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International Concrete Abstracts Portal

Showing 1-5 of 10 Abstracts search results

Document: 

SP241-09

Date: 

April 1, 2007

Author(s):

E. Nordenswan and A. Kappi

Publication:

Symposium Papers

Volume:

241

Abstract:

The throughput of precast concrete plants can be improved by controlled heating of the cast products. Presently many systems do measure maturity or degree-hours providing information about the strength development, but not sufficient data for accurate decisions for the control of heating. A heat control system has been developed based on an on-line predictive calculation of the temperature behavior of concrete and a maturity-strength model. The temperature is measured continuously and every minute a complete prediction calculation up to the target maturity and strength is made. If the target strength cannot be reached without heating by the target time limit, the system opens the valve for heating the mould, until the temperature is high enough. The predictive algorithm also provides an accurate estimation of the time when the prestress release or demoulding strength is going to be reached. The parameters for the cement heat generation model are obtained by semiadiabatic measurements of the production concrete. The system has been in use since 1999 and applied in over ten precast factories in Europe in hollow-core and railroad sleepers production. The system has reduced significantly the heating costs; reduced rejections caused by too early demoulding and improved production planning in the factories.

DOI:

10.14359/18656


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: 

SP241-03

Date: 

April 1, 2007

Author(s):

K.A. Riding, J.L. Poole, M.C.G. Juenger, A.K. Schindler, and K.J. Folliard

Publication:

Symposium Papers

Volume:

241

Abstract:

An accurate and practical method of determining the heat development of concrete mixtures under real mixing, cooling, hauling, placement, and curing conditions would greatly benefit contractors and engineers in helping predict in-place concrete member temperatures. Semi-adiabatic calorimetry was performed at several construction sites in temperature controlled rooms using concrete sampled from concrete placements. Semi-adiabatic calorimetry was also performed for comparison with concrete made under laboratory conditions from materials sampled at the respective batch plants. An energy balance-based finite difference method is presented for calculating the concrete non-linear heat generation using the measured heat of hydration determined from semi-adiabatic calorimetry. This method was used in a program which allows the direct input of values from semi-adiabatic calorimetry testing and estimates the development of in-place temperatures in mass concrete members of various geometries. Estimated concrete member temperatures are compared to the values measured on-site. Best practice suggestions are also given for performing semi-adiabatic calorimetry using concrete sampled on-site.

DOI:

10.14359/18649


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


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