Effect of Multi-Walled Carbon Nanotubes on Strength and Electrical Properties of Cement Mortar

This work aims to investigate the effects of multi-walled carbon nanotubes (MWCNTs) on the strength and electrical properties of cement mortar. MWCNTs were added to cement mortar in four different concentrations: 0.00 wt.%, 0.01 wt.%, 0.015 wt.%, and 0.02 wt.% by the mass of cement. The consistency, density, setting time and compressive and flexural strength of mixes were tested and analyzed at 28 and 90 days curing time. Mechanical performance tests confirm an increase of 25% and 20% in the ultimate compressive and flexural strength respectively, which results from MWCNT 0.02 wt.% loading at 90 days curing time. The resistivity measurements in mortars with 0.01 and 0.015 wt.% MWCNT loading result up to 10% decrement at both 28 and 90 days curing. Activation energy calculations show fully accordance with these statements, resuming that 0.01 wt.% MWCNT appears to be the most effective loading scheme to produce certain conductivity enhancement in cement mortar.     

Microstructure and Electrical Conductivity of Cement Paste Reinforced with Different Types of Carbon Nanotubes

Over the last few years, the addition of small amounts of carbon nanotubes (CNTs) to construction materials has become of great interest, since it enhances some of the mechanical, electrical and thermal properties of the cement. In this sense, single-walled and multi-walled carbon nanotubes (SWCNTs and MWCNTs, respectively) can be incorporated into cement to achieve the above-mentioned improved features. Thus, the current study presents the results of the addition of SWCNTs and MWCNTs on the microstructure and the physical properties of the cement paste. Density was measured through He pycnometry and the mass change was studied by thermogravimetric analysis (TGA). The microstructure and the phases were analyzed using scanning electron microscopy (SEM) and X-ray diffraction (XRD). Finally, the electrical conductivity for different CNT concentrations was measured, and an exponential increase of the conductivity with concentration was observed. This last result opens the possibility for these materials to be used in a high variety of fields, such as space intelligent systems with novel electrical and electronic applications.     

Study on the Carbonation Behavior of Cement Mortar by Electrochemical Impedance Spectroscopy

A new electrochemical model has been carefully established to explain the carbonation behavior of cement mortar, and the model has been validated by the experimental results. In fact, it is shown by this study that the electrochemical impedance behavior of mortars varies in the process of carbonation. With the cement/sand ratio reduced, the carbonation rate reveals more remarkable. The carbonation process can be quantitatively accessed by a parameter, which can be obtained by means of the electrochemical impedance spectroscopy (EIS)-based electrochemical model. It has been found that the parameter is a function of carbonation depth and of carbonation time. Thereby, prediction of carbonation depth can be achieved.     

Spark Plasma Sintering of Aluminum-Based Powders Reinforced with Carbon Nanotubes: Investigation of Electrical Conductivity and Hardness Properties

This paper focuses on reporting results obtained by the spark plasma sintering (SPS) consolidation and characterization of aluminum-based nanocomposites reinforced with concentrations of 0.5 wt%, 1 wt% and 2 wt% of single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs). Experimental characterization performed by SEM shows uniform carbon nanotube (CNT) dispersion as well as carbon clusters located in the grain boundary of the Al matrix. The structural analysis and crystallite size calculation were performed by X-ray diffraction tests, detecting the characteristic CNT diffraction peak only for the composites reinforced with MWCNTs. Furthermore, a considerable increment in the crystallite size value for those Al samples reinforced and sintered with 1 wt% of CNTs was observed. Hardness tests show an improvement in the composite surface hardness of about 11% and 18% for those samples reinforced with 2 wt% of SWNCTs and MWCNTs, respectively. Conductivity measurements show that the Al samples reinforced with 2 wt% of MWCNTs and with 0.5 wt% SWCNTs reach the highest IACS values of 50% and 34%, respectively.     

Valorisation of Recycled Cement Paste: Feasibility of a Short-Duration Carbonation Process

Cement paste powder (CPP) is a by-product of the recycling process of concrete with an elevated carbonation capability and potential to be recycled as a binding material in new concrete batches. The application of a carbonation treatment to CPP improves this potential even more, besides the evident gains in terms of CO₂ net balance. However, the long duration usually adopted in this treatment, from 3 to 28 days, hampers the industrial viability of the process. We studied the feasibility of a short-duration carbonation process, with a duration of two hours, carrying out a comprehensive characterization of the material throughout the process. The test was performed on CPP with an average initial water content of 16.9%, exposed to a CO₂ concentration of 80%. The results demonstrate two main carbonation rates: a rapid growth rate in the first 18 minutes of the process, involving all the calcium-bearing compounds in CPP, and a slow growth rate afterwards, where only C-S-H contributes to the carbonation reaction. During the 2 h carbonation process, the main CPP compounds, calcium silicate hydrate (C-S-H) and calcium hydroxide (CH), reached different carbonation degrees, 31% and 94%, with, however, close CO₂ uptake values, 8% and 11%, respectively. Nevertheless, the total CO₂ uptake for this process (≈19%) attained values not distant from the values usually obtained in a carbonation of 12 days or more (19–25%). Hence, these findings highlight the blocking role of C-S-H in the carbonation process, indicating that longer carbonation periods are only going to be useful if an effective carbonation of this compound is accomplished. In the present scenario, where CH is the main contributor to the reaction, the reduction in the process duration is feasible.     

Effect of Multi-Walled Carbon Nanotubes and Carbon Fiber Reinforcements on the Mechanical and Tribological Behavior of Hybrid Mg-AZ91D Nanocomposites

Magnesium matrix composites are extensively used in automotive and structural applications due to their low density, high strength, and wear-resistant properties. To reach the scope of industry needs, research is carried out regarding enhancing the mechanical and tribological behavior of the magnesium composites by reinforcing the nano-sized reinforcements. In the present work, research has been carried out to enhance the properties of the magnesium AZ91D hybrid composite by reinforcing carbon fibers (CFs) and multi-walled carbon nanotubes (MWCNTs) with varying weight percentages (AZ91D + 0.5% CF’s + 0.5% MWCNT and AZ91D + 0.75% CF’s + 0.75% MWCNT, respectively). The experimental tests were carried out to evaluate the mechanical and tribological behavior of the composites. The test results showed that the addition of CF and MWCNT reinforcements improved the hybrid Mg composite’s hardness, tensile strength, and impact strength compared to the base Mg matrix. The AZ91D + 0.75% CF’s + 0.75% MWCNT hybrid composite showed a 19%, 35%, and 66% increased hardness, tensile strength, and impact strength, respectively, compared to the base Mg AZ91D. The wear test results also showed the improved wear resistance of the Mg composite compared to the base matrix. The enhanced wear resistance of the composite is due to the addition of hard MWCNT and CF reinforcements. The wear rate of the AZ91D + 0.75%CF’s + 0.75% MWCNT composite for a load of 30 N at a sliding distance of 1500 m is lower as compared to the base matrix. The SEM micrographs of the worn surfaces revealed the existence of abrasive wear. The improved mechanical and tribological behavior of the magnesium composite is also due to the homogeneous distribution of the hard reinforcement particles along the grain boundaries.     

Strength,Carbonation Resistance,and Chloride-Ion Penetrability of Cement Mortars Containing Catechol-Functionalized Chitosan Polymer

There have been numerous recent studies on improving the mechanical properties and durability of cement composites by mixing them with functional polymers. However, research into applying modified biopolymer such as catechol-functionalized chitosan to cement mortar or concrete is rare to the best of our knowledge. In this study, catechol-functionalized chitosan (Cat-Chit), a well-known bioinspired polymer that imitates the basic structures and functions of living organisms and biological materials in nature, was synthesized and combined with cement mortar in various proportions. The compressive strength, tensile strength, drying shrinkage, accelerated carbonation depth, and chloride-ion penetrability of these mixes were then evaluated. In the ultraviolet–visible spectra, a maximum absorption peak appeared at 280 nm, corresponding to catechol conjugation. The sample containing 7.5% Cat-Chit polymer in water (CPW) exhibited the highest compressive strength, and its 28-day compressive strength was ~20.2% higher than that of a control sample with no added polymer. The tensile strength of the samples containing 5% or more CPW was ~2.3–11.5% higher than that of the control sample. Additionally, all the Cat-Chit polymer mixtures exhibited lower carbonation depths than compared to the control sample. The total charge passing through the samples decreased as the amount of CPW increased. Thus, incorporating this polymer effectively improved the mechanical properties, carbonation resistance, and chloride-ion penetration resistance of cement mortar.     

Improvement in the Carbonation Resistance of Construction Mortar with Cane Bagasse Fiber Added

In this work, sugarcane bagasse fiber, a waste product of agroindustry, was added to mortar mixes at different proportions looking to seal porosities so as to improve the resistance of concrete to carbonation and to improve its mechanical properties. To evaluate the behavior of bagasse fibers in the alkaline media typical of mortars, bagasse fibers were subjected to solutions with alkaline pH values, and their chemical structure and morphological behavior was evaluated using FTIR (Fourier transform infrared spectroscopy) and SEM (Scanning Electron Microscopy). Using mortar cylinders in an accelerated carbonation chamber to obtain results in short lapses, the compressive strength and the carbonation were evaluated. The FTIR analysis results indicate that pH values of 11 and 12 causes a delignification, while at pH 9 and 10, a swelling of the molecule occurs because of the addition of hydroxyl ions, behavior that is confirmed with SEM images. A clear effect of the fiber addition on the performance of concrete was observed as the carbonation front of 35 mm for the sample without fibers was reduced to 2 mm for the sample with 2% fiber addition, resulting in an increase of 5 MPa in compressive strength. These results indicate that in the range of mortar pH, chemical changes occured over the sugarcane surface that could cause the growth of fibers and could partially seal the porosity in the mortars, thus enhancing its performance.     

Study on the Influence of Nanosilica Sol on the Hydration Process of Different Kinds of Cement and Mortar Properties

Compared with nanosilica collected in a gaseous state, nanosilica sol has great economic value and application significance for improving the performance of concrete and mortar. In this study, the influence of nanosilica sol on the hydration process of different kinds of cement is studied by means of hydration heat analysis, X-ray diffraction analysis (XRD) and other methods, and the properties of mortar such as setting time, mechanical properties and porosity are also studied to characterize the influence of nanosilica sol on the macroscopic properties of mortar. The experimental results show that nanosilica sol can accelerate the hydration rate of two kinds of cement and promote the hydration reaction degree of cement, and this promotion effect increases with the increase in nanosilica sol content. At the same time, nanosilica sol can significantly shorten the setting time of the two kinds of cement, and it is more obvious with the increase in content. Excessive content of nanosilica sol will adversely affect the permeability resistance of mortar. It may be caused by the weak interval formed by nanosilica particle clusters in the mortar matrix, which can be supported by the mortar pore structure distribution test. At the same time, the influence of nanosilica sol on the hydration of the two kinds of cement is different, and the compressive strength of HBSAC cement mortar increases first and then decreases after adding nanosilica sol; However, the compressive strength of P·O 42.5 cement mortar increases gradually after adding nanometer silica sol. This shows that nanosilica sol does not effectively promote the hydration of β-C2S in high belite sulfoaluminate cement (HBSAC) mortar. Based on the above experimental results, it can be concluded that when the content of nanosilica sol is about 1%, it has the best promotion effect on the hydration of the two kinds of cement and the performance of mortar.     

Investigation of the Residual Mechanical and Porosity Properties of Cement Mortar under Axial Stress during Heating

The preload load on concrete during heating is considered to cause a ‘densification’ of cement mortar which led to the increased compressive strength. In order to assess the influence of coupled load and heating effects on porosity characteristics of concrete, the porosity of mortar after mechanical and thermal loading was measured by X-ray computed tomography (X-ray CT). The preload at pre-stress ratios of 0, 0.2, 0.4, and 0.6 (ratio of stress applied to the specimen to its compressive strength at room temperature) were applied on mortar specimens during heating. The residual compressive strengths of the heated and stressed mortar specimens were tested after cooling to room temperature. Combined analyses of the residual compressive strength test results and porosity test results, it shows that the porosity of the specimens under the coupled stressing and heating conditions were slightly lower than that under the unstressed conditions; however, the conclusion that the increase of compressive strength of stressed mortar was caused by the ‘densification’ of cement paste was insufficient. The preload reduced the cracks in the mortar, especially the crack induced due to the thermal mismatch in aggregates and hardened cement paste (HCP), and this may account for the increased compressive strength of stressed mortar.     

Effect of the Addition of Agribusiness and Industrial Wastes as a Partial Substitution of Portland Cement for the Carbonation of Mortars

The present research work shows the effect on the carbonation of Portland cement-based mortars (PC) with the addition of green materials, specifically residues from two groups: agricultural and industrial wastes, and minerals and fibres. These materials have the purpose of helping with the waste disposal, recycling, and improving the durability of concrete structures. The specimens used for the research were elaborated with CPC 30R RS, according to the Mexican standard NMX-C-414, which is equivalent to the international ASTM C150. The aggregates were taken from the rivers Lerma and Huajumbaro, in the State of Michoacan, Mexico, and the water/cement relation was 1:1 in weight. The carbonation analyses were performed with cylinder specimens in an accelerated carbonation test chamber with conditions of 65 +/− 5% of humidity and 25 +/− 2 °C temperature. The results showed that depending on the PC substitutions, the carbonation front advance of the specimens can increase or decrease. It is highlighted that the charcoal ashes, blast-furnace slags, and natural perlite helped to reduce the carbonation advance compared to the control samples, consequently, they contributed to the durability of concrete structures. Conversely, the sugarcane bagasse ash, brick manufacturing ash, bottom ash, coal, expanded perlite, metakaolin, and opuntia ficus-indica dehydrated fibres additions increased the velocity of carbonation front, helping with the sequestration of greenhouse gases, such as CO₂, and reducing environmental pollution.     

Experimental Study on the Effect of Carbonation Reaction on the Properties of Imitation Site Soil

In this study, sodium methylsilicate and lime were selected to prepare the same proportion of Imitation Site Soil, and according to the principle of carbonation reaction of restoration materials, the effect of carbonation reaction on the performance of restoration soil of earthen sites was studied. The study has good significance for the conservation and restoration of earthen sites. The samples were cured with CO₂ concentration and curing age as variables. After curing, the samples were tested to determine their water-resistant properties, uniaxial compressive strength, and pH value and a micro scanning electron microscope was used. The results indicated that the carbonation reaction can quickly improve the water resistance and compressive strength of imitation site soil, and reduced the water absorption by 16.67% compared to the specimens conditioned at 0.03% CO₂ concentration. The UCS of specimens at 5%, 10%, and 15% CO₂ concentrations increased by 72.22%, 131.19%, and 219.27%, respectively, compared with those at 0.03% CO₂ concentration after the specimens were environmentally maintained in the carbonation chamber at 0.03%, 5%, 10%, and 15% CO₂ concentrations for 120 h, respectively. The internal particle gradation of the imitation site soil improved after carbonation. These results provide a basis for improving the restoration technology of earthen sites.     

Influence of the Addition of Dispersible Color Powder and Polyacrylic Emulsion on the Durability of Cement Mortar

Cement mortar can be colored using color additive technology to give colorful facades to the surfaces of buildings, and to beautify the environment. In this study, weight ratios of color powder/cement at 1:80, 1:40, and 1:27, and polyacrylic emulsion/cement at a ratio of 1:5 were added as pigments to cement mortar; the fresh properties, slump, slump flow, hardened properties, compressive strength, flexural strength, ultrasonic pulse velocity, durability, surface electrical resistivity and thermal conductivity of the colored cement mortar were then examined. The results showed that adding color powder/cement at 1:80 and polyacrylic emulsion/cement at 1:5 gives the best water/cement (W/C) ratio, which equals 0.5; this can effectively improve the hardness and durability of colored cement mortar. At 28 days of aging, the strength of the various colored cement mortars was maintained at 33.1–36.8 MPa. The acrylic-based emulsion significantly improved the flexural strength of the specimen. At 91 days of aging, all of the cement mortars exceeded the control group, with an anti-bay strength of 19.9–21.7 MPa, and the strength increased with aging. Adding appropriate amounts of inorganic color powder and mixing water can effectively enhance the fresh and hardened properties and durability of the colored cement mortar, while polyacrylic emulsion may significantly improve the test pieces and flexural strength, which increases with age. Moreover, natural α-Fe₂O₃ (rust layer) is formed on the surface of the colored cement mortar samples through the addition of inorganic color powder that contains Fe(III) ion; this prevents the intrusion of noxious ions and thus increases the durability. All of the test pieces of colored cement mortar in this study had a surface resistance of over 20 kΩ-cm on the seventh day of the test period, meaning good surface compactness. In addition, because the thermal conductivity of the added inorganic color powder was higher than that of cement, the thermal conductivity was significantly improved.     

The Influence of Lime Solution in Kneading Water Substitution on Cement Roughcast and Mortar Coating

The understanding of the mechanical fixation behavior of coatings is crucial for a better comprehension of the bonding systems, especially at the interface between the mortar and the substrate. Physical adherence is related, among other things, to the contents of the materials used in the roughcast and mortar coatings, due to the colloidal water penetration into the pores of the substrate. This work evaluated the influence of different lime solution additions replacing the kneading water in the preparation of roughcast and mortar coatings. Two types of substrates were investigated:ceramic bricks and concrete blocks. Three wall masonry panels were constructed, with dimensions of 220 × 180 cm², one of concrete block and two of ceramic bricks, followed by the application of roughcast and mortar coating with an average thickness of 5 mm and 20 mm, respectively. Direct tensile bond strength tests were performed and the results, with a 95% confidence level, showed that substrate ceramic and treatment in the roughcast exhibited a better behavior regarding the distribution of the tensile bond strength of the tested specimens. However, no significant differences of the amount of addition used (0%, 5%, 10% and 15%) on the tensile bond strength were observed.     

Enhancing Crystallinity and Orientation by Hot-Stretching to Improve the Mechanical Properties of Electrospun Partially Aligned Polyacrylonitrile (PAN) Nanocomposites

Partially aligned polyacrylonitrile (PAN)-based nanofibers were electrospun from PAN and PAN/single-walled carbon nanotubes (SWNTs) in a solution of dimethylformamide (DMF) to make the nanofiber composites. The as-spun nanofibers were then hot-stretched in the oven to enhance its orientation and crystallinity. With the introduction of SWNTs and by the hot-stretched process, the mechanical properties will be enhanced correspondingly. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray scattering (XRD), differential scanning calorimetry (DSC), and the tensile test were used to characterize the microstructure and performances of the nanofibers. The orientation and crystallinity of the as-spun and hot-stretched nanofibers confirmed by X-ray have increased. Differential scanning calorimetry showed that the glass transition temperature of PAN increased about 3 °C by an addition of 0.75 wt% SWNTs indicating a strong interfacial interaction between PAN and SWNTs. The tensile strength and the modulus of the nanofibers increased revealing significant load transfer across the nanotube-matrix interface. For PAN nanofibers, the improved fiber alignment, orientation and crystallinity resulted in enhanced mechanical properties, such as the tensile strength and modulus of the nanofibers. It was concluded that the hot-stretched nanofiber and the PAN/SWNTs nanofibers can be used as a potential precursor to produce high-performance nanocomposites.     

Synergistic Effect of Screen-Printed Single-Walled Carbon Nanotubes and Phosphorylated Cellulose Nanofibrils on Thermophysiological Comfort,Thermal/UV Resistance,Mechanical and Electroconductive Properties of Flame-Retardant Fabric

Single-walled carbon nanotubes (SWCNTs) and phosphorylated nanocellulose fibrils (PCNFs) were used as functional screen-print coatings on flame-retardant (FR) fabric, to improve its thermal resistance and thermophysiological comfort (wetting, water vapour and heat transmission) properties, while inducing it with electrical conductivity and UV protection. The effect of PCNF printing, followed by applying a hydrophobic polyacrylate (AP), on the same (back/B, turned outwards) or other (front/F, turned towards skin) side of the fabric, with and without the addition of 0.1–0.4 wt% SWCNTs, was studied by determining the amount of applied coating and its distribution (microscopic imaging), and measuring the fabric’s colour, air permeability, thickness, mechanical, flame and abrasion resistance properties. Due to the synergistic effect of PCNF and SWCNTs, both-sided printed fabric (front-side printed with PCNF and back-side with SWCNTs within AP) resulted in an increased heat transfer (25%) and an improved thermal resistance (shift of degradation temperature by up to 18 °C towards a higher value) and UV protection (UPF of 109) without changing the colour of the fabric. Such treatment also affected the moisture management properties with an increased water-vapour transfer (17%), reduced water uptake (39%) and asymmetric wettability due to the hydrophilic front (Contact Angle 46°) and hydrophobic back (129°) side. The increased tensile (16%) and tear (39%) strengths were also assessed in the warp direction, without worsening the abrasion resistance of the front-side. A pressure-sensing electrical conductivity (up to 4.9∙10⁻⁴ S/cm with an increase to 12.0∙10⁻⁴ S/cm at 2 bars) of the SWCNT-printed side ranks the fabric among the antistatic, electrostatic discharge (ESD) or electromagnetic interference (EMI) shielding protectives.     

Mechanical and Electrical Properties of Rapid-Strength Reactive Powder Concrete with Assembly Unit of Sulphoaluminate Cement and Ordinary Portland Cement

Fast-hardening cement can be used to quickly repair concrete constructions. Characterizing mechanical properties by electrical properties is a promising method to evaluate the mechanical performance nondestructively. However, little attention has been paid to this area. In this paper, copper-coated fine-steel-fibers-reinforced reactive powder concrete (RPC) with compound cement was manufactured. The mass ratio of sulphoaluminate and ordinary Portland cement in the compound cement was 1:1. The influence of copper-coated fine steel fibers with the volume increasing from 0 to 3.0% by the total volume of RPC on the working performances (fluidity and setting time), mechanical properties (flexural strength and toughness, drying shrinkage rate and compressive strength) and electrical parameters (AC electrical resistance and AC impedance spectroscopy curves) was investigated. The electron microscope energy spectrum experiment was applied in analyzing the macro properties of RPC. The results exhibited that the increasing volume of steel fibers led to decreasing the fluidity and retarding the setting of RPC. The electrical resistance of RPC decreased in the form of a quartic function with the volume of steel fibers. The steel fibers volume of 1.5% was the percolation threshold value. The specimens cured for 28 days showed higher electrical resistance than the specimens cured for 1 day. The flexural or compressive strength of the specimens satisfied a specific functional relationship with the volume of steel fibers and electrical resistance. The addition of steel fibers led to improving the flexural toughness and decreasing the shrinkage rate. Furthermore, 3.0% steel fibers could improve the flexural toughness by 3.9 times and decrease the shrinkage to 88.3% of the specimens without steel fibers.     

Influence of Aggregate Coated with Modified Sulfur on the Properties of Cement Concrete

This paper proposes the mixing design of concrete having modified sulfur-coated aggregate (MSCA) to enhance the durability of Portland cement concrete. The mechanical properties and durability of the proposed MSCA concrete were evaluated experimentally. Melting-modified sulfur was mixed with aggregate in order to coat the aggregate surface at a speed of 20 rpm for 120 s. The MSCA with modified sulfur corresponding to 5% of the cement weight did not significantly affect the flexural strength in a prism concrete beam specimen, regardless of the water-cement ratio (W/C). However, a dosage of more than 7.5% decreased the flexural strength. On the other hand, the MSCA considerably improved the resistance to the sulfuric acid and the freezing-thawing, regardless of the sulfur dosage in the MSCA. The coating modified sulfur of 5% dosage consequently led to good results for the mechanical properties and durability of MSCA concrete.     

Sulfate Freeze–Thaw Resistance of Magnesium Potassium Phosphate Cement Mortar

Concrete facilities in the severe-cold areas of western China (salt lake environments and heavy saline soils) are seriously damaged by the multiple corrosion effects of freeze–thaw cycles and sulfate corrosion. Magnesium phosphate cement (MPC) cement-based material has become an ideal concrete structural component because of its superior performance. Because concrete structural repair materials are used in heavy-corrosion environments, their durability in those environments should also be considered. Regarding the salt-freezing resistance of MPC, the existing studies have all used a NaCl solution as the heat transfer medium. In addition to chlorine salt, sulfate, especially Na₂SO₄, is also common in typical use environments such as oceans, salt lakes, and groundwater. To evaluate the sulfate freeze–thaw resistance of potassium magnesium phosphate cement (MKPC) mortar, in this study the strength development, weight loss, and water absorption of MKPC mortar specimens subjected to different freeze–thaw cycles were tested and compared with those for Portland cement (P.O) mortar specimens of the same strength grade. The results showed that the P.O mortar specimen completely lost its strength after 75 cycles of rapid water freezing and thawing and 50 cycles of sodium sulfate solution (5%) freezing and thawing. However, the residual strength rating of the MKPC mortar specimen after 75 cycles of water freezing and thawing and 100 cycles of sodium sulfate solution freezing and thawing was higher than 75%. After 50 rapid freeze–thaw cycles in water and a 5% Na₂SO₄ solution, the P.O mortar specimen’s mass loss exceeded the 5% failure standard, whereas the mass loss of the MKPC mortar specimens was much less than 5%. Before the freeze–thaw cycles, the water absorption of the P.O mortar specimen was close to 8 times that of the MKPC mortar specimen, and after 50 water freeze–thaw cycles and 25 sulfate solution freeze–thaw cycles, the water absorption reached 4.88% and 5.68%, respectively. However, after 225 freeze–thaw cycles in water and the sulfate solution, the water absorption rates of MKPC mortar specimens were 2.91% and 2.51% respectively. The test and analysis results show that the freeze–thaw resistance of MKPC mortar was much higher than that of Portland cement mortar specimens. Those results provide a prerequisite for applying and expanding the use of MKPC-based materials in severe-cold areas of western China (salt lake and heavily saline soil environments).     

Improving the Autogenous Self-Sealing of Mortar: Influence of Curing Condition

With the construction of projects under severe environments, new and higher requirements are put forward for the properties of concrete, especially the autogenous self-sealing property, which is greatly affected by the curing environment and the state of the water. Herein, six types of curing conditions, including in air with a relative humidity of 30%, 60%, and 95%; flowing water; wet-dry cycles; and static water, are designed to investigate the autogenous self-sealing of mortar under different curing conditions. The results showed that the self-sealing ratios are higher than 60% and the cracks are closed for the mortar undergoing the wet-dry cycles and the static water. However, the self-sealing ratios of mortar are lower than 10% and the cracks are almost unchanged when the mortar is cured in the air with a relative humidity (RH) of 30% and 60%. The static liquid water is more conducive to the continued hydration of cement and the formation of CaCO₃ than the flowing water. The research provides guidance for the design of concrete and the improvement of autogenous self-sealing when the concrete serves in different environments.