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Fireproof inorganic coatings based on sodium silicate solution with intumescent additions were prepared and tested to assess their ability to limit the negative effect of a fire. The intumescent materials were obtained by the alkali activation of waste glass powder (obtained by the grinding of recycled soda-lime culet) and slag (waste resulting from the metallurgical industry). The replacement of talc (used as filler in paint formulation) with the intumescent materials obtained by the alkaline activation of waste glass powder (WGP), determined an increase in the intumescence coefficient (up to 65%) and decreased the activation temperature of this process. To evaluate these coatings’ abilities to prevent or delay the temperature increase in metal structures, the paints were applied on steel plates and tested in direct contact with the flame of a butane burner for 60 min. The coatings prevented the increase in the steel substrate temperature over one considered critical (500°C) for steel mechanical properties; the combination of two coatings, with different intumescence activation temperatures, correlated with the increase in the coating’s thickness, sensibly reduced the rate of temperature increase (up to 75%) in the steel substrate.

HIGHLIGHTS -Carbon black (CB) particles in nanometric domain can be successfully incorporated in cement matrices in order to obtain special concretes/mortars with self-sensing properties. -Piezorezistivity monitoring of mortars is a non-destructive method used to assess the structural characteristics of composite materials. -The presence of CB in studied mortars provides a specific electrical sensitivity which may change when curing time increases. The paper presents the manufacture and characterization of special mortars based on Portland cement (PC) and a nanopowder with electrical properties (carbon black - CB). These materials were characterized from the point of view of mechanical strengths as well as properties specific for self-sensing materials i.e. variation of electrical signal when applying a mechanical strain. The electrical signal and mechanical strength values are strongly dependent on the composition and microstructure of mortars.The values of electrical resistance are strongly correlated with the composition, morphology and curing time of the mortars. In this study significant changes of the electrical behaviour (piezoresistivity) of the mortars vs. curing time (90 or 180 days) were noticed, so this must be considered in practical applications. The best results were obtained for the mortars with 0.5-3 wt.% CB cured for 180 days.

This research work assesses the influence of a chromium-rich waste (from potassium dichromate manufacture) on the hydration and hardening processes of two types of Portland cements with limestone filler and slag additions. Therefore, mixtures of Portland cement and chromium-rich waste, corresponding to 0.5% wt. and 1% wt. Cr, were prepared and tested. The analyses performed on cement pastes with chromium waste content, showed that chromium immobilization is mainly due to the formation of Ca6Al2Cr3O18�32H2O (CrEt); this compound results by the substitution of [SO4]2- groups from ettringite lattice of with [CrO4]2-. CrEt crystals growth on the surface of clinker particles forms a diffusion barrier which explains longer setting times for cements with chromium content. The increase of chromium content in the studied systems decreases the compressive strength values but these remain above the lower limits imposed for this type of materials. The chromium content in leachates prepared according to the method described in SR EN 12457-2, was well below the legal limit of 70 mg/Kg established by Romanian legislation. A better chromium immobilisation was achieved in the cement with slag content, in good correlation with the nature and amount of formed hydrates.

The aim of this study was the valorization of titanium flakes (waste) from titanium and titanium alloy ingot production factories and using in applications related to metals recovery as retention bed for some trace metals. The titanium flakes were anodized for surface nanostructuration with TiO2 nanotubes and then annealed in order to increase the surface stability. The nanostructured titanium flakes were loaded and pressed in a retention column linked with inductively coupled plasma spectrometer (ICP-OES). This system allowed determination of trace elements such as beryllium, lanthanum, lutetium, and ytterbium from sample solutions. Beryllium recovery percentage was over 90%, while lanthanides have just a satisfactory recovery percentage (about 65% Yb and Lu and 50% La). The TiO2 nanotube architecture was not affected during utilization being able to perform for a long time. A thermodynamic and kinetic study was done for beryllium due to its successful adsorption recovery percentage. The obtained results showed that the titanium waste is a promising material for rare earth and relatively rare earth elements retention and recovery. Graphical abstract Graphical abstract.

The main objective of this study is the synthesis and characterization of low cost alkali-activated inorganic polymers based on waste glass (G-AAIPs) using a mixture of NaOH and Ca(OH)2 as alkali activators, in order to improve their hydrolytic stability. This paper also presents detailed information about the influence of composition determined by X Ray Diffraction (XRD), microstructure determined by Scanning Electronic Microscopy (SEM) and processing parameters on the main properties of G-AAIP pastes. The main factors analyzed were the glass fineness and the composition of the alkaline activators. The influence on intumescent behavior was also studied by heat treating of specimens at 600 °C and 800 °C. The use of Ca(OH)2 in the composition of the alkaline activator determines the increase of the hydrolytic stability (evaluated by underwater evolution index) of the G-AAIP materials compared to those obtained by NaOH activation. In this case, along with sodium silicate hydrates, calcium silicates hydrates (C-S-H), with good stability in a humid environment, were also formed in the hardened pastes. The highest intumescence and an improvement of hydrolytic stability (evaluated by underwater evolution index and mass loss) was achieved for the waste glass powder activated with a solution containing 70% NaOH and 30% Ca(OH)2. The increase of the waste glass fineness and initial curing temperature of G-AAIPs have a positive effect on the intumescence of resulted materials but have a reduced influence on their mechanical properties and hydrolytic stability.

This paper presents results regarding the possibility of using intumescent alkali-activated borosilicate inorganic polymers (AABSIP), obtained by alkali activation of waste glass powder with mixtures of NaOH, KOH, and borax, as passive fire protection for various substrates. In order to verify the fire behavior, four types of AABSIP intumescent coatings were applied on metal plates and commercial plasterboard and tested in direct contact with a propane flame. The presence of intumescent AABSIP coatings on the metal plates kept the temperature below 500°C (measured on the opposite face where the propane flame was applied); this temperature was critical for the structural strength of steel. AABSIP coating decreased the propagation rate of plasterboard substrate degradation as well as the thermal transfer through the plaster substrate.

In this paper was assessed the influence of carbon black (CB) powder on the hydration and hardening processes of Portland cement (PC)-based materials; this type of materials is designed to be used as cement-based sensors in structural or pavement health monitoring. The rate of PC hydration and hardening processes is influenced by the amount of CB addition, with direct consequences on some properties of these materials, i.e., water for normal consistency and setting time. These results coupled with those obtained by thermal and X-ray diffraction analyses suggest a delaying effect of PC hydration and hardening processes in the presence of carbon black powder, most likely as a result of CB nanoparticles high adsorbent surface. Compressive strength values of PC mortars with CB content up to 1 mass%, assessed after 28 days of hardening, are comparable with those of PC mortars; thus, these materials can be successfully used in construction.

In the last decade numerous research studies were performed in the attempt to recycle several types of industrial waste. This study has as main objective the obtaining and characterization of gypsum based composite materials with various amounts of industrial wastes (flue gas desulfurization gypsum and recycled rubber). The main properties assessed for these materials were setting time, compressive strength, apparent density and thermal conductivity. The gypsum binder was partially replaced with thermally treated flue gas desulfurization gypsum (FGDgp_t) without an important negative impact on the compressive strength; if the replacement amount is up to 40 wt.% the resulted binder still meets the requirements imposed for this property by specific norm for gypsum plaster - EN 13279-1. The substitution of gypsum plaster with FGDgp_t shortens the setting time, therefore it was compulsory to use also sodium citrate as retarder addition. The addition of 5 wt.% rubber waste has a positive effect on the thermal conductivity of composite materials based on gypsum binder with/without FGDgp_t. Consequently, these materials could be used for the manufacture of low cost, eco-friendly thermal insulation materials.

The paper presents the properties of a new type of alkali activated borosilicate inorganic polymers (AABSIPs) resulted by the activation of waste glass powder and fly ash with alkaline solutions. The alkali activators used in this study were mixtures of borax decahydrate with NaOH and KOH solutions. For the preparation of AABSIP mortars two types of aggregates were used i.e. sand and a waste resulted during the mechanical processing of titanium alloy ingots. The thermal treatment of these pastes and mortars determines an intumescent process i.e. significant increase of volume; consequently, these materials could be used as low-cost fire stopper blocks for passive fire protection of buildings.

The paper presents the obtention and characterization of Portland cement mortars with limestone filler and nano-calcite additions. The nano-calcite was obtained by the injection of CO2 in a nano-Ca(OH)2 suspension. The resulted nano-CaCO3 presents different morphologies, i.e., polyhedral and needle like crystals, depending on the initial Ca(OH)2 concentration of the suspension. The formation of calcium carbonate in suspensions was confirmed by X-ray diffraction (XRD), complex thermal analysis (DTA-TG), scanning electron microscopy (SEM) and transmission electron microscopy (TEM and HRTEM). This demonstrates the viability of this method to successfully sequestrate CO2 in cement-based materials. The use of this type of nano-CaCO3 in mortar formulations based on PC does not adversely modify the initial and final setting time of cements; for all studied pastes, the setting time decreases with increase of calcium carbonate content (irrespective of the particle size). Specific hydrated phases formed by Portland cement hydration were observed in all mortars, with limestone filler additions or nano-CaCO3, irrespective of curing time. The hardened mortars with calcium carbonate additions (in adequate amounts) can reach the same mechanical strengths as reference (Portland cement mortar). The addition of nano-CaCO3 in the raw mix increases the mechanical strengths, especially at shorter hardening periods (3 days).

This paper proposes a methodology to assess the rheological behavior of cement paste as a first step to linking this behavior to the robustness of the Self Compacting Mortar (SCM) and further extending this to Self-Compacting Concrete (SCC). Cement paste�s rheological behavior was assessed in terms of spread (using a mini-cone) and time of flow (using the Marsh cone). The results show that the type of superplasticizer (SP) admixture has a great influence on the rheological behavior of cement paste and for each combination of binder and superplasticizer admixture there is a specific range of water to binder ratio in which the rheology of paste seems to be appropriate for obtaining a robust SCC mix. The influence of SP and limestone filler addition on the kinetic of cement hydration process was assessed by X Ray Diffraction and thermal analysis (TG-DTA). Based on these results, i.e. an important delaying effect exerted by superplasticizer additions on cement hydration process at early ages (1 day), it can be concluded that when designing SCC for the precast industry - where the early strength of concrete is of high importance, analyzing the early strength of binder paste together with the robustness properties is very important. The correlation between the two aspects - rheology and early strength -is very important in this case in order to obtain applicable results in practice.

This paper describes the sol-gel synthesis and characterization of a titania-silica fume composite obtained by the coating of silica fume (SF) particles with TiO2 photocatalyst nanoparticles. SEM and TEM images revealed the presence of TiO2 nano-spheres at the surface of bigger SF spherical particles and HRTM confirmed the presence of anatase form. The methylene blue photodegradation tests have shown that photocatalytic activity of TiO2-SF composites is improved in the first hours, due to an efficient dispersion of the TiO2 nanoparticles at the surface of SF particles. The TiO2-SF composite powders have a good pozzolanic activity and can be used for the partial substitution of Portland cement in the preparation of self-cleaning mortar. The values of compressive strength of mortars with 3 wt%. TiO2-SF powders are higher as compared with those assessed for reference (Portland cement mortar), especially for longer hardening times (28, 90 days).

Fire events in buildings can cause losses to human life and important material damage, therefore a great deal of attention is paid nowadays to fire prevention. Buildings based on steel structures are especially affected in the event of a fire, due to the important loss of load-bearing capability when steel is heated at temperatures higher than 500 °C. Therefore, one possible method to mitigate the deleterious effect of fire is to protect steel structures from direct heating by applying protective coatings. In this paper, the ability of magnesium phosphate cement (MPC), based on dead burned magnesite and calcium magnesium phosphate cement (CMPC) coatings, to protect a steel substrate was assessed. CMPCs were obtained by mixing partially calcined dolomite with a KH2PO4 (MKP) solution, and in some cases, with a setting retarder (borax). The main mineralogical compounds assessed by X-ray diffraction and electronic microscopy (SEM-EDS) in CMPC are MgO, CaCO3, and K-struvite (KMgPO4·6H2O). The coatings based on MPC and CMPC, applied to steel plates, were tested in direct contact with a flame, the coatings of MPC and CMPC without the borax addition prevented the temperature increase of a metal substrate above 500 °C. No exfoliation of coatings (MPC and CMPC without borax addition) was noticed during the entire period of the test (45 min).

The aim of this study is to assess the possibility to solidify/stabilize a liquid waste from a municipal waste landfill using binders based on coal ash (fly ash and bottom ash) and specially designed cements for waste treatment (INERCEM). The leaching test proved that all cementitious systems are efficient for the solidification/stabilization of the studied wastes and can reduce the leaching potential of heavy metals present in both liquid waste and coal ash. Therefore, these wastes cease to be a source of environmental pollution. X-ray diffraction (XRD) and thermal complex analysis (DTA-TG) were used to assess the nature and amount of compounds formed in these cementitious systems during the hydration and hardening processes, ettringite, calcium silicate hydrates and CaCO3 were the main compounds formed in these systems assessed by these methods. The microstructure of hardened specimens was assessed by scanning electronic microscopy (SEM), the presence of hydrate phases, at the surface of cenospheres present in fly ash, proved the high pozzolanic reactivity of this phase.

The paper presents results regarding the mechanical properties of concretes prepared with various amounts of recycled concrete aggregate (RCA). RCA was obtained by the crushing of concrete rubble resulted during the demolition of a block of flats. The concretes with RCA were prepared using three different mixing approaches: one stage mixing (1SM), two stages mixing (2SM) and two stages mixing with polyvinyl acetate addition (2SM PA). Two stages mixing method in the presence of polyvinyl acetate addition, leads to an improvement of the mechanical strengths (compressive and splitting tensile strength due to a better bonding between the binding matrix formed in the new concrete and the old mortar adhered at the surface of RCA grains.

Alkali activated borosilicate inorganic polymers (AABSIP) can be obtained by the alkali activation of waste glass powder with a NaOH solution in which anhydrous borax was previously dissolved. AABSIPs have the ability to swell during the thermal treatment increasing their volume and apparent porosity. The temperature at which these materials swell is smaller as compared with the one assessed for the inorganic polymers obtained by the alkaline activation with NaOH solution of waste glass powder. The partial substitution of glass powder with fly ash (10%) do not substantially modifies the AABSIP behavior at high temperatures. The presence of fly ash improves the stability in humid environment (moisture) of AABSIP. The intumescent behavior (i.e. swelling as a result of heat/fire exposure) is less affected for the AABSIP paste with fly ash when it’s curing take place in humid medium (moisture) as compared to the composition without fly ash.

Porous alkali activated materials (AAM), can be obtained from waste glass powder and slag mixtures by alkali activation with NaOH solution. To obtain an adequate porous microstructure, the hardened AAM pastes were thermally treated at temperatures ranging between 900°C and 1000°C, for 60 or 30 minutes. Due to the intumescent behaviour specific for this type of materials, an important increase of the volume and porosity occurs during the thermal treatment. The partial substitution of waste glass powder with slag, determines the increase of compressive strength assessed before (up to 37 MPa) and after (around 10 MPa) thermal treatment; the increase of slag dosage also determines the increase of the activation temperature of the intumescent process (above 950°C). The high porosity and the specific microstructure (closed pores with various shapes and sizes) of these materials recommend them to be utilised as thermal and acoustical insulation materials., Los materiales activados alcalinamente porosos (AAM) se pueden obtener a base de polvo de residuos de vidrio y mezclas de escoria mediante activación alcalina con una solución de hidróxido de sodio (NaOH). Para obtener una microestructura porosa adecuada, las pastas de AAM endurecidas se trataron térmicamente a temperaturas que oscilan entre 900°C y 1000°C durante 60 o 30 minutos. Debido al comportamiento intumescente específico de este tipo de material, se produce un aumento significativo en el volumen y la porosidad durante el tratamiento térmico. La sustitución parcial del polvo de residuos de vidrio por escoria conlleva un aumento en las resistencias a compresión previamente evaluadas (hasta 37 MPa) y después (aproximadamente 10 MPa) del tratamiento térmico; el aumento de la dosis de escoria también determina el aumento de la temperatura de activación del proceso intumescente (por encima de 950°C). La alta porosidad y la microestructura específica de estos materiales recomiendan que se utilicen como materiales de aislamiento térmico y acústico.

This article presents the influence of three additions i.e., hydroxyethyl methyl cellulose (HEMC), sodium bicarbonate and flue gas desulfurization (FGD) gypsum on the porosity of gypsum-based materials. The specific microstructure for a material with good thermal insulation properties i.e., numerous closed pores distributed in the binding matrix, was achieved using HEMC (0.3 wt.%) and sodium bicarbonate (0.5&ndash, 2 wt.%). The addition of HEMC to the gypsum binder determines, as expected, an increase of the porosity due to its ability to stabilize entrained air. In the case of a sodium bicarbonate addition, the pores are formed in the binding matrix due to the entrapment of the gas (CO2) generated by its reaction. Sodium bicarbonate addition delays the setting of gypsum binder therefore in this study FGD gypsum (waste produced in the desulfurization process of combustion gases generated in power plants) was also added to the mixture to mitigate this negative effect. The decrease of geometrical density (up to 13%, in correlation with the additive nature and dosage) correlated with the increase of the porosity, determines, as expected, the decrease of flexural and compressive strengths (33&ndash, 75%), but improves the thermal properties i.e., decreases the thermal conductivity (9&ndash, 18%).

The synthesis and characterisation of inorganic phosphate cements based on calcium silicates (wollastonite and calcium disilicate) and phosphoric acid are presented in this paper. Nanopowders of barium titanate (BT) and biocellulose (BC) were used as additions (10 wt%) in order to improve their bioactivity for potential medical applications. The processing route of the precursors and the thermal treatment conditions had a high impact on the hardening processes and properties of calcium silicophosphate cements. The addition of BT and BC nanopowders determined the decrease of setting time (at the same liquid to powder ratio) but did not significantly influenced the mechanical properties of the resulted composites. In vitro biocompatibility tests showed no cellular oxidative stress, an increase of human stem cells proliferation on these materials and osteoconductive capacity by highlighting the presence of bone morphogenetic protein-1, osteopontin and alkaline phosphatase genes.