Mortar Pore Research Articles

The Pore Structure Characteristics of Mortar and Its Application in the Study of Chloride Ion Transport Performance

The cement-based materials widely used in infrastructure construction, such as bridges and ports, are subjected to seawater erosion and medium erosion during their service life, and their durability has always been a concern. The diffusion coefficient of chloride ions is an important indicator in the research of cement-based materials’ durability, and the pore structure is one of the most fundamental reasons affecting the diffusion behavior of chloride ions. In this paper, Mercury intrusion porosimetry (MIP), Nuclear magnetic resonance (NMR), and Nitrogen adsorption method (NAD) were used to analyze the pore structures of mortars with different volume fractions of sands. The relationship between mortar pore structure and chloride ion diffusion coefficient was established to predict its chloride ion diffusion coefficient. It may provide a new idea for studying the durability of cement-based materials. Results indicated that similar to cement paste, the pore structure of mortar satisfied the fractal characteristics of solid phase within a certain range of pores. The most probable gel pore diameter of mortars with different sand volume fractions was about 4 nm, while the most probable capillary pore diameter was approximately 46 nm, and the critical pore diameter was ranging from 50 to 60 nm. MIP results indicated that with the increase in sand volume fraction (ϕagg), the total porosity (fmip) of the mortar decreased, satisfying the relationship of fmip = 0.1859 − 0.0789ϕagg. However, the porosity of the matrix (fbase) increased with the increase in sand volume fraction, which was due to the introduction of more interfaces by the addition of aggregates. The effective chloride ion diffusion coefficient (Dcp,base) of the matrix can be obtained by fitting. Based on this, the interface transition zone (ITZ) and the cement matrix were comprehensively considered as a whole fractal phase. The predicted value of the chloride ion diffusion coefficient obtained by the Mori–Tanaka homogenization method was in good agreement with the results obtained from rapid chloride migration (RCM) experiments, and the maximum error between the simulated and experimental values did not exceed 11%. This finding can provide new ideas for accurately predicting the chloride ion diffusion coefficient of mortar and even concrete.

Quantitative Relationship Between Strength and Porosity of Nano-Silica-Modified Mortar Based on Fractal Theory

Nano-silica (NS) is an ideal modifier for mortar materials, and exploring the evolution of the fractal dimension of the pore structure in NS-modified mortar is crucial for elucidating the mechanism by which NS enhances mortar strength. In this study, NS reinforced mortar was prepared using an NS sol solution, which inhibited the aggregation of NS particles. The relationship between the strength and pore structure of NS-modified mortar was quantitatively analyzed based on fractal dimension theory and gray correlation degree. The experimental system evaluated the mortar strength, pore structure distribution, and micro-morphology. Based on this evaluation, the fractal dimension of the mortar pore volume was calculated in detail. Subsequently, models for mortar strength and NS content were further established using grey analysis. The results indicate that NS significantly enhances the strength of mortar while also increasing its porosity due to reduced fluidity. NS can improve the compressive strength of mortar by up to 35%. The curve fitting of volume fractal dimension and box dimension is effective and can accurately reflect the complexity of the pore structure. The calculation of the grey correlation analysis model shows that the impact of varying silica content on the mechanical properties of mortar specimens is not linear; the distribution and quantity of bubbles are the main factors affecting the strength of the specimen.

Experiment and modelling of degradation mechanism of cement mortar with graphene oxide nanosheets under sulfate attack

Degradation of cementitious materials caused by sulfate attack poses a significantly challenge to their durability. Using nano-additives to enhance the mechanical and durability properties of cementitious materials is a promising solution; however, the impact of graphene oxide (GO) on the sulfate resistance is not yet fully understood. While efforts have been made to study the degradation mechanism through accelerated indoor tests with high sulfate concentrations, these methods fail to accurately replicate real-world field exposure conditions. To better understand the degradation mechanism of GO-modified mortars under actual field conditions, this study examines the long-term degradation (over 24 months) of GO-modified mortars exposed to sulfate solutions with varying concentrations: 0 % (reference), 2.1 % (field condition), 5 % (laboratory condition), and 15 % (high-concentration condition). Additionally, a comprehensive chemo-mechanical model that considers multiple factors and time-varying boundary conditions was proposed. The study thoroughly discusses the effects of GO dosage, sulfate concentration, and exposure time on the degradation mechanism. Comparison with experimental data revealed that cement mortar degradation under sulfate attack is primarily driven by the crystallization pressure related to ettringite formation in diluted sulfate solutions, while the precipitation of alkali ions from mortar pore solutions occurs in concentrated sulfate solutions. In real-field conditions, cement mortar degradation primarily involves gypsum precipitation rather than ettringite formation. This study demonstrates that well-dispersed GO nanosheets can significantly enhance durability of cementitious materials against sulfate attack, offering valuable insights for strategic applications of GO nanosheets in cementitious materials.

Electromagnetic absorption properties of composite mortar with graphene and manganese-zinc ferrite

Electromagnetic wave absorption of building structures plays a crucial role in safeguarding information and mitigating electromagnetic radiation. This study delves into the absorption capabilities of composite mortar made with graphene (GR) and manganese-zinc ferrite (MFO) across frequencies of 1–18 GHz. The mechanical strength, microstructural examinations, and numerical simulations to elucidate the underlying mechanisms of wave absorption in the composite mortar are investigated. The results indicate that incorporating 30 % MFO reduces the strength of mortar due to its low bonding capacity and diluting effects, whereas GR enhances the strength of mortar by facilitating cement hydration. Electromagnetic examinations reveal that MFO boosts the magnetic loss performance, while GR augments dielectric loss properties. In addition, the presence of needle, rod, mesh, and flake hydration products in the pores of composite mortar also contributes to increased wave depletion. According to the simulation of electromagnetic absorption based on the finite difference time domain (FDTD) method, the composite mortar with GR and MFO exhibits a superior performance of electromagnetic wave absorption. With the 25 mm thickness of composite mortar with 30 % MFO, an absorption below −10 dB, covering a bandwidth of 1.68–4.34 GHz are obtained, with a peak reflection loss of −22.13 dB at 3.23 GHz. Thus, by combination magnetic loss of MFO, dielectric loss of GR, and the reflective capabilities of porous mortar, a composite mortar with a better electromagnetic wave absorption can be achieved.

Enhancing carbonated mortar durability by electro-osmotic treatment of silane

Electro-osmotic treatment (EOT) of silane for enhancing the durability of carbonated mortar was investigated. During the EOT, silane was injected into carbonated mortar pores by applying an electric field, leading to deeper penetration depths. The durability enhancements of the carbonated mortar after EOT of silane were evaluated by examining water absorption, carbonation depth, sulfate resistance and chloride diffusion. The microscopic mechanism of the electro-injected silane treatment was determined by X-ray diffraction, scanning electron microscopy and Fourier transform infrared spectroscopy. The results indicated that the resistance to water absorption, sulfate diffusion and chloride diffusion were improved by the EOT of silane. The silane treatment had a limited impact on carbonation resistance. An impervious film with a dense structure was formed in the carbonated mortar through the EOT of silane, and this treatment did not introduce new crystal phases to the hydration products within the carbonated mortar.

Evaluation of MSA mortar pore structure characteristics in water-saturated curing environment based on Talbot gradation theory

To investigate the impact of aggregate gradation on the pore structure of manufactured sand aggregate (MSA) mortar and its fractal characteristics under water-saturated curing conditions. The static pore structure characteristics of the pore structure of MSA mortar with 10 aggregate gradations were explored. The analysis is based on the Talbot gradation theory, the NMR technique, and fractal theory. The surface area and roughness of aggregate particles contribute to a reduction in the porosity of MSA mortar. The aggregate gradation is quantified using the Talbot index. The correlation characteristics and intrinsic relationships between Talbot index and different pore structure parameters, such as total porosity, pore gradation, pore fractal dimension and permeability of MSA mortar, are analyzed. Two pore division methods are employed to explore the interrelationships among pore types, fractal dimensions and Talbot index. Additionally, A correlation model between Talbot index and permeability is developed to investigate the intrinsic correlation of parameter variations from a microscopic perspective. It is found that aggregate gradation is optimal with a Talbot index of 0.4, leading to the highest number of micropores and the lowest number of larger pores, thereby enhancing resistance to seepage and dissolution. Furthermore, The contribution of pore size, content and type to permeability varies with different aggregate gradations. Overall, this study serves as a valuable guide for the design and durability evaluation of mortar concrete projects in water-saturated curing environments.

Developing a novel expression for chloride ion concentration threshold in reinforced concrete: Integration of electrochemical analysis and time-dependent modeling

Chloride ion concentration threshold is a crucial parameter for evaluating the durability of reinforced concrete. This study aimed to develop a novel expression method for this threshold by analyzing the open-circuit potential of steel in simulated mortar pore solution across three pH values. Concurrently, the correlation between pitting potential and chloride ion concentration was examined through potentiodynamic polarization testing. Additionally, Mott-Schottky analysis facilitated the investigation of the passivation film structure on the steel under both passivation and depassivation conditions. By integrating the analysis of the open-circuit potential and pitting potential models in the simulated solution, a time-dependent relationship curve between the chloride ion threshold and time was established. The findings reveal that the steel’s passivation film comprises a dual-layer structure, with its corrosion resistance enhancing as the pH value of the simulated mortar pore solution increases. Furthermore, within the simulated mortar pore solution, the chloride ion concentration threshold exhibited a decreasing trend over time, suggesting a minimum threshold value exists. This research provides a significant foundation for forecasting the corrosion state of steel in steel-reinforced engineering projects.

Self-sensing concrete masonry structures with intrinsic abilities of strain monitoring and damage detection

Self-sensing cementitious materials are emerging technologies for Structural Health Monitoring (SHM) of civil structures. Their application for SHM of concrete masonry elements was not investigated in previous studies. The effects of triaxial strain/stress states of masonry joints and units on their self-sensing response are still unknown. Therefore, this work aimed to investigate mechanical and self-sensing properties of masonry elements produced with self-sensing mortar joints, solid concrete bricks and/or hollow concrete blocks fabricated with carbon black nanoparticles. The intrinsic abilities of strain monitoring and damage detection were evaluated in piezoresistive tests of masonry prisms, based on variations in the type of unit, mortar bedding approach, bonding arrangement, relative strength of mortar and units, joint thickness and location of self-sensing regions. These variations did not affect significantly the gauge factor of cementitious sensors embedded into the prism units. In contrast, the gauge factor of self-sensing horizontal or vertical joints was statistically affected by most of these variations. Stages of balance and abrupt increases in fractional changes in electrical resistivity (FCRs) during the plastic regime of the prisms provided an anticipated warming associated with the propagation of vertical and diagonal cracks associated with tensile splitting and crushing failure of units. The strong non-linearity on the electrical output of self-sensing joints provided an evidence of the mortar pore collapse. In conclusion, the self-sensing units and mortar joints were found to be promising alternatives for strain monitoring and damage detection in smart concrete masonry structures.

Ascorbic acid: A green admixture for eco-efficient metakaolin blended cement with enhanced properties and corrosion resistance

This study explores ascorbic acid (AA) as a green, multipurpose admixture to improve the eco-efficiency of metakaolin (MK) blended cement mortar. The AA can be simply added into a mortar mix at a very small dosage to function as a hydration retarder, a water reducer, a strength enhancer, an autogenous shrinkage reducer, and a corrosion inhibitor for reinforcing bars. With four hydroxyl groups, AA can be adsorbed on the surface of cement particles, leading to slower hydration rate of cement and better dispersion of its hydration products. Both the porosity and small capillary pores of mortar are drastically reduced by the addition of AA. This leads to not only significant increase of compressive strength of MK blended cement mortar, but also significant reduction in the autogenous shrinkage. An accelerated corrosion test validated the corrosion resistance of reinforcing bar embedded in mortar by adding AA. This study broadens the range of molecules and polymers for interaction with cement and provides a new pathway for developing next the generation of chemical admixtures for concretes.

Application of electro-injection method in improving cement mortar durability

An electrochemical method for improving the durability of cement mortar by injection of nanoparticles (alumina (Al2O3)-coated silica (SiO2)) is presented. In this method, nanoparticles are injected into cement mortar pores under an external electrical field, refining the pore structure of cement mortar. The efficiency of electro-injection nanoparticle treatment with different applied electric fields was evaluated by monitoring the evolution of cement mortar resistivity. The improvement of cement mortar durability after electro-injection of nanoparticles was assessed by examining the resistance to water absorption, carbonation, sulfate attack and chloride diffusion. The microstructure of cement mortar after the electro-injection treatment was analysed using scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP), X-ray diffraction (XRD) and differential thermo-gravimetric analysis (DTG). The results show that cement mortar durability can be improved by the injection of nanoparticles under external electric field. The efficiency of electro-injection nanoparticle treatment increased with the increase of applied electric field. The resistance to water absorption, carbonation, sulfate attack and chloride diffusion were significantly improved by using the electro-injection method. The improvement in cement mortar durability can be attributed to the filling effect of nanoparticles.

Mechanical properties and abrasion resistance of polyurethane mortar subjected to freeze–thaw cycles and sulfate attack

The objective of this paper is to investigate the properties of polyurethane mortar subjected to freeze–thaw cycles in sulfate environment. Na2SO4 solutions with 5% and 10% sulfate concentrations were prepared. The mass loss, compressive strength, flexural strength and abrasion resistance of the polyurethane mortar were investigated. The interface transition zone and pore structure were then analysed. Results revealed that the damage degree of the mass, compressive strength and flexural strength of polyurethane mortar subjected to freeze–thaw cycles in sulfate solution are greater than that in water, and the high concentrations of sulfate solution can cause severe damage. The polyurethane mortar subjected to freeze–thaw cycles and sulfate attack will appear to have more severe surface damage after abrasion. The abrasion resistance of polyurethane mortar decreases as the freeze–thaw cycles and abrasion time increase. The freeze–thaw cycles and sulfate attack can cause the crack width at the interface transition zone of polyurethane mortar to expand, and the abrasion action accelerates this evolution. With the increase in freeze–thaw cycles, the gel and transition pores are gradually transformed into capillary and large polyurethane mortar pores. The volume fraction of capillary and large pores gradually increases, and the fractal dimension tends to decrease. Furthermore, the fractal dimension of the pore structure is positively correlated with mechanical properties and abrasion resistance. The mechanism analysis shows that abrasion can cause the detachment of loose mortar matrix of polyurethane mortar surface and form a weak area.

Effect of sulfoaluminate expansive additive on mechanical properties, internal relative humidity, and shrinkage of early-age mortar

Incorporating a suitable amount of sulfoaluminate expansive additive (SEA) into cementitious materials can compensate the shrinkage deformation. However, the influence of SEA on the relative humidity inside cementitious materials is still unclear. This study conducted a series of tests to investigate the mechanical properties, internal relative humidity, and shrinkage of early-age cement mortars containing different contents of SEA. Then finite element simulations of the drying of cement mortars with different contents of SEA were conducted to derive the moisture diffusion coefficient. The results reveal that the amount of expansive ettringite generated in cement mortar tends to increase with increasing SEA content, which can decrease the porosity of cement mortar and refine its pore structures. Both the compressive strength and flexural strength of cement mortar decrease with increasing SEA content. The decrease in mortar strengths is more significant during the later age. The mortar shrinkage under both sealed and drying conditions decreases with increasing SEA content. However, the compensation effect of SEA on the shrinkage deformation is less effective under drying condition. The relative humidity inside the cement mortar under sealed condition would decrease by 9.3% at 36 days when 8% SEA was used. While the decrease would be 3.4∼7.2% when the cement mortar was exposed to drying condition with RH of 60%. Moreover, since SEA densifies the microstructures and refines the pores in mortar, the moisture diffusion coefficient of mortar decreases with increasing SEA content.

Evaluation of the water penetration depth in mortar using water indicator and hyperspectral imaging

Water penetration is a potential cause of premature deterioration of reinforced concrete structures. The water indicator used for water detection cannot detect water penetration depths in samples containing high amount of blast furnace slag (BFS). Hence, hyperspectral imaging (HSI) was introduced in this study. Mortar specimens with different water-to-binder (w/b) ratios and BFS replacements were prepared. The moisture content distribution, water indicator, and HSI were used to measure the water penetration depth in the samples after water absorption exposure. The effects of the pore size and moisture content on the mechanisms of the water indicator were also investigated. HSI successfully detected the penetration depth of water in all mortar samples, even in those where detection by using the water indicator was not possible. The moisture content distribution and HSI yielded similar results for water penetration depths. The water penetration depths measured by applying the water indicator and HSI were similar in the mortars without BFS substitution. The water indicator underestimated the water penetration depths in the samples that contained BFS. The amount free water in the pores of mortar was the main factor controlling the applicability of the water indicator.

Effect of defoaming agent on the properties of cement mortars with hydroxyethyl methyl cellulose through adjusting air content gradient

Pore structure plays one of the most important role in the properties of cement-based materials. Hydroxyethyl methyl cellulose (HEMC) has the air entrainment effect, which may significantly change the pore structure and further affect the performance of this materials. Incorporating defoaming agent (DA) may weaken this effect, due to its defoaming effect which needs to be fully evaluated. Therefore, the working efficiency of DA and the changes of pore structure caused by stepwise adjustment of the air content were mainly studied. The results show that incorporating DA can effectively eliminate air bubbles, while the defoaming effect is weak with the air content approaching to 6.0%. There is a certain negative correlation between fresh bulk density and air content, and a positive correlation between fluidity and air content. Incorporating an appropriate dosage of DA is beneficial to control the air content of the cement mortars with HEMC, so as to ensure the cement mortars have better mechanical strengths and low drying shrinkages. With the increase of DA dosage, the large capillary pores, macro pores and total porosity all show a gradual decreasing trend due to the air content decreasing. The content of connected capillary pores in cement mortars tends to increase as the air content level decreases, but shows a small decrease at the low air content of less than 6.0%.

The Effects of Chicken Eggshell Powder as Fine Aggregate Replacement on Mortar Pore Structure

Using alternative resources from industrial by-products to produce aggregates while keeping production costs as low as possible would be environmentally beneficial and profitable. This study aims to examine the effect of the pore on mortar properties with eggshell powder (ESP) as its fine aggregate alternative based on two fundamental properties: microstructural and mechanical strength. The study replaced the sands (by volume) with ESP in the usual mortar mix with 10%, 20%, 30%, 40% and 50% chicken eggshell powder. The mortars underwent a wet curing period of 56 days with five observation days. The standard mortar properties, such as pH, carbonation depth, compressive strength, and sorptivity, were investigated. The findings show that the replacement rate significantly impacts the water-cement ratio, carbonation rate, sorptivity and compression strength. The additional calcareous of ESP is believed to have improved the mechanical component of the connection. There are no significant differences in pH for the control (R0) and modified mortars. The greatest replacement percentage of 20% is advantageous for carbonation rate acceleration, sorptivity and early compressive strength. However, if the specifier focuses on pH and sorptivity improvements, no formulation alteration is required.

Natural Hydraulic Lime Mortars for Hot-Humid Climates: Effects of Oyster Shells as Seeding Compound

This study explored the effects of formulation modifications of natural hydraulic lime (NHL) mortars exposed to hot temperature and high humidity conditions. The modified mortars were seeded by oyster shell powder, partially replacing the sand. The mortar samples underwent a curing period of 56 days with five observation days. The pH, carbonation depth, flexural strength, compressive strength, sorptivity, and morphology were studied. The results indicated that seeded mortars were more successful at setting and hardening high humidity settings. In addition, curing the mortars at higher temperatures hastened the hydration reaction significantly. The data indicate that seeded mortars can improve performance in several areas, notably carbonation rate (25%-45%), flexural strength (16%-60%), compressive strength (20%-55%), and sorptivity (18%-25%). The experimental protocol shows that the hardened mortar pore system is affected by the water-binder ratio, hydration level, relative humidity, and carbon dioxide concentration. The hydration of mortar greatly influences its strength. Using oyster shell powder as an aggregate substitute increased the performance of the mortars by microstructure and capillarity development. This circumstance is significant in our comprehension of modified lime mortars and seeding compounds, especially in hot-humid environments.

Effects of zeolitic imidazolate framework-8 nanoparticles on physicomechanical properties and microstructure of limestone calcined clay cement mortar

The limitations of limestone calcined clay cement (LC3) include its low mechanical strength and high drying shrinkage, in addition to its durability, which has not been addressed well in previous studies. Therefore, the objective of the present study was to investigate the feasibility of enhancing the durability and physical and mechanical properties of LC3 mortar by incorporating zeolitic imidazolate framework-8 (ZIF-8) nanoparticles. Six mixes of LC3 mortar with 0, 0.1, 0.3, 0.5, 0.7, and 0.9 wt% ZIF-8 were prepared and tested. The microstructure of the LC3-ZIF-8 mortar was characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and Raman spectroscopy. The optimal ZIF-8 content was 0.5 wt%, at which the workability was significantly reduced, and the tensile and flexural strengths were increased. Although the LC3-ZIF-8 mortar exhibited a lower compressive strength than the unmodified LC3 mortar, the former had higher flexural and tensile strengths because of the positive effect of ZIF-8 on promoting calcium hydroxide (CH) and monocarboaluminate (Mc). These findings were consistent with the SEM, XRD, and Raman spectroscopy results. The water absorption and drying shrinkage rates of the LC3-ZIF-8 mortar were lower than those of the unmodified LC3 mortar owing to the modification of the LC3 mortar pore structure upon the addition of ZIF-8 nanoparticles. This study provides a better insight into the feasibility of utilizing ZIF-8 nanoparticles as reinforcement for LC3-based materials.

Evaluation of the efflorescence resistance of calcium sulfoaluminate cement mortar: from indoor accelerated testing to outdoor exposure

Efflorescence is an inevitable phenomenon in all cementitious materials, particularly for Portland cement (PC) - based materials. Considering the relations between ion availability and crystallization, the factors influencing efflorescence involve the compositions of binders, pore structure of the hardened matrix, and so on. This study investigated the efflorescence of calcium sulfoaluminate cement (SAC) mortar at 5–40 °C from perspectives of carbonation potential and pore structure, while PC mortar was chosen as a reference. The microstructure of the efflorescence substances, such as phase assemblage and distribution, was systematically unraveled using optical microscope, in-situ Raman spectroscopy, SEM and EDS at multi scale-level. Water absorption test and XCT were employed for the pore structure characterization. Additionally, an outdoor exposure was carried out to compare with the results from the indoor accelerated experiments. Results reveal that a lower temperature has a limited effect on the efflorescence potential. The dominant efflorescence ingredient for SAC and PC mortars cured at 5–40 °C is CaCO3, with varied polymorphs. However, both primary and secondary efflorescence of SAC mortar is much slighter than that of PC mortar. The volume of fine pores (less than 0.1 mm3) in SAC mortar is higher than that of PC, accompanied by higher capillary absorption coefficient and water absorption rate. However, the low carbonation potential of ettringite tends to be more effective in reducing efflorescence risk for SAC mortar in both lab tests and outdoor exposure. The understanding of the relationship between efflorescence and carbonation provides important insights into the inhibition of efflorescence in cementitious materials.

Evolution Law of Micro-Pore Structure of Cement-Emulsified Asphalt Mortar Based on NMR

Cement emulsified asphalt mortar (CA) is widely used as the cushion of two types of ballastless track (CRTS I and CRTS II) in high-speed railways. Nowadays, the lack of durability of CA mortar has severely affected the quality of high-speed railways, failing to meet the requirements of sustainability. Since CA mortar is a kind of porous material, its performance can be significantly affected by its microstructures, which means that revealing the evolution law of its microstructures can provide the basis for improving its durability. Therefore, CA mortar species with different asphalt-cement ratio under different curing ages were prepared based on the requirements of CRTS II in this research and the pore structures were determined based on SEM and NMR methods. Then, a fractal model of CA mortar pore volume was proposed based on the concept of box fractal dimension, and the fractal dimension of pore volume was calculated. The relationship between fractal dimensions and mechanical property was analyzed based on Pearson correlation coefficient and regression analysis. The results suggested that the overall microstructure of CA mortar shows a loose porous space structure with cement hydration products being the continuous phase and asphalt being the dispersed phase. With the increase in A/C ratio, the hydration products produced by cement hydration decrease, and the total porosity and average porosity of CA mortar gradually increase due to the increase of asphalt hindering the hydration process of the cement. With the increase in curing age, the pore structure of CA mortar becomes more compact. However, the evolution law of CA mortar pore structure with age is not consistent under different A/C ratios due to the influence of asphalt. The pore structure of CA mortar was proved to have obvious fractal characteristics based on the concept of box fractal dimension and the experimental data of NMR. In addition, the correlation analysis proves that the fractal dimension of pore structure has an obvious positive correlation with the compressive and flexural strength, which suggests that the fractal dimension of pore volume can be a bridge for connecting the macro-property and micro-structures of CA mortar.

Fractal Characteristics of Geopolymer Mortar Containing Municipal Solid Waste Incineration Fly Ash and Its Correlations to Pore Structure and Strength

Compression and mercury intrusion porosimetry (MIP) tests were conducted to analyze the effect of municipal solid waste incineration fly ash (MSWIFA) content on the mechanical performance and pore structure of geopolymer mortar. The MSWIFA weight contents were 0%, 5%, 15%, 25%, and 35% and the pore diameter distribution, specific surface area, and pore volume were considered to assess the pore structure of the geopolymer mortars. The popular fractal model was used to investigate the fractal features of the geopolymer mortars. Additionally, mathematical models of fractal dimension with pore structural parameters and compressive strength were established. The results showed that the compressive strength of geopolymer mortars decreased while the total pore volume and total specific surface area of mortars increased with the increase in MSWIFA content. As the MSWIFA content increased, the harmless pores (pore diameter < 20 nm) were refined. Specifically, the pores with a diameter of 5–10 nm increased in number but the pores with a diameter of 10–20 nm decreased in number with the increase in MSWIFA content. The pore structure in the mortars showed scale-dependent fractal characteristics. All fractal curves were divided into four segments according to the pore diameter, namely, Region I (<20 nm), Region II (20–50 nm), Region III (50–200 nm), and Region IV (>200 nm). The surface fractal dimension (DS) in Region I and Region IV was between 2 and 3. However, the DS in Region II and Region III was greater than 3, indicating the pores in Region II and Region III were non-physical according to the surface geometry because of the presence of ink bottle pores which distorted the result of the MIP. The complexity of pores in Region I and Region IV was reduced by the addition of MSWIFA. The DS is a comprehensive parameter that well describes the spatial and morphological distribution of pores in geopolymer mortars and exhibited a good correlation with the specific surface area, pore volume, and compressive strength. A mathematical model based on the DS was established to predict the compressive strength of the geopolymer mortar containing MSWIFA.