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<p>Designing cementitious composites that both withstand mechanical loads and provide effective γ-ray shielding requires understanding how high-density mineral fillers alter hydration, pore structure, and radiation attenuation—knowledge that is currently fragmented for ilmenite and barite additions. This study therefore systematically evaluates Type I OPC pastes containing 5–15 wt% ilmenite or barite (with sodium lignosulfonate at 0–0.3 wt% as a water-reducing admixture). Cubic specimens were water-cured to 28 days and characterized by compressive strength and bulk density measurements, X-ray diffraction (XRD), FTIR, thermogravimetry (TG), and scanning electron microscopy (SEM) for phase and microstructure, positron annihilation lifetime spectroscopy (PALS) (interpreted via the Tao–Eldrup model) for nanoscale pore sizing, and γ-ray attenuation tests (mass and linear attenuation coefficients, and half-value layers) across relevant energies. Increasing filler content raised chemically bound water but reduced bulk density and compressive strength; ilmenite-bearing composites consistently retained higher density and strength than equivalent barite mixes. XRD/FTIR/TG/SEM show ilmenite (poorly crystalline) supplies Fe²⁺/Fe³⁺/Ti⁴⁺ that substitute into ettringite/monosulfate and suppress their formation, whereas crystalline barite (Ba²⁺) promotes hydration phase development. Lignosulfonate altered water demand and setting times (accelerating up to 0.2% then retarding) and influenced ettringite and C–S–H morphology. SEM indicated 10% barite densifies the matrix and reduces microporosity (but higher barite reverses this), while ilmenite improves packing at 20% yet coarsens pores at 30%. PALS revealed distinct nanoscale signatures: control OPC τ₃ ≈ 2.9 ns (<i>R</i> ≈ 0.2–0.3&#xa0;nm), I₃ ≈ 0.95; barite at 15% τ₃ ≈ 2.1–2.5 ns (<i>R</i> ≈ 0.35&#xa0;nm) with I₃ ≈ 1.35 (many small accessible pores); ilmenite at 15% produced larger nanopores (<i>R</i> ≈ 0.57&#xa0;nm) and reduced I₃ ≈ 0.80 (fewer accessible sites). γ-attenuation tests show neat OPC is relatively better against low-energy photons; both fillers increase porosity and generally lower mass attenuation coefficients, but ilmenite exhibits a modest improvement in attenuation with increasing loading. Barite and ilmenite impart clearly different microstructural and functional trade-offs: barite can be used to engineer a dense network of small pores (beneficial for certain durability profiles), while ilmenite produces coarser voids that preserve mechanical performance and can selectively enhance γ-ray attenuation. These findings provide a basis for tailoring radiation-attenuating cementitious composites to balance shielding efficacy, porosity, and mechanical durability.</p>

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Effect of ilmenite and barite addition on gamma rays attenuation of cement pastes: study of the pore structure by positron annihilation technique

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年12月12日

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  • Mai M. Al-Khattab,
  • M. A. Abdelzaher,
  • T. M. El-Desouky,
  • M. Abdel Geleel,
  • F. M. Ragab,
  • Mostafa I. Qassim,
  • Hamdy F. M. Mohamed,
  • M. A. Tantawy

摘要

Designing cementitious composites that both withstand mechanical loads and provide effective γ-ray shielding requires understanding how high-density mineral fillers alter hydration, pore structure, and radiation attenuation—knowledge that is currently fragmented for ilmenite and barite additions. This study therefore systematically evaluates Type I OPC pastes containing 5–15 wt% ilmenite or barite (with sodium lignosulfonate at 0–0.3 wt% as a water-reducing admixture). Cubic specimens were water-cured to 28 days and characterized by compressive strength and bulk density measurements, X-ray diffraction (XRD), FTIR, thermogravimetry (TG), and scanning electron microscopy (SEM) for phase and microstructure, positron annihilation lifetime spectroscopy (PALS) (interpreted via the Tao–Eldrup model) for nanoscale pore sizing, and γ-ray attenuation tests (mass and linear attenuation coefficients, and half-value layers) across relevant energies. Increasing filler content raised chemically bound water but reduced bulk density and compressive strength; ilmenite-bearing composites consistently retained higher density and strength than equivalent barite mixes. XRD/FTIR/TG/SEM show ilmenite (poorly crystalline) supplies Fe²⁺/Fe³⁺/Ti⁴⁺ that substitute into ettringite/monosulfate and suppress their formation, whereas crystalline barite (Ba²⁺) promotes hydration phase development. Lignosulfonate altered water demand and setting times (accelerating up to 0.2% then retarding) and influenced ettringite and C–S–H morphology. SEM indicated 10% barite densifies the matrix and reduces microporosity (but higher barite reverses this), while ilmenite improves packing at 20% yet coarsens pores at 30%. PALS revealed distinct nanoscale signatures: control OPC τ₃ ≈ 2.9 ns (R ≈ 0.2–0.3 nm), I₃ ≈ 0.95; barite at 15% τ₃ ≈ 2.1–2.5 ns (R ≈ 0.35 nm) with I₃ ≈ 1.35 (many small accessible pores); ilmenite at 15% produced larger nanopores (R ≈ 0.57 nm) and reduced I₃ ≈ 0.80 (fewer accessible sites). γ-attenuation tests show neat OPC is relatively better against low-energy photons; both fillers increase porosity and generally lower mass attenuation coefficients, but ilmenite exhibits a modest improvement in attenuation with increasing loading. Barite and ilmenite impart clearly different microstructural and functional trade-offs: barite can be used to engineer a dense network of small pores (beneficial for certain durability profiles), while ilmenite produces coarser voids that preserve mechanical performance and can selectively enhance γ-ray attenuation. These findings provide a basis for tailoring radiation-attenuating cementitious composites to balance shielding efficacy, porosity, and mechanical durability.