The challenge for the civil engineering community in the near future will be to realize the
building of structures in harmony with the concept of sustainable development, through the
use of high performance materials which have low environmental impact and can be
produced at reasonable cost. Geopolymers are novel binder materials that could provide a
route towards this objective. Although research on geopolymer has advanced, most of the
previous research conducted on geopolymers has dealt with pastes and concentrated on the
material's chemistry and microstructure. There is little information available concerning the
engineering and durability properties of geopolymer concrete and none considering the use
of natural pozzolans for production of geopolymer concrete.
This investigation has studied the potential of using five natural pozzolans from Iran as
geopolymer precursors. Most of the raw materials contain zeolites and clay minerals and
have a high loss on ignition. Therefore, trials were made where samples were calcined at
700, 800 and 900°C. The solubility of both the raw and calcined materials in an alkaline
solution was used as an indicator for pozzolanic activity. Improvements in pozzolanic
properties due to heat treatment and elevated curing temperatures (20, 40, 60, and 80°C)
were studied by using alkali solubility, XRD and compressive strength tests. It has been
found that geopolymer binders can be synthesized by activating natural pozzolans and
condensing them with sodium silicate in a highly alkaline environment. A new model is
presented which allows the prediction of the alkali activated pozzolan strength from
information on their crystallinity, chemical compositions and alkali solubility.
Two types of Iranian natural pozzolans, namely Taftan which can be activated without
calcination and Shahindej which was calcined were selected for further activation to study
the effect of the alkaline medium on the strength of the alkali-activated natural pozzolan.
The effect of the type, form, and concentration (molarities =2.5, 5.0, 7.5, 10.0 M) of the
alkaline hydroxide, the modulus of sodium silicate (Si02INa20 ratio =2.1, 2.4, 3.1) and
different curing conditions on the geopolymerisation of the above two natural pozzolans
were studied. The optimum range and contributions for each factor is suggested based on
their effect on compressive strength.
An optimum paste formulation has been developed for concrete mixing together with the
procedure of addition of the raw materials to the reaction mixture and suitable curing
methods for producing the geopolymer concrete derived from them. The properties of this
geopolymer concrete in both the fresh and hardened states have been investigated in terms
of setting time, workability, air content, compressive strength, splitting tensile strength,
static modulus of elasticity, ultrasonic pulse velocity, and drying shrinkage. Studies related
to durability such as gas permeability, chloride ion penetration, and sulphate resistance
have been undertaken and compared to these for typical OPC concretes. Some problems
were encountered in applying the standard concrete durability tests. In this study attempts
have been made to determine the relationships between the different properties of
geopolymer concrete with its compressive strength and compared to results for ope
concrete, to help to explain the differences between alkali-activated natural pozzolan
concrete and ope concrete. In the countries which have large resources of natural
pozzolan, geopolymer concrete based on alkali activation of these resources can help
decrease the energy consumption and environmental impacts involved in using traditional
cement pastes.