Mechanical Properties Of Cement-based Materials Research Articles

Research and Development of New Polylactic Acid (PLA) Fiber Concrete Materials and Performance Research

Polylactic acid (PLA) fiber concrete has broad application prospects in the field of building materials. This article summarizes the current research status of fiber-reinforced concrete and its importance in improving the mechanical properties of cement-based materials. In view of the modification of the physical properties of PLA fiber, experimental research is conducted to improve its mechanical properties, solve the problem of natural degradation, and explore the application of anti-corrosion materials. In terms of concrete preparation technology, experiments were carried out to study uneven fiber distribution and compatibility with cement slurry to determine the optimal proportion and processing technology. Mechanical property tests and theoretical studies have shown that fiber type and length have a significant impact on the performance of concrete, and it is necessary to further explore the mechanical properties of the transition zone between the fiber and the concrete matrix. Aiming at the durability, fire resistance and other issues of PLA fiber concrete, relevant experimental research plans were proposed. Finally, the mechanical properties of ultra-high toughness PLA fiber concrete were optimized by improving the mix design, optimizing fiber type and dosage, and surface treatment technology. These research results provide an important reference for the wide application of ultra-high toughness PLA fiber concrete in building structures.

A new method for improving the resistance of cement-based materials to carbonic acid water corrosion: Carbonation curing and further water curing

Accelerated carbonation curing has several advantages compared with traditional moisture curing in terms of decreasing the duration time of early curing and improving the mechanical properties, dimensional stability and durability of concrete. This study investigated the effect of accelerated carbonation curing and further water curing on corrosion behavior, corrosion products, and pore structure of cement mortar and paste samples exposed to carbonic acid water corrosion. The results indicate the accelerated carbonation curing reduces corrosion depth and mitigates the decline in compressive strength caused by carbonic acid water corrosion. The accelerated carbonation curing can lead to the decalcification of C-S-H gel, and the formation of a large amount of CaCO3 and silica gel (SiO2·γH2O) on the surface of the C-S-H gel, which play a crucial role in the corrosion resistance of carbonic acid water. CaCO3, firstly, fills pores and optimizes the pore structure, slowing down the diffusion rate of carbonic acid water. Meanwhile, an essential "protective layer" forms on the surface due to abundant CaCO3, effectively preventing further corrosion of internal C-S-H gel, CH, C2S, and C3S. At the later age of corrosion, the carbonic acid water can lead to the decalcification shrinkage of CaCO3, and the deterioration of pore structure, which adversely affects the mechanical properties of cement-based materials.

Rheological properties and workability of PVA fiber and nano-SiO2 modified cement-based materials

Nanoparticles and fibers are frequently applied to improve the mechanical properties and durability of cement-based materials (CBM). In this study, rheology, workability and compressive strength tests were carried out to investigate the effect of PVA fiber (PF) and nano-SiO2 (NS) on rheological properties, workability and mechanical properties of CBM. Also, the function relationships of PF/NS content with rheological and workability parameters, rheological parameters with compressive strength were established separately. In addition, the effect mechanism of PF and NS was explained in depth. Finally, the fuzzy matrix method was employed to make a comprehensive evaluation on CBM performance. The results indicated that PF had negative influence on both rheological properties and workability of CBM. Whereas, NS only exhibited an increase in rheological properties of CBM at 0.5% content and a slight improvement in workability at 1.0% content. The comprehensive performance of CBM reached the optimum with PF content of 0.6%.

Improving the mechanical properties of cement-based materials under high temperature: Reducing the C3S/C2S ratio

Aiming at the phenomenon of strength decline of cement stone at high temperatures, a new method was proposed to enhance its mechanical properties: the CaO/SiO2 ratio was pre-emptively reduced by decreasing the C3S/C2S ratio in the cement, which was then reinforced with an appropriate amount of silica powder. To verify the reliability of this new method, the hydration characteristics of the C3S-C2S system at 230 °C and 20.7 MPa were investigated via Vickers hardness, BJH, XRD, TGA, and SEM-EDS. Results showed no emergence of new physical phases with changes in the C3S/C2S ratio. Increasing the content of C2S facilitated the formation of additional xonotlite. Optimal Vickers hardness of the C3S-C2S system was attained at 27.69 MPa when the C3S:C2S ratio was 1:1. The compressive strength of compound cement, comprising G-class oil-well cement and low-heat cement, increased by 5–10 MPa when the C3S:C2S ratio in the compound cement was approximately 1.07:1. Both the C3S-C2S system and compound cement showed that their mechanical properties increased with increasing C2S content. Predictions suggest an optimal C3S:C2S ratio of 1:1 for the new low-calcium high-temperature-resistant cement. The future application of this new method promises material cost savings and reduced carbon emissions from cement production.

Molecular dynamics study of the mechanical properties of hydrated calcium silicate enhanced by functionalized carbon nanotubes.

The incorporation of functionalized carbon nanotubes can enhance the mechanical properties of cement-based materials. However, the types of functional groups and their roles in composite materials are not yet clear. In this study, molecular dynamics (MD) simulation methods were employed to investigate the mechanical performance of hybridized calcium silicate hydrate gel reinforced with pure carbon nanotubes, epoxy-coated carbon nanotubes, carboxylated carbon nanotubes, and hydroxylated carbon nanotubes. The results indicate that the addition of all four types of nanotubes can enhance the mechanical properties of hydrated calcium silicate gel compared to pure C-S-H. Tensile loading results show that carbon nanotubes can act as bridges for microcracks in the composite material, and functionalized nanotubes exhibit a better reinforcing effect than pure carbon nanotubes. Under tensile stress, hydroxylated nanotubes are more effective in increasing the toughness of the composite material, while carboxylated nanotubes tend to enhance the strength of the composite material. The compressive loading results indicate that the compressive strength of cement-based materials is higher than their tensile strength. Overall, carboxylated nanotubes show particularly remarkable performance in enhancing the mechanical properties of cement-based materials. Compared to pure C-S-H gel, the tensile and compressive elastic moduli of carboxylated nanotube/C-S-H composite material increased by 18.13% and 34.78%, respectively. Its tensile and compressive strengths also increased by 30.40% and 40.23%, respectively. All molecular dynamics simulations were performed on the classical computational simulation platform LAMMPS. In this paper, the parameters in the ClayFF force field are chosen to simulate calcium hydrated silicate (/C-S-H), and the ClayFF-CVFF combined force field is used to simulate the mechanical properties of the CNT/C-S-H molecular model structure.

Synergic Effect of Recycled Carbon Fibers and Microfibrillated Cellulose Gel for Enhancing the Mechanical Properties of Cement-Based Materials.

A new hybrid fiber blend containing microfibrillated cellulose (MFC) gel and recycled carbon short fiber (RCSF) was implemented for designing fiber-reinforced cement mortars, to further improve the mechanical properties and enhance the sustainability of cement-based materials. The individual impact of single fibrous fillers as well as the synergistic effect of a hybrid fiber system (MFC + RCSF) were investigated in terms of the rheological properties, mechanical strength, and microstructure of the mortars. The results indicated that the workability of fresh mixtures slightly increased after fiber addition. The fibers incorporated alone improved the materials' performance in different ways. The addition of RCSF led to improvements of up to 76% in flexural strength and 13% in compression strength for a fiber content of 0.75 wt.%. However, the addition of carbon fibers led to slight deteriorations in terms of porosity and water absorption. On the other hand, the use of MFC induced a less significant growth in terms of mechanical strength (+14% in flexural strength for 0.75 wt.% of cellulose) but greatly improved the microstructural quality of the mortar, significantly reducing its water permeability. Considering the optimum MFC dosage, MFC+RCSF hybrid mixtures showed positive effects on the mechanical properties and microstructure of the mortar, displaying further improvements in strength, while preserving a lower porosity and water absorption than the control mix.

Synergistic enhancement of the mechanical properties of cement-based materials by using microcrystalline cellulose and nano-silica composites

The flexural strength and compressive strength are the two most important parameters that characterize the mechanical properties of cement-based materials, but the two are usually mutually exclusive or negatively correlated. The flexural strength of cement-based materials cannot be effectively improved by a single nanomaterial without reducing their compressive properties. Therefore, compounding various micro–nano materials, fully utilizing their respective advantages, and developing composite materials with new properties and application characteristics are important techniques for enhancing the mechanical properties of cement-based materials. This study aimed to investigate the synergistic enhancement of the mechanical properties of concrete by using microcrystalline cellulose (MCC) and nano-silica (NS) composites. MCC and NS were mixed and modified to synthesize MCCNS materials, which were added to cement slurry for experiments. Results indicated that the flexural strength and compressive strength of the cement paste with MCCNS materials were significantly increased compared with those of the cement pastes without MCCNS or with only NS. The flexural strength of the cement paste with MCCNS-1 was increased by 47%, 20%, 6.3%, and 6.8% after curing for 1, 7, 28, and 56 days, respectively. Meanwhile, compressive strength was also increased by 14.4%, 6.3%, 6.8% and 6.5%, respectively. In addition, the reaction mechanism was speculated through a variety of test results. The addition of MCCNS material facilitated the formation of additional C-S-H, which also contributed to enhancing the mechanical properties of cement paste.

Study on the flowability and strength of cement-based materials added with limestone powder and PVA fiber

In order to improve the mechanical properties of cement-based materials, limestone powder (LP) was used as a filler as 0% to 20% cement paste replacement by volume in the mortar. Polyvinyl alcohol (PVA) fiber with 0% to 0.6% by volume were added to produce multiple sets of cement-based materials for basic mechanical properties tests including flowability, compressive strength and tensile strength. The test results indicated that an increase in the amount of PVA fiber and the replacement amount of LP continuously reduce the flowability of cement-based materials. PVA fiber led to the most significant reduction effect. The addition of an appropriate amount of PVA fiber can improve the tensile and compressive strength of cement-based materials, but excessive addition has a negative impact on the compressive strength. When the increase in replacement ratio of LP, the compressive strength of cement-based materials increased. Comparatively, the decrease in tensile strength is not significant.

Carbonation curing of modified magnesium-coal based solid waste backfill material for CO2 sequestration

CO2 sequestration is an effective method for dealing with the global climate crisis, and carbonation curing is considered an effective method of sequestering CO2 and improving the mechanical properties of cement-based materials (CBM). Regarding modified magnesium-coal based solid waste backfill material (MB), to explore its carbonation curing performance and CO2 sequestration capacity, its uniaxial compression strength (UCS), carbonation depth, microstructure, CO2 transport performance, CO2 uptake capacity, and carbonation efficiency are analyzed and characterized using UCS tests, thermogravimetric analysis (TGA), X-ray diffraction (XRD), and nuclear magnetic resonance (NMR) analysis. The results show that the early UCS of the MB is significantly improved by carbonation curing. The UCS at 7 days is 10.91 times higher than that of the MB without carbonation curing, and the UCS increases as the concentration and modified magnesium slag-based cementitious material (MC) content increase. Carbonation curing makes the microstructure of the MB significantly denser and reduces the porosity, pore diameter, and permeability. The formation of carbonated products such as calcium carbonate and hydration products makes the microstructure more compact, which is the main reason for the rapid increase in the early UCS of the MB. The maximum CO2 uptake capacity of the MB through carbonation curing is 14.3%, and the carbonation efficiency is up to 92.2%. Therefore, carbonation curing of MB has broad application potential in improving the UCS and sequestering CO2.

Influence of Carbon Nanofiber Content on the Fracture Mechanical Properties of Cement-Based Materials: Insights from Three-Point Bending and Nanoindentation Tests

Incorporating intelligent materials in concrete allows for self-sensing capabilities by reflecting the concrete’s strain and tensile status through the electrical properties. In order to enhance the self-diagnostic abilities of intelligent concrete, we conducted research on how intelligent materials affect the fracture mechanics of concrete. This study examines the fracture mechanical properties of the carbon nanofiber cement mortar and paste based on three-point bending and nanoindentation tests. The results showed that the carbon nanofiber content has negligible influence on the crack initiation toughness of the specimens. However, the instability toughness exhibited an initial increase followed by a decrease as the carbon nanofiber content increased. At a fiber content of 0.2%, the crack initiation toughness improved maximally by 13.1% compared to the control group. At a fiber content of 0.5%, both the ductility index and fracture energy increased with the nanofiber content, improving by 84% and 66.3%, respectively. The incorporation of carbon nanofibers did not alter the composition of cement paste hydration products; the fracture toughness of each hydration product varies from 0.14 to 0.59 MPa·m1/2. However, the fracture toughness of individual hydration products and un-hydrated particles is higher than the macroscopic three-point bending fracture toughness values of the specimens.

Development of Sustainable Cement-Based Materials with Ultra-High Content of Waste Concrete Powder: Properties and Improvement

The recycled powder (RP) of construction waste, as a kind of silica–aluminum waste, can have a certain gelling effect after alkali activation modification. Sodium silicate (water glass) and NaOH are used as composite alkali activators to stimulate RP to prepare alkali-activated mortar. The different micro and macro properties of RP are studied under the ultra-high substitution rates of 70%, 80%, 90%, and 100% of cementation-based materials. The results show that the mechanical properties of the regenerated powder mixture decrease gradually with the increase in the substitution rate. When the replacement rate of RP is 70%, the 3 d and 28 d compressive strength decreases by 73.63% and 69.46%, respectively. When the replacement rate reaches 100%, the 3 d and 28 d compressive strength decreases by 96.98% and 93.74%, respectively. The cement-based material after alkali excitation has the characteristics of early strength and the mechanical properties are greatly improved, and the mechanical properties of cement-based materials can be effectively increased by increasing the modulus of water glass. At 70%RP substitution rate, the compressive strength of 28 d increases by 3.59% and 107.71% when the modulus of sodium silicate is 1.0 M and 1.6 M, compared with the unactivated groups. At 100%RP substitution rate, the 28 d strength of the unexcited specimen is 0.92 MPa, and the 28 d compressive strength reaches 6.15 MPa and 12.86 MPa when the modulus of sodium silicate is 1.0 M and 1.6 M. The results show that the alkali-activated mortar has good application potential.

Experimental-Computational Investigation of the Elastic Modulus of Mortar under Sulfate Attack.

External sulfate attack is an important factor causing a decrease in the mechanical properties of cement-based materials. In this paper, a computational prediction model of elastic modulus, considering the characteristics of sulfate corrosion from outside to inside and the influence of the interface transition zone (ITZ), was established to predict the elastic modulus of mortar under the external sulfate attack. Firstly, the backscattered electron (BSE) images of mortar and the algorithm of image threshold segmenting were used to determine a reasonable thickness of corroded ITZ. Secondly, the nanoindentation test was adopted to acquire the microscopic elastic parameters of phases (sand, cement, and ITZ) in corroded mortar. Moreover, the mortar mix proportion and Lu and Torquato's model were adopted to calculate the volume fractions of phases. Finally, a computational prediction model of elastic modulus of mortar under sulfate attack was proposed with homogenization methods. The results indicate that the thickness of corroded ITZ is 20 mm, and the error values of elastic modulus between the theoretical prediction results and the experimental results are within 8%, indicating that the macroscopic elastic modulus of corroded mortar can be precisely predicted by the computational prediction model of elastic modulus.

Mechanical properties and micro-mechanism of cement-based materials strengthened by in-situ organic-inorganic polymerization

Ordinary cement-based materials face defects in practical applications, such as poor tensile strength, brittleness, and high cracking risk. Compound modification has great potential to improve cement-based material structural and mechanical performance. In this paper, cement-based materials with a three-dimensional (3D) plug-in network structure are formed by in-situ organic-inorganic polymerization. Partial acrylamide (AM) monomer is inserted into the zirconium phosphate (ZrP) interlayer, and zirconium phosphate-acrylamide (ZrP-AM) composite materials are successfully prepared. During cement hydration, AM undergoes in-situ self-polymerization and co-polymerization with ZrP-AM, forming a complete plug-in network with ZrP distributed on the polymer network. Meanwhile, the plug-in network structure is closely bound to the cement matrix due to the formation of chemical bonds. In the best mix ratio design, the ZrP-PAM-modified sample with 1 wt% ZrP and 3 wt% AM has a 105% higher flexural strength than the cement paste. Moreover, due to the enhancing effect of ZrP on the cement matrix and polymer network, the flexural and compressive strengths of the modified sample increased by 28.5% and 17%, respectively, compared to the single AM modified sample with respect to the same dosage. The formation of the plug-in network structure and chemical bonds greatly enhances the mechanical strength of cement-based materials. This synergistic modification method fully exploits the modifying effects of polymers and nanomaterials and provides a novel strategy to improve the mechanical properties of cement-based materials.

Effect of High Content Limestone Powder on Microstructure and Mechanical Properties of Cement-based Materials

Effect of High Content Limestone Powder on Microstructure and Mechanical Properties of Cement-based Materials

Degradation of limestone calcined clay cement (LC3) mortars under sulfate attack

Limestone Calcined Clay Cement (LC3 is a newly proposed low-carbon cement, which can effectively reduce energy consumption and carbon emissions of the traditional cement industry without changing the basic mechanical properties of cement-based materials. In this study, the degradation process of mortar samples of limestone and calcined clay cementitious material under sulfate attack is studied by both macroscopic and microscopic analysis. The results show that compared with pure Portland cement, the addition of calcined clay and limestone can significantly reduce the expansion rate, loss of dynamic modulus and mass loss of mortar specimens under sulfate attack. The addition of calcined clay and limestone will refine the pore size distribution of mortar specimens, then inhibiting the diffusion of sulfate and formation of corrosive products, therefore leading to a significant improvement of the sulfate resistance.

Hydration Characteristics and Mechanical Properties of Cement-Based Materials Modified by Calcined Zeolite and Montmorillonite

Montmorillonite and clinoptilolite zeolite were used as representative materials to prepare calcined clay-cement binary cementitious materials in order to study the effect of calcination treatment on the activation of clay minerals and the activity difference between layered and framed clays in this research. The influence of different calcined clay content (2%, 4%, 6%, 8%, 10%) on the fluidity, compressive strength, microstructure, phase change, and hydration heat of cement-based materials were analyzed. The calcined clay improves the fluidity of cement-based materials as compared with the uncalcined group. The addition of calcined montmorillonite (CMT) improves the development of mechanical strength, and the optimal compressive strength reaches 85 MPa at 28 days with 8% CMT. However, the activity of calcined clinoptilolite zeolite (CZL) is weak with few reaction sites, which slightly reduced the mechanical strength as compared to the blank sample. The addition of CMT changes the microscopic morphology of hydration products such as C-S-H and C-A-H, leading to the formation and transformation of ettringite in the early stage. It promotes the gradual polymerization of Si-O bonds into SiO-Si bonds simultaneously, which accelerates the early hydration process. However, CZL acts mainly as a filling function in the cementitious system. In brief, CMT as an admixture can improve the mechanical properties of cement, but CZL has little effect. This work provides a guideline for the applications of calcined clay in cement, considering the influence of clay type on workability and mechanical strength.

Graphene-Iron Ore Tailings-Based Cementitious Composites with High Early Flexural Strength.

Graphene is a two-dimensional nanomaterial with excellent mechanical, electrical and thermal properties. The application of graphene in cement-based materials has good prospects. However, the mechanical properties of cement-based materials are difficult to be significantly enhanced by ordinary graphene nanoplates. In this paper, nitrogen-doped graphene is first reported as an additive with dosages of 0.01, 0.02, 0.03, 0.04 and 0.05 wt.%, respectively, to prepare iron ore tailings-based cementitious composites. The iron ore tailings-based cementitious composite with 0.02 wt.% graphene shows an extremely high flexural strength of 15.05 MPa at 3 days, which is 134.4% higher than that of the iron ore tailings-based cementitious composite without graphene. The effects of graphene content and curing age on the flexural strength and microstructure of iron ore tailings-based cementitious composites were studied. In particular, the scanning electron microscope was adopted to observe the micromorphology of the composites. It is helpful to understand the graphene reinforcement mechanism for the high early flexural strength of iron ore tailings-based cementitious composites. By altering the morphology of iron ore tailings-based cementitious composites, graphene plays two roles in the composites. One role is to connect C-(A)-S-H gels, ettringite and other hydrated crystals to construct a three-dimensional structure. The other is to attract iron ore tailings distributed on its platform to enhance its flexural strength properties. These findings provide favorable guidance for the performance enhancement and mechanism replenishment of graphene-reinforced cementitious composites.

Study on the effect of nanosilica suspension on the properties of cement-based grouts

Abstract The agglomeration trend of nanosilica particles was found to significantly affect the properties of cement-based materials. The influence of nanosilica suspension on the fluidity, setting time, and compressive strength of cement-based grouts were studied. The hardened pastes were characterized by thermogravimetric (TG) analysis and scanning electron microscopy (SEM). The results showed that the fluidity of cement-based grouts with nanosilica suspension had obviously improved. The setting time was obviously decreased, compared with the reference sample. The compressive strengths for 1 day, 3 days, and 28 days were 12.8%, 14.3%, and 10.1% higher than that of the reference group, respectively. This paper may provide a novel route to improve the mechanical properties of cement-based materials without affecting their workability.

Strengthening mechanism of ultrasonic action on mechanical properties of cement-based materials

Aiming at the problem that aggregated or flocculated cement particles negatively affect the development of mechanical properties of cement-based materials. This paper investigates the effects of ultrasonic action on the compressive strength, dispersion, heat of hydration, rheology, and micromorphology of cement-based materials with ultrasonic dispersion of freshly mixed cement paste. Moreover, the ultrasonic strengthening mechanism of cement-based materials is proposed. The results show that the ultrasonic action can effectively disperse cement particles, strengthen the mechanical properties, reduce the dynamic yield stress and apparent viscosity of the paste, and accelerate the early hydration rate. Notably, ultrasound-induced hydration is the fundamental reason for strengthening the mechanical properties.

Strengthening Mechanism for the Mechanical Properties of Cement-Based Materials after Internal Nano-SiO2 Production.

This study focuses on overcoming the agglomeration issue of nano-SiO2 powder in cement, facilitating the strengthening mechanism of cement-based materials. A nano-SiO2 precursor solution (NSPS) was added to cement-based materials to replace nano-SiO2 powder. The influencing laws of the alkalinity and dosage of the NSPS on the mechanical properties of cement were investigated. Further, the strengthening mechanism of the mechanical properties of cement-based materials after internal nano-SiO2 production was analysed. The results show that (1) when the alkalinity of the precursor solution is a weak acid (pH = 6), the compressive strength of cement-based materials after internal nano-SiO2 production is 25%~36% higher than that of pure cement-based materials and 16%~22% higher than that of cement-based materials with silica fume; (2) when the solid content of SiO2 in the current displacement solution is about 0.16% of the cement mass, the compressive strength of the prepared cement-based material is the highest. With the continuous increase in the solid content of SiO2 in the precursor solution, the compressive strength of cement-based materials after internal nano-SiO2 production decreases but is always greater than the compressive strength of the cement-based material mixed with nano-SiO2 micro powder. According to a microstructural analysis, nano-SiO2 particles that precipitate from the precursor solution can facilitate the hydration process of cement and enrich the gel products formed on the cement particle surface. In addition, new network structures among cement particles are formed, and precipitated nano-SiO2 particles fill in the spaces among these cement particles as crystal nuclei to connect the cement particles more tightly and compact the cement-based materials. This reinforces the mechanical properties of cement-based materials.