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Leaching problems of municipal solid waste incineration bottom-ash (MSWI BA) have been extensively reported in the literature. The outstanding heavy-metal-ion binding capacity of layered double hydroxides (LDHs) can potentially address this problem. This study aimed to investigate the in-situ formation of Mg–Al LDHs in MgO–NaAlO 2-activated ground granulated blast-furnace slag (GGBS) and BA blends, and the evolution of pH, ions, reaction products, microstructure, strength, and leaching behavior were characterized. The results indicate that the formation of Mg–Al LDHs is promoted (up to 69.2%) using a higher MgO/NaAlO 2 molar ratio, which improves the heavy-metal-ion binding capacity. Simultaneously, the compressive strength increases up to 78.4% with higher MgO/NaAlO 2 molar ratios compared to NaAlO 2-activated (NA) sample. Al(OH) 4 – reacts with extra Mg 2+ ions rather than Ca 2+ ions to preferentially form Mg–Al LDHs over Ca–Al LDHs. Meanwhile, the extra Mg 2+ ions snatch the Al(OH) 4 – from Si(OH) 4, increasing the Mg–Al LDH content and reducing the zeolite content. Moreover, the in-situ-formed LDHs absorbed more SO 4 2– than Cl –.

Promoting the sustainability of the building industry is one of the major approaches to addressing energy depletion and climate change. Here, we developed scalable cementitious cooling composites (CCCs) with superior energy-free cooling performance and environmental applicability. Optical properties, phase composition, microstructure, and silica reactivity of composites are characterized and analyzed. Onsite measurements are conducted to evaluate the surface/internal cooling capacities and validate the cooling principles and such composites’ climatic applicability. Results show that calcite, C[sbnd]S[sbnd]H phases (especially tobermorite), and a higher water-to-powder ratio can increase the solar reflectivity (Rsun). Meanwhile, C[sbnd]S[sbnd]H and calcite can also increase the spectral emissivity in the atmospheric window (εaw). Optimal sizes of 0.5 μm (particles) and 1.0 μm (pore size) for Mie scattering are determined by Finite-Difference Time-Domain simulations. The Rsun of 0.90 and εaw of 0.88 are simultaneously achieved, which are comparable to exquisitely designed polymer-based coatings, metamaterials, and multi-layer composites. The surface cooling of 17.3 ℃, internal cooling of 9.2 ℃ by solar reflection, internal cooling of 4.8 ℃ by evaporative cooling, and internal cooling above 2.8 ℃ by mid-infrared (MIR) emission are observed. CCCs are proven to provide efficient cooling in different conditions, with low investment, facile production, and high environmental resistance.

Nanofilters made with high adsorption freeze-dried modified cellulose nanofiber (CNF) aerogel were produced. The modification was made using functional groups containing phthalimide, and then their ability to adsorb particulate matter (PM) was evaluated and compared with the control filter (HEPA). The results showed that the highest adsorption of PM2.5 (99.95%) belonged to the nanofilters made of 1.5% phthalimide-modified CNF aerogel, and the lowest adsorption (76.66%) was related to the control samples. Moreover, based on the results, the nanofilter produced from freeze-dried phthalimide-modified CNF aerogel showed high filtration efficiency as well as excellent resistance to temperature and humidity. This modification enables the filter to operate in different environmental conditions, especially for particles less than 0.1 μm that are mainly responsible for reducing air quality, human health, air visibility, and climate change. In conclusion, we developed an environmentally friendly biodegradable nanofilter capable of high-performance filtration functions and structural stability in different environmental conditions.

This study evaluates the air granulated BOF slag potential as a cementitious material by comparing the granulated and conventionally cooled slags. The mechanical performance of the cement-slag composites is correlated with the hydration behaviour through thermal, mineralogical, and microstructural analysis. The findings show that the granulation improved the grindability, reactivity, and compressive strength till 28 days. The ∼5% slag can be substituted as a binder and ∼35% as an inert filler. The performance decline upon 20–50% replacements is attributed to the absence of brownmillerite reactivity. Overall, the granulation did not improve the cement-slag composite performance significantly till 90 days.

This paper aims to evaluate lightweight aggregates produced with hydrated cement paste powder (HCP) using both carbonation and normal curing. The comparative study was conducted to figure out the effects of the portlandite amount in HCP I and HCP III on the aggregates during carbonation curing. The addition of up to 10 wt% silica fume to HCP I was attempted to make full use of the considerable amount of portlandite to prepare artificial aggregates under normal curing. The mechanical properties, reaction products and microstructure were analysed and the results show that the optimal carbonation periods for HCP I- and HCP III-type aggregates are different due to different amount of portlandite. HCP I-type aggregates can gain 3.14 MPa after 7-day carbonation and contain 35.60 wt% calcium carbonates. The remaining 13.95 wt% portlandite shows the enormous potential in elevating the strength and CO2 capture capacity jointly via the optimized carbonation curing method. On the contrary, HCP III-type aggregates gained 2.97 MPa after 1-day carbonation and further carbonation decomposed C–S–H and lead to the formation of calcite and amorphous silica gel with significantly elevated specific surface area (from 10.69 m2/g to 42.96 m2/g). Additionally, the individual strength development of the prepared aggregates containing silica fume benefits from the sufficiently available portlandite due to the formation of secondary C–S–H, obtaining 2.39 MPa after 28-day normal curing.

With the growing interest in foamed geopolymer manufacture, there is an increasing demand for tailoring these composites’ pore structure. The binary system of two surfactants offers a possibility for enhancing foam formation efficiency and stability in geopolymer paste, however, their effects are not well understood. The influence of binary system blends on pore formation, size, and distribution in fly ash-based geopolymer matrix is investigated and their synergistic effects are evaluated. The results show that combining a nonionic surfactant with anionic Sodium Dodecyl Sulfate (SDS) increases open porosity, whereas cationic Cetyltrimethylammonium Bromide (CTAB) promotes the development of closed pores, improving thermal insulating, hygrothermal and mechanical performance. Moreover, this paper proposes a mechanism to describe the creation of pores in the presence of mixed micelles, as well as the benefit of employing mixed surfactant systems in customizing porous composites.

Energy retrofitting of existing building stocks is essential to reduce building-related energy consumption. Cavity wall insulations are commonly applied, however, their hygrothermal performance is not well established. This study focuses on the hygrothermal performance of rehabilitated cavity walls in the Netherlands. A state-of-the-art aerogel composite developed for cavity wall retrofitting using the blown-in method is presented. The aerogel composite has a dry thermal conductivity of 22.5 mW⋅m−1⋅K−1 and low sorption isotherms. A retrofitted masonry wall with a 6 cm cavity using the aerogel composite can achieve thermal transmittance (U-value) of 0.32 W⋅m−2⋅K−1, well below the 0.71 W⋅m−2⋅K−1 required in the Netherlands. It can reduce the annual heating and cooling demand by up to 72% in a simulated building, and also provides better thermal comfort to the occupants, lowering the percentage of thermally dissatisfied occupants from 51% to 18%. The tested aerogel composite outperforms conventional insulation materials in the market, without sacrificing the thermal comfort of its occupants.

The thermal and hygric characteristics of four bio-based insulation composites (mycelium, hemp, grass and cork) are investigated, and their hygrothermal performances including mould growth potential are simulated and analysed under typical construction details and various climates profiles. The cork composite is found to have the best hygrothermal performance and is suitable under all investigated climates without mould growth, due to its hydrophobic nature and low thermal conductivity. The mycelium composite is highly susceptible to mould growth risk; whereas medium risk is observed on both hemp and grass composites. The findings underline the suitability of using different bio-based composites according to the assembly design and the local climate conditions.

Evaluation and quantification of the effects of the carbonation process on photocatalytic activity are essential for the long-term functional assurance of nano TiO2 modified photocatalytic concrete. This work focuses on the photocatalytic self-cleaning performance variation of mortar containing different dosages of nano TiO2 hydrosol at different carbonization duration. The colourimetric analysis is used to evaluate the self-cleaning performances of carbonated mortar samples. The distribution areas of anatase TiO2, hydrates, and carbonates in the mortar surface are characterized by the Confocal Raman Microscopy. The data recorded during the 28 days of carbonation show that the self-cleaning performance of mortar surfaces features a recovery phenomenon during carbonation. The correlations between photocatalytic self-cleaning performance and the possible parameters are analysed. A predictive model is suggested to evaluate the influence of carbonation degree on the photocatalytic self-cleaning ability of nano TiO2 hydrosol modified mortar.

Silica aerogel features super thermal insulating and excellent sound absorption. Although the application of silica aerogel in building materials for energy saving has been investigated recently, the role of aerogel particle size on geopolymer foam render can be crucial but is rarely studied. In this research, four kinds of silica aerogel with different particle sizes (2–40 μm, 100–700 μm, 100–1200 μm, 700–4000 μm) are applied in geopolymer foam aerogel render (GFAR) to improve the thermal insulation and acoustic absorption performance. Results show that larger silica aerogel particles are more beneficial for acoustic absorption and thermal insulation while smaller aerogel particles are less effective for insulation properties. The microstructure of GFAR is investigated in-depth with micro-CT, optical microscopy and ultrasonic pulse velocity test. The mechanism of the improved performance of GFAR with different silica aerogel is explained. The optimal geopolymer foam aerogel render (GFAR) reaches a thermal conductivity of 0.133 W/(m·K), an average value of acoustic absorption coefficient of 0.51 with a density of 715.2 kg/m3. The result of this study is essential to enlighten the use of larger silica aerogel particles in geopolymer foam render, focusing on a low dosage of silica aerogel while utilize its full benefit.

Nano-silica is an important admixture for ultra-high performance concrete (UHPC). However, complex production process and agglomeration problem of conventional nano-silica significantly limit its application in UHPC. In this study, a novel highly dispersed colloidal olivine nano-silica (C-OnS) is developed. The properties of C-OnS are characterized with laser light scattering, nuclear magnetic resonance and zeta-potential. The C-OnS is applied in UHPC to enhance the cement hydration and reduce the viscosity, while a commercial sol-gel colloidal nano-silica (C-nS) is used as a reference. The effects of C-OnS and C-nS on UHPC are investigated by calorimetry, thermal gravimetry, 29Si and 27Al nuclear magnetic resonance, nitrogen physisorption and mercury intrusion porosimeter. The results show that the performance of UHPC is enhanced by C-OnS at early ages thanks to its higher silanol content, surface area and dispersibility. The advantages of highly dispersive, strong pozzolanic reactivity and tailorable particle size provide new possibilities for application of C-OnS in cement-based materials.

To optimize the pore skeleton structure of pervious concrete to enhance its phosphorus (P) removal from stormwater, small-sized adsorptive aggregate (1–2 mm steel slag) and large-sized natural aggregate (2–5 mm basalt), are applied for the manufacture of two-sized aggregate pervious concrete. Physico-mechanical properties, adsorption performance and freeze–thaw resistance are investigated. The results show that the small-sized steel slag aggregate fills the pores between the large-sized natural aggregates and reduces the porosity and permeability of pervious concrete, significantly improving the mechanical strength and freeze–thaw resistance. The pervious concrete in this study shows an excellent P-adsorption capacity, all P is removed from the aqueous solution with an initial concentration of 168 mg/L and 307 mg/L. The harmful elements (Cr, Sr and V, etc.) leached from the concrete are lower than the maximum limit value. The orthogonal results show that cement and steel slag are the main factors affecting the P-adsorption performance of pervious concrete. Based on the current results, sample 3 (cement: 350 kg/m3, sand: 500 kg/m3, W/C: 0.37, 1–2 mm steel slag: 1385.8 kg/m3 and 2–5 mm basalt: 361.3 kg/m3) shows good P-removal capacity, which is an optimal mix for pervious concrete to remove P from stormwater, with suitable strength and durability.

Due to its low hydraulic reactivity, ladle slag is currently underutilized with nearly 80% of annual generation is either landfilled or dumped. This work investigates the joint activation of LS with Class F fly ash, and the impact of ladle slag on fly ash geopolymer with the focus on activation, hydrates assemblage, conversion process, and thermal behavior. Results reveal that the unique reaction process of ladle slag in alkali activation system shows a positive influence on fly ash geopolymers. Within an alkaline system rich in soluble Si, the initially hydrated CAH phases transform into C-A-S-H, which not only hinders the conversion and enhances the mechanical strength but also retains the geopolymerization. The hybrid geopolymer system exhibits superior thermal performance to pure fly ash geopolymers, especially under high temperature exposure. With increasing ladle slag substitution, more stable crystalline phases are formed at high temperatures. After 800 °C exposure, a high residual compressive strength of 64.7 MPa is achieved with 25 wt% ladle slag addition compared to 55.2 MPa in pure fly ash geopolymers.

The long-term degradation behavior of embedded natural fibres is one of the key factors restricting the durability of bio-based mortars and concretes. In this study, to minimize the negative impact of miscanthus fibre on the service life of bio-based miscanthus mortar, the effects of different treatments (heat treatment, milling) on the long-term performance of bio-based miscanthus mortar are investigated. Results show that the heat-treated miscanthus fibres improve the compressive strength and flexural strength of miscanthus mortar by 82.7% and 26.9%, respectively, compared to the reference fibre, thanks to the reduced porosity and enhanced compatibility. The mechanical strength degradation of miscanthus mortar mainly occurs in the first month after being soaked in water. Moreover, the alkaline environment in miscanthus mortar causes the dissolution of some cellulosic components, resulting in the degradation of the miscanthus fibre. The removal of sugar from the miscanthus fibre is conducive to the strength development and durability of bio-based miscanthus mortar. It is concluded that heat-treated miscanthus fibres can be applied to improve the dimensional stability and degradation resistance of miscanthus mortar for better application of miscanthus in sustainable building materials.

In this paper, the synthesis of dicalcium silicate (C 2S) via sol-gel (acid-catalyzed) process including aqueous route, non-aqueous route, and the Pechini method is reported. The composition of C 2S (α, β, and γ) polymorphs, by-products, and amorphous content is established by employing QXRD (quantitative X-ray diffraction) studies. The attention has been focused to comprehend assay-amorphous relationships of C 2S yield. The intermediate dried gels have been investigated via thermal analysis to monitor changes in the gel structures and precursors at low temperatures. The synthetic parameters including calcination time and temperature, Ca/Si molar ratio and mode of cooling have been optimized to get pure β-C 2S with low amorphous content. The dependency of β → γ C 2S polymorphic transformation on mean crystallite size (D cryst) is studied. Overall, the Pechini method exhibits the most promising results for the purity and tuning of β-C 2S polymorph. Moreover, the non-aqueous and aqueous routes require calcining the dried gel at a temperature higher than 1200 ℃ due to the presence of CaO precursors as CaCO 3. The theoretical calculations of amorphous content have revealed that the change in the stoichiometry from 2.0 to 1.7 Ca/Si ratio is not a viable solution to improve the C 2S product yield.

The prospect of nano-photocatalysts in cementitious systems is promising but the engineering application is still limited, caused by the insufficient insights on durability properties during the service. Mortars with different binders and photocatalysts are prepared and characterized to investigate the deterioration mechanisms of self-cleaning performance upon simultaneous hydration/carbonation. Alterations in self-cleaning performance driven by the change of microstructure, phase composition, and optical properties are analyzed. The drop in self-cleaning performance is attributed to the higher band energy with surface modification, stronger “sheltering” with solid volume increase, worsened mass transfer with reduction of gel pores, and retardation of chemical equilibrium. TiO2-SiO2 composite photocatalysts and microsilica were found to resist the deterioration of self-cleaning performance upon hydration/carbonation by promoting mass transfer and chemical equilibrium and limiting surface modification. Finally, a solution to alleviate the deterioration of self-cleaning property, with the consideration on mechanical, erosion properties and cost issues, is proposed.

In recent years, the construction industry has striven to promote environmentally friendly materials. A growing body of literature has recognised fly ash-based geopolymers as a promising alternative to Portland Cement. However, a detailed and in-depth review specifically concerning high-temperature exposure and fire resistance of fly ash-based geopolymers is still missing. This review provides a comprehensive summary on the recent research progress concerning mix design, curing and their effects on thermal and fire resistance of Class F fly ash geopolymers. Due to the wide variety of characteristics, the performance of class F fly ash is recommended to be assessed in terms of its reactive phases. The influence of different alkali sources and their effects on thermal resistance are discussed, showing that potassium-based activators contribute to better performances. By applying Factsage calculations, the role of minor elements in controlling melting temperature and phase formation as well as the mechanisms behind the initial strength increase of fly ash-based geopolymers during heating are discussed. Moreover, the evolution of material properties during high-temperature exposure and the key parameter pore interconnectivity to avoid damage such as spalling is reviewed. Finally, recommendations for further investigations are provided.

Alkali activated materials (AAMs) have gained great attention as a new low-carbon binder. However, their durability performance, e.g. chloride ingress resistance, still needs further improvement. This study attempts to enhance the chloride binding of AAMs by activating slag with sodium aluminate with the aim to promote the in-situ formation of layered double hydroxides (LDHs). The evolution of pH and ions in the pore solution, reaction products and microstructure were determined to investigate the dynamic activation process. Results show that the sodium aluminate stabilizes the pH environment at around 12.7 during the curing ages. The Mg-Al-LDH with higher Al-O tetrahedra (denoted as Al(OH)4−) contents is promoted, enhancing the chloride absorption capacity. A new reaction mechanism is proposed to describe the activation process. This study reveals that the extra Al(OH)4−in a relatively low pH environment prevents the competition between Mg2+ and Si-O tetrahedra to react with Al(OH)4−, promoting the formation of LDH and C(N)-A-S-H simultaneously.

Polysaccharides are incorporated into cement based systems in order to modify the rheological properties. Typically, cellulose ethers, sphingan gums, guar gum or starch ethers are applied. Depending upon their chemistry, molecular architecture, and adsorption tendency, polysaccharides interact differently with the entire cementitious system. Some stabilising agents like diutan gum mainly affect the cementitious paste; other stabilising agents like starch tend to interact with the sand fraction and even with the coarse aggregates. Cellulose and guar gum shows more diverse performances. Typically stabilising admixtures like polysaccharides are used, when sophisticated rheological properties are adjusted. Therefore, polysaccharides are often used in combination with superplasticisers, which are added to reduce the yield stress of concrete. This can cause interactions, particularly when the stabilising agent shows a strong tendency to adsorb on particle surfaces. Adsorptive stabilising agents may reduce the amount of adsorbed superplasticisers, thus affecting both viscosity and yield stress, while non-adsorptive stabilising agents mainly affect the plastic viscosity independently of the superplasticiser. Due to the strong influence of superplasticisers on the yield stress, influences of the stabilising agent on the yield stress retreat into the background, so that their major effect is an increase of the plastic viscosity. The paper provides a comprehensive overview of how different polysaccharide superplasticisers affect cementitious flowable systems and points out the challenges of the combined use of polysaccharides and superplasticisers. Based on rheometric experiments and observations of the hydration process, time dependent effects on the workability as well as of the hydration of cement are presented and discussed.

Selbstverdichtender Beton verhalt sich unter Temperatureinfluss anders als Normalbeton, da die Rheologie neben der fortschreitenden Hydratation zusatzlich durch die von der Zeit und dem Hydratationsfortschritt abhangige Adsorption von Fliesmitteln beeinflusst wird. Anhand rheometrischer Betonversuche an SVB unterschiedlicher Entwurfskonzepte mit variierter anionischer Ladungsdichte im Fliesmittel wird verdeutlicht, dass mehlkornreiche SVB bei niedrigen Temperaturen sehr robust sind, wahrend bei hohen Temperaturen mehlkornarmere Entwurfe zu bevorzugen sind. Daruber hinaus wird gezeigt, wie sich unterschiedliche Fliesmittelmodifikationen in bestimmten Temperaturbereichen verhalten. Anhand des Wasser-Feststoff-Verhaltnisses und des Adsorptionsverhaltens von Fliesmitteln werden die masgeblichen Prozesse erlautert und Moglichkeiten fur die Entwicklung robuster Mischungen fur individuelle Temperaturbereiche aufgefuhrt. Robustness optimisation of self-compacting concrete regarding temperature effects Regarding the temperature dependent performance, self-compacting concrete (SCC) distinguishes from normal concrete, since its rheology does not only depend upon the hydration itself but supplementary upon the adsorption of superplasticizers, which is affected by the time and the hydration progress. Based on rheometric concrete investigations with different SCC mixture compositions and varied anionic charge densities of the superplasticizers, it is shown that SCC, which is rich in powder components, shows robust performance at low temperatures, while compositions with lower powder contents are favourable at high temperatures. Furthermore, the performance of different superplasticizer modifications at different temperature ranges is demonstrated. The relevant processes are explained by means of the water to powder ratio as well as the adsorption behaviour of superplasticizers, and options for the development of robust mixture compositions for individual temperature ranges are itemised.

Stabilising admixtures are commonly used additives in repair mortars and grouts. Beyond this, such type of admixture is increasingly used in concrete and other cementitious materials. In particular when fresh mortar or concrete properties have to be adjusted reliably, stabilising agents can be beneficially used to improve workability and robustness of the mixture. The mode of operation of these admixtures varies, rather affecting either the liquid phase or the solid particles in the dispersion, both causing strong interactions with the mortar or concrete system, and significant changes in their rheological behaviour. Furthermore, these are strongly affected by the environmental temperature during the casting process. In the paper the effect of temperature on the performance of stabilising agents in cementitious systems is presented and how performance changes affect fresh and hardening mortar or concrete properties. Particular attention is placed on interactions between stabilising agents and superplasticizers. Results are discussed with special focus on self-compacting concrete.

The fresh behaviour of self-compacting concrete (SCC) at varying temperatures differs from that of normal vibrated concrete. This is because the rheology of SCC depends not only on degree of cement hydration, but also on the adsorption of superplasticizers – mostly polycarboxylate based polymers (PCE) -, which is affected by the time and hydration progress. Due to the variety of PCEs and mixture compositions for SCC a prediction of the rheology at varying temperatures is complicated. The charge densities of PCEs as well as the water to solid ratio in the paste are identified to be the main decisive parameters for robust fresh concrete properties. Rheometric concrete investigations with different SCC mixture compositions and varied anionic charge densities of the PCE were conducted. SCC which is rich in powder components showed robust performance at low temperatures while SCC with low powder content was favourable at high temperatures. High charge density PCE pointed out to be very robust at low temperatures but at high temperatures it significantly reduced the flow retention. Low charge density PCE could not generate self-compacting properties at low temperatures but retained the flow performance over sufficiently long time. Based on considerations about particle interactions and adsorption mechanisms of PCEs, the relevant processes are explained and options for the development of robust mixture compositions for individual temperature ranges are itemised.