1. Enhanced Stabilization of Expansive Soils using Nanosilica Agustin Bernier-Vega Faculty Advisor: Dr. Jong-won Choi   Texas A&M University, 4322 Honduras Drive, Corpus Christi, TX, , USA.
Abstract
The purpose of this project is to explore the effectiveness of Nanosilica to enhance the strength of cement for the purpose of reinforcing expansive soils. Nanosilica has been seen to have a significant effect on the strength of cement, and therefore its application to soil reinforcement is worthy of investigation. The research here is accomplished through the comparative testing of soil samples through compressive force testing and material characterization on a microscopic scale. The tests reveal that Nanosilica provides a significant increase in the compressive strength of the cement mixtures, and as such is a viable option for reinforcing expansive soils.
Introduction
Expansive soils shift and expand based on factors such as moisture, affecting the structural integrity of buildings, roads, and other structures. Conventional solutions include introducing a concrete mixture to reinforce the soil. Studies have indicated that nanomaterials may serve as effective reinforcing agents.
The focus of this research is on the inclusion of the nanomaterial known as nanosilica, which is a finer form of silica, also known as Silicon Dioxide (SiO2). It is known to enhance the compressive strength of concrete significantly. However, very little testing has been done with regard to expansive soils. It is also currently more expensive to manufacture than Silica Fume, a more common silica additive.
2. Methods
The experimentation process involved preparing soil samples for compression testing, in order to determine the sample’s UCS (Unconfined Compressive Strength). Samples were compacted into a mold using a modified ‘proctor test’ tool, then extracted. Initial samples were made of plain soil and water, while later samples used soil and cement mixtures. Nanosilica was added to some samples, while others used Silica Fume. The following figure demonstrates a soil sample before and after compression:
3. Data & Results
In compression testing, samples with nanosilica exhibited much higher UCS compared to conventional mixtures. While Silica Fume saw a dramatic increase (+69%) compared to the soil/cement mixture, the nanosilica was observed to perform
even better, offering a recorded (+89%) increase.
4. External Testing
Aside from compression testing, duplicate samples were exported to external facilities for Micro-characterization tests, such as Nanoindentation and SEM.
Nanoindentation tests the mechanical properties of materials by probing them with an AFM tip (made of a hard diamond) to investigate hardness. [3]
SEM (Scanning Electron Microscopy) provides information relating to microscopic topographical features, compositional differences and more. [4]
5. Conclusion
The results here showed that nanosilica provided almost double the compressive strength of the soil/cement mixture. It also outperforms Silica Fume by a considerable margin. By far the biggest drawback to Nanosilica is its cost. However as new, more cost-effective methods of production arise, nanosilica may prove to be an increasingly viable option for the purpose of soil reinforcement.
6. Acknowledgements
This study was funded by the National Science Foundation (NSF, EEC ). Any opinions, findings or recommendations expressed in this poster were created by authors and not reviewed by nor necessarily reflect the views of NSF. Special thanks to directors Dr. Hua Li & Dr. Kai Jin.
References
[1] Image Source:
[2] Image Source: lid=CM_9qcHCmNQCFQQNaQodsigMww
[3] - Poon, B; Rittel, D; Ravichandran, G (2008). "An analysis of nanoindentation in linearly elastic solids". International Journal of Solids and Structures. 45 (24): doi: /j.ijsolstr
[4] - Leonard, D. N., Chandler, G. W. and Seraphin, S Scanning Electron Microscopy. Characterization of Materials. 1–16.
Unconfined Compressive Strength (UCS)
Sample type
Psi (lb/in2)
% increase (soil)
% increase (cement)
Plain Soil
29.89 0% -
Soil & Cement
136.26
356%
w/ Silica Fume
230.00
669%
69%
w/ Nanosilica
258.85
766%
89%
Fig. 4 Strength Comparison
Fig. 1 Cracked House [1]
Fig. 5 SPM: 50 µM
Fig. 6 SEM Image
Fig. 2 Nanosilica [2]
before
after
Fig. 3 Compression Example
Proceedings of the 2018 ASEE Gulf-Southwest Section Annual Conference The University of Texas at Austin
April 4-6, 2018