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International Concrete Abstracts Portal

Showing 1-5 of 10 Abstracts search results

Document: 

SP241-08

Date: 

April 1, 2007

Author(s):

F.F. Radjy

Publication:

Symposium Papers

Volume:

241

Abstract:

Heat of hydration and its rate play key roles in concrete thermal cracking and high-early strength development for fast track construction. Heat properties are also unique indicators of both the quality and the performance of cement, cementitious materials, and chemicals in concrete. Heat Signature is an automated method of measuring concrete heat of hydration and its rate, and adiabatic temperature rise and its rate versus concrete maturity (equivalent curing age at 68 °F). The measurements are performed on full size concrete specimens via the Internet/Intranet, and together with mixture information are saved to a database. Heat signature data in combination with simulation enable projecting concrete field performance in terms of its temperature, maturity, and strength profiles as a function of job site weather conditions and placement and curing plans. The paper reviews the underlying heat signature theory, its history, and reviews and interprets typical data from the many measurements in the US. To better index a given mix design’s field performance, a consistent set of thermal cracking and high-early curing age indices are introduced.

DOI:

10.14359/18654


Document: 

SP241-02

Date: 

April 1, 2007

Author(s):

J.P. Sandberg and S. Liberman

Publication:

Symposium Papers

Volume:

241

Abstract:

This paper describes the use of a recently developed, inexpensive portable semi-adiabatic calorimeter for monitoring cement hydration in concrete and mortar. The calorimeter measures the temperature as a function of time at the bottom of eight individual 3x6 cylinders with concrete or mortar. The measured temperature profile is used to evaluate the overall hydration performance of cementitious mixtures, with special emphasis on the timing and the size of the main hydration exotherms that strongly affect setting and early strength development of cementitious mixtures. Furthermore, a method has been developed for a more precise calculation of "thermal set", with good correlation to manual set times according to ASTM C403. The field calorimeter is useful to screen the effect of type and dosage of admixtures and supplementary cementitious materials on "thermal" setting times in concrete and mortar.

DOI:

10.14359/18648


Document: 

SP241-01

Date: 

April 1, 2007

Author(s):

P. Taylor and J. Gajda

Publication:

Symposium Papers

Volume:

241

Abstract:

There is a growing interest in monitoring the temperature of cement paste, mortar and concrete, particularly at early ages. However, there also seems to be confusion about what is being achieved by this activity, and what to do with the information once it is recorded. This paper outlines the tools and techniques in use, and discusses their applications, benefits and limitations. The discussion will cover concepts such as heat of hydration, maturity, isothermal calorimetry and semi-adiabatic temperature monitoring for assessing setting times, and potential incompatibility between the reactive ingredients (cements, supplementary cementitious materials, and chemical admixtures) in a mixture.

DOI:

10.14359/18647


Document: 

SP241-06

Date: 

April 1, 2007

Author(s):

J.M Ruiz, R.O. Rasmussen, and T.R. Ferragut

Publication:

Symposium Papers

Volume:

241

Abstract:

Concrete paving mixtures are subjected to varying climatic conditions during the hydration process. The temperature of the concrete is a function of the heat generated by the cement paste and climatic conditions as well as curing procedures applied during construction. Temperature development in the concrete is closely related to the development of concrete properties and also affects the generation of internal stresses in the pavement that if not properly controlled may result in cracking and other distresses. With the FHWA HIPERPAV software, it is possible to assess the impact on the performance of the pavement that different concrete materials will have by evaluating their heat of hydration properties (heat fingerprint) and their interaction with the environment. Characterization of concrete mixtures in terms of their heat of hydration allows for a more rational selection of materials as a function of the climatic conditions to which they are exposed. Selected concrete mixtures with this approach can thus provide more confidence in that they will perform satisfactorily under the site-specific conditions to which they are subjected effectively reducing potential excessive stresses in the pavement. In this paper, the system approach to characterize concrete paving mixtures and its effect under various climatic conditions is presented.

DOI:

10.14359/18652


Document: 

SP241-07

Date: 

April 1, 2007

Author(s):

C.V. Nielsen

Publication:

Symposium Papers

Volume:

241

Abstract:

The maturity concept applying the Arrhenius equation is generally accepted as a proper way to model the temperature effects on concrete hardening. The Arrhenius equation gives the rate of hydration as a function of temperature depending on the activation energy for the cementitious binder materials. It is demonstrated how a simple three-parameter-model is sufficient to formulate the development of heat from the cement hydration process. Furthermore, the heat development is used to define the apparent degree of hydration. It is described how the heat of hydration may be determined experimentally at the con-crete plant or in nearby concrete laboratories. By means of a semi-adiabatic container the heat released from the hydration process is monitored. Finally, examples of the practical applications of the heat of hydration data for various concrete mixtures are addressed. It is demonstrated how the use of admixtures may influ-ence the heat of hydration and how difficult it is to model the complicated interactions between cement, mineral additions and admixtures without the use of experiments. The possibility of linking the heat of hydration data with the early-age mechanical properties is also illustrated.

DOI:

10.14359/18653


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