Abstract

This study investigated the feasibility of using colloidal nanosilica (nS) as microstructure modifier and polymeric microspheres (MS) as alternative air-entrainment systems for Indiana Department of Transportation (INDOT) bridge deck concrete. These admixtures have gained interest due to their potential to modify the air-void system, enhance freeze–thaw (F/T) resistance, reduce permeability, and improve early-age performance. However, their field applicability depends on understanding their sensitivity to mixture composition, type of batching process, consolidation practices, and water-to-cement (w/c) ratio. The objectives of this research were to: (1) conduct field trials incorporating nS and MS and evaluate both fresh and hardened properties, (2) compare air-void characteristics and F/T performance between field and a companion laboratory mixtures, (3) evaluate the influence of mixing method, compaction effort, and type of batching process on mechanical and durability properties, and (4) quantify the effect of w/c ratio on nS mixtures, including the extent of calcium hydroxide (CH) reduction in paste systems.

Results showed that MS significantly altered the air-void system. Slurry-based MS provided enhanced strength, and reduced secondary rate of water absorption, although F/T performance was highly dependent on MS dispersion and consolidation quality. In laboratory mixtures nanosilica increased water-reducing admixture demand and reduced hardened air content, relative to fresh measurements (no water reducing admixtures were used in field concretes). At the same time, it also produced finer air-void systems (with lower spacing factors), resulting in improved F/T resistance even at reduced total air contents. MS mixtures achieved mechanical properties comparable to or exceeding reference mixtures, while mixes with no nanosilica (nS) showed limited strength benefits. Durability testing indicated reduced secondary absorption and limited chloride ingress (but mostly at greater depths from the surface) for MS mixtures, whereas mixtures containing both ns and MS underperformed with respect to F/T resistance. Paste testing confirmed that using nS resulted only in minor reduction of the CH levels, across all ages and w/c ratios. The observed reductions were substantially lower than those observed in case of using Class C fly ash.

Keywords

nanosilica, microspheres, air-entrainment, freeze-thaw resistance, field trials, bridge deck concrete

Report Number

FHWA/IN/JTRP-2026/13

SPR Number

4718

Performing Organization

Joint Transportation Research Program

Publisher Place

West Lafayette, Indiana

Date of Version

2026

DOI

10.5703/1288284318621

Additional Files
SPR-4718 Technical Summary.pdf (1942 kB)
SPR-4718 Technical Summary
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