  
Fibrillar Morphology ◽  
Shear Mixing

AbstractThe microstructures of high strength pastes of OPC and high alumina cements prepared by the high shear mixing of a low water/cement ratio paste with water soluble polymers have been studied by transmission electron microscopy. In the case of high strength OPC, the usual hydration products are present, however, the CSH gel lacks the fibrillar morphology often observed in conventional cements. Pastes based on high alumina cement do not contain the normal crystalline calcium aluminate hydrates but a small quantity of gel containing the organic polymer forms a continuous network structure bonding clinker grains. Microanalysis of the polymer phase in high alumina cement revealed the presence of Ca and Al while Ca-rich interstitial gel material was found in OPC pastes.

The Flexural Strength and Fracture Toughness of a Normal and a High Strength Polymer Modified Portland Cement

1984 ◽  
Vol 42 ◽  
Author(s):  
N. B. Eden ◽  
J. E. Bailey
Keyword(s):  
Flexural Strength ◽  
Portland Cement ◽  
Interfacial Shear Strength ◽  
Fracture Behaviour ◽  
High Strength ◽  
Interfacial Shear ◽  
Water Soluble ◽  
Water Soluble Polymer ◽  
Cement Pastes ◽  
Cement Ratio

AbstractA model has been developed for the flexural strength of Portland cement pastes, based upon observed fracture behaviour of both normal and high strength pastes. Fibrillar or foil-like elements pull apart at a yield stress which is characteristic of the number of elements and interfacial shear strength. The former can be maximised by using a low water/cement ratio and the latter by inclusion of water-soluble polymer, followed by suitable drying. It is proposed that this is the mechanism by which high strength may be attained in Portland cement.

EM of a macro defect-free cement

1990 ◽  
Vol 48 (4) ◽  
pp. 1068-1069
Author(s):  
O. Popoola ◽  
W. M. Kriven ◽  
J.F. Young
Keyword(s):  
Detailed Examination ◽  
Particle Packing ◽  
Water Soluble ◽  
Cement Particle ◽  
Polymer Interfaces ◽  
Soluble Polymer ◽  
Water Soluble Polymer ◽  
Cement Pastes ◽  
Shear Mixing ◽  
Interparticle Friction

Engineering materials application of silicate or aluminate cements are limited because of their low strength and toughness. These poor properties can be easily attributed to the inherent macro and micro porosity of cement pastes. However in the last decade it has been found that by the addition of a water soluble polymer, high shear mixing and the by application of modest pressure during processing, cement with mechanical properties comparable to most ceramics can be obtained. The water soluble polymer, apart from filling the pores, also act as a rheological aid, reducing the interparticle friction coefficient and providing for optimum particle packing in the microstructure. Although a brief account of the microstructure of this new composite (called Macro Defect Free Cement) has been reported, a close and detailed examination of the cement particle/polymer interface remains to be performed. The aim of this communication is to report the microstructure of a macro defect free cement with particular emphasis on the cement particle/polymer interfaces. Cement nomenclature is used in this report: C= CaO, A= Al2O3, H=H2O

Hydration of sodium phosphate-modified high alumina cement

1994 ◽  
Vol 9 (5) ◽  
pp. 1291-1298 ◽  
Author(s):  
Weiping Ma ◽  
Paul W. Brown
Keyword(s):  
Isothermal Calorimetry ◽  
High Strength ◽  
High Alumina ◽  
Hydration Products ◽  
X Ray Diffraction ◽  
Alumina Cement ◽  
X Ray ◽  
Morphological Variations ◽  
High Alumina Cement ◽  
Sodium Phosphates

High strength can be achieved in high alumina cement (HAC) through the incorporation of phosphate-based additions at levels of 10 and 20 wt. %. In order to establish the mechanism that results in higher strength, the effects of a variety of condensed sodium phosphates (NaPO3)n, (NaPO3)n · Na2O, Na5P3O10, and (NaPO3)3 were studied. The influence of these additions on the kinetics of hydration was studied using isothermal calorimetry. The phosphatic additions enhanced reactivity, but x-ray diffraction analyses did not reveal evidence of new crystalline phosphate-containing hydration products. Microstructural evolution was examined in real time using environmental SEM, and hydration products exhibiting distinct morphologies were observed. The features exhibited ranged from amorphic to polygonal shapes, plates, and fibers. These frequently formed between crystalline calcium aluminate hydrate grains and by doing so appear to provide a means to enhance the strengths of these cements. In spite of the morphological variations, companion energy dispersive x-ray analysis showed that the compositions of these products did not vary widely. Their ranges of compositions are 52-60 wt. % Al2O3, 20-26 wt. % P2O5, and 20-24 wt. % CaO.

Post-Synthesis Crystallinity Tailoring of Water-Soluble Polymer Encapsulated CdTe Nanoparticles using Rapid Thermal Annealing

2009 ◽  
Vol 1207 ◽  
Author(s):  
Steven Rutledge ◽  
Abdiaziz A. Farah ◽  
Jordan Dinglasan ◽  
Darren Anderson ◽  
Anjan Das ◽  
...  
Keyword(s):  
Thermal Processing ◽  
Water Soluble ◽  
Hollow Core ◽  
X Ray Diffraction ◽  
Water Soluble Polymer ◽  
X Ray ◽  
Crystal Fiber ◽  
Cdte Nanoparticles ◽  
Post Synthesis ◽  
Polymer Capping

AbstractThe crystallinity of colloidal CdTe nanoparticles has been enhanced post synthesis. This control over the nanoparticles’ properties has been achieved using non-adiabatic thermal processing. The technique preserves the polymer capping and hence introduces no adverse effects on the nanoparticles’ optical properties. The crystallinity is probed primarily through Raman spectroscopy in a hollow core photonic crystal fiber and x-ray diffraction powder studies.

Investigation on the Effect of Hydroxyapatite Nanorod on Cement Hydration and Strength Development

2021 ◽  
Vol 21 (3) ◽  
pp. 1578-1589
Author(s):  
Han Yan ◽  
Qianping Ran ◽  
Yong Yang ◽  
Xin Shu ◽  
Qian Zhang ◽  
...  
Keyword(s):  
Isothermal Calorimetry ◽  
Superior Performance ◽  
Strength Development ◽  
Hydration Reaction ◽  
X Ray Diffraction ◽  
Early Hydration ◽  
Cement Pastes ◽  
Supplementary Cementitious Material ◽  
Acceleration Period

This work investigated the effect of hydroxyapatite (HA) nanorods on the strength development and hydration of cement. Undispersed HA nanorods (HA-UD) and dispersed HA nanorods (HA-DN) were prepared by atom-efficient neutralization. The strength of mortars modified by HA nanorods was tested, as well as their compatibility with supplementary cementitious material. The hydration of HA-modified cement pastes was characterized via in situ X-ray diffraction, isothermal calorimetry and scanning electron microscopy. As the results suggest, the undispersed HA-DN caused a considerable increase in superplasticizer demand to achieve the same level of flow. Both HA nanorods showed a significant accelerating effect on early hydration, with approximately 100% strength enhancement at 12 h at 2.0% dosage. The effect on early strength of the nanorods is retained in systems with up to 30% fly ash in the binder mass. According to the characterizations, the rate of the hydration reaction in the acceleration period was enhanced by HA nanorods, and C3S consumption was also increased. In all of the testing situations, HA-DN showed superior performance, likely due to improved spatial distribution of the hydroxyapatites. The results suggest that proper dispersion of the nanorods is necessary to optimize its performance.

scholarly journals Ag(I) Catalyzed Grafting of Acrylonitrile onto Gum Arabic by Ce(IV) in Medium: A Kinetic Study

2012 ◽  
Vol 2012 ◽  
pp. 1-7 ◽  
Author(s):  
Geeta Thota ◽  
P. Srinivas
Keyword(s):  
Electron Microscopy ◽  
Gum Arabic ◽  
Probable Mechanism ◽  
Water Soluble ◽  
Graft Polymer ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
Water Soluble Polymer ◽  
X Ray ◽  
Scanning Electron

Grafting of Acrylonitrile (AN) onto water-soluble polymer Gum arabic (GA) was carried out using ceric ammonium sulfate [Ce(IV)] as initiator in the presence and absence of Ag(I) in H2SO4 medium at 313 K. The rate of oxidation (), rate of grafting (), and grafting efficiency (GE) were determined for catalyzed and uncatalyzed grafting and suitable mechanism was proposed to explain the observed results. No homopolymerization in the absence of GA indicates that the polymer obtained is purely a graft copolymer. A probable mechanism involving the formation of Ag(I)-GA adduct followed by its oxidation with Ce(IV) to give Ag(II)-GA adduct, and its decomposition to give initiating radicals is proposed to explain the observed results. The graft polymer was characterized using Fourier-transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), X-ray diffraction, and scanning electron microscopy (SEM) considering GA as reference.

Very High Strength Cfment-Based Materials – a Prospective

1984 ◽  
Vol 42 ◽  
Author(s):  
Sidney Diamond
Keyword(s):  
Mechanical Properties ◽  
High Strength ◽  
High Technology ◽  
Critical Crack ◽  
Shrinkage Cracking ◽  
Cement Pastes ◽  
Air Voids ◽  
Shrinkage Cracks ◽  
Cement Based Materials ◽  
Very High

AbstractAn attempt is made to provide a prospective on new very high strength cement based materials. The mechanical properties of concrete and of conventional cement pastes are considered, and limitations on the behavior of paste set by the Griffith concept of a critical crack explored. Evidence is cited confirming that spherical air voids do indeed act as critical Griffith flaws in undried pastes; however it is suggested that shrinkage cracks dominate the behavior of cement paste exposed to drying. Very high strength systems.must avoid both large air voids and other pores and also be resistant to shrinkage cracking. Streams of development leading to “DSP” (Aalborg) and “MDF” (ICI) systems are described, and details of the functioning of the two classes of product are described. Current and potential commercial developments are briefly noted, and possible interrelations with the emerging areas of “high technology ceramics” mentioned. Finally, a brief summary of relevant mechanical properties is provided.

Microstructure-Property Relationships in Macro-Defect-Free Cement

MRS Bulletin ◽  
1993 ◽  
Vol 18 (3) ◽  
pp. 72-77 ◽  
Author(s):  
Jennifer A. Lewis ◽  
Waltraud M. Kriven
Keyword(s):  
Raw Materials ◽  
Cement Composite ◽  
Water Soluble ◽  
Minimal Amount ◽  
Metal Powders ◽  
Water Soluble Polymer ◽  
Cement Pastes ◽  
Mdf Cements ◽  
Novel Processing ◽  
Entrapped Air

The term “macro-defect-free” refers to the absence of relatively large voids (or defects) that are normally present in conventional cement pastes due to entrapped air or inadequate mixing. A decade ago, Birchall and co-workers developed a novel processing method that avoids the formation of these strength-limiting defects. This method, outlined schematically in Figure 1, consists of mixing hydraulic cement powder, a water-soluble polymer, and a minimal amount of water under high shear to produce a macro-defect-free (MDF) cement composite. Several cement/polymer systems can be processed by this flexible technique, although the calcium aluminate cement/polyvinyl alcohol-acetate (PVA) copolymer system is most common: MDF cements display unique properties relative to conventional cement pastes. For example, the flexural strength of MDF cement is more than 200 MPa as compared to values on the order of 10 MPa for conventional pastes. One can view MDF cements as a type of “inorganic plastic.” As is the case with plastic processing, fillers such as alumina, silicon carbide, or metal powders can be added to MDF cement to modify its performance properties (e.g., abrasion resistance, thermal or electrical conductivity, and hardness). The combined attractiveness of inexpensive raw materials and flexible, low-temperature processing has generated great interest in this new class of advanced cement-based materials.

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