Polypropylene Fiber Content Research Articles

PENGARUH STABILISASI MENGGUNAKAN POLYPROPYLENE FIBER TERHADAP TANAH LEMPUNG EKSPANSIF

Expansive clay soil is a land having the nature plasticity high when things are changing the system of ground water levels. The expansive loam if there is an increase in the moisture content of soil will spread abroad accompanied by the increase of water pressure the pressure development and emergence. An effort to improving fisis mechanical parameters and land to land stabilization will use of stabilization. This research to test the land of the clay done stabilization used polypropylene fiber to analyze the effect of the density of the stabilized soil and analyze the variation of the most optimal polypropylene fiber content used. Polypropylene is one of the kind of plastic that most often used as a fiber and have sifat-sifat can dissolve in organic compounds, stand the heat, has a tenuous, high are not poisonous, resistant to chemicals. The soil samples taken from the Hambalang village, west java. Testing done on land with a mixture of polypropylene fiber % 0,25, % 0,5, 0,75 % and 1 % with waiting time 7 day and 14 day. Optimum use of polypropylene fiber as a mixture of occurring at the level of the index 0,5% is 19,69% of plasticity the soil shear strength is 1,098 kg/cm2, primary settlement is 1,47 mm and maximum dry weight is 1,453 g/cm3 .

МОДИФИЦИРОВАННЫЕ ЦЕМЕНТНЫЕ БЕТОНЫ С ДИСКРЕТНЫМ АРМИРОВАНИЕМ

Issues related to improving the quality of the operational properties of reinforced concrete and concrete structures by introducing discrete reinforcement - fiber reinforcement are topical tasks of building materials science. The aim of the study was to obtain high-tech concretes with increased flame retardant properties by introducing an optimal combination of fiber reinforcement components. The change in the compressive strength of concrete after fire tests, depending on the percentage of polypropylene fiber, is analyzed. The TSP-27-25 program, developed at the Tver State Technical University, which allows modeling various concrete compositions, was used in the calculation of the control compositions of fiber-reinforced concrete. It has been established that the addition of fiber makes it possible to increase the fire resistance of concrete with an optimal amount of it. An assessment of the strength characteristics of the studied samples after fire exposure is given. The influence of polypropylene fiber content on the nature of concrete destruction is investigated.

Effect of Inclusion of Polypropylene Fiber on Behavior of Concrete

In this paper, a comprehensive review related to the history of polypropylene fiber, its durability, dimensional stability, permeability, and eco-friendly properties were discussed. The influence of polypropylene fiber in mechanical properties like tensile, compressive and flexural strength is explored by performing a comparative analytical study concerning conventional concrete and polypropylene fiber reinforced concrete (PPFRC). The case study was carried out to know the variation in the behavior of concrete due to different aspects such as spalling, and abrasion resistance. By the proper addition of fiber content in the concrete mix it can be predicted that there might be an increase in the physical and mechanical properties of fiber, so simultaneously by varying the polypropylene fiber content from 0.5% - 2% in terms of volume, samples are tested under controlled curing conditions and the optimum polypropylene fiber content is suggested. Fibers are distributed randomly in a concrete mix; possess to increase the energy-absorption capacity of concrete and leads to a decrease in their plastic shrinkage cracks. Further investigations are highly recommended to understand more about the mechanical properties of (FRC) fiber reinforced concrete.

Mechanical behavior and microscopic mechanism of fiber reinforced coarse aggregate cemented backfill

Backfills have traditionally served as artificial stope roofs during the mining of cemented undercut-and-fill, which still has many problems, such as weak tensile strength, brittleness, poor ductility, etc. To improve the stability of the backfill, fluidity tests, mechanical tests, and microscopic characteristics tests were conducted on fiber-reinforced coarse aggregate cemented backfill (FCCB) with different polypropylene fiber (PPF) contents and curing times based on the existing filling parameters of Longshou mine in China. The results showed that the slump and expansion of FCCB slurry presented a slight linear decrease with an increase in PPF content, and the slurry satisfied the requirement of self-flow transport. Additionally, the uniaxial compressive strength (UCS) and splitting tensile strength (STS) of FCCB showed growth to a different extent. When the PPF content was 0.10 %, the enhancement effect was optimal. However, the backfill deteriorated as the content was more than 0.10 %. Moreover, the effects of a single 15 mm PPF on UCS and STS were better than that of hybrid fibers with different scales. The peak strain and the compressive and splitting toughness index (Ti) of FCCB increased at different degrees with an increase in PPF content, which was significantly higher than that of the backfill without fiber. After adding PPF, the backfill appeared characteristic of a crack but not broken. Furthermore, the hydration products, including CSH gel, Ca(OH)2 (CH), and ettringite (AFt), increased and became thicker with curing time, the compactness of the interfacial transition zone (ITZ) increased, the pores decreased, and the adhesion of PPF and cement stone increased, enhancing the microscopic mechanical properties of FCCB. This study would improve the safety of mining and have high application value.

Static Compressive Properties of Polypropylene Fiber Foam Concrete with Concave Hexagonal Unit Cell

For the purpose of studying the influence of fiber on the negative Poisson’s ratio effect of foam concrete, a concave hexagonal unit cell structure of polypropylene fiber foam concrete was proposed. The effects of different fiber volume contents on the structural mechanical parameters, Poisson’s ratio, and energy absorption capacity of the unit cells were studied by static compression of concave hexagonal unit cells and cube specimens. The results show that the compressive strength of foam concrete is reduced by adding polypropylene fiber, and the peak stress of concave hexagonal unit cells decreases less rapidly than that of cube specimens. The proper amount of polypropylene fiber can enhance the deformation ability of the unit cells in foam concrete, and the Poisson’s ratio of the unit cells in foam concrete with 1.5% fiber content is the lowest. In the process of failure of concave hexagonal unit cells, the failure phenomenon is mainly concentrated on the concave surfaces on both sides, and the cracks are distributed in the form of “upper left and lower right” or “lower left and upper right”. When the content of polypropylene fiber is 0.5%, the total energy absorbed by the concave hexagonal cells in the compression deformation process increases by 12.98%.

Multi-scale deterioration and microstructure of polypropylene fiber concrete by salt freezing

Salt freeze damage is a significant factor impacting the durability of hydraulic concrete buildings in cold, saline soil areas. To settle the durability problem of hydraulic concrete in a salt freezing environment in cold regions, concrete specimens with different levels of polypropylene fiber dosing under two conditions of freeze–thaw cycles and freeze–thaw–sulfate erosion were prepared based on water diversion projects in cold and saline soil regions of China. The indoor accelerated deterioration test was designed, and the relative dynamic elastic modulus(RDEM) and mass loss rate, which were macroscopic indicators, were measured. The pore structure distribution in concrete with increasing test times was examined using nuclear magnetic resonance (NMR) technology. Combined with scanning electron microscope(SEM) images, the salt frost resistance of polypropylene fiber concrete was studied. The results showed that the mass loss rate of group A4 (1.2 kg/m3 of polypropylene fibers) under freeze–thaw cycles was 2.06% lower than that of group A1 (0 of polypropylene fibers), and the RDEM was 7.92% higher than that of group A1; the mass loss rate of group B4 under freeze–thaw–sulfate attack was 2.1% lower than that of group B1, and the RDEM was 20.79% higher than that of group B1; at the fine level, polypropylene fibers could inhibit the development and expansion of pores inside the concrete, which improved the salt–freezing resistance of the concrete; from the microscopic morphology, expansion products like gypsum and ettringite generated at the internal pores of the concrete are the leading cause of salt freeze damage crack development. The capability of concrete to withstand freeze-thaw cycles and salt freezing was enhanced with the increase of polypropylene fiber dosing. Compared with the concrete with polypropylene fiber content of 0.9 kg/m3, the frost resistance and salt freezing resistance of concrete with 1.2 kg/m3 content are not significantly improved. The study can provide a theoretical reference for applying polypropylene fibers to hydraulic concrete in saline soils in cold regions.

Effect of polypropylene fiber on properties of modified magnesium-coal-based solid waste backfill materials

Driven by the “dual carbon” goal, modified magnesium-coal-based solid waste backfill materials (MFPB) were gradually used in backfill mining instead of traditional backfill materials. To study the effect of polypropylene (PP) fibers with different contents and lengths on the properties of MFPB, slump tests, rheological tests, uniaxial compressive strength (UCS) tests, permeability tests, and scanning electron microscopy were carried out. The results showed that with the increase in the PP fiber content and length, the flowability of the MFPB characterized by the slump and rheological parameters deteriorated, but the UCS increased significantly, and the permeability first decreased and then increased. The mutual entanglement of PP fibers was the main reason for the poor fluidity of the MFPB. The PP fibers could effectively enhance and improve the strength and toughness of the MFPB by an anchoring effect and irregularly distributed network structure. The strengthening effect mainly occurred in the medium and long term, and the early strengthening effect was not evident. After curing for 28 d, the maximum growth rate of the UCS was 62.5%. After loading failure, the MFPB containing PP fibers still had good integrity and continuity, and there was no shedding phenomenon. The network structure that formed in the early stage due to the PP fibers did not easily segregate and precipitate. The transmission channels between the PP fibers connecting holes were the main reason that the MFPB permeability first decreased and then increased. Therefore, this study can provide a reference for the application of PP fibers to MFPB. Enhancing the performance of the backfill body has important theoretical and practical significance for the development of mine backfill.

Impact of Polypropylene Fibers on the Mechanical and Durability Characteristics of Rubber Tire Fine Aggregate Concrete.

In this research, the consequence of using rubber tire aggregates (RTA) on the durability and mechanical characteristics of polypropylene fibers (PF) reinforced concrete is evaluated. Fifteen concrete mixtures were produced and tested in the laboratory. RTA was utilized instead of fine natural aggregates (FNA) to the concrete at concentrations of 0%, 5%, 10%, 15%, and 20% by a volumetric fraction; also, the contents of PF in the concrete mixtures were 0%, 1%, and 2% by weight fraction. Finally, the following parameters were tested for all the mixtures: compressive and tensile resistances, fracture, changes in drying shrinkage, bulk electrical resistivity, elastic moduli, and resonance occurrences. The control sample was the one without RTA and PF. According to the results, by adding RTA to the mixtures, the shrinkage deformation amplified, but the PF addition caused a decrease in the shrinkage deformation. Furthermore, adding 0%, 5%, 10%, and 15% RTA, with 2% PF leads to an upsurge in the flexural resistance by 34%, 24%, 16%, and 6%, respectively, relative to the control sample without PF and RTA. Moreover, the fracture energy of mixtures increased by utilizing PF and RTA simultaneously.

Experimental study on seismic performance of hybrid steel-polypropylene fiber-reinforced recycled aggregate concrete-filled circular steel tube columns

In this paper, 1 recycled aggregate concrete-filled circular steel tube column (RACFST) and 11 hybrid steel-polypropylene fiber-reinforced recycled aggregate concrete-filled circular steel tube (HFRACFST) columns were designed given the variables of steel fiber (SF) volume content (Vsf = 0.6 %,1.2 %,1.8 %), polypropylene fiber (PPF) content fractions (Vpf = 0.05 %,0.10 %,0.15 %), concrete strengths (C40, C50, C60), thickness of steel tube (t = 2.70 mm, 3.65 mm, 4.50 mm), axial compression ratios (n = 0.25, 0.35, 0.45). Then the influence of variables on hysteretic curves, ductility, energy dissipation and stiffness degradation were studied experimentally using the pseudo-static tests. Subsequently, the restoring force models of HFRACFST were proposed based on the experimental results. The results indicated that: (1) The incorporation of HF (hybrid steel-polypropylene fiber) could enhance the hysteretic behaviour of HFRACFST columns. An increase in PPF content had little effect on the lateral bearing capacity and energy dissipation capability. Nevertheless, it could improve the ductility to some extent. As the SF content increased, the lateral bearing capacity, energy dissipation capability and ductility of the specimens increased. (2) An increase in concrete strength resulted in the increase of the bearing capacity and energy dissipation capability, but led to inferior ultimate deformation and ductility. (3) The comprehensive hysteretic behaviour was improved significantly as the thickness of steel tube increased, especially in the energy dissipation capability. (4) The specimens with higher axial compression ratio experienced inferior ultimate deformation and ductility. (5) The ductility indexes of all specimens were higher than 3.0. The yielding elastic and ultimate elastoplastic drift ratios were in the ranges 0.012–0.013 and 0.038–0.054, respectively. The hysteretic performance of HFRACFST columns could satisfy the requirement of seismic design. It is feasible to apply the HFRACFST columns to vertical load-bearing structures in the seismic zones.

Effects of air-entraining agent and polypropylene fiber on the mechanical properties, autogenous shrinkage, and fracture properties of fully recycled aggregate concrete

The effects of air-entraining agent (AEA) and polypropylene fiber (PPF) on the autogenous shrinkage and fracture properties of fully recycled aggregate concrete (FRAC) are studied to obtain FRAC with low density, low autogenous shrinkage, and superior fracture properties. Six groups of FRAC with different AEA (0, 5%, 10%) and PPF (0, 1.2 kg/m3) contents were prepared for test. The results illustrate that AEA can slightly reduce density but that it has an adverse effect on the strength and fracture properties of FRAC. The incorporation of PPFs can reduce the adverse effect of AEA on compressive strength and splitting tensile strength, but it will increase the adverse effect on fracture properties. Furthermore, the addition of PPFs alone will significantly reduce compressive strength and splitting tensile strength, whereas flexural strength and fracture properties are increased. The addition of AEA can improve the adverse effect of PPFs on compressive strength and splitting tensile strength, but flexural strength and fracture properties will decrease rather than increase. The addition of 10% AEA can greatly reduce autogenous shrinkage, and 5% AEA can reduce autogenous shrinkage at an early age. Incorporating PPFs can further reduce autogenous shrinkage. The study mainly examines the effects of AEA and PPF on the autogenous shrinkage of FRAC, and provides some new ideas for producing high-performance FRAC. At the same time, the cooperative effect of AEA and PPF on the properties of FRAC is also studied.

Study on shear behavior of high-performance polypropylene fiber-reinforced lightweight aggregate concrete beams

The effects of high-performance polypropylene fiber (HPPF) content, shear span to depth ratio, and stirrup ratio on the shear behavior of lightweight aggregate concrete (LWAC) beams were studied according to shear tests on eleven high-performance polypropylene fiber lightweight aggregate concrete (HPPLWC) beams and three LWAC beams under symmetrical concentrated load. The failure phenomenon, stirrup strain, shear capacity, and deflection of each specimen were analyzed, and it was determined that the failure patterns of the beams were classified as diagonal tensile failure, diagonal compression failure, shear compression failure, and bending shear failure, in which the beams without stirrups having the HPPF content of 0 kg/m3 and 3 kg/m3 were a diagonal tensile failure, the beam with the shear span to depth ratio of 1 was diagonal compression failure, the beams with the stirrup ratio of 0.38 % and the HPPF content of 6 kg/m3 and 9 kg/m3 were bending shear failure, and the rest of the specimens were shear compression failure. Adding HPPF to concrete could effectively improve its tensile strength, limit the growth of cracks, and further improve its initial cracking strength. By increasing the HPPF content and stirrup ratio, the shear capacity and ductility of the beams could be improved. Increasing the shear span to depth ratio of the beams could improve their deformability of the beams while simultaneously decreasing their shear capacity. Based on the experimental study, the contribution of each influencing factor to the shear capacity was analyzed, and the shear capacity model of the diagonal section of the HPPLWC beam was established. The model has great prediction accuracy as shown by error analysis.

Experimental Study on Compressive and Flexural Performances of Polypropylene Fiber-Reinforced Concrete

Plain concrete (PC) has the disadvantages of easy cracking and low resistance to deformation. In practical engineering, steel fiber or polymer fiber is usually selected to improve the tensile and crack resistance of concrete. In this study, the polypropylene fiber (PPF) was added to the concrete with the content of 0, 0.6, 0.9, and 1.5 kg/m3. The compressive and flexural tests of PC and PPF-reinforced concrete (PPFRC) at 14, 28, and 60 days of curing were conducted. As the result, when the content of PPF exceeds to 1.2 kg/m3, the workability became worse. The compressive and flexural strength of PPFRC increased compared with PC. However, the increase of strength does not always increase with the increase of fiber content. The uniaxial compressive strength of the PPFRC with the PPF of 1.2 kg/m3 is the optimal at 14- and 28-day ages, which is 20.56% and 11.24% higher than PC, respectively. PPFRC with the PPF of 0.9 kg/m3 is best of all at 60 days, which is 19.68% higher than PC. The flexural strength of the PPFRC-0.9 is the highest. Furthermore, the CFEC and CTI of PPFRC are both higher than those of PC, indicating that it has significant crack resistance and toughness.

Experimental Study on Size Effect and Fracture Properties of Polypropylene Fiber Reinforced Lightweight Aggregate Concrete

In this experimental research, the effects of polypropylene fibers on size effect and fracture properties of lightweight aggregate concrete were studied. Two methods, including size effect method and work of fracture method, were used to investigate and analyze the size effect and fracture properties on different sizes of notched beams. The polypropylene fiber contents were 0.5%, 0.75%, and 1% by volume fraction. The obtained results revealed that increasing the polypropylene fibers in lightweight aggregate concrete relatively decreased the dependence of strength on the size effect parameter, while the addition of polypropylene fibers exhibited significant influence on decreasing the size dependency of ductility and fracture energy in lightweight aggregate concrete. Moreover, the increase of polypropylene fibers improved the total fracture energy (GF), initial fracture energy (Gf), characteristic length (lch), length of fracture process zone (cf), and critical stress intensity factor (KIc) of lightweight aggregate concrete in both size effect method and work of fracture method. This increase was more significant in work of fracture method because of considering the post-peak behavior. The size effect method was suitable and accurate for plain lightweight aggregate concrete. The GF ⁄ Gf ratio increased from 2.88 in plain lightweight aggregate concrete to 12.26 in polypropylene fiber reinforced lightweight aggregate concrete.

Investigating the Mechanical and Durability Characteristics of Fly Ash Foam Concrete.

Although fly ash foam concrete (FAFC) is lightweight, heat-retaining, and insulating, its application options are constrained by its weak construction and short lifespan. The effects of various dosage ratios of the foaming agent (i.e., hydrogen peroxide), silica fume, and polypropylene fiber on the dry density, compressive strength, thermal insulation performance, pore structure parameters, and durability of FAFC were analyzed in this study, which sought to address the issues of low strength and low durability of FAFC. According to the findings, there is a negative correlation between the amount of hydrogen peroxide (as the foaming agent) and compressive strength, and, as the silica fume and polypropylene fiber (PP fiber) content rise, the strength will initially rise and then fall. The distribution of pore sizes gradually shifts from being dominated by small pores to large pores as the amount of foaming agent increases, while the porosity and average pore size gradually decrease. When the hydrogen peroxide content is 5%, the pore shape factor is at its lowest. The pore size distribution was first dominated by a small pore size and thereafter by a large pore size when the silica fume and PP fiber concentration increased. Prior to increasing, the porosity, average pore size, and pore shape factor all decreased. Additionally, the impact of PP fiber on the freeze–thaw damage to FAFC was also investigated at the same time. The findings indicate that the freeze–thaw failure of FAFC is essentially frost heave failure of the pore wall. The use of PP fiber is crucial for enhancing FAFC’s ability to withstand frost. The best frost resistance is achieved at 0.4% PP fiber content. In conclusion, the ideal ratio for overall performance was found to be 5% hydrogen peroxide content, 4% silica fume content, and 0.1% polypropylene fiber content. The results obtained could be applied in different fields, such as construction and sustainable materials, among others.

Fracture behavior of polypropylene fiber reinforced concrete modified by rubber powder exposed to elevated temperatures

• Elevated temperature tests conducted on RPFC notched beams. • Effect of different temperature on the fracture behavior of RPFC was studied. • The damage evolution within the fracture process zone was monitored by AE and DIC. • Fracture energy and fracture toughness first increase and then reduce with increasing temperature. In this paper, the deterioration of fracture properties of rubber powder modified polypropylene fiber concrete (RPFC) after elevated temperatures is discussed. Three-point bending tests were conducted on 75 notched beams to discuss the effects of rubber powder content (0%, 5%, 10%, 15%), polypropylene fibers content (0%, 1%), and ambient temperature (25℃, 100℃, 200℃, 400℃, 600℃) on the fracture properties of RPFC. In addition, digital image correlation (DIC) techniques were used to measure crack development in RPFC notched beams. The fracture patterns, micro-crack initiation and extension and macro-crack development in the fracture process were identified using acoustic emission (AE) techniques. The results show that incorporating rubber powder into polypropylene fiber concrete can delay the crack propagation process, improve the deformation ability and make the fracture path more tortuous. With the rubber powder content increase from 5% to 15%, the initiation fracture toughness of RPFC notched beam decreased, the unstable fracture toughness and the fracture energy increased. When the ambient temperature rises from 25 ℃ to 600 ℃, the fracture energy and fracture toughness of RPFC increases first and then decreases, the crack mouth opening displacement increases, and ductility increases significantly. AE analysis further shows that the growth rate of accumulate counts decrease significantly with the rubber powder content in RPFC, indicating the rate of damage development has slowed down in some extent.

Effects of content and length/diameter ratio of PP fiber on explosive spalling resistance of hybrid fiber-reinforced ultra-high-performance concrete

Ultra-high-performance concrete (UHPC) is prone to explosive spalling at high temperatures, which compromises the load-bearing capacity of the structures. In this paper, the effects of the content and length/diameter ratio of polypropylene (PP) fibers on the explosive spalling resistance of the steel and PP hybrid fiber-reinforced UHPC were investigated utilizing experimental method. First, the UHPC specimens were prepared using the conventional curing method. Second, the UHPC specimens were heated using the ISO-834 standard heating curve. Thirdly, the appearances, the first spalling time, the first spalling temperature, and the mass loss of the specimens were used to evaluate the explosive spalling resistance of the UHPC. The results demonstrated that the steel and PP hybrid fiber-reinforced UHPC has much greater explosive spalling resistance than the steel fiber-reinforced UHPC. The explosive spalling resistance of the hybrid fiber-reinforced UHPC is strongly influenced by the content and length/diameter ratio of the PP fibers. Generally, the explosive spalling resistance of the hybrid fiber-reinforced UHPC increases with the increase of the PP fiber content and length/diameter ratio.

Study on Carbonization Characteristics and Deterioration Mechanism of Recycled Concrete with Tailings and Polypropylene Fiber.

To improve the deformation performance of recycled concrete with tailings (TRC), its carbonization characteristics and deterioration mechanism with different polypropylene fiber content were analyzed macroscopically and microscopically. The results showed that the fiber had little effect on the compressive strength, which increased first and then decreased, with the optimum content being 0.6%. The splitting tensile strength first increased and then tended to be stable, with the optimum dosage ranging from 0.6% to 0.9%. The more the content, the higher the peak strain and the lower the elastic modulus. The rising section of its constitutive curve changed little, while the falling section became more gentle. Carbonization made the relative dynamic elastic modulus change small with a trend of first increasing and then decreasing, and the optimum content was 0.6–0.9%. When the fiber content was small, the influence on the carbonization depth did not remain significant, but when it was large, the depth increased obviously, and this critical content was about 0.6%. Microscopically, through nuclear-magnetic resonance (NMR) and scanning electron microscope (SEM) analysis, due to the strong tensioning effect of the fiber, when a small amount was added, the porosity and pore structure had not been significantly changed, so the impact on its resistance to carbonization was not obvious. However, after excessive addition, the interface transition zone (ITZ) between different materials became larger, resulting in a significant increase of its harmful cracks and a great impact on the anti-carbonization ability, with the optimal content being about 0.6%. This study provides a theoretical reference for the deformation performance improvement measure of TRC, which would be helpful for the rapid promotion and application of green concrete in engineering practice.

Characteristics of lightweight foamed concrete with various contents of polypropylene fiber

This study investigates the influence of polypropylene (PP) fiber content on the mechanical properties of lightweight foamed concrete (LFC). Four LFC mixtures with a target dry density of 1000 kg/m3 were designed with different PP fiber volumes of 0%, 0.25%, 0.5%, and 0.8%. The fresh unit weight (UW), dry density, compressive and flexural strengths, water absorption, thermal conductivity, ultrasonic pulse velocity (UPV), and scanning electron microscopy (SEM) of the LFC were examined. The results indicate that the fresh UW, dry density, UPV, and thermal conductivity decreased when the PP content varied from 0% to 0.8%. At 28 days, the compressive and flexural strengths of the LFC increased approximately 11.85% and 41.8% when the PP fiber amount varied from 0% to 0.8%, respectively. The result implies that the PP fiber content had a higher influence on the flexural strength content than the compressive strength. Furthermore, the results of SEM could explain well the obtained mechanical properties. The findings of this study indicate that PP fiber could be used up to 0.8% by volume to reduce the self-weight of the LFC and enhance the mechanical strength as well as thermal isolation characteristics of the LFC.

The Elastic Modulus and Damage Stress-Strain Model of Polypropylene Fiber and Nano Clay Modified Lime Treated Soil under Axial Load.

Using polypropylene fiber (PPF) and nano clay modified lime treated soil (LS), the static and dynamic properties of fiber modified lime treated soil (FLS), nano clay modified lime treated soil (NLS), and fiber nano clay composite modified lime treated soil (NFLS) were studied. Through the unconfined compressive strength (UCS) test and dynamic triaxial test of FLS, NLS, and NFLS, the static and dynamic elastic modulus characteristics at 7 day curing age were explored, and the damage stress–strain model was established. The results show that: (1) Polypropylene fiber and nano clay can significantly enhance the mechanical properties of NFLS. Nano clay can promote the reaction between lime and soil to produce calcium silicate hydrate (C-S-H) and calcium aluminate hydrate (C-A-H), thus improving the strength of NFLS, and UCS can be increased by up to 103%. Polypropylene fiber can enhance the ductility of NFLS and increase the residual ductility strength, and the residual strength can be increased by 827%. (2) Nano clay can enhance the static and dynamic elastic modulus of modified lime treated soil. The static and dynamic elastic modulus of NLS, FLS, and NFLS are linear with the change of polypropylene fiber and nano clay content. The static and dynamic elastic modulus of NLS, FLS, and NFLS are linear, exponential, and logarithmic, respectively. (3) The mesoscopic random damage model can characterize the stress–strain relationship of NFLS. Polypropylene fiber and nano clay can improve the ductility and strength of modified LS, and the composite addition of polypropylene fiber and nano clay can improve the ability of modified LS to resist damage.

Flexural Behavior and Prediction Model of Basalt Fiber/Polypropylene Fiber-Reinforced Concrete

The flexural behavior of basalt fiber (BF)/polypropylene fiber (PF)-reinforced concrete (BPRC) was investigated. When the content of BF and PF is 0.1%, the addition of fibers increases the compressive strength of concrete. A BF content of 0.1% has the most obvious effect on improving the compressive strength, but a hybrid fiber content of 0.2% exhibits a negative effect on the compressive strength. The addition of BF and PF can increase the flexural strength and the expansion tortuosity of the fracture cracks, thus enhancing the ductility of concrete. The hybrid fibers with content of 0.1% are most beneficial to increase the flexural strength. However, the ductility of concrete and the tortuosity of fracture crack decrease with the matrix strength, and the improvement proportion of fibers on the flexural strength also decreases. When the BF and PF are mixed, compared to the case of single fiber added, there is no significant change in the damage of BF, whereas the damage of PF is more severe. The flexural toughness index FTδ effectively characterizes the change in the flexural toughness of BPRC. The hybrid fiber contents of 0.1% and 0.2% exhibit the most significant improving effect on FT-l/600 and FT-l/150, respectively. Considering the influence of fibers on the compressive strength, flexural strength and flexural toughness of concrete, a hybrid content of 0.1% is the optimal choice of fiber content. A prediction model for flexural strength of BPRC is proposed based on the composite material theory.