Influence of heat treatment regimes on mechanical properties of NSC-UHPC composite members
The applicability of ultra-high performance concrete which has clearly better mechanical properties than ordinary concrete is one of the most common topics in civil engineering scientific papers. Due to the high price of this type of concrete in comparison with ordinary concrete, and the absence of design codes, practical application of this type of material is still very limited, especially in less developed countries. The idea of partial usage of UHPC in some kind of structures is being developed by other scientists (Habel 2004), however it is still the lack of information about curing conditions of composite members and shear bond strength between ordinary concrete and UHPC. In order to make reliable composite structures, it is very important to ensure sufficient interface strength. In this paper experimental data is presented, which was obtained from tests carried out by authors. The aim of experiments was to establish the influence of different heat treatment regimes on mechanical properties (including shear bond strength) of normal strength concrete and ultra-high performance concrete newly cast composite members. Bi-surface shear test method was used to determine the average shear bond strength. Three different curing regimes were analysed. It was observed from preliminary tests that after heat treatment UHPC achieved its final maturity, however ordinary concrete did not gain the same strength as concrete specimens which were cured in 20 °C water for 28 days. It is a possibility that shear bond strength of heat treated composite members was significantly reduced due to the large shrinkage deformations during the short period of time. The results presented in this paper make a significant contribution to supplement the limited information about possibilities to use normal strength concrete and UHPC in new NSC-UHPC composite structures.