scholarly journals Role of Polycarboxylate-ether superplasticizers on cement hydration kinetics and microstructural development

2018 ◽  
Vol 149 ◽  
pp. 01004 ◽  
Author(s):  
L. Valentini ◽  
M.C. Dalconi ◽  
G. Artioli
Keyword(s):  
Ad Hoc ◽  
Cement Hydration ◽  
Mechanical Performance ◽  
Growth Models ◽  
Pore Space ◽  
Microstructural Development ◽  
Detailed Knowledge ◽  
Hydration Kinetics ◽  
Polycarboxylate Ether

Polycarboxylate-ether (PCE) superplasticizers are a fundamental constituent of modern cementbased materials due to their impact on the rheology of the fresh mix and mechanical performance of the hardened material. The effect of PCEs on cement hydration kinetics has been known since their introduction in the early 1980s. However, detailed knowledge of the role played by PCE macromolecules on the basic mechanisms of cement hydration (dissolution, diffusion, precipitation) is still lacking. A better understanding of how such mechanisms are influenced by the addition of PCE is no doubt beneficial to the design of novel superplasticizing admixtures. Here, I report on some recent findings about the role of PCE superplasticizers on cement hydration kinetics and microstructural development. The interaction between PCE and C3S pastes was investigated by an ad-hoc kinetic model based on a combination of generalized forms of the Avrami and BNG (Boundary Nucleation and Growth) models. The model is used to fit the rate of C-S-H precipitation measured by in-situ X-ray powder diffraction combined with mass balance calculations. The results show that a switch from heterogeneous to homogeneous C-S-H nucleation occurs in the presence of PCEs and that the C-S-H growth rate decreases proportionally to the amount of PCE used. The predicted switch to homogeneous nucleation is in agreement with experimental results obtained by XRD-enhanced micro-tomography imaging, showing that, in the presence of PCE, C-S-H preferentially forms in the pore space rather than at the surface of clinker particles.

Microstructural Analysis during the Hydration of Cement-in-Polymer Coatings

2011 ◽  
Vol 466 ◽  
pp. 159-166 ◽  
Author(s):  
Oliver Weichold ◽  
Markus Hojczyk ◽  
Alina Adams ◽  
Alexandra Olaru ◽  
Helge Stanjek
Keyword(s):  
Vinyl Acetate ◽  
Cement Hydration ◽  
Mechanical Performance ◽  
Microstructural Analysis ◽  
Polymer Coatings ◽  
Water Ingress ◽  
Phase Development ◽  
Polymer Properties

Cement-in-polymer (c/p) dispersions allow the full utilisation of the reinforcing abilities of multifilament rovings in concrete. In this work the role of the polymer properties on the performance of the c/p dispersions is investigated and discussed. Two model polymers are chosen and c/p dispersions made with these are investigated regarding the water ingress velocity (NMR), the phase development during cement hydration (XRD), and the microstructure after cement hydration (SEM). Best mechanical performance is achieved with the hydrophobic poly(vinyl acetate) which regulates the water ingress and causes a slow hydration of the cement.

scholarly journals Structure-Process-Property Relationships in Hydroentangled Nonwovens -Part 1: Preliminary Experimental Observations

2004 ◽  
Vol os-13 (4) ◽  
pp. 1558925004os-13
Author(s):  
Behnam Pourdeyhimi ◽  
Amy Minton ◽  
Mike Putnam ◽  
Han Seong Kim
Keyword(s):  
Process Parameters ◽  
High Velocity ◽  
Mechanical Performance ◽  
High Strength ◽  
Detailed Knowledge ◽  
Nonwoven Fabrics ◽  
Fiber Properties ◽  
Process Property ◽  
The Web

Hydroentanglement describes a versatile process for manufacturing nonwoven fabrics using fine, closely spaced, high-velocity jets of water to entangle loose arrays of fibers. The resultant fabrics rely primarily on fiber-to-fiber friction to achieve physical integrity and are characterized by relatively high strength, flexibility, and conformability. These technologies can use efficiently the majority of all types of fibers and produce fabrics that could achieve properties equivalent to wovens. To develop a method for predicting the mechanical performance of hydroentangled nonwovens, one must first gather critical information about the materials, the web and the process to establish a detailed knowledge base. The first step in this process is to establish the role that the hydroentangling process parameters play in controlling the performance of the product. One must establish how efficient entanglement is attained, how such entanglement is translated into tensile and other physical properties as well as understanding the role of the intrinsic fiber properties that interact with the process. This is the first in a series of papers planned for dealing with structure-process-property relationships in hydroentangled nonwovens.

Cellulose Nanocomposites for Performance Enhancement of Ordinary Portland Cement-Based Materials

2020 ◽  
pp. 036119812095842
Author(s):  
Kavya S. Kamasamudram ◽  
Warda Ashraf ◽  
Eric N. Landis
Keyword(s):  
Compressive Strength ◽  
Flexural Strength ◽  
Portland Cement ◽  
Cement Paste ◽  
Ordinary Portland Cement ◽  
Performance Enhancement ◽  
Mechanical Performance ◽  
Early Stage ◽  
Microstructural Development ◽  
Hydration Kinetics

Cellulose nanofibril (CNF) with a high aspect ratio, elastic modulus, tensile strength, and reactive surface area is a promising nanomaterial for improving the chemo-mechanical properties of cementitious matrixes. CNFs are typically less than 0.2 mm in length and 50 nm in width, and are extracted from plants and trees. This study investigated the potential application of three types of CNF for enhancing the performance of ordinary Portland cement (OPC) pastes: pure CNF (PCNF), silica coated CNF (SCNF), and lignin-containing CNF (LCNF). The performance of the cement pastes was monitored for cement paste workability, hydration kinetics, microstructural development, and mechanical performance (compressive strength and flexural strength). The dispersion stability of CNFs measured through zeta potential showed a better dispersion for SCNF when compared with PCNF and LCNF in varied alkaline mediums. The better stability of SCNF also resulted in improved workability of the cement paste mixtures containing this type of cellulose. All of the cellulose nanomaterials accelerated the cement hydration at the early stage as a result of the nucleation effect. Such an acceleration effect was slightly higher for SCNF because of the presence of silica nanoparticles. The addition of 0.1% SCNF increased the compressive strength (90 days) by 13% when compared with the control batch and 10% compared with the PCNF batch. The addition of 0.1% of PCNF enhanced the flexural strength by 70% followed by LCNF with 40% improvement. SCNF showed little to no effect on the flexural strength.

The Mechanical Performance of Carbon Fibres- Addressing the Role of Microstructure

2019 ◽  
Author(s):  
Peter Peter ◽  
Claudia Creighton ◽  
David Fox ◽  
Pablo Mota Santiago ◽  
Adrian Hawley ◽  
...  
Keyword(s):  
Mechanical Performance ◽  
Carbon Fibres

Writing and Ritual in Deuteronomy 28

2017 ◽  
Author(s):  
Laura Quick
Keyword(s):  
Ad Hoc ◽  
Comparative Method ◽  
Literary Texts ◽  
History Of ◽  
Important Means ◽  
Written Word ◽  
Ritual Process ◽  
Different Cultures ◽  
Ritual Context

This chapter argue that ritual behaviours might be just as good a source as literary texts for the diffusion of traditional cursing and treaty material across different cultures in the ancient Near East. In particular, the role of ad hoc oral Targum in the ritual process could have been an important means by which traditions were shared between different language communities. Recognition of the ritual context of this material also provides insights for the comparative method, the dating and authorship of Deuteronomy 28, and the subversive impetus thought to have stood behind its composition. Ultimately, the function of the written word in a largely oral world is shown to be fundamental to understanding the composition, function and the early history of the curses in the book of Deuteronomy.

The African Union and Universal Jurisdiction

2017 ◽  
Author(s):  
Martin Mennecke
Keyword(s):  
Ad Hoc ◽  
Criminal Court ◽  
Universal Jurisdiction ◽  
African Union ◽  
Government Officials ◽  
African Government ◽  
Double Standards ◽  
Legal Principle ◽  
The Status

Universal jurisdiction permits states to investigate and prosecute perpetrators of certain widely condemned offences, irrespective of whether they possess any of the traditional territorial, nationality, or other jurisdictional links to the offence. As a legal principle, African states accept the principle of universal jurisdiction, but in the past decade they have pushed back against it due to the perception that the courts of various European states have unfairly targeted African government officials that they perceive as enemies. Against this background, the chapter examines the status of the universal jurisdiction debate and how it relates to the role of the International Criminal Court and that of the African Union and its member states, in addition to evaluating the proposals made by African states within the framework of the United Nations to address the African government concerns about double standards in the application of universal jurisdiction through a special ad hoc committee of the General Assembly.

scholarly journals Review of the relationship between aggregates geology and Los Angeles and micro-Deval tests

2021 ◽  
Vol 80 (3) ◽  
pp. 1963-1980
Author(s):  
Solomon Adomako ◽  
Christian John Engelsen ◽  
Rein Terje Thorstensen ◽  
Diego Maria Barbieri
Keyword(s):  
Los Angeles ◽  
Crystal Size ◽  
Grain Shape ◽  
Mechanical Performance ◽  
Pore Space ◽  
Construction Material ◽  
Engineering Properties ◽  
Coarse Grained ◽  
The Impact ◽  
The Relationship

AbstractRock aggregates constitute the enormous volume of inert construction material used around the globe. The petrologic description as igneous, sedimentary, and metamorphic types establishes the intrinsic formation pattern of the parent rock. The engineering properties of these rocks vary due to the differences in the transformation process (e.g. hydrothermal deposits) and weathering effect. The two most common mechanical tests used to investigate the performance of aggregates are the Los Angeles (LA) and micro-Deval (MD) tests. This study reviewed the geological parameters (including mineralogy, grain and crystal size, grain shape, and porosity) and the relationship to Los Angeles and micro-Deval tests. It was found that high content of primary minerals in rocks (e.g. quartz and feldspar) is a significant parameter for performance evaluation. Traces of secondary and accessory minerals also affect the performance of rocks, although in many cases it is based on the percentage. Furthermore, some studies showed that the effect of mineralogic composition on mechanical strength is not sufficient to draw final conclusions of mechanical performance; therefore, the impact of other textural characteristics should be considered. The disposition of grain size and crystal size (e.g. as result of lithification) showed that rocks composed of fine-grain textural composition of ≤ 1 mm enhanced fragmentation and wear resistance than medium and coarse grained (≥ 1 mm). The effect of grain shape was based on convex and concave shapes and flat and elongated apexes of tested samples. The equidimensional form descriptor of rocks somehow improved resistance to impact from LA than highly flat and elongated particles. Lastly, the distribution of pore space investigated by means of the saturation method mostly showed moderate (R = 0.50) to strong (R = 0.90) and positive correlations to LA and MD tests.

scholarly journals Effect of C-S-H Nucleating Agent on Cement Hydration

2021 ◽  
Vol 11 (14) ◽  
pp. 6638
Author(s):  
Wenhao Zhao ◽  
Xuping Ji ◽  
Yaqing Jiang ◽  
Tinghong Pan
Keyword(s):  
Fractal Dimension ◽  
Cement Hydration ◽  
Nucleating Agent ◽  
Crystal Nucleation ◽  
Enhancement Effect ◽  
Hydration Products ◽  
Hydration Degree ◽  
Hydration Kinetics ◽  
Cement Mortars ◽  
Early Strength

This work aims to study the effect of a nucleating agent on cement hydration. Firstly, the C-S-H crystal nucleation early strength agent (CNA) is prepared. Then, the effects of CNA on cement hydration mechanism, early strength enhancement effect, C-S-H content, 28-days hydration degree and 28-days fractal dimension of hydration products are studied by hydration kinetics calculation, resistivity test, BET specific surface area test and quantitative analysis of backscattered electron (BSE) images, respectively. The results show that CNA significantly improves the hydration degree of cement mixture, which is better than triethanolamine (TEA). CNA shortens the beginning time of the induction period by 49.3 min and the end time of the cement hydration acceleration period by 105.1 min than the blank sample. CNA increases the fractal dimension of hydration products, while TEA decreases the fractal dimension. CNA significantly improves the early strength of cement mortars; the 1-day and 3-days strength of cement mortars with CNA are more than the 3-days and 7-days strength of the blank sample. These results will provide a reference for the practical application of the C-S-H nucleating agent.

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