ASR in Concrete — PART 5

Application and Experimentations Using Nano Silica for Strength Development in Cement Composites and Concrete

In 1969, a patent was filed on an industrial production process for colloidal silica particles that measured in the millimicrons (nanometers), and had high silica purity and surface area [24]. In 2004, the first industrial-scale use of nano silica in cementitious composites was established. Brian Green of the US Army Corps of Engineers pioneered the use of nano silica to develop a rock-matching grout for military applications [25]. His work arose out of issues dealing with segregation of grouts comprised of heavyweight aggregates, specifically hematite. A nano silica dispersion was added to the heavyweight grout mixture as a viscosity-modifying agent. It increased the thickness of the grout mixture, ensuring the stable and universal suspension of the hematite aggregate while the grout was in a plastic state. The viscosity-modifying agent used was in the form of an ultra-fine amorphous colloidal silica, or nano silica, with a particle distribution ranging between three and 100 nm. Green found that the nano silica not only improved the suspension of the hematite, eliminating segregation, but also increased the density and strength of the grout [25].

One of the first documented commercial uses of nano silica in concrete was in Gypsum, Colorado at the Eagle County Airfield during the construction of a training pad for the Air and Rescue Facility. At the Eagle County Regional Airport, high in the mountains of Colorado, twenty cubic yards of concrete was enhanced with nano silica as a means to increase both the early strength of the concrete and its durability against ASR [26]. The ready-mixed concrete provider (Lafarge North America) evaluated both the fresh and hardened properties of the nano silica-enhanced concrete. The plant trails of the nano silica enhanced concrete proved to increase the compressive strength by 50% over the reference concrete (without nano silica) without compromising the workability and amount of entrained air.

The performance of nano silica in increasing early strength development has been shown to come from the greater surface area of free silica (as compared to Class F fly ash) [23]. Similar to Class F fly ash, the free silica provided by the nano silica combines with calcium hydroxide (CH) in the hydrating cementitious matrix to create more calcium-silicate-hydrate (C-S-H), the backbone of concrete strength. Due to the smaller size of the nano silica particles, there is a greater total surface area of free silica available for more immediate pozzolanic reaction and densification, thus increasing the early strength and durability of concrete [27]. Other possible means by which the nano silica size enhances the HCM are through pozzolanic reaction, nucleation of C-S-H, and accelerated dissolution of cement particles. It was hypothesized that the novel use of nano silica would maintain and possibly enhance concrete durability (with respect to ASR while accelerating early strengths of concrete and commercial strength milestones on the job-site [28].

Since the U.S. Army Corps of Engineers experience with nano silica in grout mixtures, the use of nano silica in cement composites and concrete has ranged from 0.01–10.9% replacement of OPC by weight [26, 27, 29, 30]. Despite the ever-growing popularity of nano silica in cement composites and concrete, a deeper understanding on the impact of nano silica is needed in both the academic and construction arenas to give the industry confidence in this novel technology.

Composition of nano silica dispersions

Mineral additives are used as a means to increase the engineering properties and reduce the capacity for chemical degradation of concrete mixtures [4]. Most mineral additives used in the concrete industry are by-products from coal combustion (fly ash) or the production of ferro silicon alloys (silica fume) [11, 22]. The benefits that are gained through the use of mineral additives arise from the pozzolanic reactions and from the packing densification provided by the chemistry, geometry, and particle size distribution of the additive [5, 22]. Through the advent of emerging technologies such as nano particles, advanced additives are being pursued that can effectively manipulate the molecular chemistry and structure (and hence engineering properties) of cement composites and concrete [31].

Nano silica is introduced into a concrete mixture through a colloidal dispersion of suspended particles regulated by a specific alkali type and content. Controlling the stability of nano silica dispersions is difficult due to the size of the nano particles [32]. One of the causes of this instability is the sensitivity of nano particles to Brownian motion [33]. As the nano particle decreases in particle diameter, its sensitivity to Brownian motion increases. As the potential for collision from Brownian motion increases (due to excessive particle count in a localized area), so does the probability for agglomeration and aggregation [32]. When nano silica particles come in close proximity to adjacent nano silica particles (via Brownian motion), it is the strength of the electrical potential barrier at the nano silica particle surface that impedes the propensity for agglomeration. A stronger potential barrier reduces the rate for agglomeration [32, 33].

The potential barrier at the surface of the nano silica particle reduces the propensity for aggregation and agglomeration by reducing the van der Waal forces at the surface of the nano silica particles. Nano particles in a dispersion with a particle diameter smaller than 30 nm generate a small potential barrier that cannot prevent aggregation from adjacent nano particles without a surface modification [33]. In order to enhance the dispersion of smaller particles, soluble alkalis can be adsorbed onto the nano silica surface [33]. This is done purposely to manipulate the surface of the nano silica in order to control agglomeration. The soluble alkalis effectively increase the surface potential, or electrical double layer, at the nano silica particle surface.

Figure 7 is a schematic of the change in electrical double layer (measured as surface potential at: the nano silica particle surface (O), through the interface between the nano silica particle surface and soluble alkali (O, X2), and at the soluble alkali surface (X2). Figure 7 illustrates the interface between the nano silica particle and an adsorbed soluble alkali, where ΦSA is the surface potential for the soluble alkali and ΦNS is surface potential for for the nano silica. Region I (Reg I) is the compact layer at the interface of the nano silica and soluble alkali, where the potential barrier transitions to a higher strength. Region II, the Gouy-Chapman layer, has an increase of the potential within the field of soluble alkalis [34]. The increase in potential is connected to the size of the electrical double layer at the nano particle surface [32]. As the soluble alkali content increases at the surface, the potential barrier gains strength and shielding from the forces that would cause the propensity for nano silica to agglomerate and drop out of suspension [33].

Figure 7 — Potential distribution across the nano silica and soluble alkali surface.

References

1. US-DOI. Materials in Use in the U.S. Interstate Highways. USGS Department of the Interior, 2006.

2. Thomas, M., B. Fournier, and K. Folliard. Report on Determining Reactivity of Concrete Aggregates and Selecting Appropriate Measures for Preventing Deleterious Expansion in Concrete Construction. Departmant of Transportation – FHWA, 2009. p. 1–22.

3. Kuennen, T. FHWA Research Zeroes in on Concrete Nanotechnology. Concrete Products, 2010. www.concreteproducts.com/mag/concrete_fhwa_research_zero.

4. Mindess, S., J. Young, and D. Darwin. Concrete. Prentice Hall, 2003. 2: p. 57–120.

5. Taylor, H.F.W. Cement Chemistry. Thomas Telford Books, 1997. 2: p. 89–226.

6. Belkowitz, J., and D. Armentrout. An Analysis on Nano Silica in Cement Hydration. National Ready-Mixed Concrete Association Conference Proceedings on Concrete Sustainability, 2010: p. 1–15.

7. Richardson, I. The Calcium Silicate Hydrates. Cement and Concrete Research, 2007. 38: p. 137–158.

8. Allen, A., J. Thomas, and H. Hennings. Composition and Density of Nanoscale Calcium-Silicate-Hydrate in Cement. Nature Materials, 2007. 6: p. 311–316.

9. Bentz, D. and Garboczi, E. Simulation Studies of the Effects of Mineral Admixtures on the Cement Paste-Aggregate Interfacial Zone. ACI Materials Journal, 1991: p. 518–529.

10. Bentz, D. and Stutzman, P. Evolution of Porosity and Caclium Hydroxide in Laboratory Concretes Containing Silica Fume. Cement and Concrete Research, 1994. 24: p. 1044–1050.

11. Holland, T. Silica Fume User’s Manual. Department of Transpotation — FHWA, 2005: p. 8–13.

12. Manzano, H., J. Dolado, A. Guerrero, and A. Ayuela. Mechanical Properties of Crystalline Calcium-Silicate-Hydrates: Comparison with Cementitious C-S-H Gels. Physical State Solutions, 2007. 204: p. 1775–1780.

13. Kurtis, K., P. Montiero, J. Brown, and W. Meyer-Ilse. Imaging of ASR Gel by Soft X-Ray Microscopy. Cement and Concrete Research, 1998. 28: p. 411–421.

14. Ichikawa, T. Alkali-Silica Reaction, Pessimum and Pozzolanic Effect. Cement and Concrete Research, 2009. 39: p. 716–726.

15. Rodrigues, A., P. Montiero, and G. Sposito. The Alkali-Silica Reaction:The Surface Charge Density of Silica and its Effect in Expansion. Cement and Concrete Research, 1999. 29: p. 527–530.

16. Chen, J., J. Thomas, H. Taylor, and H. Jennnings. Solubility and Structure of Calcium-Silicate-Hydrate. Cement and Concrete Research, 2004. 34: p. 1499–1519.

17. Hurcomb, D., K. Bartojay, and K. Fay. New Recommendation for ASR Mitigation in Reclamation Concrete Construction. U.S. Department of Interior MERL Laboratory, 2009.

18. Thomas, M. The Effect of Supplementary Cement Materials on Alkali-Silica Reaction: A Review. Cement and Cocnrete Research, 2011. 41: p. 1224–1231.

19. Thomas, M. Mitigating ASR in Maine Bridges – Reactive Solutions. Departmant of Transportation – FHWA, 2011. 3: p. 1–3.

20. CSA A23.2–27A. Use of Supplementary Materials for Counteracting Alkali-Silica Reaction. CSA, 2000. www.csa.ca.

21. Garcia-Diaz, E., D. Bulteel, Y. Monnin, and P. Fasseu. ASR Pessimum Behavior of Siliceous Limestone Aggregates. Cement and Concrete Research, 2010. 40: p. 546–549.

22. Helmuth, R. Fly Ash in Cement and Concrete. U.S.A.: Portland Cement Association, 1987: p. 85–138.

23. Said, A., M. Zeidan, M. Bassuoni, and Y. Tian. Properties of Concrete Incorporating Nano-Silica. Construction and Building Materials, 2012. 36: p. 838–844.

24. Iler, R. Method of Producing a Colloidal Silica by Electrodialysis of a Silicate. US Patent 3,668,088. 1969.

25. Green, B. Development of a High-Density Cementitious Rock-Matching Grout using Nano-Particles. ACI Materials Journal, 2008. SP2–54: p. 121–132.

26. Belkowitz, J., W. Belkowitz, M. Best, and F. Fisher. Colloidal Silica Admixture. Concrete International, 2014. 36: p. 59–65.

27. Nazari, A., and S. Riahi. The Effects of SiO2 Nanoparticles on Physical and Mechanical Properties of High Strength Compacting Concrete. Composites: Part B, 2011. 42: p. 570–578.

28. Hou, P., K. Wang, J. Qian, S. Kawashima, D Kong, and S. Shah. Effects of Colloidal NanoSiO2 on Fly Ash Hydration. Cement and Concrete Composites, 2012. 34: p. 1095–1103.

29. Bjornstrom, J., and I. Panas. Effects of Colloidal Nano Silica on the Early Cement Hydration of Belite Cement. Chemistry of Materials, 2000. 12: p. 1501–1522.

30. Hou, P., S. Kawashima, K. Wang, D. Corr, J. Qian, and S. Shah. Effects of Colloidal Nanosilica on Rheological and Mechanical Properties of Fly Ash–Cement Mortar. Cement and Concrete Composites, 2013. 35: p. 12–22.

31. Sanchez, F., and K. Sobolev. Nanotechnology in Concrete – A Review. Construction and Building Materials, 2009. 24: p. 3475–3484.

32. Wise, H. and Oudar, J. Material and Concepts in Surface Reactivity and Catalysis. Dover Publications, 1990. p. 239–254.

33. Iijima, M., and H. Kamiya. Surface Modification for Improving the Stability of Nanoparticles in Liquid Media. KONA Powder and Particle Journal, 2009. 7: p. 119–129.

34. Luo, G., S. Malkova, J. Yoon, D., Lin, B. Schultz, and M. Meron. Ion Distributions Near a Liquid-Liquid Interface. Science, 2006. 311: p. 216–218.

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