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Phosphorus slag (PS), an industrial waste slag, has been used in geopolymers because it is rich in silicon and calcium. The poor performance of phosphorus slag-based geopolymer is due to its aluminum deficiency. In this work, low-calcium fly ash, treated by a wet-grinding process, named wet-grinding ultrafine fly ash (WUFA) was used as an Al supplement to replace some of the phosphorus slag, and the wet-grinding, ultrafine fly ash-phosphorus slag (WUFA-PS)-based geopolymer was prepared. The effects of the substitution amount of WUFA and the activator dosage on the hydration properties, mechanical properties, pore structure and SEM of the WUFA-PS geopolymer were discussed in detail. The results indicate that WUFA and more activators contribute to the Al and high alkalinity environment, which positively induces the production of more geopolymer gels, thus releasing more heat and optimizing the pore structure of the matrix. The compressive strength increased by up to 28.1%. The enhanced performance of the WUFA-PS-based geopolymer may also arise from the filling effect and activity improvement of WUFA. This study has proved the feasibility of preparing a geopolymer by blending wet-grinding ultrafine fly ash and phosphorus slag and has provided references for the ratio and performance evaluation of WUFA-PS-based geopolymer concrete. [ABSTRACT FROM AUTHOR]

This paper reports the results of a study conducted to examine the impacts of adding graphene oxide (GO) to GBFS-fly ash-based geopolymer concrete. The geopolymer concrete's compressive strength, thermal conductivity, and modulus of elasticity were assessed. X-ray diffraction (XRD) analysis was conducted to understand the differences in mineralogical composition and a rapid chloride penetration test (RCPT) to investigate the changes in the permeability of chloride ions imposed by GO addition. The results showed that adding 0.25 wt.% GO increases the modulus of elasticity and compressive strength of GBFS-FA concrete by 30.5% and 37.5%, respectively. In contrast, permeability to chloride ions was reduced by 35.3% relative to the GO-free counterparts. Thermal conductivity was decreased as GO dosage increased, with a maximum reduction of 33% being observed in FA65-G35 wt.% samples. Additionally, XRD showed the suitability of graphene oxide in geopolymer concrete. The present research demonstrates very promising features of GO-modified concrete that exhibit improved strength development and durability compared to traditional concrete, thus further advocating for the wider utilization of geopolymer concrete manufactured from industrial byproducts. [ABSTRACT FROM AUTHOR]

Experimental evaluations were conducted to determine the water sorptivity, setting time, and resistance to a highly acidic environment, of mortar with alkali-activated ground granulated blast furnace slag (GBS) binder and also of combinations of fly ash and GBS binders. Binders were activated using mixtures of NaOH and Na2SiO3 solutions. The molarity of NaOH in the mixtures ranged from 10 mol·L−1 to 16 mol·L−1, and the Na2SiO3/NaOH ratio was varied from 1.5 to 2.5. Mortar samples were produced using three binder combinations: 1) GBS as the only binder; 2) blended binder with a slag-to-fly ash ratio of 3:1; and 3) mixed binder with 1:1 ratio of slag to fly ash. Mortar samples were mixed and cured at (22 ± 2) °C till the day of the test. The impact of activator solution alkalinity, activator ratio Na2SiO3/NaOH, GBS content on the rate of water absorption were evaluated. After 7, 28, and 90 d of immersion in a 10% sulfuric acid solution, the resistance of a geopolymer matrix to degradation was assessed by measuring the change in sample weight. The influence of solution alkalinity and relative fly ash content on setting times was investigated. Alkali-activated mortar with a slag-to-fly ash ratio of 3:1 had the least sorptivity compared to the two other binder combinations, at each curing age, and for mortars made with each of the NaOH alkaline activator concentrations. Mortar sorptivity decreased with age and sodium hydroxide concentrations, suggesting the production of geopolymerization products. No reduction in weight of sample occurred after immersion in the strong acid H2SO4 solution for three months, regardless of binder combination. This was due to the synthesis of hydration and geopolymerization products in the presence of curing water, which outweighed the degradation of the geopolymer matrix caused by sulfuric acid. [ABSTRACT FROM AUTHOR]

The need for repair and maintenance has become dominant in the European construction sector. This, combined with the urge to decrease CO2 emissions, has resulted in the development of lower carbon footprint repair solutions such as textile reinforced mortars (TRM) based on alkali-activated materials (AAM). Life cycle studies indicate that AAM CO2 savings, when compared to Portland cement, range from 80% to 30%. Furthermore, in this study, recycled aggregates were considered with the aim to promote a circular economy mindset. AAM mortars formulation based on fly ash, ladle furnace slag and metakaolin were tested for compressive and flexural strength. Three out of all formulations were chosen for an analysis on the potential of these mortars to be used for TRM applications. Tensile and shear bond tests, combined with a concrete substrate, were executed as indicators of the TRM effectiveness. Scanning electron microscopy and chemical analysis based on energy dispersive X-ray spectroscopy were used to interpret the results and reveal the reasons behind the different level of performance of these composites. Results indicated that TRM based on high calcium fly ash are unsuitable for structural strengthening applications due to low bond between matrix and/or substrate and fibers. Metakaolin-based TRM showed good performance both in terms of tensile strength and bond capacity, which suggests potential as a repair mortar.

The kaolin mining waste (KW) is a residue generated during the purification process of extracting high purity kaolin used in different industries. KW is mainly constituted by kaolinite-rich clay and other secondary minerals such as anatase and quartz. With the appropriated and controlled process, calcined kaolin mining waste (CKW). It can be thermally activated by calcination to obtain a highly reactive metakaolinite rich material, which exhibits interesting pozzolanic properties. According to its chemical composition and high reactivity, this material is used as an aluminosilicate precursor in the production of geopolymers. One of the negative effects may be the formation of efflorescence. This paper evaluated geopolymer produced with CKW at different activation conditions (alkali concentration and sodium silicate content). The leaching of alkalis was studied through the development of efflorescence on the surface of hardened samples exposed to efflorescence formation conditions (contact with air and water). The results indicated that a larger activator provided a higher compressive strength and reduced the capillary absorption and the efflorescence formation. The data showed that the efflorescence formation can be appropriately controlled by adjusting the mix design parameters, especially the sodium silicate content.

Chloride transport is a vital issue in the research on the durability of alkali-activated materials (AAMs). Nevertheless, due to its miscellaneous types, complex mix proportions, and limitations in testing methods, the reports of different studies are numerous and vary greatly. Therefore, in order to promote the application and development of AAMs in chloride environments, this work systematically reviews the chloride transport behavior and mechanism, solidification of chloride, influencing factors, and test method of chloride transport of AAMs, along with conclusions regarding instructive insights to the chloride transport problem of AAMs in future work.

This study aims to develop a material-saving performance prediction model for fast-hardening alkali-activated slag/silica fume blended pastes. The hydration process in the early stage and the microstructural properties after 24 h were analyzed using design of experiments (DoE). The experimental results show that the curing time and the FTIR wavenumber of the Si-O-T (T = Al, Si) bond in the band range of 900–1000 cm−1 after 24 h can be predicted accurately. In detailed investigations, low wavenumbers from FTIR analysis were found to correlate with reduced shrinkage. The activator exerts a quadratic and not a silica modulus-related conditioned linear influence on the performance properties. Consequently, the prediction model based on FTIR measurements proved to be suitable in evaluation tests for predicting the material properties of those binders in the building chemistry sector.

Phosphogypsum and red mud are bulk industrial solid wastes that trigger local environmental problems. In the present investigation, an efficient valorization process was developed through which phosphogypsum and red mud can be transformed into a precursor for the synthesis of high-strength, alkali-activated materials with a seawater-bearing sodium silicate solution as the alkaline activator. The effects of the activator modulus and liquid-to-solid ratio on the strength evolution of the synthesized AAMs as well as the microstructure and chemistry of the reaction products were investigated. The results showed that mineral reconstruction between PG and RM took place during calcination at 950 °C, forming ye’elimite, anhydrite and gehlenite, which then took part in the alkali-activation process and generated thenardite and C-A-S-H gel. The mechanical properties of the synthesized AAMs, ranging from 12.9 MPa to 40.6 MPa, were determined with the activator modulus and liquid-to-solid ratio. Results from the present investigation contributed to the facile and efficient valorization of phosphogypsum and red mud into cementitious construction materials.

The development of sustainable cementitious materials is essential and urgent for the construction industry. Benefiting from excellent engineering properties and a reduced greenhouse gas footprint, alkali-activated materials (AAM) are among the robust alternatives to Portland cement for civil infrastructure. Meanwhile, concrete production also accounts for around 20% of all industrial water consumption, and the global freshwater shortage is increasing. This review discusses recent investigations on seawater-mixed AAMs, including the effects of seawater on workability, reaction mechanism, shrinkage, short and long-term strength, binding of chloride and corrosion of steel reinforcement. Attention is also paid to the utilization of sea sand as aggregate, as well as discussions on the challenges and further research perspectives on the field application of AAMs with seawater and sea sand.

As a municipal solid waste, waste glass undergoes pozzolanic activity when ground to a certain fineness. In this paper, calcium carbide residue (CCR) and Na2CO3 were used as composite alkali activators for a glass powder-based composite cementitious system. A total of 60% fly ash (FA) and 40% ground granulated blast furnace slag (GGBS) were used as the reference group of the composite cementitious material system, and the effects of 5%, 10%, 15%, and 20% glass powder (GP) replacing FA on the rheological behavior, mechanical properties, and microstructure of alkali-activated composite cementitious systems were investigated. The results showed that with the increase in GP replacing FA, the fluidity of the alkali-activated materials gradually decreased, the shear stress and the equivalent plastic viscosity both showed an increasing trend, and the paste gradually changed from shear thinning to shear thickening. Compared with the reference sample, the fluidity of the alkali-activated material paste with a 20% GP replacement of FA was reduced by 15.3%, the yield shear stress was increased by 49.6%, and the equivalent plastic viscosity was elevated by 32.1%. For the 28d alkali-activated material pastes, the compressive strength and flexural strength were increased by 13% and 20.3%, respectively. The microstructure analysis showed the substitution of FA by GP promoted the alkali-activated reaction to a certain extent, and more C-A-S-H gel was formed.

The role of magnesium oxide (MgO) in the carbonation of cementitious materials, particularly alkali-activated materials (AAM), which is a promising low-carbon alternative to ordinary Portland cement (OPC), has garnered significant attention. However, there remains a lack of clear understanding regarding its underlying mechanisms and interrelation with calcium oxide (CaO) content. This study aims to understand the influence of MgO on carbonation mechanisms, carbonation products, and (C, N)–A–S–H gel micromechanical properties in AAM. Four different binder formulations were examined by varying contents of slag, class F fly ash, and light-burned MgO. A powder-type sodium metasilicate was used as an alkaline activator. CO 2 curing was conducted in a CO 2 incubator with 1 % concentration and under atmospheric pressure for up to 56 days using pulverized paste binders. The carbonation mechanism, polymorphs of carbonation products, and the micromechanical properties of the (C, N)–A–S–H gel matrix were characterized by conducting laboratory tests including pH measurement, XRD, TGA, DSC, nitrogen adsorption, and nanoindentation at various carbonation stages. A noticeable pattern of pH initially dropping and then rising was observed. Integrated XRD-TGA demonstrated the evolution, polymorphism, and amount of calcium carbonate phases. Higher MgO content in AAM binders favored the formation of aragonite and hydrotalcite. Extensive nanoindentation results and their statistical analysis revealed binder-specific trends in the pozzolanic matrix stiffness before and after carbonation. The findings of this study can be used in developing AAM binders as building materials and to provide a deeper understating of the carbonation reactions in AAM binders. • Carbonation of one-part alkali-activated materials (AAM) related to MgO and CaO was studied. • Phase characteristics and micromechanical properties due to 1 % CO 2 carbonation were examined. • AAM pastes (GGBFS and fly ash) were formulated with waterglass activator and MgO additive. • Higher MgO content in AAM binders favored the formation of aragonite and hydrotalcite phases during carbonation. • Carbonation of AAM yielded primarily amorphous CaCO 3 than crystalline CaCO 3. [ABSTRACT FROM AUTHOR]

The combined need to propose new solutions for the structural reinforcement of existing buildings and for the reduction of CO 2 emissions is leading to the development of more sustainable composite materials, such as those based on alkali-activated mortars (AAM). In this study, different formulations of AAM, based on metakaolin or fly ash, have been evaluated as possible matrices for Textile Reinforced Mortar (TRM) systems. Two different bidirectional textiles, made of AR glass or basalt fibers, were used as internal reinforcement. The physical-mechanical properties of TRM systems based on AAM were evaluated and compared with those of commercial systems with cementitious or lime-based matrices. Direct tensile tests on TRM coupons and shear bond tests on clay brick substrates were carried out. Then, their energy and environmental-related performance have been compared. Results showed that alkali-activated matrices can be very promising and eco-friendly alternative solutions to traditional mortars in TRM systems. • Development of alkali-activated mortars (AAMs), to be used as inorganic matrices for Textile Reinforced Mortar (TRM) systems. • Physical-mechanical characterization of TRM composites based on AAMs and comparison of performances with commercial TRM systems. • Evaluation of the Environmental and Energy performances, in relation to the obtained mechanical performances, of different TRM systems. [ABSTRACT FROM AUTHOR]

Even though the demand for utilizing geopolymers is growing, the need for current standard guidelines to regulate compliance to address the complexity of the mix design could be one of the major hurdles of utilizing geopolymers vastly in construction. There is no straightforward standard that addresses the complexity of the mix design of geopolymers. Thus, this work addresses main factors affecting the compressive strength of slag based geopolymers and provide a tool for predicting it. This article includes experimental work to evaluate the properties of slag-based geopolymer binders and the development of a model using Artificial Neural Network (ANN) algorithms for predicting the performance of these slag-based geopolymer binders. In this paper, we have utilized and developed ANN models for optimizing slag-based geopolymer mixes based on precursor materials' physiochemical properties and activation solutions constituents that can enhance performance compressive strength prediction in construction applications. • A high-accuracy DOE model was developed and used to characterize the Geopolymeric paste. • A developed ANN model was superior in forecasting the compressive strength of AAS systems. • The choice of the alkali activator has minimal impact on the compressive strength. • The optimal water-to-slag ratio is approximately 0.28. • The optimal alkali oxide concentration is 6 %. [ABSTRACT FROM AUTHOR]

Incorporating municipal solid waste incineration fly ash (MSWI FA) in alkali-activated materials (AAMs) production provides an economic and sustainable solution for the disposal of hazardous MSWI FA, which had succeeded in achieving desirable strength and solidification of toxic species, but the leaching of chloride originated from the MSWI FA is still an open problem that hinders the application of these AAMs. Therefore, Al 2 O 3 , MgO and CaO were used for the first time to regulate the in-situ chloride binding of AAMs with MSWI FA, where the chloride content is much higher than that in previous studies. The effect of curing temperature, chemical compositions of raw materials and carbonation on the role of three oxides in promoting chloride binding was systematically investigated. The chloride binding was quantified by IC and the reaction products were characterized by XRD, FTIR, TGA as well as SEM-EDS. The results revealed that both 10 % Al 2 O 3 and 10 % CaO improved the compressive strength but opposite effect was found with the addition of 10 % MgO. CaO was verified to be the most effective to promote chloride binding, while the mixes with MgO and Al 2 O 3 yielded the most Ht and gels, respectively. Carbonation increased the Ht content but decreased the bound chloride. The inconsistent variation in the Ht content and bound chloride indicated the necessity to consider the role of gels in chloride binding, not only the gel content but also the chemical composition. Nevertheless, the results confirmed the importance of CaO in promoting chloride binding, which is of great significance for the mix design of AAMs with MSWI FA. The obtained results hope to provide technic support for a better treatment of MSWI FA. • The 30 % MSWI FA can activate 70 % slag to obtain a compressive strength of 20 MPa at 56 d. • The chloride leaching from the alkali-activated slag with 30 % MSWI FA still exceeded the limitation of related standards. • The CaO was verified to be the most effective in promoting chloride binding followed by MgO and Al2O3. • The gel phases played important role in chloride binding when the inside chloride concentration was high. [ABSTRACT FROM AUTHOR]

Traditional activators such as sodium hydroxide and sodium silicate are commonly used in the preparation of alkali-activated materials; however, their significant environmental impact, high cost, and operational risks limit their sustainable use in treating solid waste. This study explores the innovative use of carbide slag (CS) and sodium metasilicate (NS) as alternative activators in the production of sewage sludge ash-based alkali-activated materials (SSAM) with the aim of reducing the carbon footprint of the preparation process. The results demonstrate that CS effectively activates the sewage sludge ash, enhancing the compressive strength of the SSAM to 40 MPa after curing for 28 d. When used in conjunction with NS, it synergistically improves the mechanical properties. Furthermore, the microstructure and phase composition of the SSAM are characterized. Increasing the quantities of CS and NS accelerates the dissolution of the precursor materials, promoting the formation of a higher quantity of hydration products. This significantly reduces the number of voids and defects within the samples, further enhancing the densification of the microstructure. Environmental assessments reveal that CS and NS offer substantial sustainability benefits, confirming the feasibility of activating SSAM using these materials. This approach provides a less energy-intensive and more environmentally friendly alternative to conventional activation methods and presents an effective strategy for managing large volumes of sewage sludge ash and CS. • CS used to produce sustainable SSA-based alkali-activated materials. • Trace NS enhances the activation of alkali activated SSA by CS. • CS/NS activation SSA exhibits improved properties. • CS and NS activation was a lower-carbon method for activating SSA. [ABSTRACT FROM AUTHOR]

The construction waste powder encompasses waste paste powder (WPP) and waste concrete powder (WCP), exhibiting an irregular microstructural morphology and containing mineral constituents like portlandite, C-S-H gel, calcite and quartz. Under the influence of thermal activation, certain hydrated products within construction waste powder undergo decomposition, concurrently generating new substances like CaO and C 2 S, which contribute to enhanced reactivity. Minerals within construction waste powder participate in polymerization reactions under alkali activation. Furthermore, alkali-activated mortar produced from thermally treated construction waste powder generate an increased quantity of C-A-S-H/N-A-S-H gel, resulting in a denser microstructure. When construction waste powder is thermally treated at temperatures ranging from 600°C to 800°C, the resulting alkali-activated construction waste powder mortar (AAWM) exhibits higher compressive strength. For example, the 28d compressive strength of AAWM prepared with WCP subjected to heat treatment at 800°C increased by 195.69 % compared to AAWM prepared with untreated WCP. With the increase in thermal treatment temperature of construction waste powder, the drying shrinkage of the resultant AAWM progressively diminishes, along with a gradual reduction in porosity and water absorption. For instance, the porosity and water absorption of AAWM prepared with WCP treated at 800°C decreased by 15.58 % and 18.67 % respectively compared to AAWM prepared with untreated WCP. At a thermal treatment temperature of 800°C, AAWM exhibits strong resistance to chloride penetration. Particularly, AAWM containing WPP outperforms that containing WCP in terms of chloride resistance. Consequently, this study reveals that alkali-activated materials prepared using thermally treated waste powder exhibit commendable mechanical and durability properties. • Reusing thermoactivated WPP/WCP as precursor for sustainable alkali-activated materials. • Effects of thermoactivated temperatures on performance of WPP/WCP and its alkali-activated materials. • Showing multi-performance of alkali-activated materials made with 100 % thermoactivated WPP/WCP. [ABSTRACT FROM AUTHOR]

This study investigates the drying shrinkage behaviour of metakaolin-slag-based geopolymer across six distinct relative humidity levels: 33 %, 57 %, 65 %, 75 %, 88 %, and 99 %. Additionally, it explores the potential of vegetable oil as a drying shrinkage-reducing agent. To gain a comprehensive understanding, two drying regimes, stationary and cyclic drying and wetting, were employed. The highest shrinkage was recorded at ∼65 % RH. The incorporation of oil into geopolymer resulted in a noteworthy reduction of gel and small capillary pores, consequently reducing the material's diffusion rates. This leads to substantially lower drying shrinkage and therefore minimizing the risk of cracking. Newly developed geopolymer-oil composites possess favourable characteristics for practical applications as highly durable and low-CO 2 construction materials. • Non-linear shrinkage behavior observed in geopolymer mortars with changing relative humidity. • The highest drying shrinkage was found at 65 % RH. • Vegetable oil addition reduces microporosity, mitigating drying shrinkage induced cracking. • Enhanced modulus of elasticity and reduced crack risk with oil incorporation in geopolymers. [ABSTRACT FROM AUTHOR]

Excessive autogenous shrinkage and poor bond performance associated with GGBS-based alkali-activated repairing materials are limiting factors affecting their wide applications. To address these issues, this study focuses on the use of waste glass powder (WGP) as a precursor and glass cullet (GC) as a fine aggregate in preparing alkali-activated repairing mortars (AARMs). The bond strengths and autogenous shrinkages were assessed. Results found that the optimal content of WGP in preparing AARMs was 50% for obtaining a bond strength of 1.70 MPa and shrinkage of about 3500 µstrains. In addition, it was observed that incorporating 50% WGP in combination with GC further decreased the shrinkage compared to the mixture prepared with river sand. Furthermore, the inclusion of 10 wt% MK decreased the flowability and strengths. However, it significantly reduced the autogenous shrinkage (1900 µstrains), producing a compact and intact interfacial bonding zone due to the absence of micro cracking and the presence of N-A-S-H alongside C-A-S-H gels. • WGP and GC were utilized in preparing alkali-activated repairing mortars. • The optimal content of WGP was 50%, while 100% GC was incorporated. • Microstructure and micromechanical properties at the bond area were discussed. • The achieved AARM had an intact interfacial bonding zone with no microcracking. [ABSTRACT FROM AUTHOR]

In an attempt to maintain the sustainable development goals in the construction sector via reducing the raw-materials/energy consumption and greenhouse-gas emissions related to cement production, a green nano-modified slag/bentonite-based alkali-activated material was developed. Firstly, the green composites were prepared by mixing slag and bentonite with a ratio of 2:1. Several factors like NaOH-concentration (6, 8, 10 wt%); thermal treatment of bentonite (as-received "RB" and thermally treated at 650 °C "TB"); curing conditions (normal-curing for 3 and 28-days as well as hydrothermal-curing at 3, 6, 9, 15 bar for 4 h) and meso-porous tungsten oxide nano-particles "WO 3 -NPs" inclusion (0.25, 0.5 and 1 wt%) were studied to assign the optimum conditions for fabricating composites with adequate mechanical properties and radiation-shielding ability. The mechanical performance and radiation shielding were evaluated by measuring the compressive-strengths and linear attenuation coefficient "μ"/ half value layer "HVL" using 137Cs, respectively. The results reveal the feasibility of using 8 wt% NaOH, TB, hydrothermal-curing at 3 bar/4 h and 0.5 wt% WO 3 -NPs in fabricating low-cost/pre-cast/environmentally friendly building material with superior compressive-strength (53.6 MPa). Also, the radiation shielding results substantiate that this developed composite achieved adequate μ and HVL values, referring to its efficiency as a radiation-blocker. The synergistic impact of alkali-hydrothermal-activation, the high pozzolanicity of TB and the nucleation-site/potential-seeds effect of WO 3 -NPs are the main reasons behind forming strength-giving-phases from stratlingite, hydrogarnet, analcime and pentasil zeolitic phase (ZSM-5), as proved by X-ray diffraction (XRD), thermogravimetric analysis (TGA/DTG) and scanning electron microscopy (SEM). The presence of such phases reinforced the microstructure, thus improving the mechanical performance and radiation shielding capability. [Display omitted] • Hydrothermal curing is vital to obtain bentonite geopolymer with adequate strength. • Thermal treatment of bentonite affects its pastes' fresh/hardened properties. • Slag/bentonite/nano-WO 3 geopolymeric composites can be employed as radiation-blockers. [ABSTRACT FROM AUTHOR]

This paper presents a literature review on the effects of accelerated carbonation on alkali-activated materials. It attempts to provide a greater understanding of the influence of CO2 curing on the chemical and physical properties of various types of alkali-activated binders used in pastes, mortars, and concrete. Several aspects related to changes in chemistry and mineralogy have been carefully identified and discussed, including depth of CO2 interaction, sequestration, reactions with calcium-based phases (e.g., calcium hydroxide and calcium silicate hydrates and calcium aluminosilicate hydrates), as well as other aspects related to the chemical composition of alkali-activated materials. Emphasis has also been given to physical alterations such as volumetric changes, density, porosity, and other microstructural properties caused by induced carbonation. Moreover, this paper reviews the influence of the accelerated carbonation curing method on the strength development of alkali-activated materials, which has been awarded little attention considering its potential. This curing technique was found to contribute to the strength development mainly through decalcification of the Ca phases existing in the alkali-activated precursor, leading to the formation of CaCO3, which leads to microstructural densification. Interestingly, this curing method seems to have much to offer in terms of mechanical performance, making it an attractive curing solution that can compensate for the loss in performance caused by less efficient alkali-activated binders replacing Portland cement. Optimising the application of such CO2-based curing methods for each of the potential alkali-activated binders is recommended for future studies for maximum microstructural improvement, and thus mechanical enhancement, to make some of the “low-performing binders” adequate Portland cement substitutes.

This paper studied the influence of the modulus and dosage of sodium silicate on the hydration of alkali-activated copper-nickel slag (CNS) materials. CNS was used as the main raw material, and ground granulated blast furnace slag (GBFS) powder was selected as the mineral additive. The hydration and hardening mechanisms were discussed. The experimental results showed that [SiO4]4− and [AlO4]5− with a high degree of polymerization in the CNS glassy phase more easily underwent depolymerization-condensation and produced more C-S-H gels when the modulus was small and the sodium silicate dosage was high. When the content of sodium silicate was 7.0% and the modulus of sodium silicate solution was 1.0, the 28-day compressive strength of the material reached 125 MPa. This alkali-activated copper-nickel slag material can be used for mine filling, which has certain economic and ecological benefits.

Alkali-activated materials (AAMs) result from the dissolution process and polycondensation of precursors in high pH solutions. This material is considered alternative cement with similar properties and lower environmental impact than Portland cement. However, AAMs are subjected to the same standardization applied to cement-based materials since no formal methods exist to characterize this material and/or the precursor reactivity. Therefore, this work aims to develop a method to characterize the reactivity of the main precursors used to produce AAMs. Hence, the precursors were assessed in two steps after chemical, physical, and mineralogical characterization. The first step evaluated the crystallinity change of the material after the acid attack by mixing 1 g of each material in 100 mL of 1% HF solution for 6 h at ambient temperature. The crystallinity change was evaluated by comparing the X-ray diffraction of the materials before and after the acid attack. The second step involved evaluating the formation of geopolymerization products in the pastes of studied precursors through FTIR test. The pastes were produced with Na2SiO3 and NaOH as activators. After 28 days of curing, the pastes were submitted to a FTIR test for structural analysis. This method was tested evaluating the reactivity of traditional precursors for alkali activation (i.e., silica fume (SF), blast furnace slag (BFS), and metakaolin (MK)), in addition sugarcane bagasse ash mechanically treated (SCBAM) and sugarcane bagasse ash mechanically and heat treated (SCBAMH) since SCBA is a promising precursor for alkali activation. Considering the crystallinity change of precursors (step 01), the formation of geopolymerization products (step 02), and the chemical composition of precursors (preliminary characterization), it could be concluded that: (i) surface area is not relevant to materials with small particle size (2/Al2O3 ratio of 2 to 5. Also, it could be concluded that SF and SCBAMH do not exhibit adequate reactivity while BFS, MK, and SCBAM can be classified as reactive precursors.

This article deals with the possibility of partial replacement of blast furnace slag (GGBFS) with fly ash after denitrification (FAD) in alkali-activated materials. Physical-mechanical and durability properties were tested, hydration reaction was monitored, and infrared spectroscopy was performed. Results were compared between mixtures prepared with fly ash without denitrification (FA), and also with a mixture based only on GGBFS. The basic result is that hybrid alkali-systems with FAD show similar trends to FA. The significant effect of fly ash is manifested in terms of its resistance to freeze-thaw processes. Reactions in a calorimeter show a slower development of reactions with increasing replacement of GGBFS due to the lower reactivity of the fly ash. Through testing the leaching resistance, a decrease in flexural strength was found. This may be due to the descaling of the main hydration product, C–(A)–S–H gel. After 28 days of maturation, compressive strengths of all monitored mixtures ranged from 96 to 102 MPa. The flexural strengths ranged from 6.8 to 8.0 MPa. After 28 days of maturation, the higher strengths reached mixtures without replacing GGBFS. In terms of resistance to freeze-thaw processes, the largest decrease (almost 20%) of flexural strength was achieved by a mixture with 30% of GGBFS replacement by FA. No fundamental differences were found for the mixtures in the FTIR analysis. [ABSTRACT FROM AUTHOR]

In alkali-activated slag/fly ash systems, autogenous shrinkage represents the dominant type of shrinkage. Increasing contents of added water and fly ash contents both reduce the importance of autogenous shrinkage. For a constant added water content (AW/B = 0.14), increasing the fly ash content from 20 to 40% resulted in an autogenous shrinkage reduction on paste specimens (from 5644 to 2168 μm/m at 28 days). The autogenous shrinkage of control ordinary portland cement (OPC) paste (water-cement ratio [w/cm] of 0.50) reached 505 μm/m. Alkali-activated slag/fly ash mixtures of this study had average pore radius values ranging between 3.40 and 3.55 nm, compared to 8.25 nm for the OPC paste control specimen. Smaller pores and high sodium concentrations result in higher internal pressure during the process of selfdesiccation and could be the main causes for the very high autogenous shrinkage values recorded. [ABSTRACT FROM AUTHOR]

In this study, ground granulated blast furnace slag was activated with a wide variety of sodium salts to compare the effects of their pH and anion size on the hydration progress and compressive strength development of GGBFS pastes. Research was carried out on samples activated with twelve different sodium salts and cured for one year. Changes in their phase composition (XRD), loss on ignition at different temperatures, expansion and microstructure (SEM + EDS) were examined over the entire curing period. The results showed that the presence of sodium ions is more important than the pH of the system, as activation took place even in the case of compounds whose solutions are characterized by a low pH, such as sodium tartrate or phosphate. The compressive strength of the pastes ranged from approximately 8 to 65 MPa after one year of curing. [ABSTRACT FROM AUTHOR]

Alkali-activated materials (AAMs) are considered an eco-friendly alternative to ordinary Portland cement (OPC) for mitigating greenhouse-gas emissions and enabling efficient waste recycling. In this paper, an innovative seawater sea-sand concrete (SWSSC), that is, seawater sea-sand alkali-activated concrete (SWSSAAC), was developed using AAMs instead of OPC to explore the application of marine resources and to improve the durability of conventional SWSSC structures. Then, three types of fiber-reinforced polymer (FRP) bars, that is, basalt-FRP, glass-FRP, and carbon-FRP bars, were selected to investigate their bond behavior with SWSSAAC at different alkaline dosages (3%, 4%, and 6% Na2O contents). The experimental results manifested that the utilization of the alkali-activated binders can increase the splitting tensile strength (f t) of the concrete due to the denser microstructures of AAMs than OPC pastes. This improved characteristic was helpful in enhancing the bond performance of FRP bars, especially the slope of bond-slip curves in the ascending section (i.e., bond stiffness). Approximately three times enhancement in terms of the initial bond rigidity was achieved with SWSSAAC compared to SWSSC at the same concrete strength. Furthermore, compared with the BFRP and GFRP bars, the specimens reinforced with the CFRP bars experienced higher bond strength and bond rigidity due to their relatively high tensile strength and elastic modulus. Additionally, significant improvements in initial bond stiffness and bond strength were also observed as the alkaline contents (i.e., concrete strength) of the SWSSAAC were aggrandized, demonstrating the integration of the FRP bars and SWSSAAC is achievable, which contributes to an innovative channel for the development of SWSSC pavements or structures. [ABSTRACT FROM AUTHOR]

This study presents the results of an experimental campaign on the use of municipal solid waste incinerator bottom ash (MIBA) and fly ash (FA) as precursors for the production of alkali-activated materials. MIBA was subjected to a pre-treatment stage in response to two issues: high metallic aluminum content, which reacts in a high pH solution, releasing hydrogen; and low amorphous content of silica-, aluminum- and calcium-bearing phases, which translates into a limited formation of reaction products. The proposed pre-treatment stage oxidizes most of the metallic aluminum fraction and compensates for the low reactivity of the material via the formation of additional reactants. Different combinations of MIBA and FA were tried—mass-based ratios of 0/100, 25/75, 50/50, 75/25, and 100/0 for MIBA/FA. Two mix designs of the alkaline activator with sodium hydroxide and sodium silicate were evaluated by varying the Na2O/binder and SiO2/Na2O ratios. These mortars were tested in the fresh and hardened state. The results showed that the pre-treatment stage was effective at stabilizing the dimensional variation of MIBA. Despite the lower reactivity of MIBA, mortars with 50/50 of MIBA/FA presented a maximum 28-day compressive strength of 25.2 MPa, higher than the 5.7 MPa of mortars made with MIBA only. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM), also referred as 3D printing, is a technology that enables building automated three-dimensional objects in a layer-by-layer manner. AM of cement-based and alkali-activated composites has gathered attention over the last decade and is one of the most rapidly developing civil engineering fields. Development of proper mixture compositions which are suitable in fresh and hardened state is one of the key challenges of AM technology in construction. As the behaviour of cement-based materials (CBM) and alkali-activated materials (AAM) is determined by chemical and physical processes at the nano-level, incorporation of nano- and micro-sized admixtures has great influence on the performance of printable composites. These modifications are attributed to the unique reactivity of nanoparticles associated with their small size and large surface area. This review paper summarizes recent developments in the application of nano- and micro-particles on 3D printable cementitious composites and how they influence the performance of 3D-printed construction materials. The research progress on nano-engineered CBM and AAM is reviewed from the view of fresh and hardened properties. Moreover, comparison between nano- and micro-sized admixtures including nanosilica, graphene-based materials, and clay nanoparticles as well as chemical admixtures such as viscosity-modifying admixtures and superplasticizers is presented. Finally, the existing problems in current research and future perspectives are summarized. This review provides useful recommendations toward the significant influence of nano- and micro-sized admixtures on the performance of 3D printable CBMs. [ABSTRACT FROM AUTHOR]

Newly designed mesoporous brushite-metakaolin-based geopolymer materials were examined with an idea for using this material as a potential adsorbent for Pb(II) removal from aqueous solutions. As a starting component for geopolymer synthesis, a natural raw kaolinite clay with the addition of 2 wt.%, 4 wt.%, 6 wt.%, 8 wt.%, and 10 wt.% of pure brushite was used. Phase, structural, morphological, and adsorption properties of newly synthesized mesoporous brushite-metakaolin geopolymer materials were examined in detail by the means of XRPD, FTIR, SEM-EDS, BET/BJH, and ICP-OES methods. The ICP-OES results showed that the synthesized material samples with 2 wt.%, 4 wt.%, and 6 wt.% of brushite possess significant adsorption properties and the mechanisms of the adsorption process can be attributed to chemisorption. The most notable result is that brushite-metakaolin-geopolymer with 2 wt.% of brushite have the best efficiency removal, more than 85% of Pb(II). [ABSTRACT FROM AUTHOR]

In this study, coralline-activated materials were prepared using ball-milled coral powder as cementitious material and coral sand as fine aggregate. XRF (X-ray fluorescence) and chemical dissolution tests were carried out to determine the content and reactivity of various elements in coral powder. The compressive strength of the developed composites was evaluated at different ages, and the formation and transformation of mineral crystals in coralline-activated samples were further analyzed by XRD (X-ray diffractometer). The results show that the calcium content in coral powder was as high as 89.5% (loss on ignition). However, only 56% of the active calcium could participate in the polymerization reaction. The silicon and aluminum content was too low, and the slag addition could improve the deficiency of silicon and aluminum in coral powder. With the increase in slag content (from 0% to 50%), the compressive strength of the composites increases significantly. Nevertheless, the enhancement is not pronounced when the slag content exceeds 50%. The increase in slag amount can stimulate the transformation of calcium minerals, e.g., aragonite and calcite, into hydrated calcium silicate and calcium aluminosilicate gels, which significantly enhances the resulting compressive strength. [ABSTRACT FROM AUTHOR]

The study on the physical-mechanical properties of alkali-activated materials (AAM) produced by the 'one-part' method was carried out. For this, residues such as fly ash and rice husk ash (RHA) were used. The alkaline activator (NaOH) was calcined together with RHA for 2 h at 750 °C. Dry mixes were prepared by replacing fly ash with 10%, 20%, and 30% by weight of the calcined material. The samples produced were characterized after 7 and 28 days of curing. The results showed that the investigated variables (calcined material content and curing time at room temperature) were responsible for important variations: compressive strength from 2.40 to 24.92 MPa, modulus of elasticity from 0.90 to 12.32 GPa, water absorption from 2.92% to 13.64%, apparent porosity from 4.82% to 20.02%, and density from 1.48 to 1.71 g/cm3. It was concluded that these variations were due to the high concentration of NaL2O and SiO2 in the dry mixtures. [ABSTRACT FROM AUTHOR]

Alkali‐activated materials (AAMs) and "geopolymers" are inorganic polymeric materials obtained by mixing of solid aluminosilicate precursors with an alkaline solution (generally, KOH or NaOH and Na2SiO3 mixed in various ratios). This class of aluminosilicate materials has emerged as a greener alternative to traditional concrete, for large‐scale as well as for niche applications such as conservation and restoration of built heritage. In this work we apply Raman spectroscopy both to aluminosilicate precursors (metakaolin, pumice, volcanic ash, volcanic soils, clayey sediments, ceramic waste) and to the respective AAMs. In the field of vibrational spectroscopy, Raman is much less employed in the literature with respect to Fourier transform infrared (FTIR) to have insights into the alkali activation process from a molecular point of view. The aim of this paper is to investigate the potentiality of a Raman approach to the comparison of the employed raw materials with the respective AAMs. Raman analyses during the first hours of geopolymerization were also carried out on the clayey sediments and ceramic waste‐based products. The results, differentiated according to the employed precursors, exhibit spectra relative to crystalline and amorphous phases that can give an indication about the newly formed aluminosilicate gel. [ABSTRACT FROM AUTHOR]

The construction industry is always in need of new technologies and products that improve technological characteristics. Alkali-activated materials appear as an alternative to reduce energy costs, improve technological properties and still present themselves as materials with the potential for incorporating industrial waste. The objective of this research was the development of roof tiles through the process of alkaline activation using ash from the kilns of burning of a red ceramic industry. After the process of processing the materials and their characterizations, prismatic specimens (115 × 30 × 20 mm) were made with the replacement of 0, 6.25, 12.5, 25 and 50% ash by metakaolin and subsequently separated into two groups, (i) subjected to curing at room temperature and (ii) subjected to curing at a temperature of 80 °C, in both cases with a curing time of 7, 14 and 28 days. After each curing period and group, the specimens were subjected to technological evaluation of water absorption, porosity, flexural strength and scanning electron microscopy. The results obtained demonstrate that the use of ash from ceramic waste, mainly replacing 12.5% of the metakaolin, promotes a reduction in water absorption and porosity, and an increase in flexural strength. The results obtained at 28 days in thermal curing are 44.05 MPa for 12.5% ash, much higher than the reference composition (16.02 MPa). The increase in strength happens due to the formation of tobermorite, due to the calcium present in the ash, and due to the formation of phases rich in potassium from the ash, such as kalsilite. Thus, it is concluded that the use of ash from ceramic waste is possible in the alkaline activation of roof tiles due to the occurrence of additional mechanisms of alkaline activation. [ABSTRACT FROM AUTHOR]

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Purpose: Adsorbent amendment to contaminated sediments is one in situ remediation method to decrease the bioaccessibility of pollutants from the sediments. In this work, alkali-activated blast furnace slag (BFS) granules were used in a field experiment at Lake Kivijärvi (Finland). The lake was heavily affected by a mining accident in 2012, which released a significant peak load of metals and sulfate. The purpose of this work was to evaluate the performance of the novel amendment material for in situ remediation in real conditions with a preliminary cost estimation. Methods: Alkali-activated BFS granules were prepared and characterized for composition, microstructure, and surface properties. Two mesocosms were placed in the lake: one with granule dosing and another without. Sediment and pore water samples were collected after a two-week period. Similar small-scale experiment was performed in laboratory with a three-month duration. Bioaccessibility of metals from sediments was assessed with a three-stage leaching procedure. Results: The granules were effective in decreasing the mobility of Fe, Zn, Ni, and Cr in all leaching stages by approximately 50–90% in comparison with unamended sediment in the mesocosm experiment. Laboratory-scale incubation experiments also indicated decreased release of Ba, Co, Ni, Al, Fe, Mg, Mn and S. The estimated material costs were lower than the removal of the contaminated sediments with dredging and off-site treatment. Conclusion: The results showed preliminarily the effectiveness of alkaline-activated BFS in the remediation of metal-contaminated sediments in a field experiment. However, topics requiring further study are the leaching of trace elements from the material and impact on the sediment pH. [ABSTRACT FROM AUTHOR]

In the present study, four different locally available waste glass materials (bottle glass-BG, glass wool-GW, stone wool-SW and cathode-ray tube glass-CRTG) were treated with hot concentrated potassium hydroxide (KOH) in order to obtain alternative alkali activators (AAAs). We evaluated the suitability of the solutions obtained for use as AAAs in the production of AAMs. AAMs were prepared using electric arc furnace slag and selected AAAs with a higher content of dissolved Si. We evaluated the performance of the AAMs in comparison to that of slags activated with KOH or potassium-silicate (K-silicate). The compressive strength of the AAMs prepared with KOH-based AAAs were high when Si and Al were simultaneously abundant in the AAA (9.47 MPa when using the activator sourced from the CRTG), and low with the addition of KOH alone (1.97 MPa). The AAM produced using commercial K-silicate yielded the highest compressive strength (27.7 MPa). The porosity of the KOH-based AAM was lowest when an alternative BG-based activator was used (24.1%), when it was similar to that of the AAM prepared with a K-silicate. The BG-based activator had the highest silicon content (33.1 g/L), and NMR revealed that Si was present in the form of Q0, Q1 and Q2. The concentrations of toxic trace elements in the AAAs used for alkali activation of the slag were also determined, and leaching experiments were performed on the AAMs to evaluate the immobilisation potential of alkali-activated slag. In the SW AAAs the results show acceptable concentrations of trace and minor elements with respect to the regulations on waste disposal sites, while in the activators prepared from BG, CRTG and GW some elements exceeded the allowable limits (Pb, Ba, Sb, and As).

This study compares the degradation behavior of the alkali-activated slag/fly ash (AASF) and ordinary Portland cement (OPC) mortars exposed to phosphoric acid with different pH values. The experimental results show that AASF mortars exhibit better resistance than OPC mortars against surface damage, although both systems get white deposits on the surface in phosphoric acid with a relatively high pH level. AASF mortars obtained lower mass loss than OPC mortars in phosphoric acid with pH at 2 and 3. The strength reduction in AASF mortars after immersion in phosphoric acid is more significant than that in OPC mortars. However, total degradation depth of AASF was smaller than that of OPC regardless of the pH of the acid solutions. Based on the experimental data, linear relationships were identified between the slope of degradation depth–mass loss curves and the Al/Si and Ca/Si ratios of the binders. This may indicate a new way to assess the degradation behavior of AASF and OPC based on their chemical compositions.

Fly ash, generated during the combustion of coal for producing energy, is an industrial by-product that is suitable as starting material for the synthesis of alkali-activated materials due to its amorphous aluminosilicate content that is a mandatory requirement for obtaining materials with improved mechanical properties.According to the circular economy concept and taking into account some specific issues such as waste circularity, that provides environmental and societal benefits, this work proposes the successive alkaline activation processes of already alkali-activated materials with the purpose of being recovered several times, contributing to the sustainability of the construction materials.In this work, alkali-activated materials have been prepared using fly ash as starting waste material during successive activations, maintaining constant the alkaline activator and modifying the liquid/solid ratio according to the workability of the mixtures. The materials obtained have been fully characterised. A mineralogical and microstructural study of these materials was conducted by FTIR, XRD, and ESEM-EDX. Moreover, it has been determined their bulk density, strength resistance, open porosity and efflorescence formation, confirming their suitability for being used in a second activation.

Alkali-activated materials (AAMs) are promising materials that can be used as alternatives for conventional Portland cement (PC) materials. In this paper, the fresh properties, and mechanical properties of AAMs made with glass powder (GP) as the precursor were explored and discussed. The discussions presented in this paper showed that the incorporation of GP as the precursor in AAMs resulted in an improvement in the workability and extension of the set times. However, the use of GP especially at early ages could result in a detrimental impact on the mechanical performance of AAMs due to the lower reactivity of GP compared to other precursors. Nonetheless, AAMs with acceptable mechanical performance for non-structural and structural applications can still be produced with the use of GP as the precursor.

The use of electric arc furnace slag (EAFS) as sole precursor to produce alkali-activated mortars has been experimentally investigated. EAFS, a by-product of the steel recycling industry, is a coarse material with unevenly distributed and size-extensive particles. Milling of EAFS was required to achieve a cement-like sized powder before it could be used as precursor. Different combinations of sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) were used, by varying the Na2O/binder concentration (4%, 6%, 8%, 10%, 12%) and SiO2/Na2O ratio (0, 0.5, 1.0, 1.5, 2.0, 2.5) to maximize the mechanical performance. The alkaline solutions were prepared 24 h prior to mixing to unify temperatures for all mixes. The results showed that the SiO2/Na2O ratio and strength development are directly proportional. The maximum 28-day compressive strength obtained, after being subjected to an initial 24 h thermal curing at 80 °C, was 9.1 MPa in mixes with 4% Na2O/binder and 2.5 SiO2/Na2O. However, after an additional 28 days of accelerated carbonation, the maximum compressive strength (i.e., 31 MPa compared to 3.9 MPa in uncarbonated mixes, corresponding to an 800% increase) was obtained in mixes with 12% and 1.0 for Na2O/binder and SiO2/Na2O, respectively, thus showing an alteration in the optimal alkaline activator contents. [ABSTRACT FROM AUTHOR]

The increasing consumption of Portland cement raised concerns about the large amount of CO2 generated during its production, Alkali-Activated Materials (AAM) being an alternative for its replacement in some applications. This research investigated the production of lightweight Alkali-Activated Composites (AAC), based on metakaolin and expanded polystyrene (EPS) as an agglomerate. The effects of the amount and size of EPS incorporated in the matrix (18, 35 and 53vol.-% and varied average sizes of 0.85, 2.16, and 6.00 mm) were evaluated. Increasing amounts of EPS reduced strength, from 42 MPa to 25 or 14 MPa for 18 or 53vol.-% of beads of size 0.85 mm. Strength decrease is more pronounced for larger EPS beads, i.e. to 12.2 and 1.5 MPa when 18 or 53vol.-% EPS beads with an average diameter of 6.0 mm were added. However, composites with a density as low as 0.8 to 1.2 g/cm3 were produced with strength varying between 15 and 25 MPa, demonstrating their potential as construction materials for non-structural applications. [ABSTRACT FROM AUTHOR]

Alkali-activated materials, were synthesized from glass waste powder (cullet from window-type sheets) with NaOH solution. In order to get a high porous microstructure, the hardened pastes were subjected for thermal treatment at temperatures of 400, 500, 600, 700, and 800 °C for 60 min. An important increase in the specimen's volume and porosity appeared during the thermal treatment; this is due to the foaming/intumescent phenomenon specific to this type of material. For the specimen's pastes based on the partial replacement of glass waste powder with graphite (1, 3 and 5 wt.%), it was determined that the increase of compressive strength assessed after thermally treated. The increase of graphite amount also resulted in the decrease of the initial temperature of the intumescent process (i.e., at 500 °C). The microstructure with high porosity after thermal treatment of these materials, with various sizes of closed pores, makes them suitable for use as both thermal and acoustical insulation materials.

Abstract Alkali-activated materials are a promising type of binder candidate as a substitute to Portland cement. Fly ashes can be used as binder precursors giving higher environmental benefits. In the present research, fly ashes (Type F) containing different amounts of unburned carbonaceous matter have been used to formulate mortars. Serious problems concerning the workability in the fresh state have been found when high carbon content are reached. An attempt to avoid the preliminary treatments used to eliminate the unburned matter is carried out by exploiting different mix-design receipts obtained by changing the water/binder ratio, the ratio of the alkaline activators and using different types of superplasticizer additives. Data so far collected underline that a high amount of unburned carbonaceous matter can not only compromise the mechanical properties of the materials, but also the rheological ones and underline the necessity to develop ad hoc additives for this type of binders.

The use of sodium carbonate as an alkali activator for slag to produce alkali-activated slag is promising due to its sustainable, economic and user-friendly properties. However, the lower early age performance of composites made with such binder has limited its use especially in applications where higher early age is required. Hence, in order to propel the application of this sustainable binder, it is imperative to find ways in which the early age performance can be enhanced without having a detrimental effect on later age performance. One of the effective and sustainable ways to enhance the early age strength of sodium carbonate activated slag is by incorporation of various additives as partial replacement of sodium carbonate on/and slag. In order to propel more application of sodium carbonate slag for various applications, this current study was undertaken. In this paper, an overview of the types of various additives that can be used to enhance the early age compressive strength of sodium carbonate activated slag composites was discussed. The mechanism and dosage of each of the additives were briefly discussed alongside the limitation and advantages of the additives. Findings from this overview showed that the early age compressive strength of sodium carbonate activated slag can be enhanced with the use of additives such as calcium oxide, calcium hydroxide, Portland cement, sodium hydroxide and sodium silicate.

China is the largest producer and user of ordinary Portland cement (OPC), and the rapid growth of infrastructure development demands more sustainable building materials for concrete structures. Alkali-activated materials (AAMs) are a new type of energy-saving and environmentally friendly building material with a wide range of potential applications. This paper compares the durability of AAMs and OPC-based materials under sulfate attack, acid corrosion, carbonation, and chloride penetration. Different AAMs have shown distinct durability properties due to different compositions being formed when different raw materials are used. According to the calcium (Ca) concentration of the raw materials, this paper interprets the deterioration mechanisms of three categories of AAMs: calcium-free, low-calcium, and calcium-rich. Conflicts found in the most recent research are highlighted, as they raise concerns regarding the consistence and long-term properties of AAMs. Nevertheless, AAMs show better durability performances than OPC-based materials in general.

resumo: Portland cement remains the main material of choice in construction due to its thermal, mechanical and durability properties. However, there is growing concern about the large amount of energy consumed and the environmental pollution generated during its production. The objective of this study, therefore, was to evaluate the potential of the fine residual material produced by crushing basalt rocks to form a supplementary cementitious matrix through alkaline activation. Basalt powder with a particle size of less than 53µm was prepared and activated with a sodium hydroxide solution, with a sodium silicate solution as an adjuvant. The curing process of the material was also carried out at 5 temperature levels, 75, 85, 100, 115, 125°C, according to the experimental design. The paste was dry curing at a standard digital laboratory oven for 24 hours. After curing, the compressive strength of the material was evaluated, reaching a mean value of 10.21 MPa for the H5S15T125 mixture at 28 days. The microstructure analysis was performed by X-ray microtomography, presenting the reconstruction of the internal pores and cracks, leading to the conclusion that higher curing temperatures formed more porous matrices, although with more strength. Based on the collected data, the statistical analysis of the design was performed showing that sodium hydroxide and temperature have a statistically significant effect on the response variable compressive strength. As such, the alkali-activation of basalt powder can potentially produce a cementitious material of moderate strength, giving purpose to the residue and reducing the emission of harmful particles into the atmosphere.

To address the high CO2 footprint associated with cement production, many alternative, sustainable binders are now gaining worldwide attention–including alkali-activated materials. The alkali-activation reaction of metakaolin is a fairly complex process involving transformation of one amorphous reactant (precursor metakaolin) into another amorphous product or products (N-A-S-H gel and/or disordered zeolite type phases). In spite of this complexity, researchers in the past 2 decades have gained significant knowledge on the nature of this reaction at multiple scales. Understanding and developing a clear relationship between the alkalinity of the mix and the extent of reaction is of high interest for practical applications. However, detailed and thorough investigations on this important relationship are limited. Here, in this study, we address this gap by systematically investigating a series of alkali-activated materials samples with a wide range of Na/Al ratios (0.5–1.8) using seven different yet complementary analytical techniques (isothermal calorimetry, FTIR, XRD, TGA, NMR, and Raman imaging). Applied in tandem, these tools reveal a clear but non-linear relationship between the Na/Al ratio and the extent of alkali-activation reaction indicating diminishing returns at higher Na/Al ratios, where higher Na/Al ratios cause an increase in the degree of reaction until a certain point at which the increase in Na/Al ratio does not significantly affect the reaction kinetics, but may affect the gel polymerization. These findings could potentially aid decision making for commercial applications of AAMs where alkalinity of the mix is an important parameter for performance as well as safety.