۱- Introduction

۲- Background

۳- Experimental

۴- Mix design procedure

۵- Results and discussion

۶- Conclusions

References

Abstract

A mix design procedure for geopolymer concrete (GPC) was developed in order to maintain a high compressive strength after adding micro-encapsulated phase change materials (MPCM). The most relevant factors which affect the properties of fly ash/slag based GPC containing MPCM are considered. Class F fly ash and slag, sodium hydroxide and sodium silicates were chosen as binder and alkaline solution, respectively. Two types of MPCM were used for a better understanding the effect of different MPCMs on the properties of the GPC. The setting time of geopolymer pastes was found to depend on both the amount of water adsorbed by the microcapsules, the viscosities of the samples, and possibly the latent heat. Accordingly, the initial setting time increased and the final setting time decreased with MPCM concentration. A slump test and compressive strength measurements have been utilized to examine the workability and mechanical properties of the new mix design. It was observed that the addition of MPCM reduces the slump and the compressive strength of GPC. These effects were more pronounced for the MPCM that form agglomerated structures and has a surface containing some polar groups, than for the more spherically shaped and less agglomerated MPCM with a hydrophobic surface. Although the addition of MPCM reduced the compressive strength of geopolymer concrete, the mechanical performance was higher than that of Portland cement concrete after 28 days of curing. A combination of SEM imaging and X-ray-tomography suggested that MPCM agglomeration, gaps between MPCM and the concrete matrix, an increased amount of entrapped air, and microcapsules that break under stress might contribute to the reduced compressive strength of GPC.

Introduction

The demand for cementitious materials has increased considerably in recent years. Ordinary Portland cement is normally considered as the main material for construction purposes. However, the Portland cement production has a severe impact on the environment due to the huge amount of greenhouse gases emitted to the atmosphere [1,2]. In the early 80 s geopolymers were introduced as alternative construction materials with a lower environmental impact [3]. The geopolymer binder is synthesized by mixing materials rich in silica and amorphous alumina with a strong alkaline activator [4]. Geopolymers are a very interesting concrete alternative, with an improved performance compared to traditional concretes [5], while utilizing a high proportion of industrial by-products such as fly ash (FA), coal ash and blast furnace slag. The incorporation of micro-encapsulated phase change materials (MPCM) in building materials, such as mortar and concrete can improve the thermal energy storage capacity of building structures, thereby decreasing the energy demand in buildings [6]. However, the presence of MPCM decreases the workability and mechanical strength of concrete [7]. In spite of reducing the concrete compressive strength by addition of MPCM, it is still often high enough to be used in building constructions.