Abstract
For concrete subjected to restrained conditions, autogenous deformation (AD) and thermal dilation (TD) are the main driving forces behind stress development in the hardening phase. Generally, AD in concrete is modelled by model codes or measured in the laboratory under 20 °C isothermal conditions, and then used as basis for stress calculations under realistic temperature conditions. To evaluate this common simplification, the current study investigated the effect of curing temperature on the AD of a series of fly ash concretes. A comprehensive test program was performed for fly ash concretes subjected to various temperature curing conditions. The model codes and measurements under 20 °C isothermal conditions provided AD developments in the same order of magnitude. However, when subjected to a realistic temperature history during curing, major changes in the AD developments were observed, emphasising that AD must be determined under relevant temperature conditions.
Highlights
Hardening phase volume changes in concrete, caused by autogenous deformation (AD) and thermal dilation (TD), are proven to be of considerable importance
There has been reported that a partial replacement of cement by fly ash would increase the AD [12], while other studies found a clear tendency of decreasing AD with increasing fly ash replacement under 20 C isothermal conditions [11,13]
The present paper presents a set of results from this test program: AD measurements on fly ash concretes subjected to 1) 20 C isothermal temperature curing conditions and 2) realistic temperature curing conditions
Summary
Hardening phase volume changes in concrete, caused by autogenous deformation (AD) and thermal dilation (TD), are proven to be of considerable importance. Several of these references concluded that the traditional maturity concept was not applicable to describe the AD development [5,14,28,31] It is highly questionable if AD models and experiments based on 20 C isothermal test conditions could accurately describe the AD develop ment taking place under realistic temperature curing conditions. According to thermody namics, a temperature increase in the concrete will induce an in ternal redistribution of water from gel pores to capillary pores, caused by the lower entropy of gel water than that of capillary water This redistribution is expected to lead to a shrinkage, i.e. the described thermally induced shrinkage and swelling has the opposite direction to the immediate thermal dilation. The current work provides compre hensive experimental data on various concrete mixes and temperature conditions, and aims to form a contribution to the ongoing scientific process of understanding the acting mechanisms and developing prac tical models when it comes to AD of concrete
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