Microstructure Of Concrete Research Articles

Investigating the impact of carbonation curing concentrations on the mechanical properties and microstructure of recycled concrete

This investigation examines the impact of different CO2 curing concentrations on the mechanical and microstructural properties of recycled concrete aggregates, aiming to optimize the carbonation process for enhanced practicality. Utilizing 25 recycled concrete samples, the study varied CO2 concentrations (20 %, 40 %, 50 %, 60 %, and 95 %) and pre-conservation durations (24–120 h), conducting tests for carbon sequestration, compressive strength, and splitting tensile strength to determine the effects on recycled concrete's performance. Key findings reveal a direct correlation between increased CO2 curing concentrations and carbon sequestration levels, with an observed pattern of initial increase followed by a plateau or decrease in sequestration with extended pre-conditioning. Interestingly, while compressive strength generally improved with higher CO2 concentrations, splitting tensile strength showed a decrease, suggesting different impacts of CO2 concentration on various mechanical properties. A notable observation was that at 60 % CO2 concentration, compressive strength was slightly lower (by 2.46 %) compared to the 95 % concentration, yet the splitting tensile strength was 2.84 % higher at 60 %, indicating that a 60 % CO2 curing concentration might offer an optimal balance between economic efficiency and material performance enhancement. This balance suggests significant improvements in resource utilization compared to traditional pure CO2 curing methods. In conclusion, this study provides substantial evidence supporting the optimization of CO2 curing for recycled concrete, advocating for a 60 % concentration as the most effective strategy to enhance both the environmental sustainability and the mechanical performance of recycled aggregates. These insights significantly contribute to advancing low-carbon and sustainable practices within the construction industry.

Impact of temperature and relative humidity variations on coda waves in concrete

The microstructure of concrete can be affected by many factors, from non-destructive environmental factors through to destructive damage induced by transient stresses. Coda wave interferometry is a technique that is sensitive enough to detect weak changes within concrete by evaluating the ultrasonic signal perturbation compared to a reference state. As concrete microstructure is sensitive to many factors, it is important to separate their contributions to the observables. In this study, we characterize the relationships between the concrete elastic and inelastic properties, and temperature and relative humidity. We confirm previous theoretical studies that found a linear relationship between temperature changes and velocity variation of the ultrasonic waves for a given concrete mix, and provide scaling factors per Kelvin for multiple settings. We also confirm an anti-correlation with relative humidity using long-term conditioning. Furthermore, we explore beyond the existing studies to establish the relationship linking humidity and temperature changes to ultrasonic wave attenuation.

Recycled Aggregate Integration for Enhanced Performance of Polymer Concrete.

The objective of the research outlined in this paper is to propose an eco-friendly solution that simultaneously contributes to improving the characteristics of polymer composites. The analyzed solution entails the use of recycled aggregate from crushed concrete rubble. The authors conducted experiments to test the consistency, density, flexural strength, compressive strength, and microstructure of polymer concrete (PC) with different proportions of recycled aggregate (RA). It was found that PC with RA had a higher compressive strength, 96 MPa, than PC with natural aggregate, 89.1 MPa, owing to the formation of a double-layer shell of resin and calcium filler on the surface of porous RA grains. Using a resin with a lower viscosity could improve the performance of PC with RA by filling the cracks and penetrating deeper into the pores. RA is a valuable material for PC production, especially when it contains porous grains with poor mechanical properties, which are otherwise unsuitable for other applications. This article also highlights the environmental and economic benefits of using RA in PC, as it can reduce waste generation and natural resource consumption.

Flexural behaviour of reinforced one-part geopolymer concrete beams

The recent development of “one-part geopolymer” has significantly improved construction safety and convenience, establishing it as a highly promising new type of low-carbon binder with performance comparable to traditional cement. This study investigated the flexural performance of reinforced concrete (RC) beams made from one-part geopolymer concrete (OPGC), in comparison to conventional ordinary Portland cement (OPC) concrete beams. The microstructure of OPGC and conventional concrete were firstly compared. Four-point bending tests were then conducted on nine beams, including three OPC concrete beams and six OPGC beams. The influence of longitudinal reinforcement ratio on the flexural performance of OPGC beams was examined, and the bending performance of OPGC beams and OPC concrete beams was compared. Experimental results revealed that OPGC beams exhibited similar flexural performance to those cast with OPC concrete in terms of cracking development, failure modes, load-deflection curves, and strain distribution. In addition, an analytical model for estimating the flexural capacity of OPGC beams was proposed and validated against experimental results. Finally, the environmental and economic indices between the OPGC and OPC concrete beams were compared and analysed. This research provides valuable insights for the design and analysis of OPGC structural members.

Investigating effects of comprehensive optimization of cementitious materials on early residual expansion deformation and long-term performance and microstructure of steam-cured concrete

Investigating effects of comprehensive optimization of cementitious materials on early residual expansion deformation and long-term performance and microstructure of steam-cured concrete

Enhancing Concrete with Ultrafine Fly Ash: Mechanical Strength and Frost Resistance

Fly ash, a byproduct collected from the flue gas of coal combustion, serves as an effective additive in concrete. It offers environmental benefits by converting waste into a valuable resource, thus promoting energy conservation, emission reduction, and waste utilization. Additionally, fly ash enhances the mechanical properties and frost durability of concrete. Commonly used as a partial substitute for cement, it helps conserve resources. However, its use may compromise early strength and durability, which limits its applications. The transformation of raw fly ash into ultrafine fly ash through mechanical grinding increases its fineness and specific surface area, thereby boosting its reactivity and micro-aggregate effects. This process produces denser C-S-H gel and optimizes the concrete microstructure. Research shows that although ultrafine fly ash may slightly reduce early concrete strength, it significantly enhances long-term strength, with a 10% substitution improving early compressive strength by 20.2% and later strength by 13.7%. However, excessive fly ash content can reduce frost resistance, with an optimal substitution level at 25% significantly enhancing this property compared to standard concrete. Blending ultrafine fly ash with other mineral admixtures further boosts mechanical properties and frost durability. Challenges include increased processing costs and early strength deficiencies, along with the necessity to control heavy metal content for environmental and health safety. Future research should aim to optimize fly ash particle distribution and reactivity, develop cost-effective production methods, and blend fly ash with other minerals to improve concrete’s mechanical and frost resistance properties, thus expanding its potential applications.

Effect of Clogging and Cleaning on the Air Void Microstructure of Porous Asphalt Concrete

Effect of Clogging and Cleaning on the Air Void Microstructure of Porous Asphalt Concrete

Research Progress in the Application of Calcium-based Expansive Agents as Compensation for Autogenous Shrinkage in High-strength Concrete

In this study, comprehensive investigation of the shrinkage compensation mechanisms of calcium-based expansive agents (CEAs), their effects on the properties of (ultra) high-strength concrete (HSC/UHSC), and the existing problems in applying this methodology was conducted. Analyses showed that the rational use of CEAs under certain conditions could greatly or completely inhibit the development of autogenous shrinkage of HSC/UHSC, and significantly reduce the risk of associated cracking. However, it was found that the hydration of the CEAs affected the hydration process of other binders, thereby altering the microstructure of concrete. This was in turn observed to lead to a degree of decrease in compressive strength, flexure strength and elastic modulus, and the decrease rate increasing as with the rise in proportion of CEAs. Moreover, when attempting to improve the shrinkage compensation effects, increasing the amount of CEA presented a risk of delayed expansion cracking of HSC/UHSC. Neither the expansion mechanism, expansion conditions, nor the inhibition methods have yet been fully clarified in the current stage. Lastly, newly proposed Ca-Mg composite EAs were outlined, and the research prospects of Ca-Mg composite EAs in HSC/UHSC were explored.

Effects of cold-bonded artificial aggregate properties on the behaviour of concrete

The study investigates the use of artificial aggregates (AAs), specifically manufactured from ground granulated blast furnace slag (GGBFS) and ordinary Portland cement (OPC), to mitigate environmental harm caused by illegal quarrying due to the scarcity of natural aggregates (NAs). A cold-bonded pelletization technique was employed to produce five types of AAs with varying proportions of GGBFS & OPC as 82.5:17.5, 85:15, 87.5:12.5, 90:10, 95:5. The AAs with maximum OPC content exhibited a density of 1298 kg m−3, water absorption of 4.8%, and crushing and impact values of 28.6% and 26.3%, respectively. The impact of these AAs on concrete properties was assessed, revealing that AAs facilitated the production of workable concrete with low-density ranges between 1700–2337 kg m−3. Despite a decrease in concrete strength with higher AAs content, structural requirements were met, demonstrating AAs’ potential to effectively substitute natural coarse aggregates (NCAs). The concrete microstructure confirmed the formation of a strong interfacial transition zone (ITZ) and strength-developing cement-hydrated products. This research underscores the scientific contribution of AAs to address aggregate scarcity sustainably and recommends its application in structural elements by experimental validation.

Study of the microstructure of asphalt concrete using X-ray computed tomography

A mechanical digital twin (a mechanical finite-element model) of an asphalt concrete sample has been developed in the framework of a project for recycling polymer composite materials with fibrous reinforcement (fiberglass) as an alternative for crushed stone in the asphalt concrete production. A methodology of using X-ray computed tomography (XCT) for analysis of the asphalt concrete microstructure and calculation of the mechanical properties is developed. The data processing chain for developing a digital twin of the asphalt concrete microstructure, based on X-ray micro-computed tomography (XCT) image includes the following steps: 1) image enhancement; 2) image segmentation; 3) analysis of the morphology of pores and solid particles; 4) transformation of the segmented image into a voxels-based finite element (FE) model. It is demonstrated that the XCT resolution of 40 μm is sufficient for a reliable identification of microstructural parameters, i.e., volume fractions of the components, distributions of voids (pores) in size, shape and spatial position, as well as distributions of the crushed brittle additives (fiberglass chips) in size. The FE model constitutes a digital twin of the material, and, after specifying the characteristics of the material components, can be used for simulation of the thermomechanical and functional properties of the material. The developed procedure is exemplified in the calculation of statistics of the compression and shear moduli of the asphalt concrete with addition of crushed fiberglass particles. The dependence of the calculated elastic properties on the size of the digital twin is studied. It is shown that a model size of 10 mm and more is sufficient for the microstructural representativity and calculation of the homogenization characteristics. The results can be used for analysis of the microstructure and structure-dependent thermomechanical properties of asphalt concrete. The developed finite element model can be used for modelling of the visco-elastic response of asphalt concrete and its behavior under cyclic loading.

Microstructure and durability properties of high strength self-compacting concrete using micro silica and nano silica

Microstructure and durability properties of high strength self-compacting concrete using micro silica and nano silica

Influence of polycarboxylate superplasticizer and polyacrylamide on mirror effect of fair-faced concrete

This work successfully prepared fair-faced concrete with mirror effect. The gray value standard deviation, porosity, crack rate and glossiness of the concrete surface were used to characterize the apparent quality of fair-faced concrete. The effect of polycarboxylate superplasticizer and polyacrylamide viscosity-modifying admixture on mirror effect of fair-faced concrete was investigated. The changes of hydration products and microstructure of fair-faced concrete were monitored by the measurements of X-ray diffraction (XRD), thermogravimetric analysis (TG), scanning electron microscopy (SEM) and mercury intrusion porosity (MIP), and the potential mechanism was analyzed. The results indicate that the polyacrylamide reduces the number and size of Ca(OH)2 and change the morphology of Ca(OH)2 crystals from large-size parallel stacking state to small-size edge corrosion structure. The polyacrylamide can refine the pore size of concrete, the most probable pore size at the optimum dosage is 13.73 nm, which is much lower than that at other dosages. The usage of the polycarboxylate superplasticizer will introduce air, which has adverse effect on the concrete surface. But polycarboxylate superplasticizer can also improve the flowability of concrete and make bubbles easy to discharge. The combined action of polycarboxylate superplasticizer and polyacrylamide contributes the fair-faced concrete for better mirror effect.

Microstructure and radiation shielding characteristics of PVA fiber-reinforced ultra-high performance concrete

The application of nuclear technologies simulates the development of radiation shielding materials. Traditional heavy-weight concrete used for radiation shielding is limited in practical construction due to the poor mechanical properties and durability. This study developed a PVA fiber-reinforced ultra-high performance concrete (UHPFRC) with magnetite as heavy aggregates used for radiation shielding. Due to the scientific skeleton design, UHPFRC exhibits superior mechanical properties, with compressive strength and flexural strength reaching up to 121.9 MPa and 23.2 MPa, respectively. The microstructure of UHPFRC was investigated in detail and the results revealed that the incorporation of PVA fibers refined the pore structure of UHPFRC. The interfacial transition zone between magnetite aggregates and cementitious matrix in UHPFRC was much denser than that in traditional concrete due to the low water to binder ratio. The gamma and neutron radiations shielding capacity of UHPFRC were evaluated by the combination of actual measurement and simulation. By introducing light nuclei and refining the pore structure, the incorporation of PVA fibers improved the neutron radiation shielding capabilities of UHPFRC by 5.1%.

The effect of freeze-thaw cycles and sulfuric acid attack separately on the compressive strength and microstructure of 3D-printed air-entrained concrete

3D-printed concrete (3DPC) is a promising technique for constructing structures and intricate designs. To ensure the successful performance of these structures throughout their service life, it is essential to understand their long-term properties and durability. While the use of air-entraining additives can enhance the durability of concrete against freeze-thaw cycles, investigating their impact on other properties is crucial. This study examines the effect of freeze-thaw cycles and sulfuric acid attack on the durability of 3D-printed concrete containing air-entraining additives. The results indicate that, in addition to improving resistance to freeze-thaw cycles, air-entraining additives also increases resistance to sulfuric acid attack. The drop in compressive strength of the samples containing air-entrained additive (0.08–0.12 % AEA) is 1.4–5.3 % less than the control samples against the freezing and thawing cycles. Examining the mechanisms of action of these invasive agents also shows this. Creating intentional voids to reduce the internal pressure of water expansion during freezing and reducing the number and width of possible microcracks are the dominant mechanisms of air-entraining additives against freeze-thaw cycles. Besides, their performance mechanisms during acid attacks are somewhat similar. Analysis of elements created in the matrix of the samples after acid attack indicates a decrease in calcium concentration and an increase in silica concentration. Among the observed reactions, the second reaction prevails, leading to the breakdown of the C-S-H structure into gypsum and silica hydroxide. This phenomenon is associated with changes in acid concentration. However, the presence of air bubbles causes surplus plate-like Calcium hydroxide crystals resulting from the elevated cement content in printed mixes to form within these bubbles, making them susceptible to damage and fracture during freeze-thaw and acid attacks.

Synergistic effect of CO2-mixing and steel slag addition on performance and microstructure of concrete

This study systematically investigated the influence of varying carbon dioxide (CO2) dosages and steel slag (SS) replacement rates on the fresh and hardened properties of concrete through the injection of CO2 gas during the mixing process. The composition of hydration products, degree of hydration, and the evolution of microstructural characteristics within the CO2-SS-cement system were analyzed. The results showed that CO2 addition during the mixing process enhanced early strength in SS concrete. For concrete with a 10 wt% SS replacement rate, the incorporation of CO2 ranging from 0.4 wt% to 1.2 wt% of the total mass of cementitious materials resulted in notable compressive strength increases of 1.26%–12.47%, 0.64%–6.14%, and 11.79%–18.24% at ages of 1 d, 3 d, and 7 d, respectively. CO2 rapidly reacted with SS to form calcite-type CaCO3 and promoted the generation of C-S-H through synergistic hydration with cement. However, a high CO2 dosage (1.2 wt%) led to issues such as microcrack propagation and interface loosening due to CaCO3 deposition, which could be mitigated to some extent by appropriately increasing the SS content.

Comparative analysis of microdamage-affected chloride transport in concrete under static and dynamic hydraulic pressure

Concrete structures in marine environments frequently encounter the adverse impacts of hydraulic pressure, leading to a decrease in their durability. This study aims to conduct a comparative analysis of the internal microdamage in concrete when subjected to static and dynamic hydraulic pressure of equal intensity, and to examine the influence of such damage on chloride transport. By employing potentiometric titration, MIP, N2 adsorption, and AFM tests, the chloride concentration, pore structure parameters, and microscale elastic modulus of concrete under static and dynamic hydraulic pressure were analyzed. The results indicate that dynamic hydraulic pressure accelerates chloride transport in concrete. Compared with static hydraulic pressure, dynamic hydraulic pressure — sustained at the same intensity—results in an elevated threshold pore size along with an increased most probable pore size of the concrete. Furthermore, dynamic hydraulic pressure induces the expansion of microcracks, consequently decreasing the microscale elastic modulus of concrete. The use of mineral admixtures can effectively mitigate the damage evolution of concrete microstructure subjected to dynamic hydraulic pressure. Besides, a model is developed for relative chloride diffusion based on the principle of energy conservation and from the evolution law of the microscale elastic modulus gleaned from AFM tests. Through calculations, it can be found that the crack propagation rate and the decline rate of the relative chloride diffusion coefficient Df1Df2 increase markedly when dynamic hydraulic pressure intensity surpasses 40,000 Pa. The propagation of the crack length is moderated by a larger initial crack width.

Formulation of mixture proportions and experimental study of heavyweight self-compacting concrete based on magnetite and barite

AbstractThe present study aims to determine the mix proportion of binder, heavyweight aggregates, water-to-binder ratio, and additives to develop self-compacting concrete with a bulk density higher than 2600 kg m−3. It also aims to evaluate the engineering properties, pore structure, and microstructure of established heavyweight self-compacting concrete. Barite (BA), magnetite (MAG) or their mix (MIX) were used as fillers, while binder was composed of Portland cement, blast furnace slag, metakaolin, and limestone at a ratio of 65:15:5:15. Based on text results of V-funnel, S-Cone diameter and S-Cone time, the proportion mix and binder: filler: binder to cement ration was optimized as follows: 1) BA 1: 3.5: 0.42, 2) MAG 1: 4: 0.42, and 3) MIX 1: 3.75: 0.42 with maximal aggregate size not exceeding 2 mm. Not only the bulk density was influenced by aggregate, but also, the mechanical properties, shrinkage, dynamic modulus of elasticity pore structure, and microstructure were also found to be dependent on fillers.

Research on the effect of different content of rice husk ash on the microstructure of concrete

Mercury injection porosimetry test is used to study the microstructure of rice husk ash cement paste with different content. The influence of rice husk ash on the microstructure of cement paste is analyzed through porosity, pore size distribution, the most probable pore size, pore size gradation and critical pore size analysis. The results show that with the increase of rice husk ash content, the porosity of cement paste decreases, and the pore size distribution and the most probable pore size decrease, which indicates that the addition of rice husk ash can improve the pore structure of concrete and improve the durability of concrete. With the increase of rice husk ash content, the number of harmful holes of cement paste decreases, the number of harmless holes increases, and the critical pore diameter decreases, which indicates that the addition of rice husk ash can improve the strength and impermeability of concrete.

Effect of Waste Rubber Inclusion on the Microstructure and Mechanical Performance of Low-Density Foam Concrete

Effect of Waste Rubber Inclusion on the Microstructure and Mechanical Performance of Low-Density Foam Concrete

Coupling effect of freezing-thawing cycles and dynamic loading on the accumulative deformation and microstructure of foam concrete

Coupling effect of freezing-thawing cycles and dynamic loading on the accumulative deformation and microstructure of foam concrete