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International Concrete Abstracts Portal

Showing 1-5 of 14 Abstracts search results

Document: 

SP249-12

Date: 

March 1, 2008

Author(s):

J.P. Romualdi and G.B. Batson

Publication:

Symposium Papers

Volume:

249

Abstract:

Due to copyright issues, this paper is only available by purchasing the SP-249.

The application of linear-elastic fracture mechanics reveals that the strength of concrete in tension is limited by internal holes and micro-cracks. Fracture arrest can be achieved by reducing the spacing of reinforcement to a suitable scale. Reinforcement diameter decreases in proportion to reduction in spacing in order to maintain steel percentage. Theoretical results indicate that the tensile cracking strength of concrete increases in proportion to the inverse square root of the reinforcement spacing. Tests on closely spaced wire reinforced beams support the theoretical calculations.

DOI:

10.14359/20133


Document: 

SP249-06

Date: 

March 1, 2008

Author(s):

W. Lerch

Publication:

Symposium Papers

Volume:

249

Abstract:

Due to copyright issues, this paper is only available by purchasing the SP-249.

The manner in which the added gypsum controls the setting of cement has been the subject of many investigations and of some controversy. It is generally agreed, however, thtat its effect is to stop the rapid reaction normally shown by the calcium alumniates. In the absence of precise information relative to the function of gypsum in regulating the initial hydration and in order to provide ample protection against the abnormal expansion that might result from the use of excess amounts of gypsum it has been the custom from the beginning to place a limit on the SO3 content of portland cement in standard specifications. In the A.S.T.M. specification for cement this limit has not been changed since 1917 except to permit a higher value for high early strength cement. In the belief that the quantity of gypsum required to regulate properly the hydration and hardening would vary with cement composition and fineness, the studies described in this paper were undertaken.

DOI:

10.14359/20127


Document: 

SP249-04

Date: 

March 1, 2008

Author(s):

H.F.W. Taylor

Publication:

Symposium Papers

Volume:

249

Abstract:

Due to copyright issues, this paper is only available by purchasing the SP-249.

Hydrous calcium silicates prepared at room temperature appear amorphous, but X-ray photographs show that compounds are formed having a considerable degree of crystalline character. Essentially the same product, calcium silicate hydrate (I), can be obtained by the action of water on tricalcium silicate, by double decomposition of calcium nitrate and sodium silicate, or by reaction of calcium hydroxide solution with silica gel, although crystallisation is more mared in the first cae. The composition of this phase varies between approximately CaO,SiO2,aq. and 3CaO,2SiO2,aq. Without significant change in X-ray pattern. The phase relationships between solid and solution have been investigated and are sufficiently reproducible to suggest that the results represent a fair approximation to equilibrium conditions. A second phase, calcium silicate hydrate (II), with a composition in the neighbrourhood of 2CaO,SiO3,aq. And an X-ray pattern differeing only slightly from the above, has been obtained by decomposition of tricalcium silicate and probably exists in equilibrium with calcium hydroxide solutions containing over 1-13 g./l. of CaO. A tentative interpretation fo the X-ray data of calcium silicate hydrate (I) suggests a layer structure, possibly showing some similaritites to the clay minerals.

DOI:

10.14359/20125


Document: 

SP249-10

Date: 

March 1, 2008

Author(s):

A.S. Ngab, F.O. Slate, and A.H. Nilson

Publication:

Symposium Papers

Volume:

249

Abstract:

The realtionship between tiem-dependent deformation and internal microcracking of high strength concrete was investigated experimentally. Direct comparison was made to the behavior of normal strength concrete subjected to similar relative uniaxial compressive stresses and under the same environment conditions. Sealed and unsealed specimens were analyed for microcracking after they were subjected to short-term loading, to shrinkage, and to sustained loading. Results confirm that microcracking, always present eve in unloaded specimens, is increased by short-term loading, shrinkage, and sustained loading. However, the amoutn of cracking, as well as the increase relative to the initial state, is significantly less in high strength concrete than in normal strength material. The amount of creep strain associated with internal cracking in high strength concrete is negligible, whereas such creep is significat in normal strength concrete, particularly at high stresses. The research also indicates that the ratio of the sustained load strength to the short-term strength is higher for high strength than for normal strength concrete. This also can be explained in terms of differences in microcracking. Time-dependent engineering properties for high strength concrete, such as creep coefficient, specific creep, and shrinkage characteristics, are reported in a separate paper.

DOI:

10.14359/20131


Document: 

SP249-03

Date: 

March 1, 2008

Author(s):

R.S. Barneyback Jr. and S. Diamond

Publication:

Symposium Papers

Volume:

249

Abstract:

Due to copyright issues, this paper is only available by purchasing the SP-249.

A device is described that has been used for several years for expression of pore solution from hardened portland cement pastes and mortars. Particulars with respect to the design, fabrication, and operation of such equipment are given, and methods for the analysis of the resulting small volumes of pore solutions are briefly discussed. It is believed that the compositions of the pore solutions obtained are representative of that of the bulk of the pore solution within the paste or mortar from which the solutions have been obtained.

DOI:

10.14359/20124


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