Type Of Cementitious Material Research Articles

Experimental study on the mechanical properties of non-reinforced UHPC element under biaxial stress states

The ultra high performance concrete (UHPC) has been gradually applied in bridge and building engineering to replace normal concrete as a new type of cementitious material. The biaxial strength criteria of UHPC play an essential role in engineering design and research. However, the experimental research on biaxial strength of UHPC is still lacking. In this study, four groups of biaxial loading tests on UHPC planar elements were carried out, using the Planar Bi-directional Element Tester (PBET) developed by Tsinghua University, including biaxial compressive test, biaxial tensile test, biaxial tension-compression sequential test, and biaxial tension-compression proportional test. The biaxial stress ratio is also studied as a key parameter. Based on the test results, the typical failure modes under different biaxial loading conditions as well as the biaxial strength criteria of UHPC are revealed. Taking the biaxial strength criteria of normal concrete as a reference, the complete biaxial strength envelope equations of UHPC are finally derived.

Perforated cenospheres used to enhance the engineering performance of high-performance cement-slag-limestone ternary binder

Slag-limestone-cement ternary mixed binder is a new type of cementitious material. There are 1137 published literatures on this new type of cementitious material in the Scopus database, but so far, no papers have been published on the research of reactive internal curing of this new type of cementitious material. One kind of fly ash is called a cenosphere with a very thin outer shell and a hollow center. Cenospheres generate pores through chemical etching, thereby achieving the effect of self-curing. This article conducted multiple experimental studies to ascertain the impact of perforated cenospheres regarding the execution of cement-slag-limestone binder. The mixture samples with different dosage of perforated cenospheres and cenospheres are numbered C0 (control group), P3.3 (content of perforated cenospheres in the binder is 3.3 %), P6.6 (content of perforated cenospheres in the binder is 6.6 %), and C6.6 (content of perforated cenospheres in the binder is 6.6 %). Based on the results of autogenous shrinkage and compressive strength, perforated cenospheres as an internal curing agent not only reduces the autogenous shrinkage of cement-slag-limestone concrete, but also avoids a significant decrease in strength of cement-slag-limestone concrete. In fact, because of volcanic ash reactivity of advanced cenospheres and the internal curing effect, the compressive strength of P3.3 mixed mortar increased by 0.7 and 4 MPa compared to C0 mixed mortar at 7 and 28 days of age, achieving a dual effect of reducing shrinkage and improving strength. Secondly, the experimental results of Fourier transform infrared spectroscopy and X-ray diffraction showed that perforated cenospheres can undergo volcanic ash reaction with calcium hydroxide. The scanning electron microscope images indicate that the P3.3 and P6.6 mixed paste with added perforated cenospheres exhibit better and denser bonding between the perforated cenospheres and the matrix. In summary, the microscopic reactions of perforated cenospheres can enhance concrete's macroscopic qualities, which can be utilized as reactive internal curing materials.

Comparative Studies on In-Plane Shear Behavior of Masonry Wallettes Retrofitted with Mortar, UHPC, and ECC Ferrocement: Shotcrete and Prefabricated Panels

Masonry walls, prevalent in many historical and contemporary structures, often require retrofitting to meet modern safety and performance standards. Motivated by the need for efficient and reliable retrofitting solutions, this research investigates the potential of various types of ferrocement, reinforced with high-strength steel meshes, to enhance the in-plane shear behavior of brick masonry walls. Through rigorous diagonal compression tests on nine masonry wallettes, the study evaluated the performance of ferrocement overlays in terms of overlay configuration (asymmetric or symmetric), cementitious material type (mortar, ECC, or UHPC), the presence or absence of steel mesh, and construction method (shotcrete or prefabricated panels). The results indicated that UHPC and ECC overlays significantly enhanced post-cracking deformation capacity. Compared to the asymmetric retrofit, the symmetric retrofit led to more uniform deformation in the retrofitted wallette, effectively improving the maximum shear by up to 119 %. While UHPC shotcrete was more effective in improving the shear strength, ECC shotcrete led to the highest rupture shear strain and pseudo-ductility for the retrofitted wallette, reaching 0.83 % and 17.2, respectively. Moreover, although steel mesh inclusion in the ferrocement overlay was crucial in enhancing post-peak ductility, its impact on shear strength of the retrofitted wallettes was minimal. The test results also demonstrated that the developed prefabricated UHPC panels emerged as an effective retrofitting solution to simultaneously improve the strength, deformation capacity, and ductility for masonry wallettes. In addition to the experimental investigation, a new strength model, accounting for various key design variables, was developed, offering reliable shear strength predictions for the retrofitted wallettes.

Study on impact resistance performance of MSWIFA-based low-carbon fiber-reinforced concrete

The accumulation of carbide slag (CS), red mud (RM), and municipal solid waste incineration fly ash (MSWIFA) has led to significant environmental pollution issues, necessitating urgent resource utilization. Building upon the previously developed CS-MSWIFA synergistic activation RM-slag cementitious system, this study aims to further incorporate iron tailings sand and polypropylene fibers to prepare fiber-reinforced concrete. The systematic investigation focuses on the influence of cementitious material types, aggregate types, fiber shapes, lengths, and dosages on the impact resistance of concrete. Furthermore, an impact damage evolution equation and life prediction model were developed based on the two-parameter Weibull distribution. Results indicate that the type of cementitious material and aggregate has minimal influence on the impact resistance of concrete, while the addition of fibers significantly enhances its impact resistance, shifting the failure mode from brittle to ductile. Mesh polypropylene fibers with a length of 12 mm and a volume dosage of 1.0 % demonstrate excellent impact resistance, with initial and final crack numbers reaching 78 and 105, respectively. This represents an increase of 136.4 % and 200.0 % compared to the control concrete without fibers. The findings of this study offer new avenues for the resource utilization of solid waste and provide theoretical foundations and technical support for the potential application of solid waste based fiber-reinforced concrete in structural engineering.

Study on the Effect of Fly Ash on Mechanical Properties and Seawater Freeze–Thaw Resistance of Seawater Sea Sand Concrete

When using seawater and sea sand as mixes, the mechanical properties and durability of concrete are adversely affected because the raw materials themselves contain harmful ions. Fly ash is the tailings formed in the process of industrial production, the use of which does not require the burning of clinker, reducing CO2 emissions. Moreover, it belongs to a new type of cementitious materials with low emissions and high environmental protection. Fly ash enhances the properties of concrete and reduces the effect of harmful ions on concrete. Based on the above considerations, the corresponding specimens were prepared and subjected to cubic compressive strength, flexural strength, and seawater freezing and thawing resistance tests by using fly ash admixture as the main variable. A combination of macro-analysis and micro-analysis was used to investigate the effect of fly ash on the performance of seawater sea sand concrete. The results showed that fly ash significantly enhanced the mechanical properties and resistance to seawater freezing and thawing of seawater sea sand concrete. The best improvement in compressive strength and resistance to seawater freezing and thawing was achieved at a substitution rate of 20%. The maximum increase in compressive strength was 13.22%. The maximum reduction in mass loss rate was 57.26% and the strength loss rate was 43.14% after the specimens were subjected to seawater freezing and thawing 75 times. The maximum enhancement in flexural strength was 17.06% for a substitution rate of 10%. Through microanalysis, it can be seen that the incorporation of coal ash can enhance the compactness of concrete through the microaggregate effect as well as the volcanic ash reaction to promote the secondary hydration reaction, so as to strengthen the seawater freeze–thaw resistance of seawater sea sand concrete. Finally, the damage prediction model established using the mean GM (1, 1) model of gray system theory meets the requirements of the first level of prediction accuracy and can accurately predict the damage of seawater sea sand concrete under seawater freezing and thawing.

Experimental and numerical simulation studies of electrical resistance of cementitious materials under varying temperature history

Many in-service concrete structures are normally exposed to varying temperature condition. The time-dependent and non-uniform temperature distribution in concrete structures could affect the accurate assessment of their electrical properties. Therefore, the influences of temperature change over time and the spatial variation in temperature on the measured electrical resistance of cementitious materials are still in need of investigation. The coupled thermal-electrical responses of two types of cementitious materials under varying temperature history were investigated by a series of thermal and electrical tests in this study. Then a coupled thermal-electrical finite element (FE) model was developed to simulate the coupled thermal-electrical responses. The results show that the input direct current has a minor effect on the measured electrical resistance by embedded four-probe method and the specimen temperature when it is no greater than 3 mA. The relationship between the measured temperature at 10-mm depth of the specimen and the apparent resistance is well captured by a linear equation. The coupled thermal-electrical finite element model can predict well the developments of specimen temperature and apparent electrical resistance under varying temperature history. The FE results reveal that the non-uniform temperature variation results in the redistribution of electrical current within the tested specimen. However, electrical field between the two inner electrodes is always uniform when the embedded four-probe method is used, which is not affected by the non-uniform temperature variation.

Study on the preparation, performance, and mechanism for solid waste cementitious materials

Using granulated blast furnace slag (GGBS) as the volcanic ash material and fly ash (FA) as the supplementary material, the study was conducted to investigate the mix proportions of an alkali-activated solid waste cementitious material under the stimulating effect of alkali activator carbide slag (CS). This type of cementitious material could serve as a substitute for a portion of cement usage, contributing to resource conservation and mitigating environmental pollution caused by solid waste. This facilitates green and sustainable development. Firstly, an analysis of three raw materials was conducted, and the mix proportions were designed with reference to the CaO-Al2O3-SiO2 system of Portland cement. Then 28 groups of specimens were prepared based on the designed mix proportions. The flowability and setting time of each group of specimens were tested. It was observed that an increase in the amount of CS and a decrease in the amount of GGBS resulted in decreased flowability and earlier setting times of the specimens. Additionally, FA exhibited a retarding effect on setting time. Compressive strength tests were conducted on these specimens, revealing that the optimal CS content ranged between 20 % and 40 %. Overall, FA had minimal impact on compressive strength, but it contributed to increased compressive strength in the specimens at later ages. Subsequently, microscopic characterization of the hydration products was performed using X-ray Diffraction (XRD), Fourier Transform Infrared (FTIR), Differential Thermal Analysis (DTA), Scanning Electron Microscope (SEM), and Energy Dispersive Spectrometer (EDS). The hydration products were identified as predominantly composed of calcium silicate hydrate. The quality and defects in the microstructure of gel products from various specimen formulations were compared to elucidate differences in macroscopic performance. Finally, the hydration process mechanism diagram of alkali-activated materials was presented to illustrate the stimulation and formation of gel products, primarily composed of C-S-H. This diagram revealed the principles behind the action of alkali-activated cementitious materials. The proposed design and testing methodology for the GGBS-FA-CS system in this study had certain reference significance for research in the direction of alkali-activated solid waste cementitious materials.

Determination of engineering properties of cementitiously stabilised aggregates using ultrasonic pulse velocity

Non-destructive testing methods, such as Ultrasonic Pulse Velocity (UPV), have been widely used to assess the quality and performance of cementitious stabilised aggregates. The present study reveals the robust relationship of UPV and constrained modulus (CM) with unconfined compressive strength (UCS), modulus of rupture/flexural strength (MoR), and flexural modulus (FM) in aggregates stabilised with five different stabiliser combinations, including cement, cement-ground granulated blast furnace steel slag (GGBS), cement-fly ash and cement with two commercial chemical admixtures. The high accuracy of UPV and CM in estimating destructive test parameters and approximating challenging tests like FM is convincingly demonstrated with strong correlations (R² > 0.80) and standard error ratios (Se /Sy < 0.35). Power law and logarithmic curves prove suitable for modelling the relationships between strength and stiffness with UPV and CM, respectively. Notably, however, the study reveals significant variations in correlating parameters across different cementitious stabilisers within the same mix design, emphasising the strong dependence on the specific cementitious material type. Overall, this work offers valuable insights into the use of non-destructive parameters, UPV and CM, for the characterisation of stabilised aggregates based on cementitious material type and different curing conditions.

Effect of sulfate on the compatibility between polycarboxylate superplasticizer and cement-based materials with or without silica fume

Polycarboxylate superplasticizer (PCE) is a crucial raw material used for preparing concrete. However, there has always been a compatibility issue between PCE and different types of cementitious materials due to their varying qualities. In concrete raw materials, the types and contents of sulfates have a significant impact on compatibility, and it is well-established that a competitive adsorption exists between PCE and sulfate ions solubilized in the interstitial solution of cement paste, which may cause a loss of the dispersing properties. However, previous studies focused on the effect of sulfate on the compatibility between PCE and cement, and there was a lack of research on silica fume. In this study, the workability of fresh cement and cement-silica fume paste and the mechanical properties of harden mortar were evaluated in the presence of different concentrations of five types of sulfates (Na2SO4, K2SO4, MgSO4, KAl(SO4)2, and CaSO4·2H2O) added in aqueous solution. The results show that soluble sulfates have a more adverse effect on the compatibility between PCE and cement-based materials with or without silica fume than slightly sulfate. And the effects of different sulfates on saturation points of PCE in cementitious materials and the mechanical properties of cement and cement-silica fume mortar are various. Finally, it is important to note that a high sulfate content in the solution can lead to salt precipitation of PCE, which is highly undesirable.

Effect of silt modification on the properties of magnesium phosphate cement

Magnesium phosphate cement (MPC), as a new type of cementitious material, is difficult to be popularized in practical applications due to its short setting time, high cost, and poor water resistance. Dredged silt (DS) is a kind of hazardous waste, which may cause serious damage to the ecological environment if it is not disposed of properly. The treatment of DS and its reuse in building materials is an economical and environmentally friendly treatment method, which not only realizes the recycling of DS but also avoids secondary pollution. Using the treated DS as a mineral admixture for modified MPC not only recycles the DS but also improves the properties of MPC. In this paper, the effect of DS modification on the properties of MPC was investigated by setting time test, mechanical property test, water resistance test, and RCM test, and also compared with the modification effect of common mineral admixtures, such as fly ash (FA) and metakaolin (Mk), and finally analyzed by combining with SEM pictures. With the increase of the dosage of FA, Mk, and DS, the compressive strength of the modified MPC all showed the trend of increasing and then decreasing, and the optimal dosage was 5%, 10%, and 15%, respectively. At the optimum dosage, Mk and FA could improve the resistance of MPC to chloride erosion, but DS could not. The three kinds of admixtures could prolong the setting time of MPC, with DS having the best effect, followed by FA, and Mk having the smallest effect. All three admixtures could improve the water resistance of MPC, and the effect of improvement was Mk &amp;gt; DS &amp;gt; FA. The microstructure of the specimen was denser when the dosage of DS was low, and when the dosage was too much, the hydration reaction of MPC was affected, resulting in incomplete hydration and reduced hydration products. This research has significant guiding significance for the treatment of DS and the modification of MPC.

Geopolymer vs ordinary portland cement: review of the 3-d printing of concrete

Due to the need of the construction industry to implement structures with special and complex designs, mass customization with the lowest cost, especially reducing the labor cost as well as the amount of waste and materials used, the use of concrete 3D printing can be the appropriate solution to these requirements fulfill these options. As a result, a comprehensive and practical study of the major 3D printing methods and their development in the construction industry was carried out in this study. In addition, the use of OPC-based materials and geopolymer-based materials was reviewed and compared due to the development of the materials industry and the advantages and disadvantages of using different types of cementitious materials in the 3D printing of concrete.

Recent development on optimization of bio-cementation for soil stabilization and wind erosion control

This paper reviews and analyzes recent research development on bio-cementation for soil stabilization and wind erosion control. Bio-cement is a type of cementitious materials by adopting natural biological processes for geotechnical and construction applications. Bio-cementation is usually achieved through microbially- or enzyme-induced carbonate precipitation (MICP or EICP). The use of soybean urease can be a cost-effective solution for carbonate precipitation and bio-cementation, which is named SICP. The produced calcium carbonate can cement soil particles and bring considerable strength improvement to soils. In this paper, the mechanisms and recent development on the technology optimization are reviewed first. The optimization of bio-cementation involves 1) altering the treatment materials and procedures such as using lysed cells, low pH, the salting-out technique; and 2) using cheap and waste materials for bio-cement treatment and bacterial cultivation. The objectives are to improve treatment uniformity and efficiency, use bio-cement in more scenarios such as fine-grain soils, and reduce costs and environmental impacts, etc. Studies on the mechanical behaviour and wind erosion performances of bio-cemented soil show that the wind erosion resistance can be improved significantly through the bio-cement treatment. In addition, the use of optimized method and additives such as xanthan gum and fibers can further enhance the strength, treatment uniformity or ductility of the bio-cemented soils. Attention should be paid to wind forces with saltating particles which have much stronger destructive effect than pure wind, which should be considered in laboratory tests. Field studies indicate that bio-cement can improve soil surface strength and wind erosion resistances effectively. Besides, local plants can germinate and grow on bio-cemented soil ground with low-concentration treatments.

A comprehensive review on the properties of engineered cementitious composite with a self- healing material

The most common types of cementitious materials used as building materials can be found all over the world. The fact remains, however, that deterioration is unavoidable right from the start of the service life, which is followed by maintenance and repair work. Since the cementitious materials have been observed to exhibit a self-healing phenomenon, which has been the subject of research for quite some time. This paper is focused on the review of the feasibility of (Engineered Cementitious Composite) ECC and its properties such as mechanical, physical, rheological, and chemical properties. ECC is considered to have a high self-healing potential and superior mechanical and durability performance. Self-healing concrete is typically employed for the purpose of minimizing cracks in concrete and enhancing the material's overall durability. These mechanisms are reviewed based on extensive experimental studies and practical experience. Self-healing concretes are typically employed for the purpose of mending cracks in concrete and enhancing the material's overall durability. There are many distinct varieties of self-healing processes, including natural, chemical, and biological ones. Studies were conducted with a primary emphasis on biological processes that are dependent on precipitation. In order to study the properties of self-healing with ECC, a transmission electron microscope (TEM), an environmental scanning electron microscope-energy dispersive spectroscopy system (ESEM-EDS), Fourier transform infrared spectroscopy, and X Ray Diffraction (XRD) were all implemented. To further understand the properties of self-healing, this research was conducted. This review offers a fresh perspective on the research done on the topic of treating unexpected cracking in concrete through the use of a self-healing process.

Hydration characteristics, hydration products and microstructure of reactive powder concrete

Reactive Powder Concrete (RPC) is a new type of cementitious materials with a complex hydration mechanism, and active admixtures greatly influence the hydration reaction, formation of hydration products, and evolution of microstructure. In order to comprehensively study the quantitative effects of active admixtures contents, namely silica fume, slag and fly ash, on hydration characteristics, hydration products, and microstructure of RPCs, tests of workability, setting time, electrical conductivity, bound water and mechanical properties were conducted. Furthermore, a series of properties including morphology and micro-structure characteristics of RPCs were analyzed by thermogravimetric (TG) analysis, X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), mercury intrusion porosimetry (MIP), Brunauer-Emmet-Teller (BET), and scanning electron microscope (SEM). The results indicate that the initial hydration reaction rate of RPCs is reduced by partly replacing cement with active admixtures. The pozzolanic effect created by the active admixtures enhances hydration and improves RPC's compressive and flexural strength. RPCs made of cement-silica fume mixture exhibit the best macroscopic properties. The adoption of silica fume promotes the production of C–S–H gel during hydration and exerts pozzolanic and crystal nucleation effects to promote cement hydration. RPCs made of pure cement exhibit 15.3% porosity after 28 days of hydration, with the largest proportion of less harmful pores in the microstructure. The porosity is reduced to 5.2% when cement is partially replaced with silica fume, and the microstructure is dominated by harmless pores. When replacement of silica fume is kept at 25%, using slag powder or fly ash substitute part of cement also reduces the number of less harmful pores. It is beneficial to add slag powder to increase the number of gel pores, whereas fly ash reduces the number of gel pores. The investigation presented in this paper would contribute to the production of low cost and environmentally-friendly RPCs, and accelerate the wider applications of ultra-high performance concrete (UHPC) in engineering structures.

Cyclic Behaviors of Geopolymeric Recycled Brick Aggregate Concrete-Filled Steel Tubular Column

Incorporating geopolymeric recycled brick aggregate concrete into steel tubes provides a promising solution to reduce environmental impact of construction and demolition waste. In this paper, geopolymeric recycled brick aggregate concrete-filled steel tubular column (GRBACFST) was developed to improve the environmental sustainability of composite column. Considering the replacement ratio of recycled brick aggregate (RBA), the thickness of the steel tube, type of cementitious materials and the axial compression ratio as the variation parameters, experimental research was performed to explore the cyclic behavior of GRBACFST columns, including the failure mode, bearing capacity, hysteresis curve, ductility and degradation characteristics. Results demonstrated that the failure of GRBACFST columns occurred in the region at column bottom, with the bulge of steel tube and crush of geopolymeric recycled brick aggregate concrete. The proposed GRBACFST columns exhibited favorable hysteretic behaviors with desired bearing capacity, excellent ductility, and energy dissipation behavior, which were enhanced by the increased thickness of the steel tube. The bearing capacity and ductility were reduced with the increase of axial compression ratio, while enhanced with thicker steel tube. Moreover, the degradation of stiffness and strength was more obvious under larger axial compression ratio. The increase of replacement ratio of RBA caused a significant reduction of bearing capacity, while it had few effect on the hysteretic index. It was concluded that the hysteretic behavior of proposed GRBACFST column was not sensitive to the types of cementitious material and geopolymers could serve as an eco-friendly binder for concrete.

Effects of various curing methods on the compressive strength and microstructure of blast furnace slag-fly ash-based cementitious material activated by alkaline solid wastes

The large-scale stacking of alkaline industrial solid wastes such as soda residue (SR) and calcium carbide residue (CCR) has caused serious environmental problems. Therefore, a new type of cementitious material was developed in our previous study by using SR-CCR synergistically activated blast furnace slag (BFS)-fly ash (FA), which abbreviated as SCBF. This paper further studied the effects of various curing methods on the compressive strength and microstructure of SCBF, which was expected to provide guidance for its application in the field of non-reinforced products such as baking-free brick. The results show that the optimal curing scheme was heat curing at 75 °C for 12 h. The optimal scheme significantly promoted an early hydration reaction and provided the 3d/28d strength values of 16.4/24.7 MPa, exceeding those of room-temperature (RT) sealed curing and water curing by 154/24.5 % and 264/31 %, respectively. Besides, the optimal scheme accelerated the formation of CSH gel, Hydrotalcite (6MgO·Al2O3·CO2·12H2O), Hydrocalumite (3CaO·Al2O3·CaCl2·10H2O), and other crystal products, as well as increased the consolidation rate of chlorine ion from 37.9 % (in RT sealed curing) to 64.3 %. These hydration products were evenly distributed, effectively filling the pores and reducing the macroporosity from 9.30 (in RT sealed curing) to 1.54 %, thus improving the early and later-age strength. Too high curing temperature (exceeding 75 ℃) or prolong heat curing period (exceeding 12 h) would cause microstructure deterioration, significantly increase the number of macropores and microcracks in the matrix, ultimately leading to strength retrogression.

Application of molten iron desulfurization slag to replace steel slag as an alkaline component in solid waste-based cementitious materials

Desulfurization slag (DS), generated from molten iron pre-desulfurization process, has a high alkalinity that may cause seriously environmental issues. To solve the DS-disposal problem, this research proposes a new type of cementitious material composited of DS, ground granulated blast furnace slag (GGBS), steel slag (SS), and flue gas desulfurization gypsum (FGDG). The effects of DS on cementitious material were studied by testing the working performance indexes such as mortar fluidity and compressive strength, and the microscopic analysis such as XRD, TG and SEM. The results show that DS reduces the fluidity of the mortar, and significantly improves compressive strength of 3 days. The optimal ratio of DS/SS ratio in the GGBS–SS–DS–FGDG cementitious material is 1.0, and its compressive strength of 3 days and 28 days reached 24.6 and 52 MPa, respectively. The 3 days’ compressive strength of GGBS-SS-DS-FGDG is 748% higher than that of GGBS–SS–FGDG. The high alkalinity of DS promotes the dissociation of GGBS, and enhances the early hydration rate, which shortened the hydration induction period, and enhanced the cumulative released heat. Also, DS promotes the formation of ettringite (AFt) and increases the polymerization degree of the C–(A)–S–H gel at early stage. However, cementitious material containing DS has high porosity, which can be offset by the gel pores generated by SS. In summary, the GGBS–SS–DS–FGDG as a cementitious material with low carbon emission may be used to replace cement. The results of this paper can guide the large-scale and comprehensive utilization of DS with other solid waste.

Compressive strength of cemented soil in pre-bored grouted planted piles under negative temperature environment

As a new type of pile, if the pre-bored grouted planted nodular (PGPN) pile can be successfully applied to the permafrost engineering, it will have significant economic and ecological values. However, the law of strength development of cemented soil of PGPN pile under warm permafrost environment is still unclear. In this study, the strength characteristics of cemented soil were examined through unconfined compressive strength test, and factors such as the curing time at negative temperature, the types of cementitious materials, and the dosages of cement and early strength agent (ESA) were considered. The experimental results indicate thatthe cemented soil with sulpho aluminate cement (SAC) and Ordinary Portland cement (OPC) + ESA as cementitious materials show high strength and stable performance. In addition, the Reasonable dosages of the cement and ESA were suggested, respectively.

Theoretical modification of the laboratory-determined tensile stress–strain relationship of strain hardening cementitious composites (SHCCs) for large-scale specimens

Strain hardening cementitious composites (SHCCs) are a type of cementitious material reinforced with randomly distributed short fibers that exhibit tensile strain hardening behavior and prominent crack resistance. The tensile behavior of SHCCs could be significantly affected by the distribution of the fiber orientation. In large-scale specimens, the distribution of the fiber orientation is close to ideal three-dimensional uniform random distribution. However, fiber orientation distributions in laboratory SHCC specimens are influenced by the specimen dimensions (width and thickness) and casting process, resulting in neither ideal two-dimensional nor three-dimensional uniform random distribution. Therefore, the performance of large-scale SHCC specimens may be overestimated in analysis when directly using the tensile properties of SHCCs obtained from uniaxial tensile tests of small specimens. Since the uniaxial tensile tests of large-scale SHCC specimens are difficult to be conducted, theoretical evaluation of the tensile properties of mass SHCCs in large-scale specimens were conducted by modifying the uniaxial tensile test results of small specimens. In this paper, closed-form probability distribution models for fiber orientations that consider the influence of the specimen width and thickness were theoretically derived. The effects of the specimen width and thickness on the tensile properties of SHCCs were studied by applying the proposed method to the uniaxial tensile numerical model of SHCCs, while uniaxial tensile specimens with two different geometries and dimensions were tested for verification. Both the analytical and experimental results showed that, within a certain range, the width and thickness of the specimens significantly influenced their ultimate tensile strength and ultimate tensile strain. To relate the uniaxial tensile test results of laboratory-sized specimens to that of mass SHCC in large scale specimens, reduction factors for the stress–strain relationship of SHCCs obtained by traditional tensile test specimens were proposed to account for the specimen size effect based on the model analysis. The reduced tensile stress–strain relationship was applied to a finite element model of SHCC beams under four-point bending tests. It was found that the finite element analysis results obtained by using the reduced tension stress–strain relationship are in better agreement with the test results.

Enhanced mechanical properties and environmental erosion resistance with metakaolin in a kind of Chinese traditional Lime-based mortar

The Leshan Giant Buddha, which is located in Sichuan province, China, is the world’s tallest cliff statues (71 m). Due to the deterioration of the sandstone, conservation works have been carried out in past decades, and lime-based mortars have been used to repair the buddha for several times. Chuihui is a type of cementitious material used for the conservation of the Leshan Giant Buddha in 2001, but it has exhibited some deterioration due to multiple factors. In this study, metakaolin was used to enhance the volume stability, mechanical properties and environmental erosion resistance of traditional Chuihui. The results of XRD, FT-IR and Raman analyses demonstrate that metakaolin reacts with Ca(OH)2 via pozzolanic reactions and the produced C-S-H bond improves the properties of Chuihui-Metakaolin (C-M) mortars. Additionally, the microstructure of mortars becomes more compact due to the formation of cross-linked microstructures.