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Considering the potential of geopolymer cements as an alternative to partially substitute Portland cement, this article presents a brief review, where the curing conditions of geopolymer cements are analyzed based on three variables: time, humidity, and temperature. In addition, the behavior of these variables is described according to the curing methods that have been studied and evaluated so far in fly ash-based geopolymer cements. The literature review was conducted using Scopus as the primary search tool, starting from the keyword 'geopolymeric cements.' More than 90 relevant documents were identified after applying specific filters and reviewing their abstracts. Finally, a thorough reading, and analysis of the bibliographic data were performed to extract relevant information for the study topic. The published procedures show that there is no conclusive trend in the curing method for this type of material; however, the most accepted conditions for the development of higher compressive strengths are temperatures between 60 and 80 °C, with controlled humidity (sealed), for a period of 4 to 12 hours. In general, this brief review serves as a guide to propose, study, and apply different curing processes in fly ash-based geopolymer cements. [ABSTRACT FROM AUTHOR]

The aim of this study is to evaluate the usability of new cement (NC) made by the burning of quinary by-product to make commercial binders. Chemical analysis of the by-products and NC as well as X-ray diffraction (XRD) analysis of NC, fineness, density, consistency, and setting time of NC paste, and slump in addition to compressive strength (CS) and splitting tensile strength (STS) of NC concrete (NCC) were conducted. The results suggested that chemical composition of by-products is suitable to make NC binder. The NC contains Ca3SiO5, Ca2SiO5, Ca3Al2O6, and Ca3Al2FeO10. The particles passing through the 200 um Sieve were 56% compared with 52% for Portland cement (PC). The density of the of NC was similar to that of PC. The NC needed 48% more water than PC for normal consistency. The initial and final setting-time of NC was 105 min and 225 min respectively which is much higher than that of PC (15 and 45 min). The slump, compressive strength and splitting tensile strength were slightly lower for concrete containing NC compared with that pf PC concrete. Although the CS and STS of NCC are the lowest, the rate of the CS and STS gain of NCC is greater than that of PCC. It was concluded that NC is a viable alternative to PC for the production of greener concrete.

Biochar (BC) is a porous carbon formed by pyrolysis of biomass at high temperatures under anoxic conditions. The use of pulverized BC as a cementitious materials mixture has recently gained research momentum because this usage can lock BC in inert materials and reduce cement consumption simultaneously. This paper presents a review on the use BC particles as an additive or cement replacement in cementitious composites over the last few decades. It comprehensively reviews and discusses the physicochemical properties of BC, as well as the influence of BC on the hydration kinetics, workability, physical properties, mechanical properties, and durability of mortar or concrete. The replacement of cement with 1%–3% BC, in weight, decreases the permeability and increases the mechanism strength of cementitious composites. The properties of the BC-cement composites is closely related to the carbonaceous particle fineness, feedstock, pyrolysis temperature, and treatment method of the BC. Further research is expected to discover BC-based cementitious material for preparing a specific BC for a specific use as cementitious mixture. [ABSTRACT FROM AUTHOR]

This study examines the use of natural seawater as mixing water for alkali-activated slag concrete and reports the characteristics of alkali-activated slag concrete with exposure to seawater. Preliminary experiments were conducted on pastes in order to measure pH and select optimum activator content under the experimental conditions. Wet-sieved pastes from fresh concrete were used to evaluate the mineralogical and microstructural characteristics of reaction products. Compressive strengths and chloride contents were measured with the hardened concrete samples. The activators used in alkali-activated slag concrete were sodium hydroxide (5% weight of slag) and liquid sodium silicate (5% weight of slag). The alkali-activated slag samples showed the carbonation of calcium silicate hydrate (C–S–H), which resulted in the reduction in strength with time. The seawater-mixed alkali-activated slag samples produced additional reaction products, C4AH13, and chloride-bearing hydrocalumite, and they improved the strength. The seawater-mixed alkali-activated slag samples exposed in seawater exhibited improved mechanical performance compared to other samples. C–S–H carbonation did not occur, refinement of the pore structure was confirmed, and the compressive strength increased after exposure to seawater. The release of partial chloride ions, which were bound in solid phases, occurred; however, such slight leaching did not affect the strength of the samples. The investigation within the experimental conditions of this study showed a positive result regarding the use of seawater as mixing water in alkali-activated slag concrete. [ABSTRACT FROM AUTHOR]

To potentially enable CO 2 sequestration, reactive MgO carbonate cement is emerging as an alternative binder to Portland cement. Understanding the mechanical properties of its binding phase is critical for understanding the strength development and performing materials design for reactive MgO cement systems; however, the intrinsic mechanical properties of hydromagnesite (Mg 5 (CO 3) 4 (OH) 2 ·4H 2 O), a key binding phase, remain unexplored. The present study utilized synchrotron-based high-pressure X-ray diffraction to determine the unit cell-scale, intrinsic mechanical properties of hydromagnesite for the first time. Up to hydrostatic loading of 7.7 GPa, the bulk modulus of hydromagnesite was determined as 59 GPa or 71 GPa fitted using the second-order or third-order Birch-Murnaghan equation of state, which we contextualize with binding phases in various cement systems. The experiment results are applicable in materials design of low-carbon concrete and valuable for the validation and calibration of atomistic models. [ABSTRACT FROM AUTHOR]

This article describes an initial study of the generation of geo-polymers associating comparatively reaction geopolimérica kaolin reported by several authors and a local ceramic clay. the geo-polymer binder material in the future could replace traditional building materials such as cement, block and others with low environmental impact in their production and use, in addition to greater mechanical and chemical resistance. The fl uorescence analysis and diffractometry RX kaolin and ceramic clay yielded information both chemical similarities and mineralogy of raw materials, broke kaolin with a siO2 / al2O3 ratio of 1.2 to verify chemical concentrations activator generating a matrix with experimental ions Na + 1, K + 1, Al + 3, Si-2 in an alkaline medium. the reactivity between the alkali ions and silicate ion showed start geo-polymerization reaction both kaolin clay and pottery whereas the siO2 / al2O3 ratio is 1.78 clay. Briquettes test is developed with both raw materials that were treated with the activating solution developed in the fi rst part of the study. The tests gave results as briquettes waterproof 5 hours of curing and resistance up to 32 megabytes in pascals compression tests.

Calcium aluminate layered double hydroxides (Ca-Al LDHs) constitute a considerable part of cementitious waste fines. Although cementitious waste fines have proven to be recyclable by thermal treatment at moderate temperatures (400–700 °C), understanding how each phase rehydrates and contributes to the binding properties of rehydrated cementitious materials is still necessary. In this study, the de(re)hydration of katoite is investigated through in situ techniques, and its applicability as an alternative cement or supplementary cementitious material (SCM) is discussed. The research employed X-ray diffraction, isothermal calorimetry, in situ wide-angle X-ray scattering (WAXS), and rotational/oscillatory rheometry. Katoite synthesized by a mechanochemical process was dehydrated at 400 °C, producing mainly mayenite. During rehydration, calorimetry presents high heat production in the first minutes. WAXS shows prompt recovery of katoite and increasing formation of monocarboaluminate (Ca-Al LDH) after 30 s of rehydration. The findings confirm the direct association between rapid heat release and phase reformation. Rehydrated pastes present a high yield stress and an increasing storage modulus, indicating rapid binding properties. The consolidation is also correlated with cumulative heat and monocarboaluminate formation. The results indicate the potential of calcined katoite for use as rapid set alternative cement or SCM.

M-S-H gels were synthesised via reaction of Mg(OH) 2 with silica fume, cured at 35 °C for up to 112 days, and their chemical and nanostructural evolution was examined. M-S-H gels with structural similarity to the thermodynamically stable serpentine-group mineral lizardite were formed. Quantification of 25Mg and 29Si MAS and 1H 29Si CPMAS NMR, electron microscopy, and thermogravimetric data showed dissolution of brucite and silica fume, and M-S-H formation, all occurred linearly with time up to 56 days. Data showed strong correlation with the Avrami-Erofeyey nucleation kinetic model, indicating M-S-H formation was governed by nucleation reactions. After 112 days, two distinct M-S-H gels were formed: a Si-rich M-S-H gel with molar Mg/Si = 0.55(±0.2), and a Mg-rich M-S-H gel with molar Mg/Si = 0.80(±0.5). Nanostructural rearrangement of M-S-H continues up to 112 days, with increased crosslinking and polymerisation. This new insight is important for application of M-S-H binders in both construction and radioactive/toxic waste immobilisation. [ABSTRACT FROM AUTHOR]

This study investigates the feasibility of using combination of Cement Kiln Dust (CKD) which is classified as a hazardous solid waste material and Silica Fume (SF), as a sustainable precursor to make binary binder based geopolymer paste. Furthermore, Rice Husk Ash (RHA) an agricultural waste is used as the main source for preparing amorphous silica in order to produce sustainable sodium silicate solution and also to replace it with the standard commercial sodium silicate. In this study alkaline activator solution was prepared through the combination of RHA powder with 10-M sodium hydroxide solution (NaOH) to adjust the Na 2 O/SiO 2 and H 2 O/Na 2 O molar ratio. Geopolymer paste was produced by mixing different SF/CKD proportion (15/85%, 30/70%, 45/55%, 50/50%, 55/45%, 70/30% and 85/15% by weight) with the RHA-NaOH alkaline activator solution. The compressive strength test, Fourier transform infrared spectroscopy (FTIR), mini-slump test, setting time and X-ray diffraction (XRD) were carried out to characterize the geopolymer. The results show that it was feasible to make sustainable geopolymer with combination of SF/CKD binder and sodium silicate solution from RHA. By increasing CKD up to the optimum amount (45%) the compressive strength increased linearly and then the compressive strength decreased when it exceeds the optimum amount. The results also showed that the setting time of the geopolymer can be modified by changing the SF/CKD proportion. Moreover, the XRD presented that the geopolymer paste has an amorphous to semi-crystalline phase. Also, FTIR analysis illustrated that by increasing silica content, Si-O-Si (Al) bonds which are considered as the geopolymeric fingerprint area, will shift to the higher wavenumber. • A mixture of CKD and SF is proposed as new binary binder material. • Sustainable alkaline activated solution was prepared using RHA. • It is feasible to reuse high volumes of CKD in the production of geopolymer. • By consuming 45% of CKD and 55% of SF, the highest compressive strength was achieved. [ABSTRACT FROM AUTHOR]

• XRD patterns of binders were used to study and model the hydration process of Calcium sulfo-aluminate (CSA) based composites. • Hydration of CSA-based composites is controlled by the quantity of ye'elimite, and C3A. • A chemical parameter (Mm Value) based on binder composition is proposed to predict the properties of CSA-based composites. • Compressive strength and setting time are influenced by the Mm Value of the composite binder. Calcium sulfo-aluminate (CSA) cement is an alternative cement that can be beneficial for precast, rapid, and low-temperature concrete construction. But low workability and impractically short setting time of CSA cement, prevent its application in the construction industry. The use of Portland cement (OPC) and ground granulated blast furnace slag (GGBFS) in CSA-based composite binder can provide improved workability, and setting time while maintaining early strength and low carbon footprint. This article studies the hydration process in a composite binder with CSA, GGBFS and OPC to identify the controlling reaction and chemical parameters that can be used to predict the concrete performance during the fresh and hardened state. As SCMs and alternative binders are being used more in construction, the hydration process and compatibility assessment of binders need to have a scientific basis instead of a trial-and-error process. [ABSTRACT FROM AUTHOR]

Geopolymer is an environmentally friendly cementing agent and is an alternative to Ordinary Portland Cement (OPC). Calcined Water Treatment Sludge (WTS) and Rice Husk Ash (RHA) blends are used as a sustainable precursor for developing a lightweight geopolymer binder in this research. The alkali activator is a mixture of sodium hydroxide (NaOH) and sodium silicate (Na 2 SiO 3 ). The effects of the SiO 2 /Al 2 O 3 ratio, which reflects the characteristics of chemical compositions of WTS and RHA, and the heat-curing temperature (at room temperature and 60 °C) on density, setting time and Unconfined Compressive Strength (UCS) are investigated. It is evident from this study that the density of WTS–RHA geopolymers at various SiO 2 /Al 2 O 3 ratios and temperatures is essentially the same and is approximately 3 times lower than that of OPC (of 3.15 g/cm 3 ). The SiO 2 /Al 2 O 3 ratio and temperature significantly affect the setting time and UCS. A higher SiO 2 /Al 2 O 3 ratio results in longer initial and final setting times as the condensation rate between silicate and aluminate species is faster than that between silicate and silicate species. The optimum SiO 2 /Al 2 O 3 ratio providing the highest strength is found at approximately 4.9 and 5.9 for room temperature and 60 °C curing conditions. At these optimum SiO 2 /Al 2 O 3 ratios, the UCSs of geopolymers meet the minimum requirement for OPC of 19 MPa. This research will enable WTS and RHA traditionally destined for landfills to be used in a sustainable manner as a precursor in geopolymer binders. This sustainably, in terms of economic and environmental perspectives, is also analyzed and discussed in this paper. [ABSTRACT FROM AUTHOR]

This work aims to assess the potential reactivity of a mechanically activated kaolin for its use as an alternative cement precursor. The mechanical activation was successfully achieved by grinding at different rotation speeds (250, 300, and 350 rpm) and times (60, 90, and 120 min), obtaining a highly amorphous and reactive material. The amorphization was monitored through XRD with amorphous content estimation and FTIR deconvolution. The potential reactivity was evaluated through chemical attacks, obtaining SiO 2 and Al 2 O 3 availabilities up to 95 wt% and 93 wt% of total SiO 2 and Al 2 O 3 content. XRD and FTIR also allowed the identification of the non-reactive phases on the insoluble residue after chemical attacks. NMR analysis revealed that part of the aluminium was in IV coordination, limiting the reactivity in the alkali activation process. This work demonstrated the effectiveness of mechanical activation as a greener treatment than thermal dehydroxylation to increase the raw kaolin's reactivity. • The effect of mechanical activation (MA) in kaolin's reactivity was evaluated. • MA enhances the reactivity of kaolin. • Grinding time and rotation speed's influence on kaolin's reactivity was revealed. • The MA of kaolin could lead to a higher amorphous content than in metakaolin. • The results demonstrate that activated kaolin is suitable as cement precursor. [ABSTRACT FROM AUTHOR]

• Carbonation capacity of clinker-free binder is up to 4.75 g/Kg. • Simultaneous carbonization will weaken the degree of immobilization reaction. • Compressive strength of clinker-free binder is up to 36.74 Mpa in 28 days. • Ettringite, C S H gels and portlandite were the main hydration production. • Phospho-gypsum activated binder have a high long-term strength. In this work, green clinker-free binders (GCFBs), an alternative cement, were fabricated by recycling sulfur wastes to activate ferrous metallurgical residues for immobilization of solid wastes and carbonation of carbon dioxide synchronously. The results of compressive strength revealed that GCFB-2 activated by thenardite has the highest strength (36.74 MPa) in 3–28 days, and the GCFB-3 activated by ardealite retains a positive growth rate, as well reaches the maximum strength (38.51 MPa) in 120 days. The mineral compositions of GCFBs hardened paste disclosed that ettringite, C S H gels, and portlandite are the main hydrates, which are the strength source of immobilized solid wastes. After the carbonation of carbon dioxide, the compressive strength declines, calcite was the main mineral product, and the net carbonation capacity of carbon dioxide is 2.86–4.75 g/Kg for GCFBs. GCFBs have offered the double benefits of CO 2 emission reduction and waste management, and the hardened pastes are a well better alternative aggregate due to the extremely high compressive strength. This study could provide a new perspective on the full resource utilization of industrial solid wastes, while GCFBs are an excellent alternative to cement in the field of environmental immobilization, with outstanding carbon capture and storage capacity in terms of CO 2 carbonation. [ABSTRACT FROM AUTHOR]

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[Display omitted] • MnW is viable as a supplementary cementitious material (filler) to Portland cement. • MnW increased the compressive strength and bulk density of the samples. • MnW reduces the water absorption and the voids(%) of the cement matrix. • The study encourages the development of new cement-based materials with MnW. Manganese ore is one of the most processed in the world and it is considered essential in the manufacture of iron, steel alloys, batteries etc. However, during its mining and processing, a large portion of wastes are deposited in open-air landfills causing vary environmental risks. Here, such residue (MnW) was proposed as a filler material in Portland cement. The effects of partial substitutions of cement by MnW were assessed by compressive strength, water absorption, void index, bulk density, scanning electron microstructure (SEM-EDS). The results showed that replacing cement at 6–8% with the residue increases the compressive strength, bulk density and reduces the voids and water absorption of the samples. By SEM-EDS, MnW seems to stimulate further C-S-H formation by nucleation on the cement surface. The valorization of this MnW as Supplementary Material helps the environment by giving a destination to a mining waste that occurs around the world, encourages a circular economy on the development of new cement-based products with potential local application without harming their mechanical performance. [ABSTRACT FROM AUTHOR]

Weathered bottom ash (WBA) from municipal solid waste incineration is a calcium aluminosilicate-rich material mainly used in construction and civil engineering as a secondary aggregate. However, its use is also being considered as a precursor in the manufacture of alkali-activated binders (AA-WBA). This preliminary research aimed to deepen understanding of the potential use of WBA (>8 mm fraction) as the sole precursor of alkali-activated binders. To gain better knowledge of this material, the physicochemical, mechanical, and environmental properties of AA-WBA binders were evaluated. In addition, the effect of curing temperature (25 °C, 45 °C, 65 °C, and 85 °C) and humidity conditions (oven and climate chamber) were assessed. The results of this study revealed that temperature and humidity conditions play a fundamental role during the early formation stages of AA-WBA binders. Maximum compactness and compressive strength (29.8 MPa) were obtained in the sample cured at 65 °C in the oven and room humidity. At higher temperatures (85 °C), a substantial decrease in mechanical strength (21.2 MPa) was observed due to a lower cohesion of the binder phases. Curing in the climate chamber led to an increase in humidity, and therefore a decrease in compressive strength. Finally, lower porosity and longer curing time substantially decreased the heavy metals and metalloid leaching concentration of AA-WBA binders. [ABSTRACT FROM AUTHOR]

Abstract: Cementitious composites based on 50–80% fluorgypsum, 15–50% OPC and 0–15% PFA, were wet and dry cured for up to 180days at 20 and 60°C. All pastes developed and maintained strength up to 32MPa, even under water. Characterization by thermal analysis and X-ray diffraction indicated that gypsum formed intensively in the first days, providing the initial strength jointly with a partial hydration of OPC, incomplete fluorgypsum reactions were observed. Wet curing at 20°C gradually increased the strength and the nonevaporable water. At 60°C, wet curing limited the gypsum formation and affected strength development, whereas dry curing resulted in the decomposition of the already formed gypsum and reduced the compressive strength. PFA additions were beneficial in some formulations in late periods, and its reactions were enhanced at 60°C. The microstructure consisted of gypsum crystals surrounded by calcium silicates, and with localized areas of gypsum surrounding unreacted fluorgypsum. [Copyright &y& Elsevier]

Abstract: This paper discusses the properties of rice husk ash samples produced from different types of field ovens to compare the performance of the ovens and to identify the most feasible method to produce a reactive pozzolana as an alternative to cement for building applications requiring lower strengths. Different types of ashes are produced and long-term strength of rice husk ash pozzolanas with lime or cement is investigated to suggest a sustainable affordable option in rural building applications, especially for rural housing in Kerala, a southern state of India. [Copyright &y& Elsevier]

This paper presents the microstructural properties of KOH-activated slag pastes produced with natural seawater under different salinity levels. The seawater-mixed samples exhibit higher 91-day strength compared to the control sample produced with deionized water. Their reduced total porosity and decrease in average pore size are closely related to the strength improvement. The dense microstructure is composed of reaction products resulting from the inclusion of seawater; these include Cl-hydrocalumite, Cl-hydrotalcite, AlClO, K 2 SO 4 , CaCO 3 , calcium aluminum iron oxide carbonate hydroxide hydrate, and aluminum chloride hydrate. In addition, CO 3 2− in the CO 3 -hydrotalcite and CO 3 -hydrocalumite is replaced by chloride ions, and then a Cl-bearing phase is formed, leading to a higher bound chloride content. Lastly, in the single ocean current investigated in this study, the strength of seawater-mixed samples is weakly vulnerable to salinity variation. [ABSTRACT FROM AUTHOR]

Improving the sustainability performance of construction industry is driven by two forces: regulatory push (policy initiatives), and market pull where improving a corporate sustainability performance can be financially beneficial for enterprises. Through the investigation of the sustainability hotspots and impacts, concerning social and environmental, of the steel slag mixed concrete (green concrete) the study assessed the factors relevant for its performance and examined how to improve them. Hotspot analysis and impact assessments were conducted by social and environmental life cycle assessment (LCA). The assessed green concrete represented not just the variety of geographic representation but also the product designs (three different slag contents) and the potential difference occurring from the corporate efforts, where four classes were introduced. The investigation of the social and environmental hotspots of the green concrete revealed a difference in the relation between the sustainability performance and steel slags. While the increased slag content resulted in worse social performance, the increase improved the environmental performance in all six investigated case countries. This trade-off between the social and environmental performance implied the limits of the sustainable product design and suggested the effectiveness of the supply chain management for improving the two sustainability performances for the green concrete. [ABSTRACT FROM AUTHOR]