Freeze-thaw Resistance Research Articles

High-Performance Calcium Silicate Board Reinforced by Microfibrillated Cellulose/Microsilica

The use of microfibrillated cellulose (MFC) derived from renewable natural plant fibers and microsilica (Ms) derived from industrial byproducts in calcium silicate boards (CSBs) is consistent with current trends favoring the use of green building materials. Herein, MFC and Ms synergistically reinforced CSBs were prepared by filling the pores between the MFC and the matrix using Ms to strengthen the MFC–matrix bond. The results show that adding Ms promotes the formation of calcium silicate hydrate. Furthermore, increasing the Ms content decreases the cumulative pore size of the plate, resulting in a denser structure. In addition, when the MFC and Ms contents were 0.3 and 12%, respectively, the flexural strength of the CSB reached 35.96 MPa, which is 37.4% greater than that in the absence of Ms (26.17 MPa). Moreover, a flexural strength of 25.03 MPa was retained after 25 freeze–thaw cycles, demonstrating excellent freeze–thaw resistance.

The effect of graphene oxide on dune sand cementitious composites reflected in enhancing freeze–thaw resistance: An experimental study

AbstractTo advance the utilization of dune sand, a sustainable albeit flawed resource, for structural engineering, the incorporation of graphene oxide (GO) is suggested as a potential means for improving durability of dune sand cementitious composites (DSCC). In this study, DSCC samples with varying GO concentrations were prepared. The effect of GO on the freeze–thaw resistance of DSCC was then studied by freeze–thaw cyclic test and mechanical test. In addition, to elucidate the mechanism underlying the observed enhancement in freeze–thaw resistance due to GO incorporation, thermogravimetric, mercury injection, adsorption, and morphological analyses were performed. The experimental results showed that incorporating GO into DSCC can enhance its freeze–thaw resistance without compromising its mechanical properties. The weight loss and relative dynamic modulus of elasticity of the specimen with 0.06 wt% GO decreased by 92.83% and 64.96%, respectively, as well as the compressive strength increased by 22.76% after 150 freeze–thaw cycles compared with the control specimen. The enhancing effect of adding GO on the freeze–thaw resistance of DSCC was found to be attributed to the promotion of hydration and the control of internal structure. Notably, the modification of GO on the smooth dune and the reinforcement of GO on the interface between dune sand particles and cement matrix was identified, which may be the new evidence for testifying the GO enhancement on the freeze–thaw resistance of dune sand cementitious composites.

The feasibility of using copper slag in asphalt mixtures for base and surface layers based on laboratory results

This study aims to assess the feasibility of using copper slag (CS) in asphalt mixtures in both the surface and base layers of road pavements. For this purpose, two sets of asphalt mixtures with different CS content (15 and 30%) and fraction sizes (0/8 and 0/16 mm) were prepared. The optimal binder content of each mixture was determined using the Marshall mix design method. Their laboratory performances were investigated and compared with the properties of reference asphalt mixtures, i.e. mixtures consisting exclusively of virgin materials. Test results showed that adding CS to the mixture for the surface layer improved stiffness and rutting resistance and had almost no negative impacts on the remaining properties apart from cracking resistance. Further, the addition of CS to the base-layer mixture improved cracking resistance, but negatively affected stiffness, rutting and fatigue resistance. In both cases, adding CS did not influence the strength, water sensitivity or freeze–thaw resistance. From a leaching perspective, the results showed that leachates gathered from the asphalt mixtures designed for the surface layer did not contain heavy metals. Overall, it can be concluded that CS has a potential to be used as an appropriate aggregate substitute for virgin aggregates in asphalt mixtures for both surface and base layers.

Study of the Freeze–Thaw Resistance for Composite Fiber Recycled Concrete with Sulphate Attack Exposure

The exposure of recycled concrete (RCA) to a sulphate environment in cold regions makes it crucial to overcome the freeze–thaw cycling effects of recycled concrete. Based on steel and basalt fiber reinforced recycled concrete, the freeze–thaw cycle resistance of recycled concrete was studied by exposure to a sulphate environment. The mass loss, dynamic elastic modulus loss and compressive strength loss of the specimens were studied through freeze–thaw cycle experiments. SEM techniques were used to explore the effect of fiber distribution on the freeze–thaw resistance of recycled concrete. The freeze–thaw mechanism of the basalt fiber and steel fiber recycled concrete exposed to a sulphate environment has also been summarized. The results show that, based on the sulphate environment, the composite fiber recycled concrete has a higher stability in terms of mass loss and relative dynamic modulus of elasticity than single fiber concrete. The compressive strength of S0.9RC (recycled concrete with 0.9% steel fibers) and BF5.5RC (recycled concrete containing 5.5 kg/m3 basalt fibers) increased by 8.62% and 13.62%, respectively, compared to normal recycled concrete after 28 days of maintenance; and after 150 freeze–thaw cycles, the compressive strength increased by 41.39% and 47.54%, respectively; compared to ordinary natural aggregate concrete, the compressive strength of S0.9RC and BF5.5RC increased by 32.90% and 27.36%, respectively. The compressive strength of the S1.5BF7.5RC (recycled concrete with 1.5% steel fibers and 7.5 kg/m3 basalt fibers) composite basalt fiber–steel fiber concrete also increased by 42.82%. SEM techniques indicated that the basalt fiber in the recycled concrete exhibited fracture damage, which inhibited the development of microcracks within the concrete. When the recycled concrete is subjected to coupled sulphate and freeze–thaw cycles, freezing occurs from the outside in, with ice crystals extending along the cracks into the matrix. Prior to freezing, a negative pressure is created by the compression of the air and the contraction of the salt solution, which pulls the external solution inwards. The brine is in a state where ice and water coexist during the continuous cooling process. The salt solution migrates from the inside to the outside during heating and melting.

Pore structure characteristics, mechanical properties, and freeze–thaw resistance of vegetation-pervious concrete with unsintered sludge pellets

To make full use of municipal solid waste, the sludge was used to make unsintered sludge pellets. Then unsintered sludge pellets was used to make vegetation-pervious concrete. The effects of the sludge pellet content and the water-to-cement ratio (W/C) on the pore structure characteristics, mechanical properties, ecological properties, and freeze–thaw resistance of the concrete were investigated. The results show that sludge is suitable for preparing pellets due to its good plasticity and high SiO2 and Al2O3 content. A 1:2:1 gypsum/fly ash/lime curing agent is selected to cure unsintered sludge pellets. The total porosity, hydraulic conductivity, ecological properties, and freeze–thaw resistance of the pervious concrete improve with an increase in the sludge pellet content and W/C, while its compressive and flexural strengths decrease. The plant roots penetrate the pervious concrete slab and maintain normal growth after 30 days of germination. In addition, a model considering the effective porosity and mean pore size is proposed for predicting the pore channel tortuosity of pervious concrete. The Kozeny–Carman model for calculating the hydraulic conductivity of pervious concrete is then modified based on the established calculation model of pore channel tortuosity. A model is also developed for predicting the compressive and flexural strength of pervious concrete based on its total porosity and mean pore size. In addition, the mechanism for the freeze–thaw resistance of pervious concrete is analyzed according to hydrostatic pressure. This research explains the full utilization of municipal solid waste materials and guides further research into the properties associated with pervious concrete.

In-Service Performance Evaluation of Flexible Pavement with Lightweight Cellular Concrete Subbase

The objective of engineers to improve the long-term performance of road infrastructure in changing global climate has led to the development of alternate materials for pavement construction. Lightweight cellular concrete (LCC) is a viable option for colder climates where pavements undergo several freeze-thaw cycles each year, resulting in faster deterioration of pavements. This is due to LCCs’ excellent freeze-thaw resistance, ease of placement, and potential sustainability benefits such as reduced use of virgin material and industrial by-products. However, there is a need to quantify these benefits and develop unified specifications for using LCC in the pavement structure. Therefore, this study examined the performance of flexible pavement sections that included a subbase layer, unbound granular materials for the control section, and three LCC densities (400, 475, and 600 kg/m3) for the LCC sections. Post-construction evaluation of pavement stiffness and roughness were evaluated using a Lightweight deflectometer and SurPro equipment. The results showed that LCC subbase thickness ≥ 250 mm produced over 22% smoother riding surfaces than unbound granular pavements while increasing pavement stiffness by up to 21%. Finally, this study recommends that LCC subbase thickness should not be thinner than 250 mm when using densities below 475 kg/m3 over weak subgrades.

Bond Performance of Corroded Steel Reinforcement and Recycled Coarse Aggregate Concrete after Freeze–Thaw Cycles

Freeze–thaw cycles and steel reinforcement corrosion can damage the properties of concrete structures in a frigid marine environment. In this paper, experimental and analytical research on the freeze–thaw resistance of recycled coarse aggregate concrete (RAC) and the bond performance of corroded steel reinforcement and RAC after freeze–thaw cycles was conducted. The results showed that the ultimate bond strength decreases with increasing freeze–thaw cycles and steel reinforcement corrosion rates, and the bond strength decreases more rapidly under the coupled effect of freeze–thaw cycles and steel reinforcement corrosion. Additionally, the quantitative analysis of the relationships between the ultimate bond strength and different freeze–thaw cycles and steel reinforcement corrosion rates was conducted through the relativity analysis, and analysis results revealed that freeze–thaw cycles have a more pronounced effect on the ultimate bond strength than steel reinforcement corrosion. A modified bond–slip prediction model of corroded steel reinforcement and RAC after freeze–thaw cycles was established, and the model exhibited better agreement with the test data of this and other research, demonstrating its rationality and applicability. These research results can provide experimental and analytical support for freeze–thaw-resistant design and bond performance prediction of RAC structures in a frigid marine environment.

Recent development in geopolymer concrete: A review

As a developing country, India is growing in all sectors, which leads to an extensive use of cement concrete. India stands second in production of cement globally; India’s overall cement production is increasing annually. The cement industry releases CO2 into the atmosphere, which contributes to global warming. Hence, it is necessary to resolve this problem by finding an alternative to cement concrete. Geopolymer concrete is proving to be a good alternative to replace ordinary cement concrete as it has high strength, lesser shrinkage, resistance against reinforcement corrosion, acid and sulfate resistance, freeze–thaw resistance, fire resistance and resistance to alkali-aggregate reaction. Geopolymer concrete emits less CO2 than Ordinary Portland Cement (OPC).Geopolymer concrete utilizes industrial waste materials in an effective way and ultimately aim to reduce the dumping problem of waste materials. Geopolymers are cementitious materials which can replace OPC entirely. This review article focuses on the use of different supplementary cementitious materials like Ground Granulated blast furnace slag (GGBS), fly ash, metakaolin, rice husk ash, silica fume, calcined clay for development of Geopolymer concrete and their effect on physical and mechanical properties. It is found that Geopolymer concrete with combination of different supplementary cementitious materials gives similar or superior fresh and mechanical properties than conventional cement concrete.

The geomechanical properties of soils treated with nanosilica particles

This study examines the effect of nanosilica (NS) additive to improve the mechanical properties of clay, clayey sand, and sand. The engineering properties of the soils were investigated through Atterberg limits, compaction, unconfined compression, ultrasonic pulse velocity (UPV), freeze-thaw, and direct shear tests. The NS content varied from 0% to 0.7% and cement content was 5% and 10% by the dry weight of the soil. The curing period varied from 7 d to 150 d. The consistency, compaction, and strength properties of the soils were affected by the presence of NS and cement. The optimum NS contents in clay specimens with 5% and 10% cement were 0.5% and 0.7%, respectively. It was 0.7% in sand specimens with both cement ratios, as well as 0.3% and 0.7% in clayey sand specimens with 5% and 10% cement, respectively. In terms of freeze-thaw resistance, clayey sand specimens containing 0.5% NS and 10% cement had the minimum strength loss. Exponential relationships existed between the ultrasonic pulse velocity (UPV) and the unconfined compressive strength (UCS) of soil specimens having the same curing period. The shear strength parameters of the soils also improved with the addition of NS. Scanning electron microscope (SEM) images demonstrated that cement and NS contributed to the improvement of the soils by producing a denser and more uniform structure. It was concluded that the minor addition of NS could potentially improve the geomechanical properties of the soils.

Modification of construction waste derived recycled aggregate via CO2 curing to enhance corrosive freeze-thaw durability of concrete

Although the utilization of construction waste derived recycled aggregate (CWDRA) has been reported as a promising way to reduce carbon emission and energy consumption for construction industry, the resistance of reinforced concrete containing CWDRA to corrosion and freeze-thaw (F-T) cycles are usually inferior than that containing natural aggregate. This study aims to provide a clean and efficient strategy (CO2 curing) for the modification of CWDRA to enhance corrosive F-T durability of such green concrete, and thus promote its application to marine or offshore structures under cold environment. Some experiments are conducted on specimens exposed to NaCl F-T cycles to verify the improvement effect of CO2 curing, including the mass loss, relative dynamic modulus of elasticity (RDME), mechanical properties, chloride migration coefficient (CMC) of plain concrete as well as the corrosion degradation of steel bar reinforced concrete. Results show that the concrete damage caused by NaCl F-T cycles can be significantly alleviated by CO2 treatment on CWDRA. The compressive and flexural strength of concrete after exposure to NaCl F-T cycles are enhanced by 40.1% and 25.9%, while the CMC value is reduced by 66.1%. Besides, incorporating CO2-cured CWDRA decreases the corrosion speed of reinforced concrete (by 42.4%) and particularly inhibits the progress of rust generation from steel bar (by 48.4%). The phase transformation inside material during CO2 curing makes the loose interface between mortar matrix and CWDRA grows to be rougher, which significantly promotes the improvement effect on the corrosive freeze-thaw resistance. Therefore, CO2 curing technology for CWDRA is highly recommended for the cleaner production of durable concrete in cold region offshore structures.

Utilization of raw coal gangue as coarse aggregates in pavement concrete

A large amount of raw coal gangue (RCG) is generated during coal mining, which results in serious environmental problems and vast land occupation. Considering the similarity between RCG and natural aggregates, the mechanical and durability behaviors of pavement concrete using raw coal gangue aggregate (RCGA) as coarse aggregates are investigated in this work. A total of 396 samples were produced with three RCGA ratios of 0%, 30% and 50% and two water-to-cement (w/c) ratios of 0.36 and 0.45. The fluidity, compressive, splitting tensile and flexural strengths, modulus of elasticity, abrasion, impermeability, as well as freeze–thaw resistance (waterandde-icing salt) of RCGA concrete were obtained, and the microstructures were analyzed to investigate the freeze–thaw damage to concrete. Experimental results indicated that the RCGA presented a negative influence on the mechanical and durability properties of concrete. The higher the RCGA content, the lower the strengths and elastic modulus, and the more the degradations of the abrasion, impermeability, and freeze–thaw resistance of concrete. In addition, the microstructures showed that the interfacial transition zone (ITZ) between RCGA and cement paste was the weak area of concrete. Results demonstrated that concrete containing 30% RCGA can be employed in the tertiary pavement under both freeze–thaw and deicing salt conditions following code JTG 3420-2020.

Research on the durability of nano-SiO2 and sodium silicate co-modified recycled coarse aggregate (RCA) concrete

Compared with natural aggregate (NA), recycled coarse aggregate (RCA) is of lower strength and higher porosity due to the attached mortar, which limits the application of RCA. In this paper, the nano SiO2-sodium silicate mixed solution (NMS) was prepared and used to modify RCA by improving the properties of the attached mortar. Three groups of concrete with NA, RCA, and modified RCA (MRCA), respectively, were prepared. The modification effects of NMS on the concrete were illustrated in regards to the mechanical properties and durability (impermeability, chloride ion resistance, and freezing-thawing resistance). Results indicated that the concrete with the MRCA had higher mechanical properties, better durability properties, and lower air void content. Then, the surface morphology of the MRCA and interfacial transition zone (ITZ) in concrete were both examined by scanning electron microscope (SEM) to understand the modification effect of NMS. It showed that the NMS can fill the pores and repair the cracks on the attached mortar by filling effect (brought by nano SiO2) and film-forming effect (brought by sodium silicate). Moreover, nano SiO2 and sodium silicate could also participate in secondary hydration reaction to form C-S-H gel and strengthen the microstructure of ITZ. The coupling effect both result in the improved mechanical and durable properties of the concrete prepared with MRCA.

The Effect of Expanded Glass and Crushed Expanded Polystyrene on the Performance Characteristics of Lightweight Concrete

This paper describes the production and performance characteristics of lightweight concrete (LWC) made from porous aggregates, such as expanded glass (EG), made from glass waste, and crushed expanded polystyrene waste (CEPW), obtained by crushing packaging waste from household appliances and ordinary Portland cement (OPC). During the study, the LWC density, thermal conductivity, compressive strength, bending strength, water absorption, deformations, composite structure, and freeze–thaw resistance were evaluated. By changing the amount of OPC and replacing part of the EG with CEPW, it was possible to reduce the thermal conductivity from 0.0977 to 0.0720 W/(mK). The presence of CEPW did not degrade compressive and bending strength or long-term water absorption of LWC. The influence of the amount of porous aggregates and OPC on the resistance to freezing and thawing was investigated by two methods. In one case, the freezing resistance was studied by the method of one-sided freezing of LWC structural indicators and, in the other case, the freezing resistance was determined by the decrease in compressive strength after 25, 100, and 200 freeze–thaw cycles. By modifying the structure with CEPW aggregate the durability of LWC products was increased and deformations were decreased.

Properties of super-thin layer mortar with recycled brick fines for sintered perforated block masonry

A super-thin layer of mortar with recycled brick fines (RBF) for sintered perforated block masonry was prepared. Six mortar mixtures were designed with different replacement ratios of RBF from 0 % to 50 %. The physical and mechanical properties were experimentally investigated, including compressive strength, tensile bond strength, freezethaw resistance, density, water preservation and thermal conductivity. When the RBF replacement ratio increased, the compressive strength of the mortar at 7 days, 28 days and 56 days showed an upward trend and reached its maximum value when the RBF replacement ratio was 40 %. However, when the replacement ratio of RBF was below 30 %, the tensile bond strength increased. With an increase in the RBF replacement ratio, the mass and strength loss of the mortar increased, and the thermal conductivity decreased. Furthermore, the SEM analysis results show that with an increase in the RBF replacement ratio, the microstructural characteristics of the mortar were more porous. The mechanical behavior of sintered perforated block masonry with the super-thin layer mortar was tested. The results indicated that the compressive and shear strengths of masonry were influenced by the daubing technology of super-thin layer mortar. The compressive strength and shear strength of masonry when using super-thin layer mortar daubed on both sides could reach 84% and 89%, respectively, of those with special high-cost mortar.

Study on Long Term Property of Soft Soil Solidified with Industrial Waste Residue and Regenerated Fine Aggregate

The long-term properties of solidified soft soil, including an immersion test, the dry-wet cycle and the freeze-thaw cycle, were systematically studied. Firstly, the immersion stability of solidified soft soil was confirmed. The appearance of soft soil solidified by a solidified agent and raw fine aggregate did not change significantly, and it was still intact without damage when the soaking time increased up to 28 d. Secondly, the mass and compressive strength loss of solidified soft soil were determined. When the number of dry-wet cycles was one, three, five and seven, the accumulated-mass loss rate was 1.4%, 3.0%, 4.5% and 6.0%, respectively, and the compressive-strength loss rate was -10.3%, 13.9%, 41.2% and 53.6%, respectively. Compared with solidified soft soil under standard curing environments, solidified soft soil after seven dry-wet cycles showed small cracks, and the structural compactness began to decline. Finally, the influence of the freeze-thaw cycle on the mass, compressive strength and microstructure of solidified soft soil was confirmed. When the number of freeze-thaw cycles was 5, 10, 15 and 20, the accumulated-mass loss rate was 12.6%, 16.7%, 17.9% and 18.8%, respectively. The microstructure of the solidified soft soil was damaged, and the increase in porosity was the main reason for its strength reduction or even failure. Nevertheless, soft soil with a solidified agent and recycled fine aggregate had no obvious damage to the microstructure, and the freeze-thaw resistance was relatively superior.

Combined effect of using steel fibers and demolition waste aggregates on the performance of fly ash/slag based geopolymer concrete

Developing sustainable construction products has been showing a rising trend recently. Geopolymer composites are remarkable binding materials fabricated based on recycling and sustainability. In this paper, an experimental investigation was conducted to study some mechanical and durability characteristics of steel fiber-reinforced fly ash/slag-based geopolymer concrete (GPC) with different proportions of recycled coarse aggregate. Steel fiber-reinforced geopolymer concrete mixtures incorporating recycled coarse aggregates of up to 40% at the interval of 10% were prepared, and the mixtures without recycled coarse aggregate were used as reference samples. The steel fiber ratio of 0.3% and 0.6% were used and the combined effect of steel fiber and recycled coarse aggregate on the geopolymer composites’ behavior regarding strength properties, sulfate resistance, elevated temperature resistance, abrasion resistance, and freezing-thawing resistance was addressed. A significant improvement in strength properties was observed in steel fiber reinforced recycled aggregate geopolymer concrete with increasing fiber content; however, the strength properties of geopolymer concrete were decreased with the increase of recycled coarse aggregate amount. Also, the properties such as abrasion resistance, resistance to elevated temperature, sulfate resistance, and freeze-thaw resistance were improved with the addition of steel fiber. It indicates that the synergetic effect of steel fiber and recycled aggregate helps to produce ecologically sound geopolymer concrete with good engineering properties and durability characteristics that will bring sustainability to the concrete sector. Generally, the results show that the recycled coarse aggregate ratio of up to 30% and 0.6% of steel fiber can be considered an ideal combination to make geopolymer concrete with better overall properties.

Microstructure, deformation and durability of high-strength non-steam-cured concrete with C-S-H seed

The effect of the early strength agent named calcium silicate hydrate polycarboxylate ether nanocomposite (C-S-H seed), fly ash and slag on the development of microstructure, autogenous deformation and durability, as well as the mechanism of interaction between microscopic (e.g., pore structure) and macroscopic properties of concrete, were investigated. Results showed that C-S-H seed increased the compressive strength of concrete before 7 d. The addition of C-S-H seed decreased both relative humidity and capillary pore diameter due to rapid hydration, which resulted in high negative capillary pressure and autogenous deformation of up to 40%. The higher fly ash and slag contents decreased early-age autogenous deformation. Further analysis showed that the addition of C-S-H seed decreased the percentage of pores>1000 nm and the most probable pore diameter of concrete, thus increasing resistance to chloride migration into concrete. The chloride diffusion coefficient was linearly related to the amount of cementitious material together with the water-to-binder ratio. The C-S-H seed decreased the availability of pores of critical diameter (14 nm) of concrete exposed to water freezing, leading to an increase in the freeze–thaw resistance of concrete. In addition, the C-S-H seed also reduced the overall porosity of concrete, leading to an increase in resistance to sulfate attack. Similar trends were observed for increased fly ash and slag content. Besides, the concentrations of AP and Ca2+ significantly affected sulfate resistance.

Study on the Effect of Supplementary Cementitious Material on the Regeneration Performance of Waste Fresh Concrete

In the preparation of ready-mixed concrete, it is inevitable to produce waste fresh concrete (WFC). An efficient, low-cost and environmentally friendly recycling scheme is the key to WFC recycling. In this work, we directly added some unhardened WFC to fresh concrete to prepare recycled fresh concrete (RFC); on this basis, fly ash (FA) and nano-silica (NS) were added as supplementary cementitious material (SCM) to obtain modified recycled fresh concrete (RFC-SF). Then, the mechanical properties, slump, freeze–thaw resistance, phase structure of the hydration products and hydration process in RFC were studied. The results show that the addition of FA and NS significantly improved the comprehensive performance of RFC. Compared with RFC, the compressive strength of RFC-SF with 15% FA and 3% NS increased by 15.2% and 50.3% at 7 d and 90 d, respectively, and the splitting tensile strength increased by 20.5% and 76.4%, respectively. The slump remained above 155 mm, and the mass loss rate decreased by 42.6% after freeze–thaw cycles. XRD and FTIR analysis showed that the addition of FA and NS accelerated the hydration reaction process of RFC-SF, reduced the content of calcium hydroxide (CH) and refined the grain size of CH. RFC-SF had a denser microstructure and a lower calcium-silicon ratio in SEM and EDS tests.

Freeze-thaw resistance of cement-stabilized gangue bonding materials: Effects of an ionic stabilizer

To enhance the frost resistance of cement-stabilized gangue bonding material (CSG) in road subgrade engineering, an ionic stabilizer (ICS) was added to CSG. Then, the effects of ICS on the compression resistance and freeze–thaw resistance of CSG were investigated. And the effects of ICS on the pore structure and hydration products of the CSG were analyzed by mercury intrusion porosimetry, X-ray diffraction, Fourier transform infrared spectroscopy and thermogravimetric analysis. Finally, the mechanism of action was verified by Scanning Electron Microscopy. In addition, the fractal characteristics of the pore structure of the CSG were investigated, and the pore structure characteristics and the compressive and freeze–thaw resistance properties were related. The results showed that at a short curing age, the ICS incorporation accelerated the hydration reaction rate of cement, promoted the formation of hydration products, reduced the percentage of harmful pores in the CSG, and improved the early strength and freeze–thaw resistance of the CSG. At a long curing age, the ICS incorporation increased the polymerization of silicate gel and reduced the spacing of gangue particles, which thus improved the final strength and freeze–thaw resistance of the CSG. In addition, the pore structures of the CSG under different curing ages had fractal characteristics, and t The fractal dimension provides a better and convenient demonstration of the compressive properties and freeze–thaw resistance of CSG.

How nano-bubble water and nano-silica affect the air-voids characteristics and freeze-thaw resistance of air-entrained cementitious materials at low atmospheric pressure?

With more infrastructures being built in plateau regions, low atmospheric pressure is put forward as a new factor affecting the mechanical properties and durability of cementitious materials, but its influence is inconclusive, and the failure of freeze-thaw has not been effectively solved. This research explored the influences of both nano-bubble water (NBW) and nano-silica (NS) on air-voids characteristics and freeze-thaw resistance of cementitious materials formed and cured at different air pressure (0.4P, 0.7P, P; P=1atm); and investigated the effects and its mechanisms of low air pressure on performances of cementitious materials. The air-voids structure analyser, SEM, XRD and TG-DSC were employed to evaluate the microstructure and cement hydration of hardened cement paste samples. Results show that low-pressure samples have abnormal air-void parameters and poor bubble stability, which lead to a decrease in freeze-thaw resistance. It is proved that both NBW and NS can improve the freeze-thaw resistance and mechanical strength of samples at low atmospheric pressure by accelerating cement hydration, enhancing bubble stability, and optimizing air-voids parameters. The mechanisms of low pressure, NBW and NS on properties of cementitious materials are expounded. This research proposes new perspectives for improving the durability of air-entrained cementitious materials in plateau and enables us to further comprehend the effects and principles of low air pressure on performances of cementitious materials.