Engineering properties of inorganic polymer concretes (IPCs)
Introduction
Inorganic polymer concretes (IPCs) can be made predominantly from industrial waste materials, such as fly ash (a coal combustion by-product), granulated blast furnace slag (GBFS), mine tailings and contaminated soil. These materials are often referred to as geopolymers or alkali activated cements. They contain aluminum and silicon species that are soluble in highly alkaline solutions. The dissolved species then undergo polycondensation to produce materials with desirable mechanical properties. While pozzolanic cements generally depend on the presence of calcium, inorganic polymers do not utilise the formation of calcium–silica–hydrates (CSH) for matrix formation and strength [1]. These structural differences give IPCs certain advantages, such as an earlier gain in strength compared with conventional cement-like binders [2], [3], [4]. It has been shown previously that inorganic polymers are stable materials with proven physical and chemical properties. In many cases, IPCs outperform their ordinary Portland cement (OPC) counterparts with respect to compressive strength [2] as well as acid resistance and fire resistance [5], [6]. For these reasons, IPC technology is gaining significant commercial interest, especially because it has been demonstrated that IPC formulations are cost-competitive with general-purpose cement [6], [7].
There is a significant amount of literature on the chemistry of inorganic polymer concrete [1], [2], [3], [4], [5], [8]. Some of the studies consider the environmental benefits of inorganic polymer concretes, such as the immobilisation of toxic metals [2], while others report on the mechanism of the geopolymerisation process for many different alumino-silicate minerals [9]. However, there are currently very few published studies on the engineering properties of IPCs. In order to use IPCs in structural engineering applications, a precise evaluation of these properties is essential. The engineering properties that are determined in the present work, for a variety of IPC formulations, include compressive strength, splitting tensile strength and flexural strength, static chord modulus of elasticity, and Poisson's ratio. This work will therefore serve as a basis for the future development and understanding of the structural engineering properties of IPCs.
Section snippets
Materials
Six IPC mixes were used in this study. The mix proportioning and other mix-design variables are presented in Table 1. Three different sources of Class-F Australian fly ash were used: namely, Port Augusta (PA), Gladstone (G) and Tarong (T). X-ray fluorescence spectroscopy (XRF) analysis was performed on the fly ashes. The details of the XRF analysis are presented in Table 2.
In general, the starting materials for the synthesis of IPCs include sand, fly ash, and where specified, coarse aggregates
Density of the IPC mixes
The weight and dimensions of three IPC cylinders per mix were measured in order to calculate the density (ρ) of a particular mix. The calculations were carried out in accordance with the requirements of AS 1012.12.1 [12]. The density, along with the respective compressive (fc), splitting tensile (fsts) and flexural strengths (fcf) of each particular mix, is presented in Table 3.
The mean density of the IPC mixes without coarse aggregates was found to be 2205.8 kg/m3, with a standard deviation of
Variability in IPC mixes
IPC materials derived from aluminosilicate secondary raw materials, such as fly ash, can exhibit superior chemical and mechanical properties to ordinary Portland cement (OPC). The mechanical properties, however, may greatly depend on the chemical content of the fly ash. In the following sub-sections, the variability in engineering properties of the IPC mixes are discussed in the light of results presented in this paper. For a more elaborate evaluation of the effect of fly ash on mechanical
Concluding remarks
It was observed that for a concrete density similar to OPC-based concretes, the average compressive strengths of IPC mixes (fc) have been found to be close enough to the design strength, with a mean of 52.4 MPa and a standard deviation of 3.8.
The results presented here show that the splitting tensile and flexural strength of the IPC mixes compares favorably with the models presented by the standards for OPC-based concretes. Although the difference between splitting tensile and flexural strength
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