With the rapid development of structural health monitoring, intelligence has become an important trend in cement-based materials. Recycled carbon fibers (RCF) feature favorable electrical conductivity. This study investigates the effects of varying fiber contents on the piezoresistive properties of cement mortar. The relationship between electrical signals and stress under failure and cyclic loading was analyzed. Piezoresistive performance was evaluated in terms of linearity, sensitivity, repeatability, and hysteresis, and the damage-sensing capacity was explored via acoustic emission tests. The results reveal that the incorporation of RCF significantly enhances the piezoresistive properties of cement mortar, exhibiting a favorable linear correlation between the fractional change in resistance and stress. Acoustic emission signals and resistivity variations can effectively characterize the internal damage evolution of mortar. Under cyclic loading, recycled carbon fiber cement mortar (RCFCM) presents good repeatability and stability. With rising loading amplitude, the irreversible damage of the conductive network aggravates, and the hysteresis effect increases.
This study presents a bio-circular approach for valorizing marine mucilage (MM), an emerging marine pollutant, in sustainable one-part geopolymer foam concretes (GFCs). Fly ash (FA) was used as the primary binder, MM replaced silica sand (SS, 0-50%), and polypropylene fibers (PPF, 0-2%) were incorporated. MM-PPF synergy enhanced matrix densification: compressive strength increased from 2.46 to 5.64 MPa (approximate to 129%) and flexural strength from 0.54 to 1.43 MPa (approximate to 165%). Sorptivity decreased from 30.3 to 11.6 kg/m(2) (approximate to 62%), indicating refined pore structure, while thermal conductivity rose moderately (0.31-0.46 W/m center dot K), maintaining lightweight insulation. Durability improved markedly, with >60% strength retention at 800 degrees C, <20% loss after 50 freeze-thaw cycles, and approximate to 10% mass loss under acid attack. Microstructural analysis confirmed improved gel continuity, pore refinement, and crack-bridging mechanisms. MM-PPF-modified GFCs provide an eco-efficient, low-carbon alternative with strong potential for sustainable cement-based construction materials.
This study evaluates synergistic use of prehydrated/carbonated ordinary Portland cement (OPC) and palm oil fuel ash (POFA) in limestone calcined clay cement (LC3), with emphasis on hydration behavior, microstructural evolution, mechanical performance, and embodied carbon. Different dosages of POFA were incorporated into LC3 system. The incorporation of POFA modified early hydration, as isothermal calorimetry revealed reduced initial reactivity and delayed main hydration peaks due to porous POFA structure. POFA exhibited a pronounced filler and nucleation effect, enhancing later-age hydration. TG-DTG analysis confirmed the consumption of portlandite beyond 28 days of hydration, indicating relatively slow POFA's pozzolanic reactivity. This mixture showed increased formation of C(A)SH, AFt, and AFm phases, corresponding to continuous strength development up to 57 days. Higher POFA contents limited gel formation due to portlandite depletion. Environmentally, POFA significantly reduced embodied carbon through clinker substitution and low processing energy. Overall, 10% POFA provided optimal balance between strength and carbon efficiency.
This study examines the influence of wind intensity on mixture behavior, forming quality, mechanical performance, hydration characteristics and interfacial transition zone (ITZ) of roller-compacted concrete (RCC). Meanwhile, the formation mechanism of its spatial variability is revealed through the probabilistic statistical analysis of compressive constitutive parameters. The results show that wind disturbances cause surface RCC to present increased VC values, more surface pitting, inhibited hydration and pozzolanic reactions, and reduced microhardness and compressive strength. Especially, force-9 wind increases 123.7% in porosity and 174.8% in thickness of the ITZ. With enhancing wind force, AFt tends to convert to carbonoaluminates and the reaction degree of C3A and C4AF decreases by up to 10%, exhibiting higher wind sensitivity. Statistically, the spatial variability is transmitted across scales and amplified along the thickness direction under high wind-force level, ultimately increasing the coefficients of variation of elastic modulus and peak strain by 4.8 and 2.7 times, respectively.
To enhance the low hydration activity and cementitious potential of magnesium slag (MS), this study developed an in-situ wet carbonated MS binder activated by sodium carbonate. Mechanical properties, reaction kinetics, phase assemblage, pore structure and microstructure were investigated to clarify mechanism-microstructure-performance relationships. Results reveal a concentration-dependent balance between hydration and carbonation. At moderate sodium carbonate contents, alkalinity promotes gamma-C2S dissolution and C-S-H gel formation, while carbonate induces synchronous calcite precipitation, refining pores and producing a dense composite microstructure of interwoven C-S-H and rhombohedral calcite. This synergy increases compressive strength by about 103% relative to water curing. In contrast, excessive sodium carbonate causes rapid early calcite precipitation, forming surface encrustations that consume Ca2+ and hinder subsequent hydration, leading to discontinuous gel formation and limited strength gain despite pore refinement. Without sodium carbonate, both hydration and carbonation are kinetically limited. Controlled sodium carbonate activation therefore unlocks MS reactivity and transforms this industrial residue into a stronger, denser cementitious binder.
Magnesium silicon potassium phosphate cement (MSPPC, MgO-SiO2-K2HPO4) exhibits high early strength and improved water resistance, but its shrinkage behavior remains a concern. This study investigated the effects of slag incorporation (0 to 30 wt%) on fresh properties, strength, internal relative humidity, shrinkage, and microstructural evolution of MSPPC. Increasing slag content reduced flowability from 170 mm for the control mixture without slag (M-SL0) to 125 mm for the mixture containing 30 wt% slag (M-SL30). The final setting time varied non-monotonically, increasing from 18.50 min for M-SL0 to 24.75 min for the mixture containing 10 wt% slag (M-SL10) and then decreasing to 19.75 and 18.00 min for the mixtures containing 20 wt% slag (M-SL20) and M-SL30, respectively. M-SL30 showed the lowest shrinkage strain within the investigated range and reached 96.8 MPa at 56 d. Microstructural analyses suggest that slag may regulate hydration and contribute to later-age densification.
The discovery of the feasibility of using activated clays to produce reactive aluminosilicates has significantly expanded the raw material base for supplementary cementitious materials, opening up new prospects and options for low-carbon cements. Furthermore, the potential of kaolin clays for producing pozzolans has been thoroughly studied and practically realized. However, the more widely available and accessible non-kaolin clays of the 2:1 structural type require further comprehensive studies of their suitability in relation to the variety of influencing factors. In this study, the reactivity of five montmorillonite clays calcined at 830 degrees C and milled to Dv,50 of 11.5-13.8 & micro;m was explored through chemical, mechanical, and thermal methods. Based on the consistency of results obtained through these techniques insights into the relationship between the reactivity of low-, medium, and high-grade montmorillonite clays and their chemical/mineralogical composition are presented. These findings advance the understanding of the categorization of montmorillonite clays as supplementary cementitious materials.
