•Alkali-activated materials with TiO2 nanoparticles additions were studied.•Alkali-activated binders showed good behavior and high compressive strength.•TiO2 additions in alkali-activated enhanced ...mechanical strength.•Self-cleaning properties was affected by the presence of nanoparticles.
Nowadays, alkali-activated binders have become one of the most viable options in the reduction of CO2 emissions; receiving considerable attention due to favorable mechanical properties and low energy consumption. Following from that, the effect of addition of TiO2 nanoparticles in alkali-activated binders based on metakaolin and ground granulated blast furnace slag on the mechanical properties, microstructure, formation of new reaction phases, and self-cleaning properties, was analyzed. The results indicated that synthesized materials showed an enhancement in compressive strength obtaining the best results with 0.5% of TiO2, furthermore, self-cleaning properties showed a slight modification in the presence of the nanoparticles.
•Geothermal nanosilica was used to produce metakaolin-geopolymers.•The addition of the nanosilica reduced the demand of the sodium silicate.•High contents of nanosilica increased the porosity and ...reduced the strength.•Crystallization of nepheline and albite was observed at high temperatures.•The XRD amorphous halo shifted to higher angles due to geopolymerization.
This paper investigated the effect of a nanometric silica from a geothermal waste on the compressive strength, microstructure, and reaction products formed on geopolymers cured at room temperature; the thermal stability was evaluated after exposure up to 800°C. The geothermal silica waste replaced 0–20% of the metakaolin and was suspended in the alkaline solution, to avoid agglomeration. Sodium silicate and sodium hydroxide were used as alkaline solutions and added to adjust the molar ratios of SiO2/Al2O3 at 2.8, 3.0 and 3.2, Na2O/SiO2=0.32 and H2O/Na2O=10. The compressive strength of the geopolymers was evaluated up to 60days of curing. The pastes were characterized by X-ray diffraction, Fourier transformed infrared spectroscopy, and scanning electron microscopy. X-ray diffraction showed the formation of amorphous reaction products, with a shifting in the amorphous halo related to the raw materials; on the other hand, a shift in the characteristic band of aluminosilicates in the infrared spectra also evidenced the geopolymerization process. While the addition of the geothermal silica waste reduced slightly the strength at room and high temperature due to the formation of porosity, its use diminished the demand of waterglass and therefore obtaining low-cost and more sustainable binders.
An investigation was carried out on pastes of Portland cement partially substituted by a geothermal silica waste (GSW), which was obtained as a byproduct from a power plant that uses geothermal ...underground resources. The waste is predominantly nanometric amorphous silica with sodium and potassium chlorides. Pastes containing 0, 10, and 20% GSW and 0, 10, and 20% chlorides by weight of GSW were cured at 20 and 60 °C in order to evaluate the phases formed in the presence of chlorides by means of scanning electron microscopy. The calcium hydroxide consumption was followed using X-ray diffraction. Pore solution tests were performed utilizing a leaching method, which is an alternative technique that could provide an easier and more efficient analysis method compared to the conventional pore expression methodology requiring high pressures and special equipment. The results indicated that the blended cements showed an intense consumption of calcium hydroxide by the pozzolanic reaction and a more compact matrix of hydration products. Furthermore, the high concentration of chlorides provided by the GSW affected the pore solution, reducing the pH, and increasing the concentration of sodium and potassium ions. These were related to the formation of Friedel′s salt, which could be correlated with the reduction in chloride content in the aqueous phase.
The cementitious performance of a coarse granulated blast furnace slag, 2900
cm
2/g, was investigated in concretes of 230, 280 and 330
kg binder/m
3. First, the slag partially replaced 30%, 50% and ...70% of Portland cement, the strength reduced as the amount of slag increased; however, for high binder contents, similar strengths were attained for lower Portland cement contents. Second, the slag was alkali activated with sodium silicate (moduli 1.7 and 2) at 4%, 6% and 8% %Na
2O, the strength increased with the amount of slag in the concrete and developed faster as %Na
2O increased. The microstructures of both type of concretes were dense; however, the strengths of activated slag were superior at similar binder loads, indicating that the hydration products of activated slag are of higher intrinsic strength.
► The activation of mortars of Portland cement with slag was investigated to reduce the low early strength. ► For mortars with 50–30% slag, the activation with water glass (4–10%Na2O) was not ...effective. ► For 80% slag the activation with 4–10%Na2O was effective. ► The highest strengths were for activated 100% slag cements.
Mortars of PC replaced with 0% to100% blast furnace slag were activated by waterglass at 0–10wt.% of Na2O, aiming to investigate the effect of the alkaline activation in reducing the low early strength observed in Portland cement–slag blends. For the activated blended mortars, increased %Na2O and slag contents favored strength; 80% slag showed favorable results with 6 and 10%Na2O, while 30–50% slag, the presence of the alkaline activator was unfavorable relative to the non-activated Portland cement and slag mortars. The microstructures showed denser matrices of hydration products as the amount of slag and alkali concentration were increased, corresponding to the strength observations.
The strength, hydration products, microstructure and heat of early hydration were investigated on alternative hydraulic green cements based on calcium sulphate anhydrite partially blended with ...Portland cement and pozzolans. Four pozzolans of different physical and chemical nature, namely a geothermal waste, silica fume, metakaolin and pulverized fuel ash were characterized. The composite binders showed hydraulic behavior. The use of Portland cement favoured the strength, which was also higher with the incorporation of siliceous nanometric pozzolans compared to the micrometric silicoaluminate pozzolans. The nanoparticles enhanced the early hydration and changed the gypsum morphology promoting denser matrices of hydration products. The geothermal waste pozzolan was the most effective, while one of the composites with metakaolin showed formation of ettringite and strength losses. The heat of hydration of the composites was considerably lower than that of the neat Portland cement.
Following from this background, and since there is very limited information about the use of the GW in Portland cement and its properties, this paper presents results from research aimed to ...investigate in more detail the pozzolanic behavior of GW, as well as its effect on the Portland cement hydration. The GW was characterized and experiments were carried out to determine its effect on the development of compressive strength in blended cement pastes at different replacement levels. X-ray diffraction (XRD) and thermo-gravimetric analysis (TGA) were employed to study the pozzolanic reaction.
Nowadays, concretes with better mechanical properties and durability are required, in order to develop structures with higher mechanical requirements and to resist construction aggressive ...environments. Following from that, the addition of superabsorbent polymers (SAP) as a method of internal curing in concrete, could provide a greater degree of hydration of the cement, reducing cracks generated by the self-drying of the paste, and improving concrete stability. However, the process of absorption in more complex cementitious systems has not yet been reviewed. In this investigation composite materials with and without SAP additions and with different degrees of substitution using supplementary cementitious materials were studied with the main goal to evaluate the development of the SAP additions in these complex composites. In order to analyze the hydration reactions, microstructure and mechanical behavior several tests were carried out as: compression strength, X-ray diffraction, isothermal calorimetry, scanning electron microscopy, and energy dispersion spectroscopy. The results obtained showed that the presence of SAP modified the rheology of concrete mixtures, and in some cases delaying pozzolanic reaction of the systems, having limited effects on the improvement of mechanical properties.
Nowadays, it is a common practice the incorporation of industrial wastes as alternative materials to replace ordinary Portland cement in the concrete manufacture. This technological implementation ...has as main objectives, the enhancement of concretes properties as well as mitigation of durability problem related to the corrosion phenomena; in order to increase the service life of reinforced concrete structures. Therefore, in this research was studied the electrochemical properties of black steel embedded in mortars. Mortars were fabricated using as a partial substitute of cement (0, 10, 20 and 30 wt. %) a geothermal nanosilica waste composed of amorphous nanosilica of ~20ηm and chlorides (0 and 0.4 wt. %). Mortars were subjected to a cure at 20°C (80% of relative humidity) and 60°C (100% of relative humidity). The corrosion behaviour was periodically monitorized up to 65 days using electrochemical techniques of corrosion potential (Ecorr) and corrosion current density (icorr). Values of current density (icorr) were obtained by linear polarization resistance (LPR) technique applying Stern-Geary relation to Rp values. Electrochemical results were validated by comparing with gravimetric losses. The porosity, pH and loss of the evaporated water were also evaluated in mortars. Results obtained showed that the integrity of reinforcement rods was affected with the increase of GNW at high temperatures as well as the total chlorides content in mortars.
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