Segregation and Separation in Concretes and Mortars and Their Effects on Strength, Accompanied by a Book of Prints

Hunter, W (1937) Segregation and Separation in Concretes and Mortars and Their Effects on Strength, Accompanied by a Book of Prints. PhD thesis, University of Glasgow.

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In the introductory discussion, evidence indicating water-cement ratio as the principal factor affecting strength is commented on and the view is advanced that the effects of grading and proportions are due to inequalities in cement distribution conditioned by them. Sections of mortars and concretes are shown and commented on. Evidences of cavity formation are found under the larger fragments in badly graded mixtures. It appears, however, that this is an extreme condition which is not evident in mortars. Tests of remixed concretes and mortars are then described. In these, segregations were reduced by the increased paste viscosity obtained by re-mixing after a suitable storage period. The control of paste viscosity by this means was somewhat uncertain but reduced cavitation was obtained, accompanied by increased strength. Increases in mortar strengths obtain by re-mixing were much less marked and it was concluded that cavity formation, as a factor affecting strength, was important only in badly graded concretes. It is suggested that inequalities in the density of the cementing paste have considerable influence on strength and may explain the usual grading and proportion effects which occur in normal mixtures. Mortar tests are then described and discussed from this point of view, together with mortar voids information. Rapid Hardening Portland cement was used. Specimens were water cured and broken at 7 days. Previous experience had indicated that the behaviour of this cement at this curing period was similar to that of Ordinary Portland at 28 days, and the shorter curing period simplified storage arrangements. The extension of the tests to include concretes is preceded by a discussion of basic voids and the description of a method of estimating their magnitude. This method is presented, not as a formal study of grading phenomena, but as an expedient to enable the concrete results to be reduced. It was required by circumstances but it is otherwise desirable as it makes unnecessary the somewhat troublesome process of obtaining basic voids experimentally. As the formula does not cover cavity formation, it was expected that it would not apply to concretes of outstand: :ingly bad gradings. This was found to be so, calculated strengths agreeing closely with observed strengths for normally graded mixtures but exceeding them when grading was obviously poor. Cavitation is discussed under the heading of "Particle Interference". Workability is then discussed, slump is related approximately to The writer wishes to draw attention to the fact that the method appears to be quite general, including neat pastes, mortars and concretes under the same rule.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Civil engineering
Date of Award: 1937
Depositing User: Enlighten Team
Unique ID: glathesis:1937-80095
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 03 Mar 2020 09:16
Last Modified: 03 Mar 2020 09:16

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