Search

Nowadays, basalt fibre is gaining popularity in the field of construction materials due to its low production cost and enhanced mechanical properties. However, research is still needed into the use of a single type of fibre with different lengths in composite materials. Therefore, in this paper the hybridisation of basalt fibre of various lengths and contents is studied in order to take full advantage of multi-scale characteristic(s) with a single type of fibre, while the fundamental mechanical properties of single-length basalt-fibre-reinforced cementitious composites and hybridisation of different-length basalt-fibre-reinforced composites are investigated. Additionally, a hybrid fibre coefficient is developed to evaluate the effect of hybrid fibre in cementitious materials. A total of 17 mix proportions were made containing either a single length or a combination of four different lengths of basalt fibre (3, 6, 12 and 20 mm) with various total volume contents. The paper shows that the hybridisation of four different lengths of fibres in cementitious composites generally improved mechanical properties in comparison to plain and single-length fibre-reinforced mortar. The hybrid fibre coefficient also showed good consistency with the results of mechanical properties. Scanning electron microscopy demonstrated the proper bonding of basalt fibre with cementitious composites.

A new fiber cocktail reinforced cement–based materials (NFCRCM) with steel, polyvinyl alcohol (PVA) fiber, and calcium carbonate whisker (CCW) was developed to obtain powerful fire resistan...

The calcium carbonate whisker (CW) and basalt fiber are gaining popularity due to its enhanced mechanical properties in composites. Also, the short and long fibers provide bridging role and resistance against cracking from micro- to macro-scale, respectively. The usage of long and short hybrid basalt fiber along with addition of CW in cement-based composites is still a research gap. In this work, experimental behavior of CW basalt hybrid fiber reinforced mortar is considered with various content and length (3 mm, 6 mm, 12 mm, and 20 mm) of hybrid basalt fibers. In addition to this, synergy performance index is determined to quantitatively evaluate the positive interaction of hybrid basalt fiber in cementitious materials. The strengthening effect of whiskers and basalt fibers are also studied using scanning electron microscopy. The CW with various basalt fiber contents having different length of hybrid basalt fiber is used. It was found that the four various length of hybrid basalt fiber together with CW in cement mortar exhibited enhanced compressive, flexural, and split tensile strength than that of pure mortar and single length basalt fiber reinforced cementitious mortar. The results of synergy performance index showed similar trend with the experimental results. The strengthening effect caused by step by step crack arresting mechanism was also observed in cementitious material.

The association between low density lipoprotein cholesterol (LDL-C) and all-cause mortality has been examined in many studies. However, inconsistent results and limitations still exist. We used the 1999–2014 National Health and Nutrition Examination Survey (NHANES) data with 19,034 people to assess the association between LDL-C level and all-cause mortality. All participants were followed up until 2015 except those younger than 18 years old, after excluding those who died within three years of follow-up, a total of 1619 deaths among 19,034 people were included in the analysis. In the age-adjusted model (model 1), it was found that the lowest LDL-C group had a higher risk of all-cause mortality (HR 1.708 [1.432–2.037]) than LDL-C 100–129 mg/dL as a reference group. The crude-adjusted model (model 2) suggests that people with the lowest level of LDL-C had 1.600 (95% CI [1.325–1.932]) times the odds compared with the reference group, after adjusting for age, sex, race, marital status, education level, smoking status, body mass index (BMI). In the fully-adjusted model (model 3), people with the lowest level of LDL-C had 1.373 (95% CI [1.130–1.668]) times the odds compared with the reference group, after additionally adjusting for hypertension, diabetes, cardiovascular disease, cancer based on model 2. The results from restricted cubic spine (RCS) curve showed that when the LDL-C concentration (130 mg/dL) was used as the reference, there is a U-shaped relationship between LDL-C level and all-cause mortality. In conclusion, we found that low level of LDL-C is associated with higher risk of all-cause mortality. The observed association persisted after adjusting for potential confounders. Further studies are warranted to determine the causal relationship between LDL-C level and all-cause mortality.

We added CaCO3 whiskers into polyvinyl alcohol (PVA)-steel hybrid fiber system to obtain multiscale hybrid fiber reinforced cement mortar (MHFRC). Three-point bending (3-p-b) tests were carried out on 64 notched beams to investigate fracture behavior of MHFRC. Double K Fracture Criterion (DKFC) and Work Fracture Method (WFM) were employed to obtain fracture parameters. Influence of the volume fraction of CaCO3 whiskers, content of PVA-steel hybrid fiber and water/ cement ratio (w/c) on fracture parameters are discussed. Addition of composite fibers consisting of CaCO3 whiskers and PVA-steel hybrid fibers could improve fracture behavior of MHFRC. As the content of CaCO3 whiskers increases, fracture parameters first increase and then decrease. Content of PVA-steel fibers also affect fracture behavior of the matrix. Thus, an optimum ratio between CaCO3 whiskers and PVA and steel fibers contents exist that provide the best fracture performance of cement matrix: 1 vol% of CaCO3 whiskers, 0.5 vol% of PVA fibers and 1.5 vol% of steel fibers (S15P05W10). Influence of the w/c value is also discussed. Fracture toughness (KIC) and fracture energy (GF) of S15P05W10 group decreased as w/c values increased. The synergy of fibers in S15P05W10 was evaluated quantitatively, and the results indicated positive synergy effect on unstable fracture toughness ( K IC un ) and fracture energy (GF) in cement matrix with higher w/c values. Negative synergy was observed for the initial fracture toughness ( K IC ini ). Comprehensive reinforcing index (RIv) was introduced as the characteristic parameters of the hybrid fibers. Fracture parameters increased first and then decreased as RIv increased. Furthermore, the microscope morphologies of CaCO3 whiskers, PVA and steel fibers in the cement matrix were shown. These results helped to establish microscopic reinforcing mechanism of the hybrid fibers in the cement matrix. Based on the experiment results, empirical formulas, which taking into account fiber factor RIv and matrix factor w/c, were proposed to calculate fracture parameters of MHFRC.

Calcium carbonate whisker (CW) can reinforce the flexural strength of cement paste and limit the development of micro-cracks at ambient temperature (25 ± 2 °C), but the effect of CW on mechanical properties of cement paste after exposure to high temperatures is still unknown. Therefore, mechanical properties, i.e. flexural strength, compressive strength and splitting tensile strength were measured using CW reinforced cement specimens before and after they were exposed to high temperatures. In addition, performance of CW reinforced cement paste after exposure to high temperatures was studied by ultrasonic test and mass loss test. At last, microstructural analysis (differential thermogravimetric analysis and scanning electron microscopy) were employed to study the deterioration mechanism of temperature and reinforcement mechanism of CW. These experimental results suggested that CW played a significant role in hindering the development of cracks before 600 °C. When temperatures increased up to 200 °C, the flexural strength decreased. However, the compressive strength and splitting tensile increased. When temperatures varied from 200 °C to 400 °C, the three strengths reacted differently to the elevated temperatures. Subsequently, the residual strength rapidly decreased up to 1000 °C. After that, the three strengths increased slightly. The residual strength, ultrasonic velocity and mass loss were related to the temperatures and CW content and quantitative measurement of these factors was also discussed.

Background Clinical breast cancer subtypes are categorized basing on the expression of hormone receptors and overexpression of the human epidermal growth factor receptor 2 (HER2). It is still unclear whether parity impact the risk of different breast cancer subtypes. Methods We searched eight mainstream databases for published epidemiologic studies that assessed the relationship between parity and risk of breast cancer subtypes up to January 12, 2021. Parity number were unified into nulliparity and ever parity. The random-effects or fixed-effect models were used to calculate the pooled odds ratios (ORs) and 95% confidence intervals (CIs) among different subtypes. Restricted cubic spline analysis with four knots was applied to determine the relationship of parity number and risk of breast cancer subtypes. Results We pooled sixteen case-control and four cohort studies, and performed an analysis including 7795 luminal A, 3576 luminal B, 1794 HER2-overexpressing, and 5192 triple-negative breast cancer cases among 1135131 participants. The combined ORs for ever parity versus nulliparity indicated a 34% reduction in luminal A risk (OR=0.66, 95% CI: 0.56–0.78), and a 29% reduction in luminal B risk (OR=0.71, 95% CI: 0.63–0.81), there was no significant association in HER2-overexpressing or TNBC risk. In the dose-response analysis, we observed a potentially non-linear and gradually increasing protective relationship between the number of parity and luminal breast cancer risk. Conclusions The effect of parity on breast cancer seems to vary among breast tumor subtypes, and it plays a protective role in luminal breast cancer.

In this paper, we developed a novel hybrid fiber reinforced cementitious composites (HFRCCs) using steel fibers, polyvinyl alcohol (PVA) fibers and calcium carbonate whisker (CW) with high temperature resistance and cost-effectiveness. Mechanical and physical responses of HFRCCs after exposure to high temperature and roles of different fibers were particularly studied. The results showed that partially replacing PVA fibers by CW could reduce the deterioration of strengths and flexural toughness of HFRCCs before 600 °C because of significant nucleation effect and restraining cracking of CW. PVA fibers would melt above 200 °C and thus deteriorated the flexural and splitting tensile strengths, but less effective to compressive strengths. Steel fiber was most effective to increase the residual mechanical properties among these fibers because of its higher thermostability and strong bond with matrix. Generally, high temperature deteriorated the matrix and adversely affected the quality of fibers, which was mainly related to the different thermostability between fibers.

Fire resistance research of a new building material is the important part of public protection and necessary for its large scale use in construction project. Although cheap calcium carbonate whisker (CW) could improve the mechanical properties of cementitious composites under ambient temperature, there is no information about the influence of high temperature on CW reinforced cementitious composites. In order to bridge this gap, this research studied the strength and microstructure changes of CW and CW reinforced cement paste after exposed to evaluated temperatures. CW and Portland cement paste with 0%, 10%, 20% and 30% CW having water/cement ratio of 0.30 was exposed to the temperatures of 20, 200, 300, 400, 500, 600, 700, 800, 900 and 1000°C. 40 mm × 40 mm × 160 mm specimens were employed to determine the residual flexural and compressive strength of CW reinforced cement. Scanning electron microscope (SEM), matched energy dispersive spectrometer (EDS), thermal gravimetric analyzer (TGA) and X-ray powder diffractometer (XRD) were employed to detect the microstructure changes. CW could act as micro-fiber to increase the residual flexural and compressive strength of cement and the enhancement is better than carbon fiber and polypropylene fiber from room temperature to 600°C, which means that CW can be used to replace carbon fiber and polypropylene fiber as fire resistance additional material in cementitious composites. TGA presented that in the process of cement hydration and heating, CW may bring different hydration products phase: Ca(OH)2 and C–S–H (I). CaCO3 produced by cement hydration is not as stable as CW. The onset phase transformation temperature from aragonite CaCO3 to calcite is about 400°C, which can be proved by the XRD test and the morphologies under SEM. At the same time, internal autoclaving in cement paste produced new hydration products on the surface of the calcite CW. The bond between these new hydration products and calcite was stronger than the old hydration products and aragonite CW, proved by the EDS test. Hence, after expose to temperature range from 400°C to 600°C, CW demonstrates better reinforcing effect than that at lower temperatures. CW reinforced cementitious composites may possibly be employed as a protection material for fire easily damaged structures, due to its good residual mechanical properties after expose to evaluated temperature lower than 600°C and good economical efficiency.

Nowadays, hybrid fiber reinforced concrete is being considered for structural applications due to its enhanced mechanical properties compared to concrete without fibers/plain concrete. In this work, the mechanical properties of new kind of hybrid fiber reinforced concrete, i.e. CaCO3 whisker-steel fiber-basalt fiber reinforced concrete (CSBFRC) with various basalt fibers percentages are studied. All the fiber-reinforced concretes are compared with that of plain concrete (PC). The CaCO3 whisker, steel and basalt fiber lengths are 20–30 μm, 35 mm and 12 mm, respectively. Steel fibers and CaCO3 whiskers contents are 0.32% and 0.9%, by volume, respectively. Various basalt fiber contents of 0.34%, 0.68%, 1.02% and 1.36%, by volume, are added. For each batch, cylinders and beam-lets are cast and tested under respective compressive, splitting tensile and flexural load as per ASTM standards. Stress-strain curves and load-deflection curves are obtained. Strengths, energy absorptions and toughness indices are determined against for each type of loading. The scanning electron microscopy (SEM) analysis is performed to reveal the behavior (interfacial bonding) of CaCO3 whiskers, basalt fibers and steel fibers. It is concluded that, with increasing content of basalt fibers up to 0.68%, there is an increase in the mechanical properties of hybrid fiber reinforced concrete and CSBFRC4 is found to be an optimum. However, beyond 0.68%, the mechanical properties of CSBFRC decrease with an increase in the basalt fiber content. The resistance against cracking provided by hybrid fibers is observed by SEM images.

Inclusion of hybrid fiber in cementitious composites could restrict the growth of cracks at different stages and improve the mechanical properties of concrete, and adding calcium carbonate (CaCO3) whisker would further improve the mechanical properties of cementitious composites. Nevertheless, no attention has been paid to the effects of steel- polyvinyl alcohol (PVA) hybrid fiber and whisker on ultrasonic pulse velocity (UPV) and resonant frequency (RF) of hybrid fiber reinforced cementitious composites (HyFRCC), although they have been used widely in quality assessment of concrete. In this research, 114 specimens have been used to explore the influences of steel-PVA hybrid fiber and whisker on the UPV, RF parameters and the mechanical properties. The results of this research present that there may exists “fiber gradation” in HyFRCC, because there is always a best fiber combination to reach the greatest compactness and highest non-destructive testing results. In addition, the partial substitution of PVA fiber by whisker decreased UPV and RF and increased density loss rate and compressive strength except for one mixture. Therefore, UPV, RF can reflect the effect of whisker on the inner structure and detect the variation, and have potential use to evaluate HyFRCC in engineering applications.

An innovative hybrid fibre system of steel fibres, polyvinyl alcohol (PVA) fibres and inexpensive (approximately US$230/t) calcium carbonate whiskers (CW) was assessed as a way of improving the mechanical behaviour of fibre-reinforced concrete under static and impact loads and reducing production costs. Static mechanical properties and repeated drop-weight impact tests of the designed hybrid-fibre-reinforced cementitious composites (HyFRCCs) are presented in this paper. The reinforcing effect of the new hybrid fibre system was found to be very close to that of conventional HyFRCCs (incorporating only steel and PVA fibres) under both static and impact loads. It is thus suggested that steel and PVA fibres can be partly replaced with CW to reduce production costs in large-scale construction applications. Ultrasonic pulse velocity, dynamic elastic modulus and crack width assessments were carried out to quantify the degree of damage in samples during mechanical testing. The impact energy absorbed by the specimens could be predicted using linear modelling. There is therefore potential for using such tools to evaluate the in situ structural damage under dynamic loads.

Fiber distribution is an important factor which affects the fresh and hardened properties of composites. A variety of methods are available for studying the fiber distribution but image analysis is more widely used for fiber reinforced cement-based composites (FRCs). In this paper, different fiber distribution methods are discussed in detail including optical microscope, scanning electron microscopy, fluorescence microscopy and X-ray computed tomography. It is found that fluorescence microscopy is more widely used for studying fiber dispersion in FRCs and can be applicable to the synthetic fibers.

The new models using reinforcing index to predict workability and toughness of hybrid fiber reinforced cementitious composites (HyFRCC) were systematically studied in this paper. The existing models are discussed and new quadratic function models are proposed. A RIV considering elastic modulus of fibers is employed to calculate the workability parameter of fresh HyFRCC, and the analysis indicates that the slump cone, V funnel, J-Ring and L-Box test results can all be predicted by this workability model. In addition, a RIV considering tensile strength of fibers is employed to calculate the toughness of harden HyFRCC. The analysis indicates that this toughness model can be used to predict the compressive toughness, flexural toughness, equivalent flexural strength (according to JCI-SF4), I5, I10 and I20 (according to ASTM C1018 ) of HyFRCC, without considering the matrix (mortar or concrete) and fiber combination (e.g., steel-polyvinyl alcohol fiber-whisker, steel-cellulose fiber, steel-polypropylene fiber and so on). The new models have extensive applicability and good correlation with experimental results, which can help offering good behaviors to HyFRCC fresh mixtures, even hardened states, in design and construction practice via fiber mix optimization.

A new hybrid fiber system containing steel fiber, polyvinyl alcohol fiber (PVA fiber) and calcium carbonate (CaCO3) whisker was employed to further improve hardened properties and reduce engineering cost of cement mortar. In this paper, the rheological properties, flow rate and flow spread were measured to evaluate the workability of hybrid fiber reinforced mortar in fresh state. Mechanical strength and flexural toughness of mortars were tested in hardened state. The results indicated that, flowability of fresh hybrid fiber reinforced mortar decreased after substituting PVA fiber for steel fiber and further CaCO3 whisker for PVA fiber in mortar. This is mainly due to the flexibility of PVA fiber and large specific surface area of CaCO3 whisker. The hybrid fiber reinforced mortar shows promising mechanical strength and flexural toughness due to the multi-scale crack resistance formed by micro- and macro-fibers. M5 specimen (1.5% steel fiber + 0.4%PVA fiber + 1.0% CaCO3 whisker) exerts the best flexural performance and relatively higher compressive strength, exhibiting an obviously positive hybrid effect of fibers.

The inclusion of multi-scale hybrid fibers in cement-based materials exhibits excellent crack resistance performance at multi-level than that of single type or size of fiber. Multi-scale hybrid fiber reinforced cementitious composites (MHFRCCs) can be served as a building material with stringent crack resistance requirements for civil structure such as pipeline, river levee, nuclear reactor, water tower, and sewage treatment sedimentation tank. The tensile strength (ft) and fracture toughness (KIC) are two important size independent material parameters for guiding structural safety design and stability assessment. In this study, the real ft and KIC of MHFRCCs were determined by three-point bending test based on the boundary effect model. The average aggregate particle size with a large proportion was chosen as the “representative aggregate (d1 = 0.45 mm)" by using grading curve. The fiber long axis dimensions that appear most frequently on the cross section were selected as the “representative fiber (d2 = 0.28 mm for steel fiber and d3 = 0.0794 mm for polyvinyl alcohol fiber)" according to the statistical analysis of backscattered electron imaging. The fracture failure behaviors of MHFRCC structure were predicted based on the determined ft and KIC values, and the structural fracture failure bands with ±15% variations were established. In addition, the microstructure analysis of MHFRCC revealed multi-scale enhancement mechanism in the cement matrix. Finally, the complete fracture process images and P-CMOD curve were divided into three stages: pre-cracking stage, crack stable propagation stage, and unstable failure stage. This analysis would be helpful to understand the fracture crack resistance effect of multi-scale hybrid fibers at multi-level within cement matrix.

Cementitious composites are porous material having complex structure system consist of hydration products, un-hydrated cement particles and pore solutions of various scales. Calcium carbonate whisker is a new type of low cost micro-scale filler fiber gaining popularity in the field of construction materials. However, addition of whisker has effect on physical, mechanical and microstructural characteristics of cementitious composites. Also, the low production cost of whisker will make the use of micro fiber more extensive in large scale construction projects. In this study, the effect of calcium carbonate whisker on physical, mechanical and microstructural properties of cementitious composites with different fiber contents are investigated. The fluidity, drying shrinkage, pore structure, impact resistance, compressive, flexural and splitting-tensile strength of whisker-mortar are considered. The scanning electron microscopy analysis is also performed to examine the microstructural and toughening mechanism of whisker reinforced composites. It was concluded that the addition of calcium carbonate whisker up to 10 % improves the physical and mechanical properties of cementitious composites and is suggested to be the optimize content. The calcium carbonate whisker also resists the crack propagation at micro scale and showed the toughening mechanism with better interfacial properties between whisker and matrix.

The ceramic wastes can cause strong damage to the environment. In this article, the experimental study was concentrated on the pozzolanic activity of household ceramic waste and clay bricks waste. The possibility of the partial replacement of Portland cement blended with ceramic waste powder without further heating treatment in different ratios was analyzed. The ceramic waste powder was mixed in samples in various ratios. The evaluation of the ceramic waste powder was performed by grain-size analyses using Laser granulometry, XRD, XRF, Frattini test and strength activity index (SAI) method. The results indicate that the pozzolanic activity of household ceramic waste was higher than that of clay bricks waste. The 15% of HC powder addition could be a possible upper bound for an effective substitution and may also be very cost-efficient for industrial application., The authors acknowledge the National Natural Science Foundation of China: Grant 51578109, and Fundação para a Ciência e a Tecnologia (SFRH/BPD/22680/2005).

The effects of freeze–thaw (F-T) damage on fracture properties and microstructure of steel-PVA hybrid fibers reinforced cementitious composites containing calcium carbonate whisker (CW-SPFRCC) were investigated in this paper. Three-point bending tests were carried out to study the fracture properties of CW-SPFRCC after different F-T cycles based on Double K fracture criterion. Compared with SPFRCC, the relative fracture parameters in CW-SPFRCC dropped less within 0 to 50F-T cycles, while rapid deterioration was observed in 50 to 100F-T cycles, indicating that the presence of CW could effectively delay F-T damage in SPFRCC. Moreover, fracture parameters were estimated to quickly predict the fracture behavior of CW-SPFRCC subject to F-T cycles. The microstructures of CW-SPFRCC was analyzed using scanning electron microscope (SEM), vacuum epoxy impregnation (VEI), mercury intrusion porosimetry (MIP) and optical microscope observation (OM), respectively. SEM results showed that PVA fiber and CW maintained intact morphologies subject to F-T cycles, but the surface of steel fibers was severely corroded by F-T actions. The results of VEI and MIP demonstrated that better frost resistance of SPFRCC was related to the improved pore structure because of the presence of CW. Furthermore, F-T damage was more likely to occur on the interfacial transition zone (ITZ) of steel fibers or aggregates. Finally, a parabolic model of F-T damage was developed to predict the service life on-site of CW-SPFRCC.

The bond at fiber–matrix interface is considered as one of the most important factors influencing the performance of fiber reinforced cementitious composites (FRCC). To improve such bond, adding silica fume is considered as an effective and efficient method. In modern FRCC, CaCO3 (calcium carbonate) whisker and basalt fibers witnessed increasing popularity due to their effectiveness in improving mechanical performance at multi-scales. However, systematic research still lacks for the bond improvement at their fiber–matrix interface. In this regard, silica fume of various contents was added to plain concrete (PC), CaCO3 whisker reinforced cementitious composites (CWRCC) and basalt fiber reinforced cementitious composites (BFRC). The bond strength at the fiber–matrix interface and mechanical properties of PC, CWRCC and BFRC were evaluated. Test results show that the addition of silica-fume up to 10% could enhance the interface bond and mechanical properties of CWRCC and BFRC up to 30% and 34%, respectively. SEM analysis revealed improved bond at the fiber–matrix interface with addition of silica fume as evidenced by the fact that the whisker after pulled out from the matrix was encapsulated by cement paste, as compared to that of plain composite without silica fume. Moreover, EDS energy spectrum of whisker and basalt fiber surface show that the Si content increased noticeably as a result of the increased hydration products adhering to the whisker and basalt fiber surface, thus improving the bond at the fiber–matrix interface. The incorporation of silica-fume in BFRC lead to a large number of attached hydration products to the surface of fiber after pulling out. At the initial stage of cement hydration, dispersed silica-fume particles play a role of “crystal nucleus”, which can absorb Ca + and OH– ions, and increase the number of CH nuclei. Furthermore, silica-fume continuously reacts with CH and procedure C-S-H gel which decreases the porosity of the interface layer, makes the structure more compact and improves the interfacial adhesion. The microstructure of the interface layer is enhanced by C-S-H which is generated by “secondary reaction” and increase the interfacial bond strength of fiber and matrix. Lastly, a microstructure schematic representation for the fiber–matrix interface was developed to understand the mechanism between the fiber and the cement matrix.