Geopolymer concrete: A review of some recent developments

http://jultika.oulu.fi/files/nbnfi-fe2017112150815.pdf

One-part alkali-activated materials : a review

Fly ash-based geopolymer: clean production, properties and applications

An overview on the influence of various factors on the properties of geopolymer concrete derived from industrial by-products

Role of slag in microstructural development and hardening of fly ash-slag geopolymer

This study investigates the effect of silica and alumina contents on setting, phase development, and physical properties of high calcium fly ash (ASTM Class C) geopolymers. The characteristic rapid setting properties and, hence, limited workability range of high calcium fly ash geopolymers has restricted both development and potential application of these binder systems compared to conventional geopolymer binders derived from bituminous coal, i.e., (ASTM Class F) sources or from calcined kaolin feedstocks. For this study, control of setting and hardening properties were investigated by adjusting SiO2/Al2O3 ratio of the starting mix, via series of mixes formulated with varying SiO2 or Al2O3 contents to achieve SiO2/Al2O3 in the range 2.87–4.79. Foremost is the observation that the effect of varying silica and alumina in high calcium fly ash systems on setting and hardening properties is markedly different from that observed for traditional Class F geopolymer systems. Overall, increases in either silica or alumina content appear to shorten the setting time of high calcium-based systems unlike conventional geopolymer systems where increasing Al2O3 accelerates setting. The setting process was associated primarily with CSH or CASH formation. Furthermore, there appears to be a prevailing SiO2/Al2O3 ratio that prolongs setting, rather than Ca2+ ion content itself, while NASH primarily contributes to strength development. SiO2/Al2O3 ratios in the range of 3.20–3.70 resulted in products with highest strengths and longest setting times. These results suggest that initial predominance of Ca2+ ions and its reactions effectively help maintaining a SiO2/Al2O3 ratio at which amorphous geopolymer phase is stable to influence setting and initial strength development.

Effect of SiO2 and Al2O3 on the setting and hardening of high calcium fly ash-based geopolymer systems

This paper examines the short-term resistance ability of two different cementitious systems prepared using silty clay as a major component against 5 wt% sodium sulfate and 5 wt% magnesium sulfate solutions. The two cementitious systems are clay–portland cement and clay-high calcium fly ash (FA) geopolymer. The 28-day strength of the clay-FA geopolymer is up to 1.2 times higher than that of clay-cement. The results show that the physical performance of clay-FA geopolymer when exposed to sulfate solution is better than that of clay-cement. While the geopolymer phase is prominent in the clay-FA geopolymer system, gypsum, and ettringite phases are present in both systems especially in the clay-cement system. The strength reduction in clay-cement with duration of sulfate exposure is caused by the formation of ettringite and crystallization of gypsum (observed by scanning electron microscope and X-ray diffraction) as well as the decalcification of CSH phases. There is no major change in the microstructu...

Sulfate Resistance of Clay-Portland Cement and Clay High-Calcium Fly Ash Geopolymer

The effect of ai203 and si02 on setting and hardening of na20-ai203-si02-h20 geopolymer systems

This study evaluates the role and relationship between SiO2 and Al2O3 contents of aluminosilicate material on the properties of Si-rich geopolymer systems using Australian fly ashes and existing published data. The selected fly ashes, with varying amounts of amorphous and total SiO2 and Al2O3 were assessed for their overall reactivity. XRD analyses yielded traces of sodalite in addition to conventional amorphous geopolymer phase for the fly ash mixtures with amorphous SiO2/Al2O3 = 3.31. The other two fly ashes with higher amorphous SiO2/Al2O3 ratio tended to produce sodium aluminosilicate zeolitic phases comprising mainly of Na-P1 zeolite and faujasite. These latter phases originate from Na2O–Al2O3–SiO2–H2O gel assemblages but the pathway appears to be governed by the available reactive SiO2 and Al2O3 in the reaction environment. However, indices based on the amorphous content or more precisely amorphous SiO2/Al2O3 ratio provided a relatively good correlation with the compressive strength of the final pro...

Influence and role of feedstock Si and Al content in Geopolymer synthesis

Carbonation has long been recognised as a durability issue attributed to corrosion of steel reinforcement in geopolymer materials. The currently available information, however, is not sufficient to gain a deep understanding of this issue, particularly the facet of the carbonation impact on the pore structure of such materials. This paper, thus, assessed the influence of carbonation on porosity and pore size characteristics of one-part fly ash/slag geopolymer mortar, by using neutron tomography. The cutting-edge thermal neutron tomography used in this study provided the prowess of non-destructive 3D analysis of exploring different regions within geopolymers. The results obtained showed that carbonation in the investigated geopolymer mortars drew their porosity down approximately 30% and shifted pore size regions to smaller pore areas. Other evaluations such as changing pH, carbonation front depth and elemental mapping by scanning electron microscopy (SEM) with energy dispersive X-ray spectrometry (EDS) were also performed in this study, in order to supplement the findings of neutron tomography.

Assessing carbonation in one-part fly ash/slag geopolymer mortar: Change in pore characteristics using the state-of-the-art technique neutron tomography

Pre De Silva

Papers

Effect of SiO2 and Al2O3 on the setting and hardening of high calcium fly ash-based geopolymer systems

Sulfate Resistance of Clay-Portland Cement and Clay High-Calcium Fly Ash Geopolymer

The effect of ai203 and si02 on setting and hardening of na20-ai203-si02-h20 geopolymer systems

Influence and role of feedstock Si and Al content in Geopolymer synthesis

Assessing carbonation in one-part fly ash/slag geopolymer mortar: Change in pore characteristics using the state-of-the-art technique neutron tomography