The issues associated with the fabrication of nano-silica (NS) mineral powder, such as high cost and agglomeration, can be effectively mitigated by using a precursor solution of NS as the external ...mixture of cement-based materials. Based on the liquid-phase preparation of NS mineral powder, its preparation technology was thoroughly investigated herein. The precursor solution of NS was synthesized using acid media (HCL, HNOsub.3, HBOsub.3, HCOOH, CHsub.3COOH)-the acetic acid concentration was 1~15%-and siliceous materials. (The concentration of sodium silicate was 20~38%). In addition, the pH value (pH4~pH8) of the precursor solution was measured using a pH detector. The indexes of NS, such as precipitation time, morphology, and distribution, were observed to formulate a preparation technique for the precursor solution of NS that possessed the best results for the precipitation of nanoparticles. From the acquired results, it was demonstrated that acetic acid solution (concentration ≤ 3%) and sodium silicate solution (concentration ≤ 25%) were mixed into a solution with pH = 6, which was the optimum mixing ratio for the precursor solution of NS. The prepared precursor solution of NS was also added to the Ca(OH)sub.2 saturated solution, and the precursor solution became active from a stable state. Then, NS particles were precipitated in an alkaline solution and reacted with Ca(OH)sub.2 to form calcium silicate gel, which made the solution increasingly turbid and generated many visible and uniformed flocculating substances. With time, gels were continuously produced, which then turn white. Similarly, NS particles can be precipitated when the precursor solution is added to cement paste, which reacts with the Ca(OH)sub.2 to generate CSH gel and improve the compactness of the cement paste.
The urgent need for sustainable construction that corresponds to the three pillars of sustainable development is obvious and continuously requires innovative solutions. Cementitious composites with ...TiOsub.2 nanoparticles (NT) addition show potential due to their improved durability, physico–mechanical characteristics, and self-cleaning capacity. This study aimed to evaluate the influence of NT on cementitious composites by comparing those with 2%–5% nanoparticles with a similar control sample without nanoparticles, as well as an analysis of cost growth. The experimental results showed an increase in bulk density of the material (4.7%–7.4%), reduction in large pore sizes by min. 12.5%, together with an increase in cumulative volume and cumulative specific surface area of small pore sizes, indicating densification of the material, also supported by SEM, EDS, and XRD analyses indicating acceleration of cement hydration processes with formation of specific products. The changes at microstructural level support the experimental results obtained at macrostructural level, i.e., modest but existent increases in flexural strength (0.6%–7.9%) and compressive strength (0.2%–2.6%) or more significant improvements in abrasion resistance (8.2%–58%) and reduction in water absorption coefficient (37.5%–81.3%). Following the cost–benefit analysis, it was concluded that, for the example case considered of a pedestrian pavement with a surface area of 100 msup.2, using 100 mm thick slabs, if these slabs were to be made with two layers, the lower layer made of cementitious composite as a reference and the upper layer with a thickness of 10 mm made of cementitious composite with 3% NT or 4% NT, the increase in cost would be acceptable, representing less than 15% compared to the cost for the exclusive use of cementitious composite without NT.
Phosphoaluminate cement clinker (PAC) was one type of cementitious material due to its high durability and mechanical performance. As the predominant mineral phase in PAC, the high-temperature ...formation and property of calcium phosphoaluminate mineral (C.sub.8A.sub.6P) were related closely with hydration and mechanical characteristic for PAC. Thus, the influence of BaO on the performance of C.sub.8A.sub.6P mineral phase was investigated carefully in this paper. It was found that BaO of 17.5-20% content could endow C.sub.8A.sub.6P mineral with predominant mechanical performance. This was due to the fact that C.sub.8A.sub.6P mineral was activated by BaO. Excessive BaO would lead to the formation of new unexpected phase BaO·Al.sub.2O.sub.3. The limited solid solubility of BaO in C.sub.8A.sub.6P mineral was 20%. The addition of BaO changed the ratio of hydration products of C.sub.2(A,P)H.sub.8 and C(A,P)H.sub.10 for C.sub.8A.sub.6P mineral.
The application of nano-TiOsub.2 as a photocatalytic agent in buildings’ internal surfaces has recently attracted attention to mitigate microorganism growth, soiling, and contamination in indoor ...environments. This work aimed at comparing the Rhodamine B (RhB) dye degradation efficiency of three different mortar compositions subjected to simulated internal radiation, in which nano-TiOsub.2 (10 wt% of binder mass) was dispersed by ultrasonic and mechanical methods. Mortar specimens were produced with white Portland cement, hydrated lime, sand, and water in different volume proportions of 1:1:6 (cement:lime:sand), 1:3 (cement:sand), and 1:4 (cement:sand). The first stage of the research evaluated samples exposed to the natural outdoor environment and proved the efficiency of specimens’ photoactivity when covered by a glass layer. The second and principal phase of the study simulated indoor conditions in glazed buildings through artificial weathering in which the composition of 1:1:6 was mechanically dispersed and exhibited the highest global color change (ΔE) values for RhB staining. The main finding of the study was that the mortars exposed to simulated indoor conditions presented high ΔE grades, classified as easily perceived by the human eye. This demonstrates the photocatalytic efficiency in an internal building environment that receives radiation through a glass surface.
In this paper, the mechanical properties (the flexural strength, compressive strength and the drying shrinkage rate) of COsub.2-cured alkali-activated compound mineral admixtures (blast furnace slag ...powder (BFS) and fly ash (FA)) are investigated. In addition, the corresponding chloride ion mobility coefficient is measured. Additionally, the freeze–thaw cycles with an NaCl concentration of 3% is studied. Thermogravimetric analysis and scanning electron microscopy are applied in analyzing the mechanical properties. The curing ages of the alkali-activated compound mineral admixtures are 1 day, 3 days and 28 days. Results show that the mechanical strengths are decreased by the addition of FA and increased by the increasing curing age and COsub.2 curing. The maximum reducing rates of flexural and compressive strengths by FA are 47.6% and 42.3%. Meanwhile, the corresponding increasing rates by COsub.2 curing are 26.5% and 23.1%, respectively. The improving effect of alkali-activated BFS by COsub.2 curing is higher than that of FA. Furthermore, the drying shrinkage rate is increased by the increasing dosages of BFS, the increasing curing ages and COsub.2 curing. Additionally, COsub.2 curing and the increasing dosage of BFS leads to decreasing the chloride ion mobility coefficient. Finally, COsub.2 curing and the addition of BFS can effectively improve the resistance of NaCl freeze–thaw cycles. The compactness of the hydration products is improved by the addition of BFS and the roughness of hydration products is increased by COsub.2 curing.
This paper presents the findings of an investigation into the influence of green-synthesized nano-TiO.sub.2 on the characteristics of wood ash (WA) cement mortar. Mortar specimens were prepared by ...partial replacement of cement with WA (10% by weight) and addition of 1, 2 and 3% nano-TiO.sub.2 by weight of binder; using constant water-to-binder ratio (w/b) for all mixtures. The properties evaluated are setting time of the binder and flexural and compressive strength with water absorption of the mortar. The results indicated that addition of 1 and 2% nano-TiO.sub.2 reduced setting times of WA cement paste. Also, the flexural and compressive strength of WA cement mortar were higher with the incorporation of up to 2% nano-TiO.sub.2. The water absorption of WA cement mortar was reduced when nano-TiO.sub.2 was added with 2% incorporation having the best result. The incorporation of NT in WA cement mortar improved its workability and strength characteristics.
Advances in alternative cementitious binders Juenger, M.C.G.; Winnefeld, F.; Provis, J.L. ...
Cement and concrete research,
12/2011, Letnik:
41, Številka:
12
Journal Article, Conference Proceeding
Recenzirano
There is a burgeoning interest in the development, characterization, and implementation of alternatives to Portland cement as a binder in concrete. The construction materials industry is under ...increasing pressure to reduce the energy used in production of Portland cement clinker and the associated greenhouse gas emissions. Further, Portland cement is not the ideal binder for all construction applications, as it suffers from durability problems in particularly aggressive environments. Several alternative binders have been available for almost as long as Portland cement, yet have not been extensively used, and new ones are being developed. In this paper, four promising binders available as alternatives to Portland cement are discussed, namely calcium aluminate cement, calcium sulfoaluminate cement, alkali-activated binders, and supersulfated cements. The history of the binders, their compositions and reaction mechanisms, benefits and drawbacks, unanswered questions, and primary challenges are described.
The content of individual amorphous supplementary cementitious materials (SCMs) in anhydrous and hydrated blended cements was quantified by the PONKCS 1 X-ray diffraction (XRD) method. The analytical ...precision and accuracy of the method were assessed through comparison to a series of mixes of known phase composition and of increasing complexity. A 2σ precision smaller than 2–3wt.% and an accuracy better than 2wt.% were achieved for SCMs in mixes with quartz, anhydrous Portland cement, and hydrated Portland cement.
The extent of reaction of SCMs in hydrating binders measured by XRD was 1) internally consistent as confirmed through the standard addition method and 2) showed a linear correlation to the cumulative heat release as measured independently by isothermal conduction calorimetry.
The advantages, limitations and applicability of the method are discussed with reference to existing methods that measure the degree of reaction of SCMs in blended cements.
This manuscript aims to investigate the effect of hydration characteristics, textural properties and fire resistance of cement pastes containing Fe.sub.2O.sub.3 nano-particles (NF). NF prepared from ...C.sub.2FeO.sub.4.2H.sub.2O at 300 and 500 °C at heating rate 5 °C min.sup.-1 for 2 h soaking time. TEM shows the crystal size of NF was 10-20 nm, with surface area of 50.51 m.sup.2 g.sup.-1. The cement mixes were prepared with 0, 1, 2 mass% NF with water/cement ratio of 0.35. The values of compressive strength and chemically combined water content of OPC-NF pastes up to 1 mass% show higher values than those of neat pastes. Increasing the content of NF up to 2 %, the chemically combined water content decreases, but still higher than that of the neat OPC paste. The free lime content of OPC paste increases, whereas the cement pastes containing NF decrease. SEM micrograph depocits the presence of fibrous C-S-H gel, forming interlocking dense and compact fibrous C-S-H gel. The compressive strength of thermally treated cement pastes increases up to 400 °C, then decreases up to 600-1000 °C, due to the decomposition of C-S-H and CH. It can be concluded that 1-2 % NF enhances the fire resistance of OPC cement pastes.
Nanocelluloses (NCs) are bio-based nano-structurated products that open up new solutions for natural material sciences. Although a high number of papers have described their production, properties, ...and potential applications in multiple industrial sectors, no review to date has focused on their possible use in cementitious composites, which is the aim of this review. It describes how they could be applied in the manufacturing process as a raw material or an additive. NCs improve mechanical properties (internal bonding strength, modulus of elasticity (MOE), and modulus of rupture (MOR)), alter the rheology of the cement paste, and affect the physical properties of cements/cementitious composites. Additionally, the interactions between NCs and the other components of the fiber cement matrix are analyzed. The final result depends on many factors, such as the NC type, the dosage addition mode, the dispersion, the matrix type, and the curing process. However, all of these factors have not been studied in full so far. This review has also identified a number of unexplored areas of great potential for future research in relation to NC applications for fiber-reinforced cement composites, which will include their use as a surface treatment agent, an anionic flocculant, or an additive for wastewater treatment. Although NCs remain expensive, the market perspective is very promising.
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