Nanoengineered Concrete for Improved Durability and Performance

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Summary

“Nanoengineering” can improve the properties of concrete and compensate for the challenges of using recycled aggregates. Renolith admixture contains nanoscale materials and provides a simple, effective and well-proven mechanism for creating nanoengineered concrete. Renolith significantly improves the tensile strength of concrete and imparts additional useful properties such as improved durability, negligible shrinkage, reduced porosity, reduced microcrack formation and reduced crack migration. These enhancements provide the designer with much more flexibility than conventional concrete allows.

Particle size and specific surface area related to concrete materials

Particle size and specific surface area related to concrete materials; adapted from Sobolev et al 2012

Nanoengineered Concrete with Renolith

Renolith 2.0 is a nanopolymer admixture manufactured in Europe under an ISO-9001 compliant Quality Management System. Chemically, it is a colloidal suspension comprising a latex emulsion and stable colloidal dispersion of nanosilica and nanocellulose. It is compatible with ordinary Portland cement and with binder blends containing recycled supplementary cementitious materials (SCMs) such as fly ash and ground granulated blast furnace slag (GGBFS). It is most commonly used for soil stabilisation in flexible pavement applications but is equally suitable for improving concrete performance – including concretes containing up to 100% recycled aggregate. Excerpts from the following test reports indicate the potential.

Note: “NanoTerraSoil” (NTS), “Nanoterra concrete” and “Renolith” are the same chemical formula with different brand names depending upon the country/market. “Renolith 2.0” is a double concentrate of Renolith/NTS (ie. Same active ingredients, reduced water content).

Trial report Nr. 875-07-010 – Use of concrete admixture: Nanoterra concrete (aka Renolith) (Nano Technologie Enhanced Concrete), 2006:

Concrete specimens were created containing varying amounts of “nanoterra concrete” (aka Renolith) admixture between 0% and 1.5% w/w cement. The following tests were conducted:

  • Compression resistance
  • X-ray diffractometry (XRD)
  • Thermal analysis (TG – DTA – DTG)
  • Mercury Intrusion porosimetry (MIP)
  • Micro-ground image analysis
SEM image of nano filling effect

SEM image of nano filling effect


Summary of results

All experiments reveal the positive effects of [the admixture] within the overall performance on concrete. This admixture might be applied for natural granulation as well as for recycled ones.

Essential results are summarised as follows:

    • Enhancement of concrete compression – strength after 28 days up to 20% compared with placebo
    • Early enhancement of said strength thus reducing time to retract about 20%
    • Allotment of cement thereby to be reduced helping to reduce costs significantly
    • Via effect of interacting plus the superior compaction cause no more optoelectronically detectable pores in construction-material, resulting in a less hygroscopisity as well as higher and improved durability
    • Superior compaction allows for less micro cracks, and limits migration of cracks
    • Enhanced durability via compact matrix protect against destructive agents
    • No effects by shrinking were detectable
    • The rather smooth surface allows notably for manufacture of fair-faced concrete
    • Highly reduced efflorescence of lime
    • High effective autocompression

Summing up, I certify the new admixture…to be highly potent to bring about a more compact matrix, superior and faster strengthening/compaction, improved final compression-strength thus providing for an extended durability of end-product.

Determination of the strength of concrete slabs with NTS (aka Renolith) admixture – Test report No. 875-11-006, 2011

The strength of unreinforced and reinforced concrete slabs was determined at the University of Natural Resources and Applied Life Sciences Vienna, Institute of Structural Engineering. The aim was to test the strength-enhancing effect of the polymer additive NTS® (NanoterraSoil) [aka Renolith]).

A total of five different mixtures were examined. 24 concrete slab test specimens were manufactured to approx. 500x500x80 mm. Standard concrete was used for all specimens.

Specimens were tested in a short span 3-point bending configuration as shown in the finite element model pictures below. The red areas represent compressive stresses and green areas represent tensile stresses. The model predicted that with increasing load on the force introduction plate, a compression arch forms in the lower area, which is kept in balance by a tension strut. If the concrete is no longer able to absorb these tensile stresses due to its relatively low tensile strength, cracking occurs and the stresses are rearranged until complete failure occurs.

Finite Element Model

Finite Element Model of the stress curve and crack patterns with increasing load

The load was applied at a strain rate of 0.08 mm per second until failure. The force-displacement diagram was recorded and maximum force (in kN) and displacement or distance at break (in mm) were noted. A visual comparison of Series 0 (control) and Series 1 (admixture at 8% w/w cement) specimens is shown below.

Concrete slab strength test – series 0

Concrete slab strength test – series 0 (control)

Concrete slab strength test – series 1

Concrete slab strength test – series 1 (8% NTS)

Results are summarised below. Of particular note, the addition of 8% admixture yielded a massive increase in strength of unreinforced concrete (62.61MPa to 112.78MPa = 80% increase); attributable to the improved tensile properties.

Determination of the strength of concrete slabs with NTS (aka Renolith) polymer additive

Determination of the strength of concrete slabs

Nanoengineered concrete - general

Many papers have explored the potential applications of nanomaterials in concrete. Several examples are cited below.

Sobolev et al 2012 reviewed the beneficial effects of the nanotechnology for the improvement of concrete performance:

Concrete can be nano-engineered by incorporating nano-sized building blocks or objects (e.g., nanoparticles and nanotubes) to control material behavior and add novel properties, or by grafting molecules onto cement particles, cement phases, aggregates, and additives (including nano-sized additives) to provide surface functionality, which can be adjusted to promote specific interfacial interactions. The nanoparticle is the elementary building block in nanotechnology and is comprised of up to thousands of atoms combined into a cluster of 1-100 nm. A reduction in size provides an exceptional surface area-to-volume ratio and changes in the surface energy, surface chemistry, and surface morphology of the particle, altering its basic properties and reactivity. Nanoparticles have been shown to significantly enhance the mechanical performance of a variety of materials, including metals, polymers, ceramic, and concrete composites. Nanosilica (silicon dioxide nanoparticles, nano-SiO 2), for example, has been shown to improve workability and strength in high-performance and self-compacting concrete.

Hosseini et al 2009 investigated the use of nano-SiO2 to improve microstructure and compressive strength of Recycled Concrete Aggregate (RCA). The strength of specimens produced by coarse recycled aggregates was lower than those for control mixes. The main factor of strength reduction of concrete with recycled aggregates is the existence of old mortar adhered to recycled aggregates, since the strength of mortar is much lower than the strength of natural aggregates. The test results clearly confirmed that adding nanosilica particles to the concrete matrix can significantly increase the overall strength. This observation was directly linked to super-pozzolanic behaviour of nanoparticles.

Said et al 2012 investigated the effect of colloidal nanosilica on concrete incorporating single (ordinary cement) and binary (ordinary cement + Class F fly ash) binders:

Significant improvement was observed in mixtures incorporating nano-silica in terms of reactivity, strength development, refinement of pore structure and densification of interfacial transition zone. This improvement can be mainly attributed to the large surface area of nano-silica particles, which has pozzolanic and filler effects on the cementitious matrix. Micro-structural and thermal analyses indicated that the contribution of pozzolanic and filler effects to the pore structure refinement depended on the dosage of nano-silica.

Mukharjee et al 2014 conducted an experimental investigation into the effect of colloidal nanosilica on the behaviour of concrete containing 100% recycled coarse aggregate. Compressive strength, tensile strength and Non-Destructive parameters were enhanced. Moreover, the study revealed that the characteristics of recycled aggregate concrete with the addition of a small amount of nano-silica resembles that of natural aggregate concrete.

Conclusion

“Nanoengineered” concrete can outperform conventional concrete and high-strength/high-performance concrete. However, not all nano silica particles are made the same way or have the same effect in concrete.  Renolith contains nano silica that has been proven to be effective in combination with portland cement. Renolith admixture provides a simple, effective and well-proven mechanism for creating nano-engineered concrete. Renolith significantly improves the tensile strength of concrete and imparts additional useful properties such as improved durability, reduced porosity, negligible shrinkage and reduced susceptibility to cracking. These enhancements provide the designer flexibility to achieve a combination of benefits in a wide range of applications:

  • Reduce cement/binder content
  • Reduce thickness/weight
  • Use lower carbon binders
  • Incorporate up to 100% recycled aggregates
  • Reduce or eliminate contraction joints
  • Endure harsh environments
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