Long-term Mechanical Properties Research Articles

Long-term mechanical properties of sludge-cured lightweight soil under the superimposed effects of drying-wetting and freezing-thawing

ABSTRACT Sludge-cured lightweight soils have unique advantages in roadbed treatment due to their properties such as low density and high strength. Its long-term mechanical law based on the superposition of drying-wetting and freezing-thawing (D-W-F-T) is studied through creep experiment. The test results show that: with the increase of the number of D-W-F-T, the deformation of the soil gradually increases, and the deformation tends to be stable when it reaches a certain number of times; the stress-strain isochronous curves are obviously nonlinear in general; The long-term strength increases with the increase of density and confining pressure, and decreases with the increase of the number of D-W-F-T; by comparing the isochronous stress-strain curve cluster method and the steady state creep rate vs. The comparative analysis suggests that the steady state creep rate versus stress level curve method be used to determine the long term strength.

Evaluation of long-term properties and life cycle assessment of alkali-activated concrete with varying fiber inclusions

The potential for using alkali-activated concrete (AAC) as a sustainable substitute for Portland cement (PC) concrete is a topic of ongoing research interest. The uncertainties in the raw material composition, the reportedly low tensile strength of AAC, and the lack of relevant standard codes of practice further inhibit wider industrial usage of AACs. Fiber inclusions reportedly enhance the tensile properties of traditional PC concrete. However, there is no long-term data available for fiber-reinforced alkali-activated concrete (FRAAC) mixtures. Hence, the present study is aimed at investigating the long-term mechanical properties of ambient-cured FRAAC with GGBS as the sole precursor. Four different types of fibers, viz., steel (SF), polyvinyl alcohol (PVAF), polypropylene (PPF) and glass (GF) are used in this research as reinforcements in AAC. Tests for compressive strength (fc′), splitting tensile strength (fsp) and flexural strength (fr) are conducted for FRAAC containing varying fiber contents of 0.1–0.3%. The findings demonstrated that fiber additions do not have any noticeable influence on the compressive strength of AAC. However, relative to the plain mix, the fsp and fr of FRAACs were enhanced by up to 32% and 29%, respectively. The formation of the hardened calcium aluminosilicate matrix and evolution of the fiber-matrix bonding over time was evident from the scanning electron microscopy (SEM) images. The related molecular bonds over a period of 7-d to 360-d was identified through mineralogical and chemical analyses. Furthermore, to validate its environmental sustainability, life cycle assessments were conducted. The AACs exhibited at least 43% lesser impacts than PC concrete on the ecosystem. FRAACs had only slightly higher (≤ 7% increase across all fiber types) impacts than plain AAC.

Thermal cycling-induced evolution of structure and local mechanical properties in metallic glass

The influence of thermal treatment on the long-term mechanical properties of two different kinds of metallic glasses was investigated in this study. As model systems, bulk metallic glasses (BMGs) with the composition of Pd43Cu27Ni10P20 cycled 60, 200, and 500 times between 77 K and room temperature and Zr44Ti11Cu10Ni10Be25 cycled 300, 500, and 700 times have been employed. To ensure that meaningful steady-state properties have been reached, experiments have been performed three years after sample preparation. It was found that the thermal cycling of the Pd-based BMGs had induced rejuvenation when compared to the non-cycled sample, including a higher relaxation enthalpy, lower modulus, hardness, activation volume, and shear transformation zone volume. However, for Zr-BMGs, a rejuvenation to relaxation behavior is observed. Also, while Zr-BMGs showed significantly changes in yielding behavior upon thermal cycling, fluctuations in Pd-BMGs were negligible. We speculate that the observed substantial differences between these two samples might originate because Pd-BMG has a denser structure and higher fragility, making it more difficult to induce excess free volumes.

Impact of the sintering parameters on the grain size, crystal phases, translucency, biaxial flexural strength, and fracture load of zirconia materials

ObjectivesTo investigate the influence of the zirconia and sintering parameters on the optical and mechanical properties. MethodsThree zirconia materials (3/4Y-TZP, 4Y-TZP, 3Y-TZP) were high-speed (HSS), speed (SS) or conventionally (CS) sintered. Disc-shaped specimens nested in 4 vertical layers of the blank were examined for grain size (GS), crystal phases (c/t’/t/m-phase), translucency (T), and biaxial flexural strength. Fracture load (FL) of three-unit fixed dental prostheses was determined initially and after thermomechanical aging. Fracture types were classified, and data statistically analyzed. Results4Y-TZP showed a higher amount of c+t’-phase and lower amount of t-phase, and higher optical and lower mechanical properties than 3Y-TZP. In all materials, T declined from Layer 1 to 4. 3/4Y-TZP showed the highest FL, followed by 3Y-TZP, while 4Y-TZP showed the lowest. In 4Y-TZP, the sintering parameters exercised a direct impact on GS and T, while mechanical properties were largely unaffected. The sintering parameters showed a varying influence on 3Y-TZP. Thermomechanical aging resulted in comparable or higher FL. Conclusion3/4Y-TZP presenting the highest FL underscores the principle of using strength-gradient multi-layer blanks to profit from high optical properties in the incisal area, while ensuring high mechanical properties in the lower areas subject to tensile forces. With all groups exceeding maximum bite forces, the examined three-unit FDPs showed promising long-term mechanical properties.

Non-local Maxwell model for ultraslow relaxation of concrete under different normal stress levels

Stress relaxation is widely present in concrete structures and has a significant impact on the long-term mechanical properties of materials and structural safety. The previous stress relaxation models for concrete follow exponential or power-law law, which cannot accurately describe the ultraslow relaxation phenomenon with a logarithmic law. Thus, this paper proposes a non-local Maxwell model, i.e. Hadamard fractional derivative Maxwell (HFM) model with a normalized logarithmic kernel, and derives the constitution and relaxation modulus. A set of relaxation experimental data of cement concrete under different normal stresses is used to test the HFM model. Compared with the power-law fractional Maxwell model, the HFM model shows reasonable accuracy and can effectively capture the ultraslow relaxation in concrete. The fitting results indicate that the larger derivative order in the HFM model represents faster relaxation. Interestingly, the results also show that the normal stress in the concrete specimen is positively correlated with the derivative order in the HFM model.

Durability of concrete-encapsulated GFRP bars subjected to seawater immersion

Glass fiber reinforce polymer (GFRP) bars have better durability than traditional steel bars, but there are few studies on their long-term performance in actual service environments especially the marine environment. To investigate the durability of GFRP bars used in cross-sea bridges, this research delves into the performance of 200 such bars, spanning diameters of 10, 12, 16, and 25mm, in an environment that closely mimics real-world conditions. The GFRP bars, encapsulated in concrete, were submerged in seawater solutions, maintained at either room temperature or 60°C, for periods spanning from 0 to 183 days. Then the tensile strength and elastic modulus degradation of GFRP bars were investigated by tensile tests. Scanning electron microscope (SEM) was also used to analyze the micro-degradation mechanism of GFRP bars. In addition, this paper compares the four existing models for predicting long-term mechanical properties of GFRP bars with the experimental data, so as to determine the formulas and methods to be used in the design. The result shows that the elastic modulus of GFRP bars after 183 days of immersion in concrete pore solution was almost unchanged while the tensile strength decreased significantly. Among them, the elastic modulus and tensile strength of 10mm diameter GFRP bars decreased by 5% and 35%, respectively, after 183 days of immersion at high temperatures (60°C). The SEM method revealed that the main cause of such phenomena was the weakening of the bond between the fibers and the matrix, which led to a decrease in the interface properties. Finally, by fitting and comparing the relationship between the test data and the existing prediction models for the long-term mechanical properties of GFRP bars, the residual tensile strength of GFRP bars used in the actual project of Yanzhou Bridge for 100 years was predicted according to the optimal prediction model, i.e. the Bank model, and the results showed that the residual strength of GFRP bars is able to meet the current standard requirements.

Insight into the stabilization/solidification of Cd, Pb and Zn in MSWI FA by three stages: Vulcanization, precipitation and bio-oxidation

Bio-oxidation has been perceived as a promising treatment for the solidification/stabilization (S/S) of heavy metals (HMs) in mining soils. Nonetheless, no research exists on the integration of the iron-sulfur oxidizing bacterium Acidithiobacillus ferrooxidans as a microbial agent into the treatment of municipal solid waste incineration-fly ash (MSWI-FA). The effect of vulcanization (Stage I), precipitation (Stage II) and bio-oxidation (Stage III) on the stabilization of HMs in MSWI-FA was unexplored. This study investigated the stabilization effects of Stage I and Stage II by utilizing Na2S and FeSO4 to adjust the Fe/S ratio. The findings contributed to identifying suitable methods to enhance the stabilization effect of the microbial agent on MSWI-FA (Stage III). The results indicated that the vulcanization (Stage I) increased the compressive strength of MSWI-FA to 1.87 MPa when the concentration of Na2S reached 0.03 mM. The leaching toxicity of Cd, Pb, and Zn at 28 days after Stage II was 0.12 mg/L, 0.99 mg/L, and 356 mg/L, respectively, which improved by 96.3%, 94.8%, and 26.9% compared to the untreated samples. The compressive strength of the samples peaked at 1.97 MPa when the Fe/S ratio was 0.25 (precipitation (Stage II)). Despite the inhibitory effect of MSWI-FA on microbial activity, the leaching toxicity of Cd, Pb, and Zn in the presence of Acidithiobacillus ferrooxidans decreased to 0.07 mg/L, 0.17 mg/L and 97.3 mg/L at 28 days after Stage III, with no significant further increase in compressive strength. This study suggested that bio-oxidation utilizing iron sources may change the formation of iron oxides, thereby impacting the mechanical and chemical properties of MSWI-FA-based materials. The treatment sequence of vulcanization, precipitation and bio-oxidation proved effective in immobilizing HMs, particularly Pb, Cd, and Zn in MSWI FA. This research highlighted the potential of employing this technique to treat MSWI FA, yet it is essential to identify suitable reaction systems with appropriate additives to further enhance the long-term effectiveness and mechanical properties of MSWI-FA-based materials.

Sustainable activation of sisal fiber-reinforced slag composites: Mechanical strength and microstructural insights through recycling of alkali-treated wastewaters

An alkali treatment is necessary for natural plant fibers employed as reinforcing additives in inorganic cementitious materials, aiming to diminish moisture sensitivity and facilitate interlocking between the matrix and additives. Recycling alkali-treated fiber wastewaters (ATFWs) is crucial to prevent significant environmental pollution. Sisal fiber (SF)-reinforced alkali-activated slag-based composites incorporating ATFWs were prepared and compared to the control, aiming to investigate the effects of alkali-treated SFs and recycled ATFWs on the long-term mechanical properties and microstructures. Initially, the influence of the treated duration of SFs was examined on the electrical conductivity (EC) of ATFWs. Subsequently, the effects of SFs and ATFWs on the 28-day and 360-day flexural and compressive strengths were investigated, including an observation of failure modes. Furthermore, the effect mechanism of ATFWs in SF-reinforced composites was detected concerning morphology, microstructure, and composition by using diverse analytical techniques such as Scanning Electron Microscopy (SEM), Energy-Dispersive Spectroscopy (EDS), X-ray Diffraction (XRD), Fourier-Transform Infrared Spectroscopy (FTIR), and Thermogravimetric-Differential Scanning Calorimetry (TG-DSC). The results show that the inclusion of ATFWs diminishes electrical conductivity (EC) and density while augmenting the flexural and compressive strengths of the composites. When extending the treatment duration of SFs in a 10% NaOH solution from 1 hour to 3 hours for SF-reinforced composites, the 360-day flexural and compressive strengths for samples without SFs show an enhancement of 1.1 times and 0.9 times, those with 1% SFs exhibit an increase of 0.7 times and 0.5 times, and those with 2% SFs demonstrate an improvement of 0.3 times and 0.4 times, respectively. Furthermore, the incorporation of ATFWs enables the physical embedding and sequestration of organic components released from SFs in a matrix without local aggregation. Therefore, recycling ATFWs as an alkaline activator is deemed feasible to produce SF-reinforced SP-based composites. The research outcomes offer an innovative approach for whole-waste utilization in the realm of natural fiber-reinforced composites.

Influence of Cement Kiln Dust on Long-Term Mechanical Behavior and Microstructure of High-Performance Concrete.

Cement production in the world market is steadily increasing. In 2000, it was 1600 million tons, while as of 2013, the annual amount exceeded 4000 million tons. The burning of cement clinker is associated with the generation of waste. It is estimated that the amount of cement kiln dust (CKD), during combustion, reaches about 15-20%, which means 700 million tons per year. However, not all types of by-products are reusable due to high alkali, sulfate, and chloride contents, which can adversely affect the environment. One environmentally friendly solution may be to use CKD in the production of high-performance concrete (HPC), as a substitute for some of the cement. This paper presents a study of the short- and long-term physical and mechanical properties of HPC with 5%, 10%, 15%, and 20% CKD additives. The experiments determined density, water absorption, porosity, splitting tensile strength, compressive strength, modulus of elasticity, ultrasonic pulse velocity, and evaluated the microstructure of the concrete. The addition of CKD up to 10% caused an increase in the 28- and 730-day compressive strengths, while the values decreased slightly when CKD concentration increased to 20%. Splitting tensile strength decreased proportionally with 5-20% amounts of CKD regardless of HPC age. Porosity, absorbability, and ultrasonic pulse velocity decreased with increasing cement dust, while the bulk density increased for HPC with CKD. Microstructure analyses showed a decrease in the content of calcium silicate hydrate (C-S-H), acceleration of setting, and formation of wider microcracks with an increase in CKD. From the results, it was shown that a 15% percentage addition of CKD can effectively replace cement in the production of HPC and contribute to reducing the amount of by-product from the burning of cement clinker.

Experimental and numerical investigation on the short- and long-term mechanical properties of mylonite before and after grouting reinforcement

Experimental and numerical investigation on the short- and long-term mechanical properties of mylonite before and after grouting reinforcement

Contribution to a better understanding of long-term hydration, structuration and mechanical properties of slag based cementitious materials: Experimental and modeling approaches

Blast Furnace Slag (BFS), a by-product of the steelmaking process, can be used as a mineral addition in blended cement. In addition to reduce CO2 emissions in the construction field, the use of BFS in cementitious materials also contributes to the improvement of their mechanical and durability properties. However, despite the numerous studies proposed in the literature about the hydration properties of BFS-blended cement, some aspects remain unclear, such as the influence of slag substitution rate on hydration kinetics and on the stoichiometry of hydrates formed and their impacts on both microstructural and mechanical properties. For these reasons, the present study aims firstly to better understand how BFS-blended cement hydrates based on a complete hydration model that considers both kinetics and chemical reactions. The only required input data are the formulation parameters (i.e. water-to-binder ratio (W/B), substitution rate of clinker by slag (fs)), and curing. This study does not introduce the heat of hydration, which limits the validity of other existing models to short-term hydration. Analytical laws involving calibration parameters, which are assumed to vary with the substitution rate of clinker by slag, represent the hydration kinetics of clinker and slag while a stoichiometric approach is adopted to describe the chemical formation of hydrates. In order to calibrate and validate the parameters involved in the hydration model, four different cement paste mixes formulated with 0%, 30%, 50%, and 80% (by mass) of slag are studied in terms of hydration degrees and microstructure evolutions, and completed with data from the literature. The amounts of hydrated phases and those of dry densities, particularly at later ages, are well reproduced by the hydration model. Porous structure evolutions are also investigated in terms of partition between capillary and CSH gel pores by comparing the capillary porosity predicted by the model with the total porosity measured experimentally. Finally, predictive modeling of mechanical properties (compressive strength and Young modulus) of tested materials are finally proposed based on hydration model outputs. A good agreement between experimental and predicted data is observed.

Effectiveness of Carbide Lime Waste as CO<sub>2 </sub>Capturing Materials of Mortar at Early CO<sub>2 </sub>Curing Age

This study explored the use of Carbide Lime Waste (CLW) in mortar production and its exposure to controlled CO2 curing for 24 hours. The results indicate that CLW mortar under CO2 curing has improved compressive strength and early CO2 capturing performance due to the reaction between Ca (OH)2 in CLW and CO2 gas. With a cement replacement rate of 20, a 60% solid carbonates precipitation was recorded after just 7 days of curing. In general, the longer the curing durations, the higher the CO2 capturing capability. Further investigations into the long-term mechanical and durability properties are recommended to assess its feasibility for practical applications. Re-utilization of waste materials like CLW can make significant strides towards more eco-friendly and sustainable practices.

Experimental study of macroscopic and microscopic properties of long-age hydraulic concrete based on high-temperature accelerated curing

Determining the long-term mechanical properties of hydraulic concrete currently requires time-consuming and expensive tests, which has hampered investigations into the mechanical properties of long-age hydraulic concrete. In this study, the indoor macroscopic mechanical property tests of long-age hydraulic concrete with different curing ages (90, 180 days and 1, 2, 3 years) and different fly ash contents (0%, 15%, 35%) were designed and carried out on hydraulic concrete with 0.5 water-to-binder ratio by using a high-temperature accelerated-curing method based on equivalent age theory. Further tests were carried out using SEM, XRD, and MIP tests on long-age hydraulic concrete specimens with different fly ash contents to determine and analyze the long-term evolution of the macroscopic and microscopic properties of hydraulic concrete. The results showed that the fly ash content significantly affects the activation energy Ea of hydraulic concrete and that the curing time required to reach the designed hydration degree increases with increasing fly ash content. The long-age compressive strength and splitting tensile strength of hydraulic concrete with different fly ash contents increased logarithmically with curing age. After hydration for the curing age of 3 years, the overall microscopic structure of the mortar region of the long-age hydraulic concrete becomes dense, and the main XRD peak is due to quartz. The porosity decreases with increasing curing age, and the main pore types transition from multi-harmful pores (>200 nm) to harmless pores (<20 nm) and less harmful pores (20–50 nm). The multiple correlation coefficient of the long-term strength prediction model established by using the combined exponential prediction model ranges from 0.9152 to 0.9765, which indicates that the combined exponential prediction model based on the strength at the curing age of 28 days better replicates the long-term performance of hydraulic concrete.

Observations of Short- and Long-Term Mechanical Properties of Glass Fiber Reinforced Polypropylenes with Post-Consumer Recycled Materials

Observations of Short- and Long-Term Mechanical Properties of Glass Fiber Reinforced Polypropylenes with Post-Consumer Recycled Materials

Experimental Study into the Mechanical Properties of Plastic Concrete: Compressive Strength Development over Time, Tensile Strength and Elastic Modulus

Plastic Concrete is a low-strength (fcm,28d≤ 1.0 MPa), low-stiffness, impervious concrete used for cut-off wall construction in earthen dams. To date, there has been no systematic study on the effect of mix design on the long-term time development of the mechanical properties (compressive strength, tensile strength, and elastic modulus) of Plastic Concrete. Therefore currently no Plastic Concrete specific constitutive law for cut-off wall design exists. The present study closes this gap. Ten Plastic Concrete mixes with two bentonite-cement ratios and three types of sodium bentonite were produced. Fresh concrete workability tests were performed for all mixes. Compressive strength tests were performed at ages 28 d, 56 d, 91 d and four years. Splitting tensile strength and elastic modulus tests were performed at 28 days. The workability results show a good linear correlation between slump and flow table tests. Plastic Concrete’s compressive strength development over time is notably slower than that of ordinary concrete, and a new time development model following fib MC 2020 is established using a fitted sC coefficient. The splitting tensile strength shows an overall good, linear correlation with compressive strength, with an approximate ratio of 0.135. Furthermore, the elastic modulus EC,S according to EN 12390-13 concrete tests show significantly higher elastic modulus than the available data, and a model approximation for the elastic modulus EC,S as a function of compressive strength is also provided. Overall, this study provides the first Plastic Concrete specific mechanical property models, confirming the critical role mix design plays on Plastic Concrete’s short and long-term mechanical properties. Thus, the developed models enable a more realistic Plastic Concrete cut-off wall design and provide an important basis for future research.

A novel time-dependent damage constitutive model for hard rock materials

The mechanical behavior of deep hard rocks plays a crucial role in the long-term safety and stability of engineering structures. This work focuses on studying the instantaneous and time-dependent fracture propagation of hard rock materials from a theoretical perspective. A new unified constitutive model, based on a modified Mohr–Coulomb (M-C) criterion, is proposed to accurately represent the short and long-term mechanical properties of hard rocks. To capture the strain hardening and strain softening behaviors, damage is utilized as an internal mechanism-driven variable, controlling the expansion and contraction of the plastic yield surface. Additionally, a combination of time-dependent damage law and viscoplastic theory is employed to account for nonlinear creep deformation characteristics. By considering the time-dependent effects, the model can be applied to both instantaneous loading and creep conditions. The general algorithm format is derived in detail, and an explicit integration algorithm is utilized to update the time-dependent damage evolution. Finally, the proposed model is validated by comparing its predictions with the short and long-term mechanical responses of Beishan granite and Rumei dacite. This comprehensive constitutive model improves our understanding of continuum damage mechanics and provides a scientific basis for analyzing and evaluating the long-term safety and stability of deep hard rock engineering projects.

Long-term Mechanical Properties and Microstructure of Concrete Utilizing Self-Cementing Fly Ash as A Sole Binder Material

Self-cementing fly ash, containing calcium oxide (CaO) of about 20%, has successfully become a sole binder material in concrete through hydration. A very low water-to-fly ash ratio, e.g., below 0.20, is the main key to achieving the high compressive strength of concrete. This study explores the strength evolution, long-term compressive strength, and mechanical properties of concrete that utilize self-cementing fly ash as a sole binder material. Remarkably, the long-term compressive strength continues to develop over a year, reaching nearly 50 MPa at 365 days, a 34% increase from the 28-day strength. While the other mechanical properties are slightly lower than predictions from empirical formulas for Portland cement concrete, promising results are observed. Scanning Electron Microscope (SEM) images highlight surface-restricted hydration products in self-cementing fly ash, rather than full dissolution of fly ash particles.

Predicting the Temperature-Dependent Long-Term Creep Mechanical Response of Silica Sand-Textured Geomembrane Interfaces Based on Physical Tests and Machine Learning Techniques.

Preciously assessing the creep mechanical response of sand-geomembrane interfaces is vital for the design of relevant engineering applications, which is inevitable to be influenced by temperature and stress statuses. In this paper, based on the self-developed temperature-controlled large interface shear apparatus, a series of long-term creep shear tests on textured geomembrane-silica sand interfaces in different temperatures, normal pressure, and creep shear pressure were conducted, and a database compiled from the physical creep shear test results is constructed. By adopting the database, three disparate machine learning algorithms of the Back Propagation Artificial Neural Network (BPANN), the Support Vector Machine (SVM) and the Extreme Learning Machine (ELM) were adopted to assess the long-term creep mechanical properties of sand-geomembrane interfaces while also considering the influence of temperature. Then, the forecasting results of the different algorithms was compared and analyzed. Furthermore, by using the optimal machine learning model, sensitivity analysis was carried out. The research indicated that the BPANN model has the best forecasting performance according to the statistics criteria of the Root-Mean-Square Error, the Correlation Coefficient, Wilmot's Index of Agreement, and the Mean Absolute Percentage Error among the developed models. Temperature is the most important influence factor on the creep interface mechanical properties, followed with time. The research findings can support the operating safety of the related engineering facilities installed with the geomembrane.

Effect of low-calcium fly ash inclusion on long-term mechanical properties and durability of ground granulated blast furnace slag-based cement-free mortars

The present study focused on fabricating cement-free mortar based on ground granulated blast furnace slag incorporating low-calcium fly ash as precursors in an alkaline solution of sodium hydroxide and sodium silicate. The main purposes of the study were not only to find the optimum mixture proportions to confirm the fly ash role in contributing to the long-term mechanical properties and durability but also to expand the use of fly ash in cement-free binders based on ground granulated blast furnace slag. The ground granulated blast furnace slag was replaced with fly ash in the cement-free mortar at various levels of 30, 40, 50, 60, and 70% by mass. The cement-based sample as a control sample was prepared for comparison purposes. Results showed that the cement-free mortar samples with fly ash had the more superior long-term mechanical properties (i.e. flexural and compressive strengths and volumetric compaction via ultrasonic pulse velocity test) and durability (i.e. total charge passed via rapid chloride penetration test and sulfate resistance via length change of samples exposed to sulfate solution), lower water absorption and porosity, and denser microstructure than the control sample up to 120 days. The 40% replacement of ground granulated blast furnace slag by fly ash as an auxiliary source of alumina and silica was the optimum ratio in enhancing the long-term mechanical properties and durability of the cement-free mortar samples, which is in agreement with reducing the porosity and water absorption. The results of the environmental analysis indicate that using cement-free mortar samples has much lower environmental impacts. The cement-free mortar sample using 60% ground granulated blast furnace slag and 40% fly ash is found as an optimal mixture in terms of technical and environmental features.

Mechanical Properties of Fiber-Reinforced High-Volume Fly-Ash-Based Cement Composite—A Long-Term Study

This article presents the long-term mechanical properties of a novel cement composite, no-aggregate concrete (NAC), containing 80% of low-calcium (class F) fly ash (F-FA) and 20% ordinary Portland cement (OPC) without aggregates. The study investigates the effect of adding polypropylene fibers (PPFs) in varying volume fractions to NAC by conducting compressive, splitting tensile, flexural, bond strength, and sorptivity tests, emphasizing the morphological features over a curing duration of up to three years. The results indicate that adding PPF has an insignificant effect on compressive strength. However, flexural, splitting tensile, and bond strength improve with an increasing volume fraction of PPF. The addition of PPF achieves a ductile failure which is desirable. The initial and final water absorption rate (sorptivity) reduces with the addition of PPF. Further, scanning electron microscopy (SEM) images reveal dense precipitation of C-S-H, while energy-dispersive X-ray spectroscopy (EDS) quantifies the hydration products. The ultrasonic pulse velocity (UPV) affirms the composite’s excellent quality.