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International Concrete Abstracts Portal

Showing 1-5 of 11 Abstracts search results

Document: 

SP95-01

Date: 

October 1, 1986

Author(s):

A. Williams

Publication:

Symposium Papers

Volume:

95

Abstract:

Early age concrete is subject to a temperature rise due to the hydration of the cement. Cube or cylinder reference specimens stored alongside a structure will not exhibit this temperature rise to the same degree and therefore will not have the same maturity as the concrete in the structure. Temperature matched curing is a method whereby cubes or cylinders of a similar maturity to the structure are produced, and is an extremely efficient method of determining minimum formwork striking and prestressing time. This paper gives a brief account of the history behind temperature matched curing in the United Kingdom, where the recent issue of a British Standard Institution document has focussed attention to the subject. Details are presented of the design and construction of a portable matching system for use on site. The system which is extremely robust, (but light enough to be carried by control cube temperatures to within -+, temperature within a structure. Results are given which show the advantages and disadvantages of such a system and illustrate the difference of maturity and hence strength between reference cubes stored in the curing bath and reference cubes placed next to the structure itself. one man), is able to 1oC of the concrete

DOI:

10.14359/6269


Document: 

SP95-08

Date: 

October 1, 1986

Author(s):

G.V Teodoru

Publication:

Symposium Papers

Volume:

95

Abstract:

The paper presents results concerning the correlations between on the one hand the compressive strength at early ages of hydrothermally treated concrete - steam cured, cured in heating moulds, autoclaved - and that hardened under standard conditions (20° C and 65 % R.H.) and on the other hand the rebound number (R), ultrasonic pulse velocity (V) and ultrasonic pulse attenuation (A). The importance in practice is due to the fact that on European construction sites some building components may be subjected to a hydrothermal treatment while others may not. In such a case, dif-ferent values of the compressive strength of concrete correspond to the same values of the nondestructively measured R, V and A. This leads to the conclusion that, in the absence of information on the conditions of curing and hardening of the concrete under investigation, the results of nondestructive tests can be very misleading. The paper discusses also the influence of concrete age on the coef-ficients of variation of the compressive strength, deduced both in a destructive and nondestructive way. Examples of the practice are used to illustrate the laboratory results.

DOI:

10.14359/6276


Document: 

SP95-02

Date: 

October 1, 1986

Author(s):

H-H. Gotfredsen and G.M. Idorn

Publication:

Symposium Papers

Volume:

95

Abstract:

The construction of the Faroe Bridges between Sealand and Falster in Denmark was completed early 1985. The project inclu-ded the placement of about 42,000 m3 of concrete for the substruc-tures of the bridges. Monitoring the curing of the concrete was an essential part of the efforts invested to assure satisfactory dura-bility of the structures. The operations included: I. Pre-calculations of the heat and strength (maturity) develop-ment after placing concrete in critical sections. The require-ments to be complied with were (1) maximum temperature, (2) maximum temperature differences in the concrete, and (3) at-tainment of sufficient maturity before form-removal. II. Site-control with continuous recording of the temperature de-velopment at essential positions in the concrete, including assessment of the strength development. Means for moderating the predetermined course of the curing, in case of unacceptab-le deviations, were used. The expenses for monitoring curing technology were deemed reason-able in view of the directly documented assurance that the requi-red quality of the concrete in the structures was obtained.

DOI:

10.14359/6270


Document: 

SP95-06

Date: 

October 1, 1986

Author(s):

EH. Fouad and H.L. Furr

Publication:

Symposium Papers

Volume:

95

Abstract:

This paper describes an experimental investigation that was conducted to study the behavior of mortar in flexure between three and eleven hours after mixing. A total of 32 flexural tests were performed using a test apparatus that permitted specimens to be handled before final set of the mortar. The specimens consisted of mortar beams 6-inches wide x 2-inches thick x 19-inches long, which were cast and tested in flexible molds, and cured at a controlled room temperature. The tests were conducted at ages of 3, 5, 7, 9 and 11 hours, age being reckoned from the time mixing was completed. The test specimen was loaded at the middle and rested at its ends on roller supports to simulate the action of a simple beam. Load versus mid-span deflection curves were automatically recorded and then ana 1 ysed. The tolerable curvature at first cracking, the modulus of elasticity, and the flexural strength of the material at early ages were determined. The test results are summarized and presented in various forms to provide information on the behavior of mortar at early ages.

DOI:

10.14359/6274


Document: 

SP95-04

Date: 

October 1, 1986

Author(s):

C. Gotsis, D.M. Roy, P.H. Licastro, and S. Kaushal

Publication:

Symposium Papers

Volume:

95

Abstract:

Thermal analysis was made of the effects of hydration of cylindrical configuration specimens of a slightly expansive cementitious mixture. This simulated a cylindrical borehole plug, and with modification, may be applied to other cylindrical configurations. Inputs were made to the computer program ATHENAN developed to assess the thermal history of cylindrical domains with symmetrical thermal loads. Inputs to the program were the experimental isothermal rates of heat-evolution of the cementitious mixture measured at several temperatures. Using the temperature history from ATHENAN and experimental data from the volume change and mechanical properties of the cementitious mixture in the computer program SAPIV, a stress analysis was performed, which showed that tensile stresses at the interface may arise at the early stages of hydration when the cementitious mixture tends to shrink, while small compressive stresses are present at long times in such materials when the cementitious mixture tends to expand.

DOI:

10.14359/6272


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