Metakaolin-based Geopolymer Cements Research Articles

STRENGTH AND CORROSION RESISTANCE OF METAKAOLIN-BASED GEOPOLYMER HYBRID MORTAR

The utilization of metakaolin in the manufacture of geopolymers as a cement replacement material can be improve several of the physical, mechanical, and resistance properties of mortar in a corrosive environment. This paper presents the characteristics of metakaolin-based geopolymer cement mortar tested for setting time, compressive strength, and corrosion resistance. In this study, cement of the Portland Cement Composite type was added to the mortar mixture with 5% metakaolin forming a metakaolin-based geopolymer hybrid mortar. Three mortar mixes, namely MN (Normal Mortar), MK-100 (100% metakaolin), MK-95 (95% metakaolin and 5% cement), were cast and cured under ambient temperature until the testing days at 3, 7, and 28 days respectively. The alkaline activator ratio (Na2SiO3/NaOH) of 2, water to binder ratio of 0.8 was selected to form metakaolin-based geopolymer mortar specimens and the water binder ratio of 0.5 was selected to mix the cement mortar (MN). The results show that MK-100 and MK-95 exhibited a higher compressive strength than the cement mortar (MN) on all of the testing days. However, MK-95 showed a better performance in terms of corrosion resistance with a lower corrosion rate density compared to the MN and MK-100 mortar specimens. This indicates that the metakaolin-based geopolymer hybrid mortar with a 5% cement mixture can be applied on site as a repair and coating material, particularly for construction in a corrosive environment.

STRENGTH AND CORROSION RESISTANCE OF METAKAOLIN-BASED GEOPOLYMER HYBRID MORTAR

The utilization of metakaolin in the manufacture of geopolymers as a cement replacement material can be improve several of the physical, mechanical, and resistance properties of mortar in a corrosive environment. This paper presents the characteristics of metakaolin-based geopolymer cement mortar tested for setting time, compressive strength, and corrosion resistance. In this study, cement of the Portland Cement Composite type was added to the mortar mixture with 5% metakaolin forming a metakaolin-based geopolymer hybrid mortar. Three mortar mixes, namely MN (Normal Mortar), MK-100 (100% metakaolin), MK-95 (95% metakaolin and 5% cement), were cast and cured under ambient temperature until the testing days at 3, 7, and 28 days respectively. The alkaline activator ratio (Na2SiO3/NaOH) of 2, water to binder ratio of 0.8 was selected to form metakaolin-based geopolymer mortar specimens and the water binder ratio of 0.5 was selected to mix the cement mortar (MN). The results show that MK-100 and MK-95 exhibited a higher compressive strength than the cement mortar (MN) on all of the testing days. However, MK-95 showed a better performance in terms of corrosion resistance with a lower corrosion rate density compared to the MN and MK-100 mortar specimens. This indicates that the metakaolin-based geopolymer hybrid mortar with a 5% cement mixture can be applied on site as a repair and coating material, particularly for construction in a corrosive environment.

Influence of the synthetic calcium aluminate hydrate and the mixture of calcium aluminate and silicate hydrates on the compressive strengths and the microstructure of metakaolin-based geopolymer cements

The main goal of this study is to investigate the effects of the calcium aluminate hydrate (CA04) and the mixture of calcium aluminate and silicate hydrates (CA04 + CS04) on the compressive strengths and the microstructure of metakaolin-based geopolymer cements. Bauxite, rice husk and eggshells were calcined and mixed in proper amounts to prepare CA04 and CS04. Metakaolin has been substituted by 0, 5, 10, 15 and 20 wt% of CA04, 10 and 20 wt% of (CA04 + CS04) in the formulation of geopolymer cements. The clay-like solid materials were characterized by measuring their compressive strengths, the crystalline and amorphous phases were monitored using the X-ray diffractometry analysis, their microstructures were investigated using the scanning electron microscope and mercury intrusion porosimetry and the functional groups were studied using the infrared spectroscopy. The compressive strengths of geopolymer cements containing 0, 5, 10, 15 and 20 wt% of CA04 are 49.50, 57.17, 63.59, 38.79 and 35.05 MPa, respectively. Those containing 10 and 20 wt% of (CA04 + CS04) are 40.59 and 51.19 MPa, respectively. The average pore diameters of geopolymer cements containing 0, 10 and 20 wt% of CA04 are 11.80, 10.10, 12.20 nm, respectively. Whereas the one containing 20 wt% of (CA04 + CS04) is 10.80 nm. It appears that geopolymer cement with 10 wt% of CA04 and 20 wt% of (CA04 + CS04) have higher compressive strengths and lower average pore diameters. It was found that 10 and 20 wt% of CA04 and (CA04 + CS04), respectively, could be used as additives for the preparation of geopolymer cements with higher strength development.

Concrete crack repair analysis with metakaolin-based geopolymer cement

Abstract Among the advances in the use of geopolymer cements is their use as repair materials in concrete structures. The objective of this work was to use a geopolymer cement to repair cracks in concrete specimens, observing its mechanical performance and fracture modes. Cubic test specimens were produced and two types of cracks were evaluated as variables. Cracks were induced by steel sheets during concreting. The geopolymer cement paste and an epoxy adhesive, as reference, were used for the repairs. The results showed a 13% decrease in compressive strength for unrepaired concrete, and 3.7% in concrete repaired with geopolymer. The binder presented mechanical performance similar to that of the epoxy resin regarding crack recovery. In conclusion, repairs made with geopolymer cement are a viable and efficient means of crack recovery.

Evaluation of the Antibacterial Activity of a Geopolymer Mortar Based on Metakaolin Supplemented with TiO2 and CuO Particles Using Glass Waste as Fine Aggregate

Metakaolin-based geopolymer cements were produced by alkaline activation with a potassium hydroxide and potassium silicate solution. To produce the geopolymer composites, 10 wt.% titanium oxide (TiO2) and 5 wt.% copper oxide (CuO) nanoparticles were used. The geopolymer mortar was prepared using glass waste as fine aggregate. The raw materials and materials produced were characterized by X-ray diffraction, electron microscopy, and Fourier-transform infrared spectroscopy techniques. Likewise, the geopolymer samples were characterized to determine their physical properties, including their density, porosity, and absorption. The photocatalytic activity of the materials was evaluated by activating the nanoparticles in a chamber with UV–Vis light during 24 h; then, different tests were performed to determine the growth inhibition of Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa bacteria in nutrient agar for times of up to 24 h. The study results showed that a geopolymer mortar containing glass waste as fine aggregate (GP-G) exhibited a water absorption 56.73% lower than that of the reference geopolymer paste without glass (GP). Likewise, glass particles allowed the material to have a smoother and more homogeneous surface. The pore volume and density of the GP-G were 37.97% lower and 40.36% higher, respectively, than those of the GP. The study with bacteria showed that, after 24 h in the culture media, the GP-G mortars exhibited a high inhibition capacity for the growth of P. aeruginosa from solutions of 10−4 mL and in solutions of 10−6 mL for E. coli and S. aureus. These results indicate the possibility of generating antibacterial surfaces by applying geopolymer composite.

Improvement of the reactivity of soda–lime–silica glass solution as a hardener for producing geopolymer materials

The aiming target of this study is to improve the reactivity of the soda–lime–silica glass solution as a hardener for producing metakaolin-based geopolymer cements. The hardeners with molar ratios SiO2/Na2O equal to 1.5 from rice husk ash and waste glass were prepared. Due to the low dissolution of waste glass, the molar ratio SiO2/Na2O in soda–lime–silica glass solution is less than 1.5 suggesting thus the lower soluble silica content. In order to compensate for the deficiency of soluble silica in soda–lime–silica glass solution, the hardener from rice husk ash is added to the soda–lime–silica glass solution at different percentage such as 0, 20, 30, 40, 50, 60, 70, 80 and 100 wt%. The reactivity of the obtained hardeners was evaluated by using them for producing geopolymer cements. The X-ray pattern and infrared spectrum of residual waste glass indicate the higher intensity of the broad hump structure and the higher value of the wavenumber of the main band, respectively. This corresponds to the higher amount of glass phase contained in the residual waste glass. It was found that the values of the compressive strengths and the apparent density increase with increasing the addition of hardener from rice husk ash to the one from waste glass. The micrographs of geopolymer cements from hardeners containing 40, 50 and 100 wt% of sodium waterglass from rice husk ash are homogeneous and compact microstructure. This implies the formation of the higher connectivity and the long chain of poly(sialate-siloxo) network. The new approach for the preparation of a reactive hardener from the waste glass is found promising for the significant reduction of the greenhouse gas emitted during the production of geopolymers.

Microstructure and mechanical, physical and structural properties of sustainable lightweight metakaolin-based geopolymer cements and mortars employing rice husk

ABSTRACTThis work focuses on an in-depth investigation of the formation of pores in the structure of lightweight geopolymer cements and mortars using rice husk as a foaming agent. The hardener used in this study was sodium waterglass. Metakaolin was replaced by 0, 10, 20, 30 and 40 % by mass of husk and the obtained powders were used to produce lightweight geopolymer cements and mortars. The formation of pores in the lightweight geopolymer cements was monitored using X-ray diffractometry and infrared spectroscopy while those in the mortars were assessed using apparent density and compressive strength measurements, mercury intrusion porosimetry and optical and scanning electron microscopy. The values for the compressive strength and apparent density were in the ranges of 28.92–0.75 MPa and 1.88–1.70 g/cm3, respectively. The results indicated that the values for the compressive strength and apparent density of geopolymer mortars decreased while those of the cumulative pore volume increased with increases in the metakaolin replacement level. Stereomicroscopic and scanning electron microscopic images showed the presence of rice husk and fibres of rice husk, respectively, in the networks. It was found that rice husk can be used as a foaming agent for producing sustainable lightweight geopolymer mortars.

Design of low cost semi-crystalline calcium silicate from biomass for the improvement of the mechanical and microstructural properties of metakaolin-based geopolymer cements

Abstract The main objective of this work is to use low-value SiO2 and CaO-rich wastes like rice husk ash and chicken eggshell powders, respectively for producing semi-crystalline calcium silicate with molar ratio CaO/SiO2 equal to 0.4. The prepared valuable semi-crystalline calcium silicate was used as an additive for a replacement level of metakaolin (0, 1, 3, 5, 7 and 10% by mass). The resulting powders were used to synthesize geopolymer cements using hardener obtained by mixing commercial sodium silicate, sodium hydroxide and distilled water. The final products were characterized by compressive strengths, apparent density, X-ray diffractometry, infrared spectroscopy, scanning electron and optical microscope observations. The results show that the compressive strengths of geopolymer cements were between 33.25 and 51.38 MPa. They increase when metakaolin was replaced by 5, 7 and 10% of semi-crystalline calcium silicate, but no significant change was observed on the strengths of geopolymer cements content 0, 1, 3 and 5% of semi-crystalline calcium silicate. The micrograph images of the selected geopolymer cements were homogeneous and compact and the one from 10% of semi-crystalline calcium silicate shows a coarse microstructure. It was found that the low-value silica and calcium-rich wastes such as rice husk ash and eggshell can be used to prepare semi-crystalline calcium silicate. The obtained product could be used as a low-cost additive to enhance the microstructural and mechanical properties of poly(sialate-siloxo) network.

Structural analysis of composite metakaolin-based geopolymer concrete

Abstract The study of alternative binders to Portland cement, such as geopolymer cements, offers the chance to develop materials with different properties. With this purpose, this study evaluated experimentally the mechanical behavior of a geopolymer concrete beam and compared to a Finite Element (FE) nonlinear numerical model. Two concrete beams were fabricated, one of Portland cement and another of metakaolin-based geopolymer cement. The beams were instrumented with linear variable differential transformers and strain gauges to measure the deformation of the concrete and steel. Values for the compressive strength of the geopolymer cement concrete was 8% higher than the Portland cement concrete (55 MPa and 51 MPa, respectively) and the tensile rupture strength was also 8% higher (131 kN) for the geopolymer concrete beam in relation to Portland cement concrete beam (121 kN). Distinct failure mechanisms were verified between the two samples, with an extended plastic deformation of the geopolymer concrete, revealing post-fracture toughness. The geopolymer concrete showed higher tensile strength and better adhesion in cement-steel interface.

Role of ɣ-Al2O3 on the mechanical and microstructural properties of metakaolin-based geopolymer cements

The main target of this work is to investigate the influence of ɣ-Al2O3 on the properties of metakaolin-based geopolymer cements. The kaolin used as starting material for producing geopolymer cements contains approximately 28 and 64% of gibbsite and kaolinite, respectively. This kaolin was transformed to metakaolins by calcination at 500, 550, 600, 650, and 700 °C for 1 h. Gibbsite contained in kaolin was transformed to γ-Al2O3 during the calcination process. The hardener was obtained by mixing commercial sodium silicate and sodium hydroxide solution (10 M) with a mass ratio sodium silicate/sodium hydroxide equal to 1.6:1. Geopolymer cements, GMK-500, GMK-550, GMK-600, GMK-650, and GMK-700, were obtained using the prepared hardener with a mass ratio hardener/metakaolin equal to 0.87:1. It could be seen that the specific surface area of metakaolins decreases with increasing the calcination temperature of kaolin owing to the formation of the particles of γ-Al2O3. The compressive strengths 18.21/29.14/36.61/36.51 increase in the course GMK-550/GMK-600/GMK-650/GMK-700. The X-ray patterns and micrograph images of geopolymer cements, GMK-600, GMK-650, and GMK-700, indicate the presence of γ-Al2O3 in their structure. It was typically found that γ-Al2O3 remains largely unaffected during the geopolymerisation, and therefore could act as an inert filler and reinforce the structure of geopolymer cements.

The effects of synthesized calcium phosphate compounds on the mechanical and microstructural properties of metakaolin-based geopolymer cements

Dicalcium phosphate dihydrate (DCPD) and hydroxyapatite (HAP) were prepared from oyster shell powder and phosphoric acid solution as raw materials using sol-gel process in order to study the influence of calcium phosphate compounds on the mechanical and microstructural properties of metakaolin-based geopolymer cements. The synthesized DCPD and HAP with molar ratio Ca/P equal to 1.00 and 1.65, respectively, were used as additives for replacement of metakaolin (0, 2, 4, 6, 8 and 10 wt%) and the resulting powders were used for producing geopolymer cements. The compressive strengths of geopolymer cements containing DCPD were in the range 40–48 MPa with increasing DCPD content, but when 10 wt% was used, the strength fell to 26 MPa. Similar results were obtained for HAP addition with a decrease of the compressive strength at 8 wt%. The ESEM images of geopolymers containing 4–10 wt% of HAP showed some non-reacted or partially reacted particles that do not well connect to the matrix. Samples of geopolymer with 4–8 wt% of DCPD present a lower number of unreacted particles and the matrix appeared denser than that of the control geopolymer cements. The use of calcium phosphate compounds such as brushite and hydroxyapatite led to the overall improvement in compressive strength and contribute to the densification of the structure of geopolymer cements. On the other hand, the addition of 4% of HAP and 10% of DCPD resulted in a large amount of hydroxyapatite and brushite, respectively in the systems. The matrix appear less dense indicating that a fraction of calcium phosphate addition at the aforementioned level was excessive.

Utilization of sodium waterglass from sugar cane bagasse ash as a new alternative hardener for producing metakaolin-based geopolymer cement

Sugar cane bagasse ash from SOSUCAM company in Cameroon was used to synthesize sodium waterglass as a new alternative hardener. The new hardener was used to prepare metakaolin-based geopolymer cements. The compressive strength of the resulting geopolymer cement cured at room temperature for 28days was 32.9MPa. Samples soaked for 28 days in water in parallel experiments revealed a strength of 31.4MPa. This shows that exposure of water does not lead to any weakening. The value of water absorption was 7.1% in the water-soaked cements, indicating the presence of fewer pores and voids than in the dry cements. However, in SEM micrographs, the microstructure of geopolymer cement appears rather homogeneous and compact without any change by water soaking. It can thus be concluded that sodium waterglass from sugar cane bagasse ash can be used as an alternative hardener or reactive ingredient for producing geopolymer cement with a high degree of cross-linking geopolymer framework. The use of this low-value silica-rich waste for producing sodium waterglass results in environmental benefits including a significant reduction of CO2 emission and energy consumption compared to the production of commercial sodium waterglass.

Mechanical and microstructural properties of metakaolin-based geopolymer cements from sodium waterglass and phosphoric acid solution as hardeners: A comparative study

Sodium waterglass with mass ratios SiO2/Na2O and H2O/Na2O equal to 1.5 and 10, respectively was prepared from commercial silica fume as a silica source. The phosphoric acid solution with molar concentration 10M was prepared by dilution of commercial phosphoric acid in distilled water. The ATR-infrared spectrum of alkaline hardener shows the presence of SiQ0, SiQ1 and SiQ2 units suggesting a more depolymerized solution. While the acid hardener contains H2PO4− due to the deprotonation of commercial H3PO4 indicating that the molar concentration 10M contained an appropriate amount of water necessary for the workability. The formation of H2PO4− is appropriate for the second step of geopolymerization. Metakaolin-based geopolymer cements were obtained by adding each fresh hardener to metakaolin. The results show that the compressive strength of phosphate-based geopolymer cement is 93.8MPa while the one of alkali-based geopolymer cement is 63.8MPa. The difference of the compressive strength could be related to the formation of berlinite (AlPO4) in the structure of phosphate-based geopolymer cement which acts as a filler and reinforces the structure and therefore the compressive strength of the specimen. However, the microstructures of both geopolymer cements are homogeneous and compact structure. It was typically found that phosphate-based geopolymer cement has a higher compressive strength compared to the one of alkali-based geopolymer cement. It is important to note that the hardening of metakaolin-based geopolymer cement from phosphoric acid solution required an energy gradient while metakaolin-based geopolymer cement from sodium waterglass hardens at room temperature like regular Portland cement. The purpose of this work was to compare the mechanical and microstructural properties of metakaolin-based geopolymer cements obtained in the same condition using sodium waterglass and phosphoric acid solution as hardeners. Due to their higher mechanical properties, phosphate-based geopolymer cement could be used for the construction of roads and bridges and geopolymer cements from alkaline medium could be used for building the houses.

Substitution of sodium silicate with rice husk ash-NaOH solution in metakaolin based geopolymer cement concerning reduction in global warming

Rice husk ash (RHA), a by-product from the rice industry, was used as principal source of amorphous silica for the production of sodium silicate solution (MR ∼ 3) used for the replacement of standard commercial sodium silicate in the mix-design of metakaolin based geopolymer composites. Three initial concentrations of NaOH were considered (8, 10 and 12 M) with the aim to investigate on the optimum dissolution and formation of silica oligomers capable to act as binder during the geopolymerization. Results (FT-IR and XRD) showed that RHA-NaOH sodium silicate solutions have characteristics similar to that of standard commercial sodium silicate and the residual carbonates present in the viscous pastes can be monitored during the preparation of geopolymers using the mix-design. Combined 25 vol% standard sodium silicate solution with ∼75 vol% of RHA-NaOH based sodium silicate solution conducted to good polycondensation, densification, high flexural strength (∼8 MPa) and low porosity similar to that of the standard matrix of metakaolin based composites. The new approach is found promising for the significant reduction of the Global Warming Potential of Geopolymers.

Thermal Behavior of Metakaolin-Based Geopolymer Cements Using Sodium Waterglass from Rice Husk Ash and Waste Glass as Alternative Activators

The aim of this work was to study the thermal behavior of metakaolin-based geopolymer cements using sodium waterglass (NWG) from rice husk ash and waste glass as alternative alkaline activators. Metakaolin-based geopolymer cements were obtained by adding freshly prepared NWG and metakaolin. The geopolymer cements obtained using sodium waterglass from rice husk ash and the one obtained with sodium waterglass from the waste glass were treated at room temperature for 28 days and then heated at 200, 400, 600 and 800 °C. The results show that the metakaolin-based geopolymer cements lose their compressive strength from room temperature to 400 °C. At 600 °C, the compressive strength of geopolymer cements increases relative up to 200 and 400 °C. At 800 °C, the reduction of compressive strength of geopolymer cements is assigned to the total evaporation of the rest of structural water. However, it is higher than that measured at ambient temperature for geopolymer cement obtained using the sodium waterglass from waste glass but lower for the sample obtained with sodium waterglass from rice husk ash. The total mass loss of geopolymer cements obtained with sodium waterglass from rice husk ash and one obtained with sodium waterglass from waste glass are about 12.57 and 15.04 %, respectively. This suggests that geopolymer cement obtained using sodium waterglass from waste glass are more condensed geopolymer structure indicating that it could a very suitable material for fire resistant application. The results indicate that NWG from rice husk ash and waste glass could be served as suitable alternative activators for producing metakaolin-based geopolymer cements with high-temperature performance.

Synthesis of sodium waterglass from white rice husk ash as an activator to produce metakaolin-based geopolymer cements

Rice husk from source in Cameroon was leached in HCl (5M) to remove the most of metallic ingredients and then calcined at 600°C in order to produce white rice husk ash. This white ash were applied for producing sodium waterglass with different molar ratios SiO2/Na2O (0.31; 0.47; 0.62; 0.78; 0.93; 1.09 and 1.25) and then used to synthesize metakaolin-based geopolymer cements. The obtained white rice husk ash shows the loss of crystalline mineral and reveals high amorphous silica with quartz as impurity. Geopolymers GPi (i varying from 1 to 7) were obtained using different synthesis sodium waterglass (NWG) with a mass ratio NWG/MK=0.87. It could be observed that the 28 days compressive strength (4/5/7/9/32/34/36MPa) increase with increasing the molar ratios SiO2/Na2O defined in this work in the course GP1/GP2/GP3/GP4/GP5/GP6/GP7. The micrographs show the formation of more geopolymer gels when the molar ratios SiO2/Na2O in alkaline activators are between 0.93 and 1.25. Sodium waterglass from white rice husk ash proved to be an effective alkaline activator in geopolymers preparation. It can be concluded that it is possible to replace quartz sand and sodium carbonate which is responsible to greenhouse gas emitted during the production of commercial sodium silicate solution by using rice husk as silica sources.

Thermal Behavior of Portland Cement and Fly Ash–Metakaolin-Based Geopolymer Cement Pastes

Geopolymer specimens were prepared by combination of fly ash and metakaolin activated by sodium silicate (\({{\rm Na}_{2}{\rm SiO}_{3}}\)) and sodium hydroxide (NaOH) solutions. The effect of high temperature on the compressive strength, mass loss and shrinkage of geopolymer cement pastes and ordinary portland cement (OPC) pastes were assessed experimentally. Microstructure formation and development were characterized in terms of pore structure by mercury intrusion porosimetry. The results reveal that at temperatures exceeding \({400\,^{\circ}{\rm C}}\) geopolymer cement paste is superior to OPC paste. Firstly, the compressive strength drops rapidly for the OPC paste to practically zero strength at \({600\,^{\circ}{\rm C}}\) , while it drops slowly for the fly ash–metakaolin-based geopolymer cement paste to 46 MPa at \({1000\,^{\circ}{\rm C}}\) . Secondly, while the mass loss increases for the OPC paste, it is maintained at a constant, lower value for the geopolymer cement paste. Thirdly, shrinkage of geopolymer cement paste is at least three times smaller than that of OPC paste.

Influence of gibbsite and quartz in kaolin on the properties of metakaolin-based geopolymer cements

Three different kaolins (K1, K2, K3) from sources in Cameroon were applied for producing geopolymer cements. The kaolins differ significantly in their gibbsite and quartz contents. Thermal transformation (700°C, 4h) into their metakaolins MK1, MK2, MK3 shows the total loss of crystalline kaolinite and reveal the typically rather broad bump in the X-ray pattern. Gibbsite becomes dehydrated into γ and χ-Al2O3. Geopolymer cements (GP1, GP2, GP3) were obtained using freshly prepared sodium silicate solutions (NWG) with a ratio NWG/MK=0.87. It could be observed that the initial (60/80/90min) and final (90/140/160min) setting time increases and their 28day compressive strength (49/39/30MPa) decreases in the course GP1/GP2/GP3. It is discussed that the higher content of quartz in K1 (up to 22wt.%), compared to K2 (10wt.%) and K3 (8wt.%) promotes higher strength values and decreased setting times. Gibbsite was not present in K1, but up to 11wt.% in K2 and 28 wt.% in K3, transformed in its dehydrated forms remains unreacted during geopolymerization. Therefore, the higher content of gibbsite in the kaolinite could be related to a lower strength. The reacted volumes and compositions of the geopolymer become almost the same in all three cases. A content of 30–50% of unreacted metakaolin was proved in all cases.