The document discusses the effects of curing temperature on geopolymer composites. It notes that higher curing temperatures of 50°C and 80°C lead to a more compact microstructure and higher degree of geopolymer reaction over longer curing periods. However, very high curing temperatures of 80°C result in larger pores and defects due to faster evaporation. Lower curing temperatures around room temperature help material densification as the geopolymer gel saturates microstructural voids. Higher external curing temperatures of 45°C also accelerate geopolymerization and can increase compressive strength by 55% compared to 25°C.

1. Chau-Khun Maa,
It is
amorphous rather than crystalline compared to other natural zeolitic
materials [3]. The polymerization requires a considerably
quick reaction of silica (Si)-alumina (Al) under alkaline condition
which subsequently create three-dimensional polymeric chain of
SiAOAAlAO bonds. Dissimilar to OPC or pozzolanic cements,
geopolymer utilizes the polycondensation of silica and alumina
and a high alkali content to attain compressive strength
Zhang et al. [13] that activation by NaOH alone
can form crystalline zeolite or nanosized crystals of another zeolite, depending on
the Si/Na ratio. The addition of Sodium Silicate can reduce the crystallite formation
significantly.
Matteo Sambucci
The
process, commonly defined as “geopolymerization”, produces a three-dimensional (3D)
inorganic network with an amorphous/semi-crystalline microstructure. Unlike the
ordinary PC, in which calcium silicate hydrates (C-S-H) gel is the main binding
compound, GC utilizes the polycondensation of Silica (SiO2) and alumina (Al2O3) sources
and a high-alkali environment
Nikolov et al. [28] examined the different types of activator solutions on
natural zeolite (clinoptilolite) to produce material with practical use. The
research reveals low mechanical strength tendency to shrinkage, due to the
partial dissolution of main alumino-silicate and the considerable water
demand of the fresh mixes
Curing time and temperature. Recent findings of the effect of curing treatment on the
pore system of FGC-based materials are reported in the research of Zhang et al. [44].
The authors investigated the relationship of microstructural properties development
of FGCs and its dependence on curing conditions (room temperature, 50 _C and
80 _C for 7, 28, and 49 days). For each curing temperature, the porosity rate of the
samples decreased with the heat curing period. Macro-pores (50–100 _m) constituted
the geopolymer matrix under 7 days curing time. As the heat treatment increased,
the percentage of large pores tended to decrease, but a more significant contribution

2. of microcracks due to the material’s drying occurred. In this regard, the greater the
temporal extension of the thermal treatment, the higher the geopolymer reaction
degree, increasing the inorganic gel formation that constructed a more compact microstructure
[39]. Curing temperature is crucial to the overall pore volume. Similar
pore content was observed at room and middle curing temperatures (about 5% and
4.5%, respectively, while a higher pore fraction (about 8%) was detected in the samples
cured at 80 _C. Faster water evaporation and hardening process at higher curing temperature results in a less
ordered medium of poorer quality having larger pores and
defects. On the other hand, lower curing temperatures help the material densification,
as the geopolymer gel tends to saturate the microstructural voids [45].
Lateef Assi,
reason for
the significant difference in the compressive strength is due to
the external temperature that accelerates the reaction between
the fly ash components, especially silica and alumina compounds,
and the activating solution. By comparing the compressive
strength of the samples at 45 _C (113_F) and 25 _C (77_F), the compressive
strength increased by 55% at the 45 _C (113_F) temperature.
In addition, it can be understood that using high external
temperatures accelerates the geopolymerization process of FGCsilica
fume rapidly because it provides the required energy for
enhancing the reaction between the fly ash and activating solution,
for instance, a compressive strength of 82.7 MPa (12,000 psi) in
one day was achieved. This experiment indicates that FGC-silica
fume is more suitable for hot weather conditions, such as the middle
east, since with high average temperatures, between 40 (104_F)
and 45 _C (113_F), a considerable compressive strength can be
achieved (around 68.3 MPa [9900 psi]) within 7 days. It is not only
the energy cost that is needed when increased external temperatures
are used, but also the application of this type of concrete
may be limited to prestressed and precast structures. Such reasons
lead us to use external temperature has as an important effect on
the cost, and justifies the utilizations of fly ash-based silica fume
activating solution geopolymer concrete.
As a result, the achieved compressive strength
Z Zaidahtulakmal
Curing temperature do give effect on the hardening and geopolymerisation
process in the geopolymer matrix by accelerating the reaction. The accelerated reaction enhances the
bonding between aggregate and geopolymer matrix and thus strengthened the geopolymer mortar
specimens