Geopolymerization Reaction Research Articles

Estimating strength properties of geopolymer self-compacting concrete using machine learning techniques

There has been a persistent drive for sustainable development in the concrete industry. While there are series of encouraging experimental research outputs, yet the research field requires a standard framework for the material development. In this study, the strength characteristics of geopolymer self-compacting concrete made by addition of mineral admixtures, have been modelled with both genetic programming (GEP) and the artificial neural networks (ANN) techniques. The study adopts a 12M sodium hydroxide and sodium silicate alkaline solution of ratio to fly ash at 0.33 for geopolymer reaction. In addition to the conventional material (river sand), fly ash was partially replaced with silica fume and granulated blast furnace slag. Various properties of the concrete, filler ability and passing ability of fresh mixtures, and compressive, split-tensile and flexural strength of hardened concrete were determined. The model development involved using raw materials and fresh mix properties as predictors, and strength properties as response. Results shows that the use of the admixtures enhanced both the fresh and hardened properties of the concrete. Both GEP and ANN methods exhibited good prediction of the experimental data, with minimal errors. However, GEP models can be preferred as simple equations are developed from the process, while ANN is only a predictor.

The effect of microencapsulated phase change materials on the rheology of geopolymer and Portland cement mortars

AbstractThe effect of microencapsulated phase‐change materials (MPCM) on the rheological properties of pre‐set geopolymer and Portland cement mortars was examined. Microcapsules with hydrophilic and hydrophobic shells were compared. The shear rate dependency of the viscosities fitted well to a double Carreau model. The zero shear viscosities are higher for geopolymer mortar, illustrating poorer workability. The time evolution of the viscosities was explored at shear rates of 1 and 10 s−1. New empirical equations were developed to quantify the time‐dependent viscosity changes. The highest shear rate disrupted the buildup of the mortar structures much more than the lower shear rate. Microcapsules with a hydrophobic shell affect the rheological properties much less than the microcapsules with a hydrophilic shell, due to the higher water adsorption onto the hydrophilic microcapsules. Shear forces was found to break down the initial structures within geopolymer mortars more easily than for Portland cement mortars, while the geopolymer reaction products are able to withstand shear forces better than Portland cement hydration products. Initially, the viscosity of geopolymer mortars increases relatively slowly during due to formation of geopolymer precursors; at longer times, there is a steeper viscosity rise caused by the development of a 3D‐geopolymer network. Disruption of agglomerates causes the viscosities of portland cement mortars to decrease during the first few minutes, after which the hydration process (increasing viscosities) competes with shear‐induced disruption of the structures (decreasing viscosities), resulting in a complex viscosity behavior.

Influence of the wollastonite and glass fibers on geopolymer composites workability and mechanical properties

This work aims to synthetize geopolymer composites and study the influence of the aluminum concentration, wollastonite and glass fibers on the properties of the fresh and hardened material. To this end, different metakaolin, wollastonite and glass fibers contents were used to synthesize geopolymer composites. The effect of reinforcement elements on the geopolymerization reaction has then been studied with FTIR spectroscopy and thermal analysis (DTA-TGA). Moreover, the viscosity and the setting time of the reactive mixture, as well as the compressive strength of the hardened material, have been measured for the different compositions. The results showed that the nature of the reinforcement added induces different polycondensation reactions. The wollastonite improves the viscosity and the mechanical properties by ensuring a better dissolution of the metakaolin, whereas the glass fibers act as an anchoring site during the geopolymerization reaction, leading to a ductile failure of the material. Finally, the aluminum content enables to monitor the viscosity and setting time of the reactive mixture and has a significant influence on the microstructure and the compressive strength. Thus, the initial formulation of the geopolymer composites allows controlling the properties of the fresh and hardened geopolymer composites.

Influence of nano SiO2 and nano CaCO3 particles on strength, workability, and microstructural properties of fly ash‐based geopolymer

AbstractThe influence of nano SiO2(NS) and CaCO3(NC) particles on the properties of class F fly ash based geopolymer mortar activated with different sodium ion concentrations have been investigated. Mortar mixture proportions were 1:3:0.3 for binder, sand, and water, respectively. Nano SiO2 and CaCO3 particles were replaced with a binder by weight basis at the ratios of 1, 2, and 3% in the mixtures. Sodium concentrations amount used were 8, 10, and 12% Na+ of binder content. Geopolymer mortar samples were cured at 60, 75, and 90°C in a furnace for 24, 48, and 72 hr. After the heat curing process, flexural, and compressive strength tests were performed. The changes in the microstructure of geopolymer due to influence of nanoparticles were examined by utilizing isothermal calorimetric studies on geopolymer paste, and field‐emission scanning electron microscopy (FESEM). Based on laboratory work results, it was concluded that for all sodium ion concentrations, the addition of nano SiO2 and CaCO3 particles improved the flexural and compressive strengths after 24 hr heat curing. However, the favorable effects of nanoparticles on strength properties tend to disappear after 48 and 72 hr heat curing. The results of isothermal calorimetric studies showed that nano SiO2 and CaCO3 particles accelerated the geopolymeric reactions at an early age. FESEM results showed that additions of nanoparticles made the microstructure of geopolymer products more intense and compact.

Thermal Exposure of Fly Ash-Metakaolin Blend Geopolymer with Addition of Monoaluminum Phosphate (MAP)

Recent research reveals that formulation of blended geopolymers based on the association of two aluminosilicate precursors had a better performance than one precursor geopolymers. This study presents a facile method to enhance the compressive strength of fly ash-metakaolin blend geopolymer by incorporating monoaluminum phosphate (MAP) during the geopolymerization reaction. The effect of the thermal exposure on the microstructure and compressive strength of the geopolymer are investigated. Results show that the MAP is transformed to granule structures, bonded and surrounded by geopolymer gel. The unique microstructure increases the compressive strength of the room temperature curing geopolymer from 54.7 MPa to 64.21 MPa (14.8%) with an optimum addition of 1.0 wt% MAP. This enhancement in compressive strength was ensured by the formation of an amorphous structure of aluminosilicophosphate (SiO2.Al2O3.P2O5.nH2O) phase. At higher temperatures, the formation of stable crystalline phase of berlinite and nepheline contribute to strength retention of the geopolymer. Hereby, it can be concluded that the addition of 1.0wt% MAP in the geopolymer reinforced the structure.

The effect of nanomaterials on properties of geopolymers derived from industrial by-products: A state-of-the-art review

Abstract Nanomaterials, owing to their extraordinary properties are known to improve the microstructure of concrete, enhances the fresh and hardened properties of cement concrete, are widely used in cementitious materials. Many studies have been conducted so far to understand the effects of inclusion of nanomaterials on the geopolymerisation reaction, fresh and hardened state properties, microstructure, and durability of geopolymer composites. The current paper summarizes these studies mainly focusing on the effects of various nanomaterials such as nano-SiO2, nano-Al2O3, nano-TiO2, carbon nanotubes and nano-clay on geopolymer paste, mortar and concrete derived from various industrial by-products as sources of aluminosilicates. Most of the geopolymer products revealed that nanomaterials enhance the fresh and hardened state properties if used in a controlled quantity. Nano-silica and nano clay inclusion up to 2% by weight significantly enhances the rate of geopolymerisation reaction, reduces the setting times and improves the hardened state properties. Carbon nanotubes and nano-TiO2 enhances geopolymerisation by offering additional nucleation sites. Nano-alumina more prominently reduces the porosity but lesser effective in geopolymerisation. X-ray diffraction studies report the increase in XRD peaks indicating the formation of additional hydration products that comply with SEM studies. Investigation of SEM and FTIR reveals that the inclusion of nanomaterials densify the microstructure of geopolymer composites and produce high mechanical strength. Durability studies reveal that enhanced geopolymerisation with nanomaterials also prevents interconnectivity of micropores due to the formation of a denser matrix of geopolymer gel. The possible health-related issues associated with the use of nanomaterials has also been identified. The cost effectiveness of using nanomaterials is also discussed.

Influence of the Kaolinite Calcination Conditions on the Compressive Strength of Geopolymer

Among the cementitious materials, geopolymers not only attract interest due to the low emission of CO2 in their manufacturing process, but also because of their good mechanical and chemical properties, together with their resistance to fire. They can be made from different raw materials including various wastes from industrial activities and mineral extraction. In this study, metakaolin was obtained from kaolinite calcined under different conditions. In this case kaolinite is a by-product of sand extraction. It was observed that the calcination conditions (kiln heating rate, calcination time and temperature) had a strong influence on the compressive strength of geopolymer after 28 days of cure. They also affected the composition of the geopolymer, which was prepared by mixing metakaolin, alkaline sodium silicate and sodium hydroxide solution.Compressivestrengthsintherangefrom10MPato50MPamaybeobserved, depending on the combination of these factors. A factorial design of experiments allowed the isolation of the effect of each factor and its interactions, offering new insights into the complexity of the geopolymeric reactions and highlighting the need for a rigid control of the calcination conditions of kaolinite and the composition of the geopolymer samples to obtain the desired compressive strength.
 Keywords: kaolinite, calcination, metakaolin, geopolymer, compressive strength.

Characteristics for Improvement of Compressive Strength of Geopolymers Made of Mixed Binders

Geopolymers are composite hard materials made by mixing binders, such as fly ash and slags, and activators, such as NaOH and sodium silicate. The chemical mechanism for hardening composite materials, aluminosilicate binders, with alkaline activators is known as a geopolymer reaction. Geopolymers have recently been developed to be used as a replacement for Portland cement concrete. Industrial by-products such as fly ash, steel making slags, and garbage melting furnace slags can be made into geopolymers in a process that emits less carbon dioxide than in the cement making process. This reduction in CO2 emission is important because CO2 is one of the substances known to contribute to global warming. In the future, further uses of these fly ash and slags must be explored. The development of high compressive strength geopolymers using fly ash and slags will strongly contribute to the fields of construction, geotechnical engineering, and architecture. So far, ground blast furnace slag has yielded the highest compressive strength geopolymer among various kind of binders such as fly ash, ground stainless steel-making slag, and garbage melting furnace slags. A potential use for the poor binders, yielding low compressive strength geopolymers, is to combine it with a richer binder to create stronger products. This paper examines the characteristics for improvement of compressive strength of geopolymers for the binders in various mixture ratios of poor binders and the ground blast furnace slag.

Improvement of early strength of fly ash-slag based one-part alkali activated mortar

One-part Alkali activated material (AAM) is eco-friendly replacement of OPC with adequate strength and durability characteristics. In this study, the impact of slag content, activator dosage, retarder content and curing temperature was evaluated on fresh and early-age mechanical properties of one-part fly ash/slag-based alkali activated mortar. For assessing the effect of curing temperatures, three temperatures were selected: 20 °C low ambient temperature, 35 °C high ambient temperature and 65 °C replicating heat curing. Consistency, setting time, mix temperature and pH measurements were recorded for fresh mix using standard procedures. In addition, hardened mortar specimens were tested for compressive and flexure strength in conjunction with microstructural characteristics (SEM, XRD, and FTIR analysis). The test results depicted that among all parameters, curing temperature governed the development of early age strength of one-part AAM mortar. Microstructural testing confirmed the enhancement of the geopolymerization reaction through heat curing thus leading to a substantial increase in the early strength.

Photocatalytic Degradation of Methylene Blue from Aqueous Medium onto Perlite-Based Geopolymer

In this work, geopolymer synthesized with perlite and an alkaline activator medium was evaluated as a new adsorbent and photocatalyst for degradation of methylene blue (MB) dye from an aqueous medium. The functional group, the structure, and the morphology of the raw and the synthesized materials were characterized using FT-IR, XRD, and SEM analysis. The degradation of MB in the contaminated solution was examined using the spectrophotometric technique. Several analysis methods revealed the formation of the aluminosilicate gel after the geopolymerization reaction. The kinetics data with UV and without UV irradiations were well fitted with the pseudo-second-order equation. The results indicated that the degradation efficiency of cationic dye by perlite-based geopolymer without and with UV was up to 88.94% and 97.87% in 4 hours, respectively. The degradation efficiencies of methylene blue are in the following order: perlite-based geopolymer under UV irradiations is greater than perlite-based geopolymer without UV irradiations that is larger than UV irradiations. The overall experimental results suggested that the new elaborated material with synergetic adsorption and photocatalytic activities has a great potential for the treatment of water contaminated by hazardous substances.

EVALUATION OF THE ENGINEERING PROPERTIES OF FLY ASH-BASED GEOPOLYMER BRICKS

This paper is aimed to evaluate the engineering properties of fly ash-based geopolymer bricks. Four geopolymer brick mixtures were designed with a constant solution-to-binder ratio of 0.40 and various concentrations of sodium hydroxide solution. The engineering properties of fly ash-based geopolymer bricks consisting of compressive strength, unit weight, water absorption, water permeability, and ultrasonic pulse velocity were investigated. The microstructure of fly ash-based geopolymer bricks was also investigated by using the scanning electron microscope (SEM). Test results indicated that the compressive strength, unit weight, and ultrasonic pulse velocity (UPV) of geopolymer bricks increased, while the water absorption and water permeability of geopolymer bricks reduced with increasing NaOH concentration. Moreover, brick samples with high NaOH concentration showed a higher geopolymeric reaction of fly ash than brick samples with low NaOH concentration. All geopolymer brick samples produced in this study showed a good quality with compressive strength of above 10.1 MPa, water absorption of below 9.4%, water permeability of below 1.84 L/m2 .h, and UPV of above 2500 m/s.

Mechanical, durability and fracture properties of nano-modified FA/GGBS geopolymer mortar

Fly ash (FA)-based geopolymer mortar is known to exhibit less strength development at ambient temperature due to slow progress in the polymerisation reaction. In this paper, studies are reported on geopolymer mortar made of FA, ground-granulated blast-furnace slag (GGBS) and nano silica at ambient temperature. The investigations on mechanical and durability properties of FA/GGBS-based geopolymer mortar were carried out by adding nano silica at 1% and 2% weight of FA into the mixture. For all the mixtures, the concentration of sodium hydroxide (NaOH) was maintained as 3M and the sodium silicate (Na2SiO3)/sodium hydroxide weight ratio was 2·06. The alkaline liquid/binder ratio of 0·3 and ambient curing temperature (28°C) was maintained for all the mixtures. Geopolymer mortar with an addition of 2% nano silica showed significant improvement in compressive strength, split tensile strength, flexural strength and fracture properties. The water absorption, rapid chloride penetration test and sorptivity showed better resistance in mixtures with a 2% addition of nano silica. The improved properties could have been due to an enhancement of geopolymeric reaction by the addition of amorphous nano silica, which formed additional sodium aluminosilicate hydrate (Al2H2Na2O7Si) or geopolymer gel while ultrafine particles of nano silica reduced the size of empty space in the geopolymer matrix.

Geopolymer production for conservation-restoration using Sicilian raw materials: feasibility studies

In the last decades, particular attention has been aimed to innovative materials class with high-tech features to apply in conservation-restoration of Cultural Heritage, ensuring both aesthetic compatibility and adequate properties with regards to the original rock substrate. AGM for CuHe project aims to valorise Sicilian raw materials, natural and industrial by-products, for the development of alkali-activated materials, as geopolymers. These materials are produced by the activation of an aluminosilicate precursors in alkaline environment. Volcanic raw materials (volcanic ash, volcanic paleo-soils and pumice) and ceramic industrial waste were mixed with an alkaline solution and cured at room temperature. In some cases, small quantities of metakaolin were added to the mixture to increase the reactivity of the precursors. In order to obtain the geopolymeric reaction, the precursors need to be fully characterized. A similar approach is also applied to the synthesized geopolymers in order to understand its behaviour in relation to the original building materials. Therefore, a multi-analytical approach is proposed: chemical and mineralogical studies (XRF and XRD), combined with spectroscopic (FT-IR) and morphological (SEM and μCT) analyses. These preliminary results confirm the feasibility of this eco-friendly class of materials using the proposed local raw materials.

Metakaolin-based geopolymer coatings on metals by airbrush spray deposition

Metakaolin-based geopolymer coatings with a thickness of about 60 μm were prepared on 2024 Al alloy and low carbon steel substrates by airbrush spray deposition. Curing in a sealed condition led to a limited geopolymerization reaction and corrosion of the uncoated surface in the metal substrates. Fourier-transform infrared spectroscopy and X-ray diffraction measurements of the coatings cured in an unsealed condition at 40–150°C confirmed the formation of the geopolymer network. Coatings cured at 80°C possessed a favorable microstructure, while some microcracks were present in the coatings after curing at 150°C due to shrinkage and residual stresses. The adhesion strength, measured by scratch tests, showed high values of critical load for samples cured at 80°C. For samples cured at 150°C, the coating was completely removed upon loading when the geopolymer was deposited on Al but not when on mild steel. Immersion tests demonstrated that the stability of the coatings in distilled water increased with increasing curing temperature.

Alkali Activation of Waste Clay Bricks: Influence of The Silica Modulus, SiO2/Na2O, H2O/Na2O Molar Ratio, and Liquid/Solid Ratio.

This study was conducted to investigate the influence of various reaction conditions, namely the silica modulus SiO2/Na2O, H2O/Na2O molar ratio, and liquid/solid ratio on the geopolymerization reaction of the waste fired clay bricks (Grog). The starting raw material and the generated geopolymer specimens produced by different geopolymerization reaction conditions have been characterized using different techniques: X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscope (SEM) and thermal analysis. Furthermore, physico–mechanical characterization has been carried out through the determination of bulk density, porosity, water absorption, and compressive strength for each sample at interval curing times of up to 28 days. The results indicated that the geopolymerization system of the waste fired clay bricks is influenced by the investigated reaction conditions at room temperature. The compressive strength of the geopolymer sample produced at optimum conditions increased significantly by up to 37.5 MPa, in comparison with 4.5 MPa for other conditions. Finally, an optimum recommendation and useful conclusions concerning the recycling and utilization of this waste material through the geopolymerization process are made for compatibility with construction applications.

Influence of the Nature and Rate of Alkaline Activator on the Physicochemical Properties of Fly Ash‐Based Geopolymers

The influence of alkali cations on mix design of geopolymers is essential for their mechanical, thermal, and electrical performance. This research investigated the influence of alkali cation type on microscale characteristics and mechanical, dielectric, and thermal properties of fly ash‐based geopolymer matrices. The geopolymers were elaborated via class F fly ash from the thermal plant Jorf Lasfar, El Jadida (Morocco), and several alkaline solutions. Morphological, structural, mechanical, dielectric, and thermal characteristics of materials synthesized via fly ash with different proportions of KOH and NaOH aged 28 days were evaluated. The physicochemical properties of class F fly ash‐based geopolymers were assessed using X‐ray diffraction (XRD), Fourier‐transform infrared spectrometry (FTIR), and scanning electron microscopy coupled with energy dispersive X‐ray spectroscopy (SEM/EDX) analyses. Based on readings of the results obtained, XRD and FTIR analysis detected the creation of semicrystalline potassium/sodium aluminate‐silicate hydrate (KASH/NASH) gel in the elaborated matrices after the geopolymerization reaction. The SEM analysis proved the formation of alkali alumina‐silicate hydrate gel in the raw material particles after the polycondensation stage. Experimental compressive strength data indicated that the highest compressive strength (39 MPa) was produced by the alkaline activator (75% KOH/25% NaOH). The dielectric parameters values of the elaborated materials changed depending of the mass ratios KOH/NaOH. Dielectric findings demonstrated that geopolymers containing 100% NaOH have better dielectric performances. The fire resistance study revealed that the geopolymer binders induced by KOH are stable up to 600°C. Based on these results, it can be deduced that the formulated geopolymer concrete possesses good mechanical, dielectric, and fire resistance properties.

Potential use of ceramic waste as precursor in the geopolymerization reaction for the production of ceramic roof tiles

The red ceramic industry is responsible for generating high amounts of solid wastes around the world from manufacture process failures, such as ineffective firing and issues related to the products transportation. Besides the necessity of clean alternatives to discard the solid wastes, the civil construction industry has been demanding the development of better technological properties new materials. One an example of those new materials is the geopolymeric materials, characterized by the gain of mechanical strength at early ages, high fire resistance, low water absorption and refractoriness. All these characteristics imply that geopolymers are suitable for civil construction applications. The characterization of clay bricks waste, named chamotte, and its use as an alternative precursor to produce geopolymeric materials, such as roof tiles for buildings are the aims of this present work. The chemical characterization, particle size distribution, X-ray diffraction, specific mass, pozzolanic activity index (PAI) and scanning electron microscopy (SEM) were performed, in addition to the technological tests carried out on the geopolymer specimens, such as flexural strength, water absorption, linear shrinkage and apparent porosity. The chemical and mineralogical analysis proved that the waste is rich in silica and alumina, which are fundamental compounds for the geopolymers synthesis. The chamotte also has fine particles and high pozzolanic reactivity. Thus, this waste has great potential to be used as a raw material for obtaining of ceramic roof tiles by means of geopolymeric reactions.

Fly ash and zinc slag blended geopolymer: Immobilization of hazardous materials and development of paving blocks

The potential for practical application of fly ash, zinc slag and their blends for geopolymer synthesis at ambient temperature have been investigated in this paper. Fly ash is an alumino-silicate byproduct suitable for geopolymer reaction, but its low reactivity at ambient condition is the restriction of its bulk utilization. Above limitation can be overcome by blending with zinc slag (ZS). Additionally, ZS contains heavy and toxic metals (Pb, Zn, Cr, Cd, As), which can be stabilize in Al-Si based geopolymer network structure. Isothermal conduction calorimetry (ICC) is used to monitor the geopolymer reaction with time. Slag rich specimens are characterized with higher rate of reaction with augmented peak. The mineralogy and microstructure of the geopolymers have been examined through X-ray diffraction and scanning electron microscope. The detected chief reaction product is N-(C)-A-S-H and C-(N)-A-S-H11(where, N=Na2O, C=CaO, A=Al2O3, S=SiO2 and H=H2O) type hydrated gel. Continual improvement of compressive strength of the geopolymers with increasing slag content is explained with higher degree of reaction, formation of more reaction products and development of compact microstructure. According to toxicity characteristic leaching procedure (TCLP), toxic metals leaching is within permissible limit. Paver blocks using 40−80 wt% ZS has been developed, which meets IS 15,658: 2006 standard and comply with US-EPA specification.

Properties of polyvinyl alcohol fiber reinforced fly ash based Engineered Geopolymer Composites with zeolite replacement

Engineered Geopolymer Composite (EGC), with the typical characteristics of high ductility and low environmental impact, is attracting more and more research interest. The present study focuses on studying a fly ash based EGC system with partial replacement by zeolite. Mechanical properties, i.e. tensile and compressive properties, were tested. Meso-scale studies, including three-point bending test, single crack tensile test and single fiber pullout test, were performed. The purpose was trying to correlate the meso-scale results with the macro-scale (e.g. mechanical) properties. X-ray powder diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) techniques were adopted to study the characteristics of the reaction products of the EGC materials. High tensile strain capacities were observed for all the studied mixes, with the maximum strain capacity up to 8.62%. An optimal zeolite replacement ratio, i.e. 3%, was noted with respect to the tensile properties. A preliminary discussion was conducted on the effect of sample shape and size on the compressive strength of EGC and it was concluded the effect in general can be more significant than that on normal concrete. Further, it was demonstrated that the macro-scale properties of the EGC system can be well explained by the results of a number of parameters derived from the meso-scale studies. The XRD analyses demonstrated that new crystalline phases are insignificant in the reaction products of the studied system. The FT-IR studies revealed that the reaction products are mainly amorphous aluminosilicate phases, i.e. gel-like materials resulted from geopolymerization reactions.

Response surface methodology application to fly ash based geopolymer synthesized by alkali fusion method

The rapid consumption of natural sources due to the technological development brings environmental and economic problems and makes usage of alternative sources obligatory. Fly ash is one of an industrial waste that can be used as alumina silicate source for geopolymerization. In this study, fly ash based geopolymer was synthesized by Alkali Fusion Method. The experimental set up was designed by Design Expert Trial 7 program and the optimum geopolymer synthesis conditions including additional Al2O3 ratio, curing temperature were determined by Central Composite Inscribed Design (CCI) Method. Also, ANOVA analysis and optimization were carried out. X-ray fluorescence spectrometer (XRF), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), Scanning electron microscope-Energy-dispersive X-ray (SEM-EDX) and Brunauer–Emmett–Teller (BET) analyzes were applied for the characterization studies of the raw materials and optimum geopolymer sample. According to optimization and analysis results, the optimum Al2O3 addition (%) and curing temperatures were determined as 70.76% and 36.75 °C, respectively. The degree of geopolymerization reaction for optimum geopolymer sample was found as 97%.