How Nanotechnology Can Change the Concrete World Part Two of a Two-Part Series Successfully mimicking nature’s bottom-up construction processes is one of the most promising directions. Konstantin Sobolev nanoscopic phases of materials can be Facultad de Ingeniería Civil measured.24 Universidad Autónoma de Nuevo Leon San Nicolás de los Garza, Mexico Miguel Ferrada Gutiérrez Atomic force microscopy (AFM) has been Cognoscible Technologies applied to the investigation of the amor- Santiago, Chile phous C-S-H gel structure.This has led to the discovery that this product has a highly general overview of nano- ordered structure at the nanoscale (Fig. 6).33 technology was present- ed in part one of this two- part series (see p14 in the Understanding of nanoscale structure A October issue). In this helps to influence important processes part, potential applications of nanotech- related to production and use of construc- nology to concrete are presented. tion materials, including strength develop- ment, fracture, corrosion and tailoring of desired properties. For instance, the devel- How Nanotechnology Can Change opment of paints and finishing materials that are self-cleaning, discoloration resist- Construction Materials ant, antigraffiti protected, high scratch The majority of recent nanotechnology resistant and wear resistant is extremely research in construction has focused on important for façade and interior applica- the structure of cement-based materials tions. Self-cleaning Hydrotect tile, window and their fracture mechanisms.4,24,25,32 New glass, and water-based paint have been advanced equipment makes it possible to developed by TOTO based on photocata- observe a structure at its atomic level. lyst technology.16,17 The self-cleaning effect Moreover, the strength, hardness and related to decomposition of organic pollu- other basic properties of microscopic and tants and gases is achieved when titania 16 November 2005 C-S-H crystallized Atomic resolution 2 ϫ 2 µm 20 ϫ 20 nm Figure 7 Ultrafine fumed silica particles observed using TEM.37 Courtesy Andri Vital, EMPA Mat’ls Testing & Research, Laboratory for Figure 6 Highly ordered structure of C-S-H gel (Ca/Si = 0.9) observed at a nanoscale.33 High-Performance Ceramics, Duebendorf, Courtesy Eric Lesniewska, Nanosciences Group, Physics Lab, University of Bourgogne, France. Switzerland. photocatalyst thin film is set on a be used as an additive for high-per- tubes) and improved dispersion and surface to emit active oxygen under formance and self-compacting con- alignment of the individual nano- ultraviolet light. crete that has improved workability tubes can increase the performance and strength.35–37 Nanosilica has of composite fibers or decrease the been proved to be an effective addi- volume of the nanotubes used.40 Another aspect of self-cleaning is tive to polymers to improve provided by the hydrophilicity of the strength, flexibility and durability.39–41 surface.This helps to rinse away dust Based on research conducted at the and dirt. Other examples are related University of Texas–Dallas, Dalton et to nanometer-thin coatings of con- Kang et al.39 investigated epoxy al.26,41 introduced a further break- ducting polymers that protect car- composites filled with functionalized through related to SWNT-reinforced bon steel against corrosion4,9,25 or nanosilica particles obtained using fibers.The composite fiber compris- window glass covered with an invisi- the sol–gel process.The synthesized ing 60% of nanotubes and 40% of ble silver nanolayer to enhance the uniform silica particles were either poly(vinyl alcohol) (PVA) produced thermal insulation of buildings.4,9,25 modified by substituting the surface by continuous spinning with a modi- silanol groups by epoxide ring, amine fied coagulation method achieved and isocyanate groups or by calcinat- strengths of ≥1.8 GPa.These fibers Nanochemistry with its bottom-up ing the nanosilica to remove surface matched the energy-absorbing possibilities offers new products that silanol groups. It was found that mod- capacity of spider silk up to the can be effectively applied in concrete ified particles could chemically bond breaking point of silk at 30% (165 technology. One example is related to epoxy matrix, which resulted in a J/g) and continued to absorb energy to the development of new super- decrease in the coefficient of thermal until reaching a toughness of 570 plasticizers for concrete, such as poly- expansion (CTE) of the composites. J/g, as compared with 50 and 33 J/g carboxylic ether (PCE) polymer-based With increased nanosilica content, the for Spectra and Kevlar fibers, respec- Sky.This product has been developed composites exhibited an additional tively.26 Application of these new recently by Degussa. A nanodesign decrease in CTE, an increase in glass super fibers in composite materials is approach helped to realize the transition temperature and a promising. extended slump retention of decrease in damping. concrete mixtures.34 Concrete with Nanoparticles The combination of carbon nano- It has been proposed that nanopar- tubes and conventional polymer- Mechanical properties of cement ticles can be incorporated into con- based fibers and films is another mortars with nano-iron-oxide and ventional building materials.They challenge. For example, the incorpo- nanosilica were studied by Li et al.38 then possess advanced or smart ration of 10% SWNTs into the Experimental results demonstrated properties required for the construc- strongest artificial fiber, Zylon, results an increase in compressive and flex- tion of high-rise, long-span or intelli- in a new material with 50% greater ural strengths of mortars that con- gent civil and infrastructure strength.40 It is expected that better tained nanoparticles. It was found systems.4,24,25,35–39 For example, silica exfoliation (separation of the bun- that increased nanosilica content nanoparticles (nanosilica (Fig. 7)) can dles to release the individual nano- improved the strength of the mortars. American Ceramic Society Bulletin, Vol. 84, No. 11 17 CONCRETE NANOTECHNOLOGY 1–2% of cementitious materials was The application of Gaia at a dosage Table 1. Effect of Gaia on Performance of used as a viscosity-modifying agent. of 1.3% (by weight, as a dry content) Concrete Mixtures† A constant water/cement ratio (W/C) provides almost a twofold increase Mixture parameters Plain With Gaia of 0.58 was used for all mixtures, and in concrete compressive strength at 35 Cement type (EN-197) II/A-P 42.5R II/A-P 42.5R a slump flow of 780–800 mm was ages of 7 and 28 d. The early Cement content (kg/m3) 460 460 maintained by adjusting the dosage strength of the concrete with Gaia is of an acrylic-polymer-based super- 68.2 MPa, which is ~3 times higher Admixture dosage (%) 1.3 plasticizer.To maintain the specified than that of reference concrete Air content (%) 2.7 1.1 slump flow, the superplasticizer (Table 1 and Fig. 8).The 28 d com- Slump (mm) dosage was increased by ~0.21% per pressive strength of the concrete After 5 min 60 200 each percent of nanosilica used.The made with Gaia demonstrates a clas- After 30 min 25 210 addition of nanosilica made the con- sical dependence on W/C (Fig. 9) After 60 min 15 160 crete mixture more cohesive and and, based on the available test data, After 90 min 140 reduced bleeding and segregation. a single formula is proposed to pre- Ambient temperature (°C) 20 20 At the same time, the nanosilica had dict the 28 d strength of the investi- –3.0881W/C Compressive strength (MPa) little effect on the slump loss meas- gated concretes: f28 = 208.38e 2 At 1 d 22.7 68.2 ured within the first 30 min. (at R = 97%). At 7 d 32.7 77.3 Based on the available data, the At 28 d 45.2 91.7 Although the nanosilica did not positive action of the nanoparticles †Reference 35. affect the compressive strength of on the microstructure and properties the concrete that contained various of cement-based materials can be Moreover, the strength of the forms of fly-ash, the compressive explained by the following 35–38,44 cement mortars with nanoparticles strength of the concrete that con- factors: was even higher than the strength of tained ground limestone was slightly • Well-dispersed nanoparticles mortars with silica fume. SEM study decreased.The best performance increase the viscosity of the liquid proved that the nano-iron-oxide and was demonstrated by concrete with phase, which helps to suspend the nanosilica particles filled the pores ground fly-ash, 2% nanosilica and and decreased the content of calcium cement grains and aggregates, 1.5% superplasticizer.This concrete which, in turn, improves the segrega- hydroxide within the hydration prod- had the highest compressive tion resistance and workability of the ucts.These effects resulted in the strength of 55 MPa at an age of 28 d improvement of the mechanical with the desired behavior in the system. properties of the cement mortars fresh state, i.e., low bleeding, perfect • Nanoparticles fill the voids with nanoparticles. cohesiveness, better slump flow and between cement grains, which little slump loss.The investigation results in the immobilization of free also showed that nanosilica did not water (filler effect). A laboratory study of high-volume affect concrete durability.36,37 fly-ash high-strength concrete that • Well-dispersed nanoparticles act as incorporated nanosilica was per- centers of crystallization of cement formed by Li.42 Investigation of the One of the first commercial hydrates, which accelerates the hydration process confirmed that the nanoadmixtures for concrete, Gaia, hydration. pozzolanic activity of fly-ash can be was developed by Ulmen S.A. and • Nanoparticles favor the formation significantly improved by the applica- Cognoscible Technologies to substi- of small-sized crystals (such as calci- tion of a nanosilica.