Ultra-high Performance Cement-based Composite Research Articles

Application of Cement-Based Composite Nanomaterials in Prefabricated Thin-Wall Light Steel Structure Composite Wall.

In order to solve the problem of seismic performance of prefabricated concrete shear walls connected with ultra-high performance cement-based composite (UHPC) after short lap of steel bars, the author proposes a cement-based composite nanomaterial in the prefabricated thin-walled lightweight application in steel structure composite wall. In order to explore the influence of the axial compression ratio on its seismic performance, 1 is a cast-in-place shear wall with a design axial compression ratio of 0.2, and 3 is a prefabricated shear wall with a design axial compression ratio of 0.2, 0.33, and 0.47, respectively, all the specimens were mainly damaged by shear compression. The test results show that the cracking loads of specimens PW2 and PW3 are increased by 17.04% and 38.81%, respectively, the yield load is increased by 27.74% and 50.28%, respectively, and the peak load is increased by 25.29% and 48.4%, respectively. Conclusion. With the increase of the axial compression ratio, the crack resistance and bearing capacity of the specimens are significantly improved.

Identification of fracture damage characteristics in ultra-high performance cement-based composite using digital image correlation and acoustic emission techniques

The study of fracture mechanism and damage of ultra-high performance fiber reinforced cement-based composite (UHPFRCC) is of great significance for material performance evaluation and nondestructive structural health monitoring. In this paper, three-point bending fracture tests of UHPFRCC with fiber content of 1% and 2% were carried out, and the digital image correlation (DIC) and acoustic emission (AE) technique were used to monitor the fracture simultaneously. The microcrack area of UHPFRCC1 (UHPFRCC with 1% fiber content) decreases gradually with the loading process, and the microcrack area of UHPFRCC2 (UHPFRCC with 2% fiber content) increases first and then decreases with the loading process. The macrocrack area of UHPFRCC1 and UHPFRCC2 increases gradually with the same growth trend. The matrix failure and fiber/matrix debonding behavior of UHPFRCC were identified effectively based on the unsupervised k-means clustering method, and the fiber/matrix debonding behavior was obvious when the AE amplitude was greater than 60 dB. Meanwhile, the clustering results are also verified by the evolution of FPZ length. Finally, an efficient identification model of UHPFRCC matrix failure and fiber/matrix debonding behavior based on supervised KNN algorithm is proposed, which provides theoretical support for nondestructive structural health monitoring in practical engineering.

Flexural strength and ductility of ultra high-performance cement-based composites (UHP-CC)

It has been known that concrete is weak in tension, so it requires some additional materials to have ductile behavior and enhance its tensile response. Thus, steel fibers came into use due to their advantage in controlling cracks and enhance the tensile behavior of concrete. In this study, the behavior and improvement in flexural tensile strength and strain capacity of ultra-high-performance cement-based composites (UHP-CC) were investigated. Two main variables were examined, namely the content of silica fume and steel fibers with percentages of (0%, 10%, 20% and 30%) and (0%, 1%, 2% and 3%) respectively. The experimental results show that, in the non-fibrous UHP-CC matrix, after the first crack initiation, the inclusion of steel fibers upgrades the behavior of the matrix from brittle to a plastic one and the specimen with a 1% steel fibers ratio failed immediately after crack initiation showing no possible occurrence of strain hardening or multiple cracking. In UHP-CC specimens with steel fibers of more than 1% the tensile failure was more ductile and accompanied by the development of the main crack and many multiple secondary cracks. it was found that the load increased even after the cracks initiation (strain hardening behavior) and thereafter showed gradual declination. It is revealed that after the peak point, one of the cracks widens and becomes critical, which defines the onset of crack localization showing no more development of cracks. Under increased deformation, the critical crack will open describing the stage of fibers pull-out. It was observed that the increase of the ratio of steel fibers in the range of (0% - 3%) caused a significant increase in flexural tensile strength by 244%, whereas the increase in compressive strength was only 12%.

Mesoscopic modelling of UHPCC material under dynamic tensile loadings

This paper presents a new 3D mesoscopic model of ultra-high performance cement-based composite (UHPCC) to investigate its dynamic tensile behavior. In this model, the UHPCC is regarded as a two-phase material composed of cementitious matrix and randomly distributed fibers. The model is established using the commercial software LS-DYNA and involves generating the randomly distributed fiber elements with considerations of diameter, length, orientation and volume fraction, and then fully constraining them with the matrix. In particular, to capture the slipping effect between fibers and matrix that has a strong influence on the dynamic tensile behavior, the fibers are modelled by a fictitious material represented by the load-slip relation. The strain-rate effect of slipping force neglected in most of previous studies is considered by calibrating constitutive parameters of the fictitious material under different strain-rates based on the single fiber pullout tests. Finally, the 3D mesoscopic model is validated against three sets of tension-dominated experiments covered a wide range of loading intensity. Numerical predictions demonstrate that strain-rate effect of slipping force must be considered, and the neglect of it may lead to a great underestimation of the dynamic tensile strength of UHPCC material and would unavoidably underestimate the blast resistance of UHPCC components.

Constitutive modelling of UHPCC material under impact and blast loadings

Ultra-high performance cement based composite (UHPCC) is a prospective material for protective structures subjected to intensive loadings such as impact and blast due to its prominent dynamic mechanical properties. With the aid of an accurate material model, numerical simulation plays an increasingly important role in prediction of dynamic responses of UHPCC structures. It is known that existing concrete material models are developed for traditional concrete and cannot be applied to UHPCC material directly. In the present study, a new constitutive model of UHPCC material under impact and blast loadings is developed, which involves proposing a new tensile damage model for UHPCC which is then incorporated into the Kong-Fang material model recently developed (Int J Impact Eng 2018, 120: 60-78), and calibrating parameters of this modified material model based on existing test data. The modified material model for UHPCC is implemented into the finite element code LS-DYNA through user defined material model. Single element tests including unconfined uniaxial compression and tension and triaxial compression are firstly conducted to demonstrate the improved performances of the modified material model for UHPCC material. Then three selected experiments on UHPCC structures subjected to impact and blast loadings are numerically simulated and compared with corresponding experimental data. Numerical predictions by the modified material model are well consistent with experimental data in terms of impact force, deflection and failure.

Dynamic Compression Behavior of Ultra-high Performance Cement-based Composite with Hybrid Steel Fiber Reinforcements

Ultra-high performance cement-based composites (UHPCC) is promising in construction of concrete structures that suffer impact and explosive loads. In this study, a reference UHPCC mixture with no fiber reinforcement and four mixtures with a single type of fiber reinforcement or hybrid fiber reinforcements of straight smooth and end hook type of steel fibers were prepared. Split Hopkinson pressure bar (SHPB) was performed to investigate the dynamic compression behavior of UHPCC and X-CT test and 3D reconstruction technology were used to indicate the failure process of UHPCC under impact loading. Results show that UHPCC with 1% straight smooth fiber and 2% end hook fiber reinforcements demonstrated the best static and dynamic mechanical properties. When the hybrid steel fiber reinforcements are added in the concrete, it may need more impact energy to break the matrix and to pull out the fiber reinforcements, thus, the mixture with hybrid steel fiber reinforcements demonstrates excellent dynamic compressive performance.

Hydrophobic modification of ultra-high-performance fiber-reinforced composites with matrices enhanced by aluminum oxide nano-fibers

Aluminum oxide nanoparticles can be used in small quantities to create a high-performance and ultra-high-performance cementitious composites. High volumes, up to 20% of supplementary cementitious materials such as silica fume or metakaolin, are often used to achieve the high strength of up to 150 MPa in high performance and ultra-high performance cementitious composites. This research demonstrates that when aluminum oxide (Al2O3) nano-fibers are used in cement-based composites, compressive strength of up to 175 MPa can be achieved at very low dosages of silica fume and metakaolin. This effect is achieved by using low water to cementitious materials ratio, selection of cement, and utilizing the seeding and reinforcing effects of by the nano-fibers. Furthermore, the ultra-high performance cement-based composite (UHPC) can include polyethylene fibers which provide enhanced strain hardening and multi-cracking behavior. The UHPC was tested to evaluate the effects of superhydrophobic modification. Superhydrophobic modification utilizes siloxane-based admixtures to form a well-dispersed air void system whose voids have hydrophobic properties. The experimental results demonstrate that a superhydrophobic modification may reduce the performance of advanced composites with Al2O3 nano-fibers. High-performance cementitious materials are critical for the next generation of infrastructure. This research evaluates the effects of superhydrophobic admixtures in ultra-high-strength fiber-reinforced composites with Al2O3 nano-fibers. The incorporation of small quantities of aluminum oxide nano-fibers in UHPC may prove to be a viable option for compressive strength enhancement; however, incorporating a superhydrophobic air void structure was not effective for enhancement of ductility.

Mechanical and perceptual characterization of ultra-high-performance cement-based composites with silane-treated graphene nano-platelets

An ultra-high-performance cement-based composite (UHPCC) with excellent mechanical behaviors and self-perceived properties was successfully prepared in this work. The effects of silane-treated graphene nano-platelets (ST-GNPs) on the fluidity, porosity, degree of hydration, mechanical behaviors, and self-perceived properties of UHPCC were investigated. The results revealed that the fluidity of UHPCC fresh mortar is directly related to ST-GNPs content. The fluidity decreases as the amount of ST-GNPs increases. Furthermore, when the amount of ST-GNPs was 0.05%, the porosity of UHPCC was found to be 11.5%, and the compressive strength and flexural strength reached the maximum value of 142.5 MPa and 23.8 MPa, respectively. Additionally, the microstructure of the UHPCC was investigated. Also, it was indicated that the introduction of ST-GNPs could enhance the transformation of fibrous calcium silicate hydrate (C–S–H) gel into petal-like hydration products, which has the tendency to continuous interpenetration. Further, the introduction of ST-GNPs is confirmed to reduce the resistivity of UHPCC from 18.85 kΩ·m to 6.26 kΩ·m. Finally, the self-perceived performance of UHPCC with 0.05% ST-GNPs was observed to be about double that of UHPCC without ST-GNPs, which indicates that the UHPCC prepared by adding ST-GNPs has excellent self-perceived performance.

Mechanical properties and microstructure of ultra-high performance cement-based composite incorporating RHA

The effects of the addition of rice husk ash (RHA) on the mechanical and microstructural properties of an ultra-high performance cement-based composite (UHPCC) was studied. The microstructure of the UHPCC was investigated using X-ray diffraction, mercury intrusion porosimetry, scanning electron microscopy and other analytical test methods. The results showed that the mechanical performance was improved with the addition of RHA. Mortars blended with 15% RHA showed the highest compressive and flexural strengths. For mortars reinforced with 3% steel fibres by volume, both flexural and compressive strengths were remarkably enhanced. The optimal content of RHA was found to be about 10–15%. The addition of RHA decreased the hydration heat evolution rate of the cementitious composites, but the hydration process was brought forward due to the addition of RHA. As a result of calcium hydroxide consumption through the pozzolanic reaction of the RHA, the interface was strengthened with an increase in curing time and the microstructure of the mortar containing RHA blended was denser than that of mortar without RHA. The high pozzolanic reaction and the filler effect of RHA contributed to a finer pore structure and a decrease in porosity.

Modified spherical cavity-expansion model for projectile penetration into concrete targets

A modified spherical cavity-expansion model is developed in this paper. (1) We introduce a piecewise hyperbolic yield criterion suitable for pressure less than fc/3 to describe the mechanical behavior in the elastic region for the elastic–plastic response and modify the crack occurrence condition for the elastic–cracked–plastic response. (2) The hyperbolic yield criterion and a piecewise equation of state (EOS) are adopted for a better description of the plastic behavior of concrete material. Then, the modified model is validated by several projectile penetration tests in both the normal strength concrete (NSC) and ultra-high performance cement-based composite (UHPCC) targets. Finally, the hydrostatic pressure of the targets under rigid ogive-nosed projectile penetrations is found to be nearly within (0, 1.6 GPa), which usually exceeds the range that the shear strength-pressure test data covered. The influence of yield criterion on depth of penetration is discussed and it is recommended that the pressure should arrive at least 400 MPa in the related triaxial compression tests.

Feasibility of manufacturing ultra-high performance cement-based composites (UHPCCs) with recycled sand: A preliminary study

Due to the excellent mechanical and durability properties, ultra-high performance cement-based composites (UHPCCs) have attracted a lot of attention during the past decades. It is noted that most existing UHPCCs are manufactured from raw materials with high quality, for instance, well-graded river sands. However, the huge consumption of river sands as construction materials has inevitably resulted in some serious ecological impacts, as reported around the world. In this regard, it shall be much beneficial if some substitutes, such as recycled sands produced through processing of construction and demolition waste (CDW), could be used to replace natural sands to manufacture the qualified UHPCCs. This paper presents such a preliminary study on the feasibility of manufacturing UHPCCs with recycled sands. A total of five UHPCCs are designed and cast with different replacement percentages of recycled sand, i.e., 0%, 30% 50%, 70% and 100% (in mass). The associated packing density of the mixed sands is estimated based on the linear packing model. The fresh and hardened properties of the UHPCCs, including the workability, strength and shrinkage, are experimentally examined. The test results indicate that it is possible to use recycled sand to replace natural river sand in the manufacture of UHPCCs; however, the amount of the recycled sand needs to be limited. In the case when the replacement percentage of the recycled sand is lower than 50% (in mass), the properties of the UHPCCs with the recycled sand are comparable with those containing river sand only.

Effects of metakaolin on mechanical and microstructural properties of ultra-high performance cement-based composites

The effects of metakaolin (MK) on the mechanical and microstructural properties of ultra-high performance cement-based composite (UHPCC) were studied in this paper. The microstructure of UHPCC was investigated via XRD, SEM, nanoindentation, X-ray CT, and other different analytical testing methods. The results indicated that the mechanical performance of UHPCC was improved with the adding of MK. Blended mortars with 10% MK showed the highest compressive and flexural strengths in comparison to the others. As a result of Ca(OH)2 consumption through the pozzolanic reaction of MK, the interface was strengthened with the increase of curing time and the microstructure of MK blended mortar was denser than the mortar without addition of MK. Nanoindentation results revealed that most hydrated products of MK blended mortar was UHD C–S–H and a large quality of unhydrated cement existed in the mortar. X-ray CT results indicate that MK conduced to the distribution of steel fiber, thus improved the mechanical properties of UHPCC.

Analyses of rigid projectile penetration into UHPCC target based on an improved dynamic cavity expansion model

Ultra-high performance cement based composite (UHPCC) has prominent projectile impact resistance. Aiming to theoretically predict the depth of penetration for rigid projectile penetrating UHPCC target, an improved dynamic cavity expansion model was proposed to describe the plastic behavior of UHPCC material under projectile penetration with a hyperbolic yield criterion and nonlinear equation of state (EOS). Then, combined with the Newton’s second law, rigid projectile penetration model into UHPCC target was established, which was verified by comparing with the previous penetration test data, classic empirical formula and prediction of previous cavity expansion model based on linear yield criterion and EOS. Besides, a series of practical parameters of the hyperbolic yield criterion and nonlinear EOS for the improved dynamic cavity expansion model were given and validated.

Ultra high performance cement-based composites incorporating low dosage of plasma synthesized carbon nanotubes

Ultra high performance cement-based composites (UHPCs) have gathered more attention and interest due to their excellent properties. In this study, a new type of carbon nanotubes (p-CNTs) synthesized by plasma process was used to modify the mechanical properties of UHPC at low dosage. The dispersion and sedimentation of p-CNTs were investigated and the mechanical properties of the resulting CNT modified UHPCs (CNT-UHPCs) were studied. The results showed that p-CNTs can be dispersed uniformly in water through ultrasonication without the need of surfactant or chemical modification on surface. In addition, the p-CNTs showed a much improved dispersion and stability as compared to the normal CVD synthesized CNTs. Well-dispersed p-CNTs greatly enhanced the flexural strength of UHPC from 12.5 to 21.2MPa at a dosage of only 0.067% by the weight of cement. This highlighted the importance of dispersion of CNTs which not only improved the bridging efficiency but also reduced the CNT dosage and cost. All of these make the applications of nano-material feasible and more economical attractive.

Triaxial compressive behavior of UHPCC and applications in the projectile impact analyses

For the constructions of protective structures against potential projectile high-speed impact, the optimal ultra-high performance cement based composite (UHPCC) (straight steel fiber with the volumetric ratio of 2%, high-strength basalt aggregates with the size range of 5-10mm, the designed uniaxial compressive strength of∼100MPa) was prepared. By casting two batches of 50mm×100mm cylindrical UHPCC specimens with the uniaxial compressive strengths of 95MPa and 129MPa, the triaxial compressive behavior of UHPCC under high confining pressure (up to 100MPa) was experimentally studied. Based on the deviatoric stress-strain curves under various confining pressure, the failure criteria and toughness of UHPCC under triaxial compression were discussed. At last, the dominant strength parameters of Holmquist-Johnson-Cook constitutive model were confirmed based on the present and existing triaxial compression tests on high-strength concrete. The validity of which was verified based on eleven sets of projectile penetration or perforation tests on concrete-like targets with the uniaxial compressive strength ranged from 60MPa to 157MPa.

Projectile penetration of ultra-high performance cement based composites at 510–1320 m/s

The ultra-high performance cement based composites (UHPCC) with the additions of steel fibers and basalt coarse aggregates was prepared under ambient temperature and pressure. In order to apply the UHPCC in the constructions of anti-strike protective structures, the impact resistance of UHPCC was investigated experimentally by conducting the high-speed projectile penetration tests with the broad striking velocities from 510m/s to 1320m/s. The rigid and mass abrasive penetration regimes are observed when the projectile striking velocity was lower than 1km/s and increased up to 1–1.5km/s, respectively. The experiments validated that UHPCC material has excellent projectile impact resistance, such as reducing the depth of penetration (DOP) and the crater dimensions of the rigid projectile, as well as defeating the structure and deviating the terminal ballistic trajectory of the abrasive projectile. The previously proposed models for rigid penetration depth on fiber reinforced high strength concrete as well as the limit striking velocity causing the structural destruction of mass abrasive projectile are both well validated.The parameters influential analyses further indicate that UHPCC with the compressive strength of 90MPa and steel fiber mixing ratio of 1.5% is the most efficient and economical choice for protective structure constructions. In details, within the discussed ranges: (i) the projectile impact crater dimensions enlarges with the increase of the compressive strength of the target and the projectile striking kinetic energy, and which was reduced with the increase of fiber mixing fraction and the mixed coarse aggregate. The influential degree of mixing fibers on reducing the cratering dimensions is much greater than which of compressive strength on enlarging the cratering dimensions; (ii) both of the compressive strength, the fiber mixing fraction as well as coarse aggregates can help decreasing the DOP of the projectile so as to enhance the impact resistance of the target, while the contribution of fibers is very limited for the relatively low addition ratio (⩽3%). The DOP of the projectiles are no longer decreasing obviously when the compressive strength of the target is larger than nearly 90MPa.

Influence of fibre geometry and matrix maturity on the mechanical performance of ultra high-performance cement-based composites

This paper concerns an experimental study of the influence of the geometry of the longest steel fibre and of the matrix maturity on the mechanical behaviour of an ultra high-performance multi-scale fibre reinforced cement-based composite. The following conclusions can be drawn: • Ultra high-performance cement matrix with a very low water/binder ratio continues to mature and undergoes additional densification over time. This tendency leads to a significant increase of the material modulus of rupture as the age of the material advances. • In a very dense matrix, the total number of fibres in the matrix and the specific surface of the fibre are more important parameters than the existence or not of hooks at the fibre ends . • Twisted steel fibres lead to a better material mechanical performance than steel fibres with hooks at their ends.

Experimental and numerical investigation on the dynamic tensile behavior of ultra-high performance cement based composites

In order to investigate the dynamic tensile behavior of ultra-high performance cement based composites (UHPCCs) used in defense works, UHPCC with 200MPa compressive strength is prepared by replacing a large quantity of cement by industrial waste residues such as silica fume, fly ash and slag; and substituting ground fine quartz sand (⩽600μm in diameter) with natural sand (2.5mm in diameter). Dynamic tensile tests are conducted using Split Hopkinson pressure bar (SHPB) on UHPCC with different fiber volume fraction. By using this method, the dynamic tensile strength of UHPCC and its dependence on strain rates are measured and investigated. Results show that dynamic tensile strength of UHPCC is rate sensitive and also improved with an increase of fiber volume fraction. In addition, the finite element method (LS-DYNA) is employed to simulate the whole impact process of UHPCC. The numerical simulation results are in good agreement with experimental results and can be used for further research.

Dynamic compression behavior of ultra-high performance cement based composites

In order to investigate the dynamic compression behavior of Ultra-high performance cement based composites (UHPCC) used in defense works, UHPCC with 200 MPa compressive strength is prepared by replacing a large quantity of cement by industrial waste residues such as silica fume, fly ash and slag; and substituting ground fine quartz sand (≤600 um in diameter) with natural sand (2.5 mm in diameter). Split Hopkinson pressure bar (SHPB) is performed on UHPCC with different fiber volume fraction to investigate the dynamic compression behavior. Results show that impact resistance of UHPCC is improved with an increase of fiber volume fraction. The dynamic compressive strength of UHPCC is also increased with an increase of strain rate. In addition, the finite element method (LS-DYNA) is employed to simulate the whole impact process of UHPCC. Numerical simulations demonstrate that the Johnson_Holmquist_Concrete material constitutive model can be used for the dynamic compression of concrete. The numerical values are in good agreement with experimental results.