Faculty of Engineering and Built Environment

Permanent URI for this communityhttps://wiredspace.wits.ac.za/handle/10539/5024

For information on accessing Architecture & Built Environment content please contact Katlego Chiya via email : Katlego.Chiya@wits.ac.za or Tel (W) : 011 717 1978

For information on Engineering collections content please contact Salome Potgieter by email : salome.potgieter@wits.ac.za or Tel : 011 717 1961

Browse

Filters

2003 - 200912010 - 20111

Settings

Author: search.filters.author.Ballim, Y.Subject: search.filters.subject.Heat evolution

Search Results

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    A maturity approach to the rate of heat evolution in concrete.
    (ICE Publishing, 2003) Ballim, Y.; Graham, P.C.
    This paper discusses the use of the concept of maturity as a means of combining the effects of time and temperature in describing the rate of heat evolution from hydrating cement in concrete. The proposed maturity approach allows the rate of heat evolution determined from an adiabatic test to be expressed in a form which is independent of the starting temperature of the test. This relationship can then be directly used in a time-temperature prediction model that requires a solution of the Fourier equation for heat flow. The results of an experimental study aimed at assessing the suitability of both the Arrhenius and Nurse-Saul maturity relationships is also presented. Three adiabatic calorimeter tests were conducted on each of two concrete mixtures but starting at different temperatures. The results confirm the suitability of this approach and indicate that, of the two maturity relationships assessed, the Arrhenius maturity relationship is the more suitable in this application.
  • Thumbnail Image
    Item
    Effectiveness of the fineness of two South African Portland cements for controlling early-age temperature development in concrete.
    (The South African Institution Of Civil Engineering., 2011) Graham, P.C.; Ballim, Y.; Kazirukanyo, J.B.
    Temperature gradients due to heat of hydration of cement can cause cracking and present serious structural and serviceability concerns in concrete structures. Engineers use a wide range of strategies to limit the potential for such cracking, mainly by minimising the maximum temperature in the concrete. This paper considers the possibility of using more coarsely ground cement as one of the strategies for reducing the maximum concrete temperature. Two cement clinkers were used to produce cements with five different levels of fineness. These ten cements were then used to make concretes which were tested in an adiabatic calorimeter to determine the heat evolution characteristics. The measured results were then used in a computational model to calculate the temperature profiles likely to occur in two types of concrete elements. The results indicate that the effect of increasing fineness on the total amount of heat released during hydration is dependent on the mineralogy and crystal composition of the cement clinker. Also, the use of coarse-ground cement as a means of reducing the maximum temperature in concrete is more effective in the case of concrete elements with high cement content but of moderate dimensions. In sections of larger dimension, coarse-ground cements show lower levels of temperature reduction but also lower thermal gradients.