Evaluation of packing density, pore structure, and mechanical properties of cement-free ultra-high-performance fiber-reinforced concrete with varying silica sand sizes

Jung Jun Park; Taekgeun Oh; Sungsu Park; Shack Yee Hiew; Ilhwan You; Gi Joon Park; Behzad Nematollahi; Doo Yeol Yoo

doi:10.1016/j.cemconcomp.2026.106758

Evaluation of packing density, pore structure, and mechanical properties of cement-free ultra-high-performance fiber-reinforced concrete with varying silica sand sizes

Jung Jun Park
, Taekgeun Oh
, Sungsu Park
, Shack Yee Hiew
, Ilhwan You
, Gi Joon Park
, Behzad Nematollahi
, Doo Yeol Yoo^*

^*Corresponding author for this work

Department of Rural Construction Engineering

Korean Institute of Civil Engineering and Building Technology
Yonsei University
University of Sheffield
University of British Columbia

Research output: Contribution to journal › Journal article › peer-review

Abstract

This study investigates the influence of silica sand fineness on the packing density, pore structure, and mechanical performance of Ca(OH)₂-activated cement-free ultra-high-performance fiber-reinforced concrete (UHPFRC). The individual and combined effects of two silica sand sizes (finer and coarser sands: Sands F and C, respectively) and two steel-fiber aspect ratios on the compressive, flexural, and tensile behaviors of UHPFRC are identified, and the microcrack behavior is quantified via digital-image correlation (DIC). Incorporation of finer silica sand significantly enhanced packing density, achieving an optimum at a Sand F/Sands (F + C) ratio of 0.7, which yielded higher compressive strength and elastic modulus. Variations in the sand gradation exerted a considerable influence on the void ratio, and at a Sand F/Sands (F + C) ratio of 0.7, the pore structure was optimally refined, characterized by the highest fraction of fine pores and suppressed pore coarsening. Likewise, flexural strength and toughness reached their maximum at this ratio, attributable to a denser interfacial microstructure surrounding the embedded fibers. The tensile strength at the optimum sand ratio exceeded that of ordinary Portland cement (OPC)-based UHPFRC, indicating that Ca(OH)₂-activated slag promotes more effective fiber–matrix bonding, despite its comparatively lower compressive properties relative to the OPC-based counterpart. DIC analysis revealed that finer silica sand facilitated more saturated microcrack formation and improved crack-width control, particularly at Sand F/Sands (F + C) ratios of 0.5 and 0.7, meeting the stringent 50-μm durability limit at peak tensile stress. Finally, lifecycle assessments validated that the cement-free UHPFRC provides environmental advantage than OPC-based UHPFRC via cement elimination and the use of ground granulated blast-furnace slag.

Original language	English
Article number	106758
Journal	Cement and Concrete Composites
Volume	173
DOIs	https://doi.org/10.1016/j.cemconcomp.2026.106758
State	Published - 2026.10

UN SDGs

This output contributes to the following UN Sustainable Development Goals (SDGs)

SDG 12 Responsible Consumption and Production

Keywords

Calcium hydroxide
Cement-free ultra-high-performance fiber-reinforced concrete
Global warming potential
Mechanical properties
Silica sand size

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10.1016/j.cemconcomp.2026.106758

Cite this

Park, J. J., Oh, T., Park, S., Hiew, S. Y., You, I., Park, G. J., Nematollahi, B., & Yoo, D. Y. (2026). Evaluation of packing density, pore structure, and mechanical properties of cement-free ultra-high-performance fiber-reinforced concrete with varying silica sand sizes. Cement and Concrete Composites, 173, Article 106758. https://doi.org/10.1016/j.cemconcomp.2026.106758

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title = "Evaluation of packing density, pore structure, and mechanical properties of cement-free ultra-high-performance fiber-reinforced concrete with varying silica sand sizes",

abstract = "This study investigates the influence of silica sand fineness on the packing density, pore structure, and mechanical performance of Ca(OH)2-activated cement-free ultra-high-performance fiber-reinforced concrete (UHPFRC). The individual and combined effects of two silica sand sizes (finer and coarser sands: Sands F and C, respectively) and two steel-fiber aspect ratios on the compressive, flexural, and tensile behaviors of UHPFRC are identified, and the microcrack behavior is quantified via digital-image correlation (DIC). Incorporation of finer silica sand significantly enhanced packing density, achieving an optimum at a Sand F/Sands (F + C) ratio of 0.7, which yielded higher compressive strength and elastic modulus. Variations in the sand gradation exerted a considerable influence on the void ratio, and at a Sand F/Sands (F + C) ratio of 0.7, the pore structure was optimally refined, characterized by the highest fraction of fine pores and suppressed pore coarsening. Likewise, flexural strength and toughness reached their maximum at this ratio, attributable to a denser interfacial microstructure surrounding the embedded fibers. The tensile strength at the optimum sand ratio exceeded that of ordinary Portland cement (OPC)-based UHPFRC, indicating that Ca(OH)2-activated slag promotes more effective fiber–matrix bonding, despite its comparatively lower compressive properties relative to the OPC-based counterpart. DIC analysis revealed that finer silica sand facilitated more saturated microcrack formation and improved crack-width control, particularly at Sand F/Sands (F + C) ratios of 0.5 and 0.7, meeting the stringent 50-μm durability limit at peak tensile stress. Finally, lifecycle assessments validated that the cement-free UHPFRC provides environmental advantage than OPC-based UHPFRC via cement elimination and the use of ground granulated blast-furnace slag.",

keywords = "Calcium hydroxide, Cement-free ultra-high-performance fiber-reinforced concrete, Global warming potential, Mechanical properties, Silica sand size",

author = "Park, \{Jung Jun\} and Taekgeun Oh and Sungsu Park and Hiew, \{Shack Yee\} and Ilhwan You and Park, \{Gi Joon\} and Behzad Nematollahi and Yoo, \{Doo Yeol\}",

note = "Publisher Copyright: {\textcopyright} 2026 Elsevier Ltd. All rights are reserved, including those for text and data mining, AI training, and similar technologies.",

year = "2026",

month = oct,

doi = "10.1016/j.cemconcomp.2026.106758",

language = "English",

volume = "173",

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TY - JOUR

T1 - Evaluation of packing density, pore structure, and mechanical properties of cement-free ultra-high-performance fiber-reinforced concrete with varying silica sand sizes

AU - Park, Jung Jun

AU - Oh, Taekgeun

AU - Park, Sungsu

AU - Hiew, Shack Yee

AU - You, Ilhwan

AU - Park, Gi Joon

AU - Nematollahi, Behzad

AU - Yoo, Doo Yeol

PY - 2026/10

Y1 - 2026/10

N2 - This study investigates the influence of silica sand fineness on the packing density, pore structure, and mechanical performance of Ca(OH)2-activated cement-free ultra-high-performance fiber-reinforced concrete (UHPFRC). The individual and combined effects of two silica sand sizes (finer and coarser sands: Sands F and C, respectively) and two steel-fiber aspect ratios on the compressive, flexural, and tensile behaviors of UHPFRC are identified, and the microcrack behavior is quantified via digital-image correlation (DIC). Incorporation of finer silica sand significantly enhanced packing density, achieving an optimum at a Sand F/Sands (F + C) ratio of 0.7, which yielded higher compressive strength and elastic modulus. Variations in the sand gradation exerted a considerable influence on the void ratio, and at a Sand F/Sands (F + C) ratio of 0.7, the pore structure was optimally refined, characterized by the highest fraction of fine pores and suppressed pore coarsening. Likewise, flexural strength and toughness reached their maximum at this ratio, attributable to a denser interfacial microstructure surrounding the embedded fibers. The tensile strength at the optimum sand ratio exceeded that of ordinary Portland cement (OPC)-based UHPFRC, indicating that Ca(OH)2-activated slag promotes more effective fiber–matrix bonding, despite its comparatively lower compressive properties relative to the OPC-based counterpart. DIC analysis revealed that finer silica sand facilitated more saturated microcrack formation and improved crack-width control, particularly at Sand F/Sands (F + C) ratios of 0.5 and 0.7, meeting the stringent 50-μm durability limit at peak tensile stress. Finally, lifecycle assessments validated that the cement-free UHPFRC provides environmental advantage than OPC-based UHPFRC via cement elimination and the use of ground granulated blast-furnace slag.

AB - This study investigates the influence of silica sand fineness on the packing density, pore structure, and mechanical performance of Ca(OH)2-activated cement-free ultra-high-performance fiber-reinforced concrete (UHPFRC). The individual and combined effects of two silica sand sizes (finer and coarser sands: Sands F and C, respectively) and two steel-fiber aspect ratios on the compressive, flexural, and tensile behaviors of UHPFRC are identified, and the microcrack behavior is quantified via digital-image correlation (DIC). Incorporation of finer silica sand significantly enhanced packing density, achieving an optimum at a Sand F/Sands (F + C) ratio of 0.7, which yielded higher compressive strength and elastic modulus. Variations in the sand gradation exerted a considerable influence on the void ratio, and at a Sand F/Sands (F + C) ratio of 0.7, the pore structure was optimally refined, characterized by the highest fraction of fine pores and suppressed pore coarsening. Likewise, flexural strength and toughness reached their maximum at this ratio, attributable to a denser interfacial microstructure surrounding the embedded fibers. The tensile strength at the optimum sand ratio exceeded that of ordinary Portland cement (OPC)-based UHPFRC, indicating that Ca(OH)2-activated slag promotes more effective fiber–matrix bonding, despite its comparatively lower compressive properties relative to the OPC-based counterpart. DIC analysis revealed that finer silica sand facilitated more saturated microcrack formation and improved crack-width control, particularly at Sand F/Sands (F + C) ratios of 0.5 and 0.7, meeting the stringent 50-μm durability limit at peak tensile stress. Finally, lifecycle assessments validated that the cement-free UHPFRC provides environmental advantage than OPC-based UHPFRC via cement elimination and the use of ground granulated blast-furnace slag.

KW - Calcium hydroxide

KW - Cement-free ultra-high-performance fiber-reinforced concrete

KW - Global warming potential

KW - Mechanical properties

KW - Silica sand size

UR - https://www.scopus.com/pages/publications/105044593965

U2 - 10.1016/j.cemconcomp.2026.106758

DO - 10.1016/j.cemconcomp.2026.106758

M3 - Journal article

AN - SCOPUS:105044593965

SN - 0958-9465

VL - 173

JO - Cement and Concrete Composites

JF - Cement and Concrete Composites

M1 - 106758

ER -

Evaluation of packing density, pore structure, and mechanical properties of cement-free ultra-high-performance fiber-reinforced concrete with varying silica sand sizes

Abstract

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Keywords

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