Study on the Influence of Alkali Activator Solutions on Strength Improvement of Pozzolan Calcium Hydroxide Binders

Alkali activated binder, commonly known as geopolymer cement, has replaced Portland cement in the production of mortar and concrete globally over the past few years. The density, particle size distribution, and specific surface area (SSA) are important physical parameters affecting strength and durability of alkali activated binders. This study carried out tests for physical and chemical properties of the natural pozzolan and calcium hydroxide and then determines the influence of alkali solution (sodium silicate and sodium hydroxide) on strength development of natural pozzolan calcium hydroxide binders. The particle size distribution (PSD), relative densities (RD), and specific surface areas (SSA) of powder natural pozzolan and calcium hydroxide materials and for the mixture of natural pozzolan and calcium hydroxide were determined by using Blaine air permeability apparatus. The optimum proportion of 75% natural pozzolan and 25% calcium hydroxide was obtained which produces the compressive strength of 7.5 MPa at 28 days cured paste. The mixture of natural pozzolan and calcium hydroxide were further grinded at three different finenesses and the particle size gradation, specific densities, specific surface areas and mean particles sizes for the mixture were determined. The compressive strength of alkali activated binders increased with increasing curing period and fineness. The maximum compressive strength for 28 days cured specimens was 26.1 MPa which was obtained at a solution of 8 moles sodium hydroxide concentration. The test results showed that natural pozzolan materials can be used to make geopolymer binders for mortars and concretes. The geopolymer binders for mortars and concretes reduce green gas emission from cement factory but also it can be used to produce durable mortar and concrete with comparable strengths with mortars and concrete made from conventional Portland cement.

The development of ultralightweight expanded perlite-based thermal insulation panel using alkali activator solution

The International Energy Agency(IEA)states that global energy consumption will increase by 53%by 2030.Turkey has 70%of the world’s perlite reserves,and in order to reduce energy consumption a thermal insulation panel was developed in Turkey using different particle sizes of expanded perlite(EP).In this study,0–1.18 mm(powder)and 0–3 mm(granular)EP particle sizes were selected,since they have the lowest thermal conductivity coefficients among all the particle sizes.In addition,an alkali activator solution was used as a binder in the mixtures.The alkaline activator solution was obtained by mixing sodium hydroxide solution(6,8,10,and 12 mol·L−1)and sodium silicate(Module 3)at the different ratios of Na2SiO3 to NaOH of 1,1.5,2,and 2.5.This study aimed to experimentally determine the optimum binder and distribution ratio of EP,with the lowest coefficient of thermal conductivity and the lowest density.The lowest thermal conductivity and the lowest density were determined as 0.04919 W·m−1·K−1 and 133.267 kg/m3,respectively,in the sample prepared with 83.33%powder-size EP,6 mol·L−1 sodium hydroxide solution,and ratio of Na2SiO3 to NaOH of 1.5.The density,thermal conductivity,and compressive strength of the sample showed the same trends of behavior when the Na2SiO3 to NaOH ratio was increased.In addition,the highest compressive strength was measured in 12 mol·L−1 NaOH concentration regardless of particle size.In conclusion,the study predicts that the EP-based thermal insulation panel can be used as an insulation material in the construction industry according to the TS825 Thermal Insulation Standard.

Effects of biochar-amended alkali-activated slag on the stabilization of coral sand in coastal areas

Coral sand is widely encountered in coastal areas of tropical and subtropical regions.Compared with silica sand,it usually exhibits weaker performance from the perspective of engineering geology.To improve the geomechanical performance of coral sand and meet the requirement of foundation construction in coastal areas,a novel alkali activation-based sustainable binder was developed.The alkaliactivated slag(AAS)binder material was composed of ground granulated blast-furnace slag(GGBS)and hydrated lime with the amendment of biochar,an agricultural waste-derived material.The biocharamended AAS stabilized coral sand was subjected to a series of laboratory tests to determine its mechanical,physicochemical,and microstructural characteristics.Results show that adding a moderate amount of biochar in AAS could improve soil strength,elastic modulus,and water holding capacity by up to 20%,70%,and 30%,respectively.Moreover,the addition of biochar in AAS had a marginal effect on the sulfate resistance of the stabilized sand,especially at high biochar content.However,the resistance of the AAS stabilized sand to wet-dry cycles slightly deteriorated with the addition of biochar.Based on these observations,a conceptual model showing biochar-AAS-sand interactions was proposed,in which biochar served as an internal curing agent,micro-reinforcer,and mechanically weak point.

Influence of Ultra Fine Glass Powder on the Properties and Microstructure of Mortars

This study focuses on the effect of ultrafine waste glass powder on cement strength,gas permeability and pore structure.Varying contents were considered,with particle sizes ranging from 2 to 20μm.Moreover,alkali activation was considered to ameliorate the reactivity and cementitious properties,which were assessed by using scanning electron microscopy(SEM),energy-dispersive X-ray spectroscopy(EDS),and specific surface area pore size distribution analysis.According to the results,without the addition of alkali activators,the performance of glass powder mortar decreases as the amount of glass powder increases,affecting various aspects such as strength and resistance to gas permeability.Only 5%glass powder mortar demonstrated a compressive strength at 60 days higher than that of the control group.However,adding alkali activator(CaO)during hydration ameliorated the hydration environment,increased the alkalinity of the composite system,activated the reactivity of glass powder,and enhanced the interaction of glass powder and pozzolanic reaction.In general,compared to ordinary cement mortar,alkali-activated glass powder mortar produces more hydration products,showcases elevated density,and exhibits improved gas resistance.Furthermore,alkali-activated glass powder mortar demonstrates an improvement in performance across various aspects as the content increases.At a substitution rate of 15%,the glass powder mortar reaches its optimal levels of strength and resistance to gas permeability,with a compressive strength increase ranging from 28.4%to 34%,and a gas permeation rate reduction between 51.8%and 66.7%.

Mine tailings as a raw material in alkali activation: A review

The mining industry produces billions of tons of mine tailings annually.However,because of their lack of economic value,most of the tailings are discarded near the mining sites,typically under water.The primary environmental concerns of mine tailings are related to their heavy metal and sulfidic mineral content.Oxidation of sulfidic minerals can produce acid mine drainage that leaches heavy metals into the surrounding water.The management of tailing dams requires expensive construction and careful control,and there is the need for stable,sustainable,and economically viable management technologies.Alkali activation as a solidification/stabilization technology offers an attractive way to deal with mine tailings.Alkali activated materials are hardened,concrete-like structures that can be formed from raw materials that are rich in aluminum and silicon,which fortunately,are the main elements in mining residues.Furthermore,alkali activation can immobilize harmful heavy metals within the structure.This review describes the research on alkali activated mine tailings.The reactivity and chemistry of different minerals are discussed.Since many mine tailings are poorly reactive under alkaline conditions,different pretreatment methods and their effects on the mineralogy are reviewed.Possible applications for these materials are also discussed.

The Influence of Free Water Content on Dielectric Properties of Alkali Active Slag Cement Paste

The dielectric performance of alkali activated slag （AAS） cement paste was investigated in the frequency range of 1 to 1000 MHz. The experimental results showed the unstable dielectric properties of harden paste were mostly influenced by the fraction of free water in paste or absorbed water from ambient, but not including hydration water and microstructure. The free water was completely eliminated by heat treatment at 105 ℃ about 4 hours, and then its dielectric loss was depressed; but with the exposure time in air increasing, the free water adsorption in ambient air made the dielectric property of harden cement paste to be bad. The temperature and relative humidity of environment was the key factors of free water adsorption; hence, if the influence of free water on dielectric constant was measured or eliminated, the cement-based materials may be applied in humidity sensitive materials or dielectric materials domains.

Alkali Aggregate Reaction in Alkali Slag Cement Mortars

By means of 'Mortar Bar Method',the ratio of cement to aggregate was kept as a constant 1∶2.25,the water cement ratio of the mixture was 0.40,and six prism specimens were prepared for each batch of mixing proportions with dimensions of 10×10×60mm 3 at 38±2℃ and RH≥95%, the influences of content and particle size of active aggregate, sort and content of alkali component and type of slag on the expansion ratios of alkali activated slag cement(ASC) mortars due to alkali aggregate reaction(AAR) were studied. According to atomic absorption spectrometry,the amount of free alkali was measured in ASC mortars at 90d.The results show above factors affect AAR remarkably,but no dangerous AAR will occur in ASC system when the amount of active aggregate is below 15% and the mass fraction of alkali is not more than 5% (Na 2O).Alkali participated in reaction as an independent component, and some hydrates containing alkali cations were produced, free alkalis in ASC system can be reduced enormously.Moreover,slag is an effective inhibitor, the possibility of generating dangerous AAR in ASC system is much lower at same conditions than that in ordinary Portland cement system.

Effect of alkali-activation on aluminosilicate-based cementitious materials

High-performance aluminosilicate-based cementitious materials were produced with fly ash from a coal power plant as one of the major raw materials. The structures of fly ash containing aluminosilicate-based cementitious materials were compared before and after treatment by the methods of nuclear magnetic resonance （NMR） and scanning electron microscopy （SEM）. During the 28 d curing time, the compressive strength of water glass and fly ash samples increased from 9.08 MPa to 26.75 MPa. The results show that most of the stiff shells are destroyed after mechanical grinding and chemical activation. Magic angle spinning （MAS） NMR of 27Al shows that the wide peak becomes narrow and the main peak shifts to the direction of low field, indicating the decrease of polymerization degree, the enhancing of activity, the decrease of six-coordination structure, and the increase of small and symmet- rical four-coordination polyhedron structure within the aluminum-oxygen polyhedron network. Comparisons between MAS NMR of 29Si with different treatments suggest that QO disappears, the quantity of Q2 increases, and the quantity of Q4 decreases. The polymerization degree of silicon-oxygen is reduced, and the potential activity of fly ash is increased.

Morphology Difference between the Alkali Activated Cement and Portland Cement Paste on Multi-scale

The features of alkali activated slag（AAS） and portland cement （PC） were observed on multi-scale,the crack and fracture sections were observed with naked eyes,and SEM and AFM were used to study the structure morphology differences between PC and AAS on micrometer to nano meter scale.The experimental results indicated that the AAS paste had soil like fracture texture and it was composed of mainly C-S-H gel but lacks of crystals,and it had a very strong tendency to shrink and crack.AAS paste is much denser and more homogeneous than PC,and on the nano scale C-S-H nano particle in the AAS paste is much smaller and packs much denser than PC paste.

Setting and Strength Characteristics of Alkali-activated Carbonatite Cementitious Materials with Ground Slag Replacement

The effect of the ground granulated blast-furnace slag （ GGBFS ） addition, the modulus n （ mole rutio of SiO2 to Na2O ） and the concentrution of sodium silicate solution on the compressive strength of the material, i e alkuli-activated carbonatite cemeutitious material （ AACCM for short ） was investiguted. In addition, it is found that barium chloride has a sutisfiwtory retarding effect on the setting of AACCM in which more than 20% （ by mass ） ground carbonatite was replaced by GGBFS. As a result, a cementitious material, in which ground carbonatite rock served as dominative starting material, with 3-day and 28-day compressive strength greuter them 30 MPa and 60 MPa and with continuous strength gain beyond 90 days was obtained.

Mechanical Property and Microstructure of Alkali-activated Yellow River Sediment-Coal Slime Ash Composites

This work focuses on the production of a new composite material using Yellow River sediment and coal slime ash via alkali-activating method. XRD, FTIR and SEM/EDS were used to characterize the alkali-activated products and microstructure of the composite material. Compressive strength was tested to characterize the mechanical property of the composite material. It is found that the compressive strength of the Yellow River sediment-coal slime ash composites increases as the added Ca（OH）_2 content grows. The compressive strength increases fast in the early stage but slowly after 28 days. The strength of the composites can be significantly improved via the addition of small amount of Na OH and gypsum. The products（C-S-H, ettringite and CaCO_3）, especially C-S-H, make much contribution to the enhancement of strength. The highest strength of the composites can reach 14.4 MPa after 90 days curing with 5% Ca（OH）_2, 0.2% NaOH and 7.5% gypsum. The improved properties of the composites show great potential of utilizing Yellow River sediment for inexpensive construction materials.

Optimum Calcination Condition of Waste Stabilized Adobe for Alkali Activated High Volume Adobe-Slag Binder Cured at Room Temperature

This study aims to determine the most convenient calcination temperature and calcination duration of wastestabilized Adobe(AB)to produce a new alkali-activated binder.Waste-stabilized Adobe mainly consists of soil,CaCO3 as a stabilizer,and straw(for strengthening).The availability of raw materials for making Adobe presents the waste-stabilized Adobe as a potential product for a new alkali-activated binder.Waste-stabilized Adobe collected from an abandoned damaged building in the village of Inonu in Northern Cyprus,ground and calcined at the following temperatures:450,550,650,750,850,and 950℃.The calcination at each temperature was held for different durations 1,3,5,and 7 h.Raw and calcined waste stabilized Adobe structures were investigated using XRF,TGA-DTA,XRD,FTIR,and SEM.Considering technical and environmental views related to energy consumption,waste stabilized Adobe calcined at 750℃ for 1 h presented the most promising results regarding the production of a new precursor for alkali-activated binder.This study also presents the effect of ground granulated blast furnace slag(GGBFS)usage on the fresh and hardened properties of optimum calcined AB-based alkali-activated pastes cured at room temperature.GGBFS was used to partially replace AB to form a binary composite raw material system and seven experimental groups were designed according to replacement levels of 0%,5%,10%,15%,20%,25%and 30%(by mass).Alkali-activated high volume waste-stabilized Adobe-slag pastes prepared using Na2SiO3-to-NaOH ratio of 2 and 12 M concentration of Sodium Hydroxide.The fresh property as flowability and the hardened property as the compressive strength of the alkali-activated pastes with different GGBFS contents were investigated.The results indicated that the incorporation of GGBFS increased the flowability of fresh alkali-activated pastes.A 28-day compressive strength of 43.75 MPa can be obtained by a 30%replacement level of GGBFS.

An Alkali Activated Binder for High Chemical Resistant Self-Leveling Mortar

This paper reports the development of an Alkali Activated Binder (AAB) with an emphasis on the performance and the durability of the AAB-matrix. For the development of the matrix, the reactive components granulated slag and coal fly ash were used, which were alkali activated with a mixture of sodium hydroxide (2 - 10 mol/l) and aqueous sodium silicate solution (SiO2/Na2O molar ratio: 2.1) at ambient temperature. A sodium hydroxide concentration of 5.5 mol/l revealed the best compromise between setting time and mechanical strengths of the AAB. With this sodium hydroxide concentration, the compressive and the 3-point bending tensile strength of the hardened AAB were 53.4 and 5.5 MPa respectively after 14 days. As a result of the investigation of the acid resistance, the AAB-matrix showed a very high acid resistance in comparison to ordinary Portland cement concrete. In addition, the AAB had a high frost resistance, which had been validated by the capillary suction, internal damage and freeze thaw test with a relative dynamic E-Modulus of 93% and a total amount of scaled material of 30 g/m2 after 28 freeze-thaw cycles (exposure class: XF3).

Influence of Na_(2)SiO_(3)/NaOH Ratio on Calcined Magnesium Silicate Based Geopolymer——Experimental and Predictive Study

This study aims to investigate the behavior of alkali activated mortar,which is made of naturally available magnesium silicate as source material.For magnesium silicate,ultrafine natural steatite powder(UFNSP)is used as the primary source of binder,and the activation is initiated through the alkali liquid which is proportioned in various combinations of silicate to hydroxide ratio(Na_(2)SiO_(3)/Na OH)ratio,and this ratio in this study varies from 1 to 3.The UFNSP is calcined at two difierent temperatures,700 and 1000℃.The mortar mix is proportioned as 1:3 between powder and the fine aggregate,and the mortar is prepared with hydroxide molarity(M)of 10 M.The mortar is cured for 48 hours at 60℃and the compressive strength was studied.All the mix were studied for its microstructural behavior along with compressive strength.The mix proportion of the mortar,and the results obtained through microstructural characterization were combinedly formed as input for artificial neural network(ANN)predictive modelling.The model is designed to predict the compressive strength,which is trained through Bayesian regularization algorithm with varying hidden neurons of 7 to 10.This experimental and predictive study shows that the strength is influenced by both Na_(2)SiO_(3)/Na OH ratio and calcination process.And the ANN is influenced by mainly calcination temperature and uncorrelation occurs in selected samples of 1000℃calcined UFNSP mix.

Effect of Sodium Hydroxide on the Properties of Phosphogypsum based Cement

The effect of sodium hydroxide （NaOH） amount on phosphogypsum based cement was investigated. The mechanical performances and hydration mechanism of the phosphogypsum-based cement with different proportions of NaOH and steel slag were analyzed based on setting time, volume stability, strength test, XRD and SEM analyses. The experimental results show that, NaOH as an alkali activator significantly reduces the cement setting time and improves the cement early strength. But the acceleration of hydration proces produces coarse crystalline hydration products and the osteoporosis structure of hardened paste, which has a negative effect on later age strength. The combination of 1% NaOH and 5% steel slag as alkali activating agents is optimal with respect to early and later age strengths. Overdose of NaOH not only decreases the cement strength at later age, but also may cause problem of volume stability.

THE INFLUENCE OF TEMPERATURE AND ADMIXTURES ON ACTIVATION OF LOW CALCIUM FLY ASH

According to composition and structure properties of low calcium fly ash, the activation and reaction degree of fly ash-lime and fly ash-lime-gypsum system were studied in different alkali surroundings and temperatures by thermal-gravity analysis. The degree of reaction and pore structure analysis test results show that composite alkali play an important role in the activation and degree of reaction of fly ash at I-oem temperature. But when increasing curing temperature, gypsum would play an important role in activation and hydration of fly ash.

Green Cementitious Paste Based on Recycled Materials

Cementitious alkali activated aluminosilicates pastes were produced from recycled and locally obtainable materials in Iraq. The compositions were based on recycled bricks, water glass, commercial caustic soda flakes, and nano silica. The nano silica was prepared from the abundant local ＂Iraqi anber＂ rice husks and added to the prepared pastes in different weight percentages. Another set of pastes was prepared via adding 5w% of＂A1-Najaf＇ fly ash at the expense of the recycled bricks powders. The pastes were cured for 1-28 days under ambient conditions. The compressive strengths for the cured pastes were measured. In addition, the cured pastes were characterized via X-ray diffraction, FTIR, and optical microscopy. The addition of the nano silica and longer curing times improve the microstructure packing and thus increases the compressive strengths. The added fly ash impregnates the microstructure with extra gel phase and further improves the compressive strengths of the cured pastes.

Development of a Construction Material for Indoor and Outdoor, Metakaolinite-Based Geopolymer, with Environmental Properties

Environmental problems that came from the human activity have many facets,since pollution of the atmosphere arises from vehicles,industrial emissions while pollution of water could be from organic compounds,pesticides etc.These can cause serious health effects,such as respiratory diseases,including asthma and lung cancer.Hence,in the present work,a kinetic study on the effective adsorption and photo degradation of methylene blue(MB)dye,under ultraviolet A(UVA)irradiation of an alkali activated inorganic polymer(geopolymer)with homogeneously dispersed titanium dioxide(TiO2)micro-particles is presented.In addition,antimicrobial testing of the alkali activated TiO2 material was performed showing a bacteriostatic effect.

Effect of cooking conditions and oxygen-delignification on Bambusa tulda kraft pulping using experimental design and regression models

This study was concerned on the influence of cooking liquor parameters i.e. active alkali （AA） and sulfidity, on the properties of pulp produced from Thai bamboo by means of multivariate analysis. The investigated pulp properties were cooking yield and viscosity. The experiments were performed according to a face centered cube experimental design. Then, multiple linear regression （MLR） of independent and dependent variables were conducted with SPSS software using least square method. In order to optimize process, Pareto-Optimality method was employed. The obtained regression models were characterized by both descriptive and predictive ability （R^2 ≥ 95% and Rcv^2 ≥ 93%） and allowed the kraft pulping process with an acceptable viscosity （ 1110- 1 190 ml/g） and a total yield about 50% at a sulfidity level of 20-30% with 18% AA. Results indicated that high sulfidity at a lower AA could get high viscosity and relatively low kappa number for pulps. Also oxygen delignification was studied in this research.

Mechanism of Suppressing ASR Using Ground Reactive Sandstone Powders instead of Cement

In order to understand the effect of powders ground from reactive sandstone replacing cement on reducing or suppressing alkali-silica reaction（ASR）, and to identify the mechanism of suppressing ASR by this powders, mortar and paste containing reactive sandstone powders of four replacement levels ranging from 10wt% to 40wt% and four specific surfaces areas ranging from 210 m^2/kg to 860 m^2/kg were studied. The experimental results showed that incorporation of 40wt% reactive sandstone powders could suppress ASR effectively except for mortar containing reactive sandstone powders with specific surface area of 610 m^2/kg, which disagreed with the most results reported that the higher reactive powder specific surface area, the smaller ASR expansion. By means of fl ame photometry, Fourier transform infrared spectroscopy（FT-IR） and thermo gravimetric analysis（TG）, the mechanism of reactive sandstone powders on reducing or suppressing ASR was soluble alkalis type of reactive sandstone powders and the competition of liberating and bonding alkali of cement paste containing reactive sandstone powders,when the ability of alkali bonding was greater than the ability of alkali liberation, ASR caused by reactive sandstone was supressed effectively.